Optically isolated solid state relay

Claim 1

A solid state relay comprising: sensing means for responding to an input voltage signal by producing a logic signal of a relatively fixed magnitude; a logic gate having a first input terminal operatively connected to receive said logic signal from said sensing means, an output terminal, and a second input terminal; said second input terminal having a fixed interconnection to means for generating a first signal changing in logic state only upon a predetermined change in the waveform of said logic signal from said sensing means; means for selectively overriding said first signal connected to said second input terminal; a light emitting diode responsive to said logic first signal appearing at said output terminal for generating radiation; an array of photodiodes connected in series between a pair of array electrodes and operatively coupled to said light emitting diode for developing a control voltage across said array electrodes in response to radiation from said light emitting diode; a field effect transistor including a pair of current carrying electrodes, a gate electrode and a substrate electrode, one of said array electrodes connected to said gate electrode and the other of said array electrodes connected to said substrate electrode whereby the impedance between said current carrying electrodes has one value in the absence of and a greatly different value in the presence of said control voltage between said gate electrode and said substrate electrode; means for providing a large resistive impedance between said gate electrode and said substrate electrode; and a pair of output terminals, each connected to a respective one of said current carrying electrodes.