Thyristor Silicon Controlled Rectififier (SCR) is a high-power electrical component, also known as thyristor. It has the advantages of small size, high efficiency and long life. In the automatic control system, it can be used as a high-power drive device to control high-power devices with low-power controls. It has been widely used in AC and DC motor speed control systems, power adjustment systems and servo systems.
The thyristor is divided into a unidirectional thyristor and a two-way thyristor. The two-way thyristor is also called triac, or TRIAC for short. The triac is structurally equivalent to two unidirectional thyristor reverse connections, and the thyristor has a dual-conducting function. Its on-off state is determined by the gate G. Adding a positive pulse (or a negative pulse) to the gate G can make it forward (or reverse). The advantage of this device is that the control circuit is simple and has no reverse voltage resistance, so it is especially suitable for AC non-contact switches.
working principle
Original structure
The thyristor is a P1N1P2N2 four-layer three-terminal structural component with three PN junctions. When analyzing the principle, it can be considered as consisting of a PNP tube and an NPN tube. The equivalent diagram is shown in the right figure. Two-way thyristor: A triac is a Silicon Controlled Rectifier device, also known as a triac. The device can realize the non-contact control of the alternating current in the circuit, control the large current with a small current, and has the advantages of no spark, fast action, long life, high reliability, and simplified circuit structure. From the outside, the two-way thyristor is similar to a common thyristor, and there are also three electrodes.
However, except that one of the electrodes G is still called the control electrode, the other two electrodes are usually no longer called the anode and the cathode, but are collectively referred to as the main electrodes T1 and T2. Its symbol is also different from ordinary thyristor, which is formed by reversing two thyristors together, as shown in Figure 2. Its model number is generally expressed in China as "3CTS" or "KS"; foreign materials are also represented by "TRIAC". The specifications, model, shape and electrode lead arrangement of the two-way thyristor vary from manufacturer to manufacturer, but most of the electrode pins are arranged from left to right in the order of T1, T2, and G. Pin down, facing the side marked with a character).
Thyristor Thyristor is the abbreviation of thyristor, also known as thyristor rectifier, formerly referred to as thyristor; in 1957, the United States General Electric Company developed the world's first thyristor product, and in 1958 will Commercialization; thyristor is a PNPN four-layer semiconductor structure with three poles: anode, cathode and gate; thyristor has the characteristics of silicon rectifier device, can work under high voltage and high current conditions, and its working process can be controlled, It is widely used in electronic circuits such as controllable rectification, AC voltage regulation, non-contact electronic switches, inverters and inverters.
working principle
During the operation of the thyristor, its anode (A) and cathode (K) are connected to the power source and the load to form the main circuit of the thyristor. The gate G and the cathode K of the thyristor are connected to the device for controlling the thyristor to form a control circuit for the thyristor. The thyristor is a semi-controlled power electronic device, and its working conditions are as follows:
1. When the thyristor is subjected to a reverse anode voltage, the thyristor is in a reverse blocking state regardless of the voltage applied to the gate.
2. When the thyristor is subjected to the forward anode voltage, the thyristor is turned on only when the gate is subjected to the forward voltage. At this time, the thyristor is in a forward conduction state, which is the thyristor thyristor characteristic and controllable characteristic.
3. When the thyristor is turned on, as long as there is a certain positive anode voltage, regardless of the gate voltage, the thyristor remains turned on, that is, after the thyristor is turned on, the gate loses its effect. The gate only acts as a trigger.
4. When the thyristor is turned on, the thyristor turns off when the main circuit voltage (or current) decreases to near zero.
The difference between thyristor and thyristor Thyristor (THYRISTOR), also known as thyristor, belongs to the field of power devices. It is a power semiconductor switching device. SCR is its abbreviation. According to its working characteristics, thyristor can be divided into unidirectional thyristor (SCR). Two-way thyristor (TRIAC). The thyristor, also called a thyristor, is an element composed of a PNPN four-layer semiconductor having three electrodes, an anode A, a cathode K, and a gate G. The thyristor can realize the non-contact control of the alternating current in the circuit, control the large current with a small current, and has no spark generated when the control is like the relay, and the action is fast, the service life is long, and the reliability is good. It is available in speed control, dimming, voltage regulation, temperature regulation, and various other control circuits. SCRs are unidirectional and bidirectional, and the symbols are different.
The unidirectional thyristor has three PN junctions, and two electrodes are drawn from the outermost P pole and the N pole, respectively called anode and cathode, and a control pole is drawn from the middle P pole. The unidirectional thyristor has its unique characteristics: when the anode is connected to the reverse voltage, or the anode is connected to the forward voltage but the control pole is not applied with voltage, it is not turned on, and when the anode and the control pole are connected to the forward voltage at the same time, It will become conductive. Once turned on, the control voltage loses its control, and it is always on regardless of the control voltage or the polarity of the control voltage. To turn off, only reduce the anode voltage to a certain threshold or reverse.
The pins of the triac are mostly arranged from left to right in the order of T1, T2, and G (the electrode pins are down, facing the side with characters). When the magnitude or time of the trigger pulse applied to the gate G is changed, the amount of the on current can be changed. The difference from the unidirectional thyristor is that when the polarity of the trigger pulse on the G-switch of the triac changes, the conduction direction changes with the change of the polarity, so that the AC load can be controlled. The one-way thyristor can only be turned on from the anode to the cathode in one direction after being triggered, so the thyristor has a single bidirectional division. The thyristor is commonly used in electronic production, the MCR-100 is unidirectional, and the bidirectional thyristor such as TLC336 is divided into quadrants according to the quadrant, and is divided into four-image three-terminal two-way thyristor and three-quadrant two-way thyristor; According to the package:
Divided into general semi-Plastic Package, external insulation type plastic packaging; according to the trigger current to divide: divided into micro-touch type, high sensitivity type, standard trigger type; according to voltage points: conventional voltage varieties, high-pressure varieties. Since its thyristor product has high efficiency, good control characteristics, long life, small size and strong function in circuit applications, it has developed rapidly since the 60th generation of the last century. Independent discipline. "Thyristor communication technology." The development of thyristors to today, the process is very mature, the quality is better, the yield rate is greatly improved, and the development of high voltage and high current.
The role of thyristor in the application circuit is reflected in: Controlled rectification: like diode rectification, rectifying AC to DC, and effectively controlling the DC output voltage to control rectification when the AC voltage is constant. Realize AC → variable DC transition; contactless power static switch (solid state switch):
As a power switching element, a thyristor can be used instead of a contactor or a relay for a high switching frequency. Therefore, the thyristor component is widely used in circuits of various electronic devices and electronic products, and is used for controllable rectification, inverter, frequency conversion, voltage regulation, and non-contact switching. Dimming lights, speed control fans, air conditioners, water heaters, televisions, refrigerators, washing machines, cameras, audio combinations, voice control circuits, timing controllers, induction lights, Christmas lights controllers, automatic doors, and toys in household appliances Thyristors are widely used in industrial control fields such as devices, power tool products, radio remote control circuits, and video cameras. In these application circuits, thyristor components are often used for controlled rectification, inverter, frequency conversion, voltage regulation, and non-contact switching.
