ASCT4

Application information

Doc ID 8766 Rev 5

7/13

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

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