Advantages of Solid State Relay | disadvantages of Solid State Relay

This page covers advantages and disadvantages of Solid State Relay. It mentions Solid State Relay advantages or benefits and Solid State Relay disadvantages or drawbacks.

What are Solid State Relays?

• Solid state relay is substitute for Electromagnetic relay.
• It is referred as optocoupler due to its construction.
• It consists of light source (e.g. LED) and light sensor.
• It is known by acronym "SSR".
• It is mainly used to provide isolation than switching high current.

Solid State Relay

• It is a semiconductor package.
• It switches power ON or OFF between its output terminals with response to small current and voltage between input its terminals.
• These relays use LEDs, photodiodes, SCRs and thyristors for switching a circuit ON/OFF.
• The figure depicts solid state relay.
• It is available in AC or DC variants.
• It usually functions as SPST switch with either normally open or normally close versions.
➨It is intended to switch currents of at least 1A.
Refer Relay basics and types >> for more information.

Benefits or advantages of Solid State Relay

Following are the benefits or advantages of Solid State Relay:
➨It offers very fast response usually about 1µs ON and 0.5 µs OFF.
➨It has very high life time.
➨It is smaller in size.
➨There are no physical moving parts involved in the design of solid state relay. Hence there is no mechanical noise. Moreover there will be no contact bounce and clean output signal is available.
➨It offers low power consumption due to less current requirement (5mA at 5VDC) .
➨It is highly durable.
➨There are no coils in the design which can introduce back EMF into the circuitry.
➨It is insensitive to vibration.
➨As there is complete internal separation between input and output terminals, it can be used to switch high voltages.
➨Some variants can work as low as 1.5V DC unlike Electromagnetic relay which requires at least 3V DC.

Drawbacks or disadvantages of Solid State Relay

Following are the drawbacks or disadvantages of Solid State Relay:
➨It's cost is very high.
➨It is bound by specific current/voltage characteristics.
➨There is fixed value voltage drop on output due to internal impedance. Hence it is less efficient. This is negligible for high switching voltage operation.
➨There is leakage current at the output even if relay is in OFF mode.
➨It generates waste heat during ON mode. This is proportional to voltage drop.
➨It is triggered by brief voltage spikes on the input side unlike electromagnetic relay.
➨It is more vulnerable to surges and spikes in the current which is switched on output side unlike EM relay.

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