The PhotoMOS relay has LED inputs and MOSFET outputs, hence providing good input-output isolation. When a signal current flows into the LED input pin, light emitted from the LED is detected by the photoelectric element (solar cell) which is mounted adjacent to the LED.
The photoelectric element converts the received light source to a voltage signal which in turn charges the MOSFET gate on the output side. When the voltage reaches a preset voltage level, the MOSFET begins to conduct and turns the load on.
A simplified circuit of PhotoMOS relay is shown in figure 1 below.
The PhotoMOS relay incorporates the advantages of both a semiconductor and an electro-mechanical relay.
The PhotoMOS relay utilizes the MOSFET as a switch instead of the mechanical contact, thus the contact resistance remains stable through the life of the relay. Furthermore, relay bouncing problems are eliminated.
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