Bootstrap circuit and exceeding VGS(max) of high-side n-chan FET?

[julian1]

A bootstrap circuit (capacitor and diode) look like they work as a voltage doubler.

Does this impose an indirect limit on the input voltage that can be switched by a high-side n-channel FET in source-follower configuration - since otherwise the bootstrap circuit will drive the Gate over VGS(max).

Eg. With a 20V input (on Drain), the FET is turned on, and the bootsrap will provide 40V to the mosfet driver for the Gate, which is 20 VGS. That's at the limit of a FET such as the IRF540.

Is there a way around this - perhaps with a Zener shunt?
 

[Rerouter]

I believe a zener shunt is the norm, but before the driver switched side, so you have your bootstrap supply that creates a not horrible 10V or more referenced to the source, that then gets switched between by the driver, meaning the mosfet never sees the higher gate voltage,

[Zero999]

A bootstrap circuit (capacitor and diode) look like they work as a voltage doubler.

Does this impose an indirect limit on the input voltage that can be switched by a high-side n-channel FET in source-follower configuration - since otherwise the bootstrap circuit will drive the Gate over VGS(max).

Eg. With a 20V input (on Drain), the FET is turned on, and the bootsrap will provide 40V to the mosfet driver for the Gate, which is 20 VGS. That's at the limit of a FET such as the IRF540.

Is there a way around this - perhaps with a Zener shunt?

Schematic?

What's the voltage on the source, when the MOSFET is turned on?

I hope you're aware it's the voltage between the gate and source which counts, rather than the absolute gate voltage.