WO2016071905A1

WO2016071905A1 - Frequency selective energy harvesting

Info

Publication number: WO2016071905A1
Application number: PCT/IL2015/051065
Authority: WO
Inventors: Shlomo Barukh
Original assignee: W.P. Energy (S.B.) Ltd.
Priority date: 2014-11-05
Filing date: 2015-11-04
Publication date: 2016-05-12

Abstract

A radio frequency (RF) energy harvesting device, includes a first RF antenna coupled to a first receiver, the first receiver configured to output a first digital signal based on a received signal from the first RF antenna, a digital control module configured to take as input the first digital signal and provide as output a second digital signal, and a second RF antenna coupled to a plurality of rectification circuits, wherein the plurality of rectification circuits are each configured to rectify signals from a specific frequency band, and wherein the operation of the plurality of rectification circuits is controlled by the second digital signal.

Description

FREQUENCY SELECTIVE ENERGY HARVESTING

Field of the Invention

[0001] The present invention relates generally to energy harvesting.

Background

[0002] Advances in semiconductor manufacturing technologies have resulted in dramatically increased circuit packing densities and higher speeds of operation. In turn, these advances have provided designers with the ability to produce many processor and communication functions that were not previously practical. In some instances these functions are combined in a single, highly integrated device. In other instances these functions are partitioned into two or more devices or chips.

[0003] Advances in digital systems architecture, in combination with the advances in the speed and density of semiconductors, have resulted in the availability of substantial computing power and digital communications networks for relatively low cost. In turn, this has led to a vast number electronic products, each with the ability to communicate with other electronic products.

[0004] Given the relatively low cost of integrated circuits for electronic products that incorporate computational and communication functionality, it is not surprising that there has been a rapid growth in the number of mobile devices such as, for example, smartphones, that are now in use around the world. Mobile devices, including smartphones, by their very nature require the ability to operate without being wired to an external power supply. To satisfy this requirement, mobile devices typically are powered by rechargeable batteries. Unfortunately, the rechargeable batteries installed in mobile devices are conventionally configured such that those mobile devices must periodically engage with a wired power supply in order to recharge their batteries, and thereby becoming "non-mobile" while recharging. Currently available wireless recharging solutions depend on close proximity and/or precise placement of the device to be recharged and utilize mains power as a source of energy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Embodiments of the invention are described with reference to the

accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left most digit(s) of a reference number identifies the drawing in which the reference number first appears.

[0006] Fig. 1 illustrates a system of RF harvesting devices controlled by a single self- powered harvesting control unit.

[0007] Fig. 2 is a block diagram of a wireless transmitter for controlling RF harvesting devices.

[0008] Fig. 3 is a block diagram of a self -powered wireless transceiver.

[0009] Fig. 4 is a circuit schematic of a wireless transmitter for controlling RF harvesting devices.

[0010] Fig. 5A is a block diagram of a self-powered wireless transceiver with concurrently operating RX and TX.

[0011] Fig. 5B is an alternative embodiment of a self-powered wireless transceiver.

[0012] Fig. 6A is a circuit schematic of a self-powered wireless transceiver with concurrently operating RX and TX. [0013] Fig. 6B is an alternative schematic of a self-powered wireless transceiver configured with wired connection between digital control modules.

[0014] Fig. 7 is a block diagram of an RF harvesting device that utilizes control information from a wireless transmitter to control harvesting operation.

[0015] Fig. 8 is an embodiment of an RF harvesting device configured to charge a cell-phone battery.

[0016] Fig. 9 A is a schematic of an interface of an RF harvesting device configured to charge an Apple iPhone 4.

[0017] Fig. 9B is a schematic of an interface of an RF harvesting device configured to charge an Apple iPhone 5.

[0018] Fig. 10 is a circuit schematic of an embodiment of an RF harvesting device configured to charge a cell-phone battery.

DETAILED DESCRIPTION

[0019] The following Detailed Description refers to accompanying drawings to illustrate exemplary embodiments. References in the Detailed Description to "one exemplary embodiment," "an illustrative embodiment," "an exemplary embodiment," and so on, indicate that the exemplary embodiment described may include a particular feature, structure, or characteristic, but every exemplary embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same exemplary embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an exemplary embodiment, it is within the knowledge of those skilled in the relevant art(s) to affect such feature, structure, or characteristic in connection with other exemplary embodiments whether or not explicitly described. [0020] The exemplary embodiments described herein are provided for illustrative purposes, and are not limiting. Other exemplary embodiments are possible, and modifications may be made to the exemplary embodiments within the spirit and scope of the disclosure.

