TRIAC-Symbol, Construction,Working with operation

TRIAC is detailed with construction,working operation,characteristics,applications, advantage and disadvantage in easy language.

  INTRODUCTION OF TRIAC WITH DEFINITION :- 

:-TRIAC is a bidirectional device. 

It stands for Triod AC Switch.

Symbols of TRIAC 

:-TRIAC is a three terminal four layer bilateral semiconductor device. 

:-The TRIAC is three terminal AC switch,i.e triggering into conduction  when a low energy signal is applied to its gate.

:-Their all terminal are named as MT1,MT2 and GATE.

:-Unlike the SCR the TRIAC conduction in either direction when turn ON.

:-TRIAC is made by two SCR connected in inverse parallel with a common gate terminal  in singal chip.

:-There arrangements are shown in figure. 

:-All terminal are connected by ohmnic contact  with both  N and P type  material.

 :-Triggering pulses are trigger on Gate 'G' to start device. 

Basic structure 

Construction of TRIAC:- 

• In above diagram TRIAC has three Terminal, four layer ,bilateral semiconductor device.
• It is made by two SCR connected in parallel with common Gate terminal in single chip.
• It has dopped region the gate terminal team G makes omnic contact with both N and P type material.
• The TRIAC is a bi-directional device the term anode and cathode has no meaning and therefore terminal are made as main terminal MT1 and main terminal MT2 with gate G .

Electrical equivalent circuit 

Working principle of TRIAC:-

The TRIAC can be turned on without any Gate can provide that if the supply voltage equal to break or voltage of the TRIAC . Triac can conduct current  irrespective of voltage polarity of terminal mt1 and mt2 with respect to each other and there are four personality :--

Mode of operation of TRIAC:-

1. when MT2 and gate G are positive  with respect to MT1 then the path of flowing current is P1-N1-P2-N3 .

2. when MT2 positive and gate G is negative  with respect to MT1 then the path of flowing current is P1-N1-P2-N2.

3. When MT2 and gate  G is negative with respect to MT1 then the path of flowing current is P2-N1-P1-N4.

4. When MT2 is negative and gate  G is positive with respect to MT1 then the path of flowing current is P2-N1-P1-N4.

Characteristics of TRIAC :-

Characteristics of TRIAC 

Applications of TRIAC :-

High power lamp switching. 

Ac power control. 

Advantage of TRIAC :-

TRIAC can be triggered with positive or negative polarity voltage.

A TRIAC require single heatsink of slightly larger side. 

A TRIAC Require single fuse for protection which also single fuse for protection against reverse voltage, where as a TRIAC used may work  without a diode ,as safe breakdown in either direction .

Disadvantage of TRIAC:-

TRIAC are less reliable than scr.

TRIAC available are of rating & lower than those of scr.

TRIAC have dv/dt ratings lower than of scr.