Control circuit and method for delivering power to heating element

Abstract

To provide a control circuit and a method for delivering power to heating elements.SOLUTION: In various embodiments, a control circuit is adapted to control the power supplied to a heating element by a battery. The control circuit can include a memory for storing known data and a circuit configured to control the delivery of the power from the battery to the heating element according to measured parameters, calculated parameters, and the known data.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control circuit and method for delivering power to a heating element. [Background technology]

[0002] Many electronic devices use batteries, such as lithium-ion batteries, to provide a primary power source to the electronic device. In some applications, such as electronic cigarettes (also called vaping devices, e-cigarettes, vape pens, and nicotine vaporizers), the battery powers a heating element used to heat a liquid to form vapor. Some conventional systems use open-loop heating methods that can result in the heating element reaching undesirable and / or dangerous temperatures. Alternatively, other conventional systems use closed-loop heating methods that require additional circuitry, which can increase the cost of the system, increase power losses, generate excess heat, and / or delay feedback of measured parameters (e.g., voltage, current). For optimal operation, it is desirable to provide a stable power supply to the heating element using a minimum of circuitry. Summary of the Invention

[0003] The present invention relates to a control circuit and method for delivering power to a heating element.

[0004] The technical problem solved by the present invention is that conventional systems using open-loop heating methods may result in the heating element reaching undesirable and / or dangerous temperatures, or conventional systems using closed-loop heating methods may require additional circuitry that may increase the cost of the system, increase power losses, generate excess heat, and / or delay the feedback of the measured parameters (e.g., voltage, current).

[0005] In various embodiments, the control circuitry is adapted to control power provided by the battery to the heating element. The control circuitry may include a memory for storing the known data and circuitry configured to control the delivery of power from the battery to the heating element according to the measured parameters, the calculated parameters, and the known data.

[0006] According to one aspect, a control circuit adapted to control a heating element powered by a battery includes a memory configured to store known battery data including a first profile and a second profile, a fuel gauge circuit in communication with the memory and the battery, the fuel gauge circuit configured to determine a resistance of the battery according to the first and second profiles, a logic circuit connected to the fuel gauge circuit, the logic circuit configured to calculate a first power value based on the determined resistance, and a signal generator circuit responsive to the logic circuit, the signal generator circuit configured to generate a control signal according to the calculated first power value, and the control circuit selectively connects the battery to the heating element according to the control signal.

[0007] In one embodiment of the control circuit, determining the resistance of the battery includes measuring an actual voltage of the battery, determining a capacity of the battery according to the measured actual voltage using a first profile, and determining the resistance of the battery according to the determined capacity using a second profile.

[0008] In one embodiment of the control circuit, the logic unit calculates the first power value further based on the first resistance value of the heating element at the start time.

[0009] In one embodiment of the control circuit, the memory further includes a third profile comprising a relationship between resistance of the heating element and time.

[0010] In one embodiment, the control circuit further includes a timer for measuring an elapsed operating time, the elapsed operating time being measured from a start time, and when the timer reaches a predetermined elapsed operating time, the logic unit calculates a new first power according to the second resistance value of the heating element and the third profile.

[0011] In one embodiment of the control circuit, the first profile includes a relationship between a battery voltage value and a battery capacity value, and the second profile includes a relationship between a battery resistance value and a battery capacity value.

[0012] In one embodiment of the control circuit, the control signal comprises a ratio of a predetermined target power to the calculated first power.

[0013] According to another aspect, a method of controlling delivery of power from a battery to a heating element includes measuring an actual voltage of the battery; determining a capacity of the battery according to the measured actual voltage and first known battery data, the first known battery data including a relationship between a voltage value and a capacity value; determining a resistance of the battery according to the determined capacity and second known battery data, the second known battery data including a relationship between a resistance value and a capacity value of the battery; calculating a first power according to the determined resistance of the battery and the resistance of the heating element; calculating a ratio between a predetermined target power and the calculated first power; and electrically connecting the battery to the heating element according to the calculated ratio.

[0014] In one operation of the above method, the resistance of the heating element is one of an initial resistance of the heating element when the heating element is new and the determined aged resistance.

[0015] In one operation, the method further includes measuring an elapsed operating time and determining an aged resistance value of the heating element, including utilizing the known heating element data and the elapsed operating time value.

