LM324 Power Supply with variable voltage and current

[mike_mike]

I tried a LM358N from STMicroelectronics and I found that now the current goes down to zero. Previously, I used LM358P from Texas Instruments.

Which test should I make now ? Should I reduce the output current to 1.3A and test again ?

[xavier60]

I tried a LM358N from STMicroelectronics and I found that now the current goes down to zero. Previously, I used LM358P from Texas Instruments.

Which test should I make now ? Should I reduce the output current to 1.3A and test again ?

You can do some load transient recover test to make sure it's still stable which it should be.
No need to show the traces unless something looks wrong.
Mine dips 200mV with a 1A load with about 8uS recovery.

[mike_mike]

I made some tests.
1. Vout=12V, Iout max =1.3A
Rload=20R 103_010, 103_011, 103_012

2. Vout=12V, Iout max = 1.3A
Rload=5R 103_016, 103_017

3. Vout=12V, Iout max=0.2A
Rload=10R 103_37, 103_38

4. Vout=2V, Iout max = 1.3A
Rload = 5R, 103_007 to 103_009

I tested at 1.3A and 0.2A, at 2V, 12V and 30V - a total of 18 tests.

[xavier60]

Some show an under damped response make R5 3.3K and C3 1000pF which might be a little high.

[mike_mike]

Sorry for the late response...
Please find the screenshots at:
https://ibb.co/k9Z6mHS
https://ibb.co/PC52NjF
https://ibb.co/YtZfMJL
https://ibb.co/cF6CKGL
https://ibb.co/KLZSSgH
https://ibb.co/dmJKLJY
https://ibb.co/XSqjpk4
https://ibb.co/sQ1hFHk
https://ibb.co/DCT5m06
https://ibb.co/znNPkWx
https://ibb.co/BG50Pfg
https://ibb.co/vLWGmvj
https://ibb.co/0yL09K1
https://ibb.co/LhNLxcw
https://ibb.co/rxNj2yr
https://ibb.co/LCNGZLm
https://ibb.co/C5zNdNt
https://ibb.co/ZYHxMcX
https://ibb.co/tp0FQs0
https://ibb.co/ZJWPMBM
https://ibb.co/7JYpCLX
https://ibb.co/K91CLgY
https://ibb.co/6gTwGFL


R5 = 3.3K and C3 = 1nF
1. Vout=12V, Iout max =1.3A
Rload=20R 104_0,1,2

2. Vout=12V, Iout max = 1.3A - the red led was flashing
Rload=5R 104_3,4,5

3. Vout=12V, Iout max=0.2A - the red led was flashing
Rload=10R 104_6,7,8,9

4. Vout=2V, Iout max = 1.3A
Rload = 5R, 104_10,11,12,13

5. Vout=30V, Iout max = 1.3A
Rload = 20R, 104_19,20,21,22

6. Vout = 2V, Ioutmax = 1.3A
Rload = 20R 104_14,15,16,17

[xavier60]

The response is now what it should be, no sign of any damped oscillations.
Some of the tests show it going into CC mode. Was this intended?
How long are the wires to the sziklai output transistors.

[mike_mike]

The response is now what it should be, no sign of any damped oscillations.
Some of the tests show it going into CC mode. Was this intended?
How long are the wires to the sziklai output transistors.

Yes, it was intended going into CC mode.
The wires to the sziklai output transistors are about 15cm long.

[xavier60]

The response is now what it should be, no sign of any damped oscillations.
Some of the tests show it going into CC mode. Was this intended?
How long are the wires to the sziklai output transistors.

Yes, it was intended going into CC mode.
The wires to the sziklai output transistors are about 15cm long.

There is some chance that the wire length and also R11 being at the wrong end that has caused to need for different CV compensation.
But no need to worry, it's fine the way it is.

[mike_mike]

Does the PSU require any more testing ?
For example, the CC compensation is OK ?

[xavier60]

Does the PSU require any more testing ?
For example, the CC compensation is OK ?

No, all looks fine.

[mike_mike]

That's good then. Thank you for your help.
One more question: does D8 (1N4004) act as a protection diode for the PSU, when powering inductive loads ? I am asking this because I am planning to power motors, for example the PCB drill, using this PSU...

[mike_mike]

I read a few messages from your topic, especially this one: https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2133628/#msg2133628
I found that the PSU goes into CC mode if there is connected a reverse polarity on the output, but the PSU is also protected for reverse polarity generated by the inductive loads (such as motors) ?

