PATENT DOCUMENT

Publication Number: US-8410783-B2
Application Number: US-57062209-A
Country: US
Kind Code: B2

Title: Detecting an end of life for a battery using a difference between an unloaded battery voltage and a loaded battery voltage

Abstract:
One particular implementation conforming to aspects of the present invention takes the form of a method for detecting the end of life of a battery for an electronic device. The method may include calculating the voltage of the battery in an unloaded state, holding the sampled unloaded battery voltage, measuring a loaded battery voltage, calculating the difference between the unloaded and loaded battery voltages and amplifying the calculated difference. Other implementations may take the form of a circuit to perform one or more of the operations of the above method. The circuit may include a sample and hold section and a differential amplifier to provide the amplified difference to a microcontroller for analysis. The microcontroller may also provide a warning or indication to the device or to a user of the device when the battery nears the end of life.

Claims:
The invention claimed is: 
     
       1. A circuit for detecting the end of life of a battery of an electronic device comprising:
 a first node electrically connected to a battery; 
 a load intermittently electrically connected to the first node, the load configured to be applied and removed from the circuit; 
 a sample and hold circuit electrically connected to the first node, the sample and hold circuit configured to sample and hold an unloaded battery voltage, the sample and hold circuit comprising:
 a capacitor electrically connected between a second node and ground; 
 a first operational amplifier comprising an inverting input, a non-inverting input and an output, wherein the non-inverting input is electrically connected to the second node and the output is electrically connected to the inverting input; and 
 a field effect transistor comprising a base terminal, a drain terminal, a gate terminal and a source terminal, wherein the base terminal and the source terminal are electrically connected to the first node and the drain terminal is electrically connected to the second node; and 
 
 a differential amplifier electrically connected to the sample and hold circuit, the differential amplifier configured to calculate and amplify a difference between the sampled unloaded battery voltage and a loaded battery voltage. 
 
     
     
       2. The circuit of  claim 1  further comprising:
 an analog to digital converter electrically connected to an output of the differential amplifier, the analog to digital converter configured to digitize the amplified difference between the sampled unloaded battery voltage and the loaded battery voltage; and 
 a microcontroller configured to compare the digitized amplified difference with a predetermined threshold value. 
 
     
     
       3. The circuit of  claim 1  further comprising:
 an enable input pin electrically connected to the gate terminal of the field effect transistor, wherein an enable signal is input on the enable input pin to control the flow of current through the field effect transistor and thereby control the charging of the capacitor. 
 
     
     
       4. The circuit of  claim 3  wherein the enable signal and the load are controlled by a microcontroller. 
     
     
       5. The circuit of  claim 1  wherein the differential amplifier comprises:
 a first resistor electrically connected between an output of the first operational amplifier and a non-inverting input of a second operational amplifier; 
 a second resistor electrically connected to the non-inverting input of the second operational amplifier; 
 a third resistor electrically connected between the first node and an inverting input of the second operational amplifier; and 
 a fourth resistor electrically connected between an output of the second operational amplifier and the inverting input of the second operational amplifier. 
 
     
     
       6. A method for detecting the end of the life of a battery of an electronic device comprising:
 sampling a voltage of a battery while the battery is unloaded using a sample and hold circuit that comprises:
 a capacitor electrically connected between a second node and ground; 
 a first operational amplifier comprising an inverting input, a non-inverting input and an output, wherein the non-inverting input is electrically connected to the second node and the output is electrically connected to the inverting input; and 
 a field effect transistor comprising a base terminal, a drain terminal, and a source terminal, wherein the base terminal and the source terminal are electrically connected to a first node that is electrically connected to a battery and the drain terminal is electrically connected to the second node; 
 
 storing the sampled unloaded battery voltage using the capacitor in the sample and hold circuit; 
 measuring a voltage of the battery while a load is applied to the battery; 
 calculating a difference between the sampled unloaded battery voltage and the measured loaded battery voltage; 
 amplifying the calculated difference using a differential amplifier circuit; and 
 comparing the amplified difference to a predetermined value to detect the end of the life of the battery. 
 
