LM324 Power Supply with variable voltage and current

[xavier60]

Did removing of C5 reduce the ripple in CC mode?

[mike_mike]

Removing of C5 (2n2) did not reduce the ripple, in CC mode.

[xavier60]

I should have said, remove the 220µF at the input of the LM7812, I hope that it is causing the ripple.

[mike_mike]

I removed the 220uF at the input of the LM7812, and the ripple disappeared.
Vout=2.05V (without load, with load is less than 2.05V), SlowCC=0.17-0.19A, Rload=10R.

[xavier60]

I removed the 220uF at the input of the LM7812, and the ripple disappeared.

That's wonderful news, It means that the problem is being caused by the capacitor's ripple current causing voltage drop across the ground track.
Something needs to be altered.

[mike_mike]

Something needs to be altered.

Do you mean the PCB layout ?
It can work correctly without the 220uF capacitor ?

[xavier60]

It's more likely that the capacitor's ripple current through the shunt is the main cause of the problem.
If the 7812 is proven to be stable with the small capacitor left, just leave it with the 220µF removed.
It's not worth correcting the PCB design just for this problem as the design will still remain incompletely developed for many other reasons.
This design should not be replicated as is.

[mike_mike]

This design should not be replicated as is.

Should I not use this design ?
How to check if 7812 is stable with 220uF capacitor removed ? Just connecting the oscilloscope probe to the output of the 7812 ?

[floobydust]

I think it's architecture, because the capacitor is grounded after the sense-resistor. So ripple currents on the 220uF cap appear across the sense-resistor, and it adds a little unwanted feedback loop from the raw DC (ripple) to the slow CC circuit.
I would increase R1, R2 (5R is quite low) and decrease or eliminate 220uF (C5). Guessing 47R.

[xavier60]

This design should not be replicated as is.

Should I not use this design ?
How to check if 7812 is stable with 220uF capacitor removed ? Just connecting the oscilloscope probe to the output of the 7812 ?

No, we know that the design works fine. I would rather not see it copied by others before it's fully developed. For example, the low side fast limiting should have been tested and that mess on the high side removed.
Check around the 7812 with your CRO.

[floobydust]

7812 minimum load is 5mA, I would expect he has that esp. with the LED's.

[xavier60]

3. Regarding the attached schematic, of the power supply that has been discussed earlier in this topic, if I will use a 30 Vac/ 5A transformer, what are the modifications necessary in the schematic ? I need the same output voltage and current (0-30V and 0-3A). The only thing that modifies is the transformer. If the current project will be bad, then I will use this power supply, but only if it can be used with 30 Vac transformer. I want to use the 30Vac transformer, because, using the 24Vac transfomer, when the output voltage is about 25V and the load is about 3A, then the ripple appears on the output of the power supply. But if I go with the output voltage down to 24V, then the ripple disappears.

The 10Ω resistor in the Emitter circuit of the driver transistor will be adding some extra dropout although eliminating this won't completely solve the ripple at high output voltage.
It is difficult to give  certain responses to the topic of voltage, current and heat sinking.
If there are 2 separate 15VAC secondaries, tap switching has great advantages in reducing the possibility of failure of the output transistors. 

[mike_mike]

Regarding the power supply discussed early in this topic, at pct 3, is that such a big problem, if the input ripple appears on the output of the power supply at high output voltage ?
Can the power supply be used without problems if this behavior appears ?

[xavier60]

Regarding the power supply discussed early in this topic, at pct 3, is that such a big problem, if the input ripple appears on the output of the power supply at high output voltage ?
Can the power supply be used without problems if this behavior appears ?

Yes, no problem so long as the load doesn't care.

[mike_mike]

By removing the 220uF capacitor, it is possible to make the power supply oscillate or making other "strange" things ?

[xavier60]

By removing the 220uF capacitor, it is possible to make the power supply oscillate or making other "strange" things ?

Only if the 7812 oscillates which I don't expect.

[mike_mike]

I checked with the oscilloscope on the output and on the input of the 7812.
On the output of the 7812:
1. No load 516-521.jpg
2. 2.5A load at the output of the power supply: 522-527.jpg
On the input of the 7812:
1. No load 528-532.jpg
2. 2.5A load at the output of the power supply 533-535.jpg

The wave form in 520 and 521 is noise or oscillation ?
What about the other screenshots ?

[xavier60]

Everything looks ok. You have previously proven that the high frequency noise is not produced by the power supply.
I dont know what this noise is caused by. Are you near an FM or TV transmitter?
It's usually difficult to track down.

[mike_mike]

Everything looks ok.

So I can peacefully use the power supply ?

Are you near an FM or TV transmitter?

At about 300m distance, there is a GSM antenna.
I don't know if some of my neighbors have FM or TV transmitter...

[xavier60]

yes, Just use it. Do you have meters on it so know what's happening?

[mike_mike]

I have only one analog voltage meter (0-30V dc).
For measuring the current I will use the multimeter...

[mike_mike]

I made some tests with a 5mm white led as load. I set the output voltage at maximum, then I reduced the output current to minimum and then I connected the white led and I increased the current to about 6.51mA. After about 1 hour and a half, the current through the led was 6.57mA. Then I touched the LM324, and the current dropped to about 6.52-6.53mA.

After this, I made another test. I disconnected the power supply from the mains voltage, then I reconnected it to the mains voltage. Then I measured during 1 hour the current through the led and it was initially 6.50mA and then it dropped to 6.48-6.49mA and it was constantly about 1 hour until the test was stopped by me.

Before these tests I made another one, with another amp meter and another 5k pot, and the results were the same.
Are the results of the tests good ?

[floobydust]

I think this is normal for the design and parts used.
Temperature change will cause drift in many components. Expect a voltage or current setpoint to move due to temperature. 6.51/6.57 is roughly 1% after 1.5hrs.
As the 7812 heats up, its voltage will drift 1.5mV/°C
The LM324 input offset voltage drift 70uV/°C
0.22R sense resistor is ±300ppm/°C.

I think it (CC) would be worst drifting at high current loads due to the 0.22R sense resistor heating up and then cooling down.

[mike_mike]

Can you please tell me what is the maximum Differential Input Voltage for the led signalization (IC2B) op amp ?
I am measuring maximum 9-10V between the in- and in+ of this op amp.

And I found a document (screenshot) from TI and I wanted to ask if in the LM324 datasheet, the Differential Input Voltage = max 32V, is the voltage measured between the in- and in+ pins of the op amp ?

[mike_mike]

I have found that in the datasheet there is a parameter named "input common-mode voltage".
In my design, the pin 5 is at 9.71 and pin 6 is at 9.26V, when there is no load at the output. Also, the LM324 supply voltage is 11.88V
While the CC is active, the supply voltage for LM324 is 12.33V and the output voltage from the 7812 is 11.88V. Pin 5 is at 4.73V and pin 6 is at 9.71V, with respect to ground. Why is this happening ?? Why the voltage at the LM324 power is higher than the voltage at the output of the 7812 ?