Author Topic: 0-350V 0.2A Bench Power Supply  (Read 9590 times)

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Offline 001

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0-350V 0.2A Bench Power Supply
« on: November 19, 2017, 12:26:29 AM »
I do not understand anything after page #6. Some holywar or rocket sience detected :-//
« Last Edit: December 10, 2017, 01:18:22 AM by 001 »
 

Offline Ian.M

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Re: Looking for yours opinions! HV bench power supply
« Reply #1 on: November 19, 2017, 12:36:52 AM »
Most power MOSFETs are not specified for operation in their linear region and will fail at a small percentage of their nominal rating.  The situation with BJTs is somewhat better, but even so it will be difficult to find devices that can operate in their linear region dropping >350V @ 200mA reliably.       
 

Offline Hero999

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Re: Looking for yours opinions! HV bench power supply
« Reply #2 on: November 19, 2017, 01:23:09 AM »
Don't make the transistors drop the whole voltage. Use a tap switcher or pre-regulator to reduce the voltage to something more sensible, before the pass transistors.
 

Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #3 on: November 19, 2017, 01:35:05 AM »
Thanx a lot!

High voltage MOSFETs now very common and cheap http://www.shaoguang.com.cn/pdf1/mosfet/FQA10N80C.pdf

The question not about pass transistor. But about sense & regulation circuit
 

Offline Hero999

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Re: Looking for yours opinions! HV bench power supply
« Reply #4 on: November 19, 2017, 01:45:09 AM »
Thanx a lot!

High voltage MOSFETs now very common and cheap http://www.shaoguang.com.cn/pdf1/mosfet/FQA10N80C.pdf

The question not about pass transistor. But about sense & regulation circuit
You seem to have misunderstood Ian's post.

Yes, plenty of cheap, high voltage MOSFETs are available. The trouble is, they're typically not rated for linear operation, only switching. This means that they cannot withstand the full voltage and current rating for very long before blowing up.
 

Offline Ian.M

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Re: Looking for yours opinions! HV bench power supply
« Reply #5 on: November 19, 2017, 01:53:49 AM »
Don't make the transistors drop the whole voltage. Use a tap switcher or pre-regulator to reduce the voltage to something more sensible, before the pass transistors.
Obviously that helps with the dissipation issue, but the pass transistor(s) still have to be able to drop the full voltage at the maximum current for long enough for the preregulator to respond and drop its output voltage or they'll probably blow if the output is ever shorted.
« Last Edit: November 19, 2017, 01:58:08 AM by Ian.M »
 

Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #6 on: November 19, 2017, 02:26:10 AM »
Why so many words about pass transistor?
Is  MOSFET rated to 800V 10A 240W is not ok for 350V 0.2A linear power supply?  :-// Short current limitter is not difficult thing anyway
It is more intersting how to minimise ripple voltage, what type of NFB is ok, etc
« Last Edit: November 19, 2017, 02:28:05 AM by 001 »
 

Offline mk_

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Re: Looking for yours opinions! HV bench power supply
« Reply #7 on: November 19, 2017, 02:57:13 AM »
Why so many words about pass transistor?
Is  MOSFET rated to 800V 10A 240W is not ok for 350V 0.2A linear power supply?  :-// Short current limitter is not difficult thing anyway

Search for hotspots on the die when FETs optimised for switching are used as linear pass-element. Search for a pdf called "New 500V Linear MOSFETs
for a 120 kW Active Load"

Take a look at the IXYS LinearL2 TM Series or any other one with Extended FBSOA. This Extended FBSOA is usualy a sign that these FETs can be used linear too.

Quote
It is more intersting how to minimise ripple voltage, what type of NFB is ok, etc

short detection should be fast (I mean really fast, at least in the 10us-region) but thats easy...

good luck

michael
 

Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #8 on: November 19, 2017, 03:26:24 AM »
Hi!

I`m working for a long time using my old tube bench anode supply (0-350V 0.2A max)
But it is so bulky and actualy crap. I sell it to crasy vintage collector today.  :palm:
....
Perhaps not the cleverest thing you did today.  :-DD
Using vacuum tube as series regulator is very safe, safer than Mosfet.
« Last Edit: November 19, 2017, 03:41:05 AM by oldway »
 
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Offline mk_

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Re: Looking for yours opinions! HV bench power supply
« Reply #9 on: November 19, 2017, 03:27:09 AM »
Thanx A Lot!

I see what in 350V 0.2A range where are many affordable mosfets
So it is not a problem

What You can say about this diagram?

Try it, there is no regulation, just some kind of setting...

Anyway, it should work but is not something I would call "HV bench power supply".

michael
 
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Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #10 on: November 19, 2017, 03:55:44 AM »
Even modern design HV power supply as Power designs 1547 still use tubes as seies regulator.
 
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Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #11 on: November 19, 2017, 03:58:33 AM »
Some other HV power supplies schematics....
 
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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #12 on: November 19, 2017, 04:13:23 AM »
You misunderstand me
Power designs 1547 is a 2500V supply from 1970th
but I need no more 350V 0.2A
is it problem for modern mosfets?  :-//
« Last Edit: November 19, 2017, 04:16:57 AM by 001 »
 

Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #13 on: November 19, 2017, 04:18:59 AM »
And someone made HV differencial error amp 20 years ago (pass transistor is MOSFET):
« Last Edit: November 19, 2017, 04:20:38 AM by 001 »
 

Offline Ian.M

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Re: Looking for yours opinions! HV bench power supply
« Reply #14 on: November 19, 2017, 04:26:11 AM »
You try finding those HV MOSFETs from 20-30 years ago in stock at a reputable distributor.  The same goes for high voltage BJTs that used to be used as CRT drivers.  First it was increasing integration leading to specialised HV linear driver chips, then as flat panel prces dropped, with the death of the CRT TV, most high voltage linear discrete semiconductors became obsolete and were discontinued.

There are still a few parts around that will make you life easier e.g. Microchip's (ex Supertex) LR8K4 400V three terminal adjustable regulator,  but its only good for a few mA so you'll still need a pass device that can handle 400V at 0.2A without hot-spotting and failing.   The easy option there is still a valve cathode follower.
« Last Edit: November 19, 2017, 04:36:15 AM by Ian.M »
 
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Offline jmelson

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Re: Looking for yours opinions! HV bench power supply
« Reply #15 on: November 19, 2017, 04:38:21 AM »
Why so many words about pass transistor?
Is  MOSFET rated to 800V 10A 240W is not ok for 350V 0.2A linear power supply?
No, no no!  It is called safe operating area.  Most MOSFETS are designed for switching operation, and are intended to be either fully ON, or fully OFF.  If operated in the linear region (between on and off) they do not share current evenly within the transistor's area, and the hot spot burns out.  There ARE MOSFETS designed for linear operation, mostly in audio amplifiers.  But, they are expensive, special parts, and not likely at all to be rated for 350 V.  (You'd expect to find them with 100 - 150 V ratings.)

Check the data sheets for the SOA rating of any FET you plan to use.  If not listed, try another part #.

OK, so I looked up the FCP650N80Z 800 V, 10 A continuous-rated FET.  The safe operating area chart shows that at 350 V, it can handle about 400 mA continuously.  Now, this would only be in the short-circuit condition, but a bench supply will experience that sort of incident on occasion.  So, as long as your current limit circuit will be able to pull the gate bias back fast enough, this one should work.

Definitely have more than one transistor handy while building your supply.

Jon
 
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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #16 on: November 19, 2017, 06:22:06 AM »
There are still a few parts around that will make you life easier e.g. Microchip's (ex Supertex) LR8K4 400V three terminal adjustable regulator,  but its only good for a few mA so you'll still need a pass device that can handle 400V at 0.2A without hot-spotting and failing.   The easy option there is still a valve cathode follower.

And what about 10M45? 0-450V 100mA 3pin regulator
By the way I prefer use discrete components
« Last Edit: November 19, 2017, 06:38:00 AM by 001 »
 

Offline Ian.M

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Re: Looking for yours opinions! HV bench power supply
« Reply #17 on: November 19, 2017, 06:50:44 AM »
That's a resistor programmable current source, not a voltage regulator. 
 

Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #18 on: November 19, 2017, 06:54:00 AM »
Thanx a lot!

High voltage MOSFETs now very common and cheap http://www.shaoguang.com.cn/pdf1/mosfet/FQA10N80C.pdf

The question not about pass transistor. But about sense & regulation circuit
You seem to have misunderstood Ian's post.

Yes, plenty of cheap, high voltage MOSFETs are available. The trouble is, they're typically not rated for linear operation, only switching. This means that they cannot withstand the full voltage and current rating for very long before blowing up.

The quoted MOSFET shows a straight line DC SOA.  It's fine.

FYI, BJTs are worse than MOSFETs, and IGBTs are worse still.  MOSFETs vary, with some being worse than the best BJTs, but many are available (sometimes at a premium, as the "Linear operation" types are) which specify DC SOA.

I've tested a QFET before, at voltage, and it failed just a bit past ratings (RthJC), no 2nd breakdown.

Tim
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Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #19 on: November 19, 2017, 06:56:50 AM »
And what about using HV bipolar transistors like BU208 ? (Vcex = 1.500V min.)
They where intended for use in horizontal deflection in color TV's....

EDIT: No, not possible, only 30mA at 400V... :palm:...
« Last Edit: November 19, 2017, 07:02:04 AM by oldway »
 

Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #20 on: November 19, 2017, 06:57:41 AM »
Anyway, as for control, it can be done just the same way the vacuum tube unit did it.  Indeed, you need at least a few "tube replacements" to handle the high voltage: one is the pass transistor, one is its driver (the voltage gain element).  Everything else can be at low voltage, you can use 15V and op-amps if you like.  All you're doing is scaling up op-amp voltage to B+ voltage, then scaling it back down again with a voltage sense divider.

Current sense should be done with a shunt resistor in the GND return path.  No need to touch high voltages, and it's an isolated, stand-alone power supply (right?) so you can do ground-return trickery no problem.

It may be worthwhile to use a source degeneration resistor on the pass transistor, and gate protection zener diode, to limit transient current to safe values.  When the transistor can destroy itself in 20 microseconds, you want to use it carefully. :)

Tim
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Online Marco

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Re: Looking for yours opinions! HV bench power supply
« Reply #21 on: November 19, 2017, 07:02:26 AM »
So, as long as your current limit circuit will be able to pull the gate bias back fast enough, this one should work.

Yep, he was right to say his MOSFET was specced for his use. It's an old style planar MOSFET as well, so it might actually live up to those specs. That said, the specs also say it requires quite good heatsinking at this power.
 

Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #22 on: November 19, 2017, 07:02:49 AM »
And what about using HV bipolar transistors like BU208 ? (Vcex = 1.500V min.)
They where intended for use in horizontal deflection in color TV's....

Saturated switching.  Check the SOA:
http://pdf1.alldatasheet.com/datasheet-pdf/view/2595/MOSPEC/BU208.html
15mA at 400V.

Its descendants are still available today, e.g. MJE13008 and its brethren, commonly seen in CFL inverters (and probably LEDs now, too).  Relatives are commonly seen in old computer power supplies, VCRs, DVD players, and so on.

Tim
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Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #23 on: November 19, 2017, 07:22:11 AM »
Vacuum tubes have great advantages for high voltage applications and more particularly for HV power supply.

Indeed,
- there is a large distance between anode and cathode, which is a guarantee of safety
- the current is dynamically limited by the emissivity of the cathode.
- the anode is able to absorb strong overloads of dissipation without damage
- there is no SOA.
- A vacuum tube never fails short, that's a safety feature because semiconductors mostly fail short.

Bench HV power supply must be reliable for obvious safety reasons.

Personally, I would not entrust my life by relying on a semiconductor where there is more than 400V between wires placed a few mm from each other.
« Last Edit: November 19, 2017, 07:31:53 AM by oldway »
 

Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #24 on: November 19, 2017, 07:31:16 AM »
Vacuum tubes have great advantages for high voltage applications and more particularly for HV power supply.



:P

Quote
Personally, I would not entrust my life by relying on a semiconductor where there is more than 400V between wires placed a few mm from each other.

That's alright, you guys and your old ways will die off, eventually...... but hopefully not too soon, indeed, you may some day be entrusting your life to such devices without realizing it.  SCRs and IGBTs lurk inside defib machines! :)  Quite reliable indeed.

Tim
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Offline Ian.M

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Re: Looking for yours opinions! HV bench power supply
« Reply #25 on: November 19, 2017, 07:33:22 AM »
Hmmm . . . .  Considering a possible solid state design . . .

Use a FQA10N50C or similar as a pass transistor with Zener clamping of its gate to the output for protection, and a 2.7R resistor in series with its source with a NPN transistor B-E across it, collector to the gate for very fast fixed current limiting so it doesn't die if the output's shorted.

Then to get it to regulate, a TL431 in cascode with a suitable HV transistor, and a HV current source pulling up the cascode collector or drain to provide the pass transistor gate drive    Adjustable current limiting would use a low side sense resistor and pull down the emitter or source of the cascode transistor to collapse the output voltage.
 

Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #26 on: November 19, 2017, 07:34:49 AM »
SCR's and diodes are the most reliable semiconductors and the only ones you can reliabely protect by an ultra-fast fuse.
 

Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #27 on: November 19, 2017, 09:02:34 AM »
I got rid of tubes in my gear
No way to return to dark times  :scared:


Thanx to all who told me about mosfet benefits and limits.  :-+
I'm google now for similar project. If anyone will find some, please post here
 

Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #28 on: November 19, 2017, 09:14:55 AM »
Hmmm . . . .  Considering a possible solid state design . . .

Use a FQA10N50C or similar as a pass transistor with Zener clamping of its gate to the output for protection, and a 2.7R resistor in series with its source with a NPN transistor B-E across it, collector to the gate for very fast fixed current limiting so it doesn't die if the output's shorted.

Then to get it to regulate, a TL431 in cascode with a suitable HV transistor, and a HV current source pulling up the cascode collector or drain to provide the pass transistor gate drive    Adjustable current limiting would use a low side sense resistor and pull down the emitter or source of the cascode transistor to collapse the output voltage.

That's all you need. :-+

Tim
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Offline Hero999

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Re: Looking for yours opinions! HV bench power supply
« Reply #29 on: November 19, 2017, 10:33:28 AM »
Thanx A Lot!

I see what in 350V 0.2A range where are many affordable mosfets
So it is not a problem

What You can say about this diagram?
Oh dear, not good at all. It's not really regulated at all, just a potentiometer with an amplifier on the wiper. If you don't need to vary the voltage so much, the TL431 can be used. Here's an example of a 250V regulator. Tr1 can be a MOSFET, if needs be. There's no over current protection, but that can be added if needs be.
 
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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #30 on: November 19, 2017, 08:05:31 PM »
Thanx again!

I see that Tr2 must be rated to wery HV, isn`t it?
Is it ok to use diodes or current mirror to move applied DC levels?
 

Offline richard.cs

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Re: Looking for yours opinions! HV bench power supply
« Reply #31 on: November 19, 2017, 11:33:58 PM »
It is clearly possible to do this with silicon pass elements, someone mentioned the FCP650N80Z which does look promising. Datasheet: http://www.mouser.com/ds/2/149/FCP650N80Z-908248.pdf, SOA graph on P4 shows the d.c. line: 200 mA @ 800 V,  300 mA @ 500 V, 400 mA @ 400 V.

Having said that, I have built such a supply and used a PL504 as the output device, plus two small signal valves to level shift the drive down to the all-silicon control circuitry. My spec was 200 mA at 500 V and whilst I spent a lot of time looking at silicon options it was just way more effort to create an all-silicon supply than a hybrid. Normal operation was fine, but surviving a short-circuit on the output, even transiently, was hard and it just looked too much like I'd blow up lots of transistors perfecting it. For the sake of adding a little volume (a PL504 is 28mm diameter and 90 mm tall) and the floating heater supply it was a no-brainer for me.

Consider the situation when your 350 V supply is set to max output, no load. The unregulated side might be at 360 V but let's call it 400 for simplicity. If you apply a short-circuit to the output then your pass element acts as a voltage follower backed by the low impedance of whatever capacitance you have upstream, your peak current is essentially limited by Rdson because the source has been pulled down to zero and the gate hasn't moved yet. Your pass element now sees maybe 400 A and 400 V. This is way outside the SOA of the FCP650N80Z which can do 25 A at 400 V for 10 us max, and that assumes you started with the die at 25 C. The valve wins here mainly because this instantaneous dissipation happens over a large area of sheet metal rather than a tiny die.

Essentially this always puts you outside the SOA, and all you can do is make the current limit cut in fast enough that nothing blows up. Realistically it's probably easier to design the supply as a current source controlled for voltage.
 
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Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #32 on: November 19, 2017, 11:53:18 PM »
Consider the situation when your 350 V supply is set to max output, no load. The unregulated side might be at 360 V but let's call it 400 for simplicity. If you apply a short-circuit to the output then your pass element acts as a voltage follower backed by the low impedance of whatever capacitance you have upstream, your peak current is essentially limited by Rdson because the source has been pulled down to zero and the gate hasn't moved yet. Your pass element now sees maybe 400 A and 400 V.

Hold on a second.
1. Rds(on) is a convenience, and it only applies at low voltages.  Check Fig. 3. :)  Fig.1 is more pertinent, though it doesn't show the full range.
2. As it happens, SuperJunction MOSFETs have current saturation different from traditional MOS.  Transconductance crashes beyond about 7V, so that even under a pulsed condition, more than about 40A is unlikely from this device.

IGBTs have a similar behavior, though the available transconductance tapers off less sharply, so that short circuit current tends to be limited more by Vgs(on).

I've measured STP19NM50N (from ST's SuperJunction family) which behaves this way.  See for example this measured curve:
https://www.seventransistorlabs.com/Images/STP19NM50N%20Drain%20Output%20Curves.png
I didn't plot 8V because it was almost identical to 7V.

Still, this is beyond the SOA, even for pulsed conditions.

So...

Quote
Essentially this always puts you outside the SOA, and all you can do is make the current limit cut in fast enough that nothing blows up. Realistically it's probably easier to design the supply as a current source controlled for voltage.

??? You're just going to throw your hands up?  When the solution is a resistor and transistor away?  Or a resistor and a zener?

The throwaway VCCS idea is actually quite an important concept, though much more complicated than needed here.  You need to go that route for a switching regulator, since the inductor's state variable is current. :)

Tim
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Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #33 on: November 19, 2017, 11:56:44 PM »
Thanx again!

I see that Tr2 must be rated to wery HV, isn`t it?
Is it ok to use diodes or current mirror to move applied DC levels?

Yes, HV.  As I noted earlier:

Anyway, as for control, it can be done just the same way the vacuum tube unit did it.  Indeed, you need at least a few "tube replacements" to handle the high voltage: one is the pass transistor, one is its driver (the voltage gain element).

Diodes and current mirrors aren't very helpful here, though a current source can be used to increase the voltage gain of the driver, giving better DC accuracy. :)

Everything else can be low voltage, like the TL431 circuit shown earlier (but do add current limiting, as it's not merely optional here!).

Tim
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Offline b_force

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Re: Looking for yours opinions! HV bench power supply
« Reply #34 on: November 20, 2017, 12:10:55 AM »
I build a few in the past, don't get all the very heavy complicated circuits.
In some cases you can even get away with a good old LM317, as long as you keep an eye on the voltage difference.

This very simple design worked pretty fine, unfortunately can't find the finalized schematic anymore, but it gives a general idea.
http://www2.zelfbouwaudio.nl/forum/download/file.php?id=38726&mode=view

The biggest drawback is just the power dissipation, so therefor I would highly recommend a switching supply with a (flyback) transformer or a tracking supply.
"If you can't explain it simply (or at all), you don't understand it well enough." A. Einstein

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Offline richard.cs

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Re: Looking for yours opinions! HV bench power supply
« Reply #35 on: November 20, 2017, 06:05:56 AM »
Hold on a second.
1. Rds(on) is a convenience, and it only applies at low voltages.  Check Fig. 3. :)  Fig.1 is more pertinent, though it doesn't show the full range.
2. As it happens, SuperJunction MOSFETs have current saturation different from traditional MOS.  Transconductance crashes beyond about 7V, so that even under a pulsed condition, more than about 40A is unlikely from this device.

IGBTs have a similar behavior, though the available transconductance tapers off less sharply, so that short circuit current tends to be limited more by Vgs(on).

Good points, and yes using Rdson here was an oversimplification, I had assumed that the R(I) curve in figure 3 mainly related to die temperature and therefore was more applicable to steady-state currents, but the short pulse results in figure 1 make it clear that there's more to it than that. I also wasn't aware that SuperJunction MOSFETs behaved differently, that's good to know, thanks.


??? You're just going to throw your hands up?  When the solution is a resistor and transistor away?  Or a resistor and a zener?

The throwaway VCCS idea is actually quite an important concept, though much more complicated than needed here.  You need to go that route for a switching regulator, since the inductor's state variable is current. :)

Not quite like that, I spent a lot of time playing in SPICE, and couldn't get something that I was convinced was robust enough to survive real-world lab use. I am not denying it's possible, or even saying that it's especially difficult, but for me making a hybrid design wasn't a big deal - I wasn't aiming for minimum size or anything. It was a couple of years ago now so I don't remember exactly where I got to with MOSFETs, but I remember I almost went with a design with multiple bipolars in series with some base capacitors to ensure dynamic voltage sharing.

Anyway, if the OP wants an all-silicon design that's cool, I was more sharing how I did mine.
 

Offline floobydust

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Re: Looking for yours opinions! HV bench power supply
« Reply #36 on: November 20, 2017, 06:41:36 AM »
Vacuum tubes have great advantages for high voltage applications and more particularly for HV power supply....

I use tubes for HV >500V power supplies as they are beyond tough and dirt simple circuits. They do have their place there. Thanks for posting those schematics.

Using one semiconductor for a pass-transistor is a dream. If this is truly a bench power supply that gets shorted or overloaded a lot, you've got usec to switch off your tranny with say 1,500pF gate capacitance. Commercial products use several pass-transistors in series to limit SOA, have current-limiting and much more complexity.

The fun about designing off the datasheet, is it all looks good until you build it and poof! pass transistor shorted. Charging up a few uF of the load's input capacitance, poof. This is seen routinely when powering HV loads and oops forgot to consider that requirement.




 

Offline Hero999

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Re: Looking for yours opinions! HV bench power supply
« Reply #37 on: November 20, 2017, 07:05:51 AM »
I build a few in the past, don't get all the very heavy complicated circuits.
In some cases you can even get away with a good old LM317, as long as you keep an eye on the voltage difference.

This very simple design worked pretty fine, unfortunately can't find the finalized schematic anymore, but it gives a general idea.
http://www2.zelfbouwaudio.nl/forum/download/file.php?id=38726&mode=view

The biggest drawback is just the power dissipation, so therefor I would highly recommend a switching supply with a (flyback) transformer or a tracking supply.
Yes, the LM317 will work. A cascode can be added to keep the voltage across it to a safe level.

I'd use a lower voltage zener than 39V, as that's pushing it close to the absolute maximum rating of 40V.
http://www.eevblog.com/forum/beginners/design-of-circuit-for-0-24v-5amp-regulated-power-supply/?action=dlattach;attach=352281;image

EDIT:
Don't used the circuit, linked above, for such high voltages. It will exceed the safe operating area of the BJT!

Use a MOSFET with a suitable SOA, such as the FQL40N50.
« Last Edit: December 03, 2017, 05:15:07 AM by Hero999 »
 
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Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #38 on: November 20, 2017, 08:07:18 AM »
R3 would be much better as a CCS, and then TR2 isn't so important (indeed, it can be removed if the minimum load is more than the CCS current -- it might be worth tacking on a second CCS to do just this!).

The LM317 ensures current limiting, though not very appropriate for high voltages -- a low current model (~100mA) would be welcome.  Or, a series output resistor and diode can also be used to pull down ADJ when current draw exceeds a lesser limit, and this will act as quickly as the regulator can.  Downside, output regulation is made poorer.

And of course, a MOSFET version would be better -- but that's a trivial substitution, actually. :)

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Offline b_force

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Re: Looking for yours opinions! HV bench power supply
« Reply #39 on: November 20, 2017, 08:49:27 AM »
I actually still have some switching bench supplies ideas/projects laying somewhere.
If there is some interest, I can dig them up and see if we can make something out if it.
Question is, what kind of features would it need?
"If you can't explain it simply (or at all), you don't understand it well enough." A. Einstein

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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #40 on: November 20, 2017, 10:03:51 AM »
I actually still have some switching bench supplies ideas/projects laying somewhere.
If there is some interest, I can dig them up and see if we can make something out if it.
Question is, what kind of features would it need?

Nothing extraordinary
Only old tube variable voltage ps substitution with curent limit
Simple linear issue
Ripple no more 300mV at 350v output

I'm beware switching power suply for EMI
 

Offline floobydust

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Re: Looking for yours opinions! HV bench power supply
« Reply #41 on: November 20, 2017, 12:05:11 PM »
Instead of trying to work with 350V, consider the "floating power supply rail" designs that are commonly used in low voltage 0-30V bench PSU's. The entire regulation circuit runs off say 12V, floating at the output voltage.

OP can reuse the power transformer from his old tube PSU and use one filament winding to power the high-side regulator circuit. MOSFET's or Bipolars easy to drive then.
 

Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #42 on: November 20, 2017, 03:57:46 PM »
 :wtf: read first post
 

Offline David Hess

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Re: Looking for yours opinions! HV bench power supply
« Reply #43 on: November 20, 2017, 04:23:26 PM »
Why so many words about pass transistor?

Is MOSFET rated to 800V 10A 240W is not ok for 350V 0.2A linear power supply?

Did you have a specific MOSFET in mind?

At a high drain-to-source voltage which is actually pretty low, the Vgs temperature coefficient reverses and a MOSFET intended for switching applications will suffer from something very similar to secondary breakdown in a bipolar transistor.  Linear rated MOSFETs are available which do not suffer or suffer less from this.

Why not build a solid state linear regulator which uses a power tube as a pass element?

A more complex entirely solid state design could stack 2 or more power pass elements in series to distribute the voltage drop and power across multiple devices.
 

Offline floobydust

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Re: Looking for yours opinions! HV bench power supply
« Reply #44 on: November 20, 2017, 04:24:06 PM »
Ya I thought you threw it out, not sold it.
What are you looking to use for a power transformer now? That is most of the cost for 175W output.
I'm suggesting having a small transformer to power the regulation circuit and MOSFET drive, floating with the PSU output.

