Datasheet

   
   
SLUS517C − DECEMBER 2002 − REVISED SEPTEMBER 2005
12
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APPLICATION INFORMATION
The UCC28510 series of combination controllers include a power factor correction (PFC) controller that is
synchronized with a pulse width modulator (PWM) controller integrated into one chip. The PFC controller has
all of the features for an average current mode controlled PFC. The PWM controller has all of the features for
an isolated peak current program mode controlled converter. The two controllers are synchronized at a fixed
frequency so that the PFC controller is leading edge modulated (LEM) and the PWM controller is trailing edge
modulated (TEM). The LEM/TEM combination reduces the ripple current in the energy storage capacitor of the
PFC stage. A comparison between the ripple current in the energy storage capacitor with traditional TEM/TEM
modulation versus LEM/TEM modulation is shown in Figure 2.
Q1
Q2
i
D1
i
Q2
i
ES
i
ES
= i
D1
− i
Q2
ON OFF
ON OFF
ONOFF
ON OFF
TT
TEM/TEM LEM/TEM
D1L1
+
–
D
AC
VAC
L2
i
ES
LOAD
C
ES
Q1
Q2
D2
i
D1
i
Q2
i
IN
i
L
C
OUT
PFC BOOST CONVERTER BUCK DERIVED CONVERTER
Figure 2. Equivalent PFC+PWM Power Supply System and the Comparison of the Energy Storage
Capacitor Current for Traditional TEM/TEM with LEM/TEM Controllers.