ICE1QS01 Datasheet, PDF (7/21 Pages) Infineon Technologies AG – Controller for Switch Mode Power Supplies Supporting Low Power Standby and Power Factor Correction (PFC)

ICE1QS01
Soft start
The internal reference of the IC is switched on when V_CC exceeds the V_CCon threshold. The IC
begins to work with soft start mode. Soft start is realized with an internal soft start resistor, an inter-
nal current sink, a current source and the external feedback capacitor connected at pin SRC. The
internal resistor is connected between the internal voltage reference and pin SRC. The current sink
is connected between pin SRC and GND. The value of the current is set with a timer. Immediately
after the IC is switched on the capacitor C_SRC is charged with a current source up to 2.5V. This cur-
rent source is switched off 12 µsec after beginning of soft start. The current value of the current sink
is set with a timer. Every three msec the current of the current sink is reduced and so V_SRC can
increase stepwise. The soft start is finished 24 msec after the IC is switched on. At the end of the
soft start the current sink is switched off.
Figure: Soft Start
VCC
VCCon
VSRC
VSRC2
VSRC1
ICE1QS01
timer
t=12us
2.5V
500
5V
20k
timer
tp=3ms
timer
t=24ms
up
current
t
down
D/A
counter
sink
pin SRC
ton
tp1
tp2 t
PCS (primary current simulation)
A voltage proportional to the current of the power transistor is generated at Pin PCS by the RC-com-
bination R2, C2. The voltage at Pin PCS is forced to 1.5V when the power transistor is switched off
and during its switch on time C2 is charged by R2 from the rectified mains. The relation of V_PCS and
Version 1.4
7
27 Apr 2004