Power MOSFETs are an extremely competitive market, a lot of bullshit on the datasheets. Junior engineers think "800V 10A" datasheet spec should be able to do it like a walk in the park. But not in linear mode.
I'm not sure what good a 10usec SOA value is.
« Last Edit: November 20, 2017, 04:29:19 PM by floobydust »
 
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Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #45 on: November 20, 2017, 05:43:54 PM »
I believe that 001 should realize that a high voltage bench power supply must be safe and bulletproof.

We are not at the university to study theoretical projects that could possibly work in a laboratory, but to carry out a project with the level of knowledge of 001 who is obviously not an expert in the field.

Unfortunately, he made a mistake, that of selling his old vacuum tube power supply and he tries to justify this mistake by saying that he does not want to use vacuum tube anymore.

Yet it is the simplest, safest and most accessible solution of his knowledge.

errare humanum est, perseverare diabolicum.

Of course,  the old power supply he sold was not that good.
I have posted much better schematics.

The idea of an hybrid power supply with solid state control and vacuum tube as a series regulator is excellent.
That's the way to go.

As cheap vacuum tubes still manufactured, I would choose EL34 (3 or 4 in parallel)
« Last Edit: November 20, 2017, 05:47:22 PM by oldway »
 
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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #46 on: November 20, 2017, 06:01:48 PM »
What hybrid schematc You can reccomend?
 

Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #47 on: November 20, 2017, 06:21:59 PM »
It should be developed, or you have to use a vacuum tube scheme like the BED-002 that I have already posted with some modifications for a higher current.

I unfortunately do not have time to take care of it because I am doing repairs of vintage audio devices and I have dozens of devices waiting for repairs.

EDIT: with 4 x EL34 and 400V rectified voltage, you can make a 50V to 350V ajustable power supply 250 mA without any pre-regulator.
« Last Edit: November 20, 2017, 07:05:23 PM by oldway »
 
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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #48 on: November 20, 2017, 07:12:00 PM »
It should be developed, or you have to use a vacuum tube scheme like the BED-002 that I have already posted with some modifications for a higher current.

I unfortunately do not have time to take care of it because I am doing repairs of vintage audio devices and I have dozens of devices waiting for repairs.

EDIT: with 4 x EL34 and 400V rectified voltage, you can make a 50V to 350V ajustable power supply 250 mA without any pre-regulator.

Thanx for Yours opinion

But

I'm not a tube fun  :-// So i'm going to " invent a bike" with my transistors :-DD
 

Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #49 on: November 20, 2017, 07:22:51 PM »
If you are not a tube fan, why do you need a high voltage bench power supply ?
 

Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #50 on: November 20, 2017, 07:44:25 PM »
If you are not a tube fan, why do you need a high voltage bench power supply ?

i work with homebrewed polymer films
« Last Edit: November 20, 2017, 07:47:06 PM by 001 »
 

Online prasimix

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Re: Looking for yours opinions! HV bench power supply
« Reply #51 on: November 20, 2017, 07:56:52 PM »
How "EMI" issue (many times synonymously taken for "ripple and noise" too) is then applicable for such type of application? If "not" (since today you can find "switchers" in many sensitive devices) maybe you should really start consider some switcher topology.
Maybe you can take a look at SEPIC/cuk topologies (that are inherently "lower noise"), an example can be found in LTC app-note/journal 84 (page 146). It's CV/CC SEPIC power supply with "only" 0-100 V, but that range can be easily extended to 0-350 V and beyond. Please note that input is low voltage e.g. 48 Vdc (or anything in that range). Another "harder switching" topology that is AFAIK heavily employed in solar harvesting solutions is current-fed push pull converter (could be with single or dual inductor). With it you can easily goes anywhere up to few kV and (kW too) with proper transformer (and experience/knowledge).
« Last Edit: November 20, 2017, 07:59:06 PM by prasimix »
 
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Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #52 on: November 20, 2017, 08:18:17 PM »
With this kind of application, do you really need regulated output ?
What about a variac with isolation transformer, a circuit breaker, a bridge rectifier and an electrolytic capacitor (with discharge resistor for safety) ?
 

Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #53 on: November 20, 2017, 08:28:05 PM »
I`m aware from swichers since I don`t know how to buid realy "quiet" ones  :-//

P.S. simple variac and rectifier is not ok becouse ripple voltage so high and no way to current limit
Previous tube linear supply was ok but it is wery large, hot and in fact kind of antique crap (almost all parts was needs to replacement)
all I need is to clone it with a new parts (i yet pic new industrial grade siemens [email protected] transformer) and transistors
 

Online prasimix

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Re: Looking for yours opinions! HV bench power supply
« Reply #54 on: November 20, 2017, 08:31:18 PM »
I`m aware from swichers since I don`t know how to buid realy "quiet" ones  :-//

Ok, if you decide to be more specific I believe that you can count on more valuable feedback about "quietness" from many members of this forum :)
 

Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #55 on: November 20, 2017, 08:39:14 PM »
The most common switching supply topology in diy internet is terrible in ripple and emi sence
I`m not experienced in high grade PS and I have no ideas to do it
can You post some links about quiet ps shematics? 300mV ripple voltage at [email protected] will be affordable
 

Online prasimix

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Re: Looking for yours opinions! HV bench power supply
« Reply #56 on: November 20, 2017, 08:48:22 PM »
I just posted one :). I can bet that LTC's SEPIC could go easily below that 300 mV. Going from 0-100 to 350 V shouldn't be an issue. Actually in one or other way be prepared to spend some time and energy in finding "ready to go" SEPIC transformer or to make a custom one.
As ready-made solution maybe you should consider transformers with multiple windings such as WE-FLEX+ that comes in many forms (i.e. base inductance and current). You can also try to navigate list of ready-made transformers from Feryster (available thru TME.eu).
 
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Offline oldway

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Offline 001

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« Last Edit: November 20, 2017, 09:44:48 PM by 001 »
 

Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #59 on: November 20, 2017, 09:53:52 PM »
Another solution:

http://www.advanceproductservices.co.uk/data/E350.pdf

My opinion ?
I prefer to trust in my EL34 option.... :-DD

I was making vacuum tube audio amplifiers in the past....this may explain my opinion.  :-DD
 
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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #60 on: November 20, 2017, 10:01:36 PM »
It should be developed, or you have to use a vacuum tube scheme like the BED-002 that I have already posted with some modifications for a higher current.

I unfortunately do not have time to take care of it because I am doing repairs of vintage audio devices and I have dozens of devices waiting for repairs.

EDIT: with 4 x EL34 and 400V rectified voltage, you can make a 50V to 350V ajustable power supply 250 mA without any pre-regulator.

You spend a lot of time here/ Thanx!!
Can You post shematic of YOURS OWN HV PS? The PS You daily use
 

Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #61 on: November 20, 2017, 10:09:40 PM »
Also Fug SMPS Model MCP 140-350 , very good, I already had one....

0 - 350V 400 mA.

http://www.fug-elektronik.de/en/files/259000/FuG_Catalogue.pdf

When I was developing tubes audio amplifiers, I was using an adjustable (multi taps transformer)  non regulated power supply because my amplifiers did not have HV regulated power supply.

But this was a long time ago.  :-DD......something like 1968...1970
« Last Edit: November 20, 2017, 10:12:22 PM by oldway »
 
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Offline b_force

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Re: Looking for yours opinions! HV bench power supply
« Reply #62 on: November 20, 2017, 11:03:00 PM »
The variac option is actually not so bad with a decent MOSFET regulator.
Since a variac is wise to use anyway with these kind of circuits.
"If you can't explain it simply (or at all), you don't understand it well enough." A. Einstein

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Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #63 on: November 21, 2017, 12:04:14 AM »
The most common switching supply topology in diy internet is terrible in ripple and emi sence
I`m not experienced in high grade PS and I have no ideas to do it
can You post some links about quiet ps shematics? 300mV ripple voltage at [email protected] will be affordable

The two main problems are poor layout, and lack of filtering.

Layout is critical.  A bad layout can affect the schematic, to the extent that the circuit is incapable of operating as intended (self interference)!  A good layout reduces noise sources in the first place.

Filtering can always be done, and again, layout is important.  Consider the case where all wires entering and exiting a module must pass through a shield: the shield provides a unipotential surface, and each wire passing through the shield must be filtered.  By filtering all wires against a common (unipotential) shield, all unbalanced AC currents can be eliminated.

The same method still applies if you make compromises, like common mode filtering of input and output pairs (which allows you to save on the cost of inductors).  Indeed, this is necessary for mains input, because mains is itself AC, so it can only be filtered so much before it ceases to be mains. :)

Here's an old circuit I made,



You can ignore the other outputs (like 6.3V, 2kV and -250V), and consider just the positive output (250V).  Note the input and output filters.

This exact circuit never worked very well, due to its voltage mode design, and due to excessive recovery losses in the diodes, due in part to a poor transformer design.  But the noise output was well within specification.

I later modified this design (rather aggressively; "modify" is something of a misnomer here, as more than half of the circuit board was replaced :) ) to a flyback type supply, which operates much more safely and efficiently.

Tim
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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #64 on: November 21, 2017, 01:52:15 AM »
Awesome project  :-+ Thanx!
How large transformers cores I need?
But how to redesign it to 230V mains?
 

Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #65 on: November 21, 2017, 02:15:28 AM »
For 200W power levels, something in the EE33 or ETD29 range will do for the power transformer.  Gate drive transformer and filter chokes can be off the shelf parts.  Understand that a switching power supply is a much larger challenge, and will require an oscilloscope to test.

Tim
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Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #66 on: November 21, 2017, 03:10:16 AM »
Your chance or never to learn why ALWAYS to wear safety glasses when you make experiments with Mosfet, and mostly with TO247....  :-DD
« Last Edit: November 21, 2017, 03:13:03 AM by oldway »
 

Offline T3sl4co1l

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Re: Looking for yours opinions! HV bench power supply
« Reply #67 on: November 21, 2017, 03:54:42 AM »
Your chance or never to learn why ALWAYS to wear safety glasses when you make experiments with Mosfet, and mostly with TO247....  :-DD

Good point by the way, whether silicon or vacuum filled.  Solder can splash, sparks can fly, capacitors can explode.  And safety squints aren't going to save you forever. :)

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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #68 on: November 21, 2017, 04:49:24 AM »
Solder can splash, sparks can fly, capacitors can explode.

Thanx for clarity but I solder for 48 years yet http://www.eevblog.com/forum/projects/so-old-to-learn-serious-problem/
(but still not understand some engineering :palm: )
 

Offline oldway

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Re: Looking for yours opinions! HV bench power supply
« Reply #69 on: November 21, 2017, 05:18:35 AM »
Whoever has never had a Mosfet that exploded in his face probably never worked on a switching power supply ... And the TO247 really explode violently.

I worked at Cherokee Europe, and I saw a lot of SMPS and I have some MOSFET TO 247 that exploded in my face .....

The schematics you have chosen is not problematic since the transformer driver makes it virtually impossible for both Mosfets to drive at the same time unless .... there is an insulation fault in the driver transformer .... :-DD
That's what happened with me.

In my opinion, the biggest problem is the high stress of the 2 capacitors 0.47µF because of the high rms current.

The control transformer driver, as you have projected, without additional circuit to discharge the gate condensator, is too slow to switch off.
« Last Edit: November 21, 2017, 05:22:19 AM by oldway »
 

Offline chris_leyson

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Re: Looking for yours opinions! HV bench power supply
« Reply #70 on: November 21, 2017, 05:41:12 AM »
Found this the other day https://linearaudio.nl/t-reg-tube-voltage-regulator It's a nice design and the idea is based on the obsolete MC1466L "floating" voltage regulator. The original design used tubes or enhancement mode mosfets, DN2540, and it appeared in the March 2009 edition of Elektor and very recently audioxpress http://www.audioxpress.com/article/t-reg-a-high-voltage-regulator-for-tube-amps. It had a habit of blowing up the enhancement mode mosfets when shorted out but I think the design has been updated for depletion mode mosfets with a much larger SOA. Hmmm... think I've got a spare EL34 somewhere will have to spice it up to see if it's short circuit proof. EDIT: Oops got enhancment and depletion mixed up
« Last Edit: November 21, 2017, 07:20:16 AM by chris_leyson »
 

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Re: Looking for yours opinions! HV bench power supply
« Reply #71 on: November 21, 2017, 05:47:13 AM »
Yes, first improvement is using TL598 with schottky clamp diodes to drive the GDT directly -- this gives a proper waveform, with fast fall time.  I think that was actually this, https://www.seventransistorlabs.com/Images/GateDrive1.jpg (though time/div is missing, a shame).  That prevents direct shoot-through, but overheating transistors (due to excessive switching loss and load current) will still fail shorted.

The biggest problem I had was actually diode recovery loss.  Too much LL in the transformer resulted in significant secondary-side overshoot, even with damping resistors and doubled up diodes.  Diodes don't connect in series well, either: if recovery times are not matched, then the first one that recovers sees full voltage, and avalanches, until the other one opens.  Basically, as reverse voltage increases, the diodes continue carrying full load current, until the last diode finishes recovery.  Huge dissipation.  Recovery time goes up with temperature, so it's a runaway situation.

Nowadays, it's easy enough to spend a couple bucks more and plop in a SiC schottky -- recovery loss is eliminated.  (I took this route on the "modified" version, with flyback converter: tried it with UF4007 first, got too hot -- probably as much from conduction loss as recovery, because peak current is much higher in a flyback converter.  Plopped in a C3D04060F, and she runs cool and clean.)

Tim
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Offline Hero999

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Re: Looking for yours opinions! HV bench power supply
« Reply #72 on: November 21, 2017, 11:11:43 PM »
R3 would be much better as a CCS, and then TR2 isn't so important (indeed, it can be removed if the minimum load is more than the CCS current -- it might be worth tacking on a second CCS to do just this!).

The LM317 ensures current limiting, though not very appropriate for high voltages -- a low current model (~100mA) would be welcome.  Or, a series output resistor and diode can also be used to pull down ADJ when current draw exceeds a lesser limit, and this will act as quickly as the regulator can.  Downside, output regulation is made poorer.

And of course, a MOSFET version would be better -- but that's a trivial substitution, actually. :)

Tim
I thought the requirement was for a 200mA, yet the LM317L is only rated to 100mA. I suppose a good reason for running the LM317 at a higher voltage differential than 15V, is the safe operating area protection will kick in and limit the current to around 400mA. If that's not low enough, another transistor could be added to cut-off the base drive to Tr1, when the voltage across a sense resistor exceeds its VBE threshold.

Yes using a current source for R3 would be better, at the expense of the additional complexity. Whether it's worth it or not depends on how much variation there is in the input-output differential. It's probably worth keeping Tr2, as this is for a bench power supply, which could be operated with no load. A constant current load could be added to the output, but that's probably more complex than Tr2.

EDIT:
Don't used the attached circuit for such high voltages. It will exceed the safe operating area of the BJT!

Use a MOSFET with a suitable SOA, such as the FQL40N50.
« Last Edit: December 03, 2017, 05:14:35 AM by Hero999 »
 
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Offline oldway

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Re: Solved. Tread to delete. maybe
« Reply #73 on: November 22, 2017, 01:22:32 AM »
What's the matter here? You are crazy... |O |O |O

Is this the first time you take part of a forum ?
You are not alone on earth.....This topic has a lot of informations for who need a HV power supply.....You can't delete all our work.....

Restore the original title of the topic.... :palm:
« Last Edit: November 22, 2017, 01:26:48 AM by oldway »
 
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Offline 001

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Re: Looking for yours opinions! HV bench power supply
« Reply #74 on: November 22, 2017, 03:32:30 AM »
The idea of an hybrid power supply with solid state control and vacuum tube as a series regulator is excellent.

How to substitute V1 V2 V3 with semiconductors in this shematic?
 

Offline Ysjoelfir

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Re: 0-350V 0.2A Bench Power Supply
« Reply #75 on: November 22, 2017, 06:40:03 AM »
V1 and 2 are just voltage stabilizing tube with a burning voltage of 150. You could substitute them with suitable zener diodes, potentially some of them in series.
V3 is the tube that drives the series pass element. You would have to calculate the grid voltage that needs to be present there to get the original controll range (meaning to controll the 6L6 from "flood that glass bulb with electrons" to "keep those electrons around that glowing stick") and build a control stage corresponding to that value. This could be done in many ways, pick one you feel comfortable with and start calculating :)
« Last Edit: November 22, 2017, 06:42:37 AM by Ysjoelfir »
Greetings, Kai \ Ysjoelfir
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #76 on: November 22, 2017, 10:32:31 PM »
The IP17 Heathkit power supply does not meet your specifications: nominal 100mA, 125mA max instead of 200mA.
If you have bought one, I advise you not to try to modify or to improve it, except maybe replace V1 and V2 (OA2) with zener diodes.
I have never been a fan of these cold cathode regulator tubes, but it was the only thing available at the time.
http://www.sgitheach.org.uk/ip17.html

If you want to design and manufacture your own high voltage power supply, you must follow this procedure:

1) The biggest problem is the transformers.
Can not make a  "custom" transformer for a single unit, the price would be excessive.
It is therefore necessary to use commercial transformers.

So the choice is limited and it will be necessary to use several transformers.

One option is to find out if a transformer for a tube amplifier could serve ... They usually have at least one high voltage winding and a 6.3V winding.
https://tubedepot.com/t/diy-central/transformers-and-chokes?page=1

Another option is to use for high voltage an isolation transformer that has a 400V winding. (using secundary as primary, no problem, transformer is reversible)
https://www.erea.be/fr/produits/detail/efsp160
The rectified high voltage (bridge rectifier) would then be 565V, which allows regulated output voltage up to 450V, which is ideal for those working on vacuum tube projects.

To be continued....
« Last Edit: November 22, 2017, 10:35:10 PM by oldway »
 

Offline b_force

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Re: 0-350V 0.2A Bench Power Supply
« Reply #77 on: November 22, 2017, 10:41:17 PM »
You can also use two transformers back-to-back.
But there are plenty of affordable HV transformers out there.

"If you can't explain it simply (or at all), you don't understand it well enough." A. Einstein

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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #78 on: November 22, 2017, 10:49:07 PM »
Hi

Thanx for yours opinion


But read post abowe carefully. I found awesome industrial grade siemens transformer. Awesome 230/400v transformers for decent price You can find at undeground and ubach reilroad workshops
Some of this workshops can rewind it for You. So it is not problem

I see schematic of ip17 is very basic and simple. I want to substitute el34 with pl509 (deathproof beast for decades of tube tv, 500ma catode current, $3 at garage sales) . Can i eliminate negative supply if it is not critical to have 0 zero minimum? Can i use pass tube in triode mode to elimenate screen power supply?
« Last Edit: November 22, 2017, 11:39:19 PM by 001 »
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #79 on: November 22, 2017, 11:50:34 PM »
IMHO that tube would do nicely in a hybrid supply - IC current and voltage control loops, discrete transistors for the grid driver and a tube for the main pass element.

http://www.radiovilag.hu/images/PL509.pdf

Its got a 40V heater.   If you capacitively couple a bridge rectifier to the heater supply, its trivial to derive a boosted screen grid supply 50V above the anode voltage.   Use a 20-0-20 transformer, connect the center tap to the cathode (as the max heater-cathide voltage is only 250V so you cant run the heater grounded) and add another bridge rectifier you can also use it for a floating +/- 15V regulated supply riding on the output voltage for OPAMPs in the control circuits.  The PL509 needs at least -50V grid bias for cutoff, so you'll need another capacitively coupled rectifier to get that from the filament supply. 


However the fly in the ointment is the max 30W plate dissipation.   At 400V in, that means you cant pass more than 75mA without overheating the plate with a risk of catastrophic envelope failure if sustained.   Either you are going to need 3x PL509 in parallel or you are going to need a tap-changer that tracks the output to keep the average Vak below 150V for 200mA output.

One approach  would be a 55-0-55, 50VA transformer and a 110-0-110, 100VA transformer, which after rectification gives you voltage steps of 77V and 155V respectively.  The easiest option for tap changer control would be a MCU monitoring the output driving relays.     There's enough headroom there to extend the spec to 0-400V, 0-250mA out.
« Last Edit: November 22, 2017, 11:59:06 PM by Ian.M »
 

Offline richard.cs

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Re: 0-350V 0.2A Bench Power Supply
« Reply #80 on: November 23, 2017, 12:05:44 AM »
However the fly in the ointment is the max 30W plate dissipation.   At 400V in, that means you cant pass more than 75mA without overheating the plate with a risk of catastrophic envelope failure if sustained.   Either you are going to need 3x PL509 in parallel or you are going to need a tap-changer that tracks the output to keep the average Vak below 150V.

Note that that is with the design centre rating system*, not an absolute maximum which is given as 40 W. Switching to a PL519 would get you an extra 5 W anode dissipation on an otherwise very similar valve: http://www.r-type.org/pdfs/pl519.pdf - it's essentially an uprated version.

*i.e. the manufacturer means you can design for 30 W at nominal mains voltage and component values (10% resistors, etc.) and it won't blow up in real world use. The switch from design centre to absolute maximum was a big part of why early transistors got a reputation for being fragile and easily damaged, coupled with the lower heat capacity of a microscopic silicon die compared to an anode or grid.



 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #81 on: November 23, 2017, 12:31:41 AM »
400V DC bus in, 0.2A cathode current is going to be 80W plate dissipation so even with a PL519 you'd need two in parallel to operate without a tap changer, and they would be running *HOT* at full load and low output voltage.   

Unless the tube in question is popular with the tube amp audiophiles, long term availability is likely to be an issue, so personally I'd rather minimise the number of 'bottles' required so I could afford to stock enough spares.  Keep it down to 30W and enjoy long tube life and be able to use either PL509 or PL519, depending on cost and availability.
« Last Edit: November 23, 2017, 12:39:06 AM by Ian.M »
 

Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #82 on: November 23, 2017, 12:54:02 AM »
Jim Williams used an Eimac 75TH with a plate dissipation of 75 watts in his example shown below.

Foldback current limiting would be a good idea in a general purpose power supply to limit dissipation at low output voltages.  A time constant can be used to allow maximum current for short periods.
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #83 on: November 23, 2017, 02:54:03 AM »
Simple circuits attached
Is it usable? Comment please
« Last Edit: November 29, 2017, 01:32:24 AM by 001 »
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #84 on: November 23, 2017, 03:08:46 AM »
Jim Williams used an Eimac 75TH with a plate dissipation of 75 watts in his example shown below.
I posted the same circuit awhile ago, except it used a BJT, rather than a valve. The main issue is there will be a significant minimum load requirement, due to the zener current and using 1k2 for the upper resistor in the LM317's potential divider. Reducing the resistor values and adding a PNP transistor, as in my circuit, would eliminate the need for the minimum load, at the expense of a higher quiescent current.

http://www.eevblog.com/forum/beginners/design-of-circuit-for-0-24v-5amp-regulated-power-supply/?action=dlattach;attach=352281;image

EDIT:
The above circuit won't work up to 400V. It will exceed the safe operating area of most BJTs, unless many devices are connected in parallel. Use a MOSFET, which can tolerate >0.2A @ >350V, such as the FQL40N50.


http://www.mouser.com/ds/2/308/FQL40N50-1124413.pdf
« Last Edit: November 27, 2017, 10:30:45 AM by Hero999 »
 
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Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #85 on: November 23, 2017, 03:22:08 AM »
@001,
The first circuit is unregulated, and as the IRF740 doesn't have a DC line on its S.O.A graph, it probably wont survive a sustained output short to ground even if it survives the initial transient.

The second circuit is regulated, but doesn't have a wide output voltage adjustment range, nor can it easily be modified to extend its adjustment range below the voltage stabilizer tube's operating voltage.  Also the only current limit is the pass valve cathode emission limit.

@Hero999 & David Hess,

I believe that Jim Williams circuit has severe issues if lightly loaded or if the output is ever shorted.  Look at the Eimac 75TH datasheet for the grid cutoff voltage with 2.5KV on the plate and you'll see why I'm concerned.
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #86 on: November 23, 2017, 03:55:30 AM »
@001,
The first circuit is unregulated, and as the IRF740 doesn't have a DC line on its S.O.A graph, it probably wont survive a sustained output short to ground even if it survives the initial transient.

The second circuit is regulated, but doesn't have a wide output voltage adjustment range, nor can it easily be modified to extend its adjustment range below the voltage stabilizer tube's operating voltage.  Also the only current limit is the pass valve cathode emission limit.

Thanx a lot!

Can You Help me combine theese two circuits?
I want use simple 0.2A current limitter from first circuit and tube pass from second circuit
but how I can substitute small pentode (actualy tetrode) driver to transistor (or simple common triode)?  :-//
« Last Edit: November 23, 2017, 03:57:28 AM by 001 »
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #87 on: November 23, 2017, 04:04:22 AM »
@001,
The first circuit is unregulated, and as the IRF740 doesn't have a DC line on its S.O.A graph, it probably wont survive a sustained output short to ground even if it survives the initial transient.

Old IRF740 (IR) datasheet shows thermally limited DC SOA.

I tested a new production IRF740 (Siliconix), at 300V, at significantly better than Rth(JC) max.  You get a lot of silicon for not much cost.

Current Siliconix datasheet probably doesn't specify DC SOA because of laziness or CYA.

It's not enough power in a single device for present needs, but about three in parallel would handle it.

001,

Are you looking to learn about power supplies, or are you looking for a finished, proven schematic that you can build?  There has been quite a lot of discussion in this thread about the former, and I'm beginning to suspect you want the latter.

Tim
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Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #88 on: November 23, 2017, 04:11:33 AM »
Yes
I preffer complete shematic
but now I see what hybrid variant (pass tube and transistor driver) will be ok for me
how to combine that?
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #89 on: November 23, 2017, 04:34:03 AM »
Can You Help me combine theese two circuits?
I want use simple 0.2A current limitter from first circuit and tube pass from second circuit
but how I can substitute small pentode (actualy tetrode) driver to transistor (or simple common triode)?  :-//
Its not possible to combine them due the the difference in gate/grid control action between an enhancement MOSFET, and a valve, JFET or depletion MOSFET.

However if you start with the second circuit:

The 6Zh1P cross references to 6AK5

Delete everything to the right of and below the 6AK5  apart from its 10K-3K9 screen grid divider, and swap out the 1Meg anode feed resistor for a 100K resistor, then you could put a TL431 shunt regulator (with a potential divider off the output for its Adj pin) in cascode with the 6AK5, with its control grid fed off a 12V Zener (with a pullup to unreg +HT), and also use a NPN transistor pulling down the cascode cathode and a low side current sense resistor to implement current limiting as discussed earlier in this thread.  However the  6AK5 is only rated for 180V Vak, so it wouldn't be suitable for more than a 200V PSU.

