DocID8766 Rev 7 7/14
ACST4 Application information
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Figure 17. Universal drum motor control – typical diagram
2.2 AC line transient voltage ruggedness
In comparison with standard Triacs, which are not robust against surge voltage, the ACST4
is self-protected against over-voltage, specified by the new parameter V
CL
. The ACST4
switch can safely withstand AC line transient voltages either by clamping the low energy
spikes, such as inductive spikes at switch off, or by switching to the on state (for less than
10 ms) to dissipate higher energy shocks through the load. This safety feature works even
with high turn-on current ramp up.
The test circuit of Figure 18 represents the ACST4 application, and is used to stress the
ACST switch according to the IEC 61000-4-5 standard conditions. With the additional effect
of the load which is limiting the current, the ACST switch withstands the voltage spikes up to
2 kV on top of the peak line voltage. The protection is based on an overvoltage crowbar
technology. The ACST4 folds back safely to the on state as shown in Figure 19. The ACST4
recovers its blocking voltage capability after the surge and the next zero current crossing.
Such a non repetitive test can be done at least 10 times on each AC line voltage polarity.
Universal motor
Motor direction
setting
Speed motor
regulation
Rg
AC Mains
Stator
MCU
Vcc
12V
ACST
Rotor
MCU
