Fairchild Design Guidelines for Flyback Converters Using FSQ-Series Fairchild Power Switch (FPS) Data Manual

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Application Note AN-4150 Design Guidelines for Flyback Converters Using FSQ-series Fairchild Power Switch (FPS™)

1. Introduction size and weight, while simultaneously increasing efficiency, productivity, and system reliability. The FSQ-series employs

Compared to conventional hard-switched converters with

an advanced control technique that allows converter to

fixed switching frequencies, the quasi-resonant converter

operate with narrow frequency variation, while keeping the

(QRC) topology is a very attractive alternative for power

quasi-resonant operation. When the converter operates in

supply designers. The increasing popularity of the QRC

discontinuous conduction mode (DCM), the controller finds

approach is based on its ability to reduce electromagnetic

the valley of the drain voltage and turns on the MOSFET at

interference (EMI) while increasing power conversion

the minimum drain voltage. Meanwhile, the converter can

efficiency.

operate with fixed frequency when operating in continuous The FSQ-series FPS™ (Fairchild Power Switch) is an conduction mode (CCM), which allows converter design as integrated Pulse Width Modulation (PWM) controller and simple as conventional PWM converters.

Sense FET specifically designed for quasi-resonant off-line

This application note presents practical design consider-

Switch Mode Power Supplies (SMPS) with minimal external

ations of a flyback converter employing the FSQ-series

components. Figure 1 shows the internal block diagram of

FPS™. It covers designing the transformer, output filter, and

the FSQ-series. Compared with discrete MOSFET and PWM

sync network; selecting the components; and closing the

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

feedback loop.

Sync Vstr Vcc Drain

VCC good

VBurst

VCC Vref

Idelay IFB PWM

Soft-

driver

Start

LEB 200ns

RC=80ns

6V TSD VOCP GND

2.5μs time delay

Sync 6V Vovp

Vcc good

Figure 1. Block Diagram of FSQ-Series

© 2006 Fairchild Semiconductor Corporation www.fairchildsemi.com FSQ-Series Rev. 1.0.0 10/23/06