LM324 Power Supply with variable voltage and current

[mike_mike]

I finally ordered some electronic components and I also ordered D45H11 PNP transistor.
I think that I will receive the products on tuesday or wednesday and then I should be ready to do some tests with the new PNP driver transistor.
What tests do I need to make ? The same as before ? Testing at different loads and different output voltages, and also testing on the current limit resistor ?

[xavier60]

I finally ordered some electronic components and I also ordered D45H11 PNP transistor.
I think that I will receive the products on tuesday or wednesday and then I should be ready to do some tests with the new PNP driver transistor.
What tests do I need to make ? The same as before ? Testing at different loads and different output voltages, and also testing on the current limit resistor ?

Mainly the load transient tests at various currents to check the stability. If it doesn't look right, the CV compensation will need to be altered.

[mike_mike]

One more question before testing: should I use my 20MHz scope (Owon SDS 1022) or my 100MHz scope (GW Instek GDS1102B) ?

[xavier60]

One more question before testing: should I use my 20MHz scope (Owon SDS 1022) or my 100MHz scope (GW Instek GDS1102B) ?

It doesn't matter at all. My DSO is 100MHz which I set the bandwidth limit on to 20MHz which just reduces a bit of noise sometimes, not that important.
Use the one that gives the most easiest to understand upload images where the settings can be clearly seen.

[mike_mike]

I am back with the results.
I verified at 32V output, 11R load.
Yellow trace = output of the psu
Blue trace = output of the NE555.

[xavier60]

To me it looks like the CV compensating capacitor can be a lower value to allow faster response although it's fine the way it is.

[mike_mike]

If it is fine, then I will leave the 1nF (CV) compensating capacitor unchanged, if it is possible.
I made further testing and I want to share some of the results.
1. Vout = 15V, Iout=3A, Rload=4.7R

2. Vout=15V, Iout=3A, Rload=10R

[mike_mike]

... and a few more tests. Please have a look and tell me what you think.
1. Vout= 4.8V, Iout=3A, Rl=12 ohm: 0015, 0016
2. Vout=13V, Iout=3A, Rl=4.7 ohm: 0010
3. Vout=13.2V, Iout=1.5A, Rl=10 ohm: 0021
4. Vout= 14.79V, Iout=1.5A, Rl=10 ohm: 0022
5. Vout=3.23V, Iout=almost zero A, Rl=27R: 0029
6. Vout=3.23V, Iout=almost zero A, Rl=10R: 0032, 0033 (0033 is with BW limit enabled for CH1)

The yellow trace shows the output of the psu and the blue trace shows the output of the NE555.

[mike_mike]

I also tested with the probe on the R_Shunt
1. Vout=32V, Iout=3A: 0054
2. Vout=16V, Iout=1.5A: 0052
3. Vout=about 5V, Iout=~0.5A: 0050
4. The following waveform appear on the R_Shunt resistor, when I make zoom in: 0058,0057

Please have a look and tell me what you think.

LE: I made all the tests with BW limit enabled (20MHz).

[xavier60]

Except for the crosstalk, it all looks as expected. If CH2 is the output of the 555, why is it inverted?

[mike_mike]

The signal coming from output of NE555 (pin 3) was always like this.
Please find attached the schematic of the PSU load switch. It is possible that R7 to be different value but I want to share the schematic in order to see why the CH2 is inverted.
Also, why on the 0057 and 0058 screenshots I see that signal ? (marked with red arrows)
Do you have any explanation for the crosstalk ?

[xavier60]

I see, I had forgotten about Q3 between the 555 and Gate.
Try disconnecting the probe ground lead of CH2.
It will make CH2 waveform look worse but CH1 should be more accurate.

[mike_mike]

I am using a single ground clip, which is connected at the output of the psu. CH2 does not have any ground clip.
When I tested, the ground clip was connected at the psu output gnd, and the CH1 probe at the left pin of the R_shunt.
Should I try by connecting the ground clip right on the pin of R_Shunt ?

[xavier60]

I am using a single ground clip, which is connected at the output of the psu. CH2 does not have any ground clip.
When I tested, the ground clip was connected at the psu output gnd, and the CH1 probe at the left pin of the R_shunt.
Should I try by connecting the ground clip right on the pin of R_Shunt ?

