Author Topic: LM324 Power Supply with variable voltage and current (Read 204963 times)

mike_mike · « **Reply #625 on:** October 12, 2019, 11:17:32 am »

I have a problem, again. I forgot to replace the B-E resistor at the PNP driver transistor.
Sorry for any inconvenience...
The results with 3k3 resistor replaced by 1k:
On the R_Shunt: 110-111
with the ground clip of the probe to the left hand side of the R_ Shunt:
B of Q1: 106
E of Q1: 107
with the ground clip of the probe to the right hand of the R_ Shunt
B of Q1: 109
E of Q1: 108
The above tests were made at 26.6V output and 3A output, shorting the output using the PSU Shorter.

With a 150R load resistor at 15V on the output of the power supply:
V on the 5.6V Zener = 5.57V
V on the R25 = 1.42V

xavier60 · « **Reply #626 on:** October 12, 2019, 11:31:42 am »

That's under 10 amps. It can stay that way.
Read my edit in Reply #624 about using the correct ground reference.
What is the reason for the disturbance in DS0099.jpg and DS0111.jpg, 2.5ms after the current spike?

mike_mike · « **Reply #627 on:** October 12, 2019, 11:44:55 am »

Quote from: xavier60 on October 12, 2019, 11:31:42 am

What is the reason for the disturbance in DS0099.jpg and DS0111.jpg, 2.5ms after the current spike?

I searched on the output of the NE555 and in the C of the BC337 (the NPN transistor from the PSU Shorter) and I did not found that disturbance. So it could be from other source. I don't know which source.

xavier60 · « **Reply #628 on:** October 12, 2019, 11:51:12 am »

Quote from: mike_mike on October 12, 2019, 11:44:55 am

Quote from: xavier60 on October 12, 2019, 11:31:42 am
What is the reason for the disturbance in DS0099.jpg and DS0111.jpg, 2.5ms after the current spike?
I searched on the output of the NE555 and in the C of the BC337 (the NPN transistor from the PSU Shorter) and I did not found that disturbance. So it could be from other source. I don't know which source.

If you want to, do some test at other voltage and current settings and with some resistance in series with the Shorter.

mike_mike · « **Reply #629 on:** October 12, 2019, 12:00:12 pm »

Vo=26.6V, Io=2.5A, Rl=1 $\$\Omega\$$ : 112-114
Vo=14.5V, Io=1.66A, Rl=1 $\$\Omega\$$ : 115,116

The probe was connected on the R_Shunt.

xavier60 · « **Reply #630 on:** October 12, 2019, 12:07:37 pm »

Is there activity in the warning LED circuit that occurs about 2.25ms after the current spike?

xavier60 · « **Reply #631 on:** October 12, 2019, 12:17:59 pm »

Double the Shorter's ON time to see how it affects the position of the disturbance.

mike_mike · « **Reply #632 on:** October 12, 2019, 12:33:08 pm »

New PSU_Shorter configuration in screenshot.
The results are attached.

xavier60 · « **Reply #633 on:** October 12, 2019, 12:42:22 pm »

The disturbance stays about 700µs before the Shorter turns off. The cause must be at the Shorter.
It's good that it isn't a fault of the power supply.

mike_mike · « **Reply #634 on:** October 12, 2019, 02:23:23 pm »

Should I test again with the PSU Shorter and different load resistors to see if there are oscillations ?

Will the PSU Shorter remain, during the tests, at the reply #632 configuration ?

iMo · « **Reply #635 on:** October 12, 2019, 04:54:24 pm »

It could be the disturbance indicates the end of the shorter pulse (mosfet gets OFF)..
Thus it could come from the PSU..
Show both PSU (ch1) and shorter mosfet's base (ch2) signals (in a single scope picture)..

mike_mike · « **Reply #636 on:** October 12, 2019, 05:15:08 pm »

Here are the results.
I inverted the CH1 because I used the GND of the PSU Shorter as GND for these measurements which was connected to the power supply GND.
CH1: R_Shunt (the left side of R_Shunt, during on the right side was the GND clip).
CH2: Mosfet Gate

xavier60 · « **Reply #637 on:** October 12, 2019, 05:51:36 pm »

The disturbance occurs when the MOSFET turns off, The extra 700µs of current flow would be the charging of the output capacitor back to regulation voltage. This can be confirmed by looking at the output with CH2.
You can leave the Shorter configured as is.
You next can check to see how the current settles with milder overloads applied. Set the time base to see what the current does a few hundred µs
after the overload starts.

mike_mike · « **Reply #638 on:** October 12, 2019, 06:05:32 pm »

Can you please explain what is the meaning of "milder overloads" and the "current settles" ?

