SG6741 Datasheet, PDF (1/13 Pages) Fairchild Semiconductor – Highly-Integrated Green-Mode PWM Controller

Highly-Integrated Green-Mode PWM Controller
FEATURES
„ High-voltage start-up
„ Low operating current (4mA)
„ Linearly decreasing PWM frequency to 22kHz
„ Frequency hopping to reduce EMI emission
„ Peak-current-mode control
„ Cycle-by-cycle current limiting
„ Leading-edge blanking
„ Synchronized slope compensation
„ Gate output maximum voltage clamp (18V)
„ V_DD over-voltage protection (auto restart)
„ V_DD under-voltage lockout (UVLO)
„ Internal open-loop protection
„ Constant power limit (full AC input range)
APPLICATIONS
General-purpose switch-mode power supplies and
flyback power converters, including:
„ Power adapters
„ Open-frame SMPS
DESCRIPTION
The highly integrated SG6741 series of PWM controllers
provides several features to enhance the performance of
flyback converters.
To minimize standby power consumption, a proprietary
green-mode function provides off-time modulation to
TYPICAL APPLICATION
Product Specification
SG6741
linearly decrease the switching frequency at light-load
conditions. To avoid acoustic-noise problems, the
minimum PWM frequency is set above 22KHz. This
green-mode function enables the power supply to meet
international power conservation requirements. With the
internal high-voltage start-up circuitry, the power loss due
to bleeding resistors is also eliminated. To further reduce
power consumption, SG6741 is manufactured using the
BiCMOS process, which allows operating current as low
as 4mA.
SG6741 integrates a frequency-hopping function that
helps reduce EMI emission of a power supply with
minimum line filters. Its built-in synchronized slope
compensation achieves stable peak-current-mode control.
The proprietary internal line compensation ensures
constant output power limit over a wide range of AC input
voltages, from 90VAC to 264VAC.
SG6741 provides many protection functions. In addition
to cycle-by-cycle current limiting, the internal open-loop
protection circuit ensures safety when an open-loop or
output short-circuit failure occurs. PWM output is
disabled until V_DD drops below the UVLO lower limit;
then the controller starts again. As long as V_DD exceeds
about 26V, the internal OVP circuit is triggered.
SG6741 is available in an 8-pin DIP or SOP package.
© System General Corp.
Version 1.2.1 (IAO33.0047.B2)
-1-
www.sg.com.tw • www.fairchildsemi.com
September 19, 2007