[0021] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0022] In the interest of clarity, not all of the routine features of the implementations and embodiments described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation of the inventions herein, numerous implementation- specific decisions will typically be made in order to achieve the developer's specific goals. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.

[0023] Terminology

[0024] The terms, chip, die, integrated circuit, semiconductor device, and

microelectronic device, are often used interchangeably in the field of electronics. The present invention is applicable to all the above as these terms are generally understood in the field. In general usage in the field, the terms chip and integrated circuit may each refer to either a packaged or unpackaged part. As used herein, the context in which these terms are used will make clear whether the components are packaged, unpackaged, or whether packaging is immaterial to the subject matter being described.

[0025] FET, as used herein, refers to metal-oxide-semiconductor field effect transistors (MOSFETs). An n-channel FET is referred to herein as an NFET. A p- channel FET is referred to herein as a PFET.

[0026] CMOS refers to a semiconductor manufacturing process in which both NFETs are PFETs are formed in an integrated circuit.

[0027] CMOS circuit refers to a circuit in which both NFETs and PFETs are used together.

[0028] The term "gate" is context sensitive and can be used in two ways when describing integrated circuits. As used herein, "gate" refers to a circuit for realizing an arbitrary logical function when used in the context of a logic gate. And, "gate" refers to the insulated gate terminal of a three terminal FET when used in the context of transistor circuit configuration. Although a FET can be viewed as a four terminal device when the semiconductor substrate is considered, for the purpose of describing the circuit configuration of the present invention, the FET will be described using the traditional gate-drain- source, three terminal model.

[0029] The expression "electrical circuit element" refers to any component used to form part of an electrical circuit. By way of example and not limitation, resistors, potentiometers, capacitors, varactors, coils, transformers, diodes, transistors, thyristors, fuses, anti-fuses, chips (packaged or unpackaged), antennas, crystals, switches, vacuum tubes, and the like are exemplary electrical circuit elements.

[0030] The term "nominal" as used herein refers to a desired, or target, value of a characteristic or parameter for a component or a signal, set during the design phase of a product, together with a range of values above and/or below the desired value. The range of values is typically due to slight variations in manufacturing processes or tolerances. By way of example and not limitation, a resistor may be specified as having a nominal value of 10ΚΩ, which would be understood to mean 10ΚΩ plus or minus a certain percentage (e.g., ± 5%) of the specified value.

[0031] The term vertical, as used herein, means substantially perpendicular to the surface of a substrate.

[0032] With respect to the various electrical circuits, sub-circuits, electrical circuit elements, and chips described herein, electrical signals are typically coupled between them and other electrical circuit elements via physical, electrically conductive connections. It is noted that, in this field, the point of connection for electrical signals between such circuits, sub-circuits, and electrical circuit elements is sometimes referred to as an input, output, input/output (I/O), terminal, line, pin, pad, port, interface, or similar variants and combinations. Although connections between and amongst chips are commonly made by way of electrical conductors, those skilled in the art will appreciate that chips and other circuit elements may alternatively be coupled by way of, but not limited to, optical, mechanical, magnetic, electrostatic, and electromagnetic interfaces.

[0033] RF is an acronym for radio frequency.

[0034] IR is an acronym for infrared.

[0035] It is understood by those skilled in the field of electronics, that information can be communicated wirelessly. By way of example and not limitation, RF, IR, and visible light are all magnetic and/or electromagnetic forms of energy that may be modulated to communicate information in a wireless fashion. [0036] The terms single-chip microcomputer, microcontroller, embedded controller, embedded processor and similar variants are often used interchangeably in this field and are generally meant to include digital data processing devices.

[0037] The acronym "ASIC" refers to Application Specific Integrated Circuit.

[0038] The acronym "SoC" refers to System on a Chip.

[0039] The acronym "DSP" refers to Digital Signal Processor.

