DIAC

The  construction  of  a  diac  is  similar  to  an  open  base  “NPN”  transistor.  A simple block diagram is shown in Figure.

Diac Block Construction 

The  bidirectional  transistor-like structure  exhibits  a high-impedance  blocking state  up  to  a  voltage  Breakover  point  (VBO)  above  which  the  device  enters  a negative-resistance  region.  These  basic  diac  characteristics  produce  a  bidirectional pulsing  oscillator  in  a  resistor-capacitor  AC  circuit.  Since  the  diac  is  a  bidirectional device, it makes a good economical trigger for firing triacs in phase control circuits like light dimmers, motor speed controls, etc. Figure is a simplified AC circuit using a     diac and a triac in a phase control application.

Applications of DIAC

Some of the circuit applications of diac are

i) Light dimmer circuits

ii) Heat control circuits

iii) Universal motor speed control.