Relays are a type of switching device that are often found in countless electrical assemblies, allowing for multiple circuits to be controlled with ease. Relays may come in a number of types and forms to accommodate particular applications and needs, and solid state relays (SSR) are a particular variation that utilizes semiconductors to switch high voltage circuits. Finding use for the management of AC power, motor speed control, power switching, and much more, it can be useful to have a general understanding of how such relays operate, as well as the different subtypes that are available.
While a majority of relays that manage electronic devices utilize electromechanical parts for their operations, solid state relays are completely devoid of any moving components. This can be advantageous for a number of reasons, one being that the lack of moving parts increases reliability and service lives as less wear occurs. In order to achieve switching capabilities, the solid state relay relies on either a thyristor, TRIAC, or other switching device that is managed by a control signal. If controlled circuits require isolation, an optocoupler may be used.
Solid state relays often consist of two terminal sets, those of which are the input and output terminals. The input control terminals are often attached to a low power circuit, allowing for switching to be managed with ease. Generally, the control input will be specifically designed for DC or AC circuitry. The output terminals, meanwhile, will often differ in their design and functionality based on the control input.
When a relay contains normally open (NO) terminals, the electrical connection will remain open during standard operations. Once the relay activates, the terminal will then close so that voltage can move through the system. With a normally closed (NC) circuit, meanwhile, terminals will be closed until the relay is actuated. As a result, current will continuously flow until the activation of the relays, at which point voltage flow will cease.
For the activation of solid state relays, a low voltage is first induced to the input control terminals. This causes the output load terminals to short, and the SSR relay input will activate an optocoupler in order to switch the load circuit. As the optocoupler lacks any physical connection, it will be able to isolate the low voltage circuit from the high voltage circuit. To notify a user of applied voltage, the optocoupler has an LED that is supplied light from a photo-sensor. In order for the optocoupler to sufficiently activate, it needs to have an input voltage that is higher than the forward voltage. As such, solid state relays are unable to activate when the voltage falls below specific requirements.
When searching for a particular solid state relay for your electronic devices, it is important to note that different types vary by their input/outputs or switching properties. Generally, the most popular types are the DC-to-AC SSR relay, AC-to-AC SSR relay, DC-to-DC SSR relay, and DC-to-AC/DC SSR relay. Once you have determined the particular needs of your application and have settled on a particular SSR relay type, allow the experts at NSN World to help you source all your needed parts with time and cost savings.
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