Testing method for thyristor (thyristor)

The international common name for thyristor (SCR) is Thyyistoy, abbreviated as thyristor in Chinese. It can operate under high voltage and high current conditions, with advantages such as high withstand voltage, large capacity, and small size. It is a high-power switch type semiconductor device widely used in power and electronic circuits.

1. Characteristics of thyristor.

Controllable silicon is divided into unidirectional controllable silicon and bidirectional controllable silicon. Unidirectional thyristor has three lead out pins: anode A, cathode K, and control electrode G. The bidirectional thyristor has three lead out pins: the first anode A1 (T1), the second anode A2 (T2), and the control electrode G.

Only when a forward voltage is applied between the anode A and cathode K of the unidirectional thyristor, and the required forward trigger voltage is applied between the control electrode G and the cathode, can it be triggered to conduct. At this point, A and K are in a low resistance conductive state, and the voltage drop between anode A and cathode K is about 1V. After the unidirectional thyristor is turned on, even if the controller G loses the trigger voltage, as long as the positive voltage is maintained between the anode A and the cathode K, the unidirectional thyristor continues to be in a low resistance conducting state. Only when the voltage of anode A is removed or the polarity of the voltage between anode A and cathode K is changed (AC zero crossing), the unidirectional thyristor will transition from a low resistance conducting state to a high resistance cutoff state. Once the unidirectional thyristor is turned off, even if a forward voltage is reapplied between anode A and cathode K, a forward trigger voltage still needs to be reapplied between control electrode G and cathode K before it can conduct. The conduction and cutoff states of a unidirectional thyristor are equivalent to the closed and open states of a switch, and it can be used to make a contactless switch.

Regardless of whether the polarity of the voltage applied between the first anode A1 and the second anode A2 of the bidirectional thyristor is forward or reverse, as long as a trigger voltage with different positive and negative polarities is applied between the control electrode G and the first anode A1, it can trigger conduction in a low resistance state. At this time, the pressure drop between A1 and A2 is also about 1V. Once a bidirectional thyristor is turned on, it can continue to maintain a conducting state even if the trigger voltage is lost. Only when the current of the first anode A1 and the second anode A2 decreases and is less than the holding current or when the voltage polarity between A1 and A2 changes and there is no trigger voltage, the bidirectional thyristor will cut off. At this time, only by re applying the trigger voltage can it conduct.

2. Detection of unidirectional thyristors.

Select the resistance R * 1 Ω range for the multimeter, and use the red and black probes to measure the forward and reverse resistance between any two pins until a pair of pins with a reading of tens of ohms are found. At this point, the black probe's pin is the control terminal G, the red probe's pin is the cathode K, and the other empty pin is the anode A. At this point, connect the black probe to the identified anode A and the red probe to the cathode K. At this time, the multimeter pointer should not move. Instantly short-circuit anode A and control electrode G with a short wire. At this time, the resistance range pointer of the multimeter should deflect to the right, and the resistance reading should be around 10 ohms. When anode A is connected to the black probe and cathode K is connected to the red probe, if the multimeter pointer deviates, it indicates that the unidirectional thyristor has been broken down and damaged.

3. Detection of bidirectional thyristors.

Use a multimeter resistor R * 1 Ω to measure the forward and reverse resistance between any two pins with red and black probes, and the results show that two sets of readings are infinite. If a group has tens of ohms, the two pins connected to the red and black meters of the group are the first anode A1 and the control electrode G, and the other empty pin is the second anode A2. After determining the A1 and G poles, carefully measure the positive and negative resistance between A1 and G poles. The pin connected to the black probe of the measurement with a relatively small reading is the first anode A1, and the pin connected to the red probe is the control pole G. Connect the black probe to the determined second anode A2 and the red probe to the first anode A1. At this point, the multimeter pointer should not deflect and the resistance value should be infinite. Then use a short circuit wire to instantly short-circuit the A2 and G poles, and apply a positive trigger voltage to the G pole. The resistance between A2 and A1 is about 10 ohms. Then disconnect the short circuit between A2 and G, and the multimeter reading should remain around 10 ohms. Swap the red and black probe connections, with the red probe connected to the second anode A2 and the black probe connected to the first anode A1. The pointer of the multimeter should not deflect and the resistance should be infinite. Use a short circuit wire to instantly short-circuit the A2 and G poles again, and apply a negative trigger voltage to the G pole. The resistance between A1 and A2 is also about 10 ohms. Then disconnect the short circuit between A2 and G poles, and the multimeter reading should remain unchanged at around 10 ohms. If the above rules are met, it indicates that the tested bidirectional thyristor is not damaged and the polarity judgment of the three pins is correct.

When detecting high-power thyristors, it is necessary to connect a 1.5V dry battery in series with the black pen of the multimeter to increase the trigger voltage.

4. Pin discrimination of thyristor (thyristor)

The discrimination of thyristor pins can be done using the following method: first, measure the resistance between the three pins with a multimeter in R * 1K range. The two pins with lower resistance are the control electrode and cathode, and the remaining pin is the anode. Place the multimeter in the R * 10K position, pinch the anode and the other foot with your fingers, and do not let the two feet touch. Connect the black probe to the anode and the red probe to the remaining foot. If the probe swings to the right, it indicates that the red probe is connected to the cathode, and if it does not swing, it is the control electrode.