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© 2010 Fairchild Semiconductor Corporation

www.fairchildsemi.com

Rev. 1.0.0 • 11/2/10

AN-9719

Applying Fairchild Power Switch (FPS™) FSL1x7 to

Low- Power Supplies

1. Introduction

The highly integrated FSL-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 Switched Mode

Power Supplies (SMPS) with minimal external components.

The features of the integrated PWM controller include a

proprietary

green-mode

function

providing

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 mode and burst mode functions with a low

operating current (2mA in green mode) maximize light-load

efficiency so that the power supply can meet stringent

standby power regulations.

The FSL-series has a 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,

Many protection functions; such as open–loop / overload

protection (OLP), over-voltage protection (OVP), and over-

temperature protection (OTP); are fully integrated into FSL-

series. These features improve the SMPS reliability without

increasing system cost.

Compared to a discrete MOSFET and controller or RCC

switching converter solution, the FSL-series reduces total

component count, converter size, and weight while

increasing efficiency, productivity, and system reliability.

These devices provide a basic platform for design of cost-

effective flyback converters.

Figure 1. Typical Application Circuit