Use the right valves and the basic idea would be good for a much higher voltage,  and with a TL431 providing the regulation, you could get the output down to a couple of volts minimum output.  However without a tap changer or switching preregulator, unless you use a brute of a transmitter valve as the pass element, you would run into plate dissipation issues with a high input voltage if its run for long in its current limiting mode.
« Last Edit: November 23, 2017, 04:48:13 AM by Ian.M »
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #90 on: November 23, 2017, 04:47:56 AM »
Awesome
Thanx  :-+

Can You coment theese ideas?

« Last Edit: November 23, 2017, 05:19:22 AM by 001 »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #91 on: November 23, 2017, 04:48:59 AM »
With a winding of 400V and a rectified voltage of 565V max, we will have a dissipation of about 100W in the power tubes at 0V 200mA.

If we have a winding 230V, or 325V rectified, we can do 2 ranges: one from 0 to 320V and one from 280 to 450V.
The anodic dissipation at 200mA will then be: range 1, 60W max, range 2, 40W max, which is quite reasonable and even allows to envisage a current greater than 200 mA.

I reject the custom transformer solution because it is not applicable for many.

The other transformers:

For 6.3V heating of the power tubes, a 6V transformer can be used.

For the supply of G2 of power tubes (I will explain later why it MUST be pentode, and not triode) , it is possible to use a 6V / 110V + 110V transformer powered by the 6V winding of the power tubes heating transformer.
One of the 110V secondary will be used for the G2 supply, the other to generate the negative bias voltage if the isolation level between the 110V windings is sufficient.

For the heating of the other tubes, another small 6V transformer

All these transformers are easily found.

To be continued....

« Last Edit: November 23, 2017, 04:51:27 AM by oldway »
 
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Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #92 on: November 23, 2017, 04:58:47 AM »
UGH!!! More HV PSUs from the dark ages.  The second one is at least somewhat elegant with a long tailed pair for the error amp.  The first/third is just fugly.
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #93 on: November 23, 2017, 05:23:08 AM »
UGH!!! More HV PSUs from the dark ages.  The second one is at least somewhat elegant with a long tailed pair for the error amp

Special for You!
Can You comment it?
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #94 on: November 23, 2017, 05:50:50 AM »
Well its discrete silicon, Russian and as the KT940A is a 300V 0.1A 10W device it doesn't have a snowflake's chance in hell of meeting your specs or surviving an output short-circuit.
Please don't waste out time with small variations of the same concept that you haven't even checked against your specified requirements.
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #95 on: November 23, 2017, 06:13:11 AM »
it doesn't have a snowflake's chance in hell of meeting your specs or surviving an output short-circuit.

Is tube pass circuit will survive?
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #96 on: November 23, 2017, 06:17:40 AM »
Yes.  A 30W anode dissipation valve has a *FAR* higher transient overload capability than a 100W Silicon transistor.   As long as you have some sort of current limiting circuit to 'throttle back' or trip before the anode or envelope melts, it will survive gross abuse.
« Last Edit: November 23, 2017, 06:22:36 AM by Ian.M »
 

Offline Hero999

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« Last Edit: November 23, 2017, 09:47:13 AM by Hero999 »
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #98 on: November 23, 2017, 06:37:56 AM »
Why not combine the design I posted, using LM317 & the BJT cascode, with the one posted by David, using the valve?

how to do it?
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #99 on: November 23, 2017, 07:14:34 AM »
2) choice of power tubes.

The choice must be made according to the availability of electronic tubes.
Only tubes with 6.3V heating are still manufactured.
For European tubes, they were tubes whose name begins with E.
(the P meant 300mA series heating, the voltage varies from one type to another)
We therefore remove all tubes starting with P.

I heard mentioning tubes like PL500, PL504, PL509 and PL519.
They were tubes designed to operate with very high voltages such as those found in the black and white TV flyback stage (PL500 and PL504) and TV's colors (PL509 and PL519).
These voltages were several kilovolts, which is why the anode connection was at the top of the tube and not the socket to avoid flashbacks.

In an HV power supply, one only finds about 600V, which is a little bit for a tube.

The main suitable tubes are: EL34, KT88, 6v6GC

Considering the prices and the number of manufacturers, it is the EL34 that I selected.

No problem with its ability to withstand 600V (I knew a public address amplifier using 4 EL34 push pull operating with an anode voltage of 700V)
The anode power is 20W, so it will take 3 in parallel.
To equalize the currents, it is necessary to put a resistance in series with the cathode of 47R 1W.

Choose steatite octal sockets of good quality.

The heating current will be 3 x 1.5A = 4.5A for 6.3V. (6V acceptable)

To be continued......
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #100 on: November 23, 2017, 07:18:48 AM »
The most common TV set tube here is PL509 ($3 NOS) but new and imported EL34 etc is WERY costly here
I can use also NOS Generator tubes with 12 and 27 heaters

@oldway
too many inesencial words (who don`t know what he can use?) too small practic schematics&figures  :-//
« Last Edit: November 23, 2017, 07:21:11 AM by 001 »
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #101 on: November 23, 2017, 07:30:23 AM »
The only problems with using PL509 (or PL519) is its 40V heater and the need for >50V negative grid bias to cut it off.   As I discussed earlier, one should handle the required power with a tapped transformer and a tap changer circuit, or three in parallel (with cathode current sharing resistors) if you don't want to go the tapped transformer route.   You'll probably need three transformers as tapped transformers with isolated 40V (20-0-20) heater windings are rare like hens teeth.   You've got to balance the cost of the (possibly imported) parallel tubes for the simpler circuit against the cost of the extra transformers and relays for the tap changer.

« Last Edit: November 23, 2017, 08:18:57 AM by Ian.M »
 

Offline richard.cs

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Re: 0-350V 0.2A Bench Power Supply
« Reply #102 on: November 23, 2017, 07:48:20 AM »
There are vast stocks of new and unused P-series TV line output valves making them very cheap (at least in Europe), and the 300 mA heater can be run easily enough from a suitable transformer, in some ways more conveniently than the several amps needed for the E series version of the same device. Yes they have a 7 kV peak anode rating but they were designed to be used in what is essentially a flyback converter running straight off rectified 240 Volt mains (so about 350 V d.c.) with a peak current of up to 1.5 Amps, they are relatively high-current, low-voltage devices compared to what their peak anode voltage rating might otherwise suggest. They are also ridiculously tough so long as you don't exceed the heater-cathode voltage spec.

I am sure 3x EL34 as Oldway suggests will work fine, but I see no reason 2x PL509s or similar wouldn't work as well at a significantly reduced cost.

 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #103 on: November 23, 2017, 08:06:00 AM »
There are vast stocks of new and unused P-series TV line output valves making them very cheap (at least in Europe), and the 300 mA heater can be run easily enough from a suitable transformer, in some ways more conveniently than the several amps needed for the E series version of the same device. Yes they have a 7 kV peak anode rating but they were designed to be used in what is essentially a flyback converter running straight off rectified 240 Volt mains (so about 350 V d.c.) with a peak current of up to 1.5 Amps, they are relatively high-current, low-voltage devices compared to what their peak anode voltage rating might otherwise suggest. They are also ridiculously tough so long as you don't exceed the heater-cathode voltage spec.

I am sure 3x EL34 as Oldway suggests will work fine, but I see no reason 2x PL509s or similar wouldn't work as well at a significantly reduced cost.
Yes, You understand me
 

Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #104 on: November 23, 2017, 08:07:11 AM »
Current Siliconix datasheet probably doesn't specify DC SOA because of laziness or CYA.

I did an informal search of DC safe operating area specifications a couple days ago and I would be very cagey about them.  Except in power MOSFETs intended and designed for linear operation, they strike me as grossly optimistic based on my understanding of how vertical power MOSFETs optimized for switching service behave.

My tentative conclusion was that with the right design, an indestructible linear high voltage power supply for power vacuum tube applications using power MOSFETs is very feasible.  I have been considering something like this but for much higher voltages and much lower currents where the design considerations are too different to apply.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #105 on: November 23, 2017, 08:11:21 AM »
I think you are really so old to learn .... :-DD

NB: see your topic
http://www.eevblog.com/forum/projects/so-old-to-learn-serious-problem/

Before you do a project, you have to understand what you're doing, that's what I'm trying to do.

This topic does not belong to you, there are certainly other people who are interested in this subject .... I answer you as well as to all the other interested persons.

You write that you find cheap PL509 tubes where you are, but you have not even indicated in which country you live ....

On ebay.de, PL509 are not cheap at all.....(cheap price 25 euros - only 37 hits)
EL34 tubes, you find hundreds on ebay.de (cheap price 15 euros - 493 hits), and not at exorbitant prices.

But I never forced you to use EL34, you do what you want, I do not care.

If you follow the indications and my explanations, you will be able to modify the diagram of IP17 Heathkit to make it correspond to your needs ....

You do not have patience and you make the topic go in all directions, you will not get anything like this.

I am a logical way in explaining you little by little how should be a HV power supply using what is currently available, whether one lives in the USA, Europe, Asia or Russia.

I will stop here with my participation in this topic....By By...
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #106 on: November 23, 2017, 08:21:00 AM »
@David Hess,
Did you look at SiC HV power JFETs? 
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #107 on: November 23, 2017, 08:23:00 AM »
I did an informal search of DC safe operating area specifications a couple days ago and I would be very cagey about them.  Except in power MOSFETs intended and designed for linear operation, they strike me as grossly optimistic based on my understanding of how vertical power MOSFETs optimized for switching service behave.

Old designs -- I don't think any HEXFETs had 2nd breakdown.  They weren't much more space-efficient than lateral MOS (nor any better on Qg), so weren't capable of operating at high enough current density to reach 2nd breakdown.  ST example:
https://www.seventransistorlabs.com/Images/ST_IRFP460.pdf
IRF740 is a smaller transistor so it would be even less likely to encounter problems.

Intermediate generation VDMOS exhibits 2nd breakdown.  Some of the most interesting SOA curves I've seen were from IXYS (hmm, I wonder if I can find an example).

Bizarrely, current gen SuperJunction MOS is apparently DC stable again, despite having higher power density than ever!  Maybe it's been designed for lower tempco and better current sharing?  There are some quirks in transconductance, too; who knows what else is different?

I don't have a problem with using classic MOS like these for one-offs, even for small production.  I would not do it for full production, not without a receiving inspection/qualification process in place ($$), and anyway, full DC SOA parts are available among new parts.

Tim
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Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #108 on: November 23, 2017, 10:15:06 AM »
Why not combine the design I posted, using LM317 & the BJT cascode, with the one posted by David, using the valve?

how to do it?
EDIT:
Bad circuit attached, see the link below for the corrected one:
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1359532/#msg1359532
« Last Edit: November 27, 2017, 10:20:37 AM by Hero999 »
 
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Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #109 on: November 23, 2017, 10:34:13 AM »
@David Hess,
Did you look at SiC HV power JFETs?

I did not because they cost significantly more for a given power and this is exasperated if multiple packages are used to lower case to heat sink thermal resistance.
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #110 on: November 23, 2017, 10:41:17 AM »
@Hero999,
That looks pretty dodgy - TR2 clamps the grid no more than 0.7V negative of the cathode so the valve cant cut off and the LM317 lets out its magic smoke.  Also even if you rework the current limiter so it doesn't FUBAR the cascode,  TR2 sees the whole output voltage and high voltage PNPs suitable for linear region operation are not so common.
 
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Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #111 on: November 23, 2017, 10:58:12 AM »
Chinese EL34 are £9.44 from RS components.
Quote
how to do it?
And exactly how is the EL34 current limit going to work, Tr3 isn't going to do anything ?? Been spicing the T-reg regulator https://linearaudio.nl/t-reg-tube-voltage-regulator well a simplified version of it. Got my current limit set to 100mA and at 350V HT tube dissipation is 31.5W Anode and 3.5W screen grid. You might need to consider running at least two tubes in parallel and foldback current limit. I'm aiming for maybe 350V HT, 0-250V output @ 100mA foldback current limit with a single tube. It depends on the transformer I have available, I think it was for a Maplin valve amp a long time ago.
« Last Edit: November 23, 2017, 11:01:15 AM by chris_leyson »
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #112 on: November 23, 2017, 05:10:35 PM »
Chinese EL34 are £9.44 from RS components.
Quote
how to do it?
And exactly how is the EL34 current limit going to work, Tr3 isn't going to do anything ?? Been spicing the T-reg regulator https://linearaudio.nl/t-reg-tube-voltage-regulator well a simplified version of it. Got my current limit set to 100mA and at 350V HT tube dissipation is 31.5W Anode and 3.5W screen grid. You might need to consider running at least two tubes in parallel and foldback current limit. I'm aiming for maybe 350V HT, 0-250V output @ 100mA foldback current limit with a single tube. It depends on the transformer I have available, I think it was for a Maplin valve amp a long time ago.


Wow!
Interesting project! What is main benefit of this circuit? It can't go below pass tube bias voltage so regulation range is too small, isnt it? Do You recomend this circuit as a preregulator?
« Last Edit: November 23, 2017, 05:57:02 PM by 001 »
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #113 on: November 23, 2017, 08:08:49 PM »
@Hero999,
That looks pretty dodgy - TR2 clamps the grid no more than 0.7V negative of the cathode so the valve cant cut off and the LM317 lets out its magic smoke.  Also even if you rework the current limiter so it doesn't FUBAR the cascode,  TR2 sees the whole output voltage and high voltage PNPs suitable for linear region operation are not so common.
I'll be honest. That circuit was a bit of a guess. I don't know much about valves. They're long before my time!

So the grid voltage needs to be negative, in order for to cut-off, therefore breaking the current limiter? That's a pain. Something to drop more voltage, such as a resistor or even a zener, would need to go in between the cathode and TR3's base to drop enough volts, to cut it off enough to limit the current.

EDIT:
Bad circuit attached, see the link below for the corrected one:
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1359532/#msg1359532

I think a MOSFET is probably an easier solution, although it's not as abuse tolerant.
« Last Edit: November 27, 2017, 10:20:58 AM by Hero999 »
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #114 on: November 23, 2017, 10:27:15 PM »
The Tube at Yours circuit is  strange biased  :o
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #115 on: November 24, 2017, 01:27:21 AM »
@Hero999,
That looks pretty dodgy - TR2 clamps the grid no more than 0.7V negative of the cathode so the valve cant cut off and the LM317 lets out its magic smoke.  Also even if you rework the current limiter so it doesn't FUBAR the cascode,  TR2 sees the whole output voltage and high voltage PNPs suitable for linear region operation are not so common.
I'll be honest. That circuit was a bit of a guess. I don't know much about valves. They're long before my time!

So the grid voltage needs to be negative, in order for to cut-off, therefore breaking the current limiter? That's a pain. Something to drop more voltage, such as a resistor or even a zener, would need to go in between the cathode and TR3's base to drop enough volts, to cut it off enough to limit the current.



I think a MOSFET is probably an easier solution, although it's not as abuse tolerant.

To see what you are up against here's a LTspice test jig for a PL509.   N.B. it does *NOT* fully model the valve - although  Norman Koren's Tube SPICE models are well respected, they are only approximate.

Things to note:
If you don't use fixed bias for the screen grid G1(relative to the cathode), you will need *MUCH* more negative drive to the control grid (G1) to reach cutoff.  Try the effect of tying G2 to A via a 10K resistor and you will see the issue.     

If you use the valve in cascode with a LM317 with a high screen grid voltage, you are in for a world of grief as the cathode potential at cutoff will significantly exceed the LM317's maximum input-output voltage differential even if you use a LM317HV.  Practical experiments with a reduced screen grid supply floating on the output voltage will be needed to determine if this configuration is possible.   A negative grid bias supply will also be needed - possibly derive both from capacitively coupled bridge rectifiers driven from the 40V heater transformer.

Note instructions in the SIM to enable download of model file on first run.


« Last Edit: November 24, 2017, 01:30:11 AM by Ian.M »
 
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Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #116 on: November 24, 2017, 04:07:56 AM »
Sounds like a nightmare. I'll look at the zip in a bit. Meanwhile, here's the MOSFET version, which should be fine, as long as the safe operating area, isn't exceeded.
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #117 on: November 24, 2017, 09:05:30 PM »
I've just simulated the original valve based LM317 current limiter circuit, using the models posted by Ian and it works perfectly. I connected both grids together, as the circuit was designed for a triode, not tetrode. With the current limit of just over 200mA, the valve would dissipate 80W, so it needs to be fairly chunky, possibly requiring a fan.

EDIT:
Bad circuit attached, see the link below for the corrected one:
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1359532/#msg1359532
« Last Edit: November 27, 2017, 10:21:23 AM by Hero999 »
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #118 on: November 24, 2017, 09:14:12 PM »
Why You connect grids together? :palm: if You prefer triode mode, connect second grid to anode
For normal operation tube must be properly biased so voltage across 317 must be about 40-60v i.e. 12w on this IC in standby  :-//
« Last Edit: November 24, 2017, 09:18:47 PM by 001 »
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #119 on: November 24, 2017, 09:49:28 PM »
Why You connect grids together? :palm:
Why not? What's wrong with tying the grids together?

Quote
if You prefer triode mode, connect second grid to anode
That doesn't work, according to the simulation. With one grid connected to the anode, the valve won't cut-off, until the other grid is biased negative, which is possibly what Ian was concerned about.

It works perfectly with both grids connected together. I don't know if this works with all tetrodes or if it's specific to the simulation model. I suppose the data sheet is the best place to start.

Quote
For normal operation tube must be properly biased so voltage across 317 must be about 40-60v i.e. 12w on this IC in standby  :-//
No, for proper operation, the voltage across the LM317 should be between 3V and 40V. Anything greater than 40V could damage it. Anything under 3V and it might not regulate properly. In standby (no load) the only current through the LM317 will be 1.25/R1 = 1.25/240 = 5.2mA, so the power dissipation will be low.

EDIT:
I had R3 set too high, which resulted in poor current limiting. Change it to 10k and it's much better. A current source would be best, as mentioned by T3sl4co1l.
« Last Edit: November 24, 2017, 10:08:09 PM by Hero999 »
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #120 on: November 24, 2017, 10:15:54 PM »
You cant connect grids of power tube together due different electric durability and geometric issues. The screen grid in fact not a grid but spring. Real tube will not work this way. It is si!ulator mistake :palm:

Connection 2d grid to anode directly or with limiting resistor is a common practice for decades. Why simulator dont know it?

At 1.5v bias voltage tube blow itself
 
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Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #121 on: November 24, 2017, 10:25:02 PM »
I'd take the biassing for Hero999's proposed grid configuration of strapping G1 to G2 with a *LARGE* pinch of salt as its *far* *far* away from the operating region Noman Koren's tube models are written for.  They are the product of careful curve fitting to published data sheets, and aren't based on a physics model so if you are designing outside of the datasheet limits (and zero accelerating potential between G1 and G2 is about as far outside as you can get), the model's less trustworthy than a timeshare salesman!  :popcorn:

As the PL509 (or EL509) is a beam tube, the G1 and G2 wires are supposed to be precisely aligned so strapping G1 to G2 should work, and I cant see any way it could cause damage, unless you are dumb enough to exceed 5mA pass significant G1 current under positive biass, however you'd need a whole set of experimental characteristic curves to model the resulting triode.  I strongly suspect that it will pass *FAR* less current at zero grid bias than the Koren tetrode model indicates. 

http://www.oestex.com/tubes/triode.htm is worth a read.

If anyone has suitable equipment for power tube curve tracing, and can spare the time, it would be interesting to see how the curve families for different methods of strapping a beam tetrode as a triode compare (including the proposed G1-G2 strapping) , with the datasheet screen grid biassing for tetrode operation as a control.
« Last Edit: November 24, 2017, 10:54:47 PM by Ian.M »
 
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Offline richard.cs

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Re: 0-350V 0.2A Bench Power Supply
« Reply #122 on: November 24, 2017, 10:33:12 PM »
Why not? What's wrong with tying the grids together?

...

It works perfectly with both grids connected together. I don't know if this works with all tetrodes or if it's specific to the simulation model. I suppose the data sheet is the best place to start.

Needing to bias the grid negative to cutoff is expected behaviour. Connecting the grids together is an unusual thing to do (as in, almost never done) and I suspect that the simulation model is simply not representative in that configuration. I have no idea what the valve would do in the real world. What range of grid-cathode voltage does your simulation regulate with?

Usual valve operation is that it is "on" with the grid at 0 volts relative to the cathode, and you progressively reduce the current as you bring the grid more negative with respect to the cathode. This behaviour  is like an N-channel JFET or depletion-mode MOESFET. If you make the grid positive with respect to the cathode then you can on some types turn it slightly harder on but too positive and it will start to collect electrons, and current will flow into the grid. This is generally bad because the grid is not able to dissipate much power. Grid 1 current / power limits tend to be very low (but I can't actually find it in the datasheet). Sorry if some of this is obvious but you said you don't have much experience with valves. Hopefully it's helpful to someone anyway.

PL509 datasheet is here: http://www.r-type.org/pdfs/pl509.pdf

Page 7 shows current as a function of grid 1 voltage with the valve "triode-strapped", i.e. grid 2 connected to the anode and a fixed anode voltage of 160 V. Note that the range of Vg1 is 0 to -50 V.

Pages 8 and 9 show pentode operation with grid 2 held at a fixed +160 V, 175 V and 190 V relative to the cathode but the anode voltage varied with constant Vg1. The Vg1 range is 0 to -40 V.

edit: Ian.M has posted whilst I was typing. He makes a good point about the alignment of G1 and G2, but we're in agreement that the simulation model is probably junk for this configuration.
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #123 on: November 24, 2017, 11:58:16 PM »
Well
As oldtimer I see what Hero999 circuit is not proper. Real tubes is tubes.  :-//

So the main dilemma for me is to use pass mosfet or pass tube
Ok. Few days ago I wanted eliminate all tubes from my gear
But now I uncertain
I desided to use disctrete transistor regulator circuit anyway
But what about pass element?


This circuit looks good http://www.audioxpress.com/article/t-reg-a-high-voltage-regulator-for-tube-amps
but can I strip reference and sense resistors to additional negative source to add regulation from zero insted actual minimum limited by bias voltage?
« Last Edit: November 25, 2017, 12:00:44 AM by 001 »
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #124 on: November 25, 2017, 01:50:23 AM »
I suggest you take a PL509 (or PL519 or EL509 etc.) and set it up on your bench and characterise it. You need to know how much voltage swing you need on the control grid before you start designing circuits.

 As you've sold off your HT variable supply, for the DC supply, feed an isolating transformer from a Variac, into a bridge rectifier followed by two banks of reservoir caps and a large choke (one built like a transformer) between them with a power bleeder resistor calculated to have a time constant with the total capacitance of no more than 2s so it will totally discharge in no more than 10 seconds.    For the PL5xx filaments, you need 40V at 300mA, and hopefully you have a bench supply that can do that.  Otherwise use a transformer and a rheostat, and adjust to 300mA RMS when hot. 

You need to know the minimum anode voltage with zero grid bias to get your maximum output current, and should also test at 400mA to have some margin for loss of emission with ageing and to allow for differences in individual valves.   Put an ammeter that will read up to 1A and down to <1mA between the cathode and ground for this test.  Let the valve warm up at a moderate cathode current - say 100mA for ten minutes before making any measurements.

You also need to know the negative grid bias required for cutoff, at the maximum anode voltage you valve could ever see e.g with the PSU unloaded and the mains input 10% above nominal.  You'll need to decide what minimum current you'll accept at cutoff, and will need to make sure your final design can always sink that much current right down to your minimum output voltage.      If in doubt, measurements at 1mA and 0.1mA would probably be useful.   Measure the current as voltage drop across a 10K resistor.

You may need over -250V on G1 to get full cutoff, but you only need a few mA current so to get the negative grid bias supply, capacitively couple another bridge rectifier to the transformer secondary, feeding a decoupling capacitor then a resistor  (47K 5W wirewound would be good) and another decoupling cap, then use a physically large 500K pot rated at least 1/2W between the negative supply and ground.   Decouple the pot wiper with 0.1uF to ground, and feed G1 from it.  Start with maximum negative bias and crank up the Variac slowly till the anode voltage reaches the maximum design voltage (allowing for 10% mains over-voltage) while watching the voltage across the 10K cathode resistor.   If it rises over 10V, your negative bias supply cant supply enough voltage.    Then reduce the bias until you get 1V (100uA) and 10V (1mA), measuring the G1 voltage for each.  The voltage drop across the cathode resistor adds to the G1 negative bias, so if you have -100V for 10V across the cathode resistor, your actual Vg1k bias voltage is -110V.
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #125 on: November 25, 2017, 02:00:30 AM »
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #126 on: November 25, 2017, 03:19:15 AM »
Beware of the maximum heater-cathode breakdown voltage.   In the test jig, you may want to put a beefy TVS diode between the cathode and ground to clamp it below 250V to protect your bench power supply, which should *NOT* be ground referenced when used for the filament.  Also put a 1A fast fuse rated for a minimum of 500V DC in series with the the output of the improvised variable HT supply I described above.  Ordinary glass fuses wont reliably interrupt 500V DC.
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #127 on: November 25, 2017, 05:43:00 AM »
I've been looking at the T-reg regulator and there is an update on Jan Didden's web site https://linearaudio.nl/sites/linearaudio.net/files/T-reg%203%20article.pdf. I like the floating regulator design, the error amplifier is simple and using a separate transformer for the regulator supply and tube heater avoids heater cathode breakdon problems. The 1mA current source design for setting the output voltage looks a bit elaborate and I'm sure there are better ways of doing this, also you need a -50V supply for the tube version. Tried out a spice model and added a simple current limit, seems to be OK but will need to do more work on it. Current source for the voltage setting resistor was quickly put together and I need to open up the control loop and check stability. Load resistor R5 swept from 1 ohm to 25k ohm and output voltage is plotted against cathode current. EL34/6CA7 spice model from Duncan Amps. Gave up on the foldback current limit. Foldback limiting is OK for a fixed supply but a bit tricky on variable supplies. Also, I wouldn't use some of the transistors shown in the spice model, they just happened to be convenient.
« Last Edit: November 25, 2017, 06:24:00 AM by chris_leyson »
 
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Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #128 on: November 25, 2017, 05:48:06 AM »
Ugh...
Seven Transistor Labs, LLC
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Need engineering assistance? Drop me a message!
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #129 on: November 25, 2017, 05:49:50 AM »
Quote
Ugh...
Indeed, jist doodling why not
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #130 on: November 25, 2017, 05:51:03 AM »


Thanx a lot!
Is it ok to imrove it with TL431 instead diodes?
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #131 on: November 25, 2017, 06:06:24 AM »
Quote
Is it ok to imrove it with TL431 instead diodes?
Thanks 001, that's a really neat solution for a current souce I never thought of that. To be honest I just threw something together very quickly for the current source as I was more concerned about SOA,  power dissipation and stability and the current source I could leave until later. It's a neat design, four transistors a TL431 and a tube or tubes for the pass element. Of course mosfets could be used instead and that would save the -50V supply, but hey, if anyone needs a bench supply for tube work then you need a negative bias supply anyway.
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #132 on: November 25, 2017, 07:59:27 AM »
Quote
Is it ok to imrove it with TL431 instead diodes?
Sorry, wasn't thinking. No, you would have to use LM385 or LM4041 for a transistor current source, LM385 and LM4041 feedback is referenced to cathode. TL431 will only do current sink as feedback is referenced to anode. Linear Technology LM385 is only two pin device so no good.
« Last Edit: November 25, 2017, 08:13:31 AM by chris_leyson »
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #133 on: November 25, 2017, 09:22:14 AM »
Why not? What's wrong with tying the grids together?

