Fairchild AN4138 Specifications Manual

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Application Note AN4138 Design Considerations for Battery Charger Using Green Mode Fairchild Power Switch (FPSTM)

Abstract The step-by-step design procedure described in this paper will help engineers design battery chargers more easily. In

This application note presents practical design consider-

order to make the design process more efficient, a software

ations for battery chargers employing Green Mode FPS

design tool, FPS design assistant that contains all the

(Fairchild Power Switch). It includes designing the

equations described in this paper is also provided. The

transformer and output filter, selecting the components and

design procedure is verified through an experimental

implementing constant current / constant voltage control.

prototype converter.

DR LP

Bridge rectifier

VDC CO VO

diode Rsn Csn Vsn CP

Np NS

Vbias

Drain

AC line

ref IO

FB Vcc

Current

Ra Da

Controller

Ca Na

ref VO

Voltage Controller

Figure 1. Basic Battery charger Using FPS

1. Introduction described in this paper. An experimental flyback converter from the design example has been built and tested to show

As penetration rates of portable electronics devices such as

the validity of the design procedure.

cellular phones, digital cameras or PDAs have increased significantly, the demands for low cost battery chargers are

Device Switching Current Rdson (typ.)

rising these days. Fairchild Power Switch (FPS) reduces

frequency limit

total component count, design size, weight and, at the same

FSDH0165 100 k Hz 0.35 A 15.6 Ω

time increases efficiency, productivity, and system reliability

FSD311 67 k Hz 0.55 A 14 Ω

when compared to a discrete MOSFET and controller or RCC switching converter solution. Table 1 shows the FPS FSD200 134 k Hz 0.32 A 28 Ω lineup for a battery charger application. Figure 1 shows the

FSD210 134 k Hz 0.32 A 28 Ω

schematic of the basic battery charger using FPS, which

also serves as the reference circuit for the design process Table 1. FPS lineup for a battery charger

Rev. 1.0.0

©2003 Fairchild Semiconductor Corporation