Author Topic: LM324 Power Supply with variable voltage and current (Read 198018 times)

mike_mike · « **Reply #650 on:** October 13, 2019, 07:39:47 am »

Yes, the resistor was connected across the output terminals of the power supply.

Are there any other tests that I should do ?

xavier60 · « **Reply #651 on:** October 13, 2019, 07:51:05 am »

Quote from: mike_mike on October 13, 2019, 07:39:47 am

Yes, the resistor was connected across the output terminals of the power supply.

Are there any other tests that I should do ?

I can't think of much at the moment, the important stuff all seems fine.
If you are planing to add a digital volt/amp panel meter, it might cause some complications.

mike_mike · « **Reply #652 on:** October 13, 2019, 07:54:04 am »

I will install only a analog voltmeter on the front panel of the power supply case.

Should I test again for oscillations, using different loads at different output voltages ?

mike_mike · « **Reply #653 on:** October 13, 2019, 08:01:33 am »

Also, this is the PCB - approximative - that I used in the tests. Some of the components were replaced by another value and some were strapped with a wire.

Also the FR107 diode was installed over the 22K resistor.
The 3 non plated holes are for ventilation of the 7812 heat sink and for ventilation of the power resistor.

Also, R16 was removed.

The components with reference designator formed by one letter (R,C) and 1 or 2 digits (1, 10) are corresponding with the components from the LTSPice schematic.

iMo · « **Reply #654 on:** October 13, 2019, 08:16:04 am »

What about 4x 3.2mm dia mounting holes?

mike_mike · « **Reply #655 on:** October 13, 2019, 08:17:41 am »

Quote from: imo on October 13, 2019, 08:16:04 am

What about 4x 3.2mm dia mounting holes?

I don't know were to put them ... I can't make the PCB larger because it will not fit into the case...

The previous PCB was installed using hot glue.

xavier60 · « **Reply #656 on:** October 13, 2019, 08:34:43 am »

It is good to test with many different operating conditions.
The space left by R16 can be used for the 1K PNP B-E resistor.
Mounting holes will work anywhere on the PCB where there is room, 3 is enough.

mike_mike · « **Reply #657 on:** October 13, 2019, 09:00:37 am »

I have added 4 mounting holes.

The PNP driver resistor (1k) is on the PCB for the transistor which is mounted on the heat sink.

I will test the power supply in different conditions and I will come back with the results.

xavier60 · « **Reply #658 on:** October 13, 2019, 09:20:02 am »

The high current tracks could be doubled up with top layer tracks.
Check that UVLO is still working properly.

mike_mike · « **Reply #659 on:** October 13, 2019, 09:23:15 am »

Regarding the high current traces, I can reinforce them with solder, if I will make the PCB at home.
How can I correctly check the UVLO ?

xavier60 · « **Reply #660 on:** October 13, 2019, 09:43:28 am »

Quote from: mike_mike on October 13, 2019, 09:23:15 am

Regarding the high current traces, I can reinforce them with solder, if I will make the PCB at home.
How can I check correctly the UVLO ?

Check that there is no rise in output voltage when the mains is switched off.
Be aware that there will be random spikes when the switch contacts arc.

mike_mike · « **Reply #661 on:** October 13, 2019, 09:58:15 am »

I checked with the oscilloscope set to AC coupling, the trigger also on the AC coupling. I used single shot trigger.

Testing method: I unplugged the transformer from the AC line.
The results are attached.

Probably there is a special method to find if the voltage is rising when I unplug the transformer, but I don't know that method.

LE: On the multimeter, the output voltage does not rise, but it slowly goes from 26.6V to 0V in about 3 seconds.

xavier60 · « **Reply #662 on:** October 13, 2019, 10:06:03 am »

That's the spiking caused by the arcing of the mains switch contacts.
You need to set your DSO to check that there is no rise in output voltage.
Slow auto sweep or chart mode and DC coupled.

" On the multimeter, the output voltage does not rise, but it slowly goes from 26.6V to 0V in about 3 seconds."
That's a good indication of no problem.

