What are the advantages and disadvantages of solid state relays?

2020-12-14 11:43:40

The English name of solid state relay (also called solid state relay) is solid state relay, abbreviated as SSR. It is a non-contact switching device with relay characteristics that uses semiconductor devices instead of traditional electrical contacts as switching devices. Single-phase SSR is a four-terminal active device, of which two input control terminals, two output terminals, the input and output are optical Isolation, after adding a DC or pulse signal to the input to a certain current value, the output can change from off state to on state.

Solid state relays are reliable, long life, no noise, no sparks, no electromagnetic interference, fast switching speed, strong anti-interference ability, and small size, impact resistance, vibration resistance, explosion-proof, moisture-proof, corrosion-proof, and can be compatible with TTL, DTL, HTL and other logic circuits are compatible, and can directly drive large current loads with tiny control signals.

Advantages of solid state relay

1. Long life and high reliability: SSR has no mechanical parts and solid components to complete the contact function. Since there are no moving parts, it can work under high impact and vibration environments. Due to the inherent components of solid state relays The characteristics determine the long life and high reliability of solid state relays.

2. High sensitivity, low control power, and good electromagnetic compatibility: The solid state relay has a wide input voltage range and low drive power, and is compatible with most logic integrated circuits without buffers or drivers.

3. Fast switching: Solid state relays can switch from milliseconds to subtle speeds because solids are used between them.

4. Low electromagnetic interference: The solid state relay has no input coil, no contact arc and rebound, thereby reducing electromagnetic interference. Most AC output solid state relays are zero-voltage switching, which opens at zero voltage and closes at zero current, reducing the sudden interruption of current fluctuations, thereby reducing the switching transient effect.


Disadvantages of solid state relays

1. The pressure drop of the tube after it is turned on is large, the forward voltage drop of the thyristor or two-phase thyristor can reach 1~2V, and the saturated slurry of high-power transistors is between 1~2V, and the general power field effect tube The conduction electricity progenitor is also larger than the contact resistance of the mechanical contact.

2. After the semiconductor device is turned off, there may still be a leakage current of a few microamperes to a few milliamperes, and ideal electrical isolation cannot be achieved.

3. Due to the high voltage drop in the tube, the power consumption and heat generation after power-on are also large, and the volume of high-power solid-state relays is much larger than that of the same capacity. Magnetic relays are also expensive.

4. The temperature characteristics of electronic components and electronic circuits have poor anti-interference ability and poor anti-radiation ability. If effective measures are not taken, the working reliability will be low.

5. Solid state relays are sensitive to overload and must be protected by fast fuse or RC damping circuit. The load of the solid state relay has an obvious relationship with the ambient temperature. As the temperature increases, the load capacity will drop rapidly.