Primary-Tuning Wireless Constant-Current Charger With Self-Sustained Constant-Voltage Limit Featuring Minimal Secondary Design

An inductive power transfer (IPT) converter can operate as a constant-current (CC) source for wireless battery charging. Since the output voltage of a CC power supply linearly increases with the load resistance, a constant-voltage (CV) threshold must be incorporated in the IPT converter, so as to protect the CC power supply from open-load condition and prevent the overvoltage from damaging the battery. This article proposes a primary-tuning IPT converter, which operates as a wireless CC charger with a self-sustained CV limit to feature minimal secondary design. The CC-CV behavior is achieved by only adopting and manipulating a switch-controlled capacitor (SCC) in the primary. Secondary-side control and wireless feedback communication are not necessary, and thus, the secondary is minimal and rugged. A voltage divider circuit helps with reducing the voltage stress of the SCC switches. Soft switching is permitted for all switches throughout the operating range. The operating principle and control scheme of the proposed system are explained. Experimental results are presented to demonstrate the CC-CV behavior of the proposed IPT charger.