Function of thyristor
Thyristors are rectifier devices of thyristors. Small voltage and small current can be used to control large voltage and large current, which mainly plays the role of switch. Compared with the diode, the difference is that the first control electrode is turned on in the forward direction.
After a trigger pulse is given to the control terminal, it will be turned on, and AC current can be passed, from small current to thousands of amperes or more; When the AC voltage crosses zero and reverses, the thyristor turns off automatically and needs to be triggered again before it can be turned on again. Controlling the sending time of trigger pulse, counting from the zero crossing point, also known as controlling the trigger angle, can control the average current of conduction, so as to achieve the purpose of controlling large current with small signal, which is the function of thyristor.
Working principle of thyristor
In the working process of thyristor T, its anode (A) and cathode (K) are connected with power supply and load to form the main circuit of thyristor, and its grid G and cathode K are connected with the device for controlling thyristor to form the control circuit of thyristor.
Working conditions of thyristor:
1. When the thyristor bears the reverse anode voltage, the thyristor is in the reverse blocking state no matter what voltage the gate bears.
2. When the thyristor bears the positive anode voltage, the thyristor is turned on only when the grid bears the DC voltage. At this time, the thyristor is in a forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.
3. When the thyristor is on, as long as there is a certain positive anode voltage, the thyristor will remain on regardless of the gate voltage, that is, after the thyristor is on, the gate will lose its function. The gate is just a trigger.
4. When the thyristor is turned on, when the voltage (or current) of the main circuit is reduced to close to zero, the thyristor is turned off.
Working conditions of fully controlled thyristor;
1.？ When the thyristor bears the reverse anode voltage, no matter what voltage the gate bears, the thyristor is in the reverse blocking state.
2.？ When the thyristor is subjected to positive anode voltage, the thyristor is turned on only when the gate is subjected to DC voltage (or current). At this time, the thyristor is in a forward conduction state.
3.？ Once the thyristor starts to conduct, it is clamped in the conducting state, at which time the gate current can be cancelled. The thyristor can't be turned off by the gate, it conducts like a diode. It will not turn off until the current drops to zero and a reverse bias voltage is applied to the thyristor. When the thyristor enters the forward blocking state again, the gate is allowed to trigger the thyristor to conduct again at a controllable moment.
Well, this is the function and working principle of thyristor. I believe that friends who don't know thyristors at ordinary times have a certain understanding now. In fact, thyristor not only has unidirectional conductivity, but also has stronger controllability than silicon rectifier. Moreover, thyristor has the advantages of low power control, high efficiency, no spark, low cost and fast response. However, the disadvantage of thyristor is that its overload capacity is too weak and it is easily misled by interference. Therefore, thyristors are widely used in frequency conversion devices, DC-side AC inverter devices, DC -DC conversion devices and so on.