[0040] Coaxial cables are often simply referred to in the field of electronic as coax cables. Coax cables typically have a center conductor surrounded by a dielectric material, an electrically conductive shield surrounding the dielectric material, and an insulator that covers the outer surface of the shield. In order to couple a coax cable to a board, a chassis, another coax cable, or any other point of electrical connection, a connector is fitted to an end of the coax cable, such that it may physically connect to, or mate with, a corresponding connector on the board, chassis, or other coax cable, or other point.

[0041] General Overview

[0042] Embodiments of the present invention utilize acquired local ambient energy (RF harvesting) for transduction into electrical energy. Various embodiments of the present invention provide a wireless transmitter that controls the operation of one or more RF harvesting devices. The transmitter enables the RF harvesting devices to recharge their batteries without being wired to an external power supply. The transmitter may be disposed in a transceiver including an RF receiver and an RF harvesting circuit to power the transmitter, forming a self -powered wireless transceiver. [0043] Fig. 1 illustrates an RF harvesting system with a harvesting control unit 101 wirelessly controlling 102a-102n a plurality of RF harvesting devices 103a-103n. The RF harvesting devices collect energy HOa-llOn from the ambient RF environment based on the control information provided by harvesting control unit 101. The control information may include commands to enable or disable portions of the RF harvesting devices 103a-103n, and may include data for controlling at least some portions of the RF harvesting devices 103a-103n to optimize transduction of the ambient energy. The configuration shown in Fig. 1 allows a single harvesting control unit 101 to simultaneously control any number of RF harvesting devices 103a-103n within communication range of harvesting control unit 101. The harvesting devices 103a- 103n may be incorporated into consumer electronic products such as, but not limited to, computer peripherals, remote controls, cameras, speakers, mobile phones, tablets, and laptops. Likewise harvesting devices 103a-103n may be incorporated into any other electric/electronic device or system that may benefit from the power delivered by the RF harvesting devices 103a-103n. Harvesting control unit 101 itself may contain an RF harvesting device collecting energy 110c from the ambient RF environment based on control information 102c that it may wirelessly receive from the transmitter portion of the unit. In such a configuration, the RF transmitter, RF receiver, and RF harvesting circuit of harvesting control unit 101 may all operate concurrently. In an alternative embodiment, the control information 102c may be delivered to the and RF harvesting circuit of harvesting control unit 101 by a wired, rather than wireless connection.

[0044] Fig. 2 illustrates a wireless transmitter 200 configured to transmit an RF signal to control one or more RF harvesting devices. A digital control module 220 receives a digital clock 215 from a timer circuit 210 and outputs a digital signal 225 with a predetermined periodicity. The periodicity, which may be more than 72 hours, may depend on the clock rate of digital clock signal 215. An RF modulator 230 may be a frequency modulator and may transmit at any suitable carrier frequency, for example 433 MHz. Those skilled in the art and having the benefit of this disclosure will understand the various trade-offs in selecting a carrier frequency, including but not limited to, available spectrum in given jurisdictions.

[0045] Fig. 3 illustrates a self-powered harvesting control unit 300 including an RF transmitter 200, an RF receiver 310, and an energy harvesting circuit 320. RF transmitter 200 wirelessly controls RF harvesting circuit 320 via RF receiver 310. Energy harvesting circuit 320 may be coupled to one or more energy storage devices 330a-330b, each of which may comprise, for example, a rechargeable battery or a super capacitor. When in operation, RF receiver 310 demodulates and translates the signal transmitted from RF transmitter 200 and outputs control signals 315 to energy harvesting circuit 320. RF transmitter 200, RF receiver 310, and energy harvesting circuit 320 may each be coupled to corresponding antennas 240, 340a, and 340b.

