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This brief presents a power management system for wearable technology based on a custom made electromagnetic (EM) transducer and a front-end circuit for energy harvesting (EH) and activity sensing. Due to the ac-output nature of the EM transducer, this brief proposes a reconfigurable rectifier that can switch from passive operation to a more power-efficient active topology depending on the available power in the system. The passive mode operates as a negative voltage converter during start-up, while the active configuration is enabled and driven by a control block after the available voltage at an output storage capacitor surpasses 1.8 V. This brief also introduces an activity detection circuit that enables the use of the inherent sensing capabilities of the EM transducer. The combination of both, a reconfigurable rectifier and an activity detection circuit, allows the system to gather information similar to that of an accelerometer regarding the activity of the user, but at net-zero power consumption and lower cost. The EH front-end described in this brief was implemented in a 130 nm CMOS process with an area of 0.0254 mm2. Measurements show that the circuit has a peak power conversion efficiency of 92.04%, while the power management system can extend the battery’s charge of a Fitbit Charge HR by four hours for every 30 effective minutes of a sprint interval training routine. [ABSTRACT FROM AUTHOR]

This brief introduces an integrated energy harvester system targeting Internet of Things sensor applications such as a wireless temperature sensor. The proposed design provides 1-V regulated voltage boosting the input voltage (0.27–1 V) from a thermoelectric generator (TEG). To ensure the maximum power extraction, the proposed energy harvester includes multiple circuit level techniques. First, the reconfigurable capacitor charge pump distributes on-chip capacitors to required step-up stages. This approach optimizes the silicon area by utilizing 100% of on-chip capacitors regardless of charge pump conversion gain. Second, the design is capable of 3-D maximum power point tracking, matching a source impedance to input impedance of the energy harvester. Thus, the proposed design is able to extract power from a small form factor TEG, having low source impedance. The reconfigurable capacitor charge pump has the highest power density while delivering power up to $500~{\mu W}$. Experimental results show end-to-end power efficiency of 64% @ 1–V output voltage, and an input impedance matching range of $1 {\Omega } - 5~{\mathbf{k}}{\Omega }$. The energy harvester was fabricated in 130-nm CMOS standard technology with an active area of 0.835 mm2. [ABSTRACT FROM AUTHOR]

Microbial Fuel Cell (MFC) technology is a novel Energy Harvesting (EH) source that can transform organic substrates in wastewater into electricity through a bioelectrochemical process. However, its limited output power available per liter is in the range of a few milliwatts, which results very limited to be used by an Internet of Things (IoT) smart node that could require power in the order of hundreds of milliwatts when in full operation. One way to reach a usable power output is to connect several MFCs in series or parallel; nevertheless, the high output characteristic resistance of MFCs and differences in output voltage from multiple MFCs, dramatically worsens its power efficiency for both series and parallel arrangements. In this paper, a Power Management System (PMS) is proposed to allow maximum power harvesting from multiple MFCs while providing a regulated output voltage. To enable a more efficient and reliable power-harvesting process from multiple MFCs that considers the biochemical limitations of the bacteria to extend its lifetime, a power ranking and MFC health-protection algorithm using an interleaved EH operation was implemented in a PIC24F16KA102 microcontroller. A power extraction sub-block of the system includes an ultra-low-power BQ25505 step-up DC-DC converter, which integrates Maximum Power Point Tracking (MPPT) capabilities. The maximum efficiency measured of the PMS was ~50.7%. The energy harvesting technique presented in this work was tested to power an internet-enabled temperature-sensing smart node. [ABSTRACT FROM AUTHOR]

