gardenyu wrote:

> Besides, if I can have this additional power supply, how can I turn on
> this supply to charge the boostrap cap? I don't want another output from
> microcontroller saying we want a full duty cycle,  I just want to turn
> on the supply with the 100% PWM output, if it appears. But, if PWM is
> below 100%, it won't turn on. How can I realize that? 

One possibility is to have an (one) additional supply voltage that is a bit
higher than the highest gate voltage you need, switch it with opto couplers
and limit the gate voltage at each FET.

Gerhard

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