Author Topic: LM324 Power Supply with variable voltage and current (Read 205045 times)

mike_mike · « **Reply #325 on:** May 12, 2019, 03:19:35 pm »

1. I am attaching the modified simulation file. Please have a look and tell me if it is correct.
2. It LM358 a alternative for LM324 in this design ?

iMo · « **Reply #326 on:** May 12, 2019, 03:32:12 pm »

The CC LED in V13 is ok.
Also do change the version number in the schematics plz.

Quote

2. It LM358 a alternative for LM324 in this design ?

Replace the LM324 with the LM358 in your simulation and you will see.

mike_mike · « **Reply #327 on:** May 12, 2019, 03:37:35 pm »

I fixed the version number.
The CC led should be red, or it can also be another color, for example amber or blue (I know that those led's have different dropout voltage)...

iMo · « **Reply #328 on:** May 12, 2019, 03:46:19 pm »

CC LED could be any modern high lumi LED any color.
The D8 - look at my simulations of the undervoltage lock with Blue and Red leds and take the one which does suite you better.

xavier60 · « **Reply #329 on:** May 12, 2019, 10:56:02 pm »

The UVLO should work without D8 and R16.
When the control rail gets down to 5V, the Emitter of Q1 will also be 5V. At this point it is not possible for Q1 to be turned on because only 5V is available to the whole control circuit.
R1 can be higher like 10K.

xavier60 · « **Reply #330 on:** May 13, 2019, 02:28:12 am »

This illustrates the diode clamp idea that limits drive current while allowing a lower value for R29.

Edit: corrected D9

mike_mike · « **Reply #331 on:** May 13, 2019, 11:37:57 am »

I managed to built the circuit. The built schematic is attached (.asc file).
I did not used the buffer, as you said that it could be removed.
I made some tests, with a red led (normal red led, not low current, because I did not found any low current led at the local shop), and with the 10k resistor it does not light up sufficiently.
I used 2x6800uF because I had them from an old project. If necessary I could use another capacitors.

The schematic is functional, I just tested it with a load at 25.5V and at about 19V and it seems to work.
Also the red led lights up when a short circuit is produced on the output. I also tested the variable current limit and it works.

I will test it with the PSU Shorter, but first I need to know what resistors and capacitor do I need to use for LM555 in order to generate the pulse as it needs to be ? Initially it was 220k/4k7/330nF.

mike_mike · « **Reply #332 on:** May 13, 2019, 01:47:47 pm »

I tested the power supply using the PSU Shorter and 0 ohms load resistor. The schematic is the one from reply #331.
I see some ringing on the output of the power supply, at low output voltages.
1. V out = 1.08V, Iout=3.01A
0810.jpg
2. V out = 1.08V, Iout= 1.5A
0811,0812
3. V out = 4.17V, Iout=3.01A
0814,0815
4. V out = 10.84V, Iout=3.01A
0816,0817
5. V out = 10.84V, Iout=1.5A
0820
6. V out = 25.6V, Iout=3.01A
0822.jpg

Please have a look at the attached screenshots and tell me what you think.

xavier60 · « **Reply #333 on:** May 13, 2019, 02:04:36 pm »

The ringing could just be wire inductance resonating with the MOSFET's output capacitance.
See if the ringing is larger at the MOSFET.
I can't open ASC files here. I don't know what the schematic is.
Load transient tests will give us an idea about how well it's compensated.

iMo · « **Reply #334 on:** May 13, 2019, 02:04:50 pm »

C4=4n7 to 6n2 may lower the small overshoot/ringing at the rising edge of the Vout.

mike_mike · « **Reply #335 on:** May 13, 2019, 02:24:36 pm »

With C4=4n7
Vout=1.08V, I=3.01A
0824-0826
Vout=1.08V, I=1.5A
0827-0830
Vout=4.64V, I=3.01A
0831-0833
Closer to the mosfet
0834-0836

Please have a look at the attached screenshots and tell me what you think.

iMo · « **Reply #336 on:** May 13, 2019, 03:18:06 pm »

..and with C5=4n7 (CC comp) ringing should disappear (sim).

mike_mike · « **Reply #337 on:** May 13, 2019, 04:00:15 pm »

I tried with C5=4n7 and C4=4n7, but the ringing did not disappeared.
1. V out=4.64V, I=3.01A
0837-0838
2. V out=1.21V, I=3.01A
0839-0840

Please have a look at the attached screenshots and tell me what you think.

