ACS108 查看數據表（PDF） - STMicroelectronics

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ACS108

Overvoltage protected AC switch (ACS™)

STMicroelectronics 

Alternating current mains switch - basic application

ACS108

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 16.

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 16. Typical application schematic

Power supply

Valve

Vss

MCU

Vdd

ACS108

Rg

VT

220 Ω

IT

AC Mains

2.1

2.1.1

Protection against overvoltage: the best choice is ACS

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

by the new 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.

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 17, 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 clamping voltage VCL. 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 (230 V rms,

50 Hz) ⑤ .

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DocID6518 Rev 5

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