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LT1508

Power Factor and PWM

Controller (Voltage Mode)

, LTC and LT are registered trademarks of Linear Technology Corporation.

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PFC and PWM Single Chip Solution

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Synchronized Operation up to 300kHz

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99% Power Factor Over 20:1 Load Current Range

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Voltage Mode PWM

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Instantaneous Overvoltage Protection

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Dedicated Overvoltage Protection (OVP Pin)

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Minimal Line Current Dead Zone

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Typical 250

µA Start-Up Supply Current

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Line Switching Noise Filter

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Low Quiescent Current: 13mA

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Fast 1.5A Peak Current Gate Drivers

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Separate Soft Start Control

FEATURES

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Universal Power Factor Corrected Power Supplies

and Preregulators

The LT

switching power supplies utilizing active power factor

correction. The PFC section is identical to the LT1248 PFC

controller except the EN/SYNC pin is removed because

PFC and PWM are synchronized internally.

The voltage mode PWM section (LT1509 is the current

mode counterpart) contains all the primary side functions

to convert the PFC preregulated high voltage output to an

isolated low voltage output. The PWM duty cycle is

internally limited to 47% (maximum 50%) to prevent

transformer saturation. PWM soft start begins when the

PFC output reaches the preset voltage. In the event of brief

line loss, PWM will be shut off when the PFC output

voltage drops below 73% of the preset value.

–

+

+

–

+

–

11

16

13

+

–

+

–

–

+

200

4

15

19

18

1508 BD

7.5V

7.9V

16V TO 10V

14

µA

14

µA

7

µA

7V TO

4.7V

–

+

EA

CA

–

+

CL

2.2V

M1

25k

1V

R

2R

14

10

7.5V

12

8

7

6

50

µA

RUN

RUN

R

R

Q

S

S

RQ

R

OSC

55%

DELAY

200ns

BLANKING

5

GND1

3

17

GTDR1

16V

16V

1

GND2

2

GTDR2

20

9

OVP

SS1

SS2

PWMOK

0.7V

+

–

+

–

NOTE: PWM PULSE IS DELAYED BY 55% DUTY CYCLE

AFTER PFC PULSE

–

+

–

+