Advantages of the Second Generation Planar Magnetics

  • ER core geometry reduces ATL (average turn length) thus reducing Rdc and Rac of windings.
  • Reduction in Rdc and Rac improves efficiency.
  • Total surface of planar turn is in direct contact with a core backwall, thus greatly improving thermal conductivity and reducing EMI.
  • In most applications better efficiency and better thermal management (lower thermal impedance) allow the use of smaller packages.
  • Smaller packages mean lower costs.
  • Flexible, low impedance terminations.
  • U.S. Patent No.7,129,809 SMD packages with excellent co-planarity.

Technical Comparison of Isolation Systems


Multilayer (mlt) Based


Plastic Bobbin Based

Mlt Board System laminates high potential copper layers with prepreg Copper sealed inside mlt board. Terminals soldered far from core.
High Potential copper turns mounted in a cavity inside lower half of plastic bobbin. Upper half of bobbin mates with lower half.
Stack of windings do not have any air pockets and have a direct heat dissipation path to the ferrite core.Thus, lower thermal impedance and operating temperature.
There are at least three air pockets in the system increasing thermal impedance and, consequently, windings run hot.
The thickness of isolating layers is only 8-12 mils. Low voltage copper leadframes are bonded directly to mlt boards.
Plastic bobbin wall thickness is at least 20 mils and is used from 2 to 4 times. The wall increases thermal impedance. Multiple cavity bobbins which are used for high power further increase thermal impedance.
Mlt boards are vertically spaced from one another outside the core thus forming openings for free passage of cooling air.
High potential windings are sealed inside the bobbin and can not be air cooled.

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