Abstract:
Described herein is, for example, a battery or capacitor over voltage (overcharge) and under-voltage protection circuit, that, for example, is adapted to not draw current from the battery or capacitor to be charged unless charge energy is detected and to not charge an energy storage device when an over-charge condition is sensed. The protection circuit may, for example, not be turned on unless an over voltage condition is present. Incoming energy to the system can be shunted to ground via a shunt load of various types including resistive loads and active components such as a zener diode. In some embodiments, no switching of the inbound power is required. Within limits, no regulation of inbound power is needed. When inbound power is sufficient to charge the battery or capacitor, regulation can occur via the applied shunt regulator if overcharge voltage conditions exist. Either type of charge source, voltage or current, can be used to provide charge energy. Combining said battery or capacitor over voltage (overcharge) and under-voltage protection circuit with electronic loads, such as wireless sensors, may lead to autonomously-powered wireless sensor systems.

Description:
RELATED APPLICATIONS 
       [0001]    This application is related to and claims the benefit under 35 U.S.C. §119 of U.S. provisional patent application Ser. No. 61/103,746, entitled “Environmentally-Powered Wireless Sensor Module,” filed on Oct. 8, 2008 and U.S. provisional patent application Ser. No. 61/041,841, entitled “Passive Battery or Capacitor Overvoltage Control and Protection Circuit,” filed on Apr. 2, 2008; both of which are incorporated herein by reference in their entirety. 
     
    
     TECHNICAL FIELD AND BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to, for example, an apparatus, method, and system for safely utilizing a rechargeable energy device. 
         [0003]    Some energy storage devices such as, for example, thin-film solid electrolyte batteries or capacitors may be susceptible to damage when exposed to continuous or momentary influxes of high charging voltages. Batteries may, for example, be damaged if discharged beyond their design parameters. 
         [0004]    Over-charge protection relates to a condition when a relative large voltage is allowed at the input to a battery cell or capacitor for an any time period. In order to protect against overcharge, device protection circuits may be used to monitor the current and voltage and inhibit battery charge when overcharge is sensed. 
         [0005]    Under-voltage conditions also have the potential to damage the energy storage device. In a battery, for example, during an under-voltage condition the battery may discharge beyond the point of recovery. 
         [0006]    Thus, a need exists to protect an energy storage device from over-charge and/or over-discharge conditions. 
         [0007]    To implement the functionality mentioned above, the current available art may generally require power consumption from the device to be charged for the over-charge circuitry. That is, the existing art may involve circuits using quiescent current from the battery or capacitor to be charged. Also, current known art may involve switching to disable the charging source when an overcharge condition exists despite the absence of a charging source or similar energy being present. Other known over voltage control circuits use voltage regulation schemes that clamp input power to a known voltage prior to input to the energy storage device to be charged. These may use a significant amount of power either from the rechargeable device or from input power to the system. These mechanisms may not be ideal because, for example, they increase the amounts of leakage current taken from the battery or capacitor to be charged or use input energy that may be otherwise allowed into the rechargeable energy storage device. 
         [0008]    Additionally, a demand exists for an electronic device that, for example, does not require excess storage device requirements and may be able to gather energy efficiently, even including very trace amounts of energy, without, for example, damage during operation or the recharging process, either by over-voltage or under-voltage. 
         [0009]    Further, there is a perceived need for an over-voltage and/or under-voltage protection circuit that, for example, does not operate using significant quiescent current from the energy storage device, nor essentially load or waste input charge energy with regulation when regulation is not necessary, thus consuming less energy from both the rechargeable energy storage device and the available input charge energy. 
       SUMMARY OF THE INVENTION 
       [0010]    Various aspects and embodiments of the present invention, as described in more detail and by example below, address certain of the shortfalls of the background technology and emerging needs in the relevant industries. Accordingly, the present invention is directed, for example, to substantially obviate one or more of the shortcomings or problems due to the limitations and disadvantages of the related art. 
         [0011]    Ambient energy exists in many forms and may be in many cases in useable but potentially unreliable quantities, providing an opportunity to convert this energy into a beneficial electrical form, with the assistance of an energy harvesting device combined with a passive over-voltage and/or under-voltage control protection circuit. Depending on the application, harvested energy may, for example, be used instantaneously or stored in an energy storage device such as a capacitor or a thin-film battery directly, with no active voltage control necessarily required, and used at defined time intervals or when certain environmental conditions exist, such as when a request by an attached or a remotely connected device is received. 
