AN-4138| Application Note

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Application Note AN4138

Design Considerations for Battery Charger Using Green Mode Fairchild Power Switch (FPSTM)
Abstract
This application note presents practical design considerations for battery chargers employing Green Mode FPS (Fairchild Power Switch). It includes designing the transformer and output filter, selecting the components and implementing constant current / constant voltage control. The step-by-step design procedure described in this paper will help engineers design battery chargers more easily. In order to make the design process more efficient, a software design tool, FPS design assistant that contains all the equations described in this paper is also provided. The design procedure is verified through an experimental prototype converter.

DR Bridge rectifier diode CDC VDC + Dsn FPS Drain Rd AC line FB GND Vcc Ra H11A817A CB Ca Na Da H11A817A Vbias Vsn + CO

LP CP IO VO

Rsn

Csn

IOref

Current Controller

VOref

Voltage Controller
Figure 1. Basic Battery charger Using FPS

1. Introduction
As penetration rates of portable electronics devices such as cellular phones, digital cameras or PDAs have increased significantly, the demands for low cost battery chargers are rising these days. Fairchild Power Switch (FPS) reduces total component count, design size, weight and, at the same time increases efficiency, productivity, and system reliability when compared to a discrete MOSFET and controller or RCC switching converter solution. Table 1 shows the FPS lineup for a battery charger application. Figure 1 shows the schematic of the basic battery charger using FPS, which also serves as the reference circuit for the design process

described in this paper. An experimental flyback converter from the design example has been built and tested to show the validity of the design procedure.
Device FSDH0165 FSD311 FSD200 FSD210 Switching frequency 100 kHz 67 kHz 134 kHz 134 kHz Current limit 0.35 A 0.55 A 0.32 A 0.32 A Rdson (typ.) 15.6 14 28 28

Table 1. FPS lineup for a battery charger

Rev. 1.0.0
2003 Fairchild Semiconductor Corporation