The structure, working principle and detection method of bidirectional thyristor

The structure and working principle of bidirectional thyristor
The bidirectional thyristor is made of N-P-N-P-N five-layer semiconductor material, and three electrodes are also drawn to the outside. Its structure is shown in the figure. The bidirectional thyristor is equivalent to the anti-parallel connection of two unidirectional thyristors, but there is only one control pole.
The bidirectional thyristor, like the unidirectional thyristor, also has trigger control characteristics. However, its trigger control characteristics are very different from that of a unidirectional thyristor. This is that no matter what polarity voltage is connected between the anode and the cathode, as long as a trigger pulse is added to its control electrode, it does not care about this pulse. Whatever the polarity, the bidirectional thyristor can be turned on.
Since the bidirectional thyristor can achieve trigger control at any polarity between the anode and the cathode, the main electrode of the bidirectional thyristor has no distinction between anode and cathode. These two main electrodes are usually called T1 electrode and T2 electrode. The main electrode connected to the P-type semiconductor material is called the T1 electrode, and the electrode connected to the N-type semiconductor material is called the T2 electrode.
Since the two main electrodes of the bidirectional thyristor have no difference between positive and negative, there is no difference between the positive peak voltage and the reverse peak voltage in its parameters. Instead, only one peak voltage is used. The other parameters of the bidirectional thyristor are the same as the one-way The thyristor is the same.

The structure and circuit of the bidirectional thyristor

The volt-ampere characteristic curve of the bidirectional thyristor

Because of the symmetry of the positive and negative characteristics of the bidirectional thyristor, it can be turned on in any direction and is an ideal AC switching device.
Detection method of bidirectional thyristor
(1) Electrode judgment and trigger characteristic test
Set the multimeter to the Rx1 block, and measure the resistance of any two pins of the triac. If the resistance between one pin and the other two pins is infinite, then the pin is T2 pole.
After determining the T2 pole, you can assume that one of the remaining two pins is the T1 electrode and the other is the G pole, and then use the trigger continuity test method to determine the correctness of the assumed polarity. The test method is shown in the figure. First, connect the negative test lead to the T1 pole and the positive test lead to the negative pole. The measured resistance should be infinite. Then use a wire to short-circuit the T2 pole and the G pole, which is equivalent to adding a negative trigger signal to the G pole. At this time, the measured resistance between T1-T2 poles should be about 10Ω, which proves that the bidirectional thyristor has been triggered and turned on, as shown in the figure (a ) Shown. Disconnect the short-circuit wire between the smart pole and the G pole. If the resistance value remains unchanged, it indicates that the tube can maintain the conduction state in the direction of T1→T2.
The structure, working principle and detection method of bidirectional thyristor
Then connect the positive test lead to the T1 pole and the negative test lead to the T2 pole. The measured resistance should also be infinite, and then use a wire to short the T2 pole and the G pole, which is equivalent to adding a positive trigger signal to the G pole. At this time, the measured T1 The resistance between -T2 poles should be about 10Ω, as shown in figure (b). If the resistance value of the short-circuit wire between the T2 pole and the G pole remains unchanged, it means that the tube can maintain the conduction state in the direction of T2→T1 after being triggered, and it has two-way triggering performance. The above test also proves that the assumption of polarity is correct. Otherwise, the assumption is not consistent with the actual situation. It is necessary to make a new assumption and repeat the above measurement process.
Triac test method
(2) Detection of triggering ability of high-power bidirectional thyristor
The trigger current of the low-power bidirectional thyristor is small, and the trigger performance of the tube can be checked by using the multimeter Rx1 gear. The trigger current of the high-power bidirectional thyristor is relatively large, and the multimeter Rx1 block measurement can not make the tube trigger conduction. For this reason, the method shown in the figure can be used for measurement, but power supplies of different polarities are required in the measurement to determine the bidirectional triggering capability of the tube.
Thyristor Module
Thyristor module is composed of multiple thyristors or a mixture of thyristors and rectifiers. The current capacity is generally 25~100A, and the voltage range is 400~1600V. It has the characteristics of small size, light weight, high electrical insulation between the heat sink and the circuit, convenient installation, and impact resistance. It is mainly used for power conversion and power control, such as various rectifier equipment, AC and DC motor drive circuits, and non-contact switches. And dimming devices, etc.