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Rev. 1.0.1 • 9/16/10

AN-6747

Applying FAN6747 to Control a Flyback Power Supply with

Peak Current Output

1. Introduction

Highly integrated PWM controller, FAN6747, 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.

FAN6747 provides a two-level OCP function that allows the

SMPS to stably deliver peak power during the motor

acceleration without causing premature shutdown, while

protecting the SMPS from overload condition.

Green-mode and burst-mode functions with a low operating

current 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 optimize the power stage. Protection

functions such as OCP, OLP, OVP, and OTP are fully

integrated into FAN6747, which improves the SMPS

reliability without increasing system cost.

This application note presents design considerations to

apply FAN6747 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 FAN6747.

Figure 1.

Typical Application