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The authors report the use of a coreless printed circuit board transformer for power conversion with very high power density and efficiency. A coreless PCB transformer with an outermost radius of ~1 cm and 19 turns for both the primary and secondary windings can transfer 19 W at an efficiency of 90%, resulting in a record power density of 24 W/cm2. The power density and energy efficiency of a coreless PCB transformer are higher than those of core-based microtransformers. Coreless transformers are simpler in structure, easier to implement in silicon wafer and cheaper than core-based planar transformers.
Introduction: As the sizes of electronic circuits are decreasing, planar inductor and transformers are becoming more important because of their size advantage. Active research has been carried out in recent years into microtransformers [1, 2] and planar transformers [3]. So far, most efforts have been devoted to transformer designs with magnetic cores. It is well known that as the operating frequency increases, the required size of the magnetic core will decrease. This has led to the design of very small magnetic structures [1, 2]. However, little research has been carried out into addressing the issue of when the size of the magnetic material will approach zero and become zero, although the operating frequencies in many applications have well exceeded 1 MHz. Recently, we demonstrated that it is practically feasible and economically sound to use coreless PCB transformers [3 - 6]. Several misunderstandings about the use of planar transformers without magnetic cores have been clarified....