Selecting a Transistor for a Power Supply

Thread Starter


Joined Jul 16, 2011
Hi everyone.

I hope you are all well. :)

I've been fairly busy with exams and revision (only a couple more months to go though!), but during my Easter holidays, I thought I could get a lot more electronics done than usual.

I few of my experiments I have planned require a bigger power supply than I currently have. One example is an experiment which will need a supply capable of delivering 5A at near enough 50V.

I thought that at these powers, I had better construct someone else's design, at least to begin with, so that I know the design is okay and should be safe (ish). I came across this page, with the following schematic:

Now, althought it is capable of delivering 8A at 35V, I could build two and put the in series as he talks about, however, this would be fairly relatively expensive.

Would it be possible to get some help to redesign it to give the 50V required? I presume it is not quite so simple as just changing the transformer, but what sort of specs should I be looking for, for the components?

Which leads onto my second question. He labels the power transformers Q17, 18 as just "power transformers". I have spent a while searching google and octopart for some suitable transistors, but again, I am not 100% sure what numbers I need to be checking for.

I hope you guys can help out, I really do appreciate your time and effort. :)

Many thanks,



Joined May 11, 2009
Erm..That looked quite complicated. Do you need the output to be adjustable in some range. Or are you happy with some small range output span just for fine tuning. For 50 volt 5 ampere non switching power supply. You need quite a big transformer with a about a 8A RMS current rating