Author Topic: 0-350V 0.2A Bench Power Supply  (Read 9362 times)

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Online 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.
 

Online 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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Online 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. :)

Tim
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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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Online 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.
 

Online 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
 

Online 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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Online 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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Online 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 ?
 


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