Lithium-ion battery charging using bipolar transistors

From the power dissipation breakdown calculations, the dominant loss in the charger circuit during all phases of the linear battery charging cycle is the on state loss of the pass element. The power dissipated in the fast charge phase is most significant reaching its peak when the Li-ion battery is at pre-charge voltage threshold and the constant current charge phase is initiated. The key parameters to consider in the pass element are the power and thermal ratings, saturation voltage, reverse blocking capability and packaging. Zetex's application specific low saturation voltage bipolar PNP transistors provide reverse blocking while maintaining the necessary charging voltage head-room for single cell Li-ion linear charger application.

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