This interesting circuit suggested by Motorola increases the duration of a pulse produced from the stimulus applied to an optocoupler. The pulse duration (PuIse Width PW) is given by the expression:
PW = 0.7 x R x C
With the values indicated in the diagram, a pulse of 3 us duration in the emitter and 15 mA of intensity, triggers the circuit. The output pulse has a width of 0.7 x R x C + PW1 + 6 us, where PW1 is the width of the input pulse and 6 us is the delay that occurs in the action of the optocoupler. The amplitude of the output pulse will be a function of the supply voltage and independent of the characteristics of the input signal. The MPS6515 is a low switching transistor that can be replaced by equivalents.
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