Efforts towards energy-harvesting solutions are targeted for wireless sensor node applications and focus on performing maximum power extraction and storing power, yet efforts to deliver a regulated supply to voltage-sensitive blocks in power-limited applications has yet to be fully achieved. This paper presents a low-power, autonomous power management unit (PMU) able to perform maximum power point tracking for dc-type renewable sources. It includes a startup circuit fed directly from the renewable source. The PMU delivers a regulated output voltage through a digital LDO. The main step-up operation is performed through a dynamically controlled, power-aware, capacitive dc–dc converter that performs the required voltage gain procedure. Then, the digital LDO receives the EH source power density information from the dc–dc converter and provides regulation. Information about the source-power density availability is passed on to the digital LDO in order to select the best pass device size from a bank of three arrays. The PMU allows power consumption decrease by reducing the gate driving losses associated with large pass transistor devices, and it enhances efficiency. The system was fabricated in 180 nm CMOS process, and maximum end-to-end efficiency was measured at 57% with 1.75 mW of input power. [ABSTRACT FROM PUBLISHER]

Microbial fuel cells (MFC) are alternative renewable power sources that can directly produce electricity from biodegradable substances. However, due to their low power and voltage production, power management systems (PMS) are required to process the MFC power to a more readily usable level. For this application, a monolithic PMS with an integrated maximum power extraction algorithm (MPEA) is proposed. The MPEA allows for quick and accurate pin-pointing of the matching conditions for maximum power transfer from the MFC to the PMS. The PMS delivers a regulated fixed voltage from low fluctuating voltages produced by MFC at maximum power point to a supercapacitor from which electronic devices, such as wireless sensors, for extended operation time can be directly powered. Along with the MPEA system, the PMS is composed of a dc–dc boost converter operating in discontinuous conduction mode to maximize efficiency. In addition, a zero current switching tracking loop is proposed to improve overall system efficiency and minimize losses in the PMS through accurate P-type Metal-oxide-semiconductor field-effect transistor on/off timing control. The PMS circuit was fabricated in 0.5-μm CMOS technology. The maximum dynamic efficiency measured was ∼58% for a load of ∼250 μW. [ABSTRACT FROM AUTHOR]

Microbial fuel cell (MFC) that can directly generate electricity from organic waste or biomass is a promising renewable and clean technology. However, low power and low voltage output of MFCs typically do not allow directly operating most electrical applications, whether it is supplementing electricity to wastewater treatment plants or for powering autonomous wireless sensor networks. Power management systems (PMSs) can overcome this limitation by boosting the MFC output voltage and managing the power for maximum efficiency. We present a monolithic low-power consuming PMS integrated circuit (IC) chip capable of dynamic maximum power point tracking (MPPT) to maximize the extracted power from MFCs, regardless of the power and voltage fluctuations from MFCs over time. The proposed PMS continuously detects the maximum power point (MPP) of the MFC and matches the load impedance of the PMS for maximum efficiency. The system also operates autonomously by directly drawing power from the MFC itself without any external power. The overall system efficiency, defined as the ratio between input energy from the MFC and output energy stored into the super capacitor of the PMS, was 30%. As a demonstration, the PMS connected to a 240 mL two-chamber MFC (generating 0.4 V and 512 μW at MPP) successfully powered a wireless temperature sensor that requires a voltage of 2.5 V and consumes power of 85 mW each time it transmit the sensor data, and successfully transmitted a sensor reading every 7.5 min. The PMS also efficiently managed the power output of a lower-power producing MFC, demonstrating that the PMS works efficiently at various MFC power output level. [ABSTRACT FROM AUTHOR]

This paper presents a built-in input matching technique capable of handling a wide variation of multi-array thermoelectric generator (TEG) impedances ranging two decades, from 10 s to 1000 s of ohms. Maximum power point tracking (MPPT) control for a boost converter (BC) is introduced. The analytical expressions derived offer insight on the manner in which MPPT interacts with a BC to achieve best performance. The BC operates in a discontinuous conduction mode under pulse frequency modulation to minimize power consumption and maximize efficiency for light loads. Losses are minimized by implementing a pseudo-zero current switching control via the PMOS switch on/off time, and the output voltage is set using a global clocked comparator. A prototype was fabricated in 0.5 \mu\m CMOS where efficiency measurements showed a maximum value of 61.15% for an RTEG = 33.33\ \Omega, and quiescent power consumption was 1 \mu\W. [ABSTRACT FROM PUBLISHER]