Author Topic: 0-350V 0.2A Bench Power Supply  (Read 53283 times)

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Online Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #225 on: December 02, 2017, 11:53:34 pm »
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, 05:35:05 am »
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, 05:49:05 am by oldway »
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #227 on: December 03, 2017, 06:25:12 am »
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, 06:38:01 am »
"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, 06:56:02 am »
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, 06:59:54 am »
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.)

Tim
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Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #231 on: December 03, 2017, 08:55:25 am »
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, 09:20:18 am by oldway »
 

Offline Ysjoelfir

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Re: 0-350V 0.2A Bench Power Supply
« Reply #232 on: December 03, 2017, 10:33:42 am »
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, 10:38:21 am by Ysjoelfir »
Greetings, Kai \ Ysjoelfir
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #233 on: December 03, 2017, 10:39:55 am »
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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Online chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #234 on: December 03, 2017, 11:08:41 am »
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, 11:15:56 am by chris_leyson »
 

Offline rob77

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Re: 0-350V 0.2A Bench Power Supply
« Reply #235 on: December 03, 2017, 11:15:19 am »
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, 12:37:05 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 03, 2017, 01:21:34 pm »
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 03, 2017, 01:47:54 pm by oldway »
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #238 on: December 03, 2017, 03:16:03 pm »
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 03, 2017, 03:30:49 pm »
Hoarder of 8-bit Commodore relics and 1960s Tektronix 500-series stuff. Unconventional interior decorator.
 

Online chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #240 on: December 03, 2017, 04:23:16 pm »
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 03, 2017, 04:30:08 pm »
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 ...
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Online chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #242 on: December 03, 2017, 04:49:57 pm »
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 03, 2017, 06:27:08 pm »
 

Offline floobydust

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Re: 0-350V 0.2A Bench Power Supply
« Reply #244 on: December 03, 2017, 08:53:23 pm »
 
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Online chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #245 on: December 03, 2017, 09:00:44 pm »
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 03, 2017, 09:19:04 pm »

It's chinese garbage


Au contraire. It's Chinese hobbyist enableage. YMMV
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Offline Zero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #247 on: December 03, 2017, 09:56:21 pm »
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, 07:49:39 am »
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, 08:49:06 am »
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
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