UCC28521, UCC28528

SLUS608D − JANUARY 2005 REVISED NOVEMBER 2005

11

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APPLICATION INFORMATION

U1

12

3

16

18

10

5

7

2

UCC28521/28

GT1

VSENSE

ISENSE1

IAC

GT2

VREF

VERR

RT

R20

R17

AGND

U2

C1

D3

PGND

L1

D1

VAC

Q2

C2

D4

15

14

13

11

17

19

20

PWRGND

VAOUT

1

4

6

VFF

MOUT

CAOUT

PKLMT

SS2

8

9

D_MAX

CT_BUFF

GND

ISENSE2

VCC

R3

R4

R18

C8

R15

C7

R13

C6

C11

R21

C10

R14

R16

R19

R2

R5

R11

R8

R7

AGND

C4

PGND

C5

R1

AGND

C9

REF

T1

D5

C3

R6

AGND

REF

D6

R22

R25

C12

C13

R24

R23

C14

R25

U3

TL431

GND2

GND2

PRIMARY

SECONDARY

GND2

+

−

VOUT

D2

Q1

PGND

R9

R10

R12

Figure 1. Typical Application Circuit: Boost PFC and Flyback PWM Power System

The UCC28521 combination controller includes 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 internally synchronized at a fixed frequency

with both the PFC controller and the PWM controller are trailing edge modulated (TEM).