Matched TRIAC–DIAC pair for lamp dimmers For an illumination (light dimmer) control circuit using a TRIAC trigger, is it advisable to use a matched TRIAC–DIAC pair?

Introduction / Context:Phase-control lamp dimmers commonly use a DIAC to trigger a TRIAC symmetrically on positive and negative half cycles. Matching the devices improves symmetry and jitter performance. This question asks whether such matching is advisable.

Given Data / Assumptions:

• AC mains phase-control application.
• TRIAC as the main bidirectional switch.
• DIAC as a symmetrical trigger device.

Concept / Approach:

A matched TRIAC–DIAC pair ensures similar breakover characteristics across polarities, reducing waveform asymmetry, audible hum, and flicker. It enhances repeatability of the firing angle and reduces harmonics due to unequal conduction in alternate half-cycles, especially important with sensitive lamps and dimming requirements.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturer application notes often specify recommended DIAC/TRIAC combinations for best symmetry.

Why Other Options Are Wrong:

The advice is not limited to high frequency or inductive loads; heat sinking does not address firing symmetry.

Common Pitfalls:

Assuming any DIAC will do; tolerances can create visible flicker at certain dim levels.

Final Answer:

True