March 2006

Rev 1

1/24

AN2316

Application Note

Improved ST7LITE05 AC Chopper Driver Solution

Introduction

This application note presents an AC motor or load circuital solution improvement of

efficiency over the one discussed in a previously published application note, AN1255.

Above all, this solution does not have limits on where it may be applied, embracing all types

of AC asynchronous monophase motor applications (e.g. refrigerators, hydraulic pumps,

fans, and lamps).

Due to the increasing electric pollution of the environment, European standards impose

restrictions on Electromagnetic Compatibility (EMC). The proliferation of non-linear loads

and the consequential increase in harmonics pollution in power distribution lines have

induced various technical committees to establish maximum limits on the harmonic content

produced by all industrial and domestic devices. Manufacturers of these devices are

required to conform to this new standard and develop products which function with new

operational characteristics.

The most common method used to vary the AC monophase motor voltage is a TRIAC-

based phase angle partialization technique. Although this is a simple, low-cost solution that

has been used for several years, it is problematic because of the excessive harmonic

distortion which reduces the efficiency of the entire system. These systems typically include

a complex inverter drive which is quite expensive, and, while they can solve the load’s

harmonic content problems, they do not address those same problems in the electric lines.

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