AN4149 Datasheet, PDF(1/19 Page) STMicroelectronics – Designing a CCM PFC pre-regulator based on the L4984D

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AN4149 Datasheet, PDF (1/19 Pages) STMicroelectronics – Designing a CCM PFC pre-regulator based on the L4984D

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Application Note AN4149

Design Guidelines for Quasi-Resonant Converters

Using KA5Q-series Fairchild Power Switch (FPSTM)

Abstract

In general, a Quasi-Resonant Converter (QRC) shows lower

EMI and higher power conversion efficiency compared to

the conventional hard switched converter with a fixed

switching frequency. Therefore, it is well suited for color TV

applications that are noise sensitive. This application note

presents practical design considerations of Quasi-Resonant

Converters for color TV applications employing KA5Q-

series FPSTM (Fairchild Power Switch). It includes

designing the transformer, output filter and sync network,

selecting the components and closing the feedback loop. The

step-by-step design procedure described in this application

note will help engineers design quasi-resonant converter

easily.

DR(n)

LP(n)

NS(n)

CO(n)

CP(n)

DR1

LP1

NS1

CO1

CP1

KA5Q-series

Drain

VO(n)

VO1 (B+)

Sync

PWM

GND

VFB

Vcc

DSY

Rstr

RSY1

DR2

NS2

CO2

H11A817A

LP2

CP2

Rbias

VO2 (Sound)

Linear

regulator

MCU

CSY

RSY2

KA431

Picture ON

Figure 1. Basic Quasi Resonant Converter Using KA5Q-series (Color TV Application)

1. Introduction

The KA5Q-series FPSTM (Fairchild Power Switch) is an

integrated Pulse Width Modulation (PWM) controller and a

Sense FET specifically designed for quasi-resonant off-line

Switch Mode Power Supplies (SMPS) with minimal external

components. Compared with a discrete MOSFET and PWM

controller solution, it can reduce total cost, component count,

size and weight while simultaneously increasing efficiency,

system reliability and productivity.

Figure 1 shows the basic schematic of a quasi-resonant

converter using KA5Q-series for the color TV application,

which also serves as the reference circuit for the design

process described in this paper. Vo1 is the output voltage that

powers horizontal deflection circuit while Vo2 is the output

voltage that supplies power to the Micro Controller Unit

(MCU) through a linear regulator.

Rev. 1.0.0

▷