     
     
       7. The method of  claim 6  further comprising:
 digitizing the amplified difference with a analog to digital converter prior to comparing the amplified difference to the predetermined value. 
 
     
     
       8. A system for detecting the end of the life of a battery of an electronic device comprising:
 a sample and hold circuit configured to sample the unloaded voltage of a battery, the sample and hold circuit comprising:
 a capacitor electrically connected between a second node and ground; 
 a first operational amplifier comprising an inverting input, a non-inverting input and an output, wherein the non-inverting input is electrically connected to the second node and the output is electrically connected to the inverting input; and 
 a field effect transistor comprising a base terminal, a drain terminal, and a source terminal, wherein the base terminal and the source terminal are electrically connected to a first node that is electrically connected to a battery and the drain terminal is electrically connected to the second node; 
 
 a differential amplifier circuit configured to receive the sampled unloaded battery voltage from the sample and hold circuit and calculate and amplify a difference between the sampled unloaded battery voltage and a loaded battery voltage; and 
 a microcontroller configured to receive the amplified difference from the differential amplifier and compare the amplified difference with a predetermined threshold value. 
 
     
     
       9. The system of  claim 8  further comprising:
 an analog to digital converter configured to receive the amplified calculated difference and digitize the received difference. 
 
     
     
       10. The system of  claim 9  wherein the microcontroller is further configured to provide an enable signal to activate the sample and hold circuit and apply a load to battery.

