AN-8024 Datasheet, PDF (1/10 Pages) Fairchild Semiconductor – Power Switch (FPSTM) FSBH-series to Standby Auxiliary Power Supply

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AN-8024
Applying Fairchild Power Switch (FPS^TM) FSBH-series to
Standby Auxiliary Power Supply
1. Introduction
The highly integrated FSBH-series consists of an integrated
current mode Pulse Width Modulator (PWM) and an
avalanche-rugged 700V SenseFET. It is specifically
designed for high-performance offline Switch-Mode Power
Supplies (SMPS) with minimal external components.
The integrated PWM controller features include a
proprietary green-mode function that provides off-time
modulation to linearly decrease the switching frequency at
light-load conditions to minimize standby power
consumption. The PWM controller is manufactured using
the BiCMOS process to further reduce power consumption.
The green and burst modes function with a low operating
current (2.5mA in green mode) to maximize the light load
efficiency so that the power supply can meet stringent
standby power regulations.
The FSBH-series has built-in synchronized slope
compensation to achieve stable peak-current-mode control.
The proprietary external line compensation ensures constant
output power limit over a wide AC input voltage range, from
90V_AC to 264V_AC and helps optimize the power stage.
Many protection functions, such as open-loop / overload
protection (OLP), over-voltage protection (OVP), brownout
protection, and over-temperature protection (OTP); are fully
integrated into FSBH-series, which improves the SMPS
reliability without increasing the system cost.
This application note presents design consideration to apply
FSBH-series to a standby auxiliary power supply with single
output. It covers designing the transformer, selecting the
components, feedback loop design, and design tips to
maximize efficiency. For multi-output applications, refer to
Fairchild application note AN-4137.
Figure 1. Typical Application Circuit
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 9/18/09
1
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