Solid State Relays In India

Solid state relays are well known. Such relays, with optical isolation between input and output, are also well known. In presently existing devices, many discrete components are commonly required to complete the a.c. circuit. Thus, it maytake thirty or more discrete thyristors, transistors, resistors and capacitors to manufacture a single device. Attempts have been made to integrate the various parts of the entire solid state relay, but these have met only limited success due to the mixof high voltage and high power components.

Solid state relays made in the past have also employed zero voltage crossing circuits to ensure turn on of the thruster only when the a.c. voltage is within some small "window". These circuits have also been relatively complex and difficult to integrate into the main power chip. Thus, zero cross firing circuits have required the use of a discrete resistor connected across the power terminals. These resistors have not been easily integrated into a single chip because of the difficulty of forming this resistor on the chip surface.

Since prior art relays have been relatively complex, they have required substantial volume for their housings. Moreover, solid state relays of the past have been limited to a maximum temperature rise of about 110° C., thus limiting their current-handling capability. Finally, solid state relays of the past have been relatively expensive in view of the need for large numbers of discrete components and large housings.