2

Alternating current mains switch - basic application

The ACS108 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 13. Typical application schematic

Thanks to its overvoltage protection and turn-off commutation performance, the ACS108 switch can drive a small

power high inductive load with neither varistor nor additional turn-off snubber.

Figure 13. Typical application schematic

MCU

M

AC Mains

Rg = 220 Ohm

Vdd

Vss

OUT

COM

GATE

ACS108

Solenoid

Motor

Lamp

2.1

Protection against overvoltage: the best choice is ACS

In comparison with standard Triacs the ACS108 is over-voltage self-protected, as specified by the parameter VCL.

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 IH.

As shown in Figure 14. Switching off of a high inductive load - typical clamping capability of ACS108 (Tamb = 25

°C), at the end of the last conduction half-cycle, the load current decreases ① . The load current reaches the

holding current level IH 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

ACS108-8SA

Alternating current mains switch - basic application

DS12901 - Rev 1

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