LM324 Power Supply with variable voltage and current

[mike_mike]

Vout=27.4V, Iout=3.35A
I tested at maximum output voltage and current, because I imagined that here will be more voltage overshoot.

[xavier60]

That won't be a problem for most things.
The overshoot should lessen with reduced CC setting.
This is mine at 25V and 3A.

Extra: I did add a 10uF MLCC across of output of mine. I attached it with 10mm leads so that it might not damage the PCB if it were to break down. I don't expect that it has made much change to performance.

[xavier60]

Until you find better parts, you could try a possible quick fix.
Connect a 1.5K resistor from the Shutdown pin to the 5V reference.
The idea is to pull the reference voltage down a bit while the PSU is disabled, resulting in some soft-start
effect when it's enabled again.

[mike_mike]

Tested with the 1k5 resistor from Shutdown pin to the 5V reference.

LE: I searched at my electronic components supplier and I wont be able to get the TLC072 opamp, so I would stick with the LM358.

[iMo]

FYI - I've been using a similar V/A (30V/3A) meter module in one of my PSU.. I wonder whether it could be wired to your PSU easily..

[mike_mike]

@imo, I first need the approval that my PSU is working good, then I will make a case for this PSU, and then I will probably install a V/A meter module. If not, then I will use a simple analog voltmeter, which I already have in my workshop.

[iMo]

@mike: sure, your PSU looks nice..
FYI - this is how the modules are typically wired (pictures from ebay with my comment on max voltage). There are 3-5digits meters available, afaik..
No guarantee the newer one have the same wiring (I did it years back).
Doublecheck!

[xavier60]

I made some comment about those kind of LED panel meters here, https://www.eevblog.com/forum/projects/volts-amps-digital-meters/msg3685030/#msg3685030

So I recommend getting a 4 digit  model after confirming from the photos that the board carries the small CMOS switch IC.
If the refresh is slower than advertised, complain to the seller.

[xavier60]

@mike: sure, your PSU looks nice..
FYI - this is how the modules are typically wired. There are 3-5digits meters available, afaik..
No guarantee the newer one have the same wiring (I did it years back).
Doublecheck!

I have just looked at the link. I have not seen that style of meter.

[iMo]

My module has got the wires as on the picture (4digits 30V/3A, red/blue led display).
The black wires are common afaik.
Therefore my question on how you would wire it when you are using shunt in the gnd path.

PS: I've glanced at my PSU module and the refresh rate is something like 3-4x per second at least..
PPS: I put a 7805 (with a small heatsink attached) in front of the meter's Vcc, still working  (the PSU is single voltage, 28V at filter).

[xavier60]

My module has got the wires as on the picture (4digits 30V/3A, red/blue led display).
The black ones are common afaik.
Therefore my question on how you would wire it when you are using shunt in the gnd path.

mike_mike has a separate 12V supply referenced to the PSU's 0V output terminal, so it should be fine.

[mike_mike]

Any thoughts regarding my screenshots at reply #928 ?

Tested with the 1k5 resistor from Shutdown pin to the 5V reference.

LE: I searched at my electronic components supplier and I wont be able to get the TLC072 opamp, so I would stick with the LM358.

[xavier60]

Any thoughts regarding my screenshots at reply #928 ?

Tested with the 1k5 resistor from Shutdown pin to the 5V reference.

LE: I searched at my electronic components supplier and I wont be able to get the TLC072 opamp, so I would stick with the LM358.

Looks good, no overshoot. You should check at 5V.

[mike_mike]

This is at 5V output.
Iout=3.35A.

[xavier60]

That spike could be a problem at lower voltage setting but reducing the CC setting should reduce it.

[mike_mike]

Vout=5V, Iout=1.6A
It looks like the spike is bigger, also tested at max output current and the spike is bigger.

[mike_mike]

I have retested at max output current and 5V output.

[xavier60]

I have discovered that there is more to this issue. When the PSU is enabled, the charge current of the output capacitor causes the fast current limiting to overreact and this is what is controlling the voltage rise.
I popped an LM358 into mine and did a few tests. I got some overshoot but not as much as yours before the resistor  mod.
Looks like your slow driver transistor is part of the problem.
I had mentioned earlier that my PCB has the option of breaking the reference connection to the pots.
Will the overshoot be a problem for you?
 

[mike_mike]

Are you asking about the overshoot that apoears on the oscilloscope when I enable the output ?
If yes, then it should not be a problem.

[xavier60]

Are you asking about the overshoot that apoears on the oscilloscope when I enable the output ?
If yes, then it should not be a problem.

Yes.

[mike_mike]

I don't think that the overshoot could be a problem.
What other transistors can I use for the PNP driver ?

[xavier60]

The D45H11 is the only one I have used and know as suitable. Any other suggestions will be based on fT as well as power.
MJE171G or MJE172G for now.

Added: MJE15029
           MJE253G

[mike_mike]

Ok, then I will install the PCB into a case and use the PSU.
Does the 1k5 resistor which is connected from Shutdown to the 5V reference still needed ?

[xavier60]

Ok, then I will install the PCB into a case and use the PSU.
Does the 1k5 resistor which is connected from Shutdown to the 5V reference still needed ?

No, unless you think it makes a worthwhile improvement.
I have added another possible suitable driver to the list. Its main application is as audio driver which has the same type of requirements.

[mike_mike]

Ok, I will install the PCB into the case and I will come back with some photos, probably the next week...