SMPS :noob: question

Low Rider

2007-03-03 12:12 pm
Instead of controlling the switches in a smpts with a transformer to step up the gate drive pulses, could it be done with a separate linear ps directly of the mains, with a voltage maybe 10-20V higher than
rectifed mains voltage ?

I'm a noob but i was thinking about it and while reading posts that most problems with smps arise from gate drive transformer leakege inductace and what not, it doesnt seem like a bad idea:confused:

Basically you would take a small 50 Hz transformer with a 1:1.1 ratio of the mains, rect it, filter, drive some kind of optically controlled transistors A class or simmilar amp and drive the switches gates with that...

What is Vgssat for MOSFET or BJT switches anyway?
You can even use a 1:0.1 transformer and connect rectified secondary in series with rectified mains.
Yes, it is possible, but bootstrap approach is more popular and simpler.

Mosfets do not saturate, so there isn't anything like Vgssat, they show some open channel resistance (Rdson) at open state.