[0046] Fig. 7 illustrates an RF harvesting device 700 that utilizes the control signal transmitted by the wireless transmitter 200 to control an RF harvesting circuit. An RF antenna 701 captures the control signal transmitted by the wireless transmitter 200, and the RF receiver 710 demodulates it into a digital signal 715. The digital control module 720 translates the digital signal 715 into a digital control signal 725 that is input to an RF harvesting circuit that may comprise a plurality of rectifiers 730a-730d that may have different structures or components, as well as different frequency responses. The digital control signal 725 from the digital control module 720 controls the operation of the rectifiers 730a-730d. The rectifiers 730a-730d may also input a signal 735 from second and third RF antennas 702a-702b, which may comprise a plurality of physical elements whose outputs are connected to different rectifiers 730a-730d. The rectifiers 730a-730d may be connected in serial, parallel, or a combination thereof, and may be coupled to a battery 750 to which they supply a trickle charge 745. The battery 750 may serve as a local storage for energy supplied to charge 755 a battery-powered device 760 such as a smartphone. The charging of the battery 750 and the battery-powered device 760 may be handled by a battery manager circuit 740.

[0047] Exemplary Circuits

[0048] Fig. 4 is an embodiment of RF transmitter 200. A nominal 5V Vcc 401 powers RF transmitter 200. An ICM7555 timer circuit 410 outputs a digital clock signal 415 to the WPE SB 1 SMT digital control module 420 (available from WP Energy, Ltd., Ashdod, Israel). The shown configuration is an astable configuration of timer 410 that outputs a periodic digital clock signal 415 with duty cycle and frequency being a function of the external discrete components. The frequency may be calculated as f=1.44/(Ra+2Rb)C, and the duty cycle may be calculated as D=(Ra+Rb)/(Ra+2Rb) . In one embodiment of the circuit, f is approximately 7Hz and D is approximately 0.5. The WPE SB 1 SMT digital control module 420 receives digital clock signal 415 from timer circuit 410 and outputs a digital signal 425 with a predetermined periodicity. RF modulator 230 modulates the digital signal 425 to form an RF representation of the digital signal 425. In alternative embodiments, the ICM7555 timer may be substituted by any circuitry configured to generate a similar digital clock signal.

[0049] Fig. 5A is a block diagram of the self-powered wireless transceiver 300. The RF transmitter 200 is described above in relation to Fig. 4. Transceiver 300 includes an RF demodulator 510 coupled to a WPE SB 1 SMT digital control module 520, which receives demodulated control information 515 from RF demodulator 510 and outputs another digital signal 525 to a frequency-to-voltage (F-to-V) converter 530. Alternatively or additionally, output sequence 525 may be input to an SDAT2 circuit 540, which may be connected in either serial or parallel to SDATA RF circuit 550. F- to-V converter 530, SDAT2 circuit 540 and SDATA RF circuit 550 are coupled to an energy storage device shown in Fig. 5 as a capacitor 560, as well as to the Texas Instruments BQ25504 ultra-low-power boost converter 570. The BQ25504 570 is configured for battery management in relation to a second storage device shown in Fig. 5A as battery 580. This storage device powers the transmitter circuit via the Vstore output of BQ25504 570 and a voltage booster 590. A light-emitting diode (LED) 571 is configured to turn on when the battery 580 is charged. SDAT2 circuit 540 and SDATA RF circuit 550 are connected to respective plates of a 3-electrode antenna 340b. A third electrode, a ground plate, may be connected to SDAT2 540 as discussed below in relation to Fig. 6. In some embodiments, a second booster 521 boosts the voltage of the battery 580 to provide a Vcc power signal to the WPE SB 1 SMT 520 and RF demodulator 510 via line 516.

[0050] Fig. 5B illustrates a second exemplary embodiment of the self -powered wireless transceiver 300. Relative to Fig. 5A, the transceiver in Fig. 5B utilizes a wired connection between the WPE SB 1 TX SMT 220 and the WPE SB 1 RX SMT 520, thereby bypassing the RF demodulator 510.

[0051] Fig. 6A presents a circuit diagram for self-powered wireless transceiver 300. Transceiver 300 includes RF transmitter 200 as discussed above in relation to Fig. 4. The output on pin 3 of digital control module 520 is input to the F-to-V converter, which in this embodiment is shown as a full-wave voltage quadrupler 610. The output of F-to-V converter 610 is connected to the outputs of SDAT2, also shown as a full- wave voltage quadrupler 620, and the SDAT RF, which in this embodiment comprises three bandpass half-wave rectifiers 630 connected in parallel. The bandpass half-wave rectifiers 630 may have different frequency responses by assigning different values to their respective discrete components, as a person of ordinary skill in the art would recognize. This configuration allows the incoming signals on RF ANT to be filtered and rectified differently according to their RF band.

