AMS Semiconductor Tutorials
We provide tutorials to
help our customers better understand semiconductors and other electronic
devices. Whether you have a question regarding a particular component, or simply want to
know more about semiconductors, browse through our tutorial
section for help. If you are still stuck, give us a call at (973) 377-9566 and we'll be happy to recommend a device for your application.
Diac Tutorial
The diac is a bidirectional trigger diode which is designed specifically to trigger a triac or SCR. Basically the diac does not conduct (except for a small leakage current) until the breakover voltage is reached. At that point the diac goes into avalanche conduction also at that point the device exhibits a negative resistance characteristic, and the voltage drop across the diac snaps back, typically about 5 volts, creating a breakover current sufficient to trigger a triac or SCR. A typical Diac characteristic is shown below with the Diac schematic symbol:
Although most diacs have symmetric switching voltages,asymmetric diacs are available. Typical diacs have a power dissipations ranging from 1/2 to 1 watt.
The main Diac characteristics are:
(a) Breakover voltage
(b)Voltage symmetry
(c) Breakback voltage
(d) Breakover current
(d) Power dissipation
Typical diacs that are supplied by American Microsemiconductor
| ELECTRICAL CHARACTERISTICS (T=25oC) | |||||
| DIAC NUMBERS |
Breakover Voltage
V |
Breakover Voltage Symmetry
V |
Dynamic Breakback Voltage
V |
Breakover Current
µA |
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 |