Abstract:
The present disclosure discloses an energy harvest system converting an AC source provided by an energy harvester to a desired voltage. The AC source is boosted to the desired voltage by a bi-directional booster converter comprising fourth controllable transistors configured in an H-bridge, and stored by a storage capacitor. The desired voltage is then used to power various loads.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to electronic circuits, more specifically, the present disclosure relates to apparatus that converts small mechanical movements into electrical energy. 
       BACKGROUND 
       [0002]    An energy harvester is a device that converts mechanical movements, such as vibrations, oscillations or other mechanical motions into electrical energy. This electrical energy can then be stored or used by other devices. Thus, an energy harvester could produce useful electrical power from mechanical movements. For example, the vibrations of an air duct could be converted to electrical energy by an energy harvester and the electrical energy could then be used to power a sensor that measures the temperature of air in that duct. Therefore, the sensor will not require electrical wiring to a remote source of power or periodic battery changes. 
         [0003]    Conventional technology uses a schottky diode bridge (comprised by diodes D 1 ˜D 4 ) and a boost converter to convert the electrical energy into desirable voltage levels to power various loads, as shown in  FIG. 1 . However, the schottky diode bridge is too lossy. In addition, when the electrical energy generated by the energy harvester is low, e.g., 0.5V, the schottky diode bridge can not kick startup, which limit the use of the electrical energy with low voltage. 
       SUMMARY 
       [0004]    It is an object of the present disclosure to provide an energy harvest system, which solves the above problems. 
         [0005]    In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present disclosure, an energy harvest system, comprising: an energy harvester configured to provide an AC source, the energy harvest having a first terminal and a second terminal; a storage port configured to provide a storage voltage; a first transistor coupled between the first terminal of the energy harvester and the storage port; a second transistor coupled between the first terminal of the energy harvester and a reference ground; a third transistor coupled between the second terminal of the energy harvester and the storage port; a fourth transistor coupled between the second terminal of the energy harvester and the reference ground; and a storage capacitor coupled between the storage port and the reference ground; wherein the first transistor and the second transistor operate at relatively low switching frequency, while the third transistor and the fourth transistor operate at relatively high switching frequency. 
         [0006]    In addition, there has been provided, in accordance with an embodiment of the present disclosure, a method for apparatus with energy harvester, comprising: generating an AC source from mechanical movements by an energy harvester; boosting the AC source to a desired voltage by a bi-directional boost converter; and storing the desired voltage by a storage capacitor. 
         [0007]    Furthermore, there has been provided, in accordance with an embodiment of the present disclosure, an energy harvest system, comprising: an inductor and an AC source generator coupled in series, wherein the AC source generator is configured to provide an AC source; a storage port configured to provide a storage voltage; a first transistor coupled between the inductor and the storage port; a second transistor coupled between the inductor and a reference ground; a third transistor coupled between the AC source generator and the storage port; a fourth transistor coupled between the AC source generator and the reference ground; and a storage capacitor coupled between the storage port and the reference ground; wherein when the AC source is positive, the first transistor is controlled to be ON, the second transistor is controlled to be OFF, and the third transistor and the fourth transistor are controlled to switch between ON and OFF states; and when the AC source is negative, the first transistor is controlled to be OFF, the second transistor is controlled to be ON, and the third transistor and the fourth transistor are controlled to switch between ON and OFF states to provided the storage voltage at the storage port. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  schematically shows a prior art energy harvest system converting electrical energy generated by energy harvester to desirable voltage levels to power various loads. 
           [0009]      FIG. 2  schematically shows an energy harvest system  100  in accordance with an embodiment of the present disclosure. 
           [0010]      FIG. 3  schematically shows an energy harvest system  200  in accordance with an embodiment of the present disclosure. 
           [0011]      FIG. 4  schematically shows an energy harvest system  300  in accordance with an embodiment of the present disclosure. 
           [0012]      FIG. 5  schematic shows a flowchart  400  in accordance with an embodiment of the present disclosure. 
       
    
    
       [0013]    The use of the similar reference label in different drawings indicates the same of like components. 
       DETAILED DESCRIPTION 
       [0014]    Embodiments of circuits for energy harvest system with low output voltage are described in detail herein. In the following description, some specific details, such as example circuits for these circuit components, are included to provide a thorough understanding of embodiments of the disclosure. One skilled in relevant art will recognize, however, that the invention can be practiced without one or more specific details, or with other methods, components, materials, etc. 
         [0015]    The following embodiments and aspects are illustrated in conjunction with circuits and methods that are meant to be exemplary and illustrative. In various embodiments, the above problem has been reduced or eliminated, while other embodiments are directed to other improvements. 
