May 2006

Rev 2

1/23

AN1172

Application note

ACS™

A logic-level transient-voltage protected AC switch

Introduction

Home appliances such as washing machines, refrigerators and dishwashers employ a lot of

low power loads such as valves, door lock systems, dispensers or drain pumps. Since these

loads are powered by the mains in ON / OFF mode, they were initially controlled by relays.

Recently, relays have been replaced by triacs, due to their smaller size and lower driving

energy. Nevertheless triacs don't fulfill alone the new requirements that users now need and

are used with others components.

Power switches must now be directly driven by a microcontroller unit (MCU) and must be

robust to withstand the A.C. line transients so that systems may fall into line with

electromagnetic compatibility (EMC) standards. ACSs (for Alternating Current Switches)

have been designed with this goal mind, i.e. to offer logic level and more robust

semiconductor devices.

On the other hand, ACSs have been developed adopting a functional integration approach.

They can be used directly between a MCU and the load. An external protection or a buffer

circuit are not required since these are already integrated on the die. This considerably

reduces the overall electronic board size. Moreover, the array of ACSs allows one device to

control the various loads typically required in a washer appliance.

Table 1. gives the RMS current of loads that can be controlled by ACS402-5SB4 or

ACS108-5SA/N, in ON / OFF control mode.

Table 1.

ACS108 and ACS402 targeted loads

Load

(A)

Power

Factor

(A/ms)

(V/µs)

Turn-off delay

(ms)

Door Lock

<0.3

1

0.15

0.15

<10

Lamp

<0.8

1

0.4

0.15

<20

Relay, Valve,

Dispenser,

Micromotor

<0.1

>0.7

<0.05

<2

<10

Pump

<0.2

>0.2

<0.1

<10

<10

Fan

<0.6

>0.2

<0.3

<10

<20

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