[0016] The technical effect achieved by the present invention is to provide a stable power supply to a heating element using minimal circuitry for optimal operation. [Brief description of the drawings]

[0017] A more complete understanding of the present technology may be derived by reference to the detailed description when considered in conjunction with the following illustrative figures, in which like reference numbers refer to similar elements and steps throughout.

[0018] [Figure 1] 1 depicts a representative illustration of an electronic system having a heat generating element powered by a battery, in accordance with an exemplary embodiment of the present technique;

[0019] [Diagram 2] FIG. 1 is a block diagram of an electronic system in accordance with an exemplary embodiment of the present technology.

[0020] [Diagram 3] 1 is a graph illustrating a relationship between battery voltage values ​​and battery capacity values ​​in accordance with an exemplary embodiment of the present technology;

[0021] [Figure 4] 1 is a graph showing a relationship between a battery resistance value and a battery capacity value in accordance with an exemplary embodiment of the present technology;

[0022] [Figure 5A] 1 is a graph showing a first relationship between heater element resistance and time in accordance with the present technique;

[0023] [Figure 5B] 11 is a graph showing a second relationship between heater element resistance and time in accordance with the present technique.

[0024] [Figure 5C] 13 is a graph showing a third relationship between heater element resistance and time in accordance with the present technique.

[0025] [Figure 6] 13 is a flow chart for controlling the delivery of power from a battery to a heating element in accordance with an exemplary embodiment of the present technique;

[0026] [Figure 7] 11 is an alternative flow chart for controlling the delivery of power from a battery to a heating element, in accordance with an exemplary embodiment of the present technology;

[0027] [Figure 8] 13 is a graph showing the relationship between heater power and battery capacity value when the PWM ratio is 100%.

[0028] [Figure 9] 1 is a graph showing an example relationship between a PWM ratio used to supply constant power to a heater element and a battery capacity value in accordance with an example embodiment of the present technique;

[0029] [Figure 10] 10 is a graph showing heater power versus battery capacity value after adjusting the PWM ratio according to the PWM ratios shown in FIG. 9 in accordance with an embodiment of the present technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The present technology may be described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of components configured to perform specific functions and achieve various results. For example, the present technology may employ various heating elements, signal generators, voltage sensors, current sensors, coulomb counters, logic gates, memory devices, semiconductor devices such as transistors and capacitors, etc., which may perform various functions. In addition, the present technology may be implemented with any number of systems, and the systems described are merely exemplary applications for the technology. Furthermore, the present technology may employ any number of conventional techniques for measuring voltage, measuring current, calculating the capacity of the battery, performing various mathematical calculations, storing data, etc.

[0031] Methods and apparatus for power supply control circuitry according to various aspects of the present technology may operate with any suitable electronic system and / or device, such as a home appliance, a portable device, a battery-powered heating device, etc. Referring to FIG. 1, an exemplary system 100 includes a heating element 120 powered by a rechargeable battery 105 and a control circuit 110 for controlling the amount of power provided to the heating element 120. For example, the system 100 may include an electronic cigarette including a vapor cartridge 125 containing a liquid 130. In an exemplary embodiment, the system 100 may further include a sensor 115 for detecting when a user applies a draw (i.e., a puff) to the electronic cigarette, which activates the heating element 120. The system 100 may further include a light-emitting diode (LED) 135 to simulate a "burn" and / or provide a visual response to the draw.

[0032] The battery 105 provides power to the heating element 120 and / or other components within the system 100, such as the LEDs 135 and the control circuitry 110. The battery 105 may include a lithium ion battery. Alternatively, the battery 105 may include a nickel metal hydride battery, a nickel cadmium battery, or a lithium-based battery such as a lithium cobalt, lithium iron phosphate, lithium titanate, or lithium polymer battery.

