Author Topic: LM324 Power Supply with variable voltage and current (Read 154535 times)

mike_mike · « **Reply #950 on:** October 04, 2021, 03:21:19 pm »

Hello @xavier60, I am working at the PSU's case, and I have a question about the red (CC) and green (CV) led's. Both led's have a 10k resistor in series (R30 and R31), and the led's are powered from 8V rail. This means that the current is very small, it is possible to increase the current that goes through these 2 led's ?

xavier60 · « **Reply #951 on:** October 04, 2021, 05:47:04 pm »

Yes, the LM358 should be able to easily sink 5mA or more per output.
Lastly, check for any output voltage rise during mains power down.

mike_mike · « **Reply #952 on:** October 04, 2021, 07:21:45 pm »

I replaced the 10k resistors with 2k2 resistors and the red and green led's with regular led's.
I made a few quick tests, without any load at the output of the PSU, first test with maximum output voltage and the second with about half output voltage.
Please find attached the screenshots from the oscilloscope.

It's the right way I tested ?

165_002 power on
165_003 power off
165_004 power off
165_005 power on

xavier60 · « **Reply #953 on:** October 05, 2021, 07:51:16 am »

That looks good.
I have some 10 turn pots with plastic shafts branded "Bourns" They did go scratchy but none have had broken resistance wire yet.
When that happens, the PSU's output will jump from zero to full voltage as the pot is turned up.

mike_mike · « **Reply #954 on:** October 05, 2021, 08:03:50 am »

For voltage I have a normal single turn pot, but for current I have a 10 turns pot from SR Passives.
Do you suggest adding some extra components in order to protect the load if the pot resistance broke ?

xavier60 · « **Reply #955 on:** October 05, 2021, 09:02:42 am »

Quote from: mike_mike on October 05, 2021, 08:03:50 am

For voltage I have a normal single turn pot, but for current I have a 10 turns pot from SR Passives.
Do you suggest adding some extra components in order to protect the load if the pot resistance broke ?

The single turn pot sounds much safer for the CV. There is no simple way to protect against broken wire.
If the CC pot fails, it likely wont be as instantly destructive to the load because most of the time the PSU will be operating in CV mode.
But you might not know for a while that the CC pot has failed causing the setting to be your maximum 3A.

Kleinstein · « **Reply #956 on:** October 05, 2021, 09:52:17 am »

The way the setting is done (at the set voltage side) there should be mot bis problem adding a high value pull down resistors. This would trun down the set voltage or current in case of a open wiper. This would make the scale a bit nonlinear.

Using single turn or multi turn pots has pro and cons. A single pot for the setting can be a bit coarse and difficult to set low values. A multi turn pot is slow to change over the full range. The version with separate fine an coarse adjust can be tricky with wiper failure.

For the current one could consider a simple toogle switch to choose a upper / lower range (e.g. 1/10 of max).
I currently have a single pot, and it is not really satisfactory to set low voltages (like 5 V or 3.3 V).
Still multiple ranges make the scale more complicated. Still a smaller range of maybe 1/5 can be an option, I currently consider for my supply.

mike_mike · « **Reply #957 on:** October 06, 2021, 07:49:14 am »

Can I continue with the construction of the PSU case ? Are necesary any other modfications ?

xavier60 · « **Reply #958 on:** October 06, 2021, 07:51:18 am »

Quote from: mike_mike on October 06, 2021, 07:49:14 am

Can I continue with the construction of the PSU case ? Are necesary any other modfications ?

It will be fine,

bingo600 · « **Reply #959 on:** October 13, 2021, 05:16:20 pm »

I have been looking a bit on these pages , but can't seem to locate the "Final Schematic".

Is there any pointers to that ?

Does it have a PCB layout or ?

TIA

/Bingo

xavier60 · « **Reply #960 on:** October 13, 2021, 08:57:05 pm »

Quote from: bingo600 on October 13, 2021, 05:16:20 pm

I have been looking a bit on these pages , but can't seem to locate the "Final Schematic".

Is there any pointers to that ?

Does it have a PCB layout or ?

