AC Input Photocoupler/Optocoupler

It is very common these days to see a logic circuit with an AC input photocoupler (optocoupler).

Such a bidirectional input device enables the circuit to operate safely at dangerous AC line voltages.

The most common AC input photocouplers widely used are PC814 and LTV814.

This is the internal connection of the SHARP PC814 AC Input Photocoupler:

There are two LEDs connected back-to-back on the input side so that the first LED lights and a signal is transferred when current is applied in the direction of Pin 1 to Pin 2, and the second LED lights and a signal is transferred when current is applied in the reverse direction of Pin 2 to Pin 1.

Simply put, a signal can be transferred even if the polarity between the input pins 1 and 2 is switched from positive to negative and vice versa.

The figure below shows a basic circuit connection example when AC 100V is input to an AC input photocoupler via a current-limiting resistor.

In general, the final output signal is used after smoothing by a buffer capacitor, etc.

And the next figure shows the relationship between the input and output signals of an AC input photocoupler.

In this case, the output signal obtained from the ac input photocoupler is in the form of a full-wave rectified AC input signal.

OK, if you have applications in your projects where you need to know the status of a fatal line voltage circuitry perhaps an ac input photocoupler can be of use to you too. Give it a try!

Thanks RENESAS ⨶