[0033] The heating element 120 may include an electric heater, such as an infrared heater element, a photonic source, or an inductive heater element. The heating element 120 may be implemented as a heating wire or filament. The heating element 120 may include resistive materials, such as doped ceramics, electrically "conductive" ceramics (e.g., molybdenum disilicide, etc.), carbon, graphite, metals, metal alloys, and composite materials made from ceramic and / or metallic materials. Such composite materials may include doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum, and metals from the platinum group. Examples of suitable metal alloys include stainless steels, nickel-containing alloys, cobalt-containing alloys, chromium-containing alloys, aluminum-titanium-zirconium-containing alloys, hafnium-containing alloys, niobium-containing alloys, molybdenum-containing alloys, tantalum-containing alloys, tungsten-containing alloys, tin-containing alloys, gallium-containing alloys, manganese-containing alloys, gold-containing alloys, iron-containing alloys, and superalloys based on nickel, iron, cobalt, stainless steel, Timetal®, and iron-manganese-aluminum alloys. In composite materials, the electrical resistance material may optionally be embedded in, or encapsulated or coated with, an insulating material, or vice versa, depending on the kinetics of energy transfer and the desired external physicochemical properties.

[0034] The control circuit 110 controls and / or manages the function of the battery 105, the heating element 120, and the LEDs 135 according to various input signals, such as input signals from the sensor 115. The control circuit 110 may include an integrated circuit that includes various circuits and / or systems that work together to provide desired output and / or control signals.

[0035] According to an exemplary embodiment, control circuitry 110 is connected to battery 105 and may measure various battery characteristics such as voltage, current, temperature, etc.

[0036] 2, according to an exemplary embodiment, control circuitry 110 includes a fuel gauge circuit 205, a logic circuit 215, a memory 210, a signal generator circuit 220, and a timer 225 that work together to control or otherwise manage various functions of system 100, such as controlling power to heating element 120, battery management (e.g., charge / discharge cycles), etc. Control circuitry 110 may be formed as an integrated circuit on a single chip or may be integrated across multiple chips.

[0037] According to an exemplary embodiment, control circuitry 110 selectively connects battery 105 to heating element 120. For example, control circuitry 110 may include a switch 200 positioned between the terminals of battery 105 and heating element 120 that operates to electrically connect and disconnect battery 105 to heating element 120. Switch 200 may include any device suitable for providing a selective connection between two or more devices.

[0038] The switch 200 may include a transistor, such as a field effect transistor (FET), that uses an electric field to control the electrical behavior of the device. There are many different implementations of field effect transistors. Field effect transistors may be a desirable implementation because they generally exhibit very high input impedance at low frequencies. The conductivity between the drain and source terminals is controlled by an electric field within the device, which is generated by a voltage difference between the body and gate of the device.

[0039] Memory 210 stores various battery data. In an exemplary embodiment, memory 210 may include a first profile 230 that includes known data providing a relationship between battery voltage values ​​and capacity values, such as the data shown in the graph of FIG. 3. In general, battery voltages are generally higher at higher RSOC values ​​and lower at lower RSOC values. The specific data included in first profile 230 may be determined by testing battery 105 in an environment that simulates system 100 in which battery 105 is used. First profile 230 may be implemented as a look-up table or any other suitable storage device accessible by logic circuit 215 and / or fuel gauge circuit 205.

[0040] In an exemplary embodiment, memory 210 further includes second profile 230 including known data providing a relationship between battery resistance and capacitance values, such as the data illustrated in the graph of Figure 4. The specific data included in second profile 235 may be determined by testing battery 105 in an environment that simulates system 100 in which battery 105 is used. Second profile 230 may be implemented as a look-up table or any other suitable storage device accessible by logic circuit 215 and / or fuel gauge circuit 205.

[0041] The memory may further include a third profile 240 including known heater element data providing a relationship between heater element resistance and time, such as the data shown in the graphs of Figures 5A-5C. The specific data included in the third profile 240 may be determined by testing the heater element 120 in an environment that simulates the system 100 in which the heater element 120 is used. In general, when power is applied to the heater element 120, the heater element 120 has an initial resistance at time zero, and the heater element resistance may increase, decrease, or remain constant over time according to its material properties. The third profile 240 may be implemented as a look-up table or any other suitable storage device accessible by the logic circuit 215 and / or the fuel gauge circuit 205.

[0042] The memory 210 may be further configured to store a predetermined target power value "Power2." The predetermined target power value "Power2" may vary according to the specifications of a particular system implementation. For example, the predetermined target power value "Power2" may be based on various heating element specifications, such as a maximum power rating and a maximum current rating of the heating element 120, and various battery specifications, such as a battery type (e.g., Li-ion, NiCd, NiMH, etc.), a battery reference voltage, a battery nominal voltage, a battery charging current, etc.