Description:
TECHNICAL FIELD 
     This invention relates generally to batteries in electronic devices, and more specifically to methods and circuits for detecting the end of the life of a battery powering an electronic device. 
     BACKGROUND 
     Many portable electronic devices include rechargeable batteries. However, depending on the power consumption of the electronic device, the battery may need to be periodically recharged so that the device may continue to operate uninterrupted. For example, laptop computers often include a battery that powers the device when a traditional power source is not available, but may often only operate for a limited time before the battery must be recharged. Thus, it is useful if a portable electronic device provides some indication to the user of the battery status so that the user may recharge the battery before loss of power. This is especially useful in situations where data may be lost due to a power failure, such as a laptop computer or other portable computing device. 
     An additional concern is that, although batteries may be refreshed by charging, virtually all batteries suffer degradation over time such that the battery can no longer provide the necessary power to the device even when charged. For example, a typical nickel-metal hydride (NiMH) battery can generally be recharged about 1,000 times before the battery has degraded to a point that it can no longer provide the necessary power to the device. Thus, batteries for electronic devices are typically replaced with new batteries once the performance of the battery degrades. However, in some situations, acquiring a replacement battery for the electronic device may take several days or weeks as the new battery must be obtained from a manufacturer of the device. In situations where data may be lost or usage of the device may be interrupted due to the degraded battery, a user may wish that the electronic device provide an indication to the user that the battery is nearing the end of the battery&#39;s life. Ideally, this indication is provided to the user with enough time to allow the user to locate and purchase a replacement battery before any negative effects are realized, such as loss of information or ability to use the device in a portable manner. 
     SUMMARY 
     In many electronic devices, the apparatuses utilized to detect an imminent end to a battery&#39;s life are typically complex and often utilize expensive components. Thus, what is needed is a simple method and circuit to detect the end of life of a battery such that a portable electronic device may provide advanced warning to a user of the device of the degradation of the device&#39;s battery such that the user may obtain a replacement battery for the device before any negative effects are realized. Further, some battery chemistries, such as NiMH batteries, have a nearly constant internal resistance until very near the end of life of the battery, making detecting of the degradation of the battery charge difficult. Thus, what is also needed is a method and circuit that amplifies the measured difference in internal resistance of the battery as the battery nears the end of life to provide a more accurate indication of the battery&#39;s status. 
     One embodiment may take the form of a circuit for detecting an imminent end of life of a battery powering an electronic device. The circuit may include a first node electrically connected to a battery and a load, such that the load is configured to be applied and removed from the circuit. A sample and hold circuit may also be electrically connected to the first node with the sample and hold circuit configured to sample and hold an unloaded battery voltage. A differential amplifier electrically may also be included in the circuit, connected to the sample and hold circuit, with the differential amplifier configured to calculate and amplify a difference between the sampled unloaded battery voltage and a loaded battery voltage. 
     Another embodiment may take the form of a method for detecting the end of the life of a battery powering an electronic device. The method may include the operations of sampling a voltage of a battery while the battery is unloaded, storing the sampled unloaded battery voltage, measuring a voltage of the battery while a load is applied to the battery, calculating a difference between the sampled unloaded battery voltage and the measured loaded battery voltage and amplifying the calculated difference using a differential amplifier circuit. The method may also include comparing the amplified difference to a predetermined value to detect the end of the life of the battery. 
     Still another embodiment may take the form of a system for detecting the end of the life of a battery powering an electronic device. The system may include a sample and hold circuit configured to sample the unloaded voltage of a battery and a differential amplifier circuit configured to receive the sampled unloaded battery voltage from the sample and hold circuit and calculate and amplify a difference between the sampled unloaded battery voltage and a loaded battery voltage. The system may also include a microcontroller configured to receive the amplified difference from the differential amplifier and compare the amplified difference with a predetermined threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart showing a method for determining the end of life of a battery. 
         FIG. 2  depicts a graph of the change in potential voltage of a battery as the battery degrades due to usage. 
         FIG. 3  depicts a first embodiment for a end of life battery detection circuit. 
         FIG. 4  is a flow chart showing a method for acquiring a voltage difference of a battery in a loaded and unloaded state utilizing the first embodiment. 
         FIG. 5  depicts a second embodiment for a end of life battery detection circuit utilizing matched diodes as a sampling switch. 
         FIG. 6  is a flow chart showing a method for acquiring a voltage difference of a battery in a loaded and unloaded state utilizing the second embodiment. 
