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© 2011 Fairchild Semiconductor Corporation

www.fairchildsemi.com

Rev. 1.0.0 • 4/8/11

AN-9736

Design Guideline of AC-DC Converter Using FL6961 &

FL6300A for 70W LED Lighting

Summary

This application note describes a design strategy for a Power

Factor

Correction

(PFC)

circuit

and

higher-power

conversion efficiency using FL6961 and FL6300A. Based

on this design guideline and several functions of each

controller for LED lighting applications, a design example

with detailed parameters demonstrates the performance.

Introduction

Figure 1 shows the typical application circuit, with the BCM

PFC converter in the front end and the Quasi-resonant (QR)

flyback converter in the back end. FL6961 and FL6300A

achieve high efficiency with relatively low cost for

75~200W applications where BCM and QR operation with

a single switch shows best performance. BCM boost PFC

converter can achieve better efficiency with lower cost than

Continuous Conduction Mode (CCM) boost PFC converter.

These benefits result from the elimination of the reverse-

recovery losses of the boost diode and zero-voltage

switching (ZVS) or near-ZVS (also called valley switching)

of boost switch. The QR flyback converter for the DC-DC

conversion achieves higher efficiency than the conventional

hard-switching converter with valley switching.

The FL6961 provides a controlled on-time to regulate the

output DC voltage and achieves natural power factor

correction. The maximum on-time of the switch is

programmable to ensure safe operation during AC

brownouts. The FL6300A ensures

thepower system

operates in quasi-resonant operation in wide range line

voltage and reduces switching loss to minimize switching

voltage in drain of the power MOSFET. To minimize

standby power consumption and improve light-load

efficiency, a proprietary Green-Mode provides off-time

modulation to decrease switching frequency and perform

extended valley voltage switching to keep to a minimum

switching voltage.

Figure 1. Typical Application Circuit