LM324 Power Supply with variable voltage and current

[xavier60]

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.

Im not certain what frequency cell phones use.
I see some trace thickening in the last 2 shots.

[mike_mike]

But is it a normal or an abnormal behavior for the signal to be noisy ?
I looked over the internet and I've saw that digital oscilloscopes are noisy in general ... does the noise on my scope looks higher than it should be ?

[xavier60]

Some random noise voltage might be normal but if it has a distinct frequency, then it's either circuit oscillation or some external source which maybe can be ignored. It was 100Mhz last time which shouldn't show with the 20Mhz band width limit enabled.

[mike_mike]

Ok, then I will try to do some test when I will get back to the workshop, probably tonight...
Please let me know if you have some test suggestions.

[mike_mike]

Please find attached some screenshots with the probe shorted to gnd.
1. BW Limit OFF: 0046, 0047
2. BW Limit ON: 0048, 0049

Please have a look and tell me what you think.

[xavier60]

The 2nd shot looks like SMPS hash.  If it's not coming from a nearby power supply. it could be coming through the mains and you will never likely find the source.

[mike_mike]

I made a few more tests, this time with 3x TIP35C as power transistors, with the PSU mounted into a case. The previous screenshots were with 3x 2N3055 as power transistors.
Vout=31.64V for all screenshots.
CH1=PSU output, CH2=NE555 output

1. Rload=10R: 0051,0052.png
2. Rload=0R: 0053.png

CH1=the R_Shunt, CH2=NE555 output
3. Rload=0R:0054, 0055.png

The thing that I observed is that on the R_Shunt, the voltage spike is about 1.3V, which means that 1.3V divided by 0.05 Ohms means 26A, and 26 A divided by 3 x TIP35C means 8.66A/transistor. I observed in the TIP35C datasheet, on the SOA graphic that on the 300uS and 40V CE voltage the maximum current is about 5A, while on my circuit the current is 8.66A/ transistor and the spike duration is about 40uS.

[xavier60]

I would call that spike something less than 20uS due to its shape not being a rectangular.
I'm sure that the transistors wont mind. If you want to see something less, try a faster opamp like the TLC072.
What is your driver transistor now?

[mike_mike]

The driver transistor is a BD244CG.

[mike_mike]

Hello @xavier60, it's been a while since I started using the power supply (I am talking about the last schematic). It is working good, I don't have any problems.
Your last question was about the driver transistor, and I mentioned that it is a BD244CG.
Do you have any other thoughts about the psu ?

[xavier60]

Hello @xavier60, it's been a while since I started using the power supply (I am talking about the last schematic). It is working good, I don't have any problems.
Your last question was about the driver transistor, and I mentioned that it is a BD244CG.
Do you have any other thoughts about the psu ?

That's good to hear. I had hoped that the design would have become more popular by now.
One improvement I can think of is to enable/disable the output by turning off the reference voltage rather than using the Shutdown input.
Im certain that it will cure the voltage overshoot.
I use mine almost daily.
https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2409717/#msg2409717

[mike_mike]

By turning off the reference voltage means that I should use the DC on-off switch to switch off the voltage reference by connecting to ground the K of the TL431 ?

[Kleinstein]

I would kepp the actual refrence running and shut off the voltage at the pot to set the voltage. This way the reference chip would stay warm and show a little less slow thermal settling.

The design looks nice and simple, as it can get away with a single transformer. It is definitely a step up from the LM723 based ones with usually rather poor current regulation.

[kallek]

I am going to build this power supply. Thank you xavier60 for sharing it!

Should I get the TL072, or will the LM358 work as well? And what are the requirements for the output stage transistors? Will almost any power transistors do the job, if they can dissipate enough heat?

[xavier60]

I am going to build this power supply. Thank you xavier60 for sharing it!

Should I get the TL072, or will the LM358 work as well? And what are the requirements for the output stage transistors? Will almost any power transistors do the job, if they can dissipate enough heat?

It needs to be the TLC072 or LM358. The important spec for the opamp is that it will work properly with it's inputs at ground voltage, 0V.
The TLC072 being much faster makes the fast current limiting react faster but it's not really that important.
There is nothing much better than the D45H11 for the driver and I used two TIP35C's for the output for 5A with 15VAC/30VAC secondary switching. The two TIP35C's are directly mounted to a spreader plate witch is insulated from the fan cooled heat-sink with Silpad material.
So the requirements are no different to most other linear PSU's. There are a lot of factors witch are difficult to measure and calculate, so one must go for something that's hopefully a bit of overkill.
https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873
Ill have look for the version that I'm currently using in my PSU and put the links here shortly.

 mike_mike's layout.
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3583296/#msg3583296
Mine,
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664
The LED in the Emitter circuit of Q1 can be blue or white. As discussed a few posts back, the output enable switch should be made to disconnect the 5V reference from the CV and CC pots. But leave the Shutdown input option intact.
Also you need to be prepared to do some load transient tests to make certain that is all ok,

[mike_mike]

@xavier60, leaving the power supply as it is shound be a bad idea ?

.... or how to wire the dc on/off switch in order to work in connection with the tap changer ?

[xavier60]

@xavier60, leaving the power supply as it is shound be a bad idea ?

.... or how to wire the dc on/off switch in order to work in connection with the tap changer ?

No, it's fine the way it is. It was a suggested improvement.
The switch needs to be wired so that both poles are on at the same time.

[kallek]

Thank you, I think I will read the whole thread next and start from there. Thank you mike_mike for sharing your project, it looks very nice.

[mike_mike]

I managed to make it work, but only when the 2 poles of the switch are not on at the same time (one pole on and the other pole off).
When I turn the DC off, the white led goes off for a very short time and then it goes back on. When I turn the DC on again, then the white led stays on.
Please find attached the schematic.

[xavier60]

Because you are using the pole to short circuit the reference, the switch wiring stays the same, one pole on while the other is off.
I think it might be better to use the pole to disconnect the reference 5V from the pots.

[mike_mike]

By disconnecting the 5V reference from the pots, then one end of the pots will remain disconnected ?

[xavier60]

By disconnecting the 5V reference from the pots, then one end of the pots will remain disconnected ?

Yes, while the switch's pole is off.

[mike_mike]

Something like shown in the attached schematic ?

[xavier60]

Yes, try that.

[mike_mike]

I tried the above schematic but when switching from off to on, then the relay clicks one time. And when the dc is off then the green led is still on.

LE: if possible, I would like to stick with the original design, the one before the switch modifications.