I guess milder overloads mean overloads less than 3A, for examle 1.5A. So I need to set the maximum output voltage to 1A, then I need to apply a 1.5A load and see how the current settles ?

xavier60 · « **Reply #639 on:** October 12, 2019, 06:28:19 pm »

Quote from: mike_mike on October 12, 2019, 06:05:32 pm

Can you please explain what is the meaning of "milder overloads" and the "current settles" ?

I guess milder overloads mean overloads less than 3A, for examle 1.5A. So I need to set the maximum output voltage to 1A, then I need to apply a 1.5A load and see how the current settles ?

Yes, like that with the initial current about double the set current or what ever you decide to test at. The amount of overload can be varied just by changing the voltage and current settings.
No need to show all of the results, just a few.

mike_mike · « **Reply #640 on:** October 12, 2019, 06:52:29 pm »

With the oscilloscope probe on the R_Shunt:
1. Vout=20V, Ilim=1A, Rl=0R
131,132.jpg
2. Vout=10V, Ilim=2A, Rl=0R
133
3. Vout=15V, Ilim=1A, Rl=1R
136,137
4. Vout=5V, Ilim=2A, Rl=1R
138,139
5. Vout=26.6V, Ilim=1A, Rl=10R
140,141.jpg

xavier60 · « **Reply #641 on:** October 12, 2019, 07:20:37 pm »

That all looks well behaved. The settling time has a time constant of about 10µs. I don't really know what is optimum.
So far I have not encountered a load that has made a power supply's CC loop become unstable.
My power supply is currently set to 60µs
You could increase R9 to 22K.
we only need to see 500µs of activity after the start of the overload.
I notice that your default trigger position is always in the center of the screen wasting a lot of screen width. My HP DSO has settings that all the default trigger position to be set to the LH side of the screen.

mike_mike · « **Reply #642 on:** October 12, 2019, 08:08:35 pm »

New results, using R9=22k. The probe was connected on the R_Shunt resistor.
1. Vout=26.6V, Iout=1A, Rl=10R: 143
2. Vout=15V, Iout=1A, Rl=10R: 144
3. Vout=3.6V, Iout=1A, Rl=1R: 145,146
4. Vout=26.6V, Iout=3A, Rl=1R: 147-149

I tried to show on the screenshots the entire activity were I think that it is necessary.

Regarding the trigger level, I don't know for sure were is the optimal level.

xavier60 · « **Reply #643 on:** October 12, 2019, 09:18:03 pm »

That all looks really good. The brief time that the current is allowed overshoot before smoothly settling to the set current is actually a preferred response.
Don't expect it to not destroy LEDs. This should not be a requirement of a good bench supply and I don't expect it.
DS0146.jpg is a good example of where the overshoot has just caused the speed up diode to act.
The only other test I can think of is to again check the voltage recovery after an overload.

mike_mike · « **Reply #644 on:** October 13, 2019, 06:46:12 am »

Please find attached the results with Vout=26.6V, Ilim=2A, Rload=10R, the probe connected on the output of the power supply.

xavier60 · « **Reply #645 on:** October 13, 2019, 06:53:45 am »

The load transient response is still good.
I would like to see that the voltage recovery after a short circuit overload is still good also.

mike_mike · « **Reply #646 on:** October 13, 2019, 07:06:19 am »

Voltage recovery after a short circuit:
Vout=26.6V
Iout=3A
Rload=0R

xavier60 · « **Reply #647 on:** October 13, 2019, 07:14:01 am »

It doesn't get any better than that.
There is likely to be some overshoot when unloading from a normal load. This is difficult to avoid. A permanent load resistor usually helps.

mike_mike · « **Reply #648 on:** October 13, 2019, 07:18:13 am »

I already installed a 1k/5W resistor on the output. This was installed from the last built configuration of the power supply...

xavier60 · « **Reply #649 on:** October 13, 2019, 07:38:02 am »

Quote from: mike_mike on October 13, 2019, 07:18:13 am

I already installed a 1k/5W resistor on the output. This was installed from the last built configuration of the power supply...

If the resistor is wired across the output terminals, its current will be sensed by the shunt resistor, not a serious problem.
This can be avoided by connecting the bottom end of the resistor to the LH side of the shunt.


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Author Topic: LM324 Power Supply with variable voltage and current (Read 204963 times)

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