Author Topic: LM324 Power Supply with variable voltage and current  (Read 19956 times)

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Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #675 on: October 13, 2019, 09:04:49 pm »
3A is the maximum output current, I do not have a resistor or a group of resistors which draw exactly 3A, can I use a load of 2.66A ?
Or should I test with a short circuit on the output ?
2.66A is fine. Don't allow it to go into current limiting.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #676 on: October 14, 2019, 04:07:43 am »
Voltage recovery after an 2.66A at 26.6V output voltage:
172-174.jpg

Recovery after a short circuit:
175-176

On the R_Shunt during short circuit on output:
178-180.jpg

I made a few more tests, for my curiosity.
All the tests were made using the R32 = 100R.
« Last Edit: October 14, 2019, 04:11:10 am by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #677 on: October 14, 2019, 04:22:01 am »
Im mainly curious to know what the voltage overshoot is when unloading from a normal load.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #678 on: October 14, 2019, 05:43:44 am »
The voltage overshoot is not represented in 172-174 ?
I think I am missing something... how to check the voltage overshoot ?
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #679 on: October 14, 2019, 07:24:14 am »
The voltage overshoot is not represented in 172-174 ?
I think I am missing something... how to check the voltage overshoot ?
Trigger your DSO at the high to low transition of the MOSFET's gate. This will be the time that the power supply unloads.
We are looking for how much the output voltage increases by.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #680 on: October 14, 2019, 11:58:35 am »
With yellow color is the output of the power supply and with blue color is the gate of the mosfet.
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #681 on: October 14, 2019, 12:05:54 pm »
Do the test without allowing the power supply to current limit.
Choose a resistor and voltage setting that draws a bit under 3A.
Set the current limit to maximum so that it doesn't go into current limit mode.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #682 on: October 14, 2019, 12:11:56 pm »
Vout=26.6V
Rload=10R
Ilimit=3A

With yellow = output of the power supply
With blue = gate of the mosfet

With R32 (100R) connected: 196,295
Without R32 (100R): 198, 199.
« Last Edit: October 14, 2019, 12:37:33 pm by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #683 on: October 14, 2019, 12:40:50 pm »
The 1V overshoot is one thing, maybe normal. I am puzzled by the way the voltage settles so quickly. What's causing the output capacitors to discharge so quickly.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #684 on: October 14, 2019, 12:51:29 pm »
Probably the 1k/5W resistor which is connected in parallel with the output ?

Are you saying that the transient response should be longer ?
« Last Edit: October 14, 2019, 01:22:43 pm by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #685 on: October 14, 2019, 01:34:53 pm »
I had the reason worked out a while ago then forgot it. I did the same test on my bench supply.
After the MOSFET turns off, the only place the output current can go is through the output capacitance causing a voltage rise.
The CV loop takes a few µs to reduce the drive to the output transistors. The 5µs overshoot is actually the temporary voltage drop across the capacitors' ESR. The actual capacitance gets charged by only 100mV or so.
You might see some other activity further along caused by the 100mV overshoot being corrected.
Your power supply is working properly.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #686 on: October 14, 2019, 01:57:59 pm »
Do I need to test any other things ?
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #687 on: October 14, 2019, 02:02:49 pm »
Do I need to test any other things ?
One minor thing, check that the current can be adjusted to zero, Then I suggest that you  put it into service with the recent changes.
« Last Edit: October 14, 2019, 02:04:24 pm by xavier60 »
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #688 on: October 14, 2019, 02:14:35 pm »
Yes, the current can be adjusted to zero. For example, with the 1k resistor on the output, I read 0.0mA on my multimeter, and the led lit when I rotate the current pot down to zero.

LE: and I also read 0.0mA without the 1k resistor.

LE2: ... the fine tuning of the CC and CV loop capacitors is necessary or the capacitors does not allow any tuning ?
« Last Edit: October 14, 2019, 03:25:40 pm by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #689 on: October 14, 2019, 10:12:52 pm »
Yes, the current can be adjusted to zero. For example, with the 1k resistor on the output, I read 0.0mA on my multimeter, and the led lit when I rotate the current pot down to zero.

LE: and I also read 0.0mA without the 1k resistor.

LE2: ... the fine tuning of the CC and CV loop capacitors is necessary or the capacitors does not allow any tuning ?
It's not necessary for it to go any faster. If you want to experiment on your own, start with increasing the gm of the output path by reducing R25.
The fast limiting is likely to be affected.
You should just leave it as is.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #690 on: October 15, 2019, 06:33:16 am »
One more question that I have probably previos asked but I am still blurred: if I use the power supply as it is in this moment, can it start oscillate ?
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #691 on: October 15, 2019, 07:02:45 am »
One more question that I have probably previos asked but I am still blurred: if I use the power supply as it is in this moment, can it start oscillate ?
It shouldn't, not the CV loop anyway. To be more certain, do the load transient tests while adding very low ESR capacitors across the output, near to the PCB as possible.You can use either large MLCCs or POSCAPs, https://en.wikipedia.org/wiki/Polymer_capacitor
Be aware of the voltage ratings.
If it rings for one or two cycles, it's ok.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #692 on: October 15, 2019, 08:17:43 am »
I tried to search for the mentioned capacitors but I did not found them at the local shop. Also I don't have them in my stock at home. An order on the internet only for a few components does not worth it.
Is there any other testing method ?
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #693 on: October 15, 2019, 08:54:24 am »
I tried to search for the mentioned capacitors but I did not found them at the local shop. Also I don't have them in my stock at home. An order on the internet only for a few components does not worth it.
Is there any other testing method ?
No, Just don't bother with the test. I have done the tests on my bench supply which is very similar to yours.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #694 on: October 16, 2019, 09:40:56 am »
 After all the tests, can I put the power suppy into service ?
« Last Edit: October 16, 2019, 10:05:03 am by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #695 on: October 16, 2019, 10:26:22 am »
After all the tests, can I put the power suppy into service ?
Yes, it will fine so long as no serious mistakes are made. Also, dont make the wires to the heat sink any longer than they have been, shorter is usually better. No one can easily say how long is too long.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #696 on: October 16, 2019, 12:51:40 pm »
Will the power supply work correctly if I will use TIP35C instead of TIP3055 ?
« Last Edit: October 16, 2019, 01:59:58 pm by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #697 on: October 16, 2019, 02:54:50 pm »
Will the power supply work correctly if I will use TIP35C instead of TIP3055 ?
That should be fine,
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #698 on: October 16, 2019, 04:55:16 pm »
It is a good idea to use a multi turn potentiometer (U7) for fine current adjustment instead of the standard potentiometer that I have been used ?
« Last Edit: October 16, 2019, 05:37:28 pm by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #699 on: October 16, 2019, 09:38:06 pm »
It is a good idea to use a multi turn potentiometer (U7) for fine current adjustment instead of the standard potentiometer that I have been used ?
I used 10 turn Pots for voltage and current control with my bench supply to give fine control.
Genuine branded Pots are too expensive and I have experienced some trouble with the cheap knock off Pots which ebay is flooded with.
I mentioned the problems in the other thread, https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2368746/#msg2368746
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