UCC2817A, UCC2818A

UCC3817A, UCC3818A

SLUS577B − SEPTEMBER, 2003 − REVISED FEBRUARY 2006

8

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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

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.

UDG-98183

1

11

7

16

GND

DRVOUT

R17

20

Ω

15

C3

1

µF CER

VCC

C2

100

µ F AI EI

14

C1

560pF

13

C4 0.01

µF

12

R1 12k

R3 20k

R2

499k

R4

249k

R5

10k

C5 1

µF

9

4

10

VREF

VCC

CT

SS

RT

VSENSE

OVP/EN

VREF

VAOUT

3

8

2

VFF

C6 2.2

µF

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

µF

600V

C14

1.5

µ F

400V

R13

383k

IAC

R18

24k

R15

24k

R16

100

Ω

VCC

C10

1

µ F

C11

1

µF

D7

D8

L1

1mH

D2

6A, 600V

D1

8A, 600V

C12

220

µF

450V

VOUT

385V−DC

+

−

PKLIMIT

CAOUT

CAI

MOUT

IAC

VO

UCC3817A

VLINE

85−270 VAC

VREF

C9 1.2nF

R6 30k

6A 600V

D3

Q1

F1

VO

D4

R19

499k

R20 274k

R21

383k

AC2

AC1

C15 2.2

µ F

IRFP450

Figure 1. Typical Application Circuit

(1)