modified 8 years ago

Schmitt trigger in 2 stage common emitter

00:54:51

The feedback resistor should be a bit higher-value than the input resistor. The closer they are, the more hysteresis there is. 

The resistor from base to ground centers the hysteresis. To center on half the supply voltage, it should be half the value of the feedback resistor.

2017-10-11: Added some optional output loads because they have an effect on the hysteresis. Being in parallel with the resistor from base to ground, they change the center of the effect. I guess a practical design would use another transistor as an output buffer unless its output load is known. Then again, the effect is small unless the load is large. 50k hardly makes a difference.

published 8 years ago

OHTEN

8 years ago

wap.

eekee

8 years ago

Oh dear! I made a change on another user's advice, and all my instructions on adjusting the hysteresis effect turned out to be wrong. The change was a very realistic one: changing the gain of the first transistor, because it normally varies a lot between transistors, even as much as +/-50%.

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