Use a multimeter to distinguish the three electrodes of the thyristor
Silicon controlled rectifier module is also called thyristor (SilicON Controlled Rectifier, SCR). Since its advent in the 1950s, it has developed into a large family. Its main members include unidirectional thyristors, bidirectional thyristors, light-controlled thyristors, reverse conduction thyristors, turn-off thyristors, fast thyristors, etc. What we use today is a unidirectional thyristor, which is what people often call ordinary thyristors. It is composed of four layers of semiconductor materials, with three PN junctions and three external electrodes: the electrode derived from the first layer of P-type semiconductor is called anode A. , the electrode drawn from the P-type semiconductor in the third layer is called the control electrode G, and the electrode drawn from the N-type semiconductor in the fourth layer is called the cathode K. As can be seen from the circuit symbol of the thyristor, it is a unidirectional conductive device like the diode. The key is that it has an additional control electrode G, which gives it completely different operating characteristics from the diode.
Use a multimeter to distinguish the three electrodes of the thyristor
The three electrodes of ordinary thyristors can be measured using the ohm dial R×100 of a multimeter. As we all know, there is a pN junction between thyristor G and K (Figure 2(a)), which is equivalent to a diode. G is the positive electrode and K is the negative electrode. Therefore, according to the method of testing the diode, find out two of the three poles. If the resistance is small, the black test lead of the multimeter is connected to the control electrode G, the red test lead is connected to the cathode K, and the remaining one is the anode A. To test the quality of the thyristor, you can use the teaching board circuit just demonstrated (Figure 3). When the power supply SB is turned on, if the light bulb glows, it is good; if it does not light, it is bad.
How to identify the three poles of thyristor
The method to identify the three poles of a thyristor is very simple. According to the principle of p-N junction, just use a multimeter to measure the resistance value between the three poles.
The forward and reverse resistance between the anode and the cathode is more than a few hundred kiloohms, and the forward and reverse resistance between the anode and the control electrode is more than a few hundred kiloohms (there are two p-N junctions between them, and the direction On the contrary, the anode and the control electrode are both forward and reverse connected).
There is a p-N junction between the control electrode and the cathode, so its forward resistance is in the range of several ohms to several hundred ohms, and the reverse resistance is larger than the forward resistance. However, the characteristics of the control electrode diode are not ideal. The reverse direction is not completely blocked and a relatively large current can pass through. Therefore, sometimes the measured reverse resistance of the control electrode is relatively small, which does not mean that the control electrode characteristics are not good. . In addition, when measuring the forward and reverse resistance of the control electrode, the multimeter should be placed in the R*10 or R*1 block to prevent reverse breakdown of the control electrode due to excessive voltage.
If it is measured that the cathode and anode of the component are short-circuited forward and reverse, or the anode and the control electrode are short-circuited, or the control electrode and cathode are short-circuited in the reverse direction, or the control electrode and cathode are open-circuited, it means that the component is damaged.
SCR is the abbreviation of silicon controlled rectifier element. It is a high-power semiconductor device with a four-layer structure with three pN junctions. In fact, the function of the thyristor is not only rectification, it can also be used as a switch to quickly turn on or off the circuit, realize the inversion of direct current into alternating current, and change the alternating current of one frequency into another frequency. AC, etc. Like other semiconductor devices, thyristors have the advantages of small size, high efficiency, good stability, and reliable operation. Its emergence has brought semiconductor technology from the weak current field to the strong current field, and has become a component that is eagerly adopted in industry, agriculture, transportation, military scientific research, as well as commerce and civil appliances.
