AN1172 Datasheet, PDF (1/23 Pages) STMicroelectronics – A logic-level transient-voltage protected AC switch

ACS™
AN1172
Application note
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Recently, relays have been replaced by triacs, due to their smaller size and lower driving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
I _RMS
(A)
Power
Factor
(dI_out/dt)c
(A/ms)
Door Lock
<0.3
1
0.15
Lamp
<0.8
1
0.4
Relay, Valve,
Dispenser,
Micromotor
<0.1
>0.7
<0.05
Pump
<0.2
>0.2
<0.1
Fan
<0.6
>0.2
<0.3
(dV_out/dt)c
(V/µs)
Turn-off delay
(ms)
0.15
<10
0.15
<20
<2
<10
<10
<10
<10
<20
May 2006
Rev 2
1/23
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