5

4752B–INDCO–09/05

U211B

5.

Voltage Monitoring

As the voltage is built up, uncontrolled output pulses are avoided by internal voltage surveil-

lance. At the same time, all latches in the circuit (phase control, load limit regulation, soft start)

are reset and the soft-start capacitor is short circuited. Used with a switching hysteresis of

300 mV, this system guarantees defined start-up behavior each time the supply voltage is

switched on or after short interruptions of the mains supply.

6.

Soft Start

As soon as the supply voltage builds up (t

shows the behavior of the voltage across the soft-start capacitor, which is identical with the volt-

age on the phase-control input on pin 12. This behavior guarantees a gentle start-up for the

motor and automatically ensures the optimum run-up time.

Figure 6-1.

Soft Start

C

the charging current to approximately 4 µA, the slope of the charging function is also substan-

tially reduced, so that the rotational speed of the motor only slowly increases. The charging

current then increases as the voltage across C

charging function which accelerates the motor more and more with increasing rotational speed.

The charging function determines the acceleration up to the set point. The charging current can

have a maximum value of 55 µA.

t

t

t

t

t

t