solid state relay SSR

Solid State Relay SSR is a new type of non-contact electronic switching device developed by combining modern microelectronics technology with power electronics technology. It can control the current load from 0.1A to hundreds of A with weak control signal conduction (several milliamperes to tens of milliamperes), and make or break without contact. A solid state relay is a four-terminal device, with two input terminals and two output terminals. The input terminal is connected to the control signal, and the output terminal is connected in series with the load and power supply. The SSR is actually a controlled power electronic switch, and its equivalent circuit is as shown in the figure. Related pictures of this topic are as follows: Because solid state relays have the advantages of high stability, high reliability, no contacts, and long life, they are widely used in motor speed regulation, forward and reverse control, dimming, household appliances, and oven drying tunnel heating and temperature control. , construction and transformation of power transmission and transformation grids, electric drive, printing and dyeing, plastic processing, coal mining, steel, chemical industry and military use. Working principle of solid relay circuit Solid relay is different from ordinary electromagnetic relay: no contacts, optical (electrical) isolation between input circuit and output circuit, and composed of discrete components. It is assembled from semiconductor microelectronic circuit chips and power electronic devices. It uses flame-retardant epoxy resin as raw material and uses potting technology to seal it in the shell and isolate it from the outside world. It has good pressure resistance, anti-corrosion, moisture resistance and vibration resistance. performance. Solid state relay consists of three parts: input circuit, drive circuit and output circuit. Here we only take the widely used AC zero-crossing solid relay as an example to introduce its working principle. This circuit uses zero-crossing trigger technology, which has the characteristics of turning on when the voltage crosses zero and turning off when the negative current crosses zero. A complete sinusoidal waveform can be obtained on the load, so the radio frequency interference of the circuit is very small. Related pictures on this topic are as follows: Due to different trigger signal methods, AC-SSR is also divided into two types: zero-crossing trigger (Z-type) and non-zero-crossing or random type (P-type) trigger, as shown in the picture of its working waveform. It can be seen that the difference between the zero-crossing type and the non-zero-crossing type mainly lies in the conditions for the conduction of the load AC current. At the moment t1 when the input signal Vin is applied to the zero-crossing type, since the power supply voltage is in the non-zero-crossing zone at this time, the output terminal is not conductive. Only when the power supply voltage reaches the zero-crossing zone t2, will current flow in the output load. Pass. On the other hand, for the non-zero-crossing type, at the moment t1 when the input signal Vin is applied, the load is turned on immediately regardless of the state of the power supply voltage. The shutdown conditions for these two types of solid state relays are the same.