why is it necessary to use a bootstrap capacitor for an N-Channel Mosfet on High Side ?
Why is it necessary for the gate to source voltage to be greater than the Drain to Source Voltage?
Wont the Mosfet Conduct when the gate voltage is greater than the Drain voltage?

 

1. Because the source will be at or near the supply voltage when the MOSFET is on and the gate must be about 10V higher than that. The capacitor is charged up then connected between the source and gate to turn it on.
2. The drain must always be at a higher voltage than the source in an N MOSFET. If not, it will conduct through the body diode.
3. Yes assuming it is also greater than the source voltage by enough.

Bob