[0052] The BQ25504 chip 570 is configured to control the charging of mini battery 580 via harvesting unit 620/630 and provide power to RF transmitter 200. The positive terminal of the battery 580 is coupled to the DC input pin of the BQ25504 570 through a series of diodes 640. While Fig. 6 illustrates three diodes performing this coupling, up to five diodes may be used for this purpose.

[0053] Fig. 6B illustrates a second exemplary embodiment of a circuit diagram of the self -powered wireless transceiver 300. Relative to Fig. 6A, the transceiver in Fig. 6B utilizes a wired connection between the WPE SB 1 TX SMT 420 and the WPE SB 1 RX SMT 520, thereby bypassing the RF demodulator 510.

[0054] Fig. 8 is an exemplary embodiment of an RF harvesting device 800 configured to charge a cell-phone battery. Although Fig. 8 illustrates a configuration for a Samsung smartphone, the invention is not limited to this embodiment. An RF antenna 701 captures the control signal transmitted by the wireless transmitter 200, and the RF receiver 710 demodulates it into a digital signal 715. The digital control module 720 translates the digital signal 715 into a digital control signal 725 that is input to an RF harvesting circuit that is represented in Fig. 8 as SDAT1 831, SDAT2 832, and SDATA RF 833. These three circuits 831-833, which may be variations of different rectification circuits, may have different frequency responses and structures.

[0055] The digital control signal 725 from the digital control module 720 controls the operation of these rectifying circuits 831-833. In the illustrated embodiment, the rectifiers 831-833 also receive a signal 835a-835b from second and third RF antennas 702a-702b comprising two copper plates arranged in parallel and separated by a dielectric material. The rectifying circuits 831-833 are illustrated as being connected in series but may also be connected in parallel. The rectifying circuits 831-833 are coupled with the battery 750 via the Texas Instruments BQ25504 570. The battery, in turn, supplies energy to charge the Samsung smartphone via connector 850. In this embodiment the charging is managed by the BQ25504 570 via a USB power manager/booster 840.

[0056] Figs. 9A and 9B illustrate interfaces for charging an iPhone 4 and iPhone5, respectively. These devices have different connectors and/or power requirements. While the invention is not limited to any particular class of device, manufacturer, or model, the illustrated embodiments provide exemplary circuits to interface with a subset of popular consumer electronic products.

[0057] Fig. 10 is a circuit diagram of an exemplary embodiment of an RF harvesting device 800. The digital control signal 725 output by the digital control module 720 is connected to the input of SDAT2 832, which in this embodiment is shown as a full- wave voltage quadrupler. The SDAT2 832 may be connected in serial or parallel to the SDATA RF 833, which in this embodiment comprises three bandpass half-wave rectifiers connected in parallel. The bandpass half-wave rectifiers comprising SDATA RF 833 may have different frequency responses by assigning different values to their respective discrete components, as a person of ordinary skill in the art would recognize. This configuration allows the incoming signals on RF ANT 702b to be filtered and rectified differently according to their RF band. The SDAT1 831 may have the same structure as the SDAT2 832.

[0058] The BQ25504 chip 570 is configured to control the charging of battery 750 via rectifying circuits 831-833 and to provide power to charge the battery-powered device via connector 850. The positive terminal of the battery 750 is coupled to the DC input pin of the BQ25504 570 through a series of diodes 1001. While Fig. 10 illustrates three diodes performing this coupling, more than three diodes may be used for this purpose.

[0059] It was noted above in connection with Fig. 7 that digital control module 720 translates digital signal 715 into digital control signal 725. It will be appreciated that in some embodiments, the translation of digital signal 715 into digital control signal 725 may be accomplished directly by hardware circuits, while in other embodiments this translation may be accomplished by executing a stored program by hardware such as, but not limited to, a processor. Such a stored program may be stored in a medium from which the processor may access and execute that program. And when the program is executed, the hardware processor performs the operations needed to implement the translation.

