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Characteristics of solid state relays

The solid state relay is a non-contact electronic switch with isolation function, and there are no mechanical contacts during the switching process. Therefore, in addition to the same functions as electromagnetic relays, solid state relays also have logic circuit compatibility, resistance to vibration and mechanical shock, unlimited installation locations, and good moisture, mildew, and corrosion resistance. It also has excellent performance in anti-explosion and prevention of ozone pollution. It also has the characteristics of low input power, high sensitivity, low control power, good electromagnetic compatibility, low noise, and high operating frequency.

  1. SSR has no internal mechanical parts, and the structure adopts a fully-sealed perfusion method. Therefore, SSR has the advantages of vibration resistance, corrosion resistance, long life and high reliability, and the switch life is up to 10.1 million times;
  1. Low noise: AC SSR adopts zero-crossing trigger technology, which effectively reduces the voltage rise rate dv/dt and current rise rate di/dt values on the line, so that the interference to the power grid during long-term operation of the SSR is minimized;
  1. Short switching time, about 10ms, can be used in high frequency occasions;
  1. The input circuit and output circuit adopt photoelectric isolation, and the insulation voltage is above 2500V;
  1. Its input power consumption is very low, compatible with TTL and COMS circuits;
  1. The output terminal has a protection circuit;
  1. Strong load capacity.
Solid State Relay

The difference between solid state relay and ordinary relay

Ordinary relays are generally composed of relay coils and static and dynamic contacts. The movable contact is driven by the electromagnetic attraction of the relay coil to realize the on-off of the circuit. So there is mechanical movement. When the current reaches a certain level, the contacts will produce sparks. Ordinary relays are cheap and simple in structure, but sparks and mechanical movements in operation will have a certain impact on their life.

The advantages of ordinary relays are: simple drive, good isolation, and short-term overload tolerance.
The disadvantages of ordinary relays are: large size (heavy), slow response speed (up to milliseconds) and high power consumption to drive the relay.

The comparison between traditional relays and solid state relays, as it involves many types, the following is a comparison between electromagnetic relays and corresponding solid state relays to illustrate their differences:

  1. Structural differences: Electromagnetic relays work by using the suction generated by the circuit in the input circuit between the electromagnet core and armature; solid-state relays use electronic components to perform their functions without mechanical moving components, and the input and output are isolated.
  1. The working mode is different: the electromagnetic relay uses the principle of electromagnetic induction to control the on-off of the circuit through the power of the electromagnet. Therefore, when using DC to connect the coil, the contacts can pass through AC and DC; solid state relays rely on the electrical, magnetic and optical characteristics of semiconductor devices and electronic components to complete their isolation and relay switching functions. Therefore, it is divided into DC input and AC output type and DC input branch output type, AC input and AC output type, and AC input and DC output type.
  1. Differences in working conditions: Electromagnetic relays use the suction generated between the armatures to connect and disconnect the circuit. Therefore, the action response is slow, the noise is large, and the life is limited; the solid state relay has a fast response speed, works without noise, and has a long life.
  1. Working environment: Affected by temperature, humidity, atmospheric pressure (altitude), dust pollution, chemical gases and electromagnetic interference, electromagnetic relays are generally inferior to solid state relays.
  1. Electrical performance difference: Compared with the corresponding solid-state relay, the electromagnetic relay is simple to drive, but it has large power consumption, good isolation, and good short-term overload tolerance. It is not as good as the latter in the case of high current and high power. When controlling frequently operated circuits, the life of electromagnetic relays is not as long as the latter.

In short, traditional relays and solid state relays have their own advantages. The latter is more and more popular because of its reliable work, no contact, no spark, long life, no noise, no electromagnetic interference, and fast switching speed.

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