Edit: I should have said "Roll mode" instead of "chart"

mike_mike · « **Reply #663 on:** October 13, 2019, 10:19:04 am »

I set the coupling to DC, the trigger to DC coupling and single trigger and I got the following results.
I searched in the oscilloscope manual but I didn't found the terms "auto sweep" or "chart mode".

xavier60 · « **Reply #664 on:** October 13, 2019, 10:52:16 am »

The illustration on page 27 https://www.gwinstek.com/en-global/products/downloadSeriesDownNew/2694/118 shows the DSO set to AUTO mode.
Most of the common oscilloscope terms are not searchable.
You need to figure out how to set it to AUTO mode so that it will sweep continuously without needing triggering.
Set the sweep to about 500ms/div.

I would never consider buying a DSO that has the horizontal default trigger position stuck center screen. Sadly, almost all affordable DSO's have this flaw.

mike_mike · « **Reply #665 on:** October 13, 2019, 11:00:09 am »

I set it to 500ms, then I unplugged the transformer from the AC line and when I saw that the voltage starts to go down, I stopped it and I made a screenshot.
Power supply configuration was: Vout=26.6V, Iout=3A

xavier60 · « **Reply #666 on:** October 13, 2019, 11:05:23 am »

Just confirm a few times that it goes to zero with no abnormal pulses. Try with low voltage settings also.
I would expect the voltage to fall quickly at some point.

mike_mike · « **Reply #667 on:** October 13, 2019, 11:12:43 am »

1. Vout=26.6V - at some moment it goes directly to zero volts.
166
2. Vout=15V - 168 is before 167 (chronologically) - a spike is present
167-168
3. Vout=2.1V - those are chronologically - also a spike is present
169-171

xavier60 · « **Reply #668 on:** October 13, 2019, 11:16:33 am »

That's very well behaved.

mike_mike · « **Reply #669 on:** October 13, 2019, 11:26:13 am »

Are there any other things that needs testing ?
For example, it is necessary the tuning of the CC and CV loop capacitors ? Or they can remain at the 2n2 and 470p values and just make some tests at different output voltages and currents ?

mike_mike · « **Reply #670 on:** October 13, 2019, 07:11:46 pm »

I have also found a new difference between the schematic on this topic and the built schematic. The R32 (100R) resistor is not installed in the built schematic.
Does it makes such a big difference ?
Will the schematic work correctly if this resistor is not installed ?

I attached the latest built schematic.
Differences from the schematic to the real circuit:
D1, D7 = P600, 6A6
D3 = FR107

Sorry for creating any inconveniences. I know that is really strange that there are such "problems" in my circuit.

xavier60 · « **Reply #671 on:** October 13, 2019, 08:23:39 pm »

Quote from: mike_mike on October 13, 2019, 07:11:46 pm

I have also found a new difference between the schematic on this topic and the built schematic. The R32 (100R) resistor is not installed in the built schematic.
Does it makes such a big difference ?
Will the schematic work correctly if this resistor is not installed ?

I attached the latest built schematic.
Differences from the schematic to the real circuit:
D1, D7 = P600, 6A6
D3 = FR107
Sorry for creating any inconveniences. I know that is really strange that there are such "problems" in my circuit.

The diodes are fine, a 3A diode would have been enough for D7.
R32 should be fitted. It helps the power transistors turn of more quickly. I think that the transistors take longer to turn off when they are hot.
Someone else might know more about this.

mike_mike · « **Reply #672 on:** October 13, 2019, 08:27:57 pm »

Should I install R32 (100R) and start testing again ? If yes, then which tests need to be made again ?

xavier60 · « **Reply #673 on:** October 13, 2019, 08:58:38 pm »

Quote from: mike_mike on October 13, 2019, 08:27:57 pm

Should I install R32 (100R) and start testing again ? If yes, then which tests need to be made again ?

Definitely fit R32, having B-E bleed resistors is good design practice.
You should test the voltage overshoot while unloading from a 3A normal load, before and after R32 is fitted.

mike_mike · « **Reply #674 on:** October 13, 2019, 09:02:14 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 ?


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Author Topic: LM324 Power Supply with variable voltage and current (Read 198018 times)

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