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Solid State Relays

Solid-state relays are designed to switch circuitry on and off. When there is a need for switching a load of power over a circuit, solid-state relays are an excellent option.

A solid-state relay is an electrical device that switches on or off based on an external voltage of power applied to control terminals on its exterior. The function of a solid-state relay is similar to that of an electromechanical relay; the major difference between the two is that solid-state relays do not have any moving parts. Instead, the switching is performed using a series of electrical components.

When an electrical current is passed over the control terminals of the relay, it activates a switching circuit that switches the power output of the relay on or off. Because of the way that the circuits would interact if directly connected, the control and the controlled must be kept separate and isolated from each other. One method that the control section can use to switch the controlled side is by using a light-emitting diode (LED), which activates a photo-sensitive diode on the controlled section. The photo-sensitive diode then triggers another component that handles the actual switching of the secondary circuit of power.

Solid-state relays (SSRs) have a number of advantages over their mechanical cousins.

• Size: SSRs are inherently much smaller than mechanical devices, which enable them to be used in situations where space comes at a premium. Some SSRs are packaged in a case that is the same size as a mechanical switching device, which makes it easy to swap out the components without having to rework any of the existing infrastructures around the switch.
• Noise: Because they have no moving parts, solid-state relays are completely silent. There is no audible switching noise when they are in use, which can be beneficial when it is necessary to have many switches in an area where they would be heard if they were mechanical.
• Speed: The lack of moving parts also makes these devices fast. The delay time for most SSRs is nearly entirely dependent on how long it takes for the LED to light up, which is on the order of a couple of microseconds or milliseconds.
• Increased life span: With no moving parts to break or electrical contacts to corrode, these devices can have long life spans.