DIAC device leads How many external terminals (leads) does a DIAC have?

Introduction / Context:A DIAC (Diode for Alternating Current) is a bidirectional trigger device widely used to initiate conduction in TRIAC-based phase control circuits (e.g., lamp dimmers and speed controllers). Knowing its terminal count is essential for correct wiring and understanding its symmetric behavior.

Given Data / Assumptions:

• DIAC behaves like a bilateral trigger diode.
• Breakover voltage is similar in both polarities.
• No gate terminal exists (unlike TRIAC or SCR).

Concept / Approach:

Because the DIAC must operate symmetrically for positive and negative half-cycles, it is constructed to have two main terminals (commonly marked MT1 and MT2 or simply A1 and A2). There is no control terminal; conduction begins when the applied voltage reaches the breakover level in either polarity.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets from major vendors depict a two-lead, bidirectional symbol and specify equal breakover voltages for positive and negative directions.

Why Other Options Are Wrong:

Three leads would imply a gate/control terminal; four or six leads correspond to more complex devices (e.g., opto-triacs, multi-pole components).

Common Pitfalls:

Confusing DIAC (two-lead trigger) with TRIAC (three-lead controllable bidirectional device) or with SCR (three-lead unidirectional device).

Final Answer:

2