A.C. Solid state relay circuit and structure

摘要

A solid state a.c. relay has two separate and indentical power thyristors connected in anti-parallel arrangement. The power thyristors are optically switched, lateral conduction devices with anode and cathode electrodes on the same surface. Both are switched by illuminating their surface by reflected illumination from an LED. Each thyristor is provided with a respective control circuit which includes a MOSFET transistor for clamping its respective thyristor gate wherever the voltage across the thryistor exceeds a given absolute value or whenever there is a high dV/dt transient across the thyristor. The control circuit for the control transistor includes a capacitance divider, one element of which is the distributed capacitance of the control transistor. The control circuit components can be integrated into the same semiconductor chip which contains the respective power thyristor. Each of the two identical power chips and the LED chip are spaced from one another and mounted on an alumina substrate. Two lead wires are stitch-bonded to the electrode pads of the two chips to connect them in anti-parallel relation, and are then stitch-bonded to two respective conductive sections on the alumina substrate. The chips and the LED are covered with a cap having a reflective interior so that illumination from the LED is reflected toward the chip surfaces. The interior of the cap is filled with a transparent plastic. The assembly is housed in either a single in-line pin housing or dual in-line pin housing and the entire housing is suitably encapsulated.