Kleinstein · « **Reply #338 on:** May 13, 2019, 04:20:13 pm »

It looks like there is still some ringing when going from CC to CV mode. I am not sure if this is the phase where the CC mode is still not all the way off, or more the phase where the current through the output stage is already very low. Both cases are a little difficult for the regulator.

One possible point to try would be a slightly slower current regulation (C6 larger). Another point to play with is R32 (possibly a little smaller).

There are a few effects than can make the real circuit to behave a little different than the simulation. Such things are the ESR of some caps, parasitic inductance of the shunt resistor and wiring inductance. Also transistors may be a little different from the models.

Looking at the output of the two regulating OP may give an hint to which loop is oscillating - at least it could show if both loops are active together.

iMo · « **Reply #339 on:** May 13, 2019, 04:25:05 pm »

What is your load (exactly)?

Look at the shunt next time - there you can observe the ringing better..

mike_mike · « **Reply #340 on:** May 13, 2019, 04:36:16 pm »

The output of the Op Amps looks like:
V out=1.21V, I=3.01A
1. CV op amp output 842-845
2. CC op amp output 846-850.jpg

Photos with the load:
https://imgur.com/a/PIfz20x

Later Edit: on the shunt 852-855 (Vout=1.21V, Iout=3.01A).

xavier60 · « **Reply #341 on:** May 13, 2019, 05:05:54 pm »

The CV loop should be tested separately with various static and pulsed loads without allowing the current limiting to act.
I don't know what the present design details are.

iMo · « **Reply #342 on:** May 13, 2019, 05:24:00 pm »

You are pretty fast with making pcbs

The proper pcb layout is also important with this kind of HW, maybe it should be discussed later on.

Add a ceramic 10n-100n at the output (parallel to the 47u). I would suggest the 1uF is a 50V ceramic.
Not sure the 1uF foil there is optimal.

I do not see ringing with 1.2V/3A in sim.

The R32 from 50-100ohm does not matter, below 50ohm it reduces output current.

The load - I've been asking whether the load in V14 is similar to your LOAD (the 1uF cap and Rload1=0, Rload2=100ohm).

xavier60 · « **Reply #343 on:** May 13, 2019, 05:30:47 pm »

The main current path area appears large and I don't think there is a bypass capacitor on the power input.

iMo · « **Reply #344 on:** May 13, 2019, 05:32:12 pm »

Quote from: xavier60 on May 13, 2019, 05:05:54 pm

The CV loop should be tested separately with various static and pulsed loads without allowing the current limiting to act.
I don't know what the present design details are.

@MM: set the CC to 3A limit and make tests with lower output currents than the CC limit, for example 1-2A, look at the shunt and Vout.

Also could you set your o'scope picture such the "gnd" is somehow aligned with the grid?

mike_mike · « **Reply #345 on:** May 13, 2019, 07:47:51 pm »

New tests with Imax set to 3A and output voltage set to 1.21V. As load I used an 1R resistor and no capacitor.
1. With C6 and a parallel 100nF to the 47uF:
a. on the output 0857-0859
b. on the shunt 0860-0864

2. Without C6 and a parallel 100nF to the 47uF:
a. on the output 0866-0868, 0874-0875
b. on the shunt 0869-0872, 0876

Please also find attached the schematic for the PSU Shorter.

iMo · « **Reply #346 on:** May 13, 2019, 08:21:40 pm »

I think the ringing above comes from some parasitics (5-6us period).
Considering 1.2V/1.2A setting it looks to me "normal".

mike_mike · « **Reply #347 on:** May 13, 2019, 08:52:33 pm »

Good, I will continue the tests tomorrow.

xavier60 · « **Reply #348 on:** May 13, 2019, 09:48:04 pm »

Without seeing the schematic, I don't know which suggestions have been ignored, Has R4 or C4 been removed?
There could be just too much gain in the CV loop.

mike_mike · « **Reply #349 on:** May 14, 2019, 05:19:31 am »

Please find attached the latest schematic.


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