A MOSFET relay offers superior performance to an electromechanical relay in many
applications. It is a solid-state device that replaces a coil-activated mechanical switch with
an optically isolated input stage driving a MOSFET.
Internally, a MOSFET relay includes an input-side LED and an output side with a
photodiode dome array (PDA), a control circuit, and an output FET block. The operation is
as follows:
(1) The input driver circuit causes current to flow through the LED, turning it on. The driver
circuit can be as simple as a pullup resistor on pin 1 and a switch to ground on pin 2.
(2) The light from the LED output travels through the silicone resin and is converted to
voltage by the PDA.
(3) The PDA output drives the MOSFET output block
via a control circuit. The output block contains a
double MOSFET, allowing it to pass both AC and
DC loads in either direction.
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MOSFET relay block diagram
MOSFET relay construction
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What is a MOSFET Relay?
