- Joined Oct 3, 2010
I've never understood why in bridge output circuits like MOSFET H-bridge in sine wave inverters or DC motor controls, or like the IGBT 3-phase output of a VFD, both high side switches and low side switches are both PWM'd from the same signal. Driving high side FETs is harder than low side, so why PWM them? Why not just leave them fully on for the entire period of the fundamental wave and just PWM the low side switch? And if you're going to do that, why even use a FET as the side switch? Why not use a SCR? Wouldn't that be cheaper and simpler? Especially if you're talking huge power like an EV motor controller, which is what I have in mind as I ponder this. Transistors rated 500+ amps are not cheap, unless you're talking about SCRs.