A Constant Efficiency of Rectifying Circuit in an Extremely Wide Load Range

Wireless power transmission (WPT) is actively being researched and developed. WPT transfers power to electrical load without a wire. One of the problems is that the efficiency is easily affected by load resistance and input power. Therefore, an impedance matching circuit becomes crucial for realization of high-efficiency wireless power systems. In this study, we proposed a maximum power point tracking (MPPT) method for a low-power milliwatt-level RF-dc rectifying circuit using a dc-dc converter. We proposed an RF-dc-dc circuit that consists of an RF-dc rectifier circuit and a dc-dc converter. We measured the RF-to-dc conversion efficiency of the RF-dc-dc circuit using 2.45-GHz microwave power. When the buck-boost converter is connected to the rectifying circuit, the RF-to-dc efficiency of rectifier is approximately steady at 75%, despite the load resistance changing from 100 to 5000 Ω. The overall efficiency of the RF-dc-dc circuit is still over 60%, even though the load resistance varied from 100 to 5000 Ω and the input power changed from 40 to 100 mW.