LM324 Power Supply with variable voltage and current

[iMo]

@MM: to your simulation above: doublecheck what is the ESR of the 47uF capacitor. I think you still using 0.1ohm there.

I would highly suggest NOT TO USE the built in esr, but instead add a special ESR resistor into the schematics.
You can see the ESR value directly in the schematics then, and we may refer to a particular ESR resistor.

Enclosed the SIMULATION ONLY .asc V17 - use it for the simulation.

[Kleinstein]

The test still missing and repeatedly asked for if loading the supply to less than current limiting. So this is the more classical load test. E.g. CC limit to 3 A and a test current of some 10 mA (min load) - 1 A  (e.g. 20 Ohms at 20 V) -  10 mA.

The other point would be a short load spike, so that the fast current limit engages, but not yet the slow current limit. So maybe some 5 A for some 20 µs or so.

[mike_mike]

I added a 20R resistor as load, and I set the output voltage at 20V.
SlowCC is 3A. Min load is 820R (this is the resistor that I had).
If the GND was aligned to the grid, then nothing was shown on the scope, only the blue trace.
So I was needed to reduce the V/div.
C1=220p, C5=2n2.

Please have a look at the attached screenshots and tell me what you think.

[iMo]

Sim 16mA/1A C1=470pF C5=2n2 Islow=3A Vout=21V

Sim 16mA/1A C1=220pF C5=2n2 Islow=3A Vout=21V

[mike_mike]

I see that the oscillation have smaller peak to peak values for 220pF...

What should I test next ?

[iMo]

Look a the CV opamp's output with above test.

[mike_mike]

The output of the CV op amp and the GND on the power supply output GND
Vout=21V, C1=220pF, C5=2n2, SlowCC=3A, Rload max=20R, Rload min=1.2K
0973-0976
Vout=21V, C1=470pF, C5=2n2, SlowCC=3A, Rload max=20R, Rload min=1.2K
0977-0979

If I use higher V/div, then I see only the blue trace on the screen.
I used those load resistors, because those values are the most close to the specified load currents.
Please have a look at the attached screenshots and tell me what you think.

Later Edit: The last screenshot show the pin 3 output of the 555, at PSU Shorter. I used 220k/4k7/330nF. Please also have a look at this and tell me if it is good.

[mike_mike]

I used a new configuration for the PSU Shorter.
I used 220k/220k/100nF.
Vout=20.9V, SlowCC=max (3A), Rload=20R, Rloadmin=1.2k
C1=470pF, C5=2n2.
0985-0989
0990-0992
These were measured on the output of the CV opamp.

Please have a look at the attached screenshots and tell me what you think. Does they look good or not ?

[xavier60]

The activity at the CV op-amp is expected and correct. The negative going pulse at the end is the loop's response to the slight output overshoot.
The shape of the output voltage dip pulse is correct for the load transient tests. Just the same as mine, https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg2405490/#msg2405490
I can see that the gm is 3 but this is ok because it's offset by your voltage divider having about 3 times more gain than mine.
Expect larger overshoots if a short is removed while the fast limiting is active.
Any high frequency ringing or hash that occurs at current switch off is likely due to parsitics.

[floobydust]

DS0989, DS0991 shows 500usec dip, what is taking so long.

[xavier60]

DS0989, DS0991 shows 500usec dip, what is taking so long.

There isn't much load current to discharge the output capacitance during the overshoot.

[floobydust]

With a shorted output in (slow) CC mode, the CV op-amp sits there saturated and can take a long time to recover + the slew time. It's seeing i.e. 7.4V differential (21V setpoint and 0V out). I wondered if we would see that delay, or if SPICE models stay accurate. I limit the differential input voltage on CV op-amp (internal comp cap/integrator windup) to speed up recovery, using a diode.

[xavier60]

With Kleinstein's suggestion, the compensation feedback for the CV op-amp is now taken from the diode OR-ing node.
As far as I can figure, there is no CV windup while the slow CC loop is in control.
The overshoot is caused by the reaction time of the op-amp and output transistors.

[xavier60]

Adding back the correct values for C4 and R4 wont prevent overshoot for all circumstances.
There will be a serious CV windup problem while the fast limiting is active.

[mike_mike]

I read and tried to understand all your messages.
Can you please let me know what should I test next ?

There will be a serious CV windup problem while the fast limiting is active.

Should be implemented a solution for this problem ?

...and I will double check the power transistor circuit.

[xavier60]

Try a pulsed short circuit test with a short duration like 100µs. Monitor the output for overshoot while changing the CC setting.

[Kleinstein]

I read and tried to understand all your messages.
Can you please let me know what should I test next ?

There will be a serious CV windup problem while the fast limiting is active.

Should be implemented a solution for this problem ?

...and I will double check the power transistor circuit.

The first point would be to look if the overshoot with only the fast current limit active is actually that bad.
Preventing that kind of overshoot could however get difficult, as it is hard to sense when the fast current limit will engage. My suggestion would than be a different fast current limit at the low side. A transistor could pulling down the base of Q1 if the shunt voltage exceeds 0.6 V or so.

[xavier60]

Something like this. I don't expect it to work too smoothly.

[mike_mike]

Try a pulsed short circuit test with a short duration like 100µs. Monitor the output for overshoot while changing the CC setting.

So I will need to adjust the PSU shorter to output a pulse of about 100us and then to look at the output of the power supply at different slowcc settings ?

And I will need to remove the blue led and the resistor in series with it ?

[xavier60]

Try a pulsed short circuit test with a short duration like 100µs. Monitor the output for overshoot while changing the CC setting.

So I will need to adjust the PSU shorter to output a pulse of about 100us and then to look at the output of the power supply at different slowcc settings ?

And I will need to remove the blue led and the resistor in series with it ?

Don't modify anything yet except the shorter. We want to see how bad the problem might be first.
The idea is to apply shorts of short duration that don't allow enough time to transition from fast to slow CC control.
Adjust the CC setting to find the worst voltage overshoots at the output.
No need to show us everything, just the worst of what you might find.

[mike_mike]

I think that there is a problem with the Fast CC because I am getting only 1.09V on the RShunt, so this is about 4.95A, but it should be about 8A ... Please see reply #398
I am missing something ?
I don't know what should I do ...

[xavier60]

The Base of Q1 might not be going high enough. Bridge out the blue LED.

[mike_mike]

I replaced the blue led with a short circuit, and now the current through the Rshunt is about 8A.

But if I bridge out the blue led, then when the power is cut off, the output of the supply will go to max voltage ? (I saw a short pulse on the screen of the oscilloscope when I plugged out the power supply from the mains).

[xavier60]

I replaced the blue led with a short circuit, and now the current through the Rshunt is about 8A.

But if I bridge out the blue led, then when the power is cut off, the output of the supply will go to max voltage ?

I have previously explained why I think that the UVLO should still work, best is to test it.

[xavier60]

If you have another smaller power supply use it to power the 12V rail. Then see what happens as the voltage of the 12V rail is decreased.