Unidirectional thyristor (SCR) in detection circuit

Identify each electrode

According to the structure of common thyristors, there is a PN junction between the gate G and the cathode K, which has unidirectional conductivity, and there are two PN junctions in series with opposite polarity between the anode A and the gate. Therefore, by measuring the resistance value between the pins of the common thyristor with the R×100 or R×1kQ range of the multimeter, the three electrodes can be determined.

The specific method is: connect the black probe of the multimeter to any one of the thyristor electrodes, and the red probe to the other two electrodes in turn. If the resistance is several thousand ohms (kΩ) in one measurement and several hundred ohms (Ω) in another measurement, it can be determined that the black probe is connected to the gate G. In the measurement of the resistance of several hundred ohms, the red probe is connected to the cathode K, and in the measurement of the resistance of several thousand ohms, the red probe is connected to the anode A. If the resistance values ​​measured twice are both large, it means that the black probe is not connected to the gate G. Use the same method to measure other electrodes until three electrodes are found.

You can also measure the forward and reverse resistance between any two legs. If the forward and reverse resistances are close to infinity, the two poles are the anode A and the cathode K, and the other leg is the gate G.

The electrodes of ordinary thyristors can also be identified based on their packaging form.

For example: the bolt end of a bolt-shaped ordinary thyristor is the anode A, the thinner lead end is the gate G, and the thicker lead end is the cathode K.

The lead end of the flat-plate ordinary thyristor is the gate G, the flat end is the anode A, and the other end is the cathode K.

The outer shell of the ordinary thyristor with metal shell package (T0-3) is the anode A.

The middle pin of the ordinary thyristor with plastic package (T0-220) is the anode A, and is usually connected to its own heat sink.

Figure 1 shows the pinout of several common thyristors.