         FIG. 7  depicts a third embodiment for a end of life battery detection circuit utilizing an active peak detector to hold the unloaded peak battery voltage. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One particular implementation conforming to aspects of the present invention takes the form of a method for detecting the end of life of a battery for an electronic device. The method may include calculating the voltage of the battery in an unloaded state, holding the sampled unloaded battery voltage, measuring a loaded battery voltage, calculating the difference between the unloaded and loaded battery voltages and amplifying the calculated difference. Other implementations may take the form of a circuit to perform one or more of the operations of the above method. For example, such a circuit may include a sample and hold section and a differential amplifier to provide the amplified difference to a microcontroller for analysis. The microcontroller may also provide a warning or indication to the device or to a user of the device when the battery nears the end of life. 
       FIG. 1  is a flow chart showing a method for determining the end of life of a battery. In one embodiment, a microcontroller, microprocessor, or other processing device of an electronic device may perform the operations of the method. In another embodiment, an end of battery life detection circuit may perform the operations. In still other embodiments, the operations of the method may be performed by a combination of an end of battery life detection circuit and a microcontroller, as explained in more detail below. Generally, any device including a battery may include components to perform the method to detect the end of life of the battery. As explained in more detail below with reference to the circuits of  FIGS. 2-4 , the microcontroller may perform the operations of the method by providing an enable signal, and other signals, to a circuit. Further, the microcontroller may receive the output of certain circuits or devices, including those described herein, to perform other operations of the method. 
     Beginning in operation  110 , the microcontroller or circuit may measure the voltage provided by the battery when no load is present (“the unloaded voltage”). In one particular embodiment, the microcontroller may provide an enable signal to a sample and hold circuit described below with reference to  FIG. 3  to make the unloaded voltage measurement. In other embodiments, the unloaded voltage measurement may be automatically performed through a sample and hold or active peak detector circuit without receiving an enable signal. 
     Once measured, the unloaded voltage may be stored in operation  120 . In one embodiment, a sample and hold circuit may maintain the unloaded voltage such that the value is stored within the circuit that performs the voltage measurement. In another embodiment, the microcontroller may store the measured unloaded voltage in a machine readable medium. A machine readable medium includes any mechanism for storing or transmitting information in a form (e.g., data, software, processing application) readable by a machine (e.g., a computer). Common forms of machine-readable media may include, but is not limited to, magnetic storage media (e.g., floppy diskette); optical storage media (e.g., CD-ROM); magneto-optical storage media; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of media suitable for storing electronic instructions. 
     After the unloaded voltage level of the battery has been measured and stored, the microcontroller may apply a load to the battery in operation  130 . The load may be applied through a load signal provided by the microcontroller. In one embodiment, the microcontroller may apply a resistance to the circuit through the load signal. Generally, any means to apply a load to a circuit may be utilized by the microcontroller to supply the load signal. Once loaded, the microcontroller or circuit may take a second voltage measurement of the battery in operation  140 , this time with the load applied to the battery. This value may also be stored in a similar manner as described above. 
     Once both the loaded and unloaded voltage levels are measured, a difference between the two values may be calculated in operation  150 . As explained in more detail below, a differential amplifier may be utilized to determine the difference in the voltage values. Alternatively, the microcontroller may access the stored voltage values and perform the difference operation. Further, as explained in greater detail below, the calculated difference may be amplified in operation  160 . Again, similar to the differential measurement, a differential amplifier of an end of life detection circuit may amplify the measured difference. 
     Generally, the calculated difference measurement between the loaded and unloaded battery is a function of the state of charge of the battery. As the measured difference increases due to prolonged usage of the battery, the battery may provide less power to the device. Thus, the measured difference may provide to the device an estimate of the degradation of the battery at any given moment. However, a pure difference measurement may not provide an accurate estimation of the end of life of the battery. For example, for alkaline batteries, the measured cell potential can be utilized directly to warn the device of a low battery condition. However, because the internal resistance of a NiMH battery is 5 to 10 times smaller than that of an alkaline battery, the measured difference may be amplified through an amplification circuit in operation  160  to aid the device in determining the end of life of the battery. 
