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Forum: Analog Circuits Bootstrap-circuit


Author: Alex A. (Company: Andi&Alex) (alextbg)
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Hello there,
can anyone tell me how the bootstrap circuit works? I already googeled 
it, but i haven't found anything useful. Thanks for your help!

: Moved by Moderator
Author: Kaktusbombe (Guest)
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A bootstrap circuit is a kind of charge pump. I know bootstrap circuits 
from audio amps and mosfet drivers. It is basically a capacitor 
connected from the output of the driver to the positive supply rail 
(after a diode). This enhances the output voltage swing in that way that 
the circuit can drive a N-channel mosfet in the pull-up part of the 
output driver.

Author: Bernd W. (berndwiebus)
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Hello Kaktusbombe.

Kaktusbombe wrote:
> A bootstrap circuit is a kind of charge pump. I know bootstrap circuits
> from audio amps and mosfet drivers.

I know the name "Bootstrap" also for any circuit which allows to start a 
device in the right manner.

As an example: A bootstrap is needed to delay the start of a 
microcontroller during switch on until its supply voltage is high and 
stable enough to maintain correct working.
Otherwise the brown out conditions during start uo would lead to 
uncontrolled behaviour.

Further on it could be also a kind of circuit preventing latch up 
conditions during start up, if the voltages at the inverting an non 
inverting inputs of an opamp are higher than the supply voltage of the 
opamp for a short moment. Also for the inputs at logic gates.

As an analogy parts of software preparing the start of a computer or a 
program for a similar purpose are also called "bootstrap". And this is 
the reason why you name to start your PC "booting".

Wirh best regards: Bernd Wiebus alias dl1eic
http://www.dl0dg.de

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