AN-4141| Application Note
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Application Note AN4141
Troubleshooting and Design Tips for Fairchild Power Switch (FPSTM) Flyback Applications
Introduction
This application note describes troubleshooting for problems that power supply engineers may encounter when operating FPS application circuits. This note helps engineers figure out causes and solutions to their problems starting with the symptoms. Some useful application tips are also provided. The following items are covered in this application note.
1. When the power supply does not start .....................................................................................pp.2 2. When the power supply is unstable..........................................................................................pp.3 3. When there is a transient overshoot in the output voltage........................................................pp.4 4. When the peak drain voltage exceeds the rated voltage............................................................pp.4 5. When sub-harmonic oscillation occurs......................................................................................pp.5 6. When the line frequency ripple on the output voltage is too large............................................pp.5 7. When the power conversion efficiency is too low.....................................................................pp.6 8. When the audio noise occurs .....................................................................................................pp.6 9. PCB layou
t consideration ..........................................................................................................pp.6 10. Application circuit for delayed shutdown in a over load protection..........................................pp.7 11. Application circuit for a very tight output regulation ................................................................pp.7 12. Application circuit to convert auto-restart mode into latch mode..............................................pp.8
Figure 1 shows the schematic of the basic off-line flyback converter using FPS, which also serves as the reference circuit for the troubleshooting described in this application note. It is also assumed that all the protection circuits within the FPS are in auto restart mode.
Rev. 1.0.0
2003 Fairchild Semiconductor Corporation
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