...

It works perfectly with both grids connected together. I don't know if this works with all tetrodes or if it's specific to the simulation model. I suppose the data sheet is the best place to start.

Needing to bias the grid negative to cutoff is expected behaviour. Connecting the grids together is an unusual thing to do (as in, almost never done) and I suspect that the simulation model is simply not representative in that configuration. I have no idea what the valve would do in the real world. What range of grid-cathode voltage does your simulation regulate with?

Usual valve operation is that it is "on" with the grid at 0 volts relative to the cathode, and you progressively reduce the current as you bring the grid more negative with respect to the cathode. This behaviour  is like an N-channel JFET or depletion-mode MOESFET. If you make the grid positive with respect to the cathode then you can on some types turn it slightly harder on but too positive and it will start to collect electrons, and current will flow into the grid. This is generally bad because the grid is not able to dissipate much power. Grid 1 current / power limits tend to be very low (but I can't actually find it in the datasheet). Sorry if some of this is obvious but you said you don't have much experience with valves. Hopefully it's helpful to someone anyway.

PL509 datasheet is here: http://www.r-type.org/pdfs/pl509.pdf

Page 7 shows current as a function of grid 1 voltage with the valve "triode-strapped", i.e. grid 2 connected to the anode and a fixed anode voltage of 160 V. Note that the range of Vg1 is 0 to -50 V.

Pages 8 and 9 show pentode operation with grid 2 held at a fixed +160 V, 175 V and 190 V relative to the cathode but the anode voltage varied with constant Vg1. The Vg1 range is 0 to -40 V.

edit: Ian.M has posted whilst I was typing. He makes a good point about the alignment of G1 and G2, but we're in agreement that the simulation model is probably junk for this configuration.
Thanks. I can see why my current limiting circuit is fatally flawed. I've managed to bodge it so it kind of works but it's still poor. The BJT limits the current first, then the short circuit current is determined by the characteristics of the valve. I imagine the valve's cut-off is extremely variable, like a JFET, so it won't work.

Last bad nubie valve circuit I promise.  ;)

EDIT:
Bad circuit attached, see the link below for the corrected one:
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1359532/#msg1359532
« Last Edit: November 27, 2017, 10:24:12 AM by Hero999 »
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #134 on: November 25, 2017, 11:51:25 AM »
If you are going to simulate this stuff please use a current source as the load (see component 'load') so you can use a simple .dc sweep rather than stepping a parametrised resistive load in a .op sim.  It will reduce the simulation run time by at least an order of magnitude.

You'll need an anti-parallel ideal diode across the current source load so it can only sink current and cant drive the output negative.   Use:
Code: [Select]
.model Dideal D(Ron=10n Roff=.1G Vfwd=0) ;Ideal diodeN.B. LTspice slows down drastically if the diode Ron and Roff are 12 or more decades apart.

Also, please label important intermediate nodes (e.g. round the valve and LM317) as its a PITA to be dealing with node numbers.

Now that's fixed, plot the dissipation (alt click) of Q1, and its collector current.  You've actually 'invented' a crappy shunt regulator.   Good luck finding a PNP BJT that can dissipate over 21W and withstand over 350V.  Most will be *FAR* outside their DC SOA.
« Last Edit: November 25, 2017, 12:17:46 PM by Ian.M »
 
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #135 on: November 25, 2017, 10:14:13 PM »
I wrote that I would not participate in this topic but you make me pity .... you do not know anything about electronic tubes and you try to make an absurd project to do the same thing as a simple power supply Heathkit IP17 ....  :palm:
Start by understanding how it works and what happens when you short-circuit the output of this HeathkitIP17 power supply ?

Is it protected against short circuits? If yes, how?.... :box:
It has not even a fuse in the HV rail.... :-DD

To help you answer to my question...  :-/O
What is the purpose of the characteristic curves of the tubes given by the manufacturers if you do not even consult them?  |O

And if you consult them, do not you notice an essential difference between a pentode and a triode?  :scared:

So, why do you want to use a pentode as a triode? To explode your power supply in case of short circuit?

A pentode limits the current independently of the anode voltage .... it is necessary to be stupid to not use this property.
At least it help to limit the instantaneous current of short circuit. This is intrinsically safe... :-+

The instantaneous power dissipated in the anode will be very much above the maximum power, but that does not matter, the anode has sufficient thermal inertia to accept this overload for a short time, a few seconds.

This is a sufficient time to blow a fuse, or disconnect the power supply, or have another electronic or electro-mechanical protection act.

In my project, I feed G2 of EL34 / 6CA7with 140V...I have only the curves for G2 = 250V....
« Last Edit: November 25, 2017, 10:44:43 PM by oldway »
 
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #136 on: November 25, 2017, 10:41:44 PM »
I wrote:
Quote
The idea of an hybrid power supply with solid state control and vacuum tube as a series regulator is excellent.
That's the way to go.
And what is the best way to combine high voltage power stage and semi conductor control ?
HV OPTOCOUPLER  :-+

The principle is very simple: To provide a bias of more or less -100V to G1 of EL34 to ensure full blocking of the tube and to reduce this bias by the control signal transmitted by an HV optocopler.
G1 will thus vary between -100V and 0V.

If you use several tubes in =, you must provide a cathode resistor to equalize currents between tubes.

NB: G3 internaly connected to cathode.

NB: schematic only for understanding of the principles of the project....

NB2: as I wrote:
Quote
If we have a winding 230V, or 325V rectified, we can do 2 ranges: one from 0 to 320V and one from 280 to 450V.
The anodic dissipation at 200mA will then be: range 1, 60W max, range 2, 40W max, which is quite reasonable and even allows to envisage a current greater than 200 mA.
The 2 ranges are selected by a switch. The other contacts of the switch are used in the control circuit.

NB3: heater circuit is not designed on the schematic. Heater voltage used is 12V with two heater filaments in serie. That's the reason why I choosed 4 EL34 and not 3.
« Last Edit: November 25, 2017, 11:42:21 PM by oldway »
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #137 on: November 25, 2017, 11:45:06 PM »
Quote
If you are going to simulate this stuff please use a current source as the load
Quote
It will reduce the simulation run time by at least an order of magnitude

Hi Iam.M are you refering to my spice circuit or hero999 or both maybe ?
I tried sweeping the load resistor R5 just to see how well it worked and was surprised. The simulation time in this case is probably only 100 or 200ms at most, it's done as soon as I click the mouse button. It takes orders of magnitude longer to change the plot axis from time to current ;) The problem with swept current souces or sinks is that results are sometimes unpredictable if the source or sink current exceeds the limit current even with an anti-parallel diode fitted. BTW thanks for the model suggestion for the ideal anit-parallel diode.
One thing that I did notice was that if the grid pull down resistor was greater than 250k then the regulator is unstable at or near short circuit conditions so that's why I used 100k, also probably has a lot to do with the location of the compensation cap and to some extent the spice model for the EL34/6CA7. Instability increases simulation time by orders of magnitude  :)

Thanks oldway, you just reminded me I need to look at the screen grid bias, I wired the EL34 as a triode because it was quick and sorting out proper bias and looking at screen grid power dissipation is a job for later. To be honest my spice circuit is intended as a quick look and see what happens.

Thanks 001 for the TL431 suggestion for the current source. Used an LM385 and it works well, model is available from LTSpice forum.

In all honesty I need to start over and somehow open up the control loop, check phase and gain margins for stability, check closed loop gain and hum rejection and so on. Not to worried about DC accuracy and the DC drift should be good. The hum and noise performance of the original design is really very good for such a simple circuit. BTW my circuit as posted is not intended as a working design so don't build it ! Just noticed I left R6 and R7 in the circuit, I don't need those as they are for the Mosfet version, I should take them out  :palm:
« Last Edit: November 25, 2017, 11:55:24 PM by chris_leyson »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #138 on: November 26, 2017, 12:21:49 AM »
Indeed, why make it simple and safe, if you can do complicated and dangerous .... :-DD

Our generation has been several times on the moon with very limited technological means ..... we have learned to do a lot with little ... We were ingenious and inventive engineers. It seems that this quality has been lost.  :palm:

EDIT: By using my power circuit, adjustable voltage control and current limiting circuits become extremely simple.
Just add a shunt in the negative rail to measure the current.
Control can be done by operational circuits as in any linear power supply.
There is no longer any semiconductor subjected to high voltages.
A simple + / - 12V auxiliary power supply is enough to power the control circuit.
A TL431 can be used as a reference if necessary.
« Last Edit: November 26, 2017, 12:35:14 AM by oldway »
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #139 on: November 26, 2017, 12:35:07 AM »
Yes

It is wery strange to see tubes that used this way  :-//
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #140 on: November 26, 2017, 12:38:00 AM »
There's more on the Heathkit IP17 here: http://www.sgitheach.org.uk/ip17.html, including the schematic and manual.   Heathkit got a lot out of only six tubes - two paralleled 6L6GC for the pass element, a 6BH6 to drive them and for feedback regulation, two 150V stabiliser tubes and a double diode to rectify the supply to the stabilised -300V rail.

However the complexity was the custom transformers.  They would be uneconomic to reproduce for a one-off build unless you are equipped to wind your own and are experienced at doing so.  The filament supply one is pretty simple, it only needs five 6.3V secondaries (actually three + a CT 12.6V winding), and two of those are for the user's load.  It could easily be replaced with two off-the-shelf transformers.   Its the main HT transformer that's the P.I.T.A. Its got three secondaries: 175V for the  6L6GC G2 (screen grid) bias supply, that's referenced to the cathodes, 210V for the raw unreg 600V HT rail, via a voltage doubling rectifier (*STEAL* that idea!), and 600V CT for the raw -390V that feeds the regulated -300V bias rail.   

Worst case, a 6L6GC needs less than 20mA of G2 current, so in a modern design it would be acceptable to use an isolated flyback converter to derive a 50mA G2 bias supply, possibly with a floating IC regulator to further stabilise it, and the same could be done for the -300V bias supply.  That's probably going to be significantly cheaper than the custom transformer.  A 220V:220V isolating transformer would probably be close enough for the main HT supply, though it would be preferable to use one with both 220V and 240V primary taps so it could be tapped down a bit.

@Chris Leyson,
No, I was referring to Hero999's sim.  However, there is an alternative if you want to sweep a resistor using the .dc command - use a load resistor but edit its value to R=I(Vctrl) to make a behavioral resistor, then create a voltage source Vctrl to control it.  Set the series (internal) resistance to -1 ohms  :wtf: (Yes the NEGATIVE resistance is intentional to get positive current through the source for positive source voltage), and of course, ground one side of it. 

Another approach is not to short the voltage source or set its Rser, but instead label its output node, and change the behavioural resistor expression to refer to that node voltage.  However, you then have two names to keep consistent.

One can then sweep Vctrl in a .dc command.
.dc dec Vctrl 10k 10 covers the same range as Hero999's original .stepped sim.

There's a pitfall for the unwary:  You'd think you could simply sweep a shorted current source, but LTspice deletes shorted current sources before generating the netlist so the .dc command will always bitch that it cant find your control source!  |O
One fix is don't short the source, instead use a 1 ohm  resistor, but that's more complexity
« Last Edit: November 26, 2017, 12:42:12 AM by Ian.M »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #141 on: November 26, 2017, 12:39:17 AM »
Yes

It is wery strange to see tubes that used this way  :-//
What do you mean with this ?
In the years 60, there was no optocoupler and the solution I am proposing was not possible.
It was possible to use direct coupling because 500 or 600V was no problem at all for the driving vacuum tube.
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #142 on: November 26, 2017, 12:41:17 AM »
-

It is not about Your circuit but about strange simulation results above  :palm:
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #143 on: November 26, 2017, 12:45:37 AM »
There's more on the Heathkit IP17 here: http://www.sgitheach.org.uk/ip17.html, including the schematic and manual.   Heathkit got a lot out of only six tubes - two paralleled 6L6GC for the pass element, a 6BH6 to drive them and for feedback regulation, two 150V stabiliser tubes and a double diode to rectify the supply to the stabilised -300V rail.
...

I already have  posted this link....
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1355691/#msg1355691

Of course, in my schematic, there is no need of negative rail.
Nul current in the optocoupler = fully blocked pass tubes with -100V Grid 1 negative bias.
« Last Edit: November 26, 2017, 12:52:25 AM by oldway »
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #144 on: November 26, 2017, 12:59:22 AM »
Classic horowitz & hill ideas
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #145 on: November 26, 2017, 03:57:10 AM »
Oldway, thanks for bring grid-bias (supply) back ;) That circuit looks good, add a bit of current-limiting to protect it. OP's 470uF filter cap stores 37.6J which may hurt things, that's a bit big. IP-17 is 70uF/2 lol.

I wasn't sure why the Heathkit IP-17 has a separate dedicated rail for the screens. It might be to keep 6L6 gain up at low drops? I guess we haven't looked at dropout voltage.
I recall the 6AS7/6080 was specifically designed for power supplies, but it worked with low plate voltages ~250V.

For real-life load testing HV power supplies, I use surplus 813 tetrodes with a cooling fan. I can't remember if secondary emission was a problem, thought the dynode region existed on the RCA ones I have- it might have been RF as I didn't put care into it and it's a bit tense on the workbench when the plates are glowing.

IXYS linear MOSFET IXTB30N100L 1,000V 30A looks tough but over $60 and Ciss=13,700pF (hard to shut off quickly) and TO-264 with no mounting hole
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #146 on: November 26, 2017, 04:31:24 AM »
Quote
Oldway, thanks for bring grid-bias (supply) back ;) That circuit looks good, add a bit of current-limiting to protect it.
It is protected because there are two current limits.

One instantaneous not depending of any other component than the caracteristics of the vacuum tube, wich is limited to about 100 mA/tube, another one who is slower and using the current information of a shunt resistor in the negative rail.

Here are the caracteristics of EL34 with 250V and 350V G2 voltage.....I am feeding G2 with only 140V...

With 250V G2 voltage and 0V G1 voltage (in my circuit, G1 can't go positive), Ia is limited at about 300mA with 500V anode voltage.
With 350V G2 voltage and 0V G1 voltage, Ia is limited at about 550 mA

With G2 at 140V, I am expecting a current limitation at about 100 mA/tube.

Of course, with Ua = 500V  and Ia = 0.1A, we have an anode dissipation of 50W, far too much for a 20W power tube.

But a second current limitation from the semi-conductor control unit using a shunt resistor in the negative rail will reduce further this current to the set value of 200 mA output current or 50mA/tube.
« Last Edit: November 26, 2017, 04:33:45 AM by oldway »
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #147 on: November 26, 2017, 04:56:44 AM »
I wasn't sure why the Heathkit IP-17 has a separate dedicated rail for the screens. It might be to keep 6L6 gain up at low drops? I guess we haven't looked at dropout voltage.

Beware that the screen goes toaster mode if you let it reach dropout.

Sort of like the old bipolar LDOs that increased their quiescent current a hundredfold in dropout.

Quote
IXYS linear MOSFET IXTB30N100L 1,000V 30A looks tough but over $60 and Ciss=13,700pF (hard to shut off quickly) and TO-264 with no mounting hole

Well, obviously it's not a good choice then, is it?  If that's your only comparison, tubes may well be cheaper. :P

Best cost per watt tends to be either the very old designs -- IRFxxx and the like -- or new SuperJunction FETs (Fairchild QMOS, ST MDmesh, Infineon (and licensors) CoolMos, etc.) with modest ratings.  350V * 0.2A = 70W which is okay to burn in a single TO-247 or larger (around $5 and up), or two TO-220 in parallel (maybe $2 each).

The kind without mounting hole are better in all respects.  They are easier to mount, as you don't need to worry about the screw tilting the device, concentrating mounting pressure away from the die.  Instead, you use a readily available spring clip.  (Well, you can -- and should -- use a spring clip with conventional screw mount devices, too, of course!)

This isn't a hard project, and just adding the filament transformer alone already blows out any cost savings you might imagine, using toob.

Tim
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Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #148 on: November 26, 2017, 01:22:32 PM »
Quote
Oldway, thanks for bring grid-bias (supply) back ;) That circuit looks good, add a bit of current-limiting to protect it.
It is protected because there are two current limits.

One instantaneous not depending of any other component than the caracteristics of the vacuum tube, wich is limited to about 100 mA/tube, another one who is slower and using the current information of a shunt resistor in the negative rail.

Here are the caracteristics of EL34 with 250V and 350V G2 voltage.....I am feeding G2 with only 140V...

With 250V G2 voltage and 0V G1 voltage (in my circuit, G1 can't go positive), Ia is limited at about 300mA with 500V anode voltage.
With 350V G2 voltage and 0V G1 voltage, Ia is limited at about 550 mA

With G2 at 140V, I am expecting a current limitation at about 100 mA/tube.

Of course, with Ua = 500V  and Ia = 0.1A, we have an anode dissipation of 50W, far too much for a 20W power tube.

But a second current limitation from the semi-conductor control unit using a shunt resistor in the negative rail will reduce further this current to the set value of 200 mA output current or 50mA/tube.

OK now I see how you are doing it. I saw the cathode resistors and pondered adding a current-sense transistor to help out.
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #149 on: November 26, 2017, 01:27:13 PM »
I wasn't sure why the Heathkit IP-17 has a separate dedicated rail for the screens. It might be to keep 6L6 gain up at low drops? I guess we haven't looked at dropout voltage.

Beware that the screen goes toaster mode if you let it reach dropout.

Sort of like the old bipolar LDOs that increased their quiescent current a hundredfold in dropout.

Quote
IXYS linear MOSFET IXTB30N100L 1,000V 30A looks tough but over $60 and Ciss=13,700pF (hard to shut off quickly) and TO-264 with no mounting hole

Well, obviously it's not a good choice then, is it?  If that's your only comparison, tubes may well be cheaper. :P

Best cost per watt tends to be either the very old designs -- IRFxxx and the like -- or new SuperJunction FETs (Fairchild QMOS, ST MDmesh, Infineon (and licensors) CoolMos, etc.) with modest ratings.  350V * 0.2A = 70W which is okay to burn in a single TO-247 or larger (around $5 and up), or two TO-220 in parallel (maybe $2 each).

The kind without mounting hole are better in all respects.  They are easier to mount, as you don't need to worry about the screw tilting the device, concentrating mounting pressure away from the die.  Instead, you use a readily available spring clip.  (Well, you can -- and should -- use a spring clip with conventional screw mount devices, too, of course!)

This isn't a hard project, and just adding the filament transformer alone already blows out any cost savings you might imagine, using toob.

Tim


I think it's difficult for a thread to converge on a solution that OP and others are happy with.

The design requirements - budget- low cost, low component count, current-limiting, noise/precision, robustness, building one, building 1,000 etc. seems to throw the design from MOSFET, tube, switching PSU, or a hybrid of these. I don't know what "homebrewed polymer films" need for a OP's PSU.

The tube solution is simple, proven, robust but needs an additional filament+grid-bias power transformer (windings), inefficient, older parts and has the stigma of being old technology.

The MOSFET solution is fragile, complicated SOA protection and "trial by fire". Schrapnel from a TO-247 says "no, not quite right" and hopefully the load survives as well. Replace MOSFETs and try again.

The SMPS solution is a lot of engineering. The custom HV magnetics are a bear to make, unless you have cores, bobbins, magnet wire, insulating tape etc. and a lot of patience.


I mention the Ixys linear power MOSFET to show that one (moderately exotic) pass transistor could work (with fast enough SOA protection). There are 500V 15A parts around $10 each.
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #150 on: November 26, 2017, 04:20:29 PM »
The design requirements - budget- low cost, low component count, current-limiting, noise/precision, robustness, building one, building 1,000 etc. seems to throw the design from MOSFET, tube, switching PSU, or a hybrid of these. I don't know what "homebrewed polymer films" need for a OP's PSU.

So, I'm hearing SS. ;)

Quote
The tube solution is simple, proven, robust but needs an additional filament+grid-bias power transformer (windings), inefficient, older parts and has the stigma of being old technology.

Well, that, and inherently poorer efficiency; and inherently poorer lifetime, as the tube will do 5 or 10k hours if it's a premium quality / industrial NOS part, and used at reduced ratings.  Or 2khr if you're lucky, if it's a new Chinese production type run at "ratings".

Of course you don't expect to run a bench supply at ratings, 24/7, its entire life.  But it's a time*temp thing.  It'll fail eventually, and very likely before the electrolytics will (unless you've carelessly placed them right above the tube, that is :) ).

SS doesn't suffer from that limitation; with simple consideration of SOA, and the application of MOVs or TVSs, expected lifetime is wholly the capacitor lifetime.  The SS circuit, in and of itself, can last for centuries!

Quote
The MOSFET solution is fragile, complicated SOA protection and "trial by fire". Schrapnel from a TO-247 says "no, not quite right" and hopefully the load survives as well. Replace MOSFETs and try again.

I don't get what you're making this straw man from.

You look up the part.

You look for the SOA.

If there's no SOA plot, or no DC curve, or no power-limited DC SOA, discard it and move on to the next part.

You will find many families of parts this way, which are rated for this service, and reasonably priced.

You apply an accurate and fast current limit circuit -- the BJT shunt sense method is fine, while more accurate and adjustable means can be applied additionally to get traditional CC/CV supply operation -- and the SOA is never, ever violated.

You can even put in a thermistor to throttle or fold back the current when the heatsink gets hot, to deal with clogged heatsinks.  You can use enough heatsink to avoid using a fan at all (which is the most common culprit in everything that needs them!).

Quote
The SMPS solution is a lot of engineering. The custom HV magnetics are a bear to make, unless you have cores, bobbins, magnet wire, insulating tape etc. and a lot of patience.

Yes, that would be an expert level project, for many more reasons than those alone!

FWIW, that one battery discharger design I made, is still selling well, and I'm not aware of any problems they've had with it. :)
https://bumblebeebatteries.com/products/hybrid-battery-accessories/prolong-intelligent-discharger/
I think that used a QFET (among other things).

Tim
« Last Edit: November 26, 2017, 04:22:40 PM by T3sl4co1l »
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Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #151 on: November 26, 2017, 05:08:21 PM »
A dedicated hobbyist might put as many as 12 hours a week, 48 weeks a year on their HV PSU, possibly more if they are single and retired.   That's over 8 years for a good NOS tube.   Get a couple of spares for each tube while they are reasonably cheap and it will probably last you a lifetime.
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #152 on: November 26, 2017, 06:21:29 PM »

...
I don't get what you're making this straw man from.

You look up the part.

You look for the SOA.

If there's no SOA plot, or no DC curve, or no power-limited DC SOA, discard it and move on to the next part.

You will find many families of parts this way, which are rated for this service, and reasonably priced.

You apply an accurate and fast current limit circuit -- the BJT shunt sense method is fine, while more accurate and adjustable means can be applied additionally to get traditional CC/CV supply operation -- and the SOA is never, ever violated.

You can even put in a thermistor to throttle or fold back the current when the heatsink gets hot, to deal with clogged heatsinks.  You can use enough heatsink to avoid using a fan at all (which is the most common culprit in everything that needs them!).

I think MOSFETS have two weaknesses here. I know SS is the future, lol.

Looking up the SOA- not so simple, assuming a reactive load will never be seen, needs a derating as running parts near these limits is a bad idea and their datasheets are full of hype.
TI claims:
"As a final guarantee of the reliability of our SOA curve, we de-rate each measured thermal runaway line anywhere from 30-40%, depending on how much part to part variation we see. So when you are comparing our FETs’ datasheets to competitors’, be wary of the fact that they may not be as conservative. We have seen some vendors who are. We have seen others who publish the actual failure points and claim this as their guaranteed SOA. There is no industry standard and the truth is without the underlying data demonstrating where parts actually failed, it is impossible to know which part is more reliable from the datasheet SOA curves alone."

Mainstream MOSFETS are all about switching, and parts built for tough operation in linear-mode is a gray area. You have to wonder why IXYS actually has a lineup specifically for that.

So maybe a solution is to use several of the venerable IRFP460, for example, giving generous SOA derating.

This leads to the next problem.

The reaction time of the current-limit circuit to discharge the MOSFETs' capacitance before the pulse SOA is exceeded... I think it's difficult with >10,000pF Ciss and the HV.
I hesitate to use single-slope SOA and the sense-resistor/transistor but maybe SPICE will say otherwise. The 470uF filter capacitor at 400V will dump some current into the MOSFETs for a usec or two, during a short circuit on the power supply's output. Let's be generous and add 10R series resistance. Down to 40A peak. Still a lot.

If you you feel I'm spewing hot air, perhaps let's decide tube or SS or both and keep rolling  ;)

Application Note AN-1155 Linear Mode Operation of Radiation Hardened MOSFETS
AN-4161 Practical Considerations of Trench MOSFET Stability when Operating  in Linear Mode

edit: forgot attachment
« Last Edit: November 26, 2017, 06:54:13 PM by floobydust »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #153 on: November 26, 2017, 08:15:17 PM »
Linear power supplies are no longer a modern solution and even less so when it comes to high voltages.

Initially, there was a fundamental error of 001, that one could easily realize a linear supply adjustable from 0 to 350V with semiconductors.

For obvious reasons of poor efficiency, this solution is no longer acceptable in modern technology.
The right solution would be a SMPS.  :-+

But it is a solution that is not simple and requires a high level of competence, which is not the case for 001.

