LM324 Power Supply with variable voltage and current

[xavier60]

I forgot to specify that the mentioned R25 voltage was measured with 100 mA load at 15V output voltage.

That's OK. The 1.35V was a result of my guess that the PNP driver's B-E was 0.5V.
Im certain that there will be no more problems to be found with the design.
You can easily use your basic electronics knowledge to work out why some things are the way they are.
 
Added: The output voltage has no affect on the operating conditions of Q1, only output current does.
With one exception, when regulation is lost due to dropout.

[Cliff Matthews]

OP: Are you sharing any final schematic or gerber files?  Did you resolve the final value of R32 or R25?

[mike_mike]

Please find attached the schematics in Eagle and in LTSPice.
Please ask if you need Eagle files.
I marked a few components with dnp - do not place and with strap - the component will be replaced by a wire.

[mike_mike]

Hello,
Please find attached the Eagle schematic and layout.

[Cliff Matthews]

I'm still not sure of the final values of R32 and R25 

[xavier60]

My most recent idea for the Emitter circuit  for Q1 is just a 1K in series with a white or possibly blue LED. The Vcc is dropped to 8V.
The  B-E resistor for the PNP driver will also be 1K.
I haven't actually tested yet. Ill likely be making a new regulator PCB for my bench supply.
https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873

[mike_mike]

I'm still not sure of the final values of R32 and R25 

R25 is 2k7, but I can't find R32 on my Eagle schematic...

[xavier60]

R32 is mentioned in  Reply #670. Looks like it's the B-E resistor for the 2N3055's, 100Ω.

[xavier60]

This is my latest version which uses a white LED to create a positive offset in the emitter circuit of Q1.
My original design used a simple voltage divider from the 8V rail but this causes an output voltage blip during power down only when a TLC 072 is used rather than an LM358. It's to do with the different  minimum operating voltage of the two parts.
 The attached schematic is of it reduced to its simplest working form.
It's essentially the same as what  mike_mike built up, with  unnecessary components mostly removed.

[mike_mike]

Hello @xavier60, can you please post the pcb layout of the power supply schematic from Reply #733 ?
Thank you in advance !

[xavier60]

The group of pin headers at the bottom left are for the CV and CC Pots plus other options.
The vertically orientated pair, top left of the group are for optionally switching the 5V reference to the Pots to disable the PSU's output. I haven't test it, but I expect a smoother turn on compared to using the Shutdown option.
 The horizontally orientated pair at the center of the group are for sending the Pots' wiper voltages to a control PCB that I use in my bench supply project.

Updated schematic is in Reply #741

[mike_mike]

I would like to ask what is the little bump (marked with an arrow) that appears on the screenshot ?
The screenshot was took from the LM324 power supply, with the probe on the R_shunt (0.22R). The PSU shorter was using a short circuit instead of a load. The frequency of the PSU Shorter was about 18 Hz.
The scope is a SDS 1022 (I know it could be a better one ...) from Owon.

Schematic of the power supply:

Please find attached the schematics in Eagle and in LTSPice.
Please ask if you need Eagle files.
I marked a few components with dnp - do not place and with strap - the component will be replaced by a wire.

LE: I am asking this because I wanted to test an LM723 power supply, and I found oscillations on the R_shunt of the LM723. So I checked on the LM324 Power supply to check if it is still good after one year and a half of service.

[xavier60]

I would like to ask what is the little bump (marked with an arrow) that appears on the screenshot ?
The screenshot was took from the LM324 power supply, with the probe on the R_shunt (0.22R). The PSU shorter was using a short circuit instead of a load. The frequency of the PSU Shorter was about 18 Hz.
The scope is a SDS 1022 (I know it could be a better one ...) from Owon.

Schematic of the power supply:

Please find attached the schematics in Eagle and in LTSPice.
Please ask if you need Eagle files.
I marked a few components with dnp - do not place and with strap - the component will be replaced by a wire.

LE: I am asking this because I wanted to test an LM723 power supply, and I found oscillations on the R_shunt of the LM723. So I checked on the LM324 Power supply to check if it is still good after one year and a half of service.