     Amplifying the measured difference in operation  160  may also aid in determining the end of a battery life of batteries for varying chemistries and discharge rates. As stated above, NiMH batteries have a very low internal resistance until very near the end of life of the battery, making detection of the degradation of the battery difficult.  FIG. 2  depicts a graph of the change in potential voltage of a NiMH battery as the battery degrades due to usage. The y-axis of the graph indicates the voltage provided by the battery while the x-axis is the elapsed time as the battery goes through a life cycle. Thus, as shown, continual usage of the battery (moving along the x-axis) degrades the amount of voltage the battery provides, from near 1.40 volts at the beginning of the life cycle of the battery to 1.00 volts near 5 hours of usage. At 1.00 volts, the battery may need to be replaced as it may no longer provide enough power to the electronic device. 
     As shown in the graph, the discharge rate of the battery is relatively steep for the first part of the life cycle of the battery. However, for the majority of the rest of the battery life cycle, the battery potential remains relatively flat, as shown on the graph of  FIG. 2  in the area between 1 hour and 4.5 hours. Thus, a NiMH battery at 50% degradation provides only slightly more electric potential than the same battery at 75% degradation. As a result, it may be difficult to accurately measure the un-amplified difference in the loaded and unloaded battery voltage as the battery degrades during the life cycle. By the time that a measurable difference is detected by the device, the battery may only have a small charge left to support the device. 
     To account for the relatively flat discharge curve of the NiMH battery, the measured difference between the loaded and unloaded battery voltage is amplified in operation  160 . By amplifying the measured difference, small changes in the internal resistance of the NiMH battery due to degradation may be measured more accurately, so that the electronic device may be able to better estimate the end of life of the battery. This amplification may provide a more accurate measurement of changes within the battery in the flat portion of the discharge curve of  FIG. 2 , so that an indication of the end of the battery life may be provided to the device or the user before any negative effects of battery failure are realized. For example, a 300 mV sag in the potential of the battery may be amplified to 1.25 V, such that the device may better detect the change in battery potential. 
     Returning to  FIG. 1 , the microcontroller may analyze the amplified difference in operation  165  to determine if the difference falls above a predetermined threshold value. Prior to analysis by the microcontroller, the amplified difference may be digitized using an analog to digital converter  332 . Once received, the microcontroller may compare the received value to the predetermined level. If the received value is above the threshold, the battery potential may be degraded to a point such that the end of life of the battery may be near. Thus, an indication may be provided to the device or to a user to indicate that the battery is near the end of life in operation  170 . As should be appreciated, the threshold value that triggers the warning may be set either by the device itself or a user of the device. Generally, any value that indicates to the device or user that the battery is near end of life may be used as the threshold value. 
       FIG. 3  depicts a first embodiment of a circuit that may detect the end of life of a battery. As explained above, the circuit may be used in conjunction with a microcontroller  330  of an electronic device to detect when a battery nears the end of its life. 
     The circuit  300  depicted in  FIG. 3  may be connected to a battery  302  of an electronic device. The power supply  316  depicted in  FIG. 3  represents the input from the battery of the device that is sampled or any other power source of the device. The battery  302  is connected to a first node  304  of the circuit  300 . A load  306  is also connected to the first node  304 . As explained in more detail below, the load  306  is applied to the battery by a microcontroller of the device to obtain a loaded and unloaded battery voltage. 
     A field-effect transistor (FET) device  308  is also connected to the first node  304  of the circuit  300 . Generally speaking, the FET device  308  is a p-channel metal oxide semiconductor field-effect transistor, or p-channel “MOSFET.” It should be noted that alternative embodiments may use a n-channel MOSFET, depletion mode MOSFET, and so on. The FET device  308  may have four terminals, namely a gate, a drain, a source and a body. The source and body terminals may be electrically connected to the first node  304 . The gate terminal may be electrically connected to the microcontroller or similar component of the device such that the FET  308  may operate as a switch controlled by an enable signal provided by the microcontroller. The drain terminal may be connected electrically connected to a second node  310  of the circuit  300 . Also connected to the second node  310  may be one end of a capacitor  312 , with the other end of the capacitor connected to ground. As should be noted, the value of the capacitor may vary as desired by the circuit designer depending on the operating parameters of the circuit&#39;s components. 
     A first operational amplifier (OPAMP) device  314  may also be connected to the second node  310 . More precisely, the non-inverting input of the OPAMP  314  may be connected to the second node  310 . The OPAMP may also include an inverting input, a positive and negative power supply input and an output. As shown in  FIG. 3 , the negative power supply input of the first OPAMP  314  is connected to ground while the positive power supply input is provided by the supply rails  316  of the electronic device, e.g., generally provided by the battery  302 . However, the power supplied to the OPAMPs of the circuit  300  may be provided by any power source of the device. The output of the first OPAMP  314  is fed back to the inverting input. 
     The output of the first OPAMP  314  may also be a first input to a differential amplifier section of the circuit  300  that is configured to determine the difference in voltage between a loaded and unloaded battery. Thus, the output of the first OPAMP  314  is connected in series with one end of a first resistor  318 , with the other end of the first resistor connected to the non-inverting input of a second OPAMP  322 . A second resistor  320  is connected between the non-inverting input of the second OPAMP  322  and ground. Also, the negative power supply input of the second OPAMP  322  is connected to ground while the positive power supply input is provided by the supply rails  316  of the device. 
