Bootstrap 2 stage

138

01:02:21

Built this IRL and it works.

Flip the switch to toggle bootstrap on, or off. 

published 6 years ago

hurz

6 years ago

hmmm, this is a bootstrap help for the 2.stage and wont help the input impedance to lower. Why is impedance of the 2.stage problematic. Should be solved from the 1.stage. Im afraid its more a gain change of the emitter feedback, the cap switched increases the voltage gain ofbthe 2.stage, for less AC negative feedback. But good is you have a low realistic input signal and a SWITCH for demonstration of your idea!

crake

6 years ago

The goal of this circuit was to use bootstrap to increase impedance at the CE stage, and consequently gain of the CE stage. I wanted to see if I could get more gain from the CE stage while maintaining Vcc/2 DC at the output of the CE stage.

hurz

6 years ago

but boitstrap is not a nethode to get more voltage gain. Its to draw less current from the input source by increase of impedance. The positive feedback follows the input signal an the delta voltage is less which reduces again a constant unchangeable input resistance a virtual higher impedance! That the idea of bootstrap in this context.

crake

6 years ago

I had seen it used in a book at the input of an op amp and figured if it increases impedance there then it would also work to increase gain while maintaining the DC characteristics of the circuit I set up. I put this amp together and it simulated well, then I built it and it functioned as expected. I even put a push button in my circuit so I could see the gain change on my scope.

hurz

6 years ago

there is another context in which the word bootstrap is used, you remember your eCigarret shisha ;-) idk, gain bootstrap for voltage increase over rail voltage, probably its what you mean.

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