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Missing Pulse Detector (Watchdog Timer) Circuits Using LM339/393, CD4093, or 555 2017-04-15

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crutschow

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crutschow submitted a new article:

Missing Pulse Detector Circuit Uses LM339/393 Comparator - Missing pulse detector circuit alternate to 555 designs will timeout on either high or low hang

Missing pulse detector circuits commonly use a circuit with a 555 and a transistor to perform this function.
As an alternative, here's a similar circuit using only a single active device package, the LM339/393 comparator.
The total number of parts is about the same but with one less active device.
The circuit will time out when the pulse stops, independent of the pulse DC voltage at that point.

Below is the LTspice simulation of the circuit.

View attachment 105514

Repeating pulses...
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