     Other resistors may also be included in the differential amplifier circuit. A third resistor  324  may electrically connect on one end to the inverting input of the second OPAMP  322 . The other end of the third resistor  324  may be connected to the first node  304 . Also, a fourth resistor  326  may be connected between the output of the second OPAMP  322  and the inverting input in the feedback loop of the amplifier. As should be noted, the values of the four resistors may vary as desired by the circuit  300  designer to control the amplification of the differential amplifier section of the circuit. 
       FIG. 4  is a flowchart showing a method for acquiring a voltage difference of a battery in a loaded and unloaded state utilizing the circuit described above with reference to  FIG. 3 . The operations of the flowchart may be performed by the circuit  300 . 
     First, in operation  410 , the microcontroller  330  may provide an enable signal to the FET device  308  of the circuit to activate the end of life battery detection. Once activated, the first capacitor  312  and the first OPAMP  314  may act as a sample and hold circuit to measure and hold the voltage of the unloaded battery  302  in operation  420 . Thus, once enabled, the capacitor  312  may charge to the measured voltage of the unloaded battery. This value may be held by the sample and hold section of the detection circuit  300  and provided as an unloaded battery voltage input to the differential amplifier section of the circuit. 
     In operation  430 , the microprocessor  330  may provide a load to the battery  302  at the load input  306  of the circuit  300 . As a load is applied to the battery, the voltage provided by the loaded battery may be read at the inverting input to the second OPAMP  322  through the third resistor  324  in operation  440 . This value may be provided to the differential amplifier section of the circuit  300  as a loaded battery voltage. The differential amplifier may then calculate and amplify the difference between the loaded and unloaded voltages in operation  450 . As should be appreciated, the values of the resistors of the circuit  300  may be selected by the circuit designer to set the amplification of the difference as needed. The circuit  300  may then provide the amplified difference between the loaded and unloaded battery to the microprocessor  330  at the Vout  328  of the circuit  300  in operation  460 . This information may be digitized with an analog to digital converter  332  and used by the microprocessor  330  to determine if the battery is near the end of life as explained above. 
     In another embodiment, a reference voltage may be provided to the circuit  300  to represent the unloaded battery potential. For example, the FET device  308  and the capacitor  312  may be removed from the circuit  300  and replaced with a reference voltage, optionally provided by the microcontroller  350 . This reference voltage may provide a baseline voltage from which the difference in loaded and unloaded battery potential is calculated. Thus, the reference voltage may be a value that approximates the unloaded battery voltage. In this particular embodiment, the reference voltage may be provided directly to the differential amplifier section of the circuit  300 . A load may be placed on the battery by the microcontroller  350  in a similar manner as described above. When loaded, the battery voltage may be measured and provided to the differential amplifier as the loaded battery voltage so that the output of the circuit  300  would provide the amplified difference between the loaded battery voltage and the reference voltage provided. In this manner, the reference voltage substitutes as the unloaded battery voltage for the circuit  300 . 
       FIG. 5  depicts a second embodiment for an end of life battery detection circuit including matched diodes as a sampling switch. The circuit shown in  FIG. 5  is similar to the circuit described above with reference to  FIG. 3 . Thus, similar circuit components common to the circuits have similar numerical designations. For example, the capacitor ( 312 ,  512 ) of the circuits shown in  FIGS. 3 and 5  have a similar numerical designation ending in “ 12 .” 
     As mentioned, several components of the circuit  500  of  FIG. 5  are similar to the same as those discussed above with reference to  FIG. 3 . Thus, the circuit  500  includes a battery connection  502 , a first node  504 , a load  506 , a second node  510 , a capacitor  512 , a first OPAMP  514 , a second OPAMP  522 , four resistors ( 518 - 526 ) and a supply source  516  arranged in a similar manner as circuit  300 . Additionally, the circuit  500  of  FIG. 5  also includes a first diode  550 , a second diode  552  and a third OPAMP  554 , arranged as described in more detail below. 
     The anode of the first diode  550  is connected to the first node  504  of the circuit  500 . While shown as a Schottky diode, the first and second diodes may be any electrical device that has similar functionality as a Schottky diode. The cathode of the first diode  550  is electrically connected to the non-inverting input of a third OPAMP  554 . Also, similar to the first OPAMP  514 , the output of the third OPAMP  554  may be fed back to the inverting input of the OPAMP, with the negative power supply input connected to ground and the positive power supply input provided by the supply rails  516  of the device. 
     A second diode  552  may also be connected to the circuit  500 . The anode of the second diode  552  may be connected to the first node  504  while the cathode may be connected to a second node  510 . The other components of the circuit  500  are arranged in the same manner as described above with reference to  FIG. 3 . 
