LM324 Power Supply with variable voltage and current

[mike_mike]

Yes it is more ringing at the drain of the mosfet. The mosfet is a 2SK1257.
Blue channel = output of NE555
Yellow channel = drain of the mosfet.

This means that the wiring damp the oscillation at the Drain of the mosfet ?

[mike_mike]

What should I do now ?
Is ringing normal ?
Please have a look at the previous post and tell me what you think ...

[iMo]

There is an npn transistor between the power mosfet and the 555, afaik..
Also the frequency of the ringing is aprox 15MHz.. That might come from leads inductance..

[xavier60]

What should I do now ?
Is ringing normal ?
Please have a look at the previous post and tell me what you think ...

That ringing is normal and external to the PSU.

[xavier60]

The stimulus for the ringing could be actually originating from the NE555 itself. Try putting a resistor in series with the CH2 probe tip, between 1K and 10K.

[mike_mike]

Please find attached the screenshot when I used a 4.7k resistor between the pin 3 of NE555 and the tip of CH2 probe (blue trace).
The yellow trace is the output of the PSU, Vout=2.5V, Rload = 10R.

It looks like the ringing almost disappeared.

[xavier60]

That's much cleaner.
Edit: probes should usually be set to X10.

[mike_mike]

Edit: probes should usually be set to X10.

Yes, they were set to X10.

[p.larner]

hope there will be a schematic+pcb artwork released for this when sorted!.

[xavier60]

hope there will be a schematic+pcb artwork released for this when sorted!.

My build of the design has been working well for years.
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664
My PCB files are Protel 98. I suspect that mike_mike's is Kicad which I'm sure he will share.

[mike_mike]

Please find attached the kicad files.

[xavier60]

Please find attached the kicad files.

You should also include the output stage in the schematic. Use the same reference numbers as used in mine.
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664

[p.larner]

thank you for the download merry xmas.

[mike_mike]

And the transformer tap switcher files.

[xavier60]

A word about the Emitter sharing resistors, R14 and R15. Although I have used 50mΩ, 100mΩ resistors should be used unless Q3 qnd Q4 are very well matched as mine happen to be.

[mike_mike]

So if I use 5 transistors, should I also use 0.1R emitter sharing resistors instead of 0.22R resistors ?

[xavier60]

So if I use 5 transistors, should I also use 0.1R emitter sharing resistors instead of 0.22R resistors ?

No.
Using that many transistors is usually for SOA reasons to get the current per transistor down. So, voltage loss becomes less of a concern.
The trade-off is, good sharing against voltage loss.
You can calculate the voltage loss, also measure the voltage across each resistor to check the sharing.

[xavier60]

What is your maximum current? I should have asked.

[mike_mike]

The maximum current is 5A (I mean the output current of the PSU).
I used 5 transistors, so the current through each should be 1A. So 1A*0.22R = 0.22V across each resistor.

[xavier60]

The maximum current is 5A (I mean the output current of the PSU).
I used 5 transistors, so the current through each should be 1A. So 1A*0.22R = 0.22V across each resistor.

Not a problem, leave it as is.

[dennislewis]

I want to say thanks for the time and effort put into this project. The sharing of ideas was helpful.

mike_mike the pcb looks nice.

Did any others build this and/or have comments on the project ?

[dennislewis]

Would you be so kind as to identify the components labeled R34 & R37 100mA with part number and mfg ?

Thanks

[xavier60]

Would you be so kind as to identify the components labeled R34 & R37 100mA with part number and mfg ?

Thanks

They are a 100mA Polyswitch such as RXEF010.
Added: A blue LED should work fine in place of the white LED.

[mike_mike]

I tested again with another scope (unit UTD2052CEX+) and the output of the power supply looks like this now (see the attached screenshots).
It is normally to look like this or there are some problems ?

[xavier60]

The effect might be caused by long wires. Is the probe connected directly to the PSU's output terminals?