Patent ID: 7642502

Claim:
A photo relay, comprising: a light emitting diode to emit a light signal corresponding to an input signal; a photovoltaic diode to receive the light signal from the light emitting diode, so as to generate a photovoltaic output; an output circuit having an insulated gate field effect transistor to receive the photovoltaic output, an impedance between a drain and a source of the insulated gate field effect transistor varying by changing a capacitance between a gate and the source of the insulated gate field effect transistor by the photovoltaic output; a field effect transistor having a first electrode, a second electrode, and a control electrode, the first electrode of the field effect transistor being connected to the gate of the insulated gate field effect transistor, the second electrode of the field effect transistor being connected to a cathode of the photovoltaic diode through a resistor, and the control electrode of the field effect transistor being connected to the cathode of the photovoltaic diode; a transistor having a first electrode, a second electrode, and a control electrode, the first electrode of the transistor being connected to the gate of the insulated gate field effect transistor, the second electrode of the transistor being connected to the source of the insulated gate field effect transistor, and the control electrode of the transistor being connected to the second electrode of the field effect transistor; and a diode being connected between the second electrode of the field effect transistor and the second electrode of the transistor.