## 1 Introduction  
In recent years, energy harvesting has been attracting attention along with the growing interest in IoT and a low-carbon society. Energy harvesting is a technology used to convert the energy around us, such as light, heat, and vibration, into electric power. By enabling the conversion of currently unused energy into electrical energy, it is expected to enhance overall energy efficiency. Furthermore, in the field of IoT, numerous sensors are utilized. By harvesting energy from ambient sources to power these sensors, it becomes possible to eliminate the need for battery replacement and power supply wiring, thereby reducing maintenance costs. Triboelectric nanogenerators (TENGs) are a type of energy harvesting device that convert mechanical energy, such as vibrations and friction, into electrical energy by leveraging the triboelectric effect and electrostatic induction [1]. The triboelectric effect is a phenomenon where electric charges move and materials become electrified due to the repeated contact and separation of two different types of materials. TENGs operate based on several distinct modes [2, 3, 4]. The most representative operating modes include the following: In the Vertical Contact-Separation Mode, electrical charges are transferred upon the contact of two different materials, and, as they separate, a potential difference is generated between the electrodes, causing the charge to flow through an external circuit for power generation. In the Sliding Mode, friction between two materials sliding against each other results in the transfer of charges and the generation of a potential difference, leading to the flow of charge through an external circuit. In the Single-Electrode Mode,electricity is generated through the movement of charges between a single electrode and a grounded object, such as the human body. Finally, in the Freestanding Triboelectric-Layer Mode, two stationary electrodes are arranged on the same plane, and an independent dielectric layer moves between them to generate power. They can generate electrical power not only from the vibrational energy of structures, such as iron bridges and buildings, but also from subtle and diverse energy sources, including the mechanical impact of falling raindrops, the low-velocity water flow in oceans and waterways, and the frictional interaction between snow and shoe soles during ambulation on snowy surfaces [5; 6; 7]. The advantages of these devices include their low cost, high durability, and the ability to convert low-frequency vibrations into electrical power [8; 9; 10]. Although triboelectric nanogenerators have not yet found specific applications, certain research reports have indicated successes in powering a stopwatch [11]. Furthermore, TENGs are not only utilized as power sources but are also expected to be applied as self-powered mechanical sensors by leveraging their ability to convert mechanical energy into electrical energy [12]. In fact, research is being conducted on their use as force sensors. However, due to the inherent principles of TENGs, it is not possible to achieve a constant output voltage [13]. Certain TENGs have been developed with structures designed to output a constant voltage; however, due to their structural characteristics, their applications are limited [14]. Power management circuits using PUTs and thyristors have also been studied, but while these circuits can maintain a constant output voltage, they are unable to achieve the desired voltage [15]. Therefore, regulators such as DC-DC converters are required to obtain the desired voltage. A DC-DC converter circuit includes switching elements such as FETs, and by varying the state of these switching elements using pulse-width modulation (PWM) signals, the output voltage is also adjusted. Several attempts have been made to control the output voltage of power generation elements, such as the thermoelectric generators used in energy harvesting, whose output voltage is not constant, using DC-DC converters [16; 17].