AN1379 Datasheet, PDF (1/10 Pages) STMicroelectronics – Z01 and ACS behavior compared under fast voltage transients

AN1379
Application note
Z01 and ACS behavior compared under fast voltage transients
Introduction
Home appliances such as washing machines, refrigerators and dishwashers integrate a lot
of low power loads such as valves, door lock systems, dispensers and drain pumps. These
loads are mains-powered in on / off mode, and are mostly controlled by Triacs or relays.
In most cases, the AC switching function now needs to be directly driven by a
microcontroller unit (MCU) and it must withstand the AC line transients to make the system
compliant with the new European Electromagnetic Compatibility (EMC) standards.
STMicroelectronics ACS™ (alternating current switches) have been designed to meet these
needs, as shown in this application note. Compared to Triacs, they offer high robustness and
dV/dt capability, while contributing to a substantial reduction of the overall electronic board
size.
The application specific discrete (ASD) concept, developed by STMicroelectronics, allows
several devices, such as diodes, thyristors, transistors and some passive components used
to make a complete function, to be integrated on the same silicon die. This technology has
been used to develop the new ACS structures.
An ACS embeds an integrated driver, a clamping structure, and a bidirectional, thyristor-type
switch (see Figure 1). The primary loads to be targeted by these new devices are high
inductive loads like electromagnets, where the serial inductance can reach teens of Henry
and the turn-off operation can thus cause many problems. The second section explains how
the clamping feature of ACSs enables them to directly drive any inductive load without any
external clamping device, such as metal oxide varistors, and how ACSs can also sustain
overvoltages coming from the mains.
Silicon devices are subjected not only to surge voltages but also to fast transient voltages,
as described in the IEC 61000-4-4 standard. They must not only present clamping ability but
also high immunity to high dV/dt rates. The results of tests reported in this application note
show the maximum levels withstood by ACSs and Triacs, for different gate sensitivities.
Figure 1. ACS symbol description
AC power
switch
OUT
G
Over voltage
protection
( Trisil™ -Like)
Integrated
driver
COM
TM: Trisil is a trademark of STMicroelectronics
TM: ACS is a trademark of STMicroelectronics
June 2010
Doc ID 8317 Rev 5
1/10
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