Solid-State Relays (SSR)

Solid-state relays incorporate an LED to control the gate of a photo-sensitive MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). This relay structure provides an isolation barrier between the control circuitry and the load allowing the relay to switch high voltage. It takes about 1 ms (depending on the relay) for the LED to power on, and 0.5 ms for the LED to power off. These times restrict the switching speed of this relay, yet SSRs are faster than electromechanical relays.