DIACs

 

 

DIACs
semiconductor construction  + symbol

The diac is a bidirectional trigger diode which is designed specifically to trigger a triacs or SCRs.

Diacs do not conduct (except for a small leakage current) until the breakover (reverse breakdown/avalanche) voltage is reached.

At that point the diac goes into avalanche conduction and the voltage drop across the diac snaps back. (about 5 volts)
 
This creates a breakover current sufficient to trigger a triac or SCR.

 A typical characteristic is shown below with its schematic symbol:

4a.jpg (21221 bytes)

   Most diacs have symmetric switching voltages. Typical diacs have a power dissipations ranging from 1/2 to 1 watt.

 

Typical diacs that are supplied by American Microsemiconductor

ELECTRICAL CHARACTERISTICS  (T=25oC)
PART NUMBER

Breakover Voltage

V

Breakover Voltage Symmetry

V

Dynamic Breakback Voltage

V

Breakover Current

ľA

Peak Pulse Current

A

Min  Typ  Max MAX MIN MAX MAX  
D30 28   32   36 3 5 100 2.0 
D40 35   40   45 3 5 100 2.0 
ST2 28   32   36 3.8 - 200
HT32 27    -     37 3 5 50 2.0 
DB3 28   32   36 3 5 - 1.0