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DIAC

A DIAC (Diode for Alternating Current) is a bidirectional semiconductor device used primarily for triggering TRIACs and operates in both positive and negative AC cycles. It consists of a five-layer structure without a gate terminal and transitions from a non-conducting state to a conducting state upon reaching a breakover voltage. DIACs are commonly applied in AC power control circuits, overvoltage protection, and AC motor speed control.

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16 views3 pages

DIAC

A DIAC (Diode for Alternating Current) is a bidirectional semiconductor device used primarily for triggering TRIACs and operates in both positive and negative AC cycles. It consists of a five-layer structure without a gate terminal and transitions from a non-conducting state to a conducting state upon reaching a breakover voltage. DIACs are commonly applied in AC power control circuits, overvoltage protection, and AC motor speed control.

Uploaded by

chandangpm
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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DIAC

 A DIAC (Diode for Alternating Current) is a bidirectional semiconductor


switching device.
 It is commonly used for triggering TRIAC.
 A DIAC is a two-terminal device made of a five-layer semiconductor
structure.
 It has no gate terminal.
 The device is bidirectional, meaning it works in both positive and negative
half-cycles of AC.
The 5-layer DAIC construction resembles the combination of two SCR without
the gate terminal. It has a symmetrical structure made of 2 P-layer and 3 N-
layers.

Working of DIAC

1. Off State (Non-Conducting Mode)


 When a small voltage is applied across the DIAC, it remains in the non-
conducting state because the junctions J2 in reverse bias.
 Only a very small leakage current flows.
 As the applied voltage increases and reaches the breakover voltage (V_BO)
(usually around 30-50V), the DIAC enters conduction mode.
 The breakdown happens due to avalanche multiplication, leading to a sharp
increase in current.

2. On State (Conducting Mode)


 After breakover, the resistance of the DIAC drops sharply, allowing a high
current to flow.
 It remains conducting until the current drops below the holding current level.
3. Turn-Off Condition
 When the applied voltage or current decreases below a certain threshold, the
DIAC turns off and returns to its non-conducting state.

Applications of DIAC

 Used to trigger TRIACs in AC power control circuits.


 Overvoltage protection circuits.
 AC motor speed controller.

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