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Bootstrap circuit help???

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chieeeeef

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What does a bootstrap circuit do in driving the gate of a high-side MOSFET? Can anyone help me understand what it really does? Thanks in advance!

Regards,

chieeeeef
 

HI

what about including the circuit, there is no valid opinion without it

Sal
 

As we are benefitted by MOSFET's higher input impedance ,while analysing the small signal model,the effective input impedance gets reduced because of the biasing resistor which is connected in parallel in the order of some low kΩ's.But that resistor is needed for effective biasing.
While bootstrapping the external resistor connection you make will stabilise the operating point but it will be open in the small signal model thus having no reducing effect on our deice's input impedance.
If you are more specific with your circuit, then I'll clear you efficiently.
 

Hi Sal!

I'm going to upload a schematic diagram of a bootstrap circuit that I got from an article from Unitrode, I guess. I'll include the article as well.

Regards,

Chieeeeef
 

What it does, it creates a higher voltage at the collector of the NPN transistor than the Vdrive voltage. This ensures thet the Gate of the Mosfet, drives it completely on so its on-resistance is the lower and hence the waste in heat produced in the mosfet is the minimum.
Usually the function of Bootstrap is to increase the voltage at a specific plave in the circuit.
 

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