DIAC definition — symmetry and switching mode: Evaluate the statement: “A DIAC is a bidirectional diode that has a symmetrical switching mode.”

Introduction / Context:
Understanding the role of a DIAC in AC control circuits is fundamental. DIACs are often used to provide a sharp, symmetrical trigger for TRIAC gates, improving phase-control balance between positive and negative half-cycles.

Given Data / Assumptions:

• Two-terminal device with similar breakover in both polarities.
• Used primarily as a trigger element, not a power switch.
• Idealized symmetry acknowledged; small tolerances may exist.

Concept / Approach:
A DIAC behaves like a bidirectional trigger diode. It remains in a high-impedance state until the applied voltage magnitude reaches its breakover threshold (approximately equal in positive and negative directions). At breakover, it snaps to a low-impedance state, discharging capacitors in RC phase-control networks to deliver sharp, symmetrical pulses to a TRIAC gate. This symmetrical switching is key to minimizing waveform distortion and DC offset in controlled loads.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets show near-symmetric breakover voltages (e.g., ±30 V to ±35 V) and typical negative-resistance region upon conduction, supporting the symmetrical switching description.

Why Other Options Are Wrong:

• Incorrect: Contradicts standard DIAC behavior.
• Applies only above 400 V: Breakover is tens of volts, not hundreds.
• True for TRIACs, not DIACs: TRIACs are power switches; DIACs are trigger devices, but symmetry belongs to DIACs as well.
• Depends on gate current: No gate terminal exists on a DIAC.

Common Pitfalls:
Confusing DIACs with standard diodes or thinking a DIAC requires a gate; expecting large power handling (it is a trigger component).

Final Answer:
Correct