In this paper, the development of a small-sized MPPT (maximum power point tracking) circuit and its application for maximum output conversion by a solar cell in commercialized wearable fashion is reported. Using the Texas Instruments BQ25570 Energy Harvesting IC programmable chip, we implemented a hybrid DC-DC converter circuit of boost and buck converters. We designed two types of charging methods. The first method was a USB direct charging method (5.0 V, 1.0 A) using the MCP-73 8-32-2ACI voltage regulator (step-down voltage). The second method was continuous energy harvesting with a MPPT function, using a 4 V or less low-power solar energy source. Based on the circuit design, we developed a CLT (copper lamination textile) technology, which can be used to develop a fabric using PCBs as substrate materials in electronic circuit application technologies for wearable devices. Although the circuit could not be bent completely, this textile substrate can be used for future research on wearable devices. We tested the operation and power conversion using the MPPT converter circuit as the power input for a low-power solar cell energy source under international standards for sun conditions.