I think it's caused by the CV recovering  from a slight voltage overshoot after the short is removed.
You can confirm by looking at the output of the CV opamp at the same time.
You must use the PSU's negative output terminal as ground reference for all measurements.

[mike_mike]

Another test: yellow trace is the voltage on the R_shunt (inverted - because I used the negative output of the psu as gnd) and blue trace is the CV op-amp output (pin 1 of LM324).

[xavier60]

Yes, that confirms it. It is normal operation. You can also look at the PSU's output to see what the overshoot is.

[mike_mike]

@xavier60 , can you please clarify what part number are the diodes D1, D2 and D4 ? 1N4148 should be fine ? (schematic from post #735).
Also, the Shutdown will connect to 0V in order to shut down the PSU ?
Can you also show a image with the layout which have the reference designators on the components ?

[xavier60]

@xavier60 , can you please clarify what part number are the diodes D1, D2 and D4 ? 1N4148 should be fine ? (schematic from post #735).
Also, the Shutdown will connect to 0V in order to shut down the PSU ?
Can you also show a image with the layout which have the reference designators on the components ?

D1, D2 and D4 are 1N4148 or similar.
Pulling Shutdown to 0V will shut down the power supply.
As I get time Ill add component references to the layout.

[mike_mike]

Just finished the practical circuit, and it seems to work. Sadly, I don't have TLC072, I have only LM358. I did not found TLC072 at my electronics dealer. I built de circuit using LM358. The problem that I found is that the green led (D6) is very dim, It is very hard to see if it is lighting on not. The red led is OK.
The white led is OK, but when I set the voltage to a low value (very close to 0V or even 0V) then it's glow is reduced by a little.
I used standard 5mm led's. Should I use some high brightness led's ?

I would like to ask, the circuit will work normally if using LM358 ? Does it require any modifications ?

The maximum current goes up to 4.5A, should not have been maximum 3A ?

[xavier60]

Just finished the practical circuit, and it seems to work. Sadly, I don't have TLC072, I have only LM358. I did not found TLC072 at my electronics dealer. I built de circuit using LM358. The problem that I found is that the green led (D6) is very dim, It is very hard to see if it is lighting on not. The red led is OK.
The white led is OK, but when I set the voltage to a low value (very close to 0V or even 0V) then it's glow is reduced by a little.
I used standard 5mm led's. Should I use some high brightness led's ?

I would like to ask, the circuit will work normally if using LM358 ? Does it require any modifications ?

The maximum current goes up to 4.5A, should not have been maximum 3A ?

It should work well with an Lm358 like your previous project. The white LED seems to be working normally.
With the PSU output set above 0V what is the CV opamp output voltage? And what voltage is across R31? so we can calculate the CV LED current.
The maximum current range can be reduced by increasing R8.

[mike_mike]

With the PSU output set at 12V, the CV opamp output is 3.36V. Voltage across R31 is 2.80V.

Edit: when disconnecting from the mains the PSU, after a few seconds, the white led goes brighter than when the PSU is connected to the mains.

[xavier60]

With the PSU output set at 12V, the CV opamp output is 3.36V. Voltage across R31 is 2.80V.

Edit: when disconnecting from the mains the PSU, after a few seconds, the white led goes brighter than when the PSU is connected to the mains.

That's 0.28mA if R31 is 10K. A normal high brightness LED should be bright enough. Ill check mine later. I use cheap 3mm Chinese LEDs bought on ebay. They do fail open circuit sometimes,

It's normal for the white LED to brighten when the regulation drops out because the CV opamp gives Q1 full drive,

[mike_mike]

I tried with a 3mm led, but it doesn't light as brighter as yours.

[xavier60]

Mine has 2V across R31 giving a suitable LED brightness. You could try decreasing R31 to increase the LED current. Try 3.3K.

[mike_mike]

I decreased R31 to 3.3k, and tried different types of 5mm green led's. Now the voltage across R31 is 2.85V.
Then I found a low current green led which is sufficiently bright even if I use the 10k resistor (R31). The voltage across R31 is now 2.35V, and across the green led 2.22V.
Also, I increased R8 to 330k, and now, the maximum current is about 2.6A.

[xavier60]

Have you done a pulse load test to check the response and stability?