[0043] The memory 210 may be implemented as a non-volatile memory, such as a random access memory (RAM), a read only memory (ROM), or a flash memory. A particular memory implementation may be selected according to the particular implementation of the system 100, as one type of memory may be more suitable for the particular implementation of the system 100.

[0044] Fuel gauge circuitry 205 may be configured to receive various inputs and monitor and / or measure various battery characteristics, such as voltage, current, battery capacity (which may also be expressed as a percentage of state of charge (SOC) or relative state of charge (RSOC)), battery operating mode (e.g., charge and discharge), state of health (SOH), etc. Fuel gauge circuitry 205 may also generate various types of control signals in response to the received input signals and / or battery characteristics, such as control signals for controlling charging and discharging. Fuel gauge circuitry 205 may include any number of suitable circuits and / or systems and may be implemented in any suitable manner, such as in the form of a large scale integrated (LSI) circuit.

[0045] According to an exemplary embodiment, the fuel gauge circuit 205 is configured to obtain relevant data from the first profile 230 and utilize the relevant data to determine the capacity (RSOC) of the battery 105. For example, the fuel gauge circuit 205 may first measure the actual voltage of the battery 105 using conventional voltage sensing methods and techniques. The fuel gauge circuit 205 may then determine the battery capacity according to the measured actual voltage and the first profile 230. For example, a measured actual voltage of 3.6V corresponds to an RSOC of 15%.

[0046] The fuel gauge circuit 205 may also be configured to determine the resistance of the battery 105. For example, the fuel gauge circuit 205 may determine the resistance using a previously determined battery capacity (RSOC) and the second profile 235. For example, an RSOC of 15% corresponds to a resistance value of 150 ohms. The fuel gauge circuit 205 may be configured to transmit the determined resistance value to the logic circuit 215.

[0047] Logic circuitry 215 may be configured to perform various calculations, extract data from memory 210, receive relevant data as it pertains to battery 105 and / or heating element 120, and / or provide various control signals. For example, logic circuitry 215 may be coupled to fuel gauge circuitry 205 and / or memory 210. According to an exemplary embodiment, logic circuitry 215 may be further coupled to signal generator circuitry 220 and provide a first control signal to signal generator circuitry 220. Logic circuitry 215 may include any suitable device and / or system and may be implemented through the use of hardware, logic gates, etc.

[0048] According to an exemplary embodiment, the logic circuit 215 is configured to calculate a maximum power value “Power1”, which is described as Power1=V2 / (R1+R2) (Equation 1), where V is the measured actual voltage of the battery 105, R1 is the determined resistance value of the battery 105, and R2 is the resistance value of the heating element 120.

[0049] The logic circuit 215 may be configured to obtain the resistance value R2 of the heating element 120 from the third profile 240. For example, the resistance value R2 of the heating element 120 may be a starting resistance (resistance value at time 0) or an operating resistance value (resistance value after time 0). Thus, the logic circuit 215 may select an appropriate resistance value based on the length of time the heating element 120 has been operating.

[0050] According to various embodiments, the logic circuit 215 may further calculate the battery current I according to the determined battery resistance R1 and the measured battery voltage (i.e., I=V / R). The logic circuit 215 may then verify the RSOC value by utilizing a fourth profile (not shown), e.g., stored in the memory 210, that describes the relationship between the battery current and the RSOC value.

[0051] The signal generator circuit 220 generates a second control signal for operating the switch 200. According to an exemplary embodiment, the signal generator circuit 220 may be implemented as a pulse width modulation circuit that generates a PWM signal having a square wave and a variable duty cycle. The pulse width modulation circuit may include conventional circuits. The duty cycle of the PWM signal is the ratio of a predetermined target power "Power2" value to a calculated maximum power "Power1" (i.e., PWM=Power2 / Power1 (Equation 2)). Thus, when the PWM signal is high, the switch 200 responds by closing (the switch is on), thereby connecting the battery 105 to the heating element 120. In contrast, when the PWM signal is low, the switch 200 responds by opening (the switch is off), thereby disconnecting the battery 105 from the heating element 120.

