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Thermal Management of a Planar Magnetic Micro-Transformer
Keywords: Thermal management, Hot spot spreading, Planar magnetic
One of the principal causes of power supply failure is the excessive components temperature. This can cause malfunctioning of these components or in some cases may lead to complete failure. In addition, the undesired temperature rise can reduce the life cycle of components drastically. Due to these concerns much attention is focused on the thermal management of power supplies. The other factor that puts more constrains on the thermal management in electronic industry is the miniaturization. The current trend in portable charger is towards volume reduction. Volume reduction plays an important role in reducing the transport and packaging cost. However, the volume reduction has an undesirable effect on the surface temperature, commonly known as the touch temperature. This paper reports a numerical and experimental study of micro-transformer thermal behavior in a 5W cell-phone charger. The transformer is of planar magnetic type and is 19 mm in length, 9 mm in width and 5mm in height. This kind of transformers is well adapted for low profile design. A detailed thermal management of the charger and transformer has been presented. The importance of geometric features transformer on the thermal behavior of charger is highlighted. Thermal maps of charger have been presented and thermal problem areas are illustrated. The temperature evolution curves for components are obtained experimentally. Some heat transfer enhancing strategies are put forward. A thermal solution for spreading the hot spot temperature has been proposed. It is shown that this thermal solution strategy can reduce the touch temperature (case temperature) by 13 C. In the follow up, the results of micro transformer which uses planar magnetic technology have been compared with a wire-wound transformer.
Yazdan P. Razi, Associate Manager of Testing and Design
Flextronics International
San Jose, CA

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