How to test a bidirectional thyristor with a multimeter?
Use the R×1 scale of the multimeter to determine the electrode of the bidirectional thyristor, and 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 away from the T2 pole. Therefore, the forward and reverse resistances between G-T1 are very small. When using the R×1 block to measure the resistance between any two legs, only the resistance between G-T1 is low, and the forward and reverse resistances are only tens of Ω, while the forward and reverse resistances between T2-G and T2-T1 are The reverse resistance is infinite. This shows that if there is no connection between a certain pin and the other two pins, it must be the T2 pole. In addition, for bidirectional thyristors using TO-220 packages, the T2 pole is usually connected to a small heat sink plate, and the T2 pole can also be determined based on this.
(2) Distinguish between G pole and T1 pole:
①After finding the T2 pole, first assume that one of the remaining two legs is the T1 pole and the other is the G pole.
② Connect the black test lead to the T1 pole and the red test lead to the T2 pole. The resistance is infinite. Then use the red test pen tip to short-circuit T2 and G, and add a negative trigger signal to the G electrode. The resistance value should be about 10 Ω, which proves that the tube is turned on and the direction of conduction is T1-T2. Then disconnect the red test pen tip from the G electrode (but still connect it to T2). If the resistance value remains unchanged, it proves that the tube can maintain the conductive state after being triggered.
③ Connect the red test lead to the T1 pole, and the black test lead to the T2 pole, then short-circuit T2 and G, add a positive trigger signal to the G pole, the resistance value is still about 10 Ω, if the resistance value does not change after being disconnected from the G pole, This means that after being triggered, the tube can also maintain a conductive state in the T2-T1 direction. Therefore, it has bidirectional triggering properties. This proves that the above assumption is correct. Otherwise, the assumption is inconsistent with the actual situation, and you need 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 the measurement is based on any assumption, the bidirectional thyristor cannot be triggered to conduct, proving that the tube is damaged. For 1 A tubes, R×10 block can also be used for detection. For 3A and above tubes, R×1 block should be selected. Otherwise, it will be difficult to maintain the conduction state.