[0052] According to various embodiments, the control circuit 110 may further include a timer circuit 225 for tracking and measuring the time interval (period). For example, the timer circuit 225 may start measuring when the switch 200 is first closed (t=0) and send a timer signal to the logic circuit 215 when the timer circuit 225 reaches a predetermined timer value, such as every 100 ms. When the logic circuit 215 receives the timer signal, the logic circuit 215 recalculates the maximum power value "Power1" according to the new heating element resistance value corresponding to that particular timer value. The logic circuit 215 may obtain the new heating resistance value from the third profile 240.

[0053] 1 , 3 , 4 , and 6 , in an example operation, the control circuit 110 may first measure the actual voltage of the battery 105. The control circuit 110 may then use the measured actual voltage in conjunction with the first profile 230 to determine (600) the RSOC of the battery 105. For example, the fuel gauge circuit 205 may retrieve from the memory 210 an RSOC value that corresponds to the measured actual voltage.

[0054] Control circuit 110 may then determine (605) the battery resistance using the determined RSOC (from step 600) in conjunction with second profile 235. For example, fuel gauge circuit 205 may retrieve from memory 210 a resistance value that corresponds to the determined RSOC.

[0055] The control circuit 110 may then calculate 610 a maximum power “Power1” according to the measured actual voltage, the battery resistance R1, and the heating element resistance R2. For example, the logic circuit 215 may receive and / or obtain the measured actual voltage of the battery, the battery resistance R1, and the heating element resistance R2 from the fuel gauge circuit and / or memory 210.

[0056] The control circuit 110 may then calculate (615) a PWM signal, where the PWM signal is defined as the predetermined power divided by the maximum power (i.e., Power2 / Power1). For example, the signal generator circuit 220 may receive the calculated maximum power "Power1" from the logic circuit 215 and may retrieve the predetermined target power value "Power2" from the memory 210.

[0057] The control circuit 110 may then operate the switch 200 according to the PWM signal (620). For example, if the PWM signal is 50%, then for one duty cycle, the switch 200 is closed half the time and open the other half. Similarly, if the PWM signal is 30%, then for one duty cycle, the switch is closed 30% of the time and open 70% of the time.

[0058] This operation may be used when the resistive characteristics of the heater element 120 remain constant over time, such as shown in FIG. 5C.

[0059] 1, 3, 4, 5A, 5B, and 7, the control circuit 110 may first measure the actual voltage of the battery 105. The control circuit 110 may then use the measured actual voltage in conjunction with the first profile 230 to determine (700) the RSOC of the battery 105. For example, the fuel gauge circuit 205 may retrieve from the memory 210 an RSOC value that corresponds to the measured actual voltage.

[0060] Control circuit 110 may then determine (705) the battery resistance using the determined RSOC (from step 700) in conjunction with second profile 235. For example, fuel gauge circuit 205 may retrieve from memory 210 a resistance value that corresponds to the determined RSOC.

[0061] The control circuit 110 may then calculate 710 a maximum power “Power1” according to the measured actual voltage, the battery resistance R1, and the heating element resistance R2. For example, the logic circuit 215 may receive and / or obtain the measured actual voltage of the battery, the battery resistance R1, and the heating element resistance R2 from the fuel gauge circuit and / or memory 210.

[0062] The control circuit 110 may then calculate (715) a PWM signal, where the PWM signal is defined as the predetermined power divided by the maximum power (i.e., Power2 / Power1). For example, the signal generator circuit 220 may receive the calculated maximum power "Power1" from the logic circuit 215 and may retrieve the predetermined target power value "Power2" from the memory 210.

[0063] The control circuit 110 may then operate the switch 200 according to the PWM signal (720). For example, if the PWM signal is 50%, then for one duty cycle, the switch 200 is closed half the time and open the other half. Similarly, if the PWM signal is 30%, then for one duty cycle, the switch is closed 30% of the time and open 70% of the time.

[0064] According to this embodiment, the control circuit 110 may periodically adjust (725) the heating element resistance value R2 used to calculate the maximum power "Power1". After a predetermined period of time, such as 100 ms, the logic circuit 215 may obtain a new resistance value R2 corresponding to the time that has passed and calculate a new maximum power. Because the heating element resistance R2 increases over time, the new maximum power value will be less than the value calculated at time 0. The signal generator circuit 220 may then update the PWM ratio using the new maximum power value, and the signal generator circuit 220 operates the switch 200 accordingly.

