Author Topic: 5 ~ 10 watt variable current/voltage PSU for breadboarding?  (Read 9192 times)

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Offline Rick Law

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Re: 5 ~ 10 watt variable current/voltage PSU for breadboarding?
« Reply #25 on: September 28, 2015, 08:42:45 pm »
If you had to choose between these two, which would you choose and why?:

http://www.amazon.com/gp/product/B00GZG7X9Y
http://www.amazon.com/gp/product/B013STFDTC

Julian Ilett has posted a video review warning about a bug that the first module suffers from where the current limiting does not work when the voltage and current limits are turned down to near their minimum:
...
...

This design flaw is probably common.  I have it on two different different CC/CV board I purchased.  It was not until I made my own that I understood where it may come from.

The scenario probably is when the short occurs, momentarily the main power source has a voltage sag.  The op-amp dealing with current is not having enough volt to run properly allowing the run-away current draw, this in-turn locks the op-amp in the underpower/non-performing mode thus keeping the current at run-away level.

On the one I made myself, I use a separate power source to run the control circuit.  For the purchased stuff, I have some luck reducing it by using a "reservoir capacitor" at the op-amp.  I have better luck with bigger power source (less sag thus not triggering the initial momentary run-away).

Since I have seen it on more than one kind of CC/CV board, I think one should just be mindful that with this kinds of boards, a sudden big current increase could knock the control circuitry out of action.  If you plan to use it as your PSU, testing this characteristic (using your intended power source) is important or you may be pumping 5A into your DUT giving you kind of a bad day.
« Last Edit: September 28, 2015, 08:44:45 pm by Rick Law »
 

Offline ez24

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Re: 5 ~ 10 watt variable current/voltage PSU for breadboarding?
« Reply #26 on: September 28, 2015, 09:57:16 pm »
Quote
For the purchased stuff, I have some luck reducing it by using a "reservoir capacitor" at the op-amp.

Could you explain this more?  Are you soldering components onto the buck's circuit board?

Would this work:

Julian's video shows that the buck can put out 5 amps when shorted.  What if the buck's current was set to 2 amps with a resistor and then shorted.  Would there be a problem?  Or will the current stay at 2 amps?

thanks



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Offline ez24

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Re: 5 ~ 10 watt variable current/voltage PSU for breadboarding?
« Reply #27 on: September 28, 2015, 10:03:16 pm »
Quote
For the purchased stuff, I have some luck reducing it by using a "reservoir capacitor" at the op-amp.

Could you explain this more?  Are you soldering components onto the buck's circuit board?

Would this work:

Julian's video shows that the buck can put out 5 amps when shorted.  What if the buck's current was set to 2 amps with a resistor and then shorted.  Would there be a problem?  Or will the current stay at 2 amps?

thanks



YouTube and Website Electronic Resources ------>  https://www.eevblog.com/forum/other-blog-specific/a/msg1341166/#msg1341166
 

Offline Rick Law

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Re: 5 ~ 10 watt variable current/voltage PSU for breadboarding?
« Reply #28 on: September 29, 2015, 02:10:35 am »
Quote
For the purchased stuff, I have some luck reducing it by using a "reservoir capacitor" at the op-amp.

Could you explain this more?  Are you soldering components onto the buck's circuit board?

Would this work:

Julian's video shows that the buck can put out 5 amps when shorted.  What if the buck's current was set to 2 amps with a resistor and then shorted.  Would there be a problem?  Or will the current stay at 2 amps?

thanks

Yes, I am soldering components onto the buck board.  Since you asked me to explain, let me do the explaining first so my solution description makes more sense.

The whole issue that I came across, which is exactly like the one shown, was the sudden high current draw pulled the Vin too low for the op-amp (and the rest of the control circuitry) to function, thus the run-away condition.  So, my attempted fix is to make sure that the control circuit is well juiced.

Lowering the current limit likely would not have an impact since the control circuit is not in control.  So, whatever you set doesn't matter.

My experimental fix was then to solder in from 100nF to 100uF as near the op-amp (and control circuit) as possible.  The idea is to provide enough juice for the control circuitry to run long enough to drive down the current enough before run-away occurs.  "Drive down the current enough" means the Vin sagging is no longer too low for the control circuit by the time the capacitor is drained.

That works, but not well.  However big the capacitor, there is always a path to leak it out.   When the unit is outputing 5A at near zero volt for the short, it is grabbing from everywhere since everywhere is likely > near zero volt. 

Assuming we are indeed talk about the same problem rather then two different problem but same symptom -- The best fix is of course to make sure the control circuitry has an independent power source.  I found "fatter source" to be more reliable over a "reservoir capacitor" at the op-amp.  After switching from the 9V1A to a 12V1A then a 15V3A source, I recall very rare occasions when I hit the problem with 12V1A source. I don't recall it failing since I up-ed it to 15V3A from either of my two CC/CV boards.  It is a lot easier for the 9V to sag below what is needed for the control circuitry than to have 15V sag to below what is needed.

I now switched to a digitally controlled B3603 as my main power source with a 15V3A Vin.  I misplaced the 9V1A long ago, so I am not sure if this one too can be afflicted with that sagging - the same elements are there so the same issue may affect it.

By the way, if this board is supplied by another bench PSU (with CC) like when being tested in the lab, that "power drop below necessary" situation for sure will happen.  When supply PSU hits its CC limit, the Vout from the bench supply PSU will fall like a rock and this board will not have adequate volts to run the control circuit.

- if you can attach a detail photo of each side of the board, I may be able to do some suggestions.
- also, if you want to see how a CC circuit may work, take a look at this link where I added CC to a similar CV only board to make it a CC/CV board.
https://www.eevblog.com/forum/beginners/adding-cc-to-a-cv-buck-to-make-it-cccv/
« Last Edit: September 29, 2015, 02:20:17 am by Rick Law »
 

Offline nowlan

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Re: 5 ~ 10 watt variable current/voltage PSU for breadboarding?
« Reply #29 on: September 29, 2015, 03:07:28 am »
Skullcom Hobbies did some mods for the DROK DC converter on youtube.
 

Offline ez24

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Re: 5 ~ 10 watt variable current/voltage PSU for breadboarding?
« Reply #30 on: September 29, 2015, 04:06:28 am »
Skullcom Hobbies did some mods for the DROK DC converter on youtube.


Interesting - thanks
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