Datasheet
SLUS395J - FEBRUARY 2000 - REVISED MARCH 2009
7
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APPLICATION INFORMATION
The UCC3817 is a BiCMOS average current mode boost controller for high power factor, high efficiency
preregulator power supplies. Figure 1 shows the UCC3817 in a 250-W PFC preregulator circuit. Off-line
switching power converters normally have an input current that is not sinusoidal. The input current waveform
has a high harmonic content because current is drawn in pulses at the peaks of the input voltage waveform.
An active power factor correction circuit programs the input current to follow the line voltage, forcing the
converter to look like a resistive load to the line. A resistive load has 0° phase displacement between the current
and voltage waveforms. Power factor can be defined in terms of the phase angle between two sinusoidal
waveforms of the same frequency:
PF + cos Q
Therefore, a purely resistive load would have a power factor of 1. In practice, power factors of 0.999 with THD
(total harmonic distortion) of less than 3% are possible with a well-designed circuit. Following guidelines are
provided to design PFC boost converters using the UCC3817.
NOTE: Schottky diodes, D5 and D6, are required to protect the PFC controller from electrical over stress during
system power up.
UDG-98183
1
11
7
16GND DRVOUT
R17
20
Ω
15
C3
1
µ
F CER
VCC
C2
100
µ
F AI EI
14
C1
560pF
13
C4 0.01
µ
F
12
R1 12k
R3 20k
R2
499k
R4
249k
R5
10k
C5 1
µF
9
4
10
V
REF
VCC
CT
SS
RT
VSENSE
OVP/EN
VREF
VAOUT
3
8
2
VFF
C6 2.2
µ
F
C7 150nF
R7 100k
6
5
R9
4.02k
C8 270pF
R8 12k
D6
R10
4.02k
D5
R11
10k
R12
2k
R14
0.25
Ω
3W
C13
0.47
µ
F
600V
C14
1.5
µ
F
400V
R13
383k
IAC
R18
24k
R15
24k
R16
100
Ω
VCC
C10
1
µ
F
C11
1
µ
F
D7
D8
L1
1mH
D2
6A, 600V
D1
8A, 600V
C12
220
µ
F
450V
V
OUT
385V−DC
+
−
PKLIMIT
CAOUT
CAI
MOUT
IAC
V
O
UCC3817
V
LINE
85−270 V
AC
V
REF
C9 1.2nF
R6 30k
6A 600V
D3
Q1
F1
V
O
D4
R19
499k
R20 274k
R21
383k
AC2
AC1
C15 2.2
µ
F
IRFP450
Figure 1. Typical Application Circuit