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:
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
|
|