Wolfreak said:
I'm building a 200kHz switching DC-DC converter with an input between 6V and 12V, and output of 5V at 1A. The transistor I've found that should work gets very hot with the full load, even though its saturated when running. Is this normal for any switching supply running at 1A, or is there something better? I'm also trying to run the control circuitry (inherent short protection this way, short the load, shorts out the ocillator, stops the circuit), which means I'd like my 5V PWM output to (eventually) power a transistor at 12V potential.
Switches have two separate components of loss. There are the DC
losses that are just the switch voltage drop times the switch current,
times the fraction on the cycle that the switch is on. But there is
also a switching loss that occurs every time the switch changes state,
when there is much more voltage across the switch while it still
conducts considerable current. The higher the switching frequency,
the more of these high loss events per second, so the higher the total
switching loss.
Do you have a schematic of your supply that we might criticize?
Graphic files cannot be attached to messages in this group, but they
are allowed on alt.binaries.electronics.schematics. Or a URL to a web
page that shows it would be good.