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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

ELECTRICAL CHARACTERISTICS (T=25oC)
DIAC NUMBERS Breakover Voltage

V
Breakover Voltage Symmetry

V
Dynamic Breakback Voltage

V
Breakover Current

A
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