A Self-Contained Startup Charging Circuit for Energy-Harvesting Batteryless IoT Devices

This paper presents a self-contained startup charging circuit designed for energy-harvesting batteryless IoT devices. The proposed circuit consists of a current-biasing block, a current mirror, a reference voltage generator, and a comparator circuit. The current-biasing circuit drives the current mirror, which supplies the charging current to the energy storage element. Simultaneously, the reference voltage generator—also biased by the current source—produces a stable DC reference voltage. When the energy storage device (e.g., a supercapacitor) lacks sufficient charge, the comparator enables the charging path by activating the current-biasing and mirror circuits. Once adequate energy is stored, the comparator disables these circuits to prevent overcharging. This self-contained solution is intended to autonomously initialize and manage the cold-start charging process in energy-harvesting systems without relying on external controllers. This paper highlights the circuit architecture and validated performance, demonstrating a charging current of up to 27 mA, a reference voltage of 700 mV, and an operating range from 0.9 V to 1.8 V across a temperature range of −40 °C to 85 °C.