An SSR or a Solid State Relay is a piece of electronic switching equipment which when applied by a small external voltage across its control terminal switches ON and OFF. SSRs have a sensor in them that reacts to a proper control signal (input), a piece of switching equipment that changes power to the load circuit, and a coupling process to empower the control signal to initiate this switch without the help of any mechanical parts. The relay might be made to switch either DC or AC to the load. It offers the same functionality as that of an electromechanical relay but comes with no moving parts.

Packaged Solid State Relay utilizes power semiconductors like transistors and thyristors to change the electrical current approximately to hundred Amperes. The switching speed of solid-state relays is comparatively faster than that of the electromechanical relays. In addition to that, it has no physical contacts to wear out. The devices using the Solid State Relays must take into consideration their higher value of “ON” state resistance as well as their lower capacity to hold out against momentary overload. In contrast to an electrochemical relay, the SSR offers only a limited amount of switching arrangement.

Operation

A Solid State Relay that works based on a particular MOSFET (or multiple ones in a parallel array) works well with DC loads. This MOSFET comes with a substrate diode which helps in the conduction of electricity in the reverse direction. Thus it is not possible for a particular MOSFET to stop the current in both directions. To carry out an AC operation, 2 MOSFET are positioned one after the other with their source pins integrated. The output side is connected with their drain pins. The substrate diodes are reverse biased alternately such that the current can be blocked whenever the relay is OFF. Whenever the relay is ON both the gates are positively biased comparative with the source by the photograph diode.

Parameters

Solid State Relay is governed by several parameters. They are:

• Required activating output current and voltage
• Required activating input current and voltage
• AC or DC
• Resistance or potential drop affecting the output current and thermal resistance.
• SSRs are much less sensitive to operating environment and storage factors like humidity, mechanical shock, external magnetic fields, and vibration.

Advantages of SSR over Mechanical Relays:

• Slimmer and smaller than a mechanical relay.
• It carries out a totally silent operation.
• The switching speed of SSRs is much faster than that of electromechanical relays.
• The output resistance does not vary regardless of the amount it is utilized.
• The operation is bounceless and clean.

Disadvantages:

• For the gate charged circuit an isolated bias supply is needed.
• There is a chance of false switching because of the voltage’s momentary variations.

Hope you liked going through the article on Solid State Relay. Brands that make SSRs are Crydom, Omron and Phoenix Contact. Make sure to follow them using the links as provided here. Thank you for reading.

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