Solid State Relay

The solid-state relay (SSR) is an electronic switching device that switches on or off when an external voltage is applied across its terminals. Solid State Relays (SSRs) generally switch high voltage circuits on and off using the low voltage at their control terminals. A solid-state relay (SSR) does not include moving parts, making it less prone to wear and tear and more reliable than a mechanical relay. SSRs are typically used where control signals are produced by digital circuitry, such as microprocessors or programmable logic controllers (PLCs), and AC or DC loads are controlled. Besides industrial controls, lighting controls, HVAC, process controls, and other applications requiring high voltage or high current loads, they are also used to switch loads of high voltage and high current. Solid-state semiconductors utilize semiconductors’ electrical and optical properties instead of moving components to control input-to-output actions.

It is an electronic switching device made of semiconductors with no movable parts. Due to no moving components, it is a Solid State Relay, and thus does not undergo any wear and tear on contact, making it long lasting for up  to 100 million operations.

What does Solid State Relay do?

• The major function is to switch “ON” or “OFF”  and control a high voltage load.
• It provides complete electrical isolation between their input and output contacts.
• Solid State relays control the power using a relatively low voltage input.

How does a Solid State Relay work?

• Solid State Relay input circuit: The input circuit is responsible for relaying the signal to the control system. Once the input voltage changes, the circuit activates if the input voltage exceeds the relay’s voltage range and deactivates if input voltage drops below the range.

• Solid State Relay Coupling: It is a relaying interface between the input circuit and output circuit of the SSR. It isolates the two circuits operating at different reference voltages and prevents high output load from flowing to input. SSR Coupling transmits the energization and de-energization commands to the output circuit.

• Solid State Relay trigger circuit: It drives the relay action to the system load and triggers the current to flow in the load circuit turning it ON. It may depend on the type of output load such as zero-switching, DC Switching, peak switching etc.

• Solid State Relay Output Circuit: It connects the SSR to the load that is supposed to be controlled. Once the trigger switches On, current flows in the output circuit and resultantly switching ON the load.
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