CONCLUSION

[0060] The disclosure is also directed to computer program products comprising software stored on a computer useable medium. Such software, when executed in one or more data processing device, causes a data processing device(s) to operate as described herein. Various embodiments may employ any computer useable or readable medium, known now or in the future. Examples of non-transitory computer- useable media include, but are not limited to, primary storage devices (e.g., any type of volatile or non-volatile memory devices), secondary storage devices (e.g., hard drives, solid state drives, floppy disks, CD ROMs, DVDs, tapes, magnetic storage devices, optical storage devices, etc.). Other forms of computer-useable media from which such software may be perceived include, but are not limited to, communication media (e.g., wired and wireless communications networks, local area networks, wide area networks, intranets, etc.).

[0061] It is to be appreciated that the Detailed Description section, and not the Abstract of the Disclosure, is intended to be used to interpret the claims. The Abstract of the Disclosure may set forth one or more, but not all, exemplary embodiments of the invention, and thus, is not intended to limit the invention and the subjoined Claims in any way.

[0062] It will be apparent to those skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the subjoined Claims and their equivalents.

Claims

What is claimed is:

1. A radio frequency (RF) energy harvesting device, comprising:

a first RF antenna coupled to a first receiver, the first receiver configured to output a first digital signal based on a received signal from the first RF antenna;

a digital control module configured to take as input the first digital signal and provide as output a second digital signal; and

a second RF antenna coupled to a plurality of rectification circuits, wherein the plurality of rectification circuits are each configured to rectify signals from a specific frequency band, and wherein the operation of the plurality of rectification circuits is controlled by the second digital signal.

2. The device of claim 1, wherein the plurality of rectification circuits comprises:

at least three filtered-input half-wave rectifiers connected in parallel, wherein each filtered-input half-wave rectifier comprises a capacitor connected in series to a half-wave rectifier.

3. The device of claim 1, wherein the plurality of rectification circuits includes at least one full-wave voltage quadruples

4. The device of claim 3, wherein the at least one full-wave voltage quadrupler is connected in parallel to at least three half-wave rectifiers, each connected in parallel.

5. The device of claim 1, further comprising a battery coupled to the rectification circuits, wherein the rectification circuits are configured to provide a trickle charge to the battery.

6. The device of claim 1, further comprising a power booster coupled to a battery-charging electrical connection of a battery-powered device.

7. A wireless controller for a radio frequency (RF) energy harvesting device, comprising:

a digital control module configured to output a digital signal containing information associated with each one of a plurality of frequency bands of the RF spectrum; and

an RF transmitter configured to modulate the digital signal and transmit the modulated digital signal on a first RF antenna.

8. The device of claim 7, further comprising a second RF antenna configured to receive ambient RF energy and coupled to an energy storage device charging circuit.

9. The device of claim 7, wherein the RF transmitter is configured to transmit at a nominal carrier frequency of 433 MHz.

10. The device of claim 7, further comprising a timer circuit coupled to the digital control module.

11. The device of claim 7, wherein the modulated digital signal is frequency modulated.

12. A self-powered radio frequency (RF) energy harvesting device, comprising:

a first RF antenna connected to an input of a first energy harvester circuit; a second RF antenna connected to an input of a second energy harvester circuit;

a third RF antenna connected to an RF receiver, the RF receiver configured to demodulate a modulated signal from the third RF antenna and generate a baseband signal based at least in part on the modulated signal;

a capacitor having a first terminal coupled to an output of the first energy harvester circuit and to an output of the second energy harvester circuit; and a charging circuit having an input coupled to the output of the first terminal of the capacitor, and further having an output coupled to a positive terminal of an energy storage device.

13. The device of claim 12, further comprising:

a control circuit coupled to the RF receiver and configured to produce a digital output stream based at least in part on the baseband signal of the RF receiver.

14. The device of claim 13, wherein the digital output stream is synchronized to the baseband signal of the RF receiver.

15. The device of claim 12, wherein the energy storage device comprises a rechargeable battery.

16. The device of claim 12, wherein the energy storage device comprises a supercapacitor.

17. The device of claim 12, further comprising a plurality of diodes coupled anode-to-cathode between the positive terminal of the energy storage device and the first terminal of the capacitor.

18. The device of claim 17, wherein the plurality of diodes comprises three diodes.

19. The device of claim 17, wherein the capacitor includes a second terminal coupled to ground.

20. The device of claim 12, wherein the charging circuit comprises a booster circuit.