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AMS Semiconductor Tutorials

Tutorials Graphic 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:

4a.jpg (21221 bytes)

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

DIAC NUMBERS Breakover Voltage

Breakover Voltage Symmetry

Dynamic Breakback Voltage

Breakover Current

Peak Pulse Current

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