The spike that the 2nd red arrow points to is expected, it's what the first arrow points to that I don't understand. It might even be normal.
Try disconnecting CH2 probe totally and trigger from CH1. No need to show us if it looks the same as before.
Don't change anything else.

[mike_mike]

It doesn't look exactly the same as before. The first spike is somehow bigger in comparison to the first screenshot.
Please have a look at the screenshots and tell me what you think.

I triggered on the CH1, and I disconnected CH2. The points were I connected the probe were the same as before.
If I move the GND clip right to the other end of R_Shunt, then the waveform does not change, it is the same as 0059 and 0060 screenshots.

LE: Also, I think that the first spike was also present in the previous tests that I made using the Owon oscilloscope. Please have a look there: https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3587377/#msg3587377

[xavier60]

I suspect that the first spike is being caused by the output transistors being briefly turned on by their own Miller capacitance during the rapid fall of the output voltage. This is happening before the opamp is reacting which is the 2nd spike.
So this would just be normal behavior of the design.

[xavier60]

It doesn't look exactly the same as before. The first spike is somehow bigger in comparison to the first screenshot.
Please have a look at the screenshots and tell me what you think.

Notice that there is also less positive pre-shoot, likely due to different probe usage. A lot of things can affect the way DSO's display fast signals.

[mike_mike]

Are there any other tests that I should make ?
I would like to install the psu into a new case which I think that looks better than the wooden one, if it is possible.

[xavier60]

Noting too important at this stage. Go ahead and install it.

[mike_mike]

Ok. I will specify that when installing the new case, I will use one older PCB for the main psu PCB. The difference between the older PCB and the one that I used for tests, is the position of the connectors for the voltage and current pots. Also, in the new case I will install the tap changer and a circuit that controls 2 fans which will cool the heat sink. I will use a toroidal transformer which has 150VA-200VA power and it is modified by me to have a 30Vac secondary with 17Vac median socket. After the modification I insulated the entire transformer using some electrical tape (this is what I had at that moment) which I don't know if it is good or not for using on transformers.

The older layout: https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3583296/#msg3583296 the 10M resistor from pin 2 of LM358 to the K of TL431 is now shown on the layout but it is connected in the practical circuit, also the 1k resistor between the Base and Col pads is not connected (I marked it as DNP - do not place), because I mounted it on the heat sink transistors.

[xavier60]

Ok. I will specify that when installing the new case, I will use one older PCB for the main psu PCB. The difference between the older PCB and the one that I used for tests, is the position of the connectors for the voltage and current pots. Also, in the new case I will install the tap changer and a circuit that controls 2 fans which will cool the heat sink. I will use a toroidal transformer which has 150VA-200VA power and it is modified by me to have a 30Vac secondary with 17Vac median socket. After the modification I insulated the entire transformer using some electrical tape (this is what I had at that moment) which I don't know if it is good or not for using on transformers.

The older layout: https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3583296/#msg3583296 the 10M resistor from pin 2 of LM358 to the K of TL431 is now shown on the layout but it is connected in the practical circuit, also the 1k resistor between the Base and Col pads is not connected (I marked it as DNP - do not place), because I mounted it on the heat sink transistors.

I guess snugly wrapped PVC tape should not be a hazard on the outside of the transformer. I would like to see rubber washers used.
The insulation between primary and secondary is still original?

[mike_mike]

Yes, the insulation between primary and secondary is still original.
Also, I used rubber washers when I mounted the transformer into the case.

[mike_mike]

Please find attached some photos of the practical PSU.
It is not finished yet.
I have to install 2 80x80 mm fans on the heat sink and a 9V power supply for the fans. The fans will be 12V fans, but I will power them at 9V (for less audible noise).
The red switch is for turning the psu on/off, the switch with on/off markings is for DC on/off. The first led (from top to bottom) is for AC on, the second and 3rd led's are the led's from the schematic and the last led is from the tap changer circuit.

[mike_mike]

Please find attached the photos with the fans and 9V power supply added.

Please have a look and tell me what you think.

[xavier60]

That looks like very effective cooling.
Good to see 3 power transistors. It helps compensates for the thermal resistance added by the insulating washers.
What are the washers?