That's why there are two solutions:
- or 001 buys another power supply
- or he opts for the simple solution which is that of the series regulator with tubes.

But there is another problem: he wants a complete diagram, with all the details of realization, which requires to develop this power supply and to make a prototype ...

Who has the skills and the time to develop this project on a volunteer basis for him?
Who is willing to sacrifice the costs that such a project will cause?

I gave some ideas but I have neither the time nor the money to develop projects for free.
« Last Edit: November 26, 2017, 08:17:43 PM by oldway »
 
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Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #154 on: November 26, 2017, 08:56:37 PM »
Looking up the SOA- not so simple, assuming a reactive load will never be seen, needs a derating as running parts near these limits is a bad idea and their datasheets are full of hype.

Reactive is no problem.  Fit SOA to worst case, i.e., short circuit condition.  Capacitor can't draw more than that for a short time (seconds, for a fucking huge capacitor), inductor can only draw that after some time.

Oh and, inductor can only draw current the same direction as was applied.  So, charging up a big fat 100H inductor then disconnecting it and watching that sexy arc draw off the terminals, makes absolutely no difference to the supply at all.  Current is dropping during that arc, and voltage remains fixed at the setpoint.  No flyback pulse, no crazy spikes, just a clean burn.

Derating: goes without saying.  My earlier hint seems to have gone unnoticed: to use TO-247s at under 100W, and TO-220s under 50W.  Typically, these will be rated upwards of 300W and 100W, respectively (depends on die size, some are less, too).  The derating serves two purposes: being conservative about the actual SOA, and approximate overhead for RthJC, insulator and heatsink.

Well, derating helps reduce the impact of thermal cycling, which is also nice. :)

Quote
TI claims:
"As a final guarantee of the reliability of our SOA curve, we de-rate each measured thermal runaway line anywhere from 30-40%, depending on how much part to part variation we see. So when you are comparing our FETs’ datasheets to competitors’, be wary of the fact that they may not be as conservative. We have seen some vendors who are. We have seen others who publish the actual failure points and claim this as their guaranteed SOA. There is no industry standard and the truth is without the underlying data demonstrating where parts actually failed, it is impossible to know which part is more reliable from the datasheet SOA curves alone."

I tested a smaller QFET to destruction (FQPF6N40C) and it failed very close to the RthJC limit.

I haven't tested any TI transistors to destruction, so can't speak to the validity of their claims.

Anyway, all this talk about SOA works the other way, too: you can buy a handful of different transistors, and test each one.  Once the supply is complete, and tested for operating characteristics, test it under short-circuit load (protip: don't actually short it, use a low ohm fusible resistor instead).  Test different brands and increase the current limit gradually until destruction occurs.  This plots a single point on the SOA curve.

If that point lies inside the DC SOA curve, that manufacturer is full of shit.

If outside, they're being conservative.

Like I said before, Si IRF740 is not specified for DC, but I have tested it for DC and it passed with a whopping 60% or so of headroom.

There's no secret to it.  You hook it up and either it works or it doesn't!  This is literally all the manufacturer does, and all that you need.  (Well, they also use a runaway detection circuit, so a single device can be characterized over many points, rather than destroyed for each.)

Quote
Mainstream MOSFETS are all about switching, and parts built for tough operation in linear-mode is a gray area. You have to wonder why IXYS actually has a lineup specifically for that.

Duh, marketing. :-DD

IXYS probably has a worse track record than most, on SOA capabilities.  A lot of their HiperFETs don't even have SOA curves at all.  The ones that do, drop off terribly early (1ms curves, if that; certainly not DC).  These are an exemplar of the previous generation: high power density, but high thermal sensitivity, too.

Now that they've licensed Infineon's CoolMOS, that's all in the past.  I mean, not fully, as those product lines will take a decade to close out -- but you don't have to buy them.

And, if you want the design assurance that they're actually intended for (and presumably, tested for) linear operation, you can buy those -- there's nothing wrong with that, you're just paying a premium for it.

Quote
So maybe a solution is to use several of the venerable IRFP460, for example, giving generous SOA derating.

Indeed, old MOS (like the above IR HEXFET family) tend to have crap power density, so they didn't reach into the region of thermal runaway, and are suitable for linear use.

They also have massive dies, perhaps unexpectedly for their price -- indeed, those ancient masks have fully depreciated and they cost almost nothing to make.

You can spend the same money on a new (SuperJunction type) part, and get only a third of the ultimate power dissipation (~die area).  Point being, you also get about triple the switching performance (Rds(on) * Qg), or, even better than that, actually.  Which is fantastic for switching, it just doesn't help us much for the immediate problem.

Quote
This leads to the next problem.

The reaction time of the current-limit circuit to discharge the MOSFETs' capacitance before the pulse SOA is exceeded... I think it's difficult with >10,000pF Ciss and the HV.

Have you... run the numbers on this?

Because, for a puny 2N3904 with 1k series base resistor, across a source current sense resistor, the response time is under a microsecond.  I'm not kidding!  Don't believe me?

Most of the circuits in this thread haven't even shown a base resistor (which is a rather unsafe proposition, I should add-), and so the delay will be in the hundreds of nanoseconds.  About a quarter again, if it's a damn 2N2222.

Even going from hard saturation (say, Vgs(on) ~ 10V) to soft limiting, even with very pissy gate drive, doesn't take long, and it certainly doesn't violate the SOA.

It doesn't even necessarily violate the DC SOA, let alone the 10us pulse SOA.

Example: PSMN012-80BS with 50mohm source degeneration resistor, Vgs(on) = 9V, 40V step (t_r < 1us), -20A/div.  This is another current limiting circuit I designed and built.



This is a 150W device (D2PAK, not that you'd ever be able to get 150W from it in practice), 100mJ avalanche energy so it's not a very big die (it's a newer generation -- not SuperJunction at this voltage, but nonetheless significantly improved from the IRFP days), and has a DC power limit of just a few watts in application (PCB cooling only).
https://assets.nexperia.com/documents/data-sheet/PSMN012-80BS.pdf
Fig.3 shows 10us SOA at 40V going well over 100A.

The pulse is way under the limit, and that's with inferior gate drive.  Qg(tot) is a lot lower than IRFP460, but a 2N3904 current limiter will pull down much harder than what's in this circuit, and in a linear circuit, Vgs is already near Vgs(th) -- not all the way up at Vgs(on) -- so it only needs to shove the gate a few tenths of a volt to do the job!

Don't cry Miller effect, either -- that's included in the above pulsed test, of course (at the same time current drops from its peak, to the plateau value of 60-80A, drain voltage rises to the full 40V), and anyway, don't argue from ignorance! Measure! Even SPICE will get this right!

Quote
I hesitate to use single-slope SOA and the sense-resistor/transistor but maybe SPICE will say otherwise. The 470uF filter capacitor at 400V will dump some current into the MOSFETs for a usec or two, during a short circuit on the power supply's output. Let's be generous and add 10R series resistance. Down to 40A peak. Still a lot.

Where the fuck is 40A coming from, man?  Really? :palm:

It's already in the linear range.  It's drawing as much current as it ever will.  Pentode curves at work here!

A step change in Vds will cause a step change in Vgs, yes -- this amount can be calculated or simulated, and the delta I_d found.  It won't be 40A, and it certainly won't be V(B+) / Rds(on)!

And even if it were, 1us of that is perfectly within the SOA of any device that shows a square SOA on that time scale.  For god sakes even IGBTs can handle that!

(Speaking of, and to reiterate: don't use IGBTs for linear operation.  They have even less silicon than top-performance MOSFETs.  They're made for switchin', and switchin's what they'll do.)

Quote
Application Note AN-1155 Linear Mode Operation of Radiation Hardened MOSFETS
AN-4161 Practical Considerations of Trench MOSFET Stability when Operating  in Linear Mode

edit: forgot attachment

Incidentally, note that Trench MOS is a slightly newer generation than HEXFETs -- IIRC, HEXFETs are VMOS, and Trench was roughly the next gen after(..?!).  The trench process has nicely served many designs, so you'll see the whole gamut, as far as stability and performance, in devices with that keyword.  YMMV. :)

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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #155 on: November 26, 2017, 10:09:59 PM »
All these endless discussions about the use of MOSFETS in high voltage linear regulation, all the doubts that there is about the adequate Mosfet, all that does only prove one thing: a mosfet used in these conditions is not reliable.

The most important point in a HV bench power supply is safety because 350V 200mA is lethal.

One thing is certain: pass MOSFETs (which usually fail in short circuit), can not be used in a linear HV bench power where the risks of electrocution of the operator are high, it is too unreliable technology and too dangerous !
 

Offline BrianHG

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Re: 0-350V 0.2A Bench Power Supply
« Reply #156 on: November 26, 2017, 10:31:25 PM »
Hmmm, if I were to spend around 100$ (total) making such a supply and be lazy about the design, very low noise regulated output, NO output Mosfets, I would just use PA340 power opamp at 15$, feed a few NPN transistors in emitter follower configuration, obviously series output resistors on emitters and input on base, and a voltage reference zener, however, since 350v with 60ma continuous out is the PA340's max, you would need to per-regulate it's supply to get it right up to 350v without going over using a single additional NPN to regulate the DC power input (the low voltage drop here and only around 50ma needed for the op-amp means less heat dissipation).  Your max output will be only around 345v due to output v+ limit of opamp and voltage drop across the transistors.

Second smaller regular op-amp for current limiter sensor, by muting the + input to the PA340.

The rest, a cheap surplus old heatsink to hold 8 NPN transistors + 1 smaller one for the op-amp if needed + 1 or 2 transformers to make the un-regulated 375vdc source...

https://www.digikey.com/product-detail/en/apex-microtechnology/PA340CC/598-1917-ND/2700701
https://www.apexanalog.com/resources/products/pa340u.pdf

Transistor choice FJA13009TU: https://www.digikey.com/product-detail/en/on-semiconductor/FJA13009TU/FJA13009TU-ND/1056011
You will just squeeze into the safe operating area with 8 in parallel, at full continuous 200ma load, all the way down at 1v output, I figure a 375v drop from the main un-regulated power source.  In linear operation, you cannot do this effectively with mosfets, unless you precisely match all their Vgs down to the same degree of error as in the Vbe drop of multiple BJTs over a wide temperature range.

The DC safe operating area of STMicroelectronics BUF420AW doesn't look trustworthy or complete in the data sheet, but, you would only need this 1 transistor to drive 200ma at over 375v drop and it's a high price at 11$.  Though 10x of the other transistor is also getting a little pricey at 15$.  I would just use at least 10x the FJA13009TU part since the DC soa is absolutely clearly defined in the data sheet.

I would still spend a little more for better case and protected connections.
I don't believe you can build a 350v 200ma adjustable supply that you could trust for safety and longevity for less than 100$.  And when I say longevity & safety, I don't mean it might stop working after a few weeks or months, I mean with 375v inside, it wont unexpectedly blow up or start a fire after a few weeks or months.

Also, thanks to using a standard opamp, I would also skip the analog volume adjustments and use a PIC or equiv MCU with internal dac/adc to drive the power op-amp with a nice readout adding another 25$ in parts, but with some safety features like over-temp shutdown and true voltage and current digital readings of your output + RS232 com control and push button memory controls.
« Last Edit: November 27, 2017, 12:59:33 AM by BrianHG »
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Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #157 on: November 27, 2017, 01:58:44 AM »
I've come up with a solution to the LM317+valve current limiter problem: use an NPN+valve cascode. The voltage across Q3 is limited to below 80V, even when shorted at nearly 300mA; finding a BJT which is capable of this should be possible. A Darlington device still may be a good idea, as the base current will not be high enough, at high voltage settings and paralleling two transistors is still a good idea.


I have never attempted to design a linear power supply with such a high voltage output, so rather than just relying on simulators and a bit of guesswork, I decided to do some research on the matter. The biggest challenge is the output pass device, which dissipates most of the power. Let's look at the three different devices being suggested:

1) BJTs. In short forget about it. The safe operating area of all BJTs I've seen, allows only a 20mA or so, at 400V. Try to get, even a high voltage, high power BJT to dissipate a significant amount of power at a few hundred volts and the result will be secondary breakdown causing the emission of magic smoke. The only way would be to cascode several in series, which is a pain.

2) Valves/tubes. Electrically robust and very resistant to overload. The downside is they're, inefficient, relatively short lived, mechanically fragile and require a negative voltage to turn off, like a depletion mode FET.

3) MOSFETs. These appear to be the best option. They're resistant to secondary breakdown. The only limit seems to be the thermal. 80W for a TO-220 case may be pushing it, so two could be connected in parallel and they should current share fairly well.

Tap switching should be implemented, so the output device never sees the full voltage. This can be implemented using a relay and comparator, monitoring the output voltage.

I don't think I would seriously consider building this. I'd probably opt for a switched mode design.
« Last Edit: November 27, 2017, 02:02:46 AM by Hero999 »
 

Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #158 on: November 27, 2017, 02:16:14 AM »
All these endless discussions about the use of MOSFETS in high voltage linear regulation, all the doubts that there is about the adequate Mosfet, all that does only prove one thing: a mosfet used in these conditions is not reliable.

I would not consider any pass element or control circuit reliable given pot odds which include easy electrocution.  Once was enough to teach me that excessive bulk filtering capacitance is not a good idea.  See below about including an SCR crowbar.

Quote
The most important point in a HV bench power supply is safety because 350V 200mA is lethal.

One thing is certain: pass MOSFETs (which usually fail in short circuit), can not be used in a linear HV bench power where the risks of electrocution of the operator are high, it is too unreliable technology and too dangerous !

I would include an SCR crowbar circuit on the output to blow the fuse in the event of a pass element short, control circuit failure, or high output voltage.

You apply an accurate and fast current limit circuit -- the BJT shunt sense method is fine, while more accurate and adjustable means can be applied additionally to get traditional CC/CV supply operation -- and the SOA is never, ever violated.

This is why I like using integrated regulators as pass elements; they include their own built in fast current limit and safe operating area protection.

I have seen power MOSFET designs where a thyristor was used between the gate and source to implement fast protection.  While not suitable for this application, Motorola produced the amusing MDC1000A (datasheet included below) for power MOSFET switching applications; internally it uses an SCR for fast turnoff.  These days there is no shortage of small, fast, high current, and high gain bipolar transistors suitable for driving charge through high capacitance MOSFETs.
« Last Edit: November 27, 2017, 02:47:52 AM by David Hess »
 

Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #159 on: November 27, 2017, 02:28:51 AM »
3) MOSFETs. These appear to be the best option. They're resistant to secondary breakdown. The only limit seems to be the thermal. 80W for a TO-220 case may be pushing it, so two could be connected in parallel and they should current share fairly well.

MOSFETs are *not* resistant to secondary breakdown (Do they call it that?  What do they call it?) at high voltages where the temperature coefficient of the threshold voltage reverses.  This is bad enough on a single die but multiple devices in parallel will result in current hogging.  It is not fatal but it needs to be watched.  That graph floobydust posted illustrates the problem.

Update: If I ever find one of my copies, the Siliconix MOSPOWER Applications Handbook has an excellent discussion of this issue.  Back then with low cell density and horizontal power MOSFETs, it was not nearly as much of a problem but modern high density devices are often worse than bipolar transistors except perhaps in magnitude.  3sl4co1l said that this situation has improved and some datasheets seem to indicate this which is a welcome relief.
« Last Edit: November 27, 2017, 02:46:30 AM by David Hess »
 

Offline BrianHG

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Re: 0-350V 0.2A Bench Power Supply
« Reply #160 on: November 27, 2017, 02:46:43 AM »
Get a good heatsink, and parallel 4x PA340, the data sheet claims you will get 50ma continuous each device, no secondary breakdown.  This solution would be 4x15$, plus some series resistors.  However, you would want one transistor regulating the +350v supply to maximize the supply for the op-amp.  And, the output will need series resistors to accommodate minute voltage offset between the 4 devices.  Your output voltage will range between 2v and 342v, but, with 2 series diodes on the output, you will go from 0v to 340v.

I would still use another op-amp in front to amplify a MCU's dac output to 350v, then drive the 4 parallel output driving op-amps in voltage-follower mode.  The adc's on the MCU will measure output voltage and current, and, perform the constant current mode voltage limiting.  Your voltage and current limiting output will now be digital accurate and you will have digital readout.

Your output precision and noise will be incredible, but if your MCU firmware crashes and doesn't perform proper current limiting, you'll blow them.  I would add an additional linear current-limiting circuit muting the MCU's dac output to protect the op-amps.
« Last Edit: November 27, 2017, 03:02:37 AM by BrianHG »
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #161 on: November 27, 2017, 02:58:43 AM »
Thanx a lot to all!

I see many experienced peoples here  :-+

Can You say is long-tail dual triode schematic have any benefits vs classic small pentode driver?
 

Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #162 on: November 27, 2017, 03:02:32 AM »
I would still use another op-amp in front to amplify a MCU's dac output to 350v, then drive the 4 parallel output driving op-amps in voltage-follower mode.

Be careful about exceeding the inverting and non-inverting input voltages of the operational amplifiers under any circumstances; the necessary input protection can get out of hand pretty quickly.  Of course maximum MOSFET gate to source voltage and bipolar base-emitter voltage require care as well.

This issue is why I did not recommend a bootstrapped operational amplifier implementation although it is certainly feasible to do.

Quote
The adc's on the MCU will measure output voltage and current, and, perform the constant current mode voltage limiting.  Your voltage and current limiting output will now be digital accurate and you will have digital readout.

The MCU does not need to be part of a critical feedback loop for digital accuracy and it may be undesirable for reasons of reliability.
« Last Edit: November 27, 2017, 03:49:53 AM by David Hess »
 

Offline BrianHG

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Re: 0-350V 0.2A Bench Power Supply
« Reply #163 on: November 27, 2017, 03:09:05 AM »
The MCU does not need to be part of a critical feedback loop for digital accuracy and it may be undesirable for reasons of reliability.
No, I would just use the DAC as my voltage ref set to 1 value unless maximum current is exceeded.  I don't want dac transitional noise on my outputs.  Have a linear circuit transistor mute/clamp the DAC's output if the current exceeds 200ma, a reference set by a second dac from the MCU to a small comparator/opamp on a shunt resistor at GND, with a maximum 200ma range making linear current limiter instead of a crucial software protection loop.  (I guess, making a linear supply, try to make everything crucial stay linear...) The inputs of the opamp do have that 16v maximum offset protection, I would use series resistors when feeding the op-amp inputs.

But yes, drive the inputs hard off then end, you will create a nasty problem.
« Last Edit: November 27, 2017, 03:23:20 AM by BrianHG »
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Offline BrianHG

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Re: 0-350V 0.2A Bench Power Supply
« Reply #164 on: November 27, 2017, 03:47:52 AM »
Wow, all you need is this 1 PA92 IC for a 375v, full 200ma continuous output current safe to short to GND as it has a built in programmable current limiter.  Also, you will need a heat-sink.  Though it costs.............. 163$

https://www.apexanalog.com/resources/products/pa92u.pdf

At just under 200$, this one will continuously drive 200ma, at 350v shorted to GND, with a case temperature above 70c:
PA93 https://www.apexanalog.com/resources/products/pa93u.pdf

This would be the simplest, safest assured power supply, which wont explode, as long as you follow the usage in the data sheet.
Easy to make an adjustable voltage, 200ma supply with this IC and a volume control knob and zener diode with a fraction the worry.  Nothing other than a HV transformer, diodes and cap rectification with fuses for DC power.
« Last Edit: November 27, 2017, 04:05:50 AM by BrianHG »
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #165 on: November 27, 2017, 04:24:46 AM »
I see wery intelligent people here  :-+

And I no more understand anything. I`m only homebrewer  :palm:

If You can. help me please with simple tube pass project
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #166 on: November 27, 2017, 05:10:19 AM »
All these endless discussions about the use of MOSFETS in high voltage linear regulation, all the doubts that there is about the adequate Mosfet, all that does only prove one thing: a mosfet used in these conditions is not reliable.

The most important point in a HV bench power supply is safety because 350V 200mA is lethal.

One thing is certain: pass MOSFETs (which usually fail in short circuit), can not be used in a linear HV bench power where the risks of electrocution of the operator are high, it is too unreliable technology and too dangerous !
Just about any semiconductor will fail short circuit. I don't know about valves.

Why is that a safety hazard? If the bench power supply is capable of giving a lethal voltage, then the best safety practice is to assume the output voltage has the potential to be lethal, even if it's set to a non-hazardous voltage. Never touch the output of a bench linear power supply which is powered by a lethal voltage on the other side of the pass element!

The same principle applies to a mains circuit switched of with a TRIAC or thyristor.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #167 on: November 27, 2017, 07:16:24 AM »
...Just about any semiconductor will fail short circuit. I don't know about valves.

Why is that a safety hazard? If the bench power supply is capable of giving a lethal voltage, then the best safety practice is to assume the output voltage has the potential to be lethal, even if it's set to a non-hazardous voltage. Never touch the output of a bench linear power supply which is powered by a lethal voltage on the other side of the pass element!

The same principle applies to a mains circuit switched of with a TRIAC or thyristor.
It's exactly the opposite ... The safety rules require that if a power supply is adjustable from 0 to 350V, it can be used with 12V output without any risk for the operator.
A well-designed 0 to 350V power supply meeting basic safety principles can not be more dangerous when set to 12V than a simple 12V power supply with 7812.
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #168 on: November 27, 2017, 07:23:44 AM »
All these endless discussions about the use of MOSFETS in high voltage linear regulation, all the doubts that there is about the adequate Mosfet, all that does only prove one thing: a mosfet used in these conditions is not reliable.

You're the only one with these imaginary doubts...


Quote
The most important point in a HV bench power supply is safety because 350V 200mA is lethal.

One thing is certain: pass MOSFETs (which usually fail in short circuit), can not be used in a linear HV bench power where the risks of electrocution of the operator are high, it is too unreliable technology and too dangerous !

Tubes fail shorted too.  Try melting one some day. :P

I guess we should just throw up our hands!  It's an impossible assignment!  We cannot make it shock-proof, touch-proof or lick-proof!  They'll always make a smarter fool no matter what protection we add!

Seriously.  Solid state, high voltage power supplies fly on interplanetary probes.  Indeed, this is because tubes still fly on such platforms -- it's hard to beat a TWT for flight reliability record, gain, power and so on.

Tim
« Last Edit: November 27, 2017, 07:33:19 AM by T3sl4co1l »
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #169 on: November 27, 2017, 07:26:31 AM »
@David Hess:
Quote
I would include an SCR crowbar circuit on the output to blow the fuse in the event of a pass element short, control circuit failure, or high output voltage.
Crowbar circuit is a good solution for fixed output voltage power supply but pain in the ass for variable output power supply.
Crowbar threshold must be ajusted every time you change the output voltage of your power supply.....not practical at all....
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #170 on: November 27, 2017, 07:34:45 AM »
@David Hess:
Quote
I would include an SCR crowbar circuit on the output to blow the fuse in the event of a pass element short, control circuit failure, or high output voltage.
Crowbar circuit is a good solution for fixed output voltage power supply but pain in the ass for variable output power supply.
Crowbar threshold must be ajusted every time you change the output voltage of your power supply.....not practical at all....

Easy to detect a pass device fault and activate the crowbar.

Tim
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Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #171 on: November 27, 2017, 07:35:26 AM »
Quote
I would include an SCR crowbar circuit on the output to blow the fuse in the event of a pass element short, control circuit failure, or high output voltage.

Crowbar circuit is a good solution for fixed output voltage power supply but pain in the ass for variable output power supply.
Crowbar threshold must be adjusted every time you change the output voltage of your power supply.....not practical at all....

The crowbar circuit protects against a pass element short or control circuit failure where the output voltage rises all the way to the input voltage.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #172 on: November 27, 2017, 07:38:32 AM »
All these endless discussions about the use of MOSFETS in high voltage linear regulation, all the doubts that there is about the adequate Mosfet, all that does only prove one thing: a mosfet used in these conditions is not reliable.

You're the only one with these imaginary doubts...


Quote
The most important point in a HV bench power supply is safety because 350V 200mA is lethal.

One thing is certain: pass MOSFETs (which usually fail in short circuit), can not be used in a linear HV bench power where the risks of electrocution of the operator are high, it is too unreliable technology and too dangerous !

Tubes fail shorted too.  Try melting one some day. :P

I guess we should just throw up our hands!  It's an impossible assignment!  We cannot make it shock-proof, touch-proof or lick-proof!  They'll always make a smarter fool no matter what protection we add!

Seriously.  Solid state, high voltage power supplies fly on interplanetary probes.  Indeed, this is because tubes still fly on such platforms -- it's hard to beat a TWT for flight reliability record, gain, power and so on.

Tim
The tubes are not dead, there are many applications where the tubes could never be replaced .... You use every day a microwave oven with a magnetron tube and you do not complain .

Just because you do not know anything about this technology does not mean you have to neglect it.

A tube failing shorted (NB: between anode and cathode) ? .... it is extremely rare, I have never seen one in my life .... And on the tubes with connection of the anode on the top of the tube it's just impossible.
« Last Edit: November 27, 2017, 07:40:25 AM by oldway »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #173 on: November 27, 2017, 07:45:41 AM »
Quote
I would include an SCR crowbar circuit on the output to blow the fuse in the event of a pass element short, control circuit failure, or high output voltage.

Crowbar circuit is a good solution for fixed output voltage power supply but pain in the ass for variable output power supply.
Crowbar threshold must be adjusted every time you change the output voltage of your power supply.....not practical at all....

The crowbar circuit protects against a pass element short or control circuit failure where the output voltage rises all the way to the input voltage.
How will you use you power supply with 350V output if voltage drop on Mosfet pass transistor is only a few volts ? How will you detect a shorted pass transistor ?
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #174 on: November 27, 2017, 07:47:12 AM »
The tubes are not dead, there are many applications where the tubes could never be replaced .... You use every day a microwave oven with a magnetron tube and you do not complain .

Just because you do not know anything about this technology does not mean you have to neglect it.

I know everything about this technology, from the underlying physics to the electrical characteristics of many standard parts.

I know better than anyone why tubes are nearly forgotten today, and why solid state has surpassed it in all but a few (electron-wave physics) applications.

Magnetrons are one, I gave another example (TWT) which I guess you didn't pick up on.  Particle accelerators use klystrons, and more broadly speaking, any particle accelerator is itself a large, very complicated tube filled with vacuum, a vacuum tube if you will.

