Construction principle of bidirectional thyristor _ Packaging form of bidirectional thyristor

Construction principle of bidirectional thyristor _ Packaging form of bidirectional thyristor

Bidirectional thyristor ": developed on the basis of ordinary thyristors, it can not only replace two thyristors with opposite polarity in parallel, but also only requires one trigger circuit, making it an ideal AC switching device. Its English name is TRIAC, which means three terminal bidirectional communication switch.

Principle of bidirectional thyristor construction

Although a bidirectional thyristor can be seen as a combination of two ordinary thyristors in form, it is actually a power integrated device consisting of seven transistors and multiple resistors. Small power bidirectional thyristors are generally packaged in plastic and some even come with heat dissipation plates.

Most high-power bidirectional thyristors are packaged in RD91 type.

Bidirectional thyristor belongs to the NPNPN five layer device, with three electrodes, T1 and T2、G。 Since the device can conduct bidirectionally, the two electrodes except for gate G are collectively referred to as the main terminal, represented by T1 and T2, and are no longer divided into anode or cathode. Its characteristic is that when the voltage of the G and T2 poles relative to T1 is positive, T2 is the anode and T1 is the cathode. On the contrary, when the voltage of the G and T2 poles relative to T1 is negative, T1 becomes the anode and T2 becomes the cathode. Due to the symmetry of the forward and reverse characteristic curves, bidirectional thyristors can conduct in any direction.

Bi directional thyristor packaging form

The commonly used packaging forms of thyristors include TO-92, TO-126, TO-202AB, TO-220, TO-220AB, TO-3P, SOT-89, TO-251, TO-252, etc.