2023-05-30
SCR for short, 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 driving device to realize the control of high-power equipment with low-power control. It has been widely used in AC and DC motor speed control system, power regulation system and servo system.
Thyristors are divided into two kinds: unidirectional thyristors and bidirectional thyristors. Bidirectional thyristor is also called TRIAC, or TRIAC for short. The bidirectional thyristor is structurally equivalent to two unidirectional thyristors in reverse connection, and this thyristor has a dual pilot pass function. Its on-off state is determined by the control pole G. Adding a positive pulse (or negative pulse) to the control pole G can make it forward (or reverse) conduction.
First, the structure of thyristor
The thyristor is a P1N1P2N2 four-layer three-terminal structural element with a total of three PN junctions. When analyzing the principle, it can be regarded as composed of a PNP tube and an NPN tube, and its equivalent diagram is shown in the figure on the right. Bidirectional thyristor: Bidirectional thyristor is a silicon controllable rectifier device, also known as bidirectional thyristor. This device can realize the contactless control of alternating current in the circuit, and control the large current with small current. It has the advantages of no spark, fast action, long life, high reliability and simplified circuit structure. From the appearance, the bidirectional thyristor is very similar to the ordinary thyristor, and also has three electrodes. However, in addition to one of the electrodes G is still called the control pole, the other two electrodes are usually no longer called the anode and cathode, but collectively referred to as the main electrode Tl and T2. Its symbol is also different from ordinary thyristors, which is drawn by connecting two thyristors together.
Its model is commonly used in our country as "3CTS" or "KS"; Foreign data are also represented by "TRIAC". The specification, model, shape and electrode pin arrangement of bidirectional thyristor vary according to the manufacturer, but most of its electrode pins are arranged from left to right according to the order of T1, T2 and G. When viewing, the electrode pins down, facing the side marked with characters.
Second, the identification method of thyristor
The method of identifying the three poles of thyristor is very simple, according to the principle of P-N junction, as long as the resistance value between the three poles is measured with a multimeter.
The forward and reverse resistance between the anode and the cathode is more than a few hundred thousand ohm, and the forward and reverse resistance between the anode and the control pole is more than a few hundred thousand ohm, and there are two P-N junctions between them, and the direction is opposite, so the anode and the control pole are not positive or negative.
There is a P-N junction between the control pole and the cathode, so its forward resistance is about a few Ohm - several hundred Ohm, and the reverse resistance is larger than the forward resistance. However, the characteristics of the control pole diode are not ideal, the reverse is not completely blocked, there can be a relatively large current through, therefore, sometimes measured the reverse resistance of the control pole is relatively small, and it does not show that the control pole characteristics are not good. In addition, when measuring the positive and negative resistance of the control pole, the multimeter should be placed in R*10 or R*1 gear to prevent the reverse breakdown of the control pole with too high voltage.
If the positive and negative directions of the anode and cathode of the component are short-circuited, or the anode and the control pole are short-circuited, or the control pole and the cathode are short-circuited, or the control pole and the cathode are disconnected, the component is damaged.
Thyristor is short for thyristor rectifier, which is a high-power semiconductor device with four-layer structure and three PN junctions. In fact, the function of the thyristor is not only rectification, it can also be used as a contactless switch to quickly turn on or off the circuit, to achieve the inverter of direct current into alternating current, alternating current of one frequency into alternating current of another frequency, and so on. Thyristor, like other semiconductor devices, has the advantages of small size, high efficiency, good stability and reliable operation. Its emergence has enabled semiconductor technology to enter the field of strong electricity from the field of weak current, and has become a component used in industry, agriculture, transportation, military scientific research, as well as commercial and civilian electrical appliances.
