Datasheet > AN-9737

AN-9737

更新时间： 2022-06-02 12:44:10

品牌	Logo	应用领域
飞兆/仙童 - FAIRCHILD		转换器
页数	文件大小	规格书
11页	390K
描述
Design Guideline for Single-Stage Flyback AC-DC Converter Using FL6961 for LED Lighting

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AN-9737 数据手册

www.fairchildsemi.com

ANꢀ9737

Design Guideline for SingleꢀStage Flyback ACꢀDC

Converter Using FL6961 for LED Lighting

Summary

Basic Operation: High Power Factor

Flyback Converter

This application note presents singleꢀstage Power Factor

Correction (PFC) and focuses on how to select and design

the flyback transformer for 16.8W (24V/0.7A) solution for

universal input for LED lighting applications using FL6961.

The flyback converter using FL6961 operates in Critical

Conduction Mode (CRM) and has functions such as CC/CV

feedback circuit, softꢀstarting, and the cycleꢀbyꢀcycle current

limit for LED lighting applications.

The basic idea of achieving high power factor (PF) flyback

converter is to use a Critical Conduction Mode (CRM) PFC

controller. The conventional PFC IC, such as FL6961, has

constant onꢀtime and variable offꢀtime control method,

which means the input average current always follows the

input voltage shape.

Figure 1 shows the typical application schematic of singleꢀ

stage PFC topology. The main difference of normal CRM

boost converter is that singleꢀstage PFC doesn’t use a large

electrolytic capacitor after the full rectification diode.

Normally, the singleꢀstage PFC method uses a small

capacitor (C1 in Figure 1) to act as a noise filter to attenuate

highꢀfrequency components and doesn’t use the INV pin for

output voltage regulation.

Introduction

These days, engineers use various types of LEDs for general

lighting systems because of their long life, excellent

efficacy, price, environmental benefits, and requirements

from end users. At the same time, high power factor (PF),

isolation for safety, and constant current control (CC) for

constant LED color are becoming requirements.

Conventional regulation is the minimum power factor

correction for input power base above 25W, but many want

to reduce power ratings and the new EnergyꢀStar directive

for solidꢀstate lighting requires a power factor greater than

0.9 for commercial applications. Expect PF regulations to

become more stringent.

U101

VCC

OUT

INV

Fuse

COMP

MOT

GND

ZCD

EMI filter

Feedback

Figure 1. Simplified Schematic of HighꢀPower Factor Flyback Converter with FLS6961

Rev. 1.0.0 • 4/13/11

www.fairchildsemi.com

12 3 4 5 6 7...11

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