Datasheet

( )
2
BULK
PFC IN(pk ) BULK
SW IN(pk ) IN(pk )
V
1
L V V
2 f I V
æ ö
= -
ç ÷
ç ÷
´ ´
è ø
( ) ( ) ( )
IN(avg)
START
IN(pk)
IN(pk)
START START START
P
1 sin( )
I
1 1 1
2 V
cos sin
4 2 2
´ p
- q
= ´
´
´ p - ´ q ´ q ´ - ´ q
( )
( )
2
PFC
3
1 84 V
L 2 160 V 84 V 94.9 H
2 100 10 Hz 1.033 A 2 160 V
æ ö
= ´ - = m
ç ÷
´ ´ ´ ´
è ø
UCC29910A
SLUSAK8A –MAY 2011– REVISED JUNE 2011 www.ti.com
PFC Inductor Value
The PFC inductor is designed for an inductance value that ensures DCM operation at high line (i.e. >160 V
AC
),
right up to full-peak load. With an appropriate value of inductance, operation at low line should then result in
CCM operation over most of the conduction angle at full load. The inductance required is given by:
(1)
where:
(2)
And π is the stage conversion efficiency, θ
START
is the phase angle (in radians) at which conduction starts, where
the instantaneous line voltage equals the bulk voltage. For a 100-W converter with an 84-V
BULK
DC output we
evaluate the equation at 160 V as follows.
(3)
Compared to the Boost PFC, much smaller values of PFC inductance can typically be used in the buck, because
the voltage differential that needs to be supported across the inductor is lower. Practical inductance values that
have been used in various designs have ranged from ~150 µH at 50 W, to ~80 µH to 100 µH at 90 W to 130 W.
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