AN-6861 Datasheet, PDF (1/12 Pages) Fairchild Semiconductor – a Flyback Power Supply with Peak Load Current Profile

www.fairchildsemi.com
AN-6861
Applying FAN6861 to a Flyback Power Supply with Peak
Load Current Profile
1. Introduction
Highly integrated PWM controller, FAN6861, is optimized
for applications with motor load, such as printers and
scanners, that inherently impose some kind of overload
condition on the power supply during acceleration mode.
The two-level OCP function allows the SMPS to stably
deliver peak power during the motor acceleration without
causing premature shutdown, while protecting the SMPS
from overload condition.
The green-mode and burst-mode functions with a low
operating current (2.2mA maximum in green mode)
maximize the light-load efficiency so that the power supply
can meet stringent standby power regulations.
The frequency-hopping function reduces electro-magnetic
interference (EMI) of a power supply by spreading the
energy over a wider frequency range. The constant power
limit function minimizes the component stress in abnormal
condition and helps to optimize the power stage. Protection
functions; such as OCP, OLP, OVP, and OTP are fully
integrated into FAN6861, which improves the SMPS
reliability without increasing system cost.
This application note presents design considerations to apply
FAN6861 to a flyback power supply with peak load current
profile. It covers designing the transformer, selecting the
components, and closing the feedback loop. Figure 1 shows
a typical application circuit using FAN6861.
L
AC input
N
EMI
Filter
R_{S T A RT}
3 RT
5
VDD
R_SN1 C_SN1
+
VIN
C_IN
D_DD1
R DAMP D_{DD 2}
+
CDD 1
+
C_{DD 2}
DSN
R_G
GATE 6
RSN2 CSN2
D _{OUT +}
C_{OUT 1}
C_{OUT 2}
V_{O +}
V_{O -}
2 FB
CFB
SENSE 4
GND
1
FAN6861
R_CSF
C_CSF
RCS
R_BIAS
RDB
KA431
R₁
C_F
R2
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 6/9/09
Figure 1. Typical Application
www.fairchildsemi.com