LM723 and TL082 power supply

[Harry_22]

Yes. The physical location of the connection can have a small effect on regulation, try to put it close to the PCB output point.

Yes, you are right.
I have redrawn the voltage regulator diagram to make it more intuitive. Unfortunately, it takes some time to do a comprehensive and conscious analysis.

[iMo]

Most people play with LTspice, imho..
You may put it there and simulation would be easy.. 
For example the analysis of almost similar PSU below..

[mike_mike]

I could use a tap changer circuit for this PSU, using a sigle opamp (1/2 of LM358). Am I right ?
Also the other half of LM358 I could use for controlling the fans which are mounted on the heatsink.

[B0B45]

Hey,

do you have some suggestion for the power transistor in a TO-247 package? Whats are the important characteristics on the datasheet I should look at?

Thanks - Bob

 

[mike_mike]

@B0B45 I am using TIP35C and TIP3055. I chose those transistors because they have high collector current and high power dissipation. I am using fans mounted on the heatsink to cool them better, but only on the final PSU, when I will install it into a case. I use a fan controller for turning on/off the fans. I will use 2 fans of 80x80 mm, at 12V.

[mike_mike]

I can't do right now the tests, I have problems with the software which is copying the screenshots to the pc...

[B0B45]

thank you for your reply, what about the MJL3281? Would that transistor also fit?
Link to datasheet: https://www.onsemi.com/pdf/datasheet/mjl3281a-d.pdf

[mike_mike]

I think that it will do the job.

[mike_mike]

The results:
1.1, 1.2 - Vout=30V, Ilim=3.15A, Rload=10ohms
2.2 - Vout=30V, Ilim=3.15A, Rload=27ohms
3.1 - Vout=30V, Ilim=3.15A, Rload=47ohms
4.1 - Vout=12V, Ilim=3.15A, Rload=4.7ohms
5.2 - Vout=3V, Ilim=3.15A, Rload=1ohms
6.1 - Vout=3V, Ilim=1.45A, Rload=4.7ohms
7.1 - Vout=3V, Ilim=1.45A, Rload=47ohms

EDIT: The above tests were made using R=470R and C10=470pF.

[Harry_22]

Hi, Mike!

Could you explain what is the blue curve no.2 that dropped from 10V to 0V?
Sorry I didn't find explanation.

[mike_mike]

The blue waveform is the output of the NE555. The NE555 is located in the PSU tester schematic, which I will attach below.

[mike_mike]

@xavier60 , I made the test from reply below:

The results:
1.1, 1.2 - Vout=30V, Ilim=3.15A, Rload=10ohms
2.2 - Vout=30V, Ilim=3.15A, Rload=27ohms
3.1 - Vout=30V, Ilim=3.15A, Rload=47ohms
4.1 - Vout=12V, Ilim=3.15A, Rload=4.7ohms
5.2 - Vout=3V, Ilim=3.15A, Rload=1ohms
6.1 - Vout=3V, Ilim=1.45A, Rload=4.7ohms
7.1 - Vout=3V, Ilim=1.45A, Rload=47ohms

The tests were made using R=470R and C10=470pF and TL082.

I saw that there is some noise on the yellow (the output of the PSU) waveform.
What should I do next ? are there any other test that I should make ?

[xavier60]

Try to find where the noise is from. Does the noise stay when the mains power is turned off?

[mike_mike]

Yes, the noise stay when the power is off, even if I unplug the main transformer and the 2x12V transformer from the 230VAC mains .
The big noise appears hwen the load consume low current.