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LM324 Power Supply with variable voltage and current

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mike_mike:
Hello,
I have a few questions about the attached schematic of power supply.
1. Is the schematic functional ? If not, what are the mistakes in the schematic ?
2. Is the layout correct ? If not, how it can be improved ? The DRC does not return any error, but I am wondering about ground connection and other stuff like this...
3. Is the minimum output current really 0A ?
4. I will use R3=680R, R4=2K2, R7=12K, R11=120K, because I did not found the specified values at the local electronics shop. On the VT4 footprint I will solder the wires that go to the power transistors that will be on another PCB.
Here you can find the schematic image:
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Thank you in advance.

Kleinstein:
The regulation circuit does not look good. Chances are it could oscillate and react rather slow.  The transistors VT2+VT3 add quite some nonlinear gain to the loop. With VT3 the output stage is more like current controlling and thus usually needs an accurate frequency compensation to get acceptable performance.

The way the current limit is done is also not good - the LM324 output level is not well defined when in saturation - so voltage regulation it would not be really temperature stable. Worst case, with the output voltage set to zero and a positive offset of OP1A the current limitation may not work as the voltage would only go down to the offset value.

So before thinking about the layout, one should get a working circuit. A simulation could be a good idea to get a check, as a lab supply is not such a simple circuit. Stability can be quite tricky with possible highly capacitive loads.

mike_mike:
Thank you for the reply.
Could you please recommend me a schematic wich is stable and have variable current (0-5A) and voltage (0-25 or 30V) and which can accept input voltage up to 45Vdc ?
I know that I can find on the internet lots of schematic, but I simply do not know wich of them are good...

Kleinstein:
With up to 30 V and 5 A out, a simple linear regulator would produce up to some 180 W of heat worst case. At that power level it would really help, if there is some transformer tap switching or similar.

For 30 V DC out the right transformer would be more like 28 or 30 V.  Is there already a transformer in mind or at hand ?

For more than about 25 V, my personal favorite would be the floating regulator with a small 2 nd transformer / winding to supply the regulator and display. Here using a transformer with center tap could allow for a relatively simple tap "switching" in the electron way (more like a class H amplifier). For a 30 V output this would be something like 2x15 V AC.

mike_mike:
Yes, I have: 24V/160VA and 30V/250VA transformers which I could use for power supply.
I found the attached schematic. It is a good schematic ? I would like to build the 0-30V version.

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