Detailed explanation of the working principle of solid state relay

What is a solid state relay

Solid state relay is composed of solid electronics new contactless switching device, using the switch transistor, three-terminal two-way thyristor switch characteristics of semiconductor devices and other electronic components, such as non-contact, no spark plug into disconnect circuit, so also known as the "contactless switch" solid state relay terminal 4 active device, two terminals for the input control terminals, The other end is the output control terminal. It has the function of amplification driving and isolation, and is suitable for the driving of high-power switch actuators. It has high reliability, no contact, long life, fast speed, little interference to the outside world, and is widely used.

Second, the structure and principle of solid state relay

Typical solid-state relays are mostly modular 4-terminal active devices, with input control terminals at both ends and output control terminals at the other end. The basic structure is shown in the following figure. Photoelectric couplers are used to achieve electrical isolation between input and output. The output control terminal uses the switching characteristics of the switching transistor, triterminal bidirectional thyristor and other semiconductor devices to realize the purpose of connecting and disconnecting the external control circuit without contact and spark. The whole equipment has no moving parts and contacts, and can achieve the same function as the usual electromagnetic relay.

Solid state relays can be roughly divided into direct current and alternating current according to the polarity of output. The control voltage of DC relay (DC-SSR) is input from the input terminal IN, and the control signal is coupled with the receiving circuit through the photoelectric coupler, which is amplified and processed to drive the SWITCHING transistor VT conduction. Obviously, the output end OUT of dc solid state relay has positive and negative points when it is connected with the controlled circuit. The circuit principle of AC solid state relay (AC-SSR) is different from that of DC solid state relay in that the switching element adopts three-terminal bi-directional thyristor VS or other AC switches, so the output terminal OUT has no positive and negative points and can control the on and off of AC circuit

Due to the mature and reliable photoelectric isolation technology between the input terminal and output terminal of the solid-state relay, the control weak current connected with the control strong current is completely isolated, so there is no need for additional protection circuit, etc., can be a variety of weak current equipment output signals directly applied to the input control terminal of the solid-state relay

Three. The characteristics of solid state relay

Solid state relay is a kind of non-contact electronic switch with isolation function, as there is no mechanical contact parts in the process of the switch, solid state relay, besides has the same function with the electromagnetic relay is also compatible with logic circuit, resistance to vibration, mechanical shock resistance, installation position is not restricted, moistureproof mildew corrosion protection performance is good, explosion-proof and anti-corrosion.

1) SSR has no mechanical parts inside and adopts perfusion fully sealed structure, which has the advantages of vibration resistance, corrosion resistance, long service life and high reliability. The switching life can reach 10.1 million times.

2) Low noise) Due to the zero-crossing trigger technology, the value of dv/ DT and DI /dt of voltage rising speed and di/dt of current rising speed are effectively reduced on the line, which greatly reduces the interference of SSR to commercial power during long-term operation.

3) Short switching time to about 10ms, can be applied to high frequency.

4) Photoelectric isolation is adopted between the input circuit and the output circuit, and the insulation voltage is not less than 2500V.

5) Low input power consumption, compatible with TTL and COMS circuits.

6) There is a protection circuit on the output terminal.

7) Strong carrying capacity.

The above is a detailed explanation of the working principle of solid state relay, if you need to know more, you can contact us at any time!