A Three-Transistor Energy Management Circuit for Energy-Harvesting-Powered IoT Devices

Energy harvesting (EH) provides a promising solution for powering distributed Internet of Things (IoT) devices. Due to the low-level and sporadic ambient energy supply, an EH-powered device should operate in an intermittent and energy driven mode. Commercial voltage supervisors were not optimized for the EH scenario, making it difficult to satisfy all new demands. The conventional energy management (EM) circuit has a risk of locking up during the turn -ON transient; therefore, it might fail to power the IoT load device. Previous technologies have used a relatively large circuit to solve this problem. In this article, a concise discrete three-transistor EM (3T-EM) circuit is proposed. It can track stored energy, switch ON/OFF to the load device, and provide a regulated voltage output. These key functions are realized by utilizing a minimum number of components; therefore, power consumption and manufacturing cost are largely cut. The voltage thresholds and minimum input current are theoretically derived. In experiments, the ON/OFF thresholds can be adjusted accurately, as predicted by the theory. The 3T-EM circuit can ensure the correct operation when the input current is as low as 0.4 mu A. Control experiments also prove the effectiveness and performance of the 3T-EM circuit. The proposed 3T-EM circuit shows the characteristics of low cost, low power, inherent regulation, high voltage rating, and good predictability. It is a good candidate to perform the EM task in widely distributed EH-powered IoT devices.