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Electronics => Electronics => Topic started by: izua on February 23, 2008, 02:30:57 PM

Title: transistor efficiency (for a h-bridge)
Post by: izua on February 23, 2008, 02:30:57 PM

I need to understand core concepts behind transistors. I've googled, but haven't found too much.
Basically, I want to build an efficient hbridge, if i pump 5V in it, at least 90% should be given to the motor (that's ~4.5v).

With two BJT's, i lose .7 per transistor, so that's closer to 3.6, not very good IMO. I don't know about FETs.
So basically, I know that if I have 5v available at the collector, (NPN), and i pump 5v in the base, I'll get 4.3 at the emitter. There's also the problem of heat, since the transistors is not fully open. All this translates in wasted power. I know a dude who was using dc/dc converts, and was pumping 36-40 v in irf-type FETs that were commuting ~24 V over 2 amps in pwm. These things were dangerously cool, they weren't even heatsinked, or warm, at least.

I want this type of efficiency for my h-bridge. Would fets be required? Would I need a dc converter? Will that be more inefficient than the sum of transistor inefficiency?

Title: Re: transistor efficiency (for a h-bridge)
Post by: Admin on February 27, 2008, 08:19:38 PM

Quote

I want this type of efficiency for my h-bridge. Would fets be required?

yeap, a mosfet is the way to go

look for PWM optimized mosfets