         [0012]    It is one object of certain exemplary embodiments of this invention to use an energy harvester (such as, for example, a piezoelectric mechanism or an energy-absorbing antenna), adjacently connected or incorporated onto a flexible substrate or a chip, to collect energy from one or more non-conventional sources and supply a charge energy to recharge an energy storage device such as a capacitor or battery. 
         [0013]    Another object of an embodiment of this invention relates to, for example, a device which may be used to recharge energy storage devices without subjecting the device to potentially damaging over-charge or under-voltage conditions while using minimal power from the rechargeable device and taking minimal power from the available charge energy. This may, for example, allow maximum usage of available input power to the rechargeable device. 
         [0014]    As some energy storage devices, such as, for example, thin-film solid electrolyte batteries, are sensitive to continuous or momentary influxes of high charging voltages, the over-charge and/or under-voltage circuitry may be especially useful in recharging the batteries in a safe manner. This may be particularly important, for example, in applications where energy storage devices are located in remote areas that require high reliability—the energy-harvesting system described above may recharge the energy storage devices and the over-charge and/or over-discharge circuitry may ensure that the energy storage device is not damaged by the excess and/or inadequate conditions of the charging voltage or load demand. 
         [0015]    Certain embodiments of the present invention may, for example, limit power usage from the energy storage device to be charged by monitoring voltage levels when a charging source energy is present. A power dissipation circuit may, for example, be switched on in the event that a) charging energy is present, and b) the level of the energy present from the input charge device is greater than a predetermined safe level for the device to be charged. A further benefit of this invention may be that very small energy sources may, for example, preferably be safely connected to this circuit without the need of any voltage regulation because regulation may, for example, be applied via this circuit only in the event of possible over charge voltage conditions as seen at the rechargeable device, and only when charge energy is present. 
         [0016]    The monitor and power dissipation circuitry in this invention can, for example, be powered solely by charging energy. If charging energy is not available, then only very minute amounts of leakage current may be taken from the energy storage device. Furthermore, only very small amounts of charge energy may be used to determine if an over voltage condition exists. 
         [0017]    Also in this invention, the power dissipation circuit may be switched on, for example, when an over-voltage condition exists. The existence of such condition is determined, for example, when a) charging energy is present, and b) the voltage level of the energy present from the input charge device is greater than a predetermined safe level for the device to be charged. When the over voltage condition has been removed, the protection circuit may return to a quiescent state. Because over-voltage can, for example, preferably be monitored within this circuitry, maximum voltage regulation does not have to be provided via the charge energy source. This power may, for example, be dissipated by the power dissipation circuitry. 
         [0018]    Trace energy gathering may slowly build to an overcharge condition over time. In some ambient environments, it may be critical to use all available energy without the power consumption of constant regulation. Certain embodiments of this invention may be different than the prior art in that, for example, voltage regulation may not, in those embodiments, occur unless an overcharge condition can exist at the rechargeable energy storage device, and only when recharge energy is present. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Some features and advantages of certain embodiments of the invention are described with reference to the drawings of certain preferred embodiments, which are intended to illustrate examples and not to limit the full scope of the invention. 
           [0020]    The accompanying drawings, which are included to provide a further understanding of various embodiments of the invention are incorporated in and constitute a part of this specification, and illustrate exemplary embodiments of the invention that together with the description serve to explain certain principles of the invention. In the drawings: 
           [0021]      FIG. 1  is a block diagram of an exemplary embodiment of a passive battery or capacitor over voltage control and protection circuit. 
           [0022]      FIG. 1   a  is a schematic diagram of an exemplary embodiment of a blocking circuit. 
           [0023]      FIG. 2  is a schematic diagram of an exemplary embodiment of a voltage monitor circuit. 
           [0024]      FIG. 3  is a schematic diagram of an exemplary embodiment of another voltage monitor circuit. 
           [0025]      FIG. 4  is a schematic diagram of an exemplary embodiment of another voltage monitor circuit. 
           [0026]      FIG. 5  is a schematic diagram of an exemplary embodiment of a shunt regulator power dissipation option. 
           [0027]      FIG. 6  is a schematic diagram of an exemplary embodiment of another shunt regulator power dissipation option. 
           [0028]      FIG. 7  is a block diagram of an exemplary embodiment of using multiple charge sources in parallel. 
           [0029]      FIG. 8  is a block diagram of an exemplary embodiment of using multiple charge sources in series. 
