LM324 Power Supply with variable voltage and current

[Kleinstein]

The 2 nd plateau in the current is just the current needed to charge the output caps. This is kind of normal and not a problem.

The slightly odd looking triangle like ringing can be reduced with an RC series combination of some 5 K and 5 nF (or similar values)  in parallel to R12. It than may be possible to reduce C1 a little too. This speeds up the voltage regulation, by going from a PI regulator to the PID type loop.

The ringing could also happen during normal load transients (larger resistor in series to switch). So just slowing down the current regulation (with C5) is not a full solution to the overshoot problem.

The capacitor C4 is a kind of compromise, it may be needed to avoid trouble for the voltage regulation, but it is more of a problem to the current regulation. Here some of the less normal properties of the OP come into play - the models may not be accurate here.

Having the CV loop as an inner loop for the CC regulation is not the main problem here. The trouble is more with using the poorly defined upper output limit of the lm324 as the reference level and  coupling the CC control part to the reference before the pot.

[iMo]

For example a mod of the schematics (not tested in HW):

[mike_mike]

Can I use the power supply as it is in the last simulation made by me ?
Will be there any problems ?

I am asking this because I like this design, because it does not have a lot of components and it is a simple design...

[iMo]

Look at my MOD above. It is the same number of parts, added compensation into the output divider.
With C8=6.2nF there is almost no overshoot.

[mike_mike]

I think that I will not make any other modifications.
I it too much for me to modify each project...
I am sorry.
I should have been aware that it is not a good design, from the beginning of the project.

I just wanted to ask if the power supply will work as it is in my last simulation. I do not expect state of the art performance... just to power some loads, max 3A.

[Kleinstein]

That last suggestion from IMO is more like the standard version. It avoids relying on the saturation performance of the LM324. The added R4 and C8 could also be used with the other circuit. It gets even better with R4 = 5 K.

[mike_mike]

@imo @Kleinstein
I finally managed to make the modifications. But it does not work. The output voltage is always 33V.

Please recommend me a schematic that is working. It is not necessary to be designed by you, I need only to be tested and to work.

[iMo]

Here is the LTspice sim source and a picture showing it works.
Look at it carefully before you start to solder, do simulations, and ask when any questions.
Updated.

[mike_mike]

Still nothing.
I checked about 4-5 times.
I also have the led circuit connected...

[xavier60]

In a real circuit, Q1 might not be able to turn off enough.

[mike_mike]

Yes, Q1 is saturated, it has BE voltage =0.603V

[floobydust]

No- use a transistor instead because it can completely turn off Q1 in OP's schematic. As a bonus, you can put an LED in series with base drive to indicate CC mode. Oh, and flip CC op-amp +, - inputs because things are inverted now.
I did get CV mode to work well but have to work on CC mode more to post anything usable.

[xavier60]

A BE of 0.6V doesn't mean that a transistor is saturated.  Because there is an Emitter resistor, the Base voltage sets the Collector current  which needs to go below about 0.12mA for  Q2 to be off.
The Base of Q1 needs to be able to be pulled below 1V. The CV opamp's output needs to be able to pull below 0.4V.
I don't use a simulator.
The actual reason for the output staying high needs to be found first. What voltage is being reported for the CV opamp's output?

[mike_mike]

The output of the CV op amp is always 0.86V, with respect to the ground. At any voltage pot position.

I have found this power supply, on a Russian forum: https://vrtp.ru/index.php?showtopic=16392
It is a better design that the current one in this topic ?


I have also found that on the Russian forum are multiple versions of the power supply. Does anybody knows that forum and could tell us which is the latest version of the power supply ?

[xavier60]

The output of the CV op amp is always 0.86V, with respect to the ground. At any voltage pot position.

I have found this power supply, on a Russian forum: https://vrtp.ru/index.php?showtopic=16392
It is a better design that the current one in this topic ?


I have also found that on the Russian forum are multiple versions of the power supply. Does anybody knows that forum and could tell us which is the latest version of the power supply ?

0.86V minimum at the CV op-amp's output is realistic and is not low enough to completely turn off Q1. This will cause the regulator to always output some current and the output to stay high voltage with low loads.
These recent modifications suggested by imo are making the design  become very similar to a bench supply design I  recently completed.
The problem with Q1 is solved by adding another resistor from Emitter to control  rail which is 8V in my design.
Q1's function is as a level shifter. Some designs that use a level shifter can be trouble because of the unnecessary gain it can add if not done properly.
The other circuit you linked has a level shifter.

My current design can be simplified. The TL431 reference and preload circuit are not essential. https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873

[floobydust]

I have found this power supply, on a Russian forum: https://vrtp.ru/index.php?showtopic=16392

It looks like an older 2016 thread that had problems, people complaining it oscillates or drifts or CC is sloppy etc. They really like PNP Darlington TIP146. I find the circuit weird and nothing I would build. The server was maxxed out but I got these pics for other people's opinions.

If you want a schematic that guaranteed works, then just copy a commercial bench PSU circuit.

I've never seen well-polished 0-30V 0-3A kind of PSU designs on the Internet, so I just quietly design  my own. A community approach seems to not work, in chinese or Polish forums someone ends up getting something working and making a PCB.

[mike_mike]

If you want a schematic that guaranteed works, then just copy a commercial bench PSU circuit.

Can you show me such a schematic ?
Are there on the forum schematics for commercial bench PSU, that 100% works correctly and which uses components that can be found easily ?

I found this power supply: http://www.electronics-lab.com/project/0-30v-laboratory-power-supply/
Does it have a better version ?

[Kleinstein]

The last link shows essentially the circuit from the cheap Chinese kits, with a different Layout. At least the Layout looks a little better. However with a TL081 one will not get reliably get 30 V and the 1 transistor is a somewhat on the weak side. So better only 2 A.

[floobydust]

I found the original 0-30V 2mA-2A PSU circuit, Practical Electronics Nov. 1978.
We haven't beat a 40+ year old circuit and I'm sure no one would copy it    Now I have to apologize to everyone in china for lambasting them on this little kit...

Project on pg. 41 but big 12MB pdf:   https://americanradiohistory.com/Archive-Practical-Electronics/70s/Practical-Electronics-1978-10.pdf

[mike_mike]

@floobydust
Can I build the schematic attached ?
It is a good schematic to build ?

[xavier60]

Progress was being made in a useful direction.

[mike_mike]

I read the article, and I have a few questions:
1. Why all resistors are 1/2W ? Why can't be used 1/4W resistors ?
2. I can't see where are specified the properties for the 2.2k pot ?

3. What is the meaning of 3 good quality 10k log ?

[iMo]

My MOD schematics works fine in simulation with the PSU_Shorter Vout=1V-30.6V based on CV pot's position.
Based on the activity the voltages at opamp's outputs are from 0.68V to 10.5V, and the Q1's base voltage is from 0.8 to 1.6V, the Q1's collector current is 21uA-300uA.

If I were you, I would start with LTspice. You have done a lot of great work by building various types of PSUs, the next step could be the refining of the "design phase" - here the LTspice is the right tool to use.

[mike_mike]

My MOD schematics works fine in simulation with the PSU_Shorter Vout=1V-30.6V based on CV pot's position.

Do you suspect that there is a mistake in the practical built ?

[xavier60]

The possible solution in Reply #189 didn't work?