Dimmers Guide

Introduction to Working with AC Dimmer Modules

How AC Dimming Works

AC dimming is based on cutting off part of the voltage sine wave using a TRIAC component. The TRIAC remains off when the voltage crosses zero and is turned on (by a control pulse from the microcontroller) at a specific point in each half-cycle. This controls the amount of power delivered to the load. For a deeper understanding of how the TRIAC and dimmer circuit operate, see this detailed explanation.

Why Classic PWM Cannot Be Used

Standard PWM (pulse-width modulation) is suitable for DC current only. It does not work for AC because AC voltage has a sinusoidal waveform and changes direction 50–100 times per second, depending on the power grid frequency. To properly control AC power, we need to synchronize with the zero-crossing points of the waveform and trigger the TRIAC at the right moment during each half-cycle.

What Is the Zero-Cross Sensor For?

A zero-cross sensor detects when the AC sine wave crosses the zero voltage point. This is crucial for timing control pulses accurately. With this synchronization, the TRIAC can be triggered at the correct phase angle to control brightness or power level precisely.

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