Thyristor (History & Introduction)

History:-

The first prototype of thyristor was introduced by GEC (USA) in 1957. Bell laboratories were first to fabricate a silicon based semiconductor device called “Thyristor”.

        The name “Thyristor” come into existence after a formal decision taken at a conference held by IEC (International Electrotechnical Commission) in 1963. Prior to that it was called SCR (Silicon Controlled Rectifier). At this conference, the definition of thyristor was decided as under following points.

       1) It constitute three or more P-N junction.

      2) It has two stable states. ON state & OFF state and can change its state from one to another.

Introduction:-

Fig.-1 Thyristor Symbol

The name THYRISTOR is derived by a combination of capital letters from THYRatron & transISTOR. This means Thyristor is a solid state device like a Transistor and have characteristic similar to Thyratron tube. The term thyristor denotes a family of semiconductor devices which is used for power control in A.C. & D.C. systems. One oldest member of this thyristor family called Silicon Controlled Rectifier (SCR). SCR is the most widely used device. Symbol of SCR is given in Fig.-1.

Fig.-2 Schematic Diagram of Thyristor

Other member of Thyristor family with their Symbol in Fig.-3:-

       1) SCR:- (Silicon Controlled Rectifier)

       2) LASCR:- (Light Activated Silicon Controlled Rectifier)

       3) DIAC:- (DIode that can work on A.C.)

       4) TRIAC:- (TRIode that can work on A.C.)

       5) GCS:- (Gate Controlled Switch)

       6) SCS:- (Silicon Controlled Switch)

       7) GTO:- (Gate Turn Off Thyristor)

       8) RCT:- (Reverse Conducting Thyristor)

       9) UJT:- (Uni Junction Transistor)

     10) PUT:- (Programmable Unijunction Transistor)

Fig.-3 Other member of Thyristor family with their Symbol