They only remain useful in niche applications.  Everything from DC to UHF has been superseded.  I'm not sure if GaN FETs will ever be cheap enough to replace the microwave oven magnetron, but it'll be an interesting day if it comes.

Quote
A tube failing shorted (NB: between anode and cathode) ? .... it is extremely rare, I have never seen one in my life .... And on the tubes with connection of the anode on the top of the tube it's just impossible.

Er, well... screen and grid, let's say. Not a healthy situation for any of the circuits in this thread.

Cracked or melted glass also lets in gas, which acts to increase leakage or short out (sparking) electrodes.

I don't get you, man.  Just because you can't imagine it, it doesn't exist?  What kind of thought process is that?  That's an extremely narrow, unimaginative way to go through life. :(

Tim
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Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #175 on: November 27, 2017, 07:50:32 AM »
How will you use you power supply with 350V output if voltage drop on Mosfet pass transistor is only a few volts ? How will you detect a shorted pass transistor ?

Simple -- crowbar based on the error amplifier output.

If it's commanding a low output, yet the output is high, the pass device is cacked.

If the output is high, but it's commanding even higher, it's saturated.  (It might still be failed, who knows -- you'll find out when it comes out of saturation.)

You'd also delay this decision, and add an exception for low command * low output, to avoid nuisance trips.

It's just a comparator or two, a couple transistors, and a handful of resistors and a capacitor.  :)

Tim
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #176 on: November 27, 2017, 08:08:15 AM »
The tubes are not dead, there are many applications where the tubes could never be replaced .... You use every day a microwave oven with a magnetron tube and you do not complain .

Just because you do not know anything about this technology does not mean you have to neglect it.

I know everything about this technology, from the underlying physics to the electrical characteristics of many standard parts.

I know better than anyone why tubes are nearly forgotten today, and why solid state has surpassed it in all but a few (electron-wave physics) applications.

Magnetrons are one, I gave another example (TWT) which I guess you didn't pick up on.  Particle accelerators use klystrons, and more broadly speaking, any particle accelerator is itself a large, very complicated tube filled with vacuum, a vacuum tube if you will.

They only remain useful in niche applications.  Everything from DC to UHF has been superseded.  I'm not sure if GaN FETs will ever be cheap enough to replace the microwave oven magnetron, but it'll be an interesting day if it comes.

Quote
A tube failing shorted (NB: between anode and cathode) ? .... it is extremely rare, I have never seen one in my life .... And on the tubes with connection of the anode on the top of the tube it's just impossible.

Er, well... screen and grid, let's say. Not a healthy situation for any of the circuits in this thread.

Cracked or melted glass also lets in gas, which acts to increase leakage or short out (sparking) electrodes.

I don't get you, man.  Just because you can't imagine it, it doesn't exist?  What kind of thought process is that?  That's an extremely narrow, unimaginative way to go through life. :(

Tim
I'm old enough to be your father and I learned electronics at a time when almost all devices used vacuum tubes.
I started repairing TVs at a time when color did not exist yet and whe were using 90 °  black and white cathode ray tubes with an ion trap.
I lived the time of the tubes, so do not try to give me lessons in this area, I have an experience you will never know.
The reality is that you are prejudiced against tubes simply because it is old technology.

You still have not posted any diagrams on your 0 to 350V 200mA power supply solution ..... you only criticize without bringing any practical solution.

At least, the solution I propose is simple and safe, which is perfectly suited to a realization by someone who, as he admitted, knows almost nothing in electronics.
« Last Edit: November 27, 2017, 08:13:18 AM by oldway »
 
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Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #177 on: November 27, 2017, 08:32:17 AM »
The reality is that you are prejudiced against tubes simply because it is old technology.

I get that you have lots of experience, but I'm not seeing a reason why that should be applicable to design.

You know how to repair any damn TV or radio, I get that.  But we're talking design here, and we're talking solid state -- both things that -- I guess you admit? -- are at best, on the edge of your scope of knowledge?

Your knee-jerk reaction about my experience is based on your prejudices, not mine; you could at least do me the respect of looking up some projects on my website, like this,
https://www.seventransistorlabs.com/Images/DistAmp2.jpg
or this,
https://www.seventransistorlabs.com/Radio_20m/
or even this, somewhat jokingly as you'll see from the design approach:
https://www.seventransistorlabs.com/Images/Borg.gif

Quote
You still have not posted any diagrams on your 0 to 350V 200mA power supply solution ..... you only criticize without bringing any practical solution.

A rejection of criticism is rather abhorrent to the ideals of this democratic process of development...

Several of the diagrams above are already close enough that I don't need to draw one up myself.  A reading of my posts shows this: I have noted that some are going in the wrong direction, while some are very nearly complete.  None have been exactly satisfactory, but there's no accounting for taste.

I'd gladly draw up a proper design -- simulation and BOM included -- if sponsored for it. :)

I welcome any constructive criticism of my ideas.

Tim
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #178 on: November 27, 2017, 08:44:55 AM »
Quote
I'd gladly draw up a proper design -- simulation and BOM included -- if sponsored for it. :)

Ask this to 001 ..... good chances, ... he already complains for a few dollars difference between the price of a PL509 and an EL34 .....  :-DD
 

Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #179 on: November 27, 2017, 09:03:06 AM »
The crowbar circuit protects against a pass element short or control circuit failure where the output voltage rises all the way to the input voltage.

How will you use you power supply with 350V output if voltage drop on Mosfet pass transistor is only a few volts? How will you detect a shorted pass transistor?

In a high voltage power supply, I would expect more than just a few volts of difference at maximum output.  It is not like efficiency is at a premium so a minimum difference can be enforced to make a simple crowbar circuit work reliably.

There are alternative ways to detected a shorted pass element as T3sl4co1l suggested.
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #180 on: November 27, 2017, 10:04:32 AM »
How will you use you power supply with 350V output if voltage drop on Mosfet pass transistor is only a few volts ? How will you detect a shorted pass transistor ?

Simple -- crowbar based on the error amplifier output.

If it's commanding a low output, yet the output is high, the pass device is cacked.

If the output is high, but it's commanding even higher, it's saturated.  (It might still be failed, who knows -- you'll find out when it comes out of saturation.)

You'd also delay this decision, and add an exception for low command * low output, to avoid nuisance trips.

It's just a comparator or two, a couple transistors, and a handful of resistors and a capacitor.  :)

Tim

Yes a crowbar circuit could be added to the error amplifier, but that won't protect against the adjustment potentiometer failing open.

...Just about any semiconductor will fail short circuit. I don't know about valves.

Why is that a safety hazard? If the bench power supply is capable of giving a lethal voltage, then the best safety practice is to assume the output voltage has the potential to be lethal, even if it's set to a non-hazardous voltage. Never touch the output of a bench linear power supply which is powered by a lethal voltage on the other side of the pass element!

The same principle applies to a mains circuit switched of with a TRIAC or thyristor.
It's exactly the opposite ... The safety rules require that if a power supply is adjustable from 0 to 350V, it can be used with 12V output without any risk for the operator.
A well-designed 0 to 350V power supply meeting basic safety principles can not be more dangerous when set to 12V than a simple 12V power supply with 7812.
What safety rules?

If a power supply is adjustable, up to a hazardous voltage, then the operator should beware that it can fail, causing the output to rise to the maximum possible voltage setting, plus a bit more. As long as the operator is aware of this fact, then there's no additional risk, other than a few blown components.

By the way, the LM7812 can fail short circuit input-to-output too, although it's not a safety hazard, because the maximum rated input voltage is under 35V.
 

Offline Neomys Sapiens

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Re: 0-350V 0.2A Bench Power Supply
« Reply #181 on: November 27, 2017, 10:34:38 AM »
I'm not sure if there are no other solutions: my Heinzinger TNs300-120 does 300V 400mA with 2 transistors and a thyristor preregulator. And it is compact as well as totally reliable.
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #182 on: November 27, 2017, 11:04:53 AM »
Faintly tried a LTSPICE IV simulation to estimate how much current IRFP460's would experience and the 2N3904 current-limiter, transient under a short-circuit.
Before this thread exceeds its own SOA  :popcorn:

I find you really need the parasitics - lead inductance, ESR, ESL and even then I'm getting pretty much bullshit results.

At first it's what I expect... the 2N3904 seeing 1.7Apk discharging the MOSFETs' gate capacitance, and IRFP460 seeing around 3-4Apk drain current (1.3kWpk) each, for nanoseconds.
But changing output capacitance C2 from 0.22pF to 0.22uF drastically changes those values; 2N3904 seeing 0.039Apk discharging the MOSFET's gate capacitance, and IRFP460 seeing around 0.2Apk drain current, at C2=0.22uF

So the my simulation bullshit detector  :bullshit: went off and I stopped.
Perhaps someone can explain what is going on. Strange SPICE results, but I'm not expert-level with it.


I notice the current-limit setpoint (2N3904 vbe) is sloppy as it seems to be working a bit too hard here. I think Zetex parts are better suited.
Sims missing MOSFET lead, gate resistor and PCB inductance.

I drew up a design using my own SS power supply regulator scheme that works well for me, but hold I'll off until flames and smoke subside, lol.
« Last Edit: November 27, 2017, 11:08:59 AM by floobydust »
 
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Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #183 on: November 27, 2017, 11:25:27 AM »
Yes a crowbar circuit could be added to the error amplifier, but that won't protect against the adjustment potentiometer failing open.

Always wire the potentiometer so that an open causes a low voltage or current fault.
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #184 on: November 27, 2017, 12:31:53 PM »
At first it's what I expect... the 2N3904 seeing 1.7Apk discharging the MOSFETs' gate capacitance, and IRFP460 seeing around 3-4Apk drain current (1.3kWpk) each, for nanoseconds.

Quite a lot better than 40A, wouldn't you say? :)  Well within SOA too, of course.

Quote
But changing output capacitance C2 from 0.22pF to 0.22uF drastically changes those values; 2N3904 seeing 0.039Apk discharging the MOSFET's gate capacitance, and IRFP460 seeing around 0.2Apk drain current, at C2=0.22uF

Well, if you're going to go beyond the semiconductor core and include bypass caps and stray inductance, you'll see a lot more.

Nothing that can't be calculated.  0.2uH + 0.22uF is about 1 ohm and 760kHz.  So the FET source will be pulled down in about 1/4 wave of that or 330ns.

The switch will see a peak current of around 350V / 1 ohm = 350A, but only for that fraction of a microsecond as the cap is discharged.  What do you expect, you put a cap across the output and of course it's going to spark when you short it out. ;D

If you want a supply that's so fast and current limited that you could connect an LED to it without damage, well... you can't actually, because of drain capacitance.  With lots of series resistance, you might be able to get peak current * pulse width manageable, but anyway this sort of extremely cautious output characteristic is unusual for high voltage supplies, for this very reason, and not really very useful (most things you'll hook up to a power supply will have their own local bypass caps, so, who cares?..).

Quote
So the my simulation bullshit detector  :bullshit: went off and I stopped.
Perhaps someone can explain what is going on. Strange SPICE results, but I'm not expert-level with it.

Slower rise time suggests more time for the current limiter to respond, and less peak current in both 2N3904 and IRFP460.  Seems fine to me.  :-//

Tim
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Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #185 on: November 27, 2017, 05:18:05 PM »
It does look like slowing down dV/dt on the (source) output is really lowering the stress on the MOSFETs and current-limiter.
I was out to lunch on the 40Apk by a factor of 10, not bad really :P but the instantaneous power blip can be extremely high.

I'm used to some output capacitance for regulator stability. It needs to be >0.1uF to slow things down, but adding >33uH inductor also works and gets rid of that sparking cap. It just adds some back-EMF and resonance to dampen.

On the SOA thing, it was also discussed in EEVblog #1023 - Rigol DL3021 Electronic Load Teardown.  The IRFP250N's Rigol using qty. 6 for 40A/150V, qty. 8 for 60A/150V and discussion about HP load. To have some idea of derating required in the absence of DC SOA specs.
Link in that thread of NASA (SOA related) MOSFET failures paper is quite a good read.

Everything is saying SOA curves are antiquated, fudged by many manufacturers, the semiconductor (failure) physics are not fully understood hence no accurate model exists, and the push to switching applications has made parts weaker in linear operation.
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #186 on: November 27, 2017, 07:46:21 PM »
Yes a crowbar circuit could be added to the error amplifier, but that won't protect against the adjustment potentiometer failing open.

Always wire the potentiometer so that an open causes a low voltage or current fault.
How? It's possible to connect a potentiometer like that, so it fails low, if the wiper contact fails, but not if there's a break in the track.

I suppose a good quality wire wound potentiometer could be used, which is extremely unlikely to go open circuit, if it's used at a fraction of its power rating.
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #187 on: November 27, 2017, 08:21:11 PM »
Yes a crowbar circuit could be added to the error amplifier, but that won't protect against the adjustment potentiometer failing open.

Always wire the potentiometer so that an open causes a low voltage or current fault.
How? It's possible to connect a potentiometer like that, so it fails low, if the wiper contact fails, but not if there's a break in the track.

I suppose a good quality wire wound potentiometer could be used, which is extremely unlikely to go open circuit, if it's used at a fraction of its power rating.

Potentiometer paranoia concerns the wiper going open -- which is the typical case when you have a pot going scratchy.  Scratchy pots are more common with DC bias, a prime concern here.

Usual method is simply a resistor from wiper to whichever side is safe.  In this case, wiper to VOUT.  The value is large enough that the pot dominates the adjustable range (so as not to noticeably distort the voltage(angle) characteristic), and with the divider values so that it pulls to a safe value when the wiper opens up (or any other part of the pot, if possible -- which should also be somewhat reasonable in this case).

Tim
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #188 on: November 28, 2017, 04:17:24 AM »
I made it
It works
Thanx
I'm stunned, a masterpiece, you're a genius, an Einstein of electronics, you even invented a triode circuit with G1 grid floating ....  :-DD

I bow, you are too strong .... And the next invention, what will it be? A space ship, a trip back and forth on the moon?  :-DD

Let's be serious ! Have I not explained to you why you have to use a pentode and not a triode (nor a pentode connected in triode) to limit the current in the event of a short circuit at the output?

Have I not provided you with a schematics that can control the pass pentode by opto coupler so that all voltage regulation and current limiting can be done by operational amps, with great accuracy and stability?

How will you reduce the voltage below 200V if you have two zeners of 75V, or 150V, in the cathode of the driver tube?

What will happen if you short circuit the output terminals? Did you even try it?

What's this long tail diagram (differential amplifier) with the grid 1 of one of the two triodes "in the air"?

I am asking me why whe are loosing our time to try to help you.....  |O
« Last Edit: November 28, 2017, 04:50:36 AM by oldway »
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #189 on: November 28, 2017, 04:54:24 AM »
Meanwhile I've been contemplating how to minimise the cost of the transformers for a 2x PL509 based HV PSU, 0-500V 0-250mA, without doing *STUPID* things like hoping that the insulation between two secondaries of a modern off-the-self low voltage transformer is good for 600V!  :-DD

I don't see much if any benefit going to a 6.3V heater tube like EL509 or EL84 for the pass device as then you'll need another transformer (or switching PSU) for the semiconductor control electronics.

Its going to need a 20-0-20V transformer for the heater supply, with its secondary  floating at the output voltage so it doesn't exceed the heater-cathode breakdown voltage. If you make the filament transformer 50VA, its got enough spare current to drive a 110V:18-0-18V 10VA transformer backwards to get your floating (cathode referenced) screen grid supply, and a bridge rectifier and a positive and negative regulator for a floating +/-15V supply for the control electronics.   Unfortnately you cant run grounded control electronics that way.

The negative grid bias required can be got by a charge pump off the main HT transformer and stabilised by a chain of 33V 1W Zeners,  with a pull-down resistor to the bias supply so the default pass device state is hard off,  with a cascode chain of KSA1156YS 400V PNPs for the control circuit to pull up the grid from down around -200V to the max output voltage of 500V.   There's probably something better (probably a MOSFET) that can do the grid drive in one device, but availability and leakage current are serious issues.  I wouldn't be adverse to opto-coupling the control signal down to the negative bias rail.

Not sorted out yet is tap-changing or thyristor preregulation to avoid the need for more than two 'bottles',  and the resulting specs for the HT transformer to give approx 600V unreg when the output is at 500V, though if possible I want to use a 220V:220V isolating transformer (for easy off-the-shelf availability) and a voltage doubling rectifier circuit. I also haven't done any significant work on the floating regulator control circuit and current limit.
« Last Edit: November 28, 2017, 05:03:33 AM by Ian.M »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #190 on: November 28, 2017, 05:19:18 AM »
Using PL509 instead of EL34 is nonsense for the following reasons:

- The PL509 was a flyback pentode for color tv, it is no longer manufactured and, at least in Europe, it is more expensive than an EL34.
EL34 is still manufactured for tube amplifiers and will continue to be manufactured for a long time.

Its anode / cathode isolation is sufficient since it was used in public address amplifiers with 700V of anode voltage, which means at least 1400V peak in operation

By using two tubes in series, a heating voltage of 12.6V can be used. In practice 12V is enough .... There are hundreds of 12V used transformers for sale for a few bucks because everyone changes the 12V halogen lights by leds ....

For the G1 polarization voltage and G2 power supply, just a second transformer 12V / 110 + 110V powered by the 12V output voltage of the first.

For the anode voltage, we provide 2 ranges, one from a 400V winding, the other from a 230V winding.
Range switching is manual.
We only use transformers with one secondary....isolation between one secondary and another does not apply.

Isolation between primary and secondary must be at least 2400V in every commercial transformer. It is fully safe !

Do not use a voltage doubler because the impedance is higher, so the voltage drop too .... Prefer a bridge rectification.

 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #191 on: November 28, 2017, 06:19:40 AM »
Well done 001, hey I like the floating grid :) I'm still going to have a stab at the T-reg with a pair of EL34s with screen grid supply and not wired as triodes, found a little note on that by the way http://www.pmillett.com/hv_bench_supply.htm and no, I'm not going to build it ). Found a 350V 200mA transformer intended for the Maplin 4-20 amplifier so will use that and the 6.3V 5A winding will go to the front panel. Just need a small 6V heater transformer for the EL34s and another for the variable C- supply. BTW is there any harm in using a 6V rather than 6.3V transformer for the EL34 heaters, will a 10% drop in power matter ? Will fix the current limit at 150mA just in case. Would be nice if I could find a single transformer to do the job but I don't see that happening, it's getting harder to find harware for tube projects these days. It's been an interesting topic.
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #192 on: November 28, 2017, 07:51:52 AM »
Using PL509 instead of EL34 is nonsense for the following reasons:

- The PL509 was a flyback pentode for color tv, it is no longer manufactured and, at least in Europe, it is more expensive than an EL34.
EL34 is still manufactured for tube amplifiers and will continue to be manufactured for a long time.
Unfortunately the EL84 iis only rated for 12W max anode dissipation and 65ma cathide current.  As an EL509 or PL509 is rated for 30W max anode dissipation and 500mA max cathode current, as long as one can get an adequate supply of N.O.S tubes without paying silly prices, designing in a pair of PL509 tubes is far from nonsense.  Yes they need higher bias voltages, but it will take five EL84s to do the same job.

If you can suggest an affordable beast of a power tube that's still in production as an alternative to the 509s, I'm all ears, but please don't bug me unless its rated for 600V, 25W Pa and 150mA Ik.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #193 on: November 28, 2017, 08:44:31 AM »
EL34, not EL84...... :palm:
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #194 on: November 28, 2017, 09:05:48 AM »
Thanks, I *was* being stupid,  |O  EL84 EL34 design center ratings of  800V, 25W and 150mA are much more what's needed.
« Last Edit: November 28, 2017, 09:48:55 AM by Ian.M »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #195 on: November 28, 2017, 09:27:29 AM »
EL34 or 6CA7 ratings.
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #196 on: November 28, 2017, 10:09:51 AM »
Yes. I grabbed the Mullard 1962 EL34 datasheet, so I think we are on the same page at last. 

What would you suggest for optimum  Vg2-k bias?   A nominal 110V RMS winding as you suggested earlier, would give peak 155V so around 140-150V after filtering it to smooth it.

What sort of G2 current is that likely to give?
Also how much headroom on Va-k does it need to prevent it going into G2 toaster mode?
« Last Edit: November 28, 2017, 01:09:44 PM by Ian.M »
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #197 on: November 28, 2017, 12:48:36 PM »
Bigger tubes presently in production equipment like guitar amps, might be easier towards a single power tube.
KT-90 or KT-120; ; 6550 (KT-88) is a bit under spec.
SPICE models of some here: http://tdsl.duncanamps.com/dcigna/tubes/spice/index.html
 
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #198 on: November 28, 2017, 10:26:51 PM »
Yes. I grabbed the Mullard 1962 EL34 datasheet, so I think we are on the same page at last. 

What would you suggest for optimum  Vg2-k bias?   A nominal 110V RMS winding as you suggested earlier, would give peak 155V so around 140-150V after filtering it to smooth it.

What sort of G2 current is that likely to give?
Also how much headroom on Va-k does it need to prevent it going into G2 toaster mode?
I'm planning a G2 current of about 5mA/tube.

II do not have anode current / anode - cathode voltage curves for a G2 voltage equal to 140V, only for G2 voltages of 250V and 350V.
But I expect an anode current limited to about 200 mA with G1 at 0V and with a G2 voltage of 140V.

The minimum expected cathode / anode voltage (headroom) is 100V, so there is no risk of G2 overheating.
In addition, a current limiting resistor of 120 to 180 ohms is provided in series with each G2.

About power tubes, there are a lot who can be choosed.....the lower cost and most easily available are: 6V6, 6L6, EL34, KT88

NB: It is recommended to use 12V heating voltage (two tubes in serie) as 12V transformers are cheap and easily available.

KT120 is nonsense....It cost more than 100 $US ... An EL34 cost only about 15 $US
 
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Offline CopperCone

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Re: 0-350V 0.2A Bench Power Supply
« Reply #199 on: November 29, 2017, 09:00:55 AM »
http://www.ixys.com/Documents/Articles/Article_Linear_Power_MOSFETs.pdf

ixys knows power mosfets pretty good

check out IXYS Linear L2™ series.

I would not buy ebay power components
« Last Edit: November 29, 2017, 09:04:15 AM by CopperCone »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #200 on: November 29, 2017, 04:14:33 PM »
Using a linear power Mosfet to build a programmable resistive load and using it as pass transistor in an HV power supply are quite a different thing....In the first case, safety problems are not involved

Your link is only confirming what we all knows: There are real troubles with Power Mosfet forced into linear mode of operation.
 

Offline oldway

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Re: Power supply gonzo holywar
« Reply #201 on: November 29, 2017, 10:54:11 PM »
What happens with you ?
It's the fourth time that you change the title of this Topic, you can't do this.  :scared:

The original title was:
looking-for-yours-opinions!-hv-stabilized-power-supply

Than you changed for
Solved. Tread to delete. maybe

I advised you that you can't delete a thread and loose all the informations whe provide for you.
You changed the title again to :
0-350V 0.2A Bench Power Supply

That was good because this is realy the subject of the topic.

And now, again, a new title :
Power supply gonzo holywar   |O |O |O

This Topic is full of schematics of HV bench power supplies and has a lot of usefull technical informations, you can't destroy all this with a so stupid title who has nothing to do with the subject of this topic.  :-- :--

I will claim to the moderators.
 
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Online Simon

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Re: 0-350V 0.2A Bench Power Supply
« Reply #202 on: November 29, 2017, 11:00:51 PM »
Lets keep a sensible topic name shall we. Power is indeed to be used responsibly
The µCurrent has landed in Europe and now also selling Probe Master probes: http://www.simonselectronics.co.uk New stock now in.
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #203 on: November 29, 2017, 11:46:25 PM »
I do not understand anything after page #6.  :palm:
Some holywar or rocket sience detected
  :blah: :blah: :blah:
 

Online Simon

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Re: 0-350V 0.2A Bench Power Supply
« Reply #204 on: November 29, 2017, 11:48:01 PM »
I do not understand anything after page #6.  :palm:
Some holywar or rocket sience detected
  :blah: :blah: :blah:

So don't read it or ask for clarification.
The µCurrent has landed in Europe and now also selling Probe Master probes: http://www.simonselectronics.co.uk New stock now in.
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #205 on: November 30, 2017, 12:07:10 AM »
There's no holy war here, there's just a clear consensus that a robust MOSFET based pass element PSU is going to be difficult and expensive for an amateur without prior high power high voltage MOSFET experience, to design, build and construct as a one-off, hence the various valve proposals.   I think just about everyone who's done their homework is ruling out BJT pass elements due to secondary breakdown SOA limits.    There has been a lively debate on which valve to use and the most economic way to power and bias it.   Give it another week or two and we may yet see a complete design proposal for the PSU.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #206 on: November 30, 2017, 12:55:01 AM »
We are not vacuum tube fools, we are only looking for the simplest and safest solutions, even if they are not modern.
The real solution, both in terms of safety and performance, would be a SMPS with variable output voltage and adjustable current limit.

But it is clear that it requires a great mastery of power electronics to plan and build such a power supply and that it is not within the reach of 001
« Last Edit: November 30, 2017, 12:56:39 AM by oldway »
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #207 on: November 30, 2017, 08:09:16 AM »
There's no holy war here, there's just a clear consensus that a robust MOSFET based pass element PSU is going to be difficult and expensive for an amateur without prior high power high voltage MOSFET experience, to design, build and construct as a one-off, hence the various valve proposals.   I think just about everyone who's done their homework is ruling out BJT pass elements due to secondary breakdown SOA limits.    There has been a lively debate on which valve to use and the most economic way to power and bias it.   Give it another week or two and we may yet see a complete design proposal for the PSU.

And thus proving the fallacy of the forum: shout louder and more often, and your voice becomes truth.

Well, at least a wise person reading this thread will be able to see reason.

I've stated the facts.  Others have simply continued beyond the point of reason... ::)

Tim
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Offline james_s

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Re: 0-350V 0.2A Bench Power Supply
« Reply #208 on: November 30, 2017, 11:22:36 AM »
How about a buck regulator? Then you are operating the switching element as a switch, the voltages involved should not be too difficult to deal with.

