Design of a Variable-Frequency Inductive Charger for Low-Power Electronic Device Applications

The circuit design method and control strategy of a variable-frequency inductive charger are introduced. The target application is low-power inductive charging systems where the coupling coefficient is relatively stable, e.g., mobile phone chargers with mechanical positioning aids. On the transmitter side, a high-order compensation circuit is deployed to achieve a monotonous frequency-power relation, which allows the output power to be regulated by frequency tuning. Only a half-bridge inverter is required and soft switching is achievable at most operating points. On the receiver side, the load impedance is fixed around the optimal value to improve the energy efficiency. Experimental results show that with low-loss circuit components, the proposed scheme achieves good efficiency performance under full and partial loads.