Planar transformer

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Exploded drawing of a planar transformer
Wound planar transformer (hybrid) with integral heat sink : turns of enamelled copper wire (primary winding 600 volts) or copper tape (secondary winding 50 volts); Transmission power 4000 watts, working frequency 145 kHz

A planar transformer is a special type of transformer that is characterized by its flat design.

Layout and function

Planar transformers are mainly used in power electronics with transmission capacities between 200 and 5000 watts. They are particularly small due to the good dissipation of power loss. The windings usually, but not necessarily, consist of conductor tracks on a printed circuit board or of appropriately shaped copper sheets that are separated by insulating layers. This not only results in advantages in terms of manufacturing technology, but the flat conductor shape also accommodates the skin effect which is decisive with the usually high working frequencies .

Planar transformers can be manufactured as individual components or integrated on a printed circuit board . In such a planar transformer integrated into the circuit board, the windings are present as conductor tracks on or in the circuit board, the two-part ferrite transformer core is glued or clamped from both sides onto the circuit board, which has openings for this purpose. This construction is cheaper than conventional, wound transformers, especially for large quantities. However, the development effort is higher because prototypes are more complex to produce.

In addition to the large surface-to-volume ratio, which is already better suited for heat dissipation, a further reduced thermal resistance can be achieved by means of attached heat sinks, which in other transformers fails due to the low heat conduction through the volume.

Planar transformers are usually operated at frequencies of 0.1 to several megahertz , which, like other switched-mode power supplies, requires special precautions with regard to electromagnetic compatibility (EMC). In addition to the skin effect , the proximity effect also plays a role, which somewhat relativizes the advantages of the design.

For better integration or to achieve a certain transformation ratio, several transformers are often connected in series or in parallel as required. This also further improves the thermal and high-frequency properties. Storage chokes are also manufactured using the same technology .

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