April 2009

Doc ID 1863 Rev 2

1/11

AN392

Application note

Microcontrollers and TRIAC-based dimmers

Introduction

Today, electronics is used in home appliances for applications as widely varying as motor

regulation in a washing machine, control of a vacuum cleaner, dimming of a lamp or heating

in a coffee machine. This evolution has increased pace rapidly because appliances require

enhanced features that are easy to build and modify while electronics-based solutions

become cheaper and more sophisticated.

Within this evolution, microcontrollers (MCU) progressively replace analog controllers and

discrete solutions even in low cost applications. MCUs are more flexible, often need less

components and provide shorter time to market. With an analog IC, the designer is limited to

a fixed function frozen inside the device. With a DIAC control, features like sensor feedback

or enhanced motor drive cannot be easily implemented. With an MCU the designer can

include his own ideas and test them directly using EPROM or one time programmable (OTP)

versions.

The TRIAC is the least expensive power switch to operate directly on the 110/240 V mains.

Thus it is the optimal switch for most of the low-cost power applications operating online.

The logic level or snubberless TRIACs can operate with low gate current and can be directly

triggered by the MCU.

This application note describes two different MCU based applications: a universal motor

drive, and a light dimmer. They all operate with the same user interfaces and almost the

same software and hardware.

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