Introduce the output pulse and the time constant RC isolated trigger

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A flip-flop is a logic circuit that has a memory function and its state can be quickly flipped under the action of a trigger pulse.
In this circuit, the falling time of V1 is slow until D1 becomes forward biased. When D1 becomes forward biased, a regenerative transition occurs (the larger the R7 value, the faster the initial descent speed; otherwise the value of R7 is not critical). The Zener diode is chosen such that E is smaller than V, so the Ee transition only occurs on the fast slope along V1. C uses 22 microfarads, the frequency is less than 15 Hz, and it is easy to achieve a rise time and fall time of a few tenths of a microsecond. Since the timing elements of the flip-flop are well isolated from the output, the frequency is kept constant for any load.