[xavier60]

I read a few messages from your topic, especially this one: https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2133628/#msg2133628
I found that the PSU goes into CC mode if there is connected a reverse polarity on the output, but the PSU is also protected for reverse polarity generated by the inductive loads (such as motors) ?

It will tolerate briefly applied reverse polarity. D8 and the PTC R34 protect the preload circuit. If the PSU is to be used in series with another PSU, an 1N5408 or similar should be fitted between the output binding posts.
I did see the discussion but I still don't understand how a DC motor can cause damage.

Extra: I have used my PSU to test small automotive motors like seat motor. Nothing bad happened. I had the 1N4508 across the output at the time.

[mike_mike]

Extra: I have used my PSU to test small automotive motors like seat motor. Nothing bad happened. I had the 1N4508 across the output at the time.

1N4508 is a 22A diode, do you mean 1N5408 ?
If using an 1N5408 or P600J across the output, does the PSU require any further testing or modifications ?

[xavier60]

Extra: I have used my PSU to test small automotive motors like seat motor. Nothing bad happened. I had the 1N4508 across the output at the time.

1N4508 is a 22A diode, do you mean 1N5408 ?
If using an 1N5408 or P600J across the output, does the PSU require any further testing or modifications ?

Yes, I meant "1N5408".
The PSU would not even know that the diode is there if the polarity is correct. No testing needed.

[mike_mike]

I added the diode to my schematic (D11).
Please have a look and tell me if the connection of the diode is correct ?

[xavier60]

I added the diode to my schematic (D11).
Please have a look and tell me if the connection of the diode is correct ?

Yes, that's correct.
What is the part number of C2?

[mike_mike]

C2 is a electrolytic 47uF/63V capacitor made by Samxon, 105*C, KM(M), C9A.

Edit: part number is KM 47U/63V.

Edit 2:I found that I run out of TIP35C transistors, and I wanted to build the PSU into a case, using a different type of heatsink for the power transistors. What other type of power transistors can be used for this PSU, in order to maintain its stability and performance ? I have TIP3055 and 2N3055. Can one of those 2 transistor part number be safely used for the PSU ?

[xavier60]

C2 is a electrolytic 47uF/63V capacitor made by Samxon, 105*C, KM(M), C9A.

Edit: part number is KM 47U/63V.

Edit 2:I found that I run out of TIP35C transistors, and I wanted to build the PSU into a case, using a different type of heatsink for the power transistors. What other type of power transistors can be used for this PSU, in order to maintain its stability and performance ? I have TIP3055 and 2N3055. Can one of those 2 transistor part number be safely used for the PSU ?

Either of those 2 transistor types should be stable. Can you temporarily try them before you make the case?
With long leads, there might be an advantage having R11 directly across B-E of the driver transistor. What is the driver transistor?
 Check the current sharing  by measuring the voltage drop across the Emitter resistors. The batch of TIP35C transistors I bought were very well matched, requiring only 0.05Ω resistors.

I can't say much about the safety. There are too many unknown variables and difficult calculations.

[mike_mike]

My driver transistor is an BD244CG from On Semiconductor. I used 2x 0.1R/5W current sharing resistors for the 2 NPN power transistors. One 0.1R resistor for each transistor. R11 is close to the driver transistor (2 cm away).
I'll try the 2N3055, should I test as usual, for example at 1A load ?

[xavier60]

My driver transistor is an BD244CG from On Semiconductor. I used 2x 0.1R/5W current sharing resistors for the 2 NPN power transistors. One 0.1R resistor for each transistor. R11 is close to the driver transistor (2 cm away).
I'll try the 2N3055, should I test as usual, for example at 1A load ?

That sounds fine. The BD244CG is a slower transistor than the DH4511 which might also explain the different compensation.
It doesn't matter so long as the PSU is stable.
Test at 1A for a smooth response like shown, https://ibb.co/PC52NjF

[mike_mike]

I will test the PSU and I will come back later with the results.

[mike_mike]

Using 2x2N3055:
1. Vout = 20V, Imax = 2.6A, Rload=20R
15_000, 15_001
2. Vout=10V, Imax = 2.6A, Rload=10R
15_002, 15_003

[xavier60]

That is a good response. Looking back at your previous design, the equivalent compensation is the same. Its compensation resistor is 3 times larger at 10K but this is offset by Q1's Emitter resistor being about 3 times larger, 2.7K instead of 1K. So it all works out to being the same loop gain.

[mike_mike]

That's good then.
Are there any other tests that I should make ?