UCC2819A

UCC3819A

SLUS579 − OCTOBER, 2003

8

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APPLICATION INFORMATION

The UCC3819A is based on the UCC3818 PFC preregulator. For a more detailed application information for

this part, please refer to the UCC3818 datasheet product folder.

The main difference between the UCC3818 and the UCC3819A is that the non-inverting input of the voltage

error amplifier is made available to the user through an external pin (VAI) in the UCC3819A. The SS pin and

function were eliminated to accommodate this change.

The benefit of VAI pin is that it can be used to dynamically change the PFC output voltage based on the line

voltage (RMS) level or other conditions. Figure 1 shows one suggested implementation of the tracking boost

PFC converter as this approach is sometimes referred to. The VAI pin is tied to the VFF pin and hence output

voltage scales up with the line voltage. The benefit of this approach is that at lower line voltages the output

voltage is lower and that leads to smaller boost inductor value, lower MOSFET conduction losses and reduced

component stresses. In order for this feature to work, the downstream converter has to operate over a wider

input range.

UDG−01008

1

11

7

16

GND

DRVOUT

R17

15

C3

C2

14

C1

13

C4

12

R1

R3

R2

R4

R5

C5

9

4

10

VREF

VCC

CT

VAI

RT

VSENSE

OVP/EN

VREF

VAOUT

3

8

2

VFF

C6

C7

R7

6

5

R9

C8

R8

D6

R10

D5

R11

R12

R14

C13

C14

R13

IAC

D2

D1

C12

VOUT

+

−

PKLIMIT

CAOUT

CAI

MOUT

IAC

VO

UCC3819A

VLINE

VREF

C9

R6

D3

Q1

F1

VO

D4

R19

R20

R21

AC2

AC1

C15

VFF

VCC (FROM BIAS SUPPLY)

Figure 1. Suggested Implementation of UCC3819A in a Tracking Boost PFC Preregulator