Bootstrapping circuit

[traxx]

Hello,

can someone explain this circuit in detail? Thank you!

https://www.circuitlab.com/editor/#?id=nds8yxxwdvq9

All what I can see on this circuit is, if SW1 is open SW2 is closed and vice versa.
But off course there is a lot of things going on here.

 

[BradtheRad]

Suppose we apply 12V to turn On M1. This causes the node labelled 'out' to convey 12V. That has the effect of negating the bias on M1 which makes M1 shut off (entirely or partially). Hence to keep M1 turned on its bias voltage must be a few volts greater than its source voltage.

This creates the need for a bootstrap capacitor. Ideally C1 is switched so it acquires 12V and becomes part of a voltage doubler. This is switched to apply 24V to M1 bias at the proper time turning it On.