Classification and working principle of solid state relay

 

Solid-state relay (SSR) is a non-contact electronic switch consisting of discrete components, a thin-film specific resistance network and a chip assembled by a hybrid process to achieve electrical isolation and signal coupling between the control loop (input circuit) and the load loop (output circuit). Solid state devices perform the switching function of the load and have no external moving parts. Although there are many types and specifications of solid-state relays on the market, they all work in a similar way. It is mainly composed of input (control) circuit, drive circuit and output (load) circuit

The input circuit of the solid state relay provides a loop for the input control signal, making it the trigger signal source of the solid state relay. Most of the input circuits of solid-state relays are DC input and some are AC input. Dc input circuit is divided into resistance input and constant current input. The input control current of the resistive input circuit is changing linearly with the input voltage. Constant current input circuit, when the input voltage reaches a certain value, the current will not increase significantly with the increase of voltage. The relay is suitable for a small range of input voltages

The driving circuit of solid state relay may include isolation coupling circuit, function circuit and trigger circuit. At present, optical couplers and high frequency transformers are widely used in isolated coupling circuits. Common optical couplers include optical triode, optical bidirectional thyristor, optical diode array (photovoltaic) and so on. High-frequency transformer coupling is to form a self-excited oscillation of about 10MHz under a certain input voltage, and transmit the low-frequency signal to the secondary side of the transformer through the transformer core. The functional circuit may include detection and rectification, zero crossing, acceleration, protection, display and other functional circuits. The function of the trigger circuit is to provide a trigger signal to the output device

The output circuit of the solid state relay realizes the on-off switching of the solid state relay under the control of the trigger signal. The output circuit mainly consists of an output device (chip) and a transient inhibitory absorption circuit, sometimes including a feedback circuit. At present, the output devices used by various solid-state relays mainly include transistors, thyristors or thyristors, bidirectional thyristors, MOSFET, IGBT and so on

Principle of Solid-state relay Solid-state relay (SSR) is a new type of contactless switch composed of solid-state electronic components. It uses the switching characteristics of electronic components such as switching triodes, bidirectional thyristors and other semiconductor components to achieve contactless, sparkless purposes, and can connect and disconnect circuits. For this reason, it is also known as a "non-contact switch". In CONTRAST TO PREVIOUS "COILED-REED CONTACT" RELAYS (EMR), SSR HAS NO MOVABLE MECHANICAL PARTS AND NO MECHANICAL ACTIONS DURING OPERATION. Compared with the electronic medical record, it has slow response speed, high reliability, short service life (the switching times of the solid state relay can reach 108 "109 times, 100 times lower than the usual EMR 106) no action noise, impact resistance, mechanical impact resistance, good moisture, mildew, rust resistance characteristics. These characteristics make solid state relay widely used in military, chemical and various industrial and civil electronic control equipment. The power required for control signals in solid-state relays is very high, so small signals can be used to control strong currents. At the same time, AC solid-state relay adopts zero-crossing trigger technology, so that solid-state relay can be safely used in the computer output interface, which will not cause a series of interference to the computer like electronic medical record, or even cause a slight crash. Dip encapsulation is common. According to the application, the control voltage and load voltage can be divided into AC and DC. Therefore, there will be DC-AC, DC-DC, AC-AC, and AC-DC. They are used as load switches on AC or DC power supplies and cannot be used together

According to the type of load power supply, solid state relay can be divided into AC solid state relay (AC SSR) and DC solid state relay (DC SSR). Ac solid state relay is a solid state relay that uses bidirectional thyristors as switching devices to turn on or off power to AC loads. The control triggering mode of AC solid state relay is different, which can be divided into zero-crossing triggering type and random conduction type. After the input control signal, when the AC power supply passes near zero voltage, it will carry out zero-crossing triggering AC second harmonic recovery, so the interference is very large. Random conduction type AC secondary side relays turn on or off at any phase of the AC power supply, so less interference may be generated at the moment of conduction