July 2009

Doc ID 15727 Rev 1

1/18

AN2986

Application note

AC switch triggering with 3.3 V power supply

Introduction

This document focuses on the calculation of gate current consumption of various types of

AC switches when using a 3.3 V power supply. Until now, the standard of a 5 V power supply

was used. In home appliance applications there is a bigger focus on the MCU working with

a 3.3 V power supply, and a lower supply voltage brings additional constraints on gate

circuitry. This application note provides a precise calculation process in order to correctly set

the necessary parameters.

This application note concerns Q2 and Q3 operation (i.e. for negative power supply) as this

is the most common mode of operation for AC switches, but advice and comments for

operation in Q1 and Q4 quadrants (i.e. for positive power supply) are also given.

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