How to measure the power supply of bidirectional thyristor? Method of judging good and bad

Thyristor is a high-power semiconductor device in semiconductor devices. Mainly used for rectification, quick disconnection or insertion of power supply, widely used in equipment support in industries, communication, transportation, and other fields. It is also a key equipment in electronic circuits. A bidirectional thyristor is equivalent to two unidirectional thyristors connected in reverse parallel. That is to say, a unidirectional silicon anode is connected to another negative electrode, and its output end is called T1 electrode. One unidirectional silicon anode is connected to the other anode, and its output end is called T2 electrode, while the rest are control electrodes (G).

1. Identification of unidirectional and bidirectional thyristors: First measure the two poles, and if the forward and reverse measuring pointers do not move (R × 1st gear)

It may be A, K or G, A-pole (unidirectional thyristor) or T2, T1 or T2, G-pole (bidirectional thyristor). If one of the measurement indications is tens to hundreds of euros, it must be a unidirectional thyristor. And the red pen is the K-pole, the black pen is the G-pole, and the remaining ones are the A-pole. If the approval for forward and reverse testing is tens to hundreds of euros, it must be a bidirectional thyristor. Then turn the knob to R × 1 or R × 10 gear retest, one of which must be slightly larger, so the slightly larger red pen is the G-pole, the black pen is the T1 pole, and the remaining is the T2 pole. 2. Feature difference: Turn the knob to R × 1st gear, 1-6A unidirectional thyristor, with red pen connected to K pole and black pen connected to G and A poles simultaneously. Cut off G pole while ensuring that the black pen does not get rid of A pole. The pointer should indicate tens to 100 ohms. At this point, the thyristor has been opened, and the opening voltage is low (or the opening current is low). Then immediately cut off the A pole and connect it again, and the pointer should return to the ∞ position, indicating that the thyristor is excellent.

For 1-6A bidirectional thyristor, the red pen is connected to T1 pole, while the black pen is connected to both G and T2 poles. The G pole is cut off while ensuring that the black pen does not get rid of T2 pole. The pointer should be marked at tens to 100 euros or more (depending on the current of the thyristor, different manufacturers). Then exchange twice and repeat the above process once. The pointer mark is slightly larger than last time by tens to tens of euros, indicating that the thyristor is excellent and the opening voltage (or current) is small. If the G pole is disconnected when connecting to the A pole or T2 pole, the pointer will immediately return to the ∞ position to indicate that the thyristor is powered on.

The quality of bidirectional thyristor can be determined using a multimeter, but specific parameters cannot be measured.

The method for measuring a multimeter is as follows:

1. Determination of T2 pole: Measure the reverse resistance of each pin using the R * 1 or R * 100 range of a multimeter. If the forward and reverse resistance of two pins is very small (about 100 ohms), it is T1 and G poles, and the remaining is T2 pole.

2. The difference between T1 and G poles: Assuming either pole is T1 and the other pole is G, set the multimeter to R * 1, touch the established T2 pole and the assumed T1 pole with two pens (regardless of positive or negative), and touch the assumed G pole at the same time. While ensuring that the assumed T1 pole continues to be opened, cut off the assumed G pole, and the multimeter still displays a guided state.

3. Swap pens and test using the same method. If the multimeter still represents the same result, then the assumed T1 and G poles are correct. If, while ensuring the continued opening of the assumed T1 pole, the assumed G pole is cut off, and the assumed T1 and G poles are opposite, the test results must be correct.

If the above results cannot be measured, it indicates that the bidirectional thyristor is faulty. Although this method cannot measure actual parameters, it is reasonable to determine whether it is available.

Service conditions of bidirectional thyristor

(1) It is allowed to exceed the positive turning voltage under additional voltage, otherwise the control pole will not work.

(2) From a safety perspective, the average on state current of thyristors is generally 1.5 to 2 times the maximum current.

(3) To ensure reliable opening of the control pole, the opening current of the added control pole generally exceeds its rated value. In addition, assurance measures must also be taken. Generally speaking, the guarantee measure for overcurrent should be to string the fast fuse into the circuit. The rated voltage is approximately 1.5 times the average value of thyristor current. Its connection position can be on the AC or DC side. For example, on the AC side, the rated voltage should be higher.

The former is usually chosen. Overvoltage protection usually occurs on inductive circuits, or caused by surge voltage on the AC side or temporary processes on the AC side. Due to the high peak overvoltage and short efficacy time, resistor and capacitor absorption circuits are often used to suppress it.

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