           [0030]      FIG. 9  is a block diagram of an exemplary embodiment of charging multiple batteries, battery cells, or capacitors in parallel. 
           [0031]      FIG. 10  is a block diagram of an exemplary embodiment of charging multiple batteries, battery cells, or capacitors in series. 
           [0032]      FIG. 11  is a circuit diagram of an exemplary embodiment of an under-voltage protection circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    These and other aspects of the invention will now be described in greater detail in connection with exemplary embodiments that are illustrated in the accompanying drawings. 
         [0034]    It is to be understood that the present invention is not limited to the particular methodology, compounds, materials, manufacturing techniques, uses, and applications described herein, as these may vary. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. It must be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “an element” is a reference to one or more elements and includes equivalents thereof known to those skilled in the art. Similarly, for another example, a reference to “a step” or “a means” is a reference to one or more steps or means and may include sub-steps and subservient means. All conjunctions used are to be understood in the most inclusive sense possible. Thus, the word “or” should be understood as having the definition of a logical “or” rather than that of a logical “exclusive or” unless the context clearly necessitates otherwise. Structures described herein are to be understood also to refer to functional equivalents of such structures. Language that may be construed to express approximation should be so understood unless the context clearly dictates otherwise. 
         [0035]    Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Preferred methods, techniques, devices, and materials are described, although any methods, techniques, devices, or materials similar or equivalent to those described herein may be used in the practice or testing of the present invention. Structures described herein are to be understood also to refer to functional equivalents of such structures. 
         [0036]    All patents and other publications identified are incorporated herein by reference for the purpose of describing and disclosing. For example, the methodologies described in such publications that might be used in connection with the present invention. These publications are provided solely for their disclosure prior to the filing date of the present application. Nothing in this regard should be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention or for any other reason. 
         [0037]      FIG. 1  is a block diagram of an exemplary embodiment of a passive battery or capacitor over voltage control and protection circuit. In this embodiment, an input charge device  105  may be coupled to an impedance matching capacitor  104 . The input charge device  105  may be, for example, a piezo electric source coupled to a rectifier and filter such that pulse energy is obtained via vibration, flexing, or impact events and generate a voltage across capacitor  104 . Impedance matching capacitor(s)  104  of certain of these embodiments are application specific and can be chosen for the charge source. Voltage Monitor Circuit  100  and Blocking Circuit  101  may be connected to the same input node  107 . The battery or capacitor or other energy storage device to be charged  106  may be connected to the output node  108  of the Blocking Circuit  101 . Also, the input of a Shunt Power Dissipation Circuit  102  may be connected to the energy storage device  106  while the output Shunt Power Dissipation Circuit  102  may be connected to node  109 . In the exemplary embodiment illustrated in  FIG. 1 , node  109  is connected to ground, but in other embodiments, node  109  may be connected to other items, such as an energy storage device. The Shunt Power Dissipation Circuit  102  may also be connected to the output node of Voltage Monitor Circuit  100 . In this configuration, a signal from Voltage Monitor Circuit  100  may, for example, cause Shunt Power Dissipation Circuit  102  to operate. 
         [0038]    In several embodiments, an input charge device  105  may be an energy harvesting mechanism based on a radio frequency energy transducer or a device that can convert solar power, wind power, vibration, pedestrian activity such as walking or jogging, water movement, temperature variations, magnetic fields, or rotational movements into usable energy such as electricity. Additionally, input charge device  105  may also include a voltage boost converter. 
         [0039]    In addition to a battery or capacitor, an energy storage device  106  may also be a mechanical energy storage device, such as, for example, a flywheel, micro-flywheel, micro electromechanical system (MEMS), or a mechanical spring. The energy storage component may also be a thermal energy storage device, such as a thermal mass container, or it could be a chemical energy storage device, such as, for example, a hydrogen generator with hydrogen container or an ozone generator with ozone container. Each one of these devices may be used to store energy based on exemplary elements of the system. 
         [0040]      FIG. 1   a  is a schematic diagram of an exemplary embodiment of a blocking circuit. In this embodiment, a Schottky Diode  110  may be used as the blocking circuit to prevent current flow from the device to be charged  106  to the Voltage Monitor Circuit  100 . To achieve the same functionality, other mechanisms may also be used as blocking circuits, such as, for example, an active semiconductor device, such as, for example, a MOSFET switch and control circuitry, a relay, or a Micro Electro Mechanical Switch. A Schottky Diode may be a preferable component due to simplicity in design and its very low forward voltage drop, resulting preferably in increased charge efficiency. 
