How to detect bidirectional thyristor with multimeter?
Answer: The method of judging the electrode of bidirectional thyristor with multimeter R×1 can also check the triggering ability.
(1) Determine the T2 pole: the G pole of the bidirectional thyristor is close to the T1 pole and far from the T2 pole. Therefore, the forward and reverse resistances between G and G-T1 are very small. When measuring the resistance between any two feet with R×1, only the resistance between G and T1 is low, and the positive and negative resistances are only tens of ω, while the positive and negative resistances between T2-G and T2-T1 are infinite. This shows that if one foot and the other two feet are blocked, it must be T2 pole. In addition, the T2 pole of the TO-220-encapsulated bidirectional thyristor is usually connected with a small heat dissipation plate, so the T2 pole can also be determined.
(2) distinguish between G pole and T1 pole:
① After finding the T2 pole, first assume that one of the remaining two feet is the T1 pole and the other is the G pole.
② Connect the black stylus to the T1 pole and the red stylus to the T2 pole, and the resistance is infinite. Then short-circuit T2 and G with the tip of a red meter, and add a negative trigger signal to G pole. The resistance value should be about 10 Ω, which proves that the tube has been conducted, and the conducting direction is T1-T2. Then disconnect the pen tip of the red meter from the G pole (but it is still connected to T2). If the resistance value remains unchanged, it proves that the tube can maintain the conduction state after being triggered.
(3) Connect the red stylus to the T1 pole and the black stylus to the T2 pole, then short-circuit T2 and G, and add a positive trigger signal to the G pole, and the resistance value is still about 10 Ω. If the resistance value remains unchanged after being disconnected from the G pole, it means that the tube can maintain the conduction state in the T2-T1 direction after being triggered, so it has the property of bidirectional triggering. This proves that the above assumption is correct. Otherwise, the assumption is inconsistent with the actual situation, and it is necessary to make another assumption and repeat the above measurement. Obviously, in the process of identifying G and T1, the triggering ability of the bidirectional thyristor is also checked. If measured according to any assumption, the bidirectional thyristor can not be triggered to conduct, which proves that the tube has been damaged. For tubes with 1 A, R×10 can also be used for detection. For tubes with 3A and above, R× 1 should be selected, otherwise, it is difficult to maintain the conduction state.
