Solid State Relay Related Knowledge

May 10, 2019

Overview

Solid State Relay (SSR) is a non-contact switch consisting of microelectronic circuits, discrete electronic devices, and power electronic power devices. The isolation between the control terminal and the load terminal is realized by the isolation device. The input of the solid state relay uses a small control signal to directly drive a large current load.
Solid state relay (SOLIDSTATERELAYS, hereinafter abbreviated as "SSR") is a new type of non-contact switching device consisting entirely of solid-state electronic components. It utilizes the switching characteristics of electronic components such as switching transistors and triacs. It can achieve the purpose of turning on and off the circuit without contact and without spark, so it is also called "contactless switch". The solid state relay is a four-terminal active device, in which two terminals are input control terminals, and the other ends are output controlled terminals. It has both amplification driving and isolation, and is suitable for driving high-power switching actuators. Compared with electromagnetic relays, it has higher reliability, no contact, long life, fast speed, and little interference to the outside world. It has been widely used.

theory

It uses semiconductor devices instead of traditional electrical contacts as switching devices with relay characteristics. Single-phase SSR is a four-terminal active device. There are two input control terminals and two output terminals. The input and output are optically isolated. When DC or pulse signals are added to the input terminal to a certain current value, the output terminal can be changed from broken state to on-state. AC solid state relay can be divided into voltage zero-crossing conduction type (hereinafter referred to as zero-crossing type) and random conduction type (hereinafter referred to as random type) according to switching mode. According to the output switching elements, there are two-way thyristor output type (ordinary type) and one-way thyristor reverse parallel type (enhanced type).

According to installation method, there are needle-and-insert type (natural cooling, without radiator) for printed circuit board and device type (cooling by radiator) fixed on metal base plate.

In addition, the input terminal has a wide range of input (DC3 ~ 32V) constant current source type and series resistance current limiting type.

SSR solid state relay can be divided into zero voltage (Z) and phase modulation (P) relays in the form of trigger.

When an appropriate control signal IN is applied at the input end, the P-type SSR is turned on immediately. When the IN is cancelled, the SSR is turned off when the load current is lower than the current maintained by the bidirectional thyristor (AC commutation). Zero-crossing detection circuit is included in Z-type SSR. When input signal IN is applied, SSR can be turned on only when load power supply voltage reaches zero-crossing area, which may cause the maximum delay of half cycle of power supply. Z-type SSR has the same switching-off condition as P-type, but it is widely used because the working current of the load is similar to sinusoidal wave and the high-order harmonic interference is small. The SSR of Beijing Lingtong Electronics Co., Ltd. is divided into two types: ordinary type (S, using bidirectional thyristor element) and enhanced type (HS, using unidirectional thyristor element) because of different output devices. When an inductive load is added, the bidirectional thyristor is turned on before the input signal is cut off t1, and the current lags behind the supply voltage 90O (pure inductance). At t1, the input control signal is cancelled, and the bidirectional thyristor is turned off when the current is less than the maintained current (t2). The thyristor will withstand the reverse voltage with high voltage rise rate dv/dt. This voltage will be fed back to the gate through the junction capacitance inside the bidirectional thyristor. If the dv/dt index of bidirectional thyristor commutation (typical value 10V/s) is exceeded, the commutation recovery time will be long or even fail. The one-way thyristor (enhanced SSR) is in unipolar working state, which is limited by the static voltage rise rate (typical value 200V/s), so the reversing dv/dt index of the enhanced solid-state relay HS series is 5-20 times higher than that of the conventional SSR. Due to the use of two high-power one-way thyristors in reverse parallel, the current distribution and thermal conductivity conditions are changed, and the output power of SSR is increased. Enhanced SSR surpasses conventional solid state relays in high power applications, such as inductive or resistive loads, voltage and current shock resistance, and product reliability.

USAGE

The special solid-state relay can provide short circuit protection, overload protection and overheat protection. The combination logic solidification package can realize the intelligent module needed by users, and can be directly used in the control system.

Solid state relay has been widely used in computer peripheral interface equipment, constant temperature system, temperature regulation, electric furnace heating control, motor control, numerical control machinery, remote control system, industrial automation device; signal lamp, dimming, scintillator, lighting stage lighting control system; instrument and instrument, medical equipment,

photocopier, automatic washing machine; automatic fire control, security system, and as an electric power. Switching switches of power capacitors compensated by network power factors are widely used in explosion-proof, moisture-proof and corrosion-proof occasions such as chemical industry and coal mine.

Feature

Solid state relay is a contactless electronic switch with isolation function, and there is no mechanical contact component in the switching process. Therefore, solid state relay not only has the same function as electromagnetic relay, but also has logic circuit compatibility, vibration resistance and mechanical impact resistance, unlimited installation location, good moisture-proof, mildew-proof and corrosion-proof performance, explosion-proof and ozone pollution-proof performance is very good. Good, low input power, high sensitivity, low control power, good electromagnetic compatibility, low noise and high working frequency.

(1) There are no mechanical parts in SSR, and the structure of SSR is fully sealed by filling. Therefore, SSR has the advantages of vibration resistance, corrosion resistance, long life and high reliability, and its switching life is as high as 10.1 million times.

(2) Low noise: AC SSR adopts zero-crossing triggering technology, which effectively reduces the voltage rise rate dv/dt and current rise rate di/dt on the line, so that the long-term operation of SSR has minimal interference to the power market;

(3) The switching time is short, about 10 ms, which can be used in high frequency situations.

(4) Photoelectric isolation is used between the input circuit and the output circuit, and the insulation voltage is more than 2500V.

(5) Low input power, compatible with TTL and COMS circuits;

(6) There is a protective circuit at the output end.

(7) Strong load capacity.