A Solid-State Relay

In a solid-state relay-like device, the switching can be achieved by field effect transistors driven by photodiodes. Light-emitting diodes (LED) provide the illumination required. The only coupling between drive and load portions of the circuit is optical. Experimental results are presented here and indicate that this can be a useful relay replacement for many applications. The advantages are no switching contacts, no moving parts, long life, reliability, etc.