AN10881
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© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 26 September 2011
36 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
7.2.3 PFCCOMP in the PFC voltage control loop
SNSBOOST sets and controls the PFC output voltage. The internal error amplifier with a
reference voltage of 2.5 V senses the voltage at SNSBOOST. The amplifier converts the
input error voltage with a transconductance g
m
= 80
A/V to its output. This output is
available at COMPPFC for adding an external loop compensation network. The current
from the error amplifier results in a loop voltage at COMPPFC. This COMPPFC voltage, in
combination with the voltage at pin SNSMAINS, determines the PFC switching-on time.
A compensation network, typically comprising one resistor and two capacitors at pin
COMPPFC, is used to stabilize the PFC control loop.
The transfer function has a pole at 0 Hz, a zero by
R
comp
/C
comp2
and a pole again by
C
comp1
/C
comp2
. Set the zero frequency to 10 Hz while the next pole frequency is at 40 Hz.
The zero point and pole frequencies of the compensation network can be calculated as
follows:
(8)
(9)
The choice also concerns a trade-off between power factor and transient behavior. A
lower regulation bandwidth leads to a better power factor but the transient behavior
becomes poorer. A higher regulation bandwidth leads to a better transient response but a
poorer power factor.
Fig 17. Basic PFC voltage control loop with PFCCOMP
001aal027
MAINS
VOLTAGE
RBOOST
4.7 M
Ω
RBOOST
4.7 M
Ω
4.7 nF
Ccomp1
C4
R4
R3
R2
R1
CX1
Ccomp2
Rcomp
gm
Rmeasure(SNSBOOST)
60 k
Ω
24
t
ON
2
K
SNSBOOST
SNSMAINS
1
COMPPFC
2.5 V
VBOOST
TEA1713
f
z
1
2
R
comp
C
comp2
---------------------------------------------------
=
f
p
C
comp1
C
comp2
+
2
R
comp
C
comp1
C
comp2
---------------------------------------------------------------------------
=
