TRIAC light dimmer with DIAC
Each half-cycle, the capacitor charges through the pot. When it reaches the DIAC’s 32 V the DIAC fires a pulse into the TRIAC’s gate, the TRIAC switches on and the lamp gets the rest of that half-cycle. More resistance means a later firing angle and a dimmer lamp.
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How it works
Firing angle α (from the zero crossing) delays conduction; a resistive lamp then receives
P ÷ P_full = 1 − α/π + sin(2α)/(2π).
Try it on the bench
- Turn the pot from 0.1 to 0.9 of its range and watch the angle and power.
- Set the pot to its maximum: the capacitor never reaches 32 V and the lamp stays off.
Parts on the bench
In the course
Electronics Technician, module “Transistor circuits”.