Abstract: A high voltage multiplexer comprising as the switching elements for each nnel thereof a pair of series connected double diffused metal oxide semiconductor transistors connected source-to-source to obtain very high `off` resistance, with optical links comprising LEDs to switch the pairs of transistors `on` and `off`. A logic chip controls the switching of the transistors in accordance with externally applied signals. Circuitry is provided for rapidly discharging any voltage remaining on the gate-to-source capacity of the series-connected transistors upon the switching `off` of any channel.

Abstract: A solid state relay having a light-emitting diode, an array of series connected photodiodes, a field-effect-transistor (FET) and optically controlled switch for FET turn off is described.The light-emitting diode is optically coupled to the array of photodiodes. Turn on of the transistor is determined entirely by the voltage developed by the array of photodiodes. Turn off of the transistor is determined by the state of the optically controlled switch.