A thyristor is a semiconductor device that is made on the basis of a single crystal of the same semiconductor, usually with three (possibly more) junctions. Two fairly stable states are recorded behind the thyristors - closed with low conductivity and open with high conductivity.
This device can be considered and used as an electronic switch or key, which are controlled using a load with weak signals, and can also be switched from one mode to another. The total number of modern thyristors is divided according to the control method and the degree of conductivity, which means one direction or two (such devices are also called triacs).
Thyristors are also characterized by a non-linear current-voltage characteristic with a negative differential resistance section. This feature makes such devices similar to transistor switches, but there are differences between them. So in thyristors, the transition from one state to another in an integral electrical circuit occurs by an avalanche jump, as well as by the method of external influence on the device itself. The latter is carried out in two ways - current voltage or exposure to light from a photothyristor.
Application and types of thyristors
The scope of application of these devices is quite diverse - these are electronic keys, modern CDI systems, mechanically controlled rectifiers, dimmers or power regulators, as well as inverter converters.
As mentioned above, such devices are divided into diode and triode. The first type is also called dinistors with two terminals, it is divided into devices that do not have the ability to conduct conductivity in the opposite direction, into the type with conductivity in the opposite direction and into symmetrical devices. The second includes reverse conduction SCRs, reverse conduction devices, symmetrical thyristors, asymmetric devices, and lockable thyristors.
Apart from the number of conclusions, there are no significant and fundamental differences between them. But, if the opening occurs in the dinistor after reaching a voltage between the anode and cathode, which depends on the type of device, then the existing voltage in the thyristor can be several times reduced or completely removed by applying a current pulse.
There are differences between SCRs and latching devices. So in the first type, switching to the closed state occurs after a decrease in the current or after a change in polarity, and in lockable devices, the transition to an open state is carried out by the action of a current on the control electrode.