Solid state relay working principle

6.3V220UF Volume: 5X8 own factory direct sales - solid capacitor - patch aluminum

Guide: Solid state relay is an electronic switching device. This article mainly introduces the working principle of solid state relay . Let's learn how it works with Xiaobian.

1. Solid State Relay Working Principle--Introduction

Solid State Relay (SSR) is a new type of contactless electronic switching device developed by combining modern microelectronic technology with power electronics technology. It is a four-terminal device with two terminals as the input and the other two as the output. The isolation device is used to realize the electrical isolation of the input and output. Solid state relays can be classified into AC type and DC type according to the type of load power supply. According to the switch type, it can be divided into normally open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type and photoelectric isolation type, and the photoelectric isolation type is the most.

2. Solid state relay working principle - structure

Solid state relays are a new type of contactless electronic switching device developed by combining modern microelectronic technology with power electronics technology. It can control the 0.1A up to several hundred A current load with a weak control signal to perform contactless switching or breaking. The solid state relay consists of three parts: the input circuit, the isolation and the output circuit.

Input circuit ---- According to different types of input voltage, the input circuit can be divided into DC input circuit, AC input circuit and AC/DC input circuit.

Isolation Coupling----The isolation and coupling of the input and output circuits of solid state relays are optocoupler and transformer coupling.

Output Circuit ---- The power switch of SSR is directly connected to the power supply and the load end to realize on-off switching of the load power supply.

3. The working principle of solid state relay

Here, only the AC zero-crossing solid state relay with more applications is taken as an example to introduce its working principle. The circuit adopts the zero-crossing triggering technology, which has the characteristic of turning on when the voltage crosses zero, and turns off when the negative cutting current crosses zero. A complete sinusoidal waveform can be obtained on the load, so the radio frequency interference of the circuit is small.

The circuit is composed of a signal input circuit, a zero voltage detection control circuit, a work indication circuit, a triac control circuit and an absorption circuit. The photocoupler GD is used as an isolation element between the input circuit and the output circuit, and the VD is to prevent Vin from being positively and negatively connected to the anti-burnout GD.

Circuit operation process: When there is no input signal, the phototransistor in GD is cut off, VT1 is the AC voltage zero detector, the base current is obtained by R3 and satisfies the conduction, and the gate of VTH is clamped to the low potential and is turned off. status. When there is an input signal, the phototransistor is turned on. At this time, the state of VTH is determined by VT1. When the power supply voltage is greater than the zero-crossing voltage, the voltage of the voltage divider P of the voltage divider R3 and R2 is greater than VBE1, and the VT1 is saturated. The SCR gate is turned off due to the clamp being at a low potential, and the gate of the TR is turned off due to the absence of a trigger pulse. Only when the power supply voltage is less than the zero-crossing voltage, when the voltage at point P is less than VBE1, G1 is turned off, and the SCR gate is turned on by the trigger signal. A trigger pulse is obtained at the gate of the TR, and the TR is turned on, thereby turning on the load power.

Expand reading:

1. The difference between DC solid state relay and AC solid state relay

2. Introduction to solid state relays and working principle

3. Those circuit design tools that engineers can't do without

cell phone battery