4. Phase Control 1)
The phase angle of the trigger pulse is derived by comparing the ramp voltage (which is mains
synchronized by the voltage detector) with the set value on the control input pin 12. The slope of
the ramp is determined by C2 and its charging current. The charging current can be varied using
R2 on pin 6. The maximum phase angle αmax can also be adjusted by using R2.
When the potential on pin 7 reaches the nominal value predetermined at pin 12, a trigger pulse
is generated whose width tp is determined by the value of C2 (the value of C2 and hence the
pulse width can be evaluated by assuming 8µs/nF). At the same time, a latch is set, so that as
long as the automatic retriggering has not been activated, no more pulses can be generated in
that half cycle.
The current sensor on pin 1 ensures that, for operations with inductive loads, no pulse will be
generated in a new half cycle as long as a current from the previous half cycle is still flowing in
the opposite direction to the supply voltage at that instant. This makes sure that “gaps” in the
load current are prevented.
The control signal on pin 12 can be in the range of 0V to –7V (reference point pin 2).
If V12 = –7V, the phase angle is at maximum (αmax), i.e., the current flow angle, is at minimum.
The phase angle is minimum (αmin) when V12 = V2.
5. Voltage Monitoring 1)
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
300mV, this system guarantees defined start-up behavior each time the supply voltage is
switched on or after short interruptions of the mains supply.
Note: 1. The descripten refers to the DIP18 package version which is no longer available.