Planar Magnetic Component Development

Focus:

This 18-page paper presents detailed examples of planar transformer designs within the context of actual power converter designs. These power converters consist of an 8-W flyback converter with 5-V and +/-15-V outputs, a 2-W flyback converter with a single -35-V output, and two 0.8-J capacitive discharge units (CDUs). These converters require the design of a 3-output flyback transformer, a -35-V flyback transformer, and a current-viewing transformer (CVT) capable of monitoring 50 A peaks (one CVT is required for each CDU). The design of these transformers is described in detail including their implementation as planar magnetic components, and the complete design of the power converters is described. The magnetic components are tested individually and also within the power converter prototypes and test results are presented. Design changes required to improve magnetic component and power converter performance are described. Techniques for reducing magnetic component cost are discussed. Prior to discussion of the design examples, the paper begins by offering instructions and tips for building planar transformers with many details on PCB manufacturing constraints that influence the design. Appendices show calculations for resistance an etched spiral, energy lost in an inductor, and transformer calculations.

What you’ll learn:

• How to design and build planar transformers for flyback converters
• How to account for pc-board manufacturing constraints when designing planar magnetic components
• How to reduce costs when designing planar magnetic components

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Author & Publication:

Robert L. Nagel, Custom Magnetics, Capacitors, Interconnections Department, and Michael E. Partridge,Instrumentation Engineering and Technology Department, Sandia National Laboratories, Albuquerque, New Mexico , Laboratory Website, Sep 01 1994

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