TIA

/Bingo

On this page are schematics of the simple and full versions. And including the following page, PCB screen dumps.
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/725/
Let us know what you plan to do in case improvements can be suggested.
A few pages on, a transformer tap changer is developed.

mike_mike · « **Reply #961 on:** November 28, 2021, 06:52:00 pm »

Hello, I am coming with news about the PSU.
Finally I managed to install it into a case. Please have a look at the photos.

https://ibb.co/mGdJ6X2
https://ibb.co/x3VNsx4
https://ibb.co/T2hn1cs
https://ibb.co/v32sg24

not1xor1 · « **Reply #962 on:** November 29, 2021, 06:02:10 am »

Quote from: mike_mike on November 28, 2021, 06:52:00 pm

Hello, I am coming with news about the PSU.
Finally I managed to install it into a case. Please have a look at the photos.

https://ibb.co/mGdJ6X2
https://ibb.co/x3VNsx4
https://ibb.co/T2hn1cs
https://ibb.co/v32sg24

a cyber.... or... maybe a woodenpunk PSU ?

just kidding, I used to encase electronics in wooden boxes like your ages ago... when I was young
BTW how do you intend to cover it? Remember to leave a way out for the hot air...

mike_mike · « **Reply #963 on:** December 02, 2021, 03:28:27 am »

I will cover it using a piece of plywood and I will drill some holes for the hot air.
The fan is taking out the air from the inside of the PSU, and it is not blowing the air from outside to the inside.

mike_mike · « **Reply #964 on:** December 14, 2021, 04:19:16 pm »

Hi! I got a new scope (GDS-1102B), and I wanted to use it for the first time testing the PSU again.
The results are comparable with the old scope, but I wanted to know why it looks more noisy than my old Owon, even if I use the BW Limit (20MHz) ? CH1 = output of the PSU, CH2 = output of the LM555 at PSU Shorter
The last character of the PNG file:
4 = the output with 2.7A switched load (with the PSU Shorter)
5 = with the output shorted (with PSU Shorter)
6,7 = on the R_Shunt with the output shorted (with PSU Shorter)
8 = the output of the PSU, without any load.

xavier60 · « **Reply #965 on:** December 14, 2021, 05:24:37 pm »

While taking that last reading, turn off the mains to the power supply.

mike_mike · « **Reply #966 on:** December 14, 2021, 05:30:16 pm »

With the power supply mains turned off.

xavier60 · « **Reply #967 on:** December 14, 2021, 05:35:42 pm »

Try adjusting the Time Base and Trigger Level to get a lock on signal. Its frequency might give a clue about the source of it.

mike_mike · « **Reply #968 on:** December 14, 2021, 05:46:54 pm »

I adjusted the Trigger Level and Time Base and also the V/div for the CH1 and I got the following screenshots: DS0011, DS0012
It is possible to appear this signal due to long wires and/or radio interference with the scope ?
If I short to ground the CH1 probe: DS0013.

xavier60 · « **Reply #969 on:** December 14, 2021, 05:54:24 pm »

There looks to be more than one signal. The main one is about 100Mhz, an FM radio broadcast maybe.

mike_mike · « **Reply #970 on:** December 24, 2021, 07:24:20 am »

A few more tests using different capacitor values for C3. R5 was 4k7 in all tests. CH1 was connected to the PSU output and CH2 to NE555 output (PSU Shorter). Rload was 9R, Vout was 27V.
1. Missing C4: 0014.png

2. C4=100pF: 0015-16.png

3. C4=470pF: 0018.png

4. C4=560pF: 0019.png

5. C4=820pF: 0020.png

6. C4=1nF: 0022.png

xavier60 · « **Reply #971 on:** December 24, 2021, 07:47:14 am »

The last one looks good. You should try to keep the DSO settings the same.
Also set your trigger zero reference to the left side of the screen, if your DSO allows this.
Having the trigger zero reference in the middle wastes a lot of the trace, showing nothing useful.

mike_mike · « **Reply #972 on:** December 28, 2021, 04:49:26 pm »

In my project initially R2 was 4k7, but now I modified it to 3k9 as it was in @xavier60 original schematic. With 4k7 the max output voltage was about 27V, now with 3k9 it is 32.77V.
Please find attached the screenshots:
1. CH1 on PSU output, CH2 on 555 output, with Rload = 0 R - 0038, 0039, 0040
2. CH1 on R_Shunt, CH2 on 555 output, Rload = 0 R - 0041, 0042
3. CH1 on PSU output, CH2 on 555 output, Rload = 10R - 0043, 0044, 0045.png

I used a 32Vac/200VA step down power transformer.

xavier60 · « **Reply #973 on:** December 28, 2021, 11:09:02 pm »

[ Specified attachment is not available ]That's a good response. Changing R2 shouldn't change the compensation.
Did you find the source of the high frequency?

mike_mike · « **Reply #974 on:** December 29, 2021, 03:54:51 am »

No I didn't found the source of the high frequency.
There is an cell phone antenna on a building at about 200-300 meters from my workplace, could it be the reason for the high frequency ?

All the screenshots from my previous reply were made with 20MHz bandwidth limit ON.


EEVblog Main Site	EEVblog on Youtube	EEVblog on Twitter	EEVblog on Facebook	EEVblog on Odysee

Author Topic: LM324 Power Supply with variable voltage and current (Read 154535 times)

Share me