The working principle and advantages and disadvantages of optical relays

Solid state relay is an improved form of relay, which is composed of solid materials and has better characteristics than typical relays. Relays are used for automatic power switching, to eliminate typical switching techniques that are manual and difficult to handle. Solid state relay is a type of switch, which is a non-contact switch. The manufacturing material of solid-state relays is solid-state components, and the advantage of using solid-state components is that they can control high load currents with smaller control signals. In solid-state relays, due to the characteristics of the solid-state components used in the relay, there is no possibility of ignition. It can easily achieve the turn off and conduction states of solid-state relays, and also has the advantages of logic circuit compatibility, vibration resistance, mechanical shock resistance, unlimited installation position, good moisture, mold, and corrosion resistance. It also has good performance in explosion prevention and ozone pollution prevention, low input power, high sensitivity, and low control power.
Solid state relay (also known as SSR, SS relay, SSR relay or SSR switch) is an integrated non-contact electronic switch device, tightly assembled from integrated circuits (IC) and discrete components. Its function is the same as that of an electromechanical relay, but without moving parts, so its service life is longer, but it has essentially the same function as an electromechanical relay. SSR consists of a sensor that responds to appropriate inputs (control signals), a solid-state electronic switch device that switches power to the load circuit, and a coupling mechanism that enables control signals to activate the switch without mechanical components. This relay can be designed to switch between AC or DC loads.
Encapsulated solid-state relays use power semiconductor devices such as thyristors and transistors to switch currents up to around 100 amperes. Compared to electromechanical relays, solid-state relays have faster switching speeds and no wearable physical contacts. Users of solid-state relays must consider that SSRs cannot withstand large instantaneous overloads like electromechanical relays, as well as their high "on" resistance.
Solid state relay is a four terminal active device, with two of the four terminals being input control terminals and the other two terminals being output control terminals. Although there are many types and specifications of SSR switches, their structures are similar and mainly consist of three parts: input circuit (control circuit), drive circuit, and output circuit (controlled circuit).
The input circuit of a solid-state relay, also known as the control circuit, provides a loop for the input control signal, making the control signal the trigger source of the solid-state relay. According to the different types of input voltage, input circuits can be divided into three types: DC input circuits, AC input circuits, and AC/DC input circuits.