The three electrodes of a thyristor can be distinguished using a multimeter.

The three electrodes of a thyristor can be distinguished using a multimeter.

The three electrodes of an ordinary thyristor can be measured using the R×100 range of the multimeter's ohmmeter. As we know, there is a pN junction between the G and K electrodes of a thyristor [Figure 2(a)], which is equivalent to a diode, with G being the positive pole and K being the negative pole. Therefore, following the method of testing a diode, find two of the three electrodes and measure their forward and reverse resistances. When the resistance is low, the black test lead of the multimeter is connected to the gate 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 demonstrated just now (Figure 3). Turn on the power supply SB. If the light bulb lights up, the thyristor is good; if not, it is bad.

How to Identify the Three Electrodes of a Thyristor

The method of identifying the three electrodes of a thyristor is very simple. According to the principle of the p - N junction, you only need to measure the resistance values between the three electrodes with a multimeter.

The forward and reverse resistances between the anode and the cathode are above several hundred kilohms, and the forward and reverse resistances between the anode and the gate are also above several hundred kilohms (there are two p - N junctions between them, and their directions are opposite, so there is no conduction in both the forward and reverse directions between the anode and the gate).

There is a p - N junction between the gate and the cathode. Therefore, its forward resistance is approximately in the range of a few ohms to several hundred ohms, and the reverse resistance is larger than the forward resistance. However, the diode characteristics of the gate are not ideal. The reverse direction is not completely in a blocking state, and a relatively large current can pass through. Therefore, sometimes a relatively small measured reverse resistance of the gate does not necessarily mean that the characteristics of the gate are poor. Additionally, when measuring the forward and reverse resistances of the gate, the multimeter should be set to the R×10 or R×1 range to prevent the gate from being reverse - broken down by excessive voltage.

If it is measured that the forward and reverse directions between the anode and the cathode of the component are short - circuited, or the anode and the gate are short - circuited, or the gate and the cathode are reverse - short - circuited, or the gate and the cathode are open - circuited, it indicates that the component is damaged.

A thyristor is the abbreviation of a thyristor rectifier element. It is a high - power semiconductor device with a four - layer structure and three pN junctions. In fact, the function of a thyristor is not limited to rectification. It can also be used as a non - contact switch to quickly connect or disconnect a circuit, achieve the inversion of converting direct current into alternating current, and convert alternating current of one frequency into alternating current of another frequency, etc. Like other semiconductor devices, thyristors have the advantages of small size, high efficiency, good stability, and reliable operation. Its emergence has enabled semiconductor technology to enter the field of high - power electricity from the field of low - power electricity, making it a component that is widely adopted in industries, agriculture, transportation, military research, and even in commercial and household appliances.