To address an ever-increasing demand for more power in less space, designers are turning to Planar Transformers as an attractive alternative to conventional core shapes where low-profile magnetic devices are required.
These devices provide functions critical to the effective operation of DC-DC converters and have a greater consistency of performance than traditionally wound devices.
A planar transformer is a flat, low profile transformer fabricated using PCB technology. The basic construction method of a planar transformer consists of creating a multi-layer printed circuit board. These windings are then placed in low profile, E/E or E/I ferrite core combinations.
Planar transformers provide the electrical isolation, voltage transformation and energy transfer functions of conventional wire wound transformers in a smaller surface mount device footprint.
Planar transformers fabricated on PCB comprise the following elements:
|Windings etched as tracks on PCB
|Windings made from insulated wires
|PCB dielectric material
|Ferrite, iron alloys, etc.
|Extremely compact and low profile
|Larger, significant height
|Very low due to tight coupling
|Higher due to poorer coupling
|Low as limited overlapping area
|High due to more overlapping wires
|Low as wider copper tracks
|Higher due to thinner winding wires
|Turns Ratio Range
|Typical 1:1 to 1:5
|Wide – 10:1 or more
|Lower – less than 10W usually
|Higher power handling capacity
|Lower due to PCB process
|Higher labor for hand winding
|Excellent, embed directly to PCB
|Moderate, but requires mounting
|Very consistent and controlled
|Poorer tolerance and unit-unit variation
|>90% in well designed planar transformers
|>95% in conventional transformers
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