Semiconductor switching circuit

Claim 1

A semiconductor switching circuit comprising a diode array optically coupled to a light emitting element which generates a light signal in the presence of an input current for generating a photovoltaic output responsive to said light signal, a resistor connected in series with said photovoltaic diode array, an output FET having a gate, a source and a drain, said output FET being connected to said photovoltaic diode array to be turned from a first impedance state to a second impedance state upon application of said photovoltaic output to the gate and source, a depletion-mode driving FET having a gate, a source and a drain, said driving FET being connected at the drain and source to the gate and source of said output FET and at the gate and source to both ends of said resistor and capable of being biased into an OFF state by a voltage across the resistor upon generation of said photovoltaic output at the photovoltaic diode array, and a constant-voltage conduction element connected in parallel with said resistor to be conductive upon application of a voltage higher than a threshold voltage of said depletion mode driving FET and contributive, with a conduction current upon said conduction, to a charge between the gate and the source and to a discharge between the drain and the gate of the output FET.