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SC4911

Bias/Primary Side PWM Controller

with Ultra Low Start-up Current

POWER MANAGEMENT

Revision: April 5, 2006

Description

Features

Applications

Typical Application Circuit

Programmable switching frequency up to 500kHz

Line UVLO Protection

Undervoltage Lockout

Low startup current (45µA)

Cycle by cycle current limit

8 pin MSOP. Available in Lead-free, fully WEEE and

RoHS compliant

The SC4911 is a highly integrated bias/primary side PWM

controller designed for off-line or isolated dc-dc convert-

ers in telecommunication and data communication ap-

plications. The high degree of integration minimizes the

amount of discrete parts needed and leads to substan-

tial cost and space saving converter designs.

The circuitry of the SC4911 includes line voltage UVLO

featuring startup current less than 50µA and program-

mable switching frequency. The device supply is derived

from an auxiliary winding on the transformer. The auxil-

iary winding could also provide output feedback informa-

tion if an optocoupler is not used.

Vout

R5

R9

C3

R1

R7

C6

D2

C2

D1

U1 SC4911

3

4

5

7

FB

COMP

ILIM

OUT

C4

R4

Vin

C7

C1

R8

R2

Q1

R6

T1

C8

R3

C5

Telecom isolated converters

Offline isolated power supplies

Instrumentation power supplies

Battery chargers