I still have an ancient Heathkit IP-32 power supply I use for HV work, vacuum tubes really do have some nice advantages when high voltages are involved. The thing must be around 50 years old now and has never had any problems, despite getting plenty of abuse when I was a kid.
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #209 on: November 30, 2017, 12:37:04 PM »
@Tim, James and anyone else who wants to see the end of tubes,

If there's an easy robust and reliable way for a relative novice to do it with a MOSFET that's in-stock at Digikey or Mouser, that you will guarantee to survive the output being shorted when set for the full 350V, 0.2A the O.P,. requested and already loaded to 100mA, then yes, state the facts again.   *NO-ONE* wants to have a big fragile glass 'bottle' in their PSU, with its heater dissipating an extra 10W one doesn't want, let alone more than one of them, and the two extra transformers required to provide their heater supply and bias.   

I wouldn't go quite as far as Widlarising a working PSU containing tubes - I'd rather sell it off on EBAY - but I'd certainly listen if an easy to build MOSFET based PSU was proposed - no custom transformers or magnetics , no handwaving about the regulator design - just a schematic, and a list of semiconductors required all in stock at a major distributor, and hints about any pitfalls for the unwary, e.g. where poor layout or heatsinking can cause disaster.
« Last Edit: November 30, 2017, 12:38:48 PM by Ian.M »
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #210 on: November 30, 2017, 12:43:42 PM »
@Tim, James and anyone else who wants to see the end of tubes,

If there's an easy robust and reliable way for a relative novice to do it with a MOSFET that's in-stock at Digikey or Mouser, that you will guarantee to survive the output being shorted when set for the full 350V, 0.2A the O.P,. requested and already loaded to 100mA, then yes, state the facts again.

I laid out the design process, multiple times.

I think most novices are better at reading... :palm:

You also seem to be implying tubes are indestructible, which is an amusing implication.

Quote
but I'd certainly listen if an easy to build MOSFET based PSU was proposed - no custom transformers or magnetics , no handwaving about the regulator design - just a schematic, and a list of semiconductors required all in stock at a major distributor, and hints about any pitfalls for the unwary, e.g. where poor layout or heatsinking can cause disaster.

Show me where in this thread a:
- Schematic
- Semiconductor with full SOA
- Hints
was wholly absent.

There is much thread to go through; I'll wait. ;)

Tim
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Offline james_s

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Re: 0-350V 0.2A Bench Power Supply
« Reply #211 on: November 30, 2017, 12:47:56 PM »
I don't want to see the end of tubes, I quite like tubes, they have a nostalgic charm and for some applications they still have advantages. The extra load and heat presented by the heater(s) is not too big a deal in a *linear* power supply which is already going to dissipate much of the energy going into it as heat. I'm not advocating one way or the other here though, it's certainly possible to do this entirely solid state, though it may not be quite as trivial as it first seems. I don't really understand the source of conflict here, there are any number of ways to build such a power supply with no one definitive "right" way to do it.

Some very old HeNe laser power supplies used a linear current regulator, in those it was common to have a string of several power BJTs in series to get the required voltage. Another possibility is an IGBT, I've only ever used these as switches but they may work ok as a linear pass element, there are certainly some high voltage/high current parts available these days.
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #212 on: November 30, 2017, 01:56:30 PM »
@Tim, James and anyone else who wants to see the end of tubes,

If there's an easy robust and reliable way for a relative novice to do it with a MOSFET that's in-stock at Digikey or Mouser, that you will guarantee to survive the output being shorted when set for the full 350V, 0.2A the O.P,. requested and already loaded to 100mA, then yes, state the facts again.

I laid out the design process, multiple times.

I think most novices are better at reading... :palm:

You also seem to be implying tubes are indestructible, which is an amusing implication.

Quote
but I'd certainly listen if an easy to build MOSFET based PSU was proposed - no custom transformers or magnetics , no handwaving about the regulator design - just a schematic, and a list of semiconductors required all in stock at a major distributor, and hints about any pitfalls for the unwary, e.g. where poor layout or heatsinking can cause disaster.

Show me where in this thread a:
- Schematic
- Semiconductor with full SOA
- Hints
was wholly absent.

There is much thread to go through; I'll wait. ;)

Tim

You agreed that some MOFETs have adequate DC S.O.A for the job (e.g FQA10N80C)
You posted a schematic of a switcher that unfortunately was well above novice level (custom wound magnetics).
You posted hints on various pitfalls.

However all of the above were for different PSUs.

Others posted some links to 'ready to build' linear MOSFET HV PSUs
e.g.
I think I found what you are looking for...  :popcorn:

http://hpm-elektronik.de/projekte/nt350-400/hv-nt-350v-schaltplan.jpg

http://hpm-elektronik.de/ng350-0400-netzteil.htm
The SPW20N60S5 MOSFET it uses is listed as obsolete/NRND, 0 stock at Digikey and Mouser - It looks like they are still  available from other reputable suppliers + the manufacturer: Infineon Technologies, so its still in the game,  but Oldway who proposed it said he didn't trust its current limiting.  :(

Found this the other day https://linearaudio.nl/t-reg-tube-voltage-regulator It's a nice design and the idea is based on the obsolete MC1466L "floating" voltage regulator. The original design used tubes or enhancement mode mosfets, DN2540, and it appeared in the March 2009 edition of Elektor and very recently audioxpress http://www.audioxpress.com/article/t-reg-a-high-voltage-regulator-for-tube-amps. It had a habit of blowing up the enhancement mode mosfets when shorted out but I think the design has been updated for depletion mode mosfets with a much larger SOA. Hmmm... think I've got a spare EL34 somewhere will have to spice it up to see if it's short circuit proof. EDIT: Oops got enhancment and depletion mixed up
Red emphasis added by me.   Worth investigating but that's a pretty large pitfall right there.  :-\

Then at least half the thread went to pot (or rather 'bottle'. You even linked to a 'bottle' design on your own site, albeit 'jokingly') and the remaining solid staters didn't seem to converge on anything a novice would be able to build from.

Several of the diagrams above are already close enough that I don't need to draw one up myself.  A reading of my posts shows this: I have noted that some are going in the wrong direction, while some are very nearly complete.  None have been exactly satisfactory, but there's no accounting for taste.

I'd gladly draw up a proper design -- simulation and BOM included -- if sponsored for it. :)
We recognise that you are in the design business and expect to make a living, so aren't expecting an actual design from you unless you have cold cash in your hand, but, if you can spare the time for continued participation in this thread, your comments on the only two MOSFET designs that are at a novice buildable level (see quotes in this post), or any other third party design you care to link to, that is at a similar level of buildability, would be most welcome.    I don't think I've missed any other ready to build MOSFET based linear designs - please feel free to correct me if I have.


 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #213 on: November 30, 2017, 04:28:59 PM »
Hi!

I`m working for a long time using my old tube bench anode supply (0-350V 0.2A max)
But it is so bulky and actualy crap. I sell it to crasy vintage collector today for about $200 :palm:

Now I see around a lot of cheap power MOSFETs
It looks not so difficult to make HV linear stabiliser.
But I`m not "bicycle inventor"  :) May be someone was made similar project? Any info highly wanted

Thanx  :-+

P.S.: I do not understand anything after page #6. Some holywar or rocket sience detected :-//

I think it's good to remember the level of knowledge in electronics of 001 .... In fact, the answer to his post was given to him immediately: no, it's not so easy that you believe to do a linear series regulator with Mosfet.

Why make a linear regulator? There is no technical specification other than ajustable from 0 to 350V 0.2A .... Nothing about the how much % regulation, nothing regarding the level of ripple or noise, .....

The HV linear regulator is dangerous if the pass device can fail in short circuit.
A linear regulator is a central heating, an unacceptable loss of energy.

It is obvious that the linear regulation solution is not the right one.

The right solution is a switched mode power supply.
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #214 on: November 30, 2017, 04:41:16 PM »
I think it's good to remember the level of knowledge in electronics of 001 .... In fact, the answer to his post was given to him immediately: no, it's not so easy that you believe to do a linear series regulator with Mosfet.

Why make a linear regulator? There is no technical specification other than ajustable from 0 to 350V 0.2A .... Nothing about the how much % regulation, nothing regarding the level of ripple or noise, .....

The HV linear regulator is dangerous if the pass device can fail in short circuit.
A linear regulator is a central heating, an unacceptable loss of energy.

It is obvious that the linear regulation solution is not the right one.

The right solution is a switched mode power supply.
IMHO you are 100% right if you add two little words!  At the O.P's experience level, "The right solution is to buy a switched mode power supply."
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #215 on: November 30, 2017, 04:46:30 PM »
Not exactly....For 001, the right solution was NOT TO SELL the vacuum tube HV power supply he had....
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #216 on: November 30, 2017, 04:49:05 PM »
Unfortunately he didn't post here before closing that deal . . . .
 

Offline forrestc

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Re: 0-350V 0.2A Bench Power Supply
« Reply #217 on: November 30, 2017, 05:07:06 PM »
I`m working for a long time using my old tube bench anode supply (0-350V 0.2A max)
But it is so bulky and actualy crap. I sell it to crasy vintage collector today for about $200 :palm:

I don't see anyone who has pointed you toward this direction, although maybe they've hinted at it:

There are lots and lots of 8-32V in to 45-390V boost converters available for around $5US on ebay, for example, https://www.ebay.com/itm/DC-DC-8-32V-to-45-390V-Step-up-Booster-Module-Power-Voltage-Boost-Converter-ZVS-/263052186020?_trksid=p2349526.m4383.l4275.c10

In the US (and possibly other countries) you can also get them from amazon for around $10, for example https://www.amazon.com/Qianson-Converter-±45V-390V-Adjustable-Capacitor/dp/B01IVMU2XI/ref=sr_1_1?ie=UTF8&qid=1512021716&sr=8-1&keywords=390V+boost

Most of them seem to be rated to 0.2A on the output.   If the output is too noisy there are filtering circuits you could probably add to the output.

I'm sure someone has warned you about the dangers of high voltage.   
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #218 on: November 30, 2017, 08:16:04 PM »
High quality bench magic smoke generator ?  :-DD
 

Offline Ysjoelfir

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Re: 0-350V 0.2A Bench Power Supply
« Reply #219 on: December 02, 2017, 02:18:44 AM »
I have a few of those linked boost converters. They kind of work. I use them for Nixie and tube projects with a fixed voltage and not very high needs for ripple and noise rejection.
I have also blown up some of those already. They can deliver 200ma, but they can also deliver quite some more - if shorted.
Oh, and some of them require a minimum load.

So... not realy suitable for a bench power supply.

Sadly my knowledge about the quirks and pitfalls in PSU design isn't good enough that I would say that i could build the beginner proof perfect solution...  :/
that is why I thought about making a new thread (since the discussion about valve vs FET distracts quite a bit from the actual goal of this thread) with the mission to build an "eevblog forum "high" voltage power supply" step by step, collecting ideas, working with everyone together to get a good result that is suitable for a beginner and so on. Any comments on that? Could be a quite interesting group colaboration project.
Greetings, Kai \ Ysjoelfir
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Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #220 on: December 02, 2017, 09:18:28 AM »
I think it's proven group collaboration on forums such as this don't do well and rarely finish something when the project is poorly defined, or there is no leadership on the project.
The requirements have to be complete enough and nailed down, and that was not clear here so the solutions were all over the place but it was a good discussion   :P

Forum format is not much different than the 1980's BBS, a long thread of opinions with free and paid experts, noobs and trolls mashed together to try hammer something out among the flames.
You can start a new thread with "solid-state" added to the title but OP is the one to ultimately build and finish it- as they initiated the thread.
Commanding to be given a finished design and bill-of-materials, as some do - sorry but you'll actually have to do some work. Or instead, purchase the product you need.

Many here know how to make a solution, but community member's time, money, and energy to build and test... compared to spew out some text in a post, there are limits and no real incentive to design and build for free.

I think the forum format needs to evolve to successfully build things, it hasn't really been found on the Internet the best way to crowd source something.
So many open source "let's build X" threads that die and fizzle out. This all should be another discussion, a thread somewhere else.
 
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #221 on: December 02, 2017, 10:05:33 PM »
Generally, the one who needs a bench HV power supply for his hobby and wants to make it himself is someone who makes projects and experiments for vacuum tube amplifiers.
For this purpose, 350V is not enough, it needs up to 450V  output voltage.

So, of course, the HV tube power supply option is the best option for such hobbiests.

The schemas and the realization are simple as demonstrated by the many schematics that I posted.

The only real problem is finding the necessary components, including the transformer.
It is difficult to make an "universal" project because everyone will use the components they already have.

For those who need an HV power supply for professional use, they will not waste their time making it themselves, the only option is the purchase of such a power supply

I remain convinced that the hybrid HV power solution I proposed is the best. (tube pass power stage with op. amplifiers control)

Two ranges of output voltages, manually switched, to reduce the dissipation of the pass tubes, a pass tubes stage, normally blocked by a G1 voltage of -100V and controlled by an optocoupler, voltage regulation and current limiting being made by operational circuits.

As designed, the tube pass stage has intrinsic current limiting which is the result of the characteristic curves of a pentode.
All this makes this power supply very safe

NB: I complete this post by EDIT to avoid multiple posts.

The hybrid solution has several other advantages:
1) the impossibility of overshoot at start-up because the tubes must heat up first.
2) Voltage regulation and current limiting by operational amplifiers allows high accuracy in settings and high stability.
3) this hybrid solution allows to add features like:
- adjustable soft start (switchable).
- Voltage / Current dropping characteristic with adjustable slope to simulate unstabilized power supply.
« Last Edit: December 02, 2017, 11:36:03 PM by oldway »
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #222 on: December 02, 2017, 11:46:07 PM »
Thanks Ysjoelfir, fobbydust and oldway for your comments. A linear tube supply is probably the easiest way to go for hobby use. You can still find transformers these days with a variety of secondaries, for example, Oxford Electrical Producs in the UK have some transformers with 240-0-240 and 290-0-290 volt secondaries and a good range of output transformers for tube amps. I already have a transformer and some EL34s but finding a chassis isn't so easy, I'm looking at something like RS Components 754-6017 but can't see how to mount a base plate, their data sheet is less than helpful.

 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #223 on: December 03, 2017, 12:20:41 AM »
To make the chassis is very simple: a rectangular aluminum plate 3mm thick folded in U.
The size of the aluminum plate should be chosen according to the area needed to install the main components.
Both sides of the U will be 5 to 6 cm high.

The front and rear panels are aluminum plates also 3mm thick and dimensions corresponding to the width of the frame.
The height is to be chosen according to the height of the components.
The case can be made of wood with 3mm grooves to fit the chassis + the front and rear panels.

Provide cutouts in the upper and lower part of the housing for ventilation, with aluminum grid glued.
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #224 on: December 03, 2017, 08:25:38 AM »
I agree that a linear regulator isn't the best idea, as it will dissipates 80W to 100W and the high voltage complicates things but I've seen equally high power dissipating linear regulators discussed here.

There seem to be plenty of MOSFETs available, which can dissipate 250mA at 400V.

The circuit doesn't have to be complex, just use a big, generously overrated, MOSFET. Here's a design with the TL431. On reflection, it could do with some output capacitance (100nF ceramic, in parallel with 10µF electrolytic) and a 15V zener between the gate and source would be a good idea too.

EDIT:
I've just remembered this needs to be adjustable down to 0V! The attached circuit won't work down below 30V, unless R4 and R5 are also changed and even then, the minimum voltage with the TL431 is 2.5V, unless a negative supply is used. It seems a bit of a crazy requirement though. Use a separate 0V to 30V PSU for lower voltages! As mentioned earlier in the thread, semiconductors can fail short circuit, so don't expect the output to be safe to touch, even if it's set to a non-hazardous voltage.
« Last Edit: December 03, 2017, 10:49:17 AM by Hero999 »
 

Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #225 on: December 03, 2017, 10:53:34 AM »
Due to SOA considerations for smaller readily available HV BJTs, Q1 will probably need to be a pair of transistors in cascode - split R5 to get the base bias for the upper one.  It also limits Vce to under 200V which opens up a much wider choice of parts.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #226 on: December 03, 2017, 04:35:05 PM »
There are big differences between theory and practice.
For example, in practice, V1 is not a fixed voltage: this voltage comes from a transformer + bridge rectifier + filter capacitor and it varies:
1) according to mains voltage variations (+/- 10%)
2) according to the current consumed.

"so don't expect the output to be safe to touch, even if it's set to a non-hazardous voltage."In my opinion, this is not acceptable in a bench power supply... :scared:
It should be AT LEAST as safe as an old IP17 HEATHTKIT.....If with all the modern technology whe have, you don't succeed to do better than this old stuff, then copy this old stuff...... :popcorn:
« Last Edit: December 03, 2017, 04:49:05 PM by oldway »
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #227 on: December 03, 2017, 05:25:12 PM »
Change R4 to a zener, say 5V, and Q1 to a low current HV MOSFET. :)

Hmm, both zeners (S-G and R4) could be 9V or so, which has the advantage that Vgs is limited to less accidentally-destructive levels if it should happen to become needed.

It can even be a zener from bottom of R3 to gate, serving the same purpose as Q2 but faster.

I also like to put series resistance on Q2 (so it isn't destroyed under short circuit conditions :) ).

You can then easily make the current limiting foldback, by adding a resistor from +V to Q2 base.  Q2 can be temp compensated by adding a B-E resistor with thermistor (picking just the right values).

Ah, but each one these simple little tweaks will surely be considered an excuse upon excuse not to use transistors... cue the luddites... :palm:

Tim
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Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #228 on: December 03, 2017, 05:38:01 PM »
"so don't expect the output to be safe to touch, even if it's set to a non-hazardous voltage."In my opinion, this is not acceptable in a bench power supply... :scared:
It should be AT LEAST as safe as an old IP17 HEATHTKIT.....If with all the modern technology whe have, you don't succeed to do better than this old stuff, then copy this old stuff...... :popcorn:

You're really grasping at straws.

It's over 42V.  It is, by definition, hazardous voltage.  If you aren't using insulated connectors, following safe practices (lockout-tagout for large changes, verifying zero-energy condition, or at least wearing rubber gloves if you absolutely must work on a live circuit) is a must.

FWIW, supply voltage can be even higher under mains transient conditions: swells and surges (and in North America, rare, bizarre crap like broken neutral leading to 120-240 OCV with limited current).  Surges are usually filtered alright by transformers and electrolytic capacitors.

Anyway, this all goes into the safety derating factor.  Afraid of B+ swelling to 600V? Use 800V MOSFETs, or more.

Tim
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #229 on: December 03, 2017, 05:56:02 PM »
I know you don't like vacuum tubes but HV bench power supply is generally used by vacuum tube aficionados.... :-DD  :-DD
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #230 on: December 03, 2017, 05:59:54 PM »
I know you don't like vacuum tubes but HV bench power supply is generally used by vacuum tube aficionados.... :-DD  :-DD

Don't know why you still think I don't like tubes.  I mean, that's why I made these:



6.3V and 100-300V (two ranges) 100W flyback supplies.

Here's one in use: https://www.seventransistorlabs.com/Images/DistAmp2.jpg

(These designs aren't applicable to the present thread BTW, as the design is only adjustable over a narrow range.  The 150-300V range is about as much as you can possibly do.  That's why I didn't bring them up before.)

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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #231 on: December 03, 2017, 07:55:25 PM »
In the flyback power supplies, I did not see any vacuum tubes.

As for your distributed amplifier, you simply had no other alternative, you had to use tubes.

It does not proove you like vacuum tubes.

But indeed, a SMPS would be the right solution, but not a linear pass power Mosfet, it is too dangerous.

NB: hazardous voltages : >50Vrms or >70Vdc

Telephone line is not an hazardous voltage ; nominal 48Vdc but normally up to 53-54V
« Last Edit: December 03, 2017, 08:20:18 PM by oldway »
 

Offline Ysjoelfir

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Re: 0-350V 0.2A Bench Power Supply
« Reply #232 on: December 03, 2017, 09:33:42 PM »
It is quite amusing watch you two fight about liking or hating tubes. Why does anyone HAS TO like / dislike tubes? There are many ways to skin a cat (wrote he while the cat is sleeping on his feet...), neither of which has to be considerably the better one. both have pros and cons. As far as I see it, Tim just states the fact that it is not necessary to use a tube for the application and he personally would not do it, I guess mainly because of his experience designing circuits with semiconductors which alows him to design a suitable circuit without any problem.

But: If we are looking for a simple, cheap'ish, beginner proof method to build a high'ish voltage PSU my best guess would be that this will be used for tube experiments. So there should be tubes available for the person interested in this project which is the reason I PERSONALLY would choose tubes for the pass element, as they are relatively easy to get, potentially even in the future thanks to audiophoolery (and yes, i for myself like tube amps, so don't you dare to take offense from that!) and quite easy to handle compared to most modern FETs and IGBTs which are often only designed for switching purpose with no SOA for linear applications which would make them pretty hard to substitute for a beginner not knowing how to judge if THAT particular FET in his hands is suitable or not. For the U/I regulation circuit I would, whatsoever, choose semiconductors. That should not be too hard to do with jellybean parts.

I would also make restrictions to the voltage range. Why the hell would you need 0-350V? I would much prefer something like 100-600V for tube experiments. Could simplify the circuit a bit. Right now a very crude, old regulator based on EF80 and EL34 which i build years ago is sitting on my bench, that one outputs around 150 to 450V. I found myself more often limited by the 450V than the 150. The region between 60 (standard for most dual voltage lab power supplys) and 150V is not that commonly needed, at least for the projects I work on.
« Last Edit: December 03, 2017, 09:38:21 PM by Ysjoelfir »
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Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #233 on: December 03, 2017, 09:39:55 PM »
As for your distributed amplifier, you simply had no other alternative, you had to use tubes.

Well no, if I needed an amplifier of that capacity (about 20W 30MHz), I'd have purchased an LDMOS transistor capable of about two decades more bandwidth, and costing far less (I spent days tweaking all those coils -- thus satisfying one of my goals, learning why nobody uses distributed amps anymore :-DD ).

Actually, just purchasing those sweep tubes, you'll spend more than an RF transistor.  The prices are ridiculous for the most common types.  Audiophools and TV restorers both want 'em.  I got them for free though.

Quote
It does not proove you like vacuum tubes.

Cognitive dissonance sure is a strange thing.  I can tell you exactly how I feel, and you'll still say you know better than I do...

Quote
But indeed, a SMPS would be the right solution, but not a linear pass power Mosfet, it is too dangerous.

Well...  When you figure out that switchmode devices are actually analog, it'll blow your mind. :P


Quote
NB: hazardous voltages : >50Vrms or >70Vdc

Telephone line is not an hazardous voltage ; nominal 48Vdc but normally up to 53-54V

Telephone is typically TNV type (e.g. by IEC 60950-1).  I wouldn't recommend wiring it to your body.  Phones and modems are heavily insulated and isolated for good reason!

Tim
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Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #234 on: December 03, 2017, 10:08:41 PM »
Ysjoelfirs' recent post about boost converters for small nixie and tube projects got me thinking. Why not use a small off line flyback transformer but use it backwards, should work in principle. Use a ready made transformer from Wurth if you don't want to wind one. Just found a UC2843 controller so should be good for 12V to 15V primary supply. Might get 150V at 100mA or 300V at 50mA out of it if I'm lucky. Got some gapped EFD25 cores and EFD25 bobbins so might have to wind a transformer as I'm on a budget of zero at the moment.
EDIT: Just read Ysjoelfirs' latest post, well maybe I could stretch it to 400V output but why would you want 600V ? Just curious
« Last Edit: December 03, 2017, 10:15:56 PM by chris_leyson »
 

Offline rob77

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Re: 0-350V 0.2A Bench Power Supply
« Reply #235 on: December 03, 2017, 10:15:19 PM »
In the flyback power supplies, I did not see any vacuum tubes.

you don't see tubes there because they are made for tubes. think a bit about the voltages they produce.. 6.3V AND 150-300V .... what do you think the 6.3V is for ?? 6.3V for the filament of a vacuum tube and the 150-300V is for the anode ;)
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #236 on: December 03, 2017, 11:37:05 PM »
Relevant teardown from TSP:



It's good enough for B&K. ;D

Good illustration of safe design principles, which have been mentioned in this thread, and many of which I recognize from a brief look at that main board. :)

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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #237 on: December 04, 2017, 12:21:34 AM »
Interesting .... this power supply has failed badly and dangerously, exactly as I said ....!!!!
And it is an HV power supply probably designed by several engineers ....

I can hardly imagine anyone with the knowledge of 001 making an HV power supply with this kind of technology ....  :phew:

NB: Model 9185 discontinued.  Why ? Too dangerous ? Too much problems ?  :palm:....
http://www.bkprecision.com/products/power-supplies/9185-dual-range-dc-power-supply-0-400v-0-500ma-400-600v-0-350ma.html
« Last Edit: December 04, 2017, 12:47:54 AM by oldway »
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #238 on: December 04, 2017, 02:16:03 AM »
Linear and uses six of STW15NK90Z 900V 15A MOSFETs. Still not tough enough, and costing more than a tube lol.

Notable is the adjustable slew rates V/msec and A/msec , and an LED mode with fast current limit. Released in 2014. Not sure why they are discontinued, parts do roast when fail. I see no HV PSU offerings from BK now.

https://youtube.com/watch?v=N2MGH3fhoag
 

Offline Alex Eisenhut

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Re: 0-350V 0.2A Bench Power Supply
« Reply #239 on: December 04, 2017, 02:30:49 AM »
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #240 on: December 04, 2017, 03:23:16 AM »
Good grief ! Thanks Alex well spotted, I just had to click buy it now  :) Damn I just found one cheaper  :palm: Never mind. I wonder what the controller chip is ?
 

Offline Alex Eisenhut

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Re: 0-350V 0.2A Bench Power Supply
« Reply #241 on: December 04, 2017, 03:30:08 AM »
Good grief ! Thanks Alex well spotted, I just had to click buy it now  :) Damn I just found one cheaper  :palm: Never mind. I wonder what the controller chip is ?

LOL well you ain't getting my 5$!  :-DD

I have one of the lower voltage ones, and the controller IC is an 8 pin DIP with only Chinese characters on it.  :-//

Could it be a venerable UC3843 style thing? Probably.

