PNP negative voltage control

[shebu18]

Hello all,


i want to design a small psu like the tuxgraphix psu. My question is about the negative voltage control. Where can i read about the negative voltage control with a pnp transistor and driving it with a opamp.


thank you.

[sorin]

https://www.eevblog.com/forum/projects-designs-and-technical-stuff/bench-power-supply-school-project/msg166244/#msg166244

[shebu18]

Thanks.


Some other information about this? i want to make a +/-10V and 1A PSU from a transformer.

[Thor-Arne]

What transformer?

Using linear regulators would be the first thing I'd consider.
Very easy to work with, but dissipate a lot of heat if input voltage is considerably higher than output voltage.

(I wonder why nobody using/suggesting the 78xx/79xx series?) 

[TriodeTiger]

Thanks.


Some other information about this? i want to make a +/-10V and 1A PSU from a transformer.

Well, maybe if you get 15/15V out of the transformer, rectification and regulation will drop the range roughly to 10 or 12V... an LM317 can get you 1.2-10V, and an LM337 will do the same except for the negative rail! You can do some tricks with an op-amp to offset 1.2 to 0V if going down to 0V is important...(assuming you mean adjustable of course!)

So in other words, a split secondary (or centre tapped secondary) transformer is what you need to start with. Anywhere from 12 to 18 sounds good... Try to find what VA rating you need yourself as a learning exercise.

Constant current should not be too difficult to add, just an op amp, sense resistor and fet might do it...

[shebu18]

Sorry, i did not express my self correct. I wnat to make a +/-0-10V 1A PSU with descrete components. I found a solution for the positive part of the coltage control but for the negative part i did not fount one.

[shebu18]

I simulated a PNP darlington configuration driven by a op amp and it worked, so i will use this to regulate the negative voltage and a npn darlington to regulate the positive voltage. Now i need to read more about current measurement with op amps.