This is a pulse stretcher circuit using optocoupler. This circuit uses a 4N26 opto-coupler combined with a standard one-shot circuitry. This circuit is triggered by pulse about 3μs (minimum width) at 15mA. The output’s amplitude of this circuit is not depend on the input’s amplitude. The output pulse amplitude is a function of (or proportional to) supply voltage on the output side. Here is the schematic diagram of the circuit:
The minimum input of this circuit is 15mA of current and pulse width of 3μs (PWin). The output pulse width of this circuit is determined by the following equation:
Where PWmin=PWin +6μs.
This circuit produces output voltage level of 5.0V for high If R>=4.7K and 0.2V for Low. [Circuit’s schematic diagram source: seekic.com]