SC4810EITSTRT datasheet(9/24 Pages) SEMTECH

9 / 24 page

 2004 Semtech Corp.

www.semtech.com

SC4810A/B/C/D/E

POWER MANAGEMENT

Application Information

Introduction

The SC4810A/B/C/D/E is a 16 pin BICMOS peak current

mode controlled PWM controller for isolated DC-DC and

off-line switching power supplies. It features a high

switching frequency of operation, programmable limits

for both power transformer voltage-second product and

maximum PWM duty cycle, line under-voltage lockout,

auxiliary switch activation complementary to main power

switch drive, programmable leading-edge delay time

between activation of each switch, multiple protection

features with programmable cycle -by-cycle current limit

and hiccup mode over-current protection plus soft-restart.

It operates in a fixed frequency programmed by external

components. The separate sync pin simplifies

synchronization to an external clock. Feeding the oscillator

of one device to the sync of another forces biphase

operation which reduces input ripple and input and output

filter size.

The SC4810 can be applied in an active clamp forward

topology with the input voltage ranging from 36V to 72V.

This topology allows the converter to achieve an efficiency

of 92.4% at normal input voltage of 48V.

Circuit Description

The schematic of the active clamp forward converter is

illustrated in Figure. 1 below. T4 is the power transformer.

M17 is the N-channel main switching MOSFET and M15

is the auxiliary N-channel MOSFET. C35 is the reset

capacitor for resetting the power transformer’s core. M14

and M16 construct the synchronous rectification circuit.

L2 and C32 and C33 construct the low-pass output

filtering circuit. T6 is the current sensing transformer. R62

is the reset resistor for resetting the magnetic core of

the current sensing transformer. D18 is the rectifying

diode. R63 is the current sensing resistor. R60 and C41

construct the low-pass filtering circuit for the sensed

current signal. The primary bias circuit consists of R55,

R58, D17, Q8, C40, C31, D14 and R51. R55 and R58

construct a voltage divider, which limits the bias voltage

to 6.9V until the line voltage reach 36V. D17 is a zener

diode that limits the bias voltage to under 8V. R51, D14

and C31 construct the peak charge circuit. The peak

charge circuit will provide bias to the PWM IC U9 (SC4810)

and the driver U8 (SC1302A) after the converter starts

Figure 1: Active Clamp Forward Converter

R52

10K

R50

5.11

100uF

C32

C35

3300pF

R78

5.6K

C40

10uF

3.3V/30A

R70

open

C31

0.1uF

C46

open

C43

100pF

R74

4.3K

R77

18K

D16

open

R53

10K

M16

Si4842DY

R80

1.47K

R72

5.11K

1.3uH

R67

R64

165k

C47

0.01uF

R76

3.01K

FMMT718

R62

10K

C49

180pF

R59

C44 220pF

C45

open

D17

open

P8208T

R58

FZT458

R73

3.01K

R66

open

R57

5.11K

D20

1N5819HW

R79

100K

D14

1N4148WS

C50

1000pF

D13

1N4148WS

C51

0.01uF

R61

1.1M

D18

1N4148WS

M14

Si4842DY

R54

20K

SC4810

RCT

SYNC

OUT1

DMAX

DELAY1

RAMP

VREF

OUT2

DELAY2

C42

open

48V

M15

Si4488DY

C39

0.1uF

C48

0.1uF

R55

30K

R51

5.11

C33

680uF

FZT458

C41

330pF

R56

10K

R75

100K

U10

SC431

R69

10K

SC1302A

R68

U11

MOC207

R65

100K

PE68386

M17

Si4488DY

C36

0.1uF

R63

6.8

1u,100V

C34

C37

0.1uF

R81

4.7K

R71

10K

D19

1N5819HW

R82

5.11K

C38

0.1uF

R60

D15

1N4148WS

SC4810EITSTRT Datasheet(PDF) 9 Page - Semtech Corporation

SC4810EITSTRT Datasheet(HTML) 9 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL