The three electrodes of thyristor can be distinguished by multimeter.
Thyristor module is also called SilicON Controlled Rectifier, SCR). Since it came out in 1950s, it has developed into a large family, and its main members are unidirectional thyristors, bidirectional thyristors, light-controlled thyristors, reverse thyristors, turnoff thyristors, fast thyristors, and so on. Today, people use unidirectional thyristors, which are often referred to as ordinary thyristors. They are composed of four layers of semiconductor materials, with three PN junctions and three external electrodes: the first layer of P-type semiconductor is called anode A, the third layer of P-type semiconductor is called control electrode G, and the fourth layer of N-type semiconductor is called cathode K.. As can be seen from the circuit symbol of thyristor, it is a unidirectional conductive device like diode, and the key is to add a control electrode G, which makes it have completely different working characteristics from diode.
Three electrodes of thyristor can be distinguished by multimeter.
The three electrodes of common thyristor can be measured by R×100 ohm block of multimeter. As we all know, there is a pN junction between thyristors G and K [Figure 2 (a)], which is equivalent to a diode, with G as the positive electrode and K as the negative electrode. Therefore, according to the method of testing diodes, find out two of the three poles and measure their positive and negative resistances. When the resistance is small, the black stylus of the multimeter is connected to the control electrode G, the red stylus is connected to the cathode K, and the remaining one is the anode A. To test the quality of thyristor, you can use the teaching board circuit just demonstrated (Figure 3). When the power supply SB is connected, the light bulb is good if it shines, and it is bad if it doesn't.
How to identify three poles of SCR
The method of identifying the three poles of SCR is very simple. According to the principle of p-N junction, just use multimeter to measure the resistance between the three poles.
The forward and reverse resistances between the anode and the cathode are above several hundred kiloohms, and the forward and reverse resistances between the anode and the control electrode are above several hundred kiloohms (there are two p-N junctions between them, and the directions are opposite, so both the anode and the control electrode are blocked).
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 diode characteristics of the control electrode are not ideal, and the reverse direction is not completely blocked, so a relatively large current can pass. 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 R*10 or R*1 to prevent the control electrode from reverse breakdown due to excessive voltage.
If it is measured that the anode and cathode of the element are short-circuited, or the anode is short-circuited with the control electrode, or the control electrode is short-circuited with the cathode, or the control electrode is open-circuited with the cathode, the element is damaged.
Silicon controlled rectifier is the abbreviation of silicon controlled rectifier, which is a high-power semiconductor device with three pN junctions and four-layer structure. In fact, the function of silicon controlled rectifier is not only rectification, but also can be used as a switchless switch to quickly turn on or off the circuit, realize the inverter to change DC into AC, and change AC of one frequency into AC of another frequency, and so on. Silicon controlled rectifier, like other semiconductor devices, has the advantages of small size, high efficiency, good stability and reliable operation. Its appearance has made semiconductor technology enter the field of strong electricity from the field of weak electricity, and it has become an element to be used in industry, agriculture, transportation, military scientific research, commerce and civil appliances.
