LM324 Power Supply with variable voltage and current

[mike_mike]

I powered a 24V 92x92mm fan (model TYP3414 NGH) at Vout=24V.
I got the attached screenshots.

[xavier60]

Are you certain that the fan is causing that? The frequency is very high and there isn't much of it anyway.

[mike_mike]

The same waveforms appear when the fan is removed from the PSU output.
The scope probe was connected right on the PSU's output with the crocodile clip connected on the PSU's GND.

[mike_mike]

@xavier60 Regarding the above test what do you think about the screenshots ?

[xavier60]

@xavier60 Regarding the above test what do you think about the screenshots ?

Very unlikely to be from the PSU itself.

[mike_mike]

Should I install the PSU into the case and use it, or are necessary any other modifications ?

[xavier60]

Should I install the PSU into the case and use it, or are necessary any other modifications ?

Just use it unless you notice anything unusual.

[mike_mike]

I just tested a old PCB of the PSU using another group of 5 transistors (5x TIP3055).
I noticed a small bump on the rising edge of the PSU's output when testing with a 6.2 ohms load at 31V ouptut and Ilim=5.12A.
Could be that a problem ?

[xavier60]

The cause for that would be difficult to find, I'm sure it will not cause any problems.

[mike_mike]

The screenshot is took when the output is switched off from the switch.
Yellow = output of the PSU
Blue = the signal which comes from the D4 Catode to the relay on tap switcher pcb.

Is this waveform still good ?

LE: I updated the screenshot.

[xavier60]

Remember to include a link to the schematic,
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg5677315/#msg5677315

The output is well behaved, no voltage jump.
The hash in both traces would be due to arcing in the mains switch. The voltage drop at K of D4 is likely a normal response to the decreasing PSU output voltage.

EDIT: Im not so sure about that, we need to see waht the supply to tap changer is doing also.

[mike_mike]

It is not about the mains switch is about the DC-off switch.

[xavier60]

It is not about the mains switch is about the DC-off switch.

I dont understnd for now why K of D4 is 4V before the PSU switch off. What state is the switch in? I see the output is 12V

[mike_mike]

The switch is in ON state. When the switch goes into OFF state then the PSU's output is switched OFF.
I remember that we made some modifications to the switch.

[xavier60]

The switch is in ON state. When the switch goes into OFF state then the PSU's output is switched OFF.
I remember that we made some modifications to the switch.

Yes, I remember that now.
With the PSU ON, what are the voltages on all of the opamp pins?
I need to go out shortly.

[mike_mike]

Pin 1 = 6.83V
2 = 0V
3 = 0.25V
4 = 0V
5 = 1.85V
6 = 1.85V
7 = 3.33V
8 = 8.06V
 with respect to output GND
Vout=12.15V

[xavier60]

I thought the tap switcher was powered with 12V? Most of the voltages also look wrong.

[mike_mike]

The tap switcher is powered from a separate transformer and it has his dedicated 12V regulator (L7812).

Why the voltages look wrong ?

[mike_mike]

Do you mean the PSU tap switcher OpAmp ?

[xavier60]

Do you mean the PSU tap switcher OpAmp ?

Yes.

[xavier60]

Actually, my mistake, I thought we were talking about D4 on the tap switcher PCB.
The main thing to check for is that the tap switcher relay K2 shouldn't click when the PSU is turned on and off at the same output voltage setting.
If it does click when the PSU is set close to the tap switcher's threshold, we should be able to fix it by increasing C1 on the tap switcher or other ways.

[mike_mike]

K2 shouldn't click when the PSU is turned on and off at the same output voltage setting.

Using the DC off switch or from the main switch ?

[xavier60]

K2 shouldn't click when the PSU is turned on and off at the same output voltage setting.

Using the DC off switch or from the main switch ?

The DC off switch.

[mike_mike]

I set the output voltage at 31.8V, and by turning on and off the PSU from the DC off switch the main relay K2 does not make any click.
Same thing happens when the output voltage is 11.93V.

[xavier60]

I set the output voltage at 31.8V, and by turning on and off the PSU from the DC off switch the main relay K2 does not make any click.
Same thing happens when the output voltage is 11.93V.

All good then.