[0065] This operation may be used when the resistance characteristics of the heater element 120 change (increase or decrease) over time, as shown in Figures 5A and 5B. Therefore, the heating element resistance value R2 may be adjusted periodically. For example, when the timer 225 reaches a predetermined elapsed time, the logic unit 215 recalculates the maximum power "Power1", and the variable "R2" in the above equation 1 is the updated heating element resistance value corresponding to the elapsed time. In contrast, when the heating element 120 exhibits stable characteristics, as shown in Figure 5C, the above equation 1 is calculated using the initial heating element resistance value, in other words, the variable "R2" is the initial heating element resistance value at time 0.

[0066] In conventional systems, the power supplied from the battery 105 to the heating element 120 is not stable across a range of battery capacity values ​​(e.g., as shown in FIG. 8). However, embodiments of the present technology adjust the PWM ratio during operation (e.g., as shown in FIG. 9), so that the battery 105 provides a stable supply of power to the heating element 120 (e.g., as shown in FIG. 10).

[0067] In the foregoing description, the technology has been described with reference to certain exemplary embodiments. The specific implementations shown and described are illustrative of the technology and its best mode, and are not intended to otherwise limit the scope of the technology in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the methods and systems may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent example functional relationships and / or steps between the various elements. Many alternative or additional functional relationships or physical connections may exist in a practical system.

[0068] The present technology has been described with reference to certain exemplary embodiments. However, various modifications and changes can be made without departing from the scope of the present technology. The description and drawings should be regarded as illustrative, not restrictive, and all such modifications are intended to be included within the scope of the present technology. Thus, the scope of the technology should be determined by the general embodiments described and their legal equivalents, and not merely by the specific examples described above. For example, the steps described in any method or process embodiment may be performed in any order, unless expressly stated otherwise, and are not limited to the explicit order presented in the specific examples. Furthermore, the components and / or elements described in any apparatus embodiment may be assembled or otherwise configured to operate in various permutations to produce substantially the same results as the present technology, and therefore are not limited to the specific configurations described in the specific examples.

[0069] Benefits, other advantages, and solutions to problems have been described above with respect to particular embodiments. However, any benefit, advantage, solution to a problem, or any element that may cause or make more pronounced any particular benefit, advantage, or solution should not be construed as a critical, required, or essential feature or component.

[0070] The terms "comprises," "comprising," or any variation thereof, are intended to refer to a non-exclusive inclusion, such that a process, method, article, composition, or apparatus that includes a list of elements includes not only the recited elements, but may also include other elements not expressly recited in, or inherent to, such process, method, article, composition, or apparatus. In addition to those not specifically recited, other combinations and / or modifications of the above-described structure, arrangement, application, proportions, elements, materials, or components used in the practice of the present technology may be changed or otherwise specifically adapted to particular environments, manufacturing specifications, design parameters, or other operating requirements without departing from the same general principles.

[0071] The present technology has been described above with reference to exemplary embodiments. However, changes and modifications may be made to the exemplary embodiments without departing from the scope of the technology. These and other changes or modifications are intended to be included within the scope of the technology, as expressed in the following claims.

[0072] According to one aspect, a control circuit adapted to control a heating element powered by a battery includes a memory configured to store known battery data including a first profile and a second profile, a fuel gauge circuit in communication with the memory and the battery, the fuel gauge circuit configured to determine a resistance of the battery according to the first and second profiles, a logic circuit connected to the fuel gauge circuit, the logic circuit configured to calculate a first power value based on the determined resistance, and a signal generator circuit responsive to the logic circuit, the signal generator circuit configured to generate a control signal according to the calculated first power value, and the control circuit selectively connects the battery to the heating element according to the control signal.

[0073] In one embodiment, determining the resistance of the battery includes measuring an actual voltage of the battery, determining a capacity of the battery according to the measured actual voltage using a first profile, and determining a resistance of the battery according to the determined capacity using a second profile.

[0074] In one embodiment, the logic unit calculates the first power further based on a first resistance value of the heating element at the start time.

[0075] In one embodiment, the memory further includes a third profile comprising a relationship between resistance of the heating element and time.

[0076] In one embodiment, the control circuitry further includes a timer for measuring an elapsed operating time, the elapsed operating time being measured from a start time.

