Rectifier Circuit Using Active Switches for Low-Amplitude Energy Harvesting
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Solution Overview
Problem
Energy harvesting systems face inefficiencies due to impedance mismatch between transducers and scavenging interfaces, leading to reduced power transfer and limited energy storage when signal amplitudes are low, causing the system to fail in harvesting environmental energy effectively.
Innovation Solution
The rectifier circuit employs actively controlled switches (MOSFETs) to manage energy transfer, reducing voltage drops and enabling efficient energy recovery even at low signal amplitudes, with a control logic that dynamically controls the switches to optimize power transfer to a capacitor or load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a diode-bridge rectifier circuit is used as the scavenging interface, then the circuit structure is simple, but the efficiency drops rapidly when the transducer signal amplitude is lower than VOUT + 2VTH_D
Solution Approach 1:
The patent changes the operating parameters of the rectifier circuit by using actively controlled switches (MOSFETs) instead of passive diodes. The control logic dynamically adjusts the switching states based on the relationship between Vin and Vout, enabling the circuit to operate efficiently across a wider range of signal amplitudes including cases where Vin < Vout + 2VTH_D
Solution Approach 2:
The patent introduces an inductor as an intermediary energy storage element between the transducer and the output capacitor. This inductor enables energy transfer even when the direct voltage difference is insufficient to drive current through diodes, effectively mediating the energy transfer when Vin < Vout + 2VTH_D
2Adaptability or versatility
If the transducer signal amplitude is low, then the system can operate with smaller vibrations, but the maximum energy that can be stored in the capacitor is limited
Solution Approach 1:
The patent employs periodic switching of the MOSFETs synchronized with the AC signal from the transducer. The control logic switches the MOSFETs on and off during each half-cycle, enabling cumulative energy transfer to the capacitor over multiple cycles even when individual cycle energy is small, thus increasing total stored energy
Solution Approach 2:
The inductor serves as an energy accumulation intermediary that stores energy during MOSFET on-periods and releases it during off-periods. This allows energy to be accumulated over multiple low-amplitude cycles, overcoming the limitation of single-cycle energy transfer when signal amplitude is low
3Loss of energy
If actively controlled switches are used instead of diodes, then the scavenging interface efficiency increases to 70-85%, but the device complexity increases
Solution Approach 1:
The control logic is designed to automatically sense the voltage relationship between Vin and Vout and adjust the MOSFET switching states accordingly without external intervention. The system self-regulates based on real-time voltage conditions, eliminating the need for complex external control circuits while maintaining high efficiency
Solution Approach 2:
The control logic is integrated directly into the rectifier circuit, combining the functions of voltage sensing, decision-making, and switch control into a unified control unit. This integration reduces the overall system complexity compared to having separate control circuits while achieving the required 70-85% efficiency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the scavenging interface efficiency to 70-85%, allowing energy harvesting from low-amplitude signals and increasing the autonomy of energy-dependent systems like TPM sensors by storing high voltages, while minimizing space requirements and maintaining efficiency across varying conditions.
Implementation Method 1
a transducer 2, for example of an electromagnetic type, which is adapted to convert the mechanical energy of environmental mechanical vibrations into electrical energy, typically into AC voltages
Implementation Method 2
a scavenging interface 4, for example comprising a diode-bridge rectifier circuit, configured for receiving at input the AC signal generated by the transducer 2 and supplying at output a DC signal for charging a capacitor 5
Data Source
AI summary
An energy-scavenging interface (24) having input terminals (25', 25") that can be connected to a transducer (22) including a storage element (22b), for receiving an input signal (VIN) , and output terminals (26', 26"), which can be connected to an electrical load (27, 28) for supplying to the electrical load an output signal (VOUT), said energy-scavenging interface (24) comprising: a first switch (30), which receives a signal that is a function of the electrical input signal (VIN, I); a first current-conduction element (36); and a control logic (60) configured for: (a) closing the first switch (30) for a first time interval having a first duration (TDELAY) proportional to a time constant (τTRANSD) of the transducer (22), during which the storage element (22b) stores the electrical charge; (b) opening the first switch (30) for a second time interval subsequent to the first time interval, in which the electrical load is supplied through the first current-conduction element by means of the electrical charge stored in the storage element, and until the electrical energy accumulated by the storage element (22b) reaches a first threshold value (ITH).