         [0041]    Referring back to  FIG. 1 , if the energy storage device  106  is in an under-voltage condition and requires charging, the energy seen at impedance matching capacitor  104  may cause current to flow into the energy storage device  106 . In many cases, particularly with low energy input charge devices, this energy may not energize the Power Dissipation Circuit  102  because, due to the current draw of the energy storage device, the voltage seen at input node  107  may be only slightly above the voltage on the battery or capacitor  106 . As the energy storage device  106  becomes fully charged, its voltage, as seen at node  108 , may rise and reach a predetermined level. This predetermined level may be related to the safe fully charged level of the energy storage device. The predetermined level of a fully-charged thin film battery, for example, may be 4.10V. When the energy storage device  106  has reached a charged voltage level at or above the predetermined value, subsequent charge pulses developed by the input charge device may raise the voltage at node  107  to a level greater than the predetermined charge level, and the Power Dissipation Circuit  102  can, for example, turn on and dissipate the charge pulse out through node  109 . 
         [0042]    In some embodiments, low current is generated by the input charge device  105 , such as with a solar array that has insufficient light to operate in the voltage mode or an antenna that collects very small amounts of ambient electromagnetic energy from radio waves, etc. In such conditions, current generated by the low current input charge device  105  may still build a voltage, albeit over a longer period of time, on capacitor  104 . As the voltage on capacitor  104  builds to a level slightly higher than the voltage on the energy storage device  106  (accounting for the voltage drop across the Blocking Circuit  101 ), current may flow into the energy storage device  106 . In these embodiments, only if voltage builds on the energy storage device  106  to the predetermined level—indicating that it is fully charged—may the Voltage Monitoring Circuit  100  energize. As a result, power may not be lost to the Voltage Monitoring Circuit  100  until the energy storage device  106  is fully charged. This may be true for other charge sources  105  including but not limited to DC source in either voltage or current mode, rectified AC source in either voltage or current mode, piezo electric source, peltier source, fuel cell source, solar source in either voltage or current mode, RF source, inductive source, magnetic source and radio isotope (active) to electric conversion source. 
         [0043]    In some embodiments, an energy load (not shown) may be connected to node  108  and powered directly from the energy storage device  106 . In other embodiments, an energy load may be connected to node  107  and powered directly from input charge device  105 . In yet other embodiments, an energy load may be connected to the output of Power Dissipation Circuit  102 . Whether the energy load is connected to one or more of these loads may depend on the anticipated parameters of the energy supplied by the input charge device  105  as well as the sensitivity of the energy load. 
         [0044]    In these and other embodiments, one or more of many sorts of sensors may be powered by the energy storage device connected to the protection circuit, thereby serving as the energy load and creating a system for sensing one or more parameters. Some embodiments may also include communication circuitry and one or more antennas that may allow the system to communicate. In such embodiments, when combined with an energy harvesting device (collecting ambient energy), the system may serve as an autonomous powered wireless communication system. These systems may for example include a plurality of transmitting and/or receiving (or having both capabilities) devices. These systems may be used, for example, as a wireless signal listening device, tuned to a plurality of frequencies, and collecting transmitted information and/or performing a function, such as, for example, transmitting a signal, based on certain information that is received. These systems, when having other types of sensors, may function as wireless sensors and communicate data that is measured by the sensor. The system may also be used, for example, as a wireless receiver component to an autonomous electrical circuit which, upon receiving a wireless command signal, performs a function. 
         [0045]    In several embodiments, some or all of the elements of the passive power management unit, the input charge device, and the energy storage device are all formed on a single substrate such as, for example, a flexible circuit board or semiconductor chip. 
         [0046]    In the several embodiments in which the energy storage device is a rechargeable device, such as, for example, a thin-film battery or capacitor, this will present an opportunity whereby the present invention may be capable of performing nearly indefinitely. The present invention may, for example, allow for energy created through radio frequency, wind power, solar power, vibration, human activity, water movement, temperature variations and rotational movements to be harvested in an energy harvesting mechanism and for that harvested energy to ensure that the rechargeable energy storage device may be so charged. 
