Author Topic: LM324 Power Supply with variable voltage and current (Read 194446 times)

xavier60 · « **Reply #1100 on:** December 12, 2023, 07:31:10 pm »

Adding 0.5mA for R7 totals 5.7mA which is within spec for a TI part which can be as low as 10mA output sinking.
I still don't like it.

mike_mike · « **Reply #1101 on:** December 12, 2023, 07:39:02 pm »

Then what is your recomendation ?

xavier60 · « **Reply #1102 on:** December 12, 2023, 07:53:34 pm »

Quote from: mike_mike on December 12, 2023, 07:39:02 pm

Then what is your recomendation ?

Find brighter LEDs. All modern LEDs will be much brighter than what you have. Im using cheap 3mm LEDs I got on ebay with 10K resistors.
The PSU should be ok to use so long as it's regulating properly. To be certain, you need to confirm that both opamps are able to pull the Base
of Q1 well below cutoff. Not a simple test.

xavier60 · « **Reply #1103 on:** December 12, 2023, 08:29:25 pm »

If your PSU has R41 fitted, it should allow the CC setting to go below zero which will make the CC LED light up with no output load and the CC pot set to minimum.
If this is the case, this is when the Base voltage of Q1 can be checked for cutoff.

mike_mike · « **Reply #1104 on:** December 12, 2023, 08:55:10 pm »

I modified R30 and R31 to 10k, and I used 5mm high brightess led's. The PSU has R41 fitted.
Look what I found on the oscilloscope:
I don't know why there is that waveform (the yellow channel). The blue channel is the output signal from the PSU testing circuit (psu shorter).

xavier60 · « **Reply #1105 on:** December 12, 2023, 09:11:55 pm »

That is odd. Try doing the test with the ground lead for CH2 disconnected.

mike_mike · « **Reply #1106 on:** December 12, 2023, 09:29:26 pm »

It happened after replacing de R30 and R31 by 10k resistors and after installing the brighter led's.
So I suspect that something does not work because of the replaced components.

xavier60 · « **Reply #1107 on:** December 12, 2023, 09:33:37 pm »

Quote from: mike_mike on December 12, 2023, 09:29:26 pm

It happened after replacing de R30 and R31 by 10k resistors and after installing the brighter led's.
So I suspect that something does not work because of the replaced components.

I dont see why, one way to prove it, put it all back the way it was.
Very long wiring could possibly cause that affect.

xavier60 · « **Reply #1108 on:** December 12, 2023, 10:02:07 pm »

I did a test on mine at 10V and 2A with the TLC072 replaced by an LM358. I got a nice clean voltage dip of the expected shape measured directly at the PSU's output terminals.

mike_mike · « **Reply #1109 on:** December 13, 2023, 02:52:26 pm »

I replaced R30 and R31 by 2k2 as it was initially.
Now the waveform looks ok.
What should I do next ?

xavier60 · « **Reply #1110 on:** December 13, 2023, 03:08:28 pm »

Quote from: mike_mike on December 13, 2023, 02:52:26 pm

I replaced R30 and R31 by 2k2 as it was initially.
Now the waveform looks ok.
What should I do next ?

Im not really sure. I have not been able to reproduce the same problem here.
You could just leave it like that or ate the LEDs too bright now?

mike_mike · « **Reply #1111 on:** December 13, 2023, 03:20:07 pm »

Now the led's are too bright (currently they are high brighness led's), but I will replace them by normal led's, and their brightness will be ok.

Later edit: I changed the led's to normal led's and they are not too bright now.

mike_mike · « **Reply #1112 on:** December 13, 2023, 04:55:52 pm »

I remember that the PSU worked on my project when I first built it. Why it isn't work correctly anymore ?
I replaced: the bridge rectifier, the power transistors, the 10k (R30 and R31) resistors, the 2 led's (green and red), the load which I used at the load switcher.

Edit: If I remove the red and the green led, then the response looks almost normal.

xavier60 · « **Reply #1113 on:** December 13, 2023, 05:08:53 pm »

Are there other problems than the mis-shaped load transient pulse?

mike_mike · « **Reply #1114 on:** December 13, 2023, 05:13:50 pm »

Quote from: xavier60 on December 13, 2023, 05:08:53 pm

Are there other problems than the mis-shaped load transient pulse?

Until now, no.

xavier60 · « **Reply #1115 on:** December 13, 2023, 10:37:49 pm »

Is it only the presence of the CV LED that distorts the pulse shape? The opamp's supply rail should be checked.
Edit:
Try another opamp if not done already.

mike_mike · « **Reply #1116 on:** December 14, 2023, 03:28:03 am »

This is the opamp supply waveform (from pin 4 to pin 8 ).
I tried another opamp, the result is the same as before.

xavier60 · « **Reply #1117 on:** December 14, 2023, 03:35:41 am »

I think that's normal.
Check the output of the CV and CC opamps. The output of the CC opamp should be always pinned high.
The output of the CV opamp should look the same as the Base of Q1. Show one of them if the same.

xavier60 · « **Reply #1118 on:** December 14, 2023, 03:42:06 am »

Connect CH1 ground clip to the output side of the CS resistor. Don't connect CH2 ground to anything.

mike_mike · « **Reply #1119 on:** December 14, 2023, 03:46:58 am »

I connected CH1 ground to the output side of CS resistor.
1. on pin 1: 231_000.jpg
2. on pin 7 231_001.jpg
3. on B of Q1 231_002.jpg

xavier60 · « **Reply #1120 on:** December 14, 2023, 03:59:54 am »

001 appears to be the Emitter of Q1 but that's ok.
I can't see anything unusual at that time base. Expand the the + transition at center screen.

mike_mike · « **Reply #1121 on:** December 14, 2023, 04:07:32 am »

The base of Q1.

xavier60 · « **Reply #1122 on:** December 14, 2023, 04:19:14 am »

I see you do show it. The distortion is visable there, I dont know why.

mike_mike · « **Reply #1123 on:** December 14, 2023, 04:50:44 am »

What should I do next ?

mike_mike · « **Reply #1124 on:** December 14, 2023, 05:16:46 am »

I tried another pcb and the same waveform appeared on the oscilloscope .


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Author Topic: LM324 Power Supply with variable voltage and current (Read 194446 times)

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