ACS108-6S Alternating current line switch - basic application
Doc ID 11962 Rev 4 7/12
2 Alternating current line switch - basic application
The ACS108-6S switch is triggered by a negative gate current flowing from the gate pin G.
The switch can be driven directly by the digital controller through a resistor as shown in
Figure 16.
Thanks to its overvoltage protection and turn-off commutation performance, the ACS108-6S
switch can drive a small power high inductive load with neither varistor nor additional turn-off
snubber.
Figure 16. Typical application program
2.1 Protection against overvoltage: the best choice is ACS
In comparison with standard triacs, which are not robust against surge voltage, the
ACS108-6S is over-voltage self-protected, specified by the new parameter V
CL
. This feature
is useful in two operating conditions: in case of turn-off of very inductive load, and in case of
surge voltage that can occur on the electrical network.
2.1.1 High inductive load switch-off: turn-off overvoltage clamping
With high inductive and low RMS current loads the rate of decrease of the current is very
low. An overvoltage can occur when the gate current is removed and the OUT current is
lower than I
H
.
As shown in Figure 17 and Figure 18, at the end of the last conduction half-cycle, the load
current decreases (1). The load current reaches the holding current level I
H
(2), and the
ACS turns off (3). The water valve, as an inductive load (up to 15 H), reacts as a current
generator and an overvoltage is created, which is clamped by the ACS (4). The current flows
through the ACS avalanche and decreases linearly to zero. During this time, the voltage
across the switch is limited to the clamping voltage V
CL
. The energy stored in the inductance
of the load is dissipated in the clamping section that is designed for this purpose. When the
energy has been dissipated, the ACS voltage falls back to the mains voltage value (5).
AC Mains
ACS108-6S
Valve
Power supply
MCU
V
dd
V
ss
Rg