         [0016]      FIG. 2  schematically shows an energy harvest system  100  in accordance with an embodiment of the present disclosure. In the example of  FIG. 2 , the energy harvest system  100  comprises: an energy harvester  101  configured to provide an AC source, the energy harvest  101  having a first terminal  101   a  and a second terminal  101   b;  a storage port  102  configured to provide a storage voltage V s ; a first transistor Q 1  coupled between the first terminal  101   a  of the energy harvester and the storage port  102 ; a second transistor Q 2  coupled between the first terminal  101   a  of the energy harvester and a reference ground; a third transistor Q 3  coupled between the second terminal  101   b  of the energy harvester and the storage port  102 ; a fourth transistor Q 4  coupled between the second terminal  101   b  of the energy harvester and the reference ground; and a storage capacitor C s  coupled between the storage port  102  and the reference ground; wherein the first transistor Q 1  and the second transistor Q 2  operate at relatively low switching frequency, while the third transistor Q 3  and the fourth transistor Q 4  operate at relatively high switching frequency. 
         [0017]    In one embodiment, the energy harvest comprises an inductor and an AC source generator coupled in series. 
         [0018]    In one embodiment, the AC source generator comprises a vibrator generator. 
         [0019]    In one embodiment, the first to fourth transistors Q 1 ˜Q 4  are characterized in low gate-threshold. 
         [0020]    In one embodiment, the AC source having a frequency range of 10˜50 Hz. 
         [0021]    During the operation of the energy harvest system  100 , when the AC source is positive, e.g., the first terminal  101   a  of the energy harvester is electrical positive and the second terminal  101   b  of the energy harvester is electrical negative, the first transistor Q 1  is controlled to be ON, the second transistor Q 2  is controlled to be OFF, and the third transistor Q 3  and the fourth transistor Q 4  are controlled to switch between ON and OFF states. As a result, the energy harvest system  100  forms a boost converter, and the AC source is boosted to a higher storage voltage. On the contrary, when the AC source is negative, e.g., the first terminal  101   a  of the energy harvester is electrical negative and the second terminal  101   b  of the energy harvester is electrical positive, the first transistor Q 1  is controlled to be OFF, the second transistor Q 2  is controlled to be ON, and the third transistor Q 3  and the fourth transistor Q 4  are controlled to switch between ON and OFF states. As a result, the energy harvest system  100  also forms a boost converter, and the AC source is also boosted to a higher storage voltage. A storage voltage V s  with desired voltage level is regulated by applying appropriate control scheme to the third transistor Q 3  and the fourth transistor Q 4 . 
         [0022]    The storage voltage V s  generated by the energy harvest system may be used to power variable loads, as shown in  FIG. 3 , an energy harvest system  200  powering a micro-controller through a LDO (low dropout) is schematically illustrated. Specifically speaking, the energy harvest system  200  comprises an energy harvester  201 , first to fourth transistors Q 1 ˜Q 4 , and a storage capacitor C s  coupled similarly as those in the energy harvest system  100  in  FIG. 2 . The energy harvest system  200  further comprises a LDO and a Micro-controller μC coupled in series between the storage port  202  and the reference ground. 
         [0023]    In one embodiment, the Micro-controller μC wasters low power, and may be used to execute sensing, testing, monitoring, and etc. 
         [0024]    When the system needs measure, calibration, data transmission, etc., a buck converter may be needed.  FIG. 4  schematically shows an energy harvest system  300  powering a load via a buck converter in accordance with an embodiment of the present disclosure. Similarly, the energy harvest system  300  comprises an energy harvester  301 , first to fourth transistors Q 1 ˜Q 4 , and a storage capacitor C s  coupled similarly as those in the energy harvest system  100  in  FIG. 2 , and the energy harvest system  300  further comprises a buck converter and a load coupled in series between the storage port  302  and the reference ground. 
         [0025]    In one embodiment, the buck converter comprises a synchronous buck converter. 
         [0026]    Several embodiments of the foregoing energy harvest system provide desired voltage level with reduced power loss and simple structure compared to conventional technique discussed above with reference to  FIG. 1 . Unlike the conventional technique, several embodiments of the foregoing energy harvest system comprise controllable transistors to form a bi-directional boost, thus reducing the power loss and getting easily started up in low AC power source with simple structure. 
         [0027]      FIG. 5  schematic shows a flowchart  400  of a method for apparatus with energy harvester in accordance with an embodiment of the present disclosure. The method comprises: 
         [0028]    Step  401 , generating an AC source from mechanical movements by an energy harvester. 
         [0029]    Step  402 , boosting the AC source to a desired voltage by a bi-directional boost converter. In one embodiment, the bi-directional boost converter comprises fourth transistors configured in an H-bridge, wherein the H-bridge has a first bridge arm operating at relatively low frequency and a second bridge arm operating at relatively high frequency. In one embodiment the fourth transistors are characterized in low gate-threshold. And 
         [0030]    Step  403 , storing the desired voltage by a storage capacitor. 
         [0031]    In one embodiment, the method further comprises powering a Micro-controller via a LDO. 
         [0032]    In one embodiment, the method further comprises powering a load via a buck converter. 
         [0033]    This written description uses examples to disclose the disclosure, including the best mode, and also to enable a person skilled in the art to make and use the disclosure. The patentable scope of the disclosure may include other examples that occur to those skilled in the art.