Abstract: A semiconductor relay circuit includes a MOS FET receiving a photovoltaic output generated across a photovoltaic diode array. The photovoltaic diode array is responsive to a light signal from a light-emitting element. A cross gate and source electrodes of a MOS FET is connected a control circuit which is at a high impedance state during the generation of the photovoltaic output but to be at a low impedance state upon disappearance of the output. Additionally, resistors are inserted in series respectively in each of current, one path flowing from the photovoltaic diode array across the gate and source electrodes of the MOS FET and the other path flowing a discharge current from a capacity across the gate and source electrodes of the MOS FET to the control circuit, whereby the setting of rise and fall of circuit output signals can be made easier.

Abstract: A semiconductor relay circuit includes an output FET connected to a diode array. The diode array generates a photovoltaic output in response to a light signal from a light emitting element. Across the drain and gate of the FET is a series circuit of a semiconductor device and a rectifier is connected, the switching transistor is being made conductive upon receipt at the diode array of the light signal and forms a charge current path for an accumulated charge across the gate and source of the FET. The rectifier restrains a photocurrent from reversely flowing between the drain and gate of the FET. Turning-on and turning-off operations of the relay circuit can be thereby made both achievable at a higher speed, and the reverse flow of the photocurrent upon the conduction of the output FET can be prevented from occurring.

Abstract: A light receiving element is formed by a plurality of light receiving cells connected in series with one another and arranged for optical coupling to a light source, the cells having respectively a surface area varied depending on light input intensity from the light source. The light receiving cells are thereby made to maintain excellent light receiving efficiency without causing optical loss at any one of them.

Abstract: A semiconductor switching circuit comprises an output FET receiving a photovoltaic output generated by a diode array responsive to a light signal from a light emitting element, a depression mode driving FET connected at the drain and source to the gate and source of the output FET, and a constant voltage conduction element connected in parallel with a resistor connected across the gate and source of the driving FET. The sensitivity of the circuit is elevated by setting the value of this resistor relatively high, whereas high speed operation can be assured by having discharge current of an accumulated charge across the drain and gate of the output FET bypassed through the resistor.