Fairchild Design Guidelines for Offline Flyback Converters using FPS
Summary
Accelerate your SMPS design process with this professional application note on off-line flyback converters. This comprehensive guide is essential for engineers who need to build reliable Switched Mode Power Supplies (SMPS). It details a practical, step-by-step procedure for designing and selecting optimal components—including transformers, capacitors, and MOSFETs—to ensure efficient and stable converters. Use these proven guidelines to minimize design iterations and successfully integrate high-performance flyback converter solutions.
Page 1 Text Content
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Application Note AN4137 Design Guidelines for Off-line Flyback Converters Using Fairchild Power Switch (FPS)
Abstract The step-by-step design procedure described in this paper helps engineers to design SMPS easily. In order to make the
This paper presents practical design guidelines for off-line
design process more efficient, a software design tool, FPS
flyback converters employing FPS (Fairchild Power
design assistant that contains all the equations described in
Switch). Switched mode power supply (SMPS) design is
this paper is also provided. The design procedure is verified
inherently a time consuming job requiring many trade-offs
through experimental prototype converter.
and iterations with a large number of design variables.
DR(n) LP(n)
Bridge rectifier
VDC Rsn
diode Csn Vsn Np
NS(n)
VO(n)CP(n)
CO(n)
FPS DR1 LP1
Drain
CO1 CP1 VO1
AC line
FB Vcc
Da Ra
Rbias
Ca H11A817A
Na R1
RF CF
KA431
Figure 1. Basic Off-line Flyback Converter Using FPS
1. Introduction and output filter, selecting the components and closing the feedback loop. The design procedure described herein is
Figure 1 shows the schematic of the basic off-line flyback
general enough to be applied to various applications. The
converter using FPS, which also serves as the reference
design procedure presented in this paper is also imple-
circuit for the design process described in this paper.
mented in a software design tool (FPS design assistant) to
Because the MOSFET and PWM controller together with
enable the engineer finish their SMPS design in a short time.
various additional circuits are integrated into a single
In the appendix, a step-by-step design example using the
package, the design of SMPS is much easier than the discrete
software tool is provided. An experimental flyback converter
MOSFET and PWM controller solution. This paper provides
from the design example has been built and tested to show
a step-by-step design procedure for a FPS based off-line
the validity of the design procedure.
flyback converter, which includes designing the transformer
Rev. 1.2.0
©2003 Fairchild Semiconductor Corporation
Page Summary Contents For Fairchild Design Guidelines for Offline Flyback Converters using FPS
Manual Details
| Brand | Fairchild |
|---|---|
| Pages | 20 |
| File Size | 399.90 KB |
| Published | July 22, 2026 |
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Frequently Asked Questions
How do I generally start the SMPS design procedure?
The process begins by defining the system specifications, followed by determining the DC link capacitor and transformer parameters.
What is the recommended DC link capacitor value?
Use 2-3uF per watt for universal input range or 1uF per watt for European input range.
Is specialized software available to simplify the design process?
Yes, the FPS flyback converters utilize a dedicated software tool (FPS design assistant) to make SMPS design much easier and faster.
What is the policy regarding life support applications?
Fairchild products are not authorized for use as critical components in life support devices or systems without express written approval.