Abstract
A DC-DC converter scheme for thermoelectrically powered wristwatch is described. The converter consists of a variable-stage switched-capacitor (SC) circuit, a clock circuit, and a control circuit. The converter boosts the output voltage of thermoelectric (TE) generator that outputs a voltage of over 0.25V and supplies the generating power to a rechargeable battery with a voltage of 1.3V. A simple maximum-power-point-tracking technique makes it possible to extract power, which is close to maximum power, from the TE generator with a large internal resistance of 1.2kΩ. The maximum power point was automatically obtained by detecting the output open voltage of the variable-stage SC circuit and also by selecting the stage of multi-stage SC circuits. To verify the effectiveness of our converter, we fabricated a prototype with a 0.6μm CMOS process and measured the power extracted from a TE generator. The power extraction efficiency to the converter is 89% and the total conversion efficiency of the power supply module is 29%.