         [0047]      FIG. 2  is a schematic diagram of an exemplary embodiment of a voltage monitoring circuit. The monitoring circuit  200  can be, for example, a series of precision low current shunt voltage references  202  with a high impedance amplifier  204  to provide isolation, powered solely by the input charge energy source, isolating the reference current until sufficient energy is available from the input charge device. Device  204  may be a high impedance, low quiescent current operational amplifier that is powered via the same line as its non-inverting input. This exemplary device may not use power unless the power is available via the input line  210  or when charging power is available. The usage of operational amplifiers this way in this exemplary embodiment may help to achieve desired low power operations because if there is no charge energy from the input charge device, there may be no quiescent current usage by the voltage monitor circuit. Device  208 , which operates when device  204  is operating, can be another operational amplifier that functions as a comparator. Device  208  can be powered by the same line as its non-inverting input. Diodes  202  can be, for example, “off the shelf” 1.25V shunt references. Optionally, voltage divider resistors  206  and  207  can be used to ensure voltage at the non-inverting input of device  208  is preferably within a predetermined limit for maximum voltage. 
         [0048]      FIG. 3  is a schematic diagram of an exemplary embodiment of another voltage monitor circuit. This figure illustrates that, to achieve the same functionality as shown in  FIG. 2 , a voltage monitor circuit  300  may include, for example, only one precision low current shunt voltage reference  302 , voltage divider resistors  306  and  307 , a high impedance amplifier  304  to provide isolation, powered solely by the input charge energy source, isolating the reference current until the energy storage device (not shown) is charged and/or sufficient energy is available from the input charge device (not shown). 
         [0049]      FIG. 4  is a schematic diagram of an exemplary embodiment of another voltage monitor circuit. It illustrates a particular single chip solution for voltage monitor. The chip can be a semiconductor  402 , powered solely by the input charge energy source, isolating the reference current until sufficient energy is available from the input charge device. One example of such semiconductor chip may be a Seiko S-1000 voltage detector, which has extremely low quiescent current, and a fixed detection voltage value. 
         [0050]      FIG. 5  is a schematic diagram of an exemplary embodiment of a shunt power dissipation circuit  500 . In this embodiment, circuit  500  may contain a power dissipation circuit switch  516  made from a pair of field effect transistors (FETs)  502  and  504  with a forward bias resistor  506 . Although the use of dual FET switches  502  and  504 , which are shown as serially coupled, may make the leakage current extremely small, one FET may be used instead to further reduce losses. Circuit  500  also contains a shunt voltage reference circuit  508 . The shunt voltage reference circuit  508  may contain an adjustable zener diode shunt load  511  through two resistors  512  and  514 . Circuit  500  can be powered solely by an input charge energy source (not shown) as seen through a voltage monitor circuit (not shown) and connected to input node  510 , thereby isolating the power dissipation circuit  500  until sufficient energy is available from the input charge device and an over voltage condition exists. When there is excess energy supplied by the charge energy source, a voltage monitor may operate the power dissipation circuit switch  516  to drain the excess energy from the energy storage device (connected to Vbat) to shunt voltage reference circuit. 
         [0051]      FIG. 6  is a schematic diagram of an exemplary embodiment of another shunt regulator power dissipation circuit  600 . In circuit  600 , a power dissipation circuit switch device  612  may contain dual FET switches  602  and  604  and forward bias resistor  506 , similar to the one shown in  FIG. 5 . Unlike  FIG. 5 , however, circuit  600  may contain only a simple resistive load  608 . Circuit  600  may be powered solely by the input charge energy source (not shown) as seen through a voltage monitor circuit (not shown) and connected to input node  610 , thereby isolating the power dissipation circuit  600  until sufficient energy is available from the input charge device and an over voltage condition exists. In certain embodiments, the voltage monitor circuit, which can be connected to the input  610  can maintain its reference voltage and switch the power dissipation circuit  600  “on” and “off” as required. The reference voltage can be maintained through the determination of whether a charge pulse is developed and causes the voltage to rise past the predetermined charge level. 
         [0052]      FIGS. 5 and 6  illustrate certain exemplary options for power dissipation circuit switch devices and power dissipation circuits containing discrete devices. Other examples of power dissipation circuit switching device may include circuits using one or a more of a bipolar transistor, field effect transistor, relay, Micro Electro Mechanical Switch (MEMS) relay, or semiconductor circuit. 
         [0053]    Examples of other shunt power dissipation circuits may include, for example, the use of a semiconductor circuit. All these examples may, for example, be powered solely by the input charge energy source, isolating the power dissipation circuit until excess energy is entering from the input charge device and an over voltage condition exists for the energy storage device. 
