A Novel Wireless Fast Charger Using Unregulated IPT Stage

The inductive power transfer (IPT) technique has many merits in battery charging compared to traditional charging methods. However, in low-power applications, most of the existing wireless chargers would employ redundant power conversion and isolation stages in order to be compatible with the wire-connected chargers, which leads to low overall charging efficiency. This paper proposes a novel wireless fast charger by using a two-stage configuration. An unregulated IPT stage can not only offer galvanic isolation but also provide high step-down conversion ratio, and it works like a transformer-based isolated converter. Then the whole charger only needs one more regulation stage to meet the output requirement. This paper focus on the IPT stage with high-input voltage and low-output voltage. The LCC-C compensation is selected for the voltage step-down purpose. In the analysis, the influence of layout size, resonance frequency, and the power level are discussed, based on which the circuit parameters are optimally designed. Finally, a 2MHz 25W IPT stage is used as an example to achieve 120V /12V conversion. The measured peak efficiency is 82 %, which is 9 % higher than the stage of the art product (5W, 5V/5V conversion).