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schmitt trigger using just diodes?

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neazoi

neazoi

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Is it possible to make a schmitt trigger using just diodes (zeners etc)?
I need a voltage of about less than 1v to be read as 0v and voltage of about more than 1v to be read as logic 1
 

Schmitt trigger - no way, it would be impossible to make a circuit with different high and low thresholds.

As a simple high voltage detector - maybe but it depends on the logic level you want out of it. Basically, you can use the diodes as fixed voltage droppers, as long as the high input voltage makes them conduct you could measure something at the output but if the input fell below the Vf threshold, the output would disappear (barring leakage currents). It wouldn't be very good or fast acting and the threshold voltage would be poorly defined and gradual rather than rapidly switching state.

Brian.
 

You need some sort of active circuit. A comparator such as an LM339 with a small amount of positive feedback for the Schmitt trigger action would work well.
 

Actually, I lied. I think it is possible to make one using a tunnel diode but the threshold voltage would be fixed and the output would be a very fast pulse (a few nS at best). It wouldn't be practical to make and would be expensive to buy. Tunnel diodes are hard to find!

Brian.
 

A Diac would sort of a schmitt trigger function, as it switches from withstanding to conduction.
To release it from the conduction state it will be a function of current, not voltage.
 

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