         [0054]    Circuits shown as separate entities above may also be combined into a single chip solution by using a combined semiconductor circuit. For example, a voltage monitor circuit and a power dissipation circuit can be combined into a semiconductor circuit. As another example, a voltage monitor circuit, a blocking circuit, and a power dissipation circuit may also be combined into a semiconductor circuit. Such a configuration, may, for example, have as few as three external connections: an input connect to the input charge device, and output to connect to the energy storage device, and a drain to connect to ground or a device that can use or collect the excess energy. A single combined semiconductor circuit may also include circuits that are not shown in any previously illustrated exemplary embodiments. For instance, in addition to a voltage monitor circuit, a blocking circuit, or a power dissipation circuit, a semiconductor circuit may also include a combination of a rectification circuit for conversion of AC charge input to DC, a voltage boost converter, and a voltage boost converter that has no upper voltage regulation requirement. All such combined semiconductor circuits may be powered solely by the input charge energy source, isolating the power dissipation circuit until sufficient energy is available from the input charge device and an over voltage condition exists. 
         [0055]    The present invention applies not only to one input charge device and one battery or capacitor to be charged, as shown in  FIG. 1  ( 105  and  106 ), but also may be applied to multiple input charge devices in series or parallel and multiple batteries or capacitors to be charged in series or parallel. 
         [0056]      FIG. 7  shows a block diagram of an exemplary embodiment for using multiple input charge devices in parallel. In  FIG. 7 , multiple input charge devices  702  are coupled in parallel to serve as a single input source for both a blocking circuit and a voltage monitor circuit. All input charge devices may further be connected to the same impedance matching capacitor  704 . Note that the multiple input charge devices  702  are not necessarily the same type of device, as, in certain applications, it may be beneficial to obtain energy through a variety of methods. 
         [0057]      FIG. 8  shows a block diagram of an exemplary embodiment depicting the use of multiple input charge devices in series. In  FIG. 8 , multiple input charge devices  802  can be serially connected to serve as a single input source for both blocking circuit and voltage monitor circuit. Each input charge device can be coupled to, for example, a corresponding impedance matching capacitor  804 . As previously mentioned, multiple input charge devices  802  are not necessarily the same type of device, as, in certain applications, it may be beneficial to obtain energy through a variety of methods. 
         [0058]      FIG. 9  shows a block diagram of an exemplary embodiment for charging multiple batteries, battery cells, or capacitors in parallel. In  FIG. 9 , multiple batteries or capacitors to be charged  902  can be coupled in parallel to the output of a single blocking circuit  904 . 
         [0059]      FIG. 10  shows a block diagram of an exemplary embodiment of charging multiple batteries, battery cells, or capacitors in series. In  FIG. 10 , multiple batteries or capacitors to be charged  1002  can be serially connected to the outputs of multiple blocking circuits  1004 . Each individual battery or capacitor to be charged may be, for example, coupled to its corresponding blocking circuit. Voltage can be controlled for each battery or capacitor to be charged individually through the corresponding blocking circuit, which also has a corresponding power dissipation circuit. 
         [0060]    When charging multiple batteries or capacitors in series, it is also, for example, possible to only monitor voltage at the top of the stack and regulate from the top of the stack. In this case, there may preferably need to be only one blocking circuit and one power dissipation circuit for all the batteries or capacitors connected serially. 
         [0061]      FIG. 11  shows a circuit diagram of an optional under-voltage protection circuit  1100 . If connected, the input terminal is connected to node  108  while the output terminal would be connected to an electronic user circuit (not shown). The under-voltage protection circuit operates by monitoring the voltage at node  108  and, when it falls below the minimum predetermined under-voltage level, the electronic user circuit is disconnected from the energy storage device by a switching circuit (not shown). Once the voltage of the energy storage device reaches a value above the predetermined under-voltage level, circuit  1100  operates to reconnect the energy storage device to the electronic user circuit. A predetermined low-voltage level is generally specific to the type of energy storage device used. For example, a thin film battery may have a save operating range above 2.0V and the predetermined voltage level may therefore be set to 2.5V. 
         [0062]    The embodiments and examples described above are exemplary only. One skilled in the art may recognize variations from the embodiments specifically described here, which are intended to be within the scope of this disclosure and invention. As such, the invention is limited only by the following claims. Thus, it is intended that the present invention cover the modifications of this invention provided they come within the scope of the appended claims and their equivalents.