[0077] In one embodiment, when the timer reaches a predetermined elapsed operating time, the logic unit calculates a new first power according to the second resistance value of the heating element and the third profile.

[0078] In one embodiment, the control circuit further includes a switch positioned between the battery and the heating element, the switch responsive to a control signal to electrically connect the battery to the heating element.

[0079] In one embodiment, the first profile includes a relationship between a battery voltage value and a battery capacity value, and the second profile includes a relationship between a battery resistance value and a battery capacity value.

[0080] In one embodiment, the control signal includes a ratio of a predetermined target power to the calculated first power.

[0081] According to another aspect, a method of controlling delivery of power from a battery to a heating element includes measuring an actual voltage of a battery, determining a capacity of the battery according to the measured actual voltage and first known battery data, determining a resistance of the battery according to the determined capacity and second known battery data, calculating a first power according to the determined resistance of the battery and the resistance of the heating element, calculating a ratio between a predetermined target power and the calculated first power, and electrically connecting the battery to the heating element according to the calculated ratio.

[0082] In one operation, the resistance of the heating element is the initial resistance of the heating element when the heating element is new.

[0083] In one operation, the first known battery data includes a relationship between a voltage value and a capacitance value, and the second known battery data includes a relationship between a resistance value and a capacitance value of the battery.

[0084] In one operation, the method further includes measuring an elapsed operating time and determining an aged resistance value of the heating element, including utilizing the known heating element data and the elapsed operating time value.

[0085] In one operation, the resistance of the heating element is the aged resistance determined.

[0086] According to yet another aspect, a system for powering a heating element includes a battery configured to supply power to the heating element and a control circuit configured to control delivery of power from the battery to the heating element in accordance with a control signal, the control signal being based on a calculated first power and a predetermined target power, the calculated first power being based on a resistance of the heating element and a resistance of the battery.

[0087] In one embodiment, the control circuit includes a memory configured to store a first profile including a relationship between a battery voltage value and a battery capacity value, and a second profile including a relationship between a battery resistance value and a battery capacity value.

[0088] In one embodiment, the control circuitry is further configured to measure an actual voltage of the battery and determine an actual capacity of the battery according to the measured actual voltage and the first profile.

[0089] In one embodiment, the control circuitry is further configured to determine a resistance of the battery according to the measured actual capacity of the battery and the second profile.

[0090] In one embodiment, the memory is further configured to store a third profile comprising a relationship between resistance of the heating element and time.

[0091] In one embodiment, the control signal is a ratio of a predetermined target power to the calculated first power.

Claims

1. A control circuit adapted to control a heating element powered by a battery, comprising: a memory configured to store known battery data including a first profile and a second profile; a fuel gauge circuit in communication with the memory and the battery, the fuel gauge circuit configured to determine a resistance of the battery according to the first and second profiles; a logic circuit coupled to the fuel gauge circuit, the logic circuit configured to calculate a first power value based on the determined resistance; and a signal generator circuit responsive to the logic circuit, the signal generator circuit configured to generate a control signal in accordance with the calculated first power value; the control circuit selectively connects the battery to the heating element in accordance with the control signal; Control circuit.

2. Determining the resistance of the battery Measuring an actual voltage of the battery; Utilizing the first profile to determine a capacity of the battery according to the measured actual voltage; and determining the resistance of the battery according to the determined capacity utilizing the second profile.

3. the logic unit further based on the first resistance value of the heating element at a start time:

2. The control circuit of claim 1, further comprising: a first power value calculating unit for calculating said first power value.

4. 4. The control circuit of claim 3, wherein the memory further comprises a third profile comprising a relationship between resistance of the heating element and time.

5. The method further comprises the steps of: the elapsed operating time is measured from the start time; When the timer reaches a predetermined elapsed operating time, the logic unit: a second resistance value of the heating element; and The control circuit of claim 4 , further comprising: a control circuit for calculating a new first power according to the third profile.

6. The first profile includes a relationship between a battery voltage value and a battery capacity value; 2. The control circuit of claim 1, wherein the second profile includes a relationship between a battery resistance value and the battery capacity value.

7. 2. The control circuit of claim 1, wherein the control signal comprises a ratio of a predetermined target power to the calculated first power.

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