Using 16f628 to make quasi-3-phase 400 Hz

I think a phase shift oscillator is simpler, if you don't need a PWM drive for the output. 3 opamps connected in a ring with a resistor and capacitor as feedback. I think I have a schematic somewhere.

Yes, that depends on the required power level. For 10W that might be doable. Above somewhere comes the level where a switcher is better, meaning the increased complexity pays power wise. You'll need a control loop whenthe load is not just a resistor, but something dynamic, a nonlinear 4 quadrant load.

Rene

You might want to look at the Hitachi 3048 chip. It has a 3 phase pwm generator, you can get an evaluation/starter kit for a few hundred.

fuel-tank

If you are proficient in code writing, the PIC is a good solution whether you need single phase or three phase. I wouldn't use a linear amplifier though, I'd have the PIC drive FET switches directly in a PWM mode. Overall that would use the least number of parts and be much more stable in both frequency and amplitude than any analog oscillator-amplifier scheme. Furthermore, it would not dissipate much power and would be applicable for any power level from several watts to many kilowatts depending of the FETs and their drive. It would be very good for low power, battery operation as well if that is a requirement. On the other hand, if you don't know anything about code writing in assembly or C, etc. Then your in for some headaches and a simple oscillator-amplifier might be a better choice. Bob