     To generate the amplified difference between the loaded and unloaded battery, the circuit  500  may operate in a manner as shown in  FIG. 6 . First, in operation  610 , the second diode  552  may conduct when no load is present on the battery such that the capacitor  512  begins to charge with the voltage of the unloaded battery  502 . In operation  620 , this value may be held by the sample and hold section of the detection circuit  500  and provided as a first input to the differential amplifier section of the circuit. Next, in operation  630 , a load may be provided to the circuit  500  by a microcontroller  530 . Once loaded, the second diode  552  may cease conducting while the first diode  550  continues to conduct, providing the loaded voltage to the third OPAMP  554  to be held in operation  640 . Both of the unloaded and loaded voltages are provided as inputs to the differential amplifier section of the circuit  500  from the respective OPAMPS. The differential amplifier may then measure and amplify the difference between the unloaded battery voltage and the loaded battery voltage in operation  650 . The differential amplifier may then, in operation  660 , provide the amplified difference between the loaded and unloaded battery to the microprocessor at the V out    528  of the circuit  500 . This information may be digitized with an analog to digital converter  532  and used by the microprocessor to determine if the battery is near the end of life. 
       FIG. 7  depicts a third embodiment for a end of life battery detection circuit including an active peak detector to hold the peak unloaded battery voltage. Again, the circuit shown in  FIG. 7  is similar to the circuits described above with reference to  FIGS. 3 and 5 . Thus, similar circuit components common to the above-described circuits have similar numerical designations. 
     The circuit  700  of  FIG. 7  includes many components similar to the components described above with reference to  FIGS. 3 and 5 . Thus, the circuit  700  includes a battery connection  702 , a first node  704 , a load  706 , a capacitor  712 , a first OPAMP  714 , a second OPAMP  722 , four resistors ( 718 - 726 ) and a supply source  716  arranged and functioning in a similar manner as in embodiments described above. Additionally, the circuit  700  of  FIG. 7  also includes a first diode  750 , a second diode  752 , a fifth resistor  754 , a sixth resistor  760  and a third OPAMP  756 , arranged as described in more detail below. 
     Beginning at the first node  704 , the non-inverting input to the third OPAMP  756  is connected to the first node. The output of the third OPAMP  756  is electrically connected to the anode of the first diode  750 , with the cathode of the first diode is connected to a second node  758 . Also connected to the second node is the anode of the second diode  752 , with the cathode connected to a third node  760 . The capacitor  712  of the circuit  700  is connected between the third node  760  and ground. The third node  760  is also connected to the inverting input to the third OPAMP  756 . 
     The non-inverting input to the first OPAMP  714  is similarly connected to the third node  760 . In addition, the output of the first OPAMP  714  is fed back to the inverting input of the first OPAMP. Connected between the inverting input of the first OPAMP  714  and the second node  758  is a fifth resistor  754 . 
     The circuit  700  of  FIG. 7  operates in a similar manner as the embodiment described in the flowchart of  FIG. 6 . Thus, the circuit  700  measures and holds the value of the unloaded battery at the output of the first OPAMP  714 . To acquire the unloaded battery voltage, the third OPAMP  756 , first diode  750 , second diode  752 , and the capacitor  712  operate as a active peak detector to hold the peak of the battery when it is unloaded. This peak value is provided to the differential amplifier of the circuit  700  as the output of the first OPAMP  714 , similar to the embodiments described above. Thus, when the battery is unloaded, the active peak detector section of the circuit  700  samples the peak voltage of the battery and holds that value, providing it to the differential amplifier. When a load is applied to the battery by a microcontroller (at the load input  706 ), the loaded battery voltage is provided to the differential amplifier through the third resistor  724 . The differential amplifier may then provide the amplified difference between the loaded and unloaded battery to the microprocessor at the Vout  728  of the circuit  700 . This information may be digitized with an analog to digital converter  732  and used by the microprocessor  730  to determine if the battery is near the end of life. 
     It should be noted that the flowcharts of  FIGS. 1 ,  4  and  6  are illustrative only. Alternative embodiments of the present invention may add operations, omit operations, or change the order of operations without affecting the spirit and scope of the present invention. 
     The foregoing merely illustrates certain principles and embodiments of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements and methods which, although not explicitly shown or described herein, embody the principles of the invention and are thus within the spirit and scope of the present invention. From the above description and drawings, it will be understood by those of ordinary skill in the art that the particular embodiments shown and described are for purposes of illustrations only and are not intended to limit the scope of the present invention. References to details of particular embodiments are not intended to limit the scope of the invention.

Metadata:
Filing Date: 20090930
Publication Date: 20130402
Grant Date: 20130402
Priority Date: 20090930
Inventors: STATON KENNETH L.
Assignee: APPLE INC
CPC Classifications: [{"code": "G01R31/386", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01R31/392", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R31/392", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R31/386", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 43127178