UCC2817A, UCC2818A
UCC3817A, UCC3818A
SLUS577C − SEPTEMBER, 2003 − REVISED MARCH 2009
APPLICATION INFORMATION
The UCC3817A is a BiCMOS average current mode boost controller for high power factor, high efficiency
preregulator power supplies. Figure 1 shows the UCC3817A 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
(1)
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 UCC3817A.
NOTE: Schottky diodes, D5 and D6, are required to protect the PFC controller from electrical over stress during
system power up.
R16
100Ω
VCC
R15
24k
D7
D8
L1
1mH
D1
8A, 600V
D2
6A, 600V
Q1
IRFP450
VOUT
C12
385V−DC
220µ F
450V
−
UCC3817A
R12
2k
R9
4.02k
R10
4.02k
1
2
R11
10k
D5
3
4
VREF
R8 12k
C9 1.2nF
6
C8 270pF
R1 12k
D6
C7 150nF
R7 100k C15 2.2µ F
7
C6 2.2µ F
8
R6 30k
VREF
9
VREF
VFF
R20 274k
OVP/EN
10
C5 1
µF
R5
10k
VAOUT
RT
VSENSE
12
11
R3 20k
IAC
SS
13
5
CAOUT
CAI
MOUT
CT
14
C4 0.01µ F
C1
560pF
GND
PKLIMIT
VCC
15
C2
100µ F AI EI
DRVOUT
16
D4
VCC
C3
1µ F CER
R17
20Ω
VO
+
C14
1.5µ F
400V
D3
AC1
6A 600V
R14
0.25Ω
3W
C13
0.47µ F
600V
C10
1
µ
F
C11
1
µ
F
R21
383k
IAC
R13
383k
R18
24k
AC2
VLINE
85−270 V
AC
F1
R2
499k
R19
499k
VO
R4
249k
UDG-98183
Figure 1. Typical Application Circuit
8
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