NXP Semiconductors AN10881, Application Note, Page: 37 / 102

AN10881 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Application note Rev. 2 — 26 September 2011 37 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
7.2.4 Mains compensation in the PFC voltage control loop
The mathematical equation for the transfer function of a power factor corrector, contains
the square of the mains input voltage.
(10)
In a typical application this results in a low bandwidth for low mains input voltages, while at
high mains input voltages the MHR requirements can be hard to meet.
The TEA1713 contains a correction circuit to compensate for the mains input voltage
influence. SNSMAINS measures the average mains voltage, which is used for internal
compensation.
Figure 18 shows the relationship between the SNSMAINS voltage,
COMPPFC voltage and the on-time. With this compensation it is possible to keep the
regulation loop bandwidth constant over the complete mains input voltage range, yielding
a fast transient response on load steps, while still complying with class-D MHR
requirements.
7.3 PFC demagnetization and valley sensing
The PFC MOSFET is switched on for the next stroke, if the voltage at the drain of the
MOSFET is at its minimum (valley switching), to reduce switching losses and EMI
(see
Figure 19 ).
Fig 18. Relationship between on-time SNSMAINS voltage and COMPPFC voltage
K V
mains
 
A
V
mains
2
----------------
=
on-time
V
max-ton
V
zero-ton
V
PFCCOMP
001aal028
0
t
on,max(lowmains)
t
on,max(highmains)
V
SNSMAINS
= 0.9 V
V
SNSMAINS
= 3.3 V