What Is a Solid-State Relay and How Does It Work?

Relays are important electronic devices that open and close circuit contacts, and the solid state relay (SSR) is a specialized type capable of performing its job without using any moving parts. Solid state relays utilize semiconductor elements to manage circuits, and while performing the same duties as a conventional electromechanical type, SSRs face much less wear and tear due to their motionless design. Despite their various advantages, solid state relays perform best under specific conditions and applications, making it important to have a better understanding of their design, functionality, and use before making a purchasing decision.

As stated before, solid state relays are quite similar to electromechanical relays, both utilizing a control circuit and separate circuit to switch a load. Despite this, their operating principle is where they differ from one another. To begin relay operations, voltage will need to first be applied to the input of the SSR, that of which sources from a photocoupler, diode, LED, resistor, or transistor. From the relay input, an electrical signal is transferred over to the trigger circuit that is situated in the output circuits, and this causes the switching element to turn on. With the activation of the switching element, a load current will begin to flow, allowing for the connected device to be governed. To switch the SSR off, the input voltage simply needs to be removed.

Typically, solid state relays are divided into two groups based on their operation, those of which are relays that switch at zero-crossing and those that are random-on relays. Zero-crossing solid state relays are those that switch on and activate upon the voltage crossing zero, while they will deactivate when the current reaches zero. With their basic set of operations, zero-crossing relays are generally relied on for applications where there is a need for the management of resistive, inductive, or capacitive loads. Random-on, or instant, relays actuate when the control voltage is first applied, meaning that it is able to turn on very quickly. As such, it is often used when a fast response time is needed or desired, such as when inductive loads are being managed.

With either option, there are a few factors that one should consider before making a final decision. For instance, knowing the load voltage, maximum load current, leakage current, and output ON voltage drop values of a relay is important to ensure that it will perform reliably in an application. Once you have determined the exact requirements of your project, let the experts at Nascent Aero help you secure all you require with ample time and cost savings.

At Nascent Aero, we have over 2 billion items in stock, those of which cater to a diverse set of industry verticals. Take the time to peruse our massive set of offerings as you see fit, and note that all items you come across are ready for purchase at any time. If you would like a quote for your comparisons, simply fill out and submit an RFQ form at your earliest convenience, and a team member will reach out within 15 minutes or less to present you with a customized solution based on your needs. Get in touch with a representative today through phone or email and see how we can serve as your strategic sourcing partner for all your operational needs!