Solid State Relay abbreviated SSR (Solid State Relay), is a non-contact resistance switch composed of separate solid electronic components (such as optocouplers, transistors, thyristors, resistors, capacitors, integrated circuits, etc.)!

Please note here that compared with relays and contactors, solid state relays are non-contact coupling switches.

Therefore, it is widely used in computer peripheral interface equipment, constant temperature, temperature adjustment system, control electric furnace heating, etc. In addition, it is also widely used in fields such as chemical industry and coal mines that require corrosion resistance and moisture resistance.

Shape of solid state relay

The input and output of solid state relays are electrically insulated. Compared with ordinary electromagnetic relays, SSR is small in size, fast in switching speed, and has no mechanical contacts, so there is no oxidation or mechanical wear.

Because solid-state relays rely on the coupling of semiconductor devices, their interior is similar to filling glue to wrap the internal circuit, and they are not afraid of harmful gas corrosion and mechanical vibration.

In addition, SSR's low driving voltage and low current are also one of the reasons for its widespread popularity in the market.

Electricity is divided into direct current and alternating current. In the industrial field, solid state relays are divided into direct current (DCSSR) solid state relays and alternating current (ACSSR) according to different current categories.

DCSSR working principle diagram

The above schematic diagram shows that there are two pins together, namely 2, 3, 4, and 5. Among them, 4 and 5 are used for input control voltage, and pins 2 and 3 are used for output control voltage.

4N25 is a coupling circuit, and the rest are trigger circuits. When the input voltage is greater than the forward voltage drop of the light-emitting diode, IIN flows through, and then IOUT flows through. The larger the UIN, the larger the Iout, until saturation.

The external diode VD1 in the above figure is used for inductive loads (such as motors, solenoid valves, etc.) to prevent excessive voltage caused by the sudden cut-off of DCSSR.