Power·Jan 1, 2023

AC Dimmer Circuit

Phase-angle AC dimmer for smoothly controlling mains lamp brightness.

Overview

This power-electronics project controls AC load brightness using phase-angle dimming. A zero-cross reference and optically isolated TRIAC drive allow the controller to delay the firing angle each half cycle, producing smooth lamp-power control.

Specifications

RoleCircuit designer and prototype builder

MicrocontrollerArduino-class controller

SensorsZero-cross detector

ModulesTRIACOptotriac driverPotentiometer / control input

ProtocolsGPIOInterrupt timing

Tech tagsAC DimmerTRIACZero CrossOpto-IsolationPower Electronics

Architecture

Zero-cross signal triggers the timing routine. The controller waits a programmed delay and fires the TRIAC to set delivered load power.

Project photos

Videos

Implementation details

Firmware

Firmware detects zero-cross events, calculates firing delay, and triggers the TRIAC gate through an opto-isolated driver.

PCB

Circuit uses isolation between controller and mains trigger path. PCB/layout must maintain safe creepage and clearance for AC use.

Power

Powered from a low-voltage logic supply while switching an isolated mains load through the TRIAC path.

Components / BOM

TRIAC, Optotriac driver, Zero-cross detector, Microcontroller, Lamp/load terminal

Engineering challenges

Mains safety and stable timing around zero-cross were the main design constraints.

Solutions

Used opto-isolation and interrupt-based timing to separate low-voltage control from AC switching.

Results & metrics

Demonstrates smooth dimming behavior on an AC lamp load.

Future improvements

Add enclosure, fuse, EMI filtering, calibrated knob/display, and closed-loop power feedback.