I wish I could take a pic for you but my camera's shutter is stuck and my phone is so old the camera takes 5 minutes to respond ...
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #242 on: December 04, 2017, 03:49:57 AM »
Quote
Could it be a venerable UC3843 style thing? Probably.
looks like it could be, hope so, because you just know I have to short circuit test it, but only after reverse engineering teardown.  :)
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #243 on: December 04, 2017, 05:27:08 AM »
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #244 on: December 04, 2017, 07:53:23 AM »
 

Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #245 on: December 04, 2017, 08:00:44 AM »
You spotted the HV rectifier heatsinking then  :) probably have to replace that. Chip is something power electronics and it's probably a UC2843 clone. Current sense resistor looks a bit underated but maybe that is a safety feature  ;)
 

Offline Alex Eisenhut

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Re: 0-350V 0.2A Bench Power Supply
« Reply #246 on: December 04, 2017, 08:19:04 AM »

It's chinese garbage


Au contraire. It's Chinese hobbyist enableage. YMMV
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #247 on: December 04, 2017, 08:56:21 AM »
Due to SOA considerations for smaller readily available HV BJTs, Q1 will probably need to be a pair of transistors in cascode - split R5 to get the base bias for the upper one.  It also limits Vce to under 200V which opens up a much wider choice of parts.
Actually, Q1 should be fine, even with small parts. The current is only around 1mA, which is within the safe operating area of the parts I could find, specified at DC.
http://www.mouser.com/ds/2/115/ZXTN08400BFF-95503.pdf
http://www.mouser.com/ds/2/115/ZTX658-91828.pdf

"so don't expect the output to be safe to touch, even if it's set to a non-hazardous voltage."In my opinion, this is not acceptable in a bench power supply... :scared:
It should be AT LEAST as safe as an old IP17 HEATHTKIT.....If with all the modern technology whe have, you don't succeed to do better than this old stuff, then copy this old stuff...... :popcorn:
The circuit I posted is no more dangerous, than the one you mentioned. In both cases, the pass device(s) can fail short circuit, causing the output to sit at the full voltage.
http://www.pmillett.com/file_downloads/IP17.pdf

Change R4 to a zener, say 5V, and Q1 to a low current HV MOSFET. :)

Hmm, both zeners (S-G and R4) could be 9V or so, which has the advantage that Vgs is limited to less accidentally-destructive levels if it should happen to become needed.

It can even be a zener from bottom of R3 to gate, serving the same purpose as Q2 but faster.

I also like to put series resistance on Q2 (so it isn't destroyed under short circuit conditions :) ).

You can then easily make the current limiting foldback, by adding a resistor from +V to Q2 base.  Q2 can be temp compensated by adding a B-E resistor with thermistor (picking just the right values).

Ah, but each one these simple little tweaks will surely be considered an excuse upon excuse not to use transistors... cue the luddites... :palm:

Tim
All good suggestions.

Actually, the first thing I'd do, is use a centre tapped transformer, to give 200V and 400V supplies use another TL431 as a comparator to switch between them, depending on the output voltage  Here's a quick sketch. I haven't done an in depth simulation, hence why I haven't attached the .asc file. It probably needs some modifications to be a practical solution.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #248 on: December 04, 2017, 06:49:39 PM »
Quote
The circuit I posted is no more dangerous, than the one you mentioned. In both cases, the pass device(s) can fail short circuit, causing the output to sit at the full voltage.
http://www.pmillett.com/file_downloads/IP17.pdf
Not at all, it's a problem of probability: the probability of a tube to fail in short circuit is practically nil.  :box:
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #249 on: December 04, 2017, 07:49:06 PM »
Actually, the first thing I'd do, is use a centre tapped transformer, to give 200V and 400V supplies use another TL431 as a comparator to switch between them, depending on the output voltage  Here's a quick sketch. I haven't done an in depth simulation, hence why I haven't attached the .asc file. It probably needs some modifications to be a practical solution.

Pretty reasonable. :)

Tweaks like threshold current (TL431 is only accurate above 1mA) come down to merely pushing around resistors.

Or use TLV431, since it's cascoded in both instances and the lower voltage limit is not a hindrance.  Saving a couple mA helps a lot at this voltage. :)

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Offline james_s

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Re: 0-350V 0.2A Bench Power Supply
« Reply #250 on: December 05, 2017, 10:49:32 AM »
If you're worried about the pass device failing, install a meter on the panel connected across the output so you can monitor it. Any HV power supply should be considered live and dangerous regardless what the output is set at. It's like a firearm, always treat any gun as if it is loaded even if you know that it's not. There are other ways for the output to go to maximum uncommanded besides fail shorted of the pass element. A bad pot to set the voltage, a resistor going open, bad connection, someone bumping the knob, foreign object causing a short, this stuff happens.
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #251 on: December 05, 2017, 07:55:35 PM »
Quote
The circuit I posted is no more dangerous, than the one you mentioned. In both cases, the pass device(s) can fail short circuit, causing the output to sit at the full voltage.
http://www.pmillett.com/file_downloads/IP17.pdf
Not at all, it's a problem of probability: the probability of a tube to fail in short circuit is practically nil.  :box:
A tiny ingress of air could cause the valve to arc over internally and the probability of it happening is double because there are two in parallel.

Actually, the first thing I'd do, is use a centre tapped transformer, to give 200V and 400V supplies use another TL431 as a comparator to switch between them, depending on the output voltage  Here's a quick sketch. I haven't done an in depth simulation, hence why I haven't attached the .asc file. It probably needs some modifications to be a practical solution.

Pretty reasonable. :)

Tweaks like threshold current (TL431 is only accurate above 1mA) come down to merely pushing around resistors.

Or use TLV431, since it's cascoded in both instances and the lower voltage limit is not a hindrance.  Saving a couple mA helps a lot at this voltage. :)

Tim
I agree, the TLV431 is much more suitable!

If you're worried about the pass device failing, install a meter on the panel connected across the output so you can monitor it. Any HV power supply should be considered live and dangerous regardless what the output is set at. It's like a firearm, always treat any gun as if it is loaded even if you know that it's not. There are other ways for the output to go to maximum uncommanded besides fail shorted of the pass element. A bad pot to set the voltage, a resistor going open, bad connection, someone bumping the knob, foreign object causing a short, this stuff happens.
Exactly.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #252 on: December 05, 2017, 08:17:52 PM »
Quote
A tiny ingress of air could cause the valve to arc over internally and the probability of it happening is double because there are two in parallel.
Another wrong answer....!!!! You said you don't know nothing about vacuum tubes and you proove it... Tubes have a getter to eliminate tiny ingress of air....Breakdown voltage in air is 3KV/mm.....distances between anode and cathode (and their connections) is far more than a mm !

Tubes like P(E)L500, PL504, PL509, PL519 works normally with 6KV peak voltage without any damage....
807 tubes can withstand several KV's.....
EL34 is used in public address audio amplifiers with 700V anode voltage in push pull schematic, that means it withstand an anode / cathode voltage of at least 1400V.....No match at all with semi-conductors !

About safety, primary protection is to prevent dangerous events, not only signalizing it.

Signalizing a danger is only a secundary safety, not the principal one.

Further more, for the same output current and same max output voltage, you must use more Mosfets in parallel than tubes, the risks are also greater for this reason....
« Last Edit: December 05, 2017, 08:36:36 PM by oldway »
 
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Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #253 on: December 05, 2017, 08:36:31 PM »
It used to be that vacuum tubes such as the humble EL509 held one final advantage over semiconductors: performance at high voltages.

Parts like this approach it:
https://media.digikey.com/pdf/Data%20Sheets/IXYS%20PDFs/IXTx02N250(S).pdf
2500V 200mA, 450 ohms.  An EL509 has closer to 50 ohms on-resistance, and around 7kV peak plate voltage handling.

But since then, parts like this have been introduced:
http://ixapps.ixys.com/DataSheet/DS100458B(IXTL2N450).pdf
at a price competitive with a lone EL509 even, let alone including heater and screen supply.

For still-more-specialty applications, there are SiC MOSFETs up to 10kV (though not generally available anywhere, AFAIK), which are significantly better than hard modulator tubes.

Hmm, they're probably not generally available because pulse generators are "munitions".  I suppose because of radar and detonator applications?  Who knows.

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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #254 on: December 05, 2017, 08:43:32 PM »
Using a pentode with (relatively !) low voltage G2 is Intrinsically safe because it limits the short circuit current without need of additional components.

If you want to use semiconductors, you must go to the SMPS technology, not the linear technology with pass Mosfet .....
« Last Edit: December 05, 2017, 09:01:58 PM by oldway »
 

Offline james_s

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Re: 0-350V 0.2A Bench Power Supply
« Reply #255 on: December 06, 2017, 07:27:32 AM »
The getter will absorb tiny quantities of residual gas but it will quickly be overwhelmed by any sort of leak. I've certainly seen gassy tubes that arced internally, happened to one of the output tubes in my friend's guitar amp several years ago. I've also seen it in a CRT once, a microscopic leak somewhere allowed enough air in that the neck glowed bright purple when it was energized.

I would agree that a tube is less likely to fail shorted than a semiconductor but IMHO this is a moot point.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #256 on: December 06, 2017, 07:57:56 AM »
It is extremely rare.....

it's a problem of probability: the probability of a tube to fail in short circuit or arcing is practically nil.

Guitars amplifiers are often abused, transported in trucks without any care, sometimes they even drops them, so it may happen that the glue of the octal socket comes off and there are breaks in the glass at the socket connections which can cause an air inlet.

This can not happen with a bench power supply that is not subject to this kind of mechanical stress.
« Last Edit: December 06, 2017, 08:02:00 AM by oldway »
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #257 on: December 06, 2017, 10:53:15 AM »
it's a problem of probability: <snip>

Guitars amplifiers are often ... <snip>

"It's not a problem. Except when it is."

Nice conditional probability there.  I give it Bayes out of 10.  :clap:

Tim
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Offline Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #258 on: December 06, 2017, 01:59:39 PM »
Anyone who thinks the probability of failure of two tubes from the same batch, run in parallel, in adjacent sockets isn't strongly correlated is a fool.

Gassy CRTs are *RARE*.   It requires enough of a leak to let sufficient air in for the tube to support ionised conduction, without there being enough oxygen present for the filament to fail.  In a lifetime in the service trade you might see a few cases, but mostly a leaky tube will be very obvious - flat milky white getter and a blown filament.

If you want to 'gold plate' what was originally intended to be a cheap but usable HV bench supply,  use a dual gang pot and add a crowbar circuit for output overvoltage >10%, and if it uses tubes, loss of negative grid bias rail, or excessive G2 current.

If multiple tubes are used, to prevent overloading, their filaments should be in series so they all cut out if one fails.
 
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #259 on: December 06, 2017, 04:41:33 PM »
Tube vs Solid-state reliability, each has their own aging and failure mechanisms.
Should we go biplane or helicopter?  ;D

If I needed something built in an hour, this is a junkbox tube design.
If I'm designing this professionally, it's SS with much greater effort, cost and risk.

There is no guidance on how much to derate low-cost switching MOSFET's SOA.
Using a bunch in linear mode, subject to thermal instability due to hot spots, with no DC SOA spec. is like walking into the casino.
Getting around this SS issue is expensive - or use tubes.

We need a "burning HV power supply" contest, with a scope giveaway and DMM's for the runners up.
If community members could place wagers on which design will win, my kind of casino  :popcorn:
 
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #260 on: December 06, 2017, 10:37:09 PM »
I found a bunch of Ls50 tubes. Looks good, isn't it?
How to add transistor driver to it?

I heared what some kepco in 70' use some sort of transistor driver and current limiter with two stage pass tubes (one is for preregulator and the second is for stabiliser)
Nothing against the LS50 tube, it is a 40W transmitting pentode, it can be used as pass device without any problem. Heating voltage is 12.6V.
But the socket seems more expensive than the tube itself.

No way to find schematics or service manual of Kepco products  as they are copyrighted.
But you can order by Kepco every old service manual you need for a fee of....$400 !!!!!!
http://www.kepcopower.com/support/svcman.htm

For hybrid solution, see schematic I have posted over pass tube controlled by optpcoupler.
« Last Edit: December 06, 2017, 10:42:21 PM by oldway »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #261 on: December 07, 2017, 10:39:15 PM »
Don't you think it would be fair to send a mail to Kepco asking them if they permit you to publish this schematic or not ?  :palm:

Quote
Look easy to build ?
  :-/O You don't even have the voltages of the secundaries of transformers...

It is a 2000V 100mA power supply with floating output.
It is quite different of Heathkit IP17 power supply because it is a much higher voltage and it is a floating output ....IP17 has negative polarity grounded.

The first tubes (you name preregulator) are limiting max Vak voltage (and also max. Pa)  of the regulator tubes.
When Vak of the regulator tubes became higher than a fixed value, preregulator start blocking and limit this voltage.
Control circuit is referenced with + output polarity, for this reason there is no need of high voltage drivers transistors.

As everyone of the polarities may be grounded , the control circuit can be at high voltage compare to ground.

For sure, there are a lot of precautions of safety.....(potentiometers and switches mounted on isolating board, plastic axles, ...)
« Last Edit: December 07, 2017, 10:43:01 PM by oldway »
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #262 on: December 11, 2017, 10:35:24 AM »
Quote
A tiny ingress of air could cause the valve to arc over internally and the probability of it happening is double because there are two in parallel.
Another wrong answer....!!!! You said you don't know nothing about vacuum tubes and you proove it... Tubes have a getter to eliminate tiny ingress of air....Breakdown voltage in air is 3KV/mm.....distances between anode and cathode (and their connections) is far more than a mm !
I'm no expert on valves but I do know more than nothing. I know about Paschen's law, which means that the breakdown voltage will at first reduce, if any air gets in. The getter is a highly reactive material and will only work up to a certain point, until it's depleted. If there's a leak, it won't go on absorbing air forever. Air will get in, first causing the breakdown voltage to reduce, causing arcing over. It's true that the breakdown voltage will go up again, but it depends on how quick the leak is.

Irrespective of the above arguments: any components which are safety critical need to be appropriately approved and rated. Semiconductors are generally not to be relied upon to protect against electric shock and I doubt thermionic valves are either: do you have any links to safety standards which suggest contrary?
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #263 on: December 11, 2017, 04:35:26 PM »
I agree with you that a linear HV power supply with a pass device is not safe and that it is not the right solution.
A modern solution would be a switch mode power supply who is less likely to fail with uncontrolled HV output voltage.

But this is too sphisticated for hobby use.

A lot of HV power supplies have been made with a very simple circuit using a pentode as pass element, and, so far I know, no accident did occured.

Nobody ever said that it was impossible to have an arc in a tube, but that it is an extremely rare event.
For an arc to be possible, there must be a weak air inlet such that the internal pressure remains low.
Generally, oxygen causes the burning of the filament.

As already said, the risk is much less than with a MOSFET.

Those who knew the time of the tubes, like me, know that a gassy tube is extremely rare .... It would be necessary to split the glass or that a solder glass / metal of the connections should fail .... There is no reason for this to happen unless there are exaggerated mechanical stresses on these connections.
It is only in output tubes of guitar amplifiers that I saw this kind of thing happening.
These amplifiers are often abused.
On tube tV set's, I have never seen that happen. (and I repaired hundreds of them in the years 60's and 70's)

 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #264 on: December 12, 2017, 05:32:44 AM »
Those who knew the time of the tubes, like me, know that a gassy tube is extremely rare ....
...
It is only in output tubes of guitar amplifiers that I saw this kind of thing happening.
These amplifiers are often abused.

Which are, gosh, 90% of tube amps today?

Hardly seems "extremely rare"!

Speaking as a professional engineer, I would not hesitate to use a pass regulator design for any application.  If high reliability were required, I would use redundant design methods.

I would use a switching design where efficiency is more important, that's all.

If high safety were required, that would be solved through a combination of protective circuits (e.g. crowbar) and mechanical interlocks.  You're a fool to think there's anything remotely safe, in practice or in legal terms, about a >70V power supply.  Such systems also go well beyond the scope of this thread.

But, as professional advice goes, it's only worth what you paid for it, right?...

Tim
Seven Transistor Labs, LLC
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #265 on: December 12, 2017, 08:03:50 AM »
Air in a tube gives lower and lower transconductance, then the filament fails. Never seen arcing from it. Air ingress only due to physical abuse or many decades of age.

One of six pass-MOSFETS shorted in that B&K 9185. Did nobody notice a commercial product's catastrophic failure?
Something got a full-blast 650VDC surprise instead of whatever it was set to  :o should I call my lawyer?

SS vs tube for safety, this seems like just a pissing match.
 
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #266 on: December 12, 2017, 10:55:21 AM »
Air in a tube gives lower and lower transconductance, then the filament fails. Never seen arcing from it. Air ingress only due to physical abuse or many decades of age.

One of six pass-MOSFETS shorted in that B&K 9185. Did nobody notice a commercial product's catastrophic failure?
Something got a full-blast 650VDC surprise instead of whatever it was set to  :o should I call my lawyer?

SS vs tube for safety, this seems like just a pissing match.
How to transfer years of experience and knowledge about tubes to beginners in the field, who, at most, have made a single project with tubes in their life?

That's the problem with this frorum, there are lots of people writing about things they do not know.

We have confidence in the tubes thanks to our experience of many years in projects, repairs and tests of tubes gears.
Only those who are over 65/70 years old have such an experience ....
 

Offline james_s

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Re: 0-350V 0.2A Bench Power Supply
« Reply #267 on: December 12, 2017, 11:14:54 AM »
Publish the info? Answer questions to those who ask? We all accumulate information throughout our lives and it's depressing to think how much knowledge is lost as older segments of the population die off. At the same time it's not realistic to expect all of it to remain useful or of value to younger folks. I expect that by the time I'm 60-70 very few people will care about my knowledge and experience repairing CRT displays, setting up the convergence and purity on a color tube, knowing how the scan circuits video amplifiers work, but times change and like other vacuum tubes CRTs will have largely disappeared from daily life. Again like other vacuum tubes I'm sure there will remain loyal pockets of people who like them for niche applications but otherwise society will have moved on and found new ways to do things regardless of what merits some of the old tech may still have. That's just life, things change, but people will manage.

I still don't understand why this debate is even still going. When dealing with a 350V power supply design any number of things can go wrong besides catastrophic failure of the pass element, regardless of what topology is used it should incorporate features to prevent a failure of any sort from causing injury. Even with every possible failsafe one should never put themselves in a situation where they will be harmed if the output unexpectedly goes to full voltage. When you work on the wiring in your house you wouldn't fret about the possibility of a light switch failing and causing a shock, you'd (hopefully) shut off and tag the circuit breaker in the panel and still avoid grabbing onto exposed conductors.
 

Offline Alex Eisenhut

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Re: 0-350V 0.2A Bench Power Supply
« Reply #268 on: December 12, 2017, 12:14:46 PM »


How to transfer years of experience and knowledge about tubes to beginners in the field, who, at most, have made a single project with tubes in their life?

Here's a good start:
http://www.john-a-harper.com/tubes201/
« Last Edit: December 12, 2017, 12:25:04 PM by Alex Eisenhut »
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #269 on: December 12, 2017, 12:39:00 PM »
You would put the pro's and con's of the part/architecture, weighing things like cost, size, reliability, complexity etc. into  a 'decision matrix' to choose.
The forum (format) can't accomplish this- the requirements are poorly defined and the endless debate continues...

We're up against the stigma of an old technology where people don't know why it's "old"- it is to be scorned. Although it's solid and proven to work.
We're up against the marketing hype of new technology where people don't know the datasheets are full of deceptive bullshit. It's guess work as far as reliability. SPICE SOA models are unfortunately not there yet.


 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #270 on: December 13, 2017, 10:05:22 PM »
I continue to look for high voltage power supplies and technical solutions adopted on commercial gears.

I found Kikusui HV power supplies 350V 3.5A and 600V 2A.
http://www.kikusui.co.jp/en/product/detail.php?IdFamily=0003

How do they work?
https://www.kikusui.co.jp/common/product/pdf/pan-a.pdf
http://www.kikusui.co.jp/kiku_manuals/P/PAN_A_VE3_E6.pdf

First, they are solid state linear power supplies that use a phase-controlled pre-regulator, which reduces the risks since in normal operation, the voltage difference on the pass transistors is low.
In case of short circuit of the pass elements, overvoltage will be reduced to only a tenth of volts over the adjusted output voltage.
The phase control is made by MOSFET's, not by SCR's.

On the other hand, Kikusui does not use Mosfets as pass devices, but bipolar transistors.
In addition, there are several safety features including adjustable crowbar protection.

« Last Edit: December 13, 2017, 10:07:20 PM by oldway »
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #271 on: December 14, 2017, 05:43:12 AM »
The Kikusui HV power supplies look interesting, 50usec response time.
I did chuckle at their weight though: 350V 3.5A  (2,100VA in) 79lbs/36kg. I'd need a forklift  :P
That, and using a universal manual for the 16V-600V products... "Connect an electrolytic capacitor (C) with a capacity of a few thousands of uF to a few tens of thousands of uF across the load terminals."  :popcorn:
Any idea on cost?

I' ve used Xantrex HV power supplies, now under the Ametek/Sorensen brand. Inside they have SMPS and use ZVS, modern designs.

The XG 850W 600V 1.4A is USD $1,600, about $2/watt.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #272 on: December 14, 2017, 07:38:28 AM »
My interest in talking about kikusui power supplies was to see which technology was used in a linear solid state commercial HV power supply.

This does not change my point of view that, for a hobby application and home-made power supply, the vacuum tube solution is the simplest and safest.

However, I note that those who advocated to use a solid state solution neglected 2 important points: the use of a pre-regulator to avoid semiconductors to operate  under a high voltage difference, and secondly, the choice of bipolar transistors instead of Mosfets.

As for the need for additional protections, like the adjustable crowbar, it was actually mentioned.
 

Offline eliocor

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Re: 0-350V 0.2A Bench Power Supply
« Reply #273 on: December 14, 2017, 09:13:23 AM »
I'm asking for some schematics suggestions.
My minimum requirement are the following:
- 0-350 Vdc (higher can be better)
- 0-30 mA (my MAXIMUM needs)
- regulation: CV/CC
- low ripple
- good stability

At this date for my experiments I'm using a Tennelec TC-952 power supply (0-3000Vdc, 10mA, 2mV ripple typ.) but it has no current regulation.
I also own a Fluke 415B (0-3000Vdc, 30mA, even more precise and with lower ripple) but it also has no current regulation; BTW this one uses a valve/tube, just to satisfy people who love them!  ;)

What I'm asking is for some good suggestions on a schematics which can satisfy my requirements: output voltage can even be higher than 350V but current limits will never be higher than 30mA.
Otherwise any hint on a not too expensive instrument (used or new) is welcome.

P.S.: as you can see, from the output voltage of my power supplies, I already have some experience working with high voltage...  ;D
 

Offline Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #274 on: December 14, 2017, 08:08:42 PM »
My interest in talking about kikusui power supplies was to see which technology was used in a linear solid state commercial HV power supply.

This does not change my point of view that, for a hobby application and home-made power supply, the vacuum tube solution is the simplest and safest.
I'd choose a switched mode power supply myself. It's not that difficult nowadays, even for hobbyists, with the vast range of controllers and high performance MOSFETs available.

Quote
However, I note that those who advocated to use a solid state solution neglected 2 important points: the use of a pre-regulator to avoid semiconductors to operate  under a high voltage difference, and secondly, the choice of bipolar transistors instead of Mosfets.
I posted a design, using a tap changer to halve the voltage across the pass device. It might not be as good as a proper pre-regulator, but it's a lot simpler.
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1365710/#msg1365710
And regarding BJTs, rather than MOSFETs: I think BJTs were ruled out awhile ago, because at high collector-emitter voltages, the safe operating area, limits the maximum current to too lower level. Plenty of MOSFETs are available, which can dissipate >400V, at >200mA.
« Last Edit: December 14, 2017, 10:35:11 PM by Hero999 »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #275 on: December 14, 2017, 09:22:28 PM »
My interest in talking about kikusui power supplies was to see which technology was used in a linear solid state commercial HV power supply.

This does not change my point of view that, for a hobby application and home-made power supply, the vacuum tube solution is the simplest and safest.
I'd choose a switched mode power supply myself. It's not that difficult nowadays, even for hobbyists, with the vast range of controllers and high performance MOSFETs available.
...
Yes I fully agree with this  :-+, but did you looked at the crap schematic that 001 has posted.

Do you really believe he is able to developp and to build a switch mode power supply ?  :-DD

In first instance, we should try to answer to him with an answer he is able to use....

And who will developp this switch mode power supply for him ?
Have you time and money to do it ?
You will not only have to post the schematic but also to give him all the informations about how to build the ferrite transformer and inductors....
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #276 on: December 14, 2017, 11:17:08 PM »
I'm asking for some schematics suggestions.
My minimum requirement are the following:
- 0-350 Vdc (higher can be better)
- 0-30 mA (my MAXIMUM needs)
- regulation: CV/CC
- low ripple
- good stability

At this date for my experiments I'm using a Tennelec TC-952 power supply (0-3000Vdc, 10mA, 2mV ripple typ.) but it has no current regulation.
I also own a Fluke 415B (0-3000Vdc, 30mA, even more precise and with lower ripple) but it also has no current regulation; BTW this one uses a valve/tube, just to satisfy people who love them!  ;)

What I'm asking is for some good suggestions on a schematics which can satisfy my requirements: output voltage can even be higher than 350V but current limits will never be higher than 30mA.
Otherwise any hint on a not too expensive instrument (used or new) is welcome.

P.S.: as you can see, from the output voltage of my power supplies, I already have some experience working with high voltage...  ;D

Hybrid linear power supply 0 - 450V 30 mA Max.

Schematic of isolated power stage.
Solid state control CC/CV through opto coupler

NB: pass tube: 40W power pentode LS50 / GU50 with 12.6V heating voltage + ceramic socket
https://tubes-store.com/product_info.php?products_id=183

ERRATA : T2 BF421 or BF423, not BC327
« Last Edit: December 14, 2017, 11:48:04 PM by oldway »
 

Offline eliocor

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Re: 0-350V 0.2A Bench Power Supply
« Reply #277 on: December 14, 2017, 11:33:45 PM »
Thanks for the hint:
may I ask the origin of the schematics?
Was it tested before? I ask this because is clearly incomplete.
Nothing to worry about: I can simulate it to see if it really works
Any suggestion for the pentode to be used? Regarding Valves/Tubes I'm really a noob!

P.S.: I only now note your references to LS50/GU50 and the filament voltage!!! Sorry!!!!
« Last Edit: December 14, 2017, 11:47:22 PM by eliocor »
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #278 on: December 14, 2017, 11:57:41 PM »
Origin: my project.
Not tested.
I don't need a HV power supply, I'm retired but I'm repairing a lot of vintage audio stuffs (tubes and transistors), I'm very busy and I have no time to developp such a project, nor time and money to build a prototype.
If I should make one, it would be a 0-450V at least 300 mA in two ranges.

Solid state control CC/CV is quite easy to design for who's have knowledge and experience in op amps.
It can be very stable as every solid state power supply.
Also low ripple.
 


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