ICE1QS01 Datasheet, PDF (14/21 Pages) Infineon Technologies AG – Controller for Switch Mode Power Supplies Supporting Low Power Standby and Power Factor Correction (PFC)

ICE1QS01
Fold back point correction
With increasing mains voltage the switch on time becomes shorter and so the frequency becomes
higher. With higher frequency also the maximal possible output power becomes higher. With higher
power the danger in case of failure increases.
To avoid this, the foldback point correction circuit senses main voltage to reduce the on-time of the
switch. Mains voltage is sensed at the supply coil of V_CC voltage via a resistor connected to pin RZI.
During on-time of the MOS-FET switch current is pulled out from pin RZI. When this current is
higher than 500 µA, one fifth of the current higher than this threshold is driven into pin PCS to
increase the voltage slope charging the capacitor connected to this pin.
IPCSFO
=
-^I-^R----^Z----^I---^–----⁰---^,--⁵---^m-----^A--
5
,(I
RZI
>
500uA)
Figure: Fold Back Point Correction
Vpcs with fold back point correction
Vpcs at high mains voltage
5V
Vpcs
Pmax without fold back point correction
Pmax
Vpcs at low mains
voltage
Pmax with fold back point correction
t0
t1 t2
t3
t
Vmains
Version 1.4
14
27 Apr 2004