ICL5101_16 Datasheet, PDF (23/44 Pages) Infineon Technologies AG – Resonant controller IC with PFC for LED driver

ICL5101
Functional Description
2.3.5
THD Correction via Zero Crossing Detection Signal
An additional feature is the THD correction (Figure 17). In order to optimize the THD (especially in the zones A
shown in Figure 17, ZCD @ AC input voltage), there is a possibility to extend the pulse width of the gate signal
(blue part of the PFC gate signal) via the variable PFC ZCD resistor from the ZCD pin to the PFC choke in
addition to the gate signal controlled by the V_PFCVS signal (gray part of the PFC gate signal).
ZCD @ AC Input Voltage
ZCD @ DC Input Voltage
Rectified
AC Input Voltage
A
B
A
0
DC Input Voltage
Voltage at ₀
ZCD-Winding
PFC Gate Drive
Voltage
0
PFC gate signal (gray) controlled by the V_PFCVS
PFC gate signal (blue) controlled by the ZCD
Figure 17 THD Improvement – Automatic Pulse Width Extension
In the case of DC input voltage, the pulse width gate signal is fixed as a combination of the gate signal
controlled by the V_PFCVS pin (gray) and the additional pulse width signal controlled by the ZCD pin (blue) ZCD @
DC input voltage.
The PFC current limitation at pin PFCCS interrupts the ON time of the PFC MOSFET if the voltage drop at the
PFC shunt resistors exceeds V_PFCCS = 1.0 V. This interrupt will restart after the next sufficient signal from ZCD
becomes available (auto restart). The first value of the resistor can be calculated as the ratio of the PFC mains
choke and ZCD winding times the bus voltage to a current of typically 1.5 mA (Equation 1). An adjustment of the
ZCD resistor causes an optimized THD.
R_ZCD

N _ZCD
N _PFC
*V_BUS
1.5mA
Equation 1: R_ZCD – A Good Practical Value
Datasheet
23
Rev. 1.3, 2016-01-15