Induction heating device with voltage converter

Abstract

1. An induction heating apparatus (1) for heating an aerosol-generating substrate using a susceptor, the induction heating apparatus comprising: a DC power supply (4) for supplying a DC supply voltage; a heater module (204) comprising an inductor (8) arranged to inductively couple to the susceptor; and a DC / AC voltage converter including or connected to the inductor and configured to convert the heater module input voltage to an AC voltage for driving the inductor; the induction heating apparatus further comprising a DC / DC voltage converter (206) configured to convert the DC supply voltage to the heater module input voltage.

Description

[Technical field]

[0001] The present disclosure relates to an induction heating device for heating an aerosol-generating substrate using a susceptor. In particular, but not by way of limitation, one or more embodiments of the present disclosure may relate to a handheld, electrically operated induction heating device that includes a heater module and a DC / DC voltage converter. The present disclosure also relates to an induction heating system that includes a plurality of induction heating devices and a DC / DC voltage converter. [Background technology]

[0002] A number of electrically operated aerosol generating devices have been proposed in the art, which have an electric heater for heating an aerosol-forming substrate, such as a tobacco plug. One purpose of such aerosol generating devices is to reduce known harmful smoke components of the type produced by the combustion and pyrolysis of tobacco in conventional cigarettes. Typically, the aerosol-generating substrate is provided as part of an aerosol-generating article that is inserted into a chamber or cavity in the aerosol generating device.

[0003] In some known devices, a resistive heating element, such as a heating blade, is inserted into or around the aerosol-forming substrate when the article is received within the aerosol generating device in order to heat the aerosol-forming substrate to a temperature capable of releasing volatile components capable of forming an aerosol.

[0004] Other aerosol-generating devices use inductive heating rather than resistive heating to heat the aerosol-forming substrate, and such devices are referred to herein as "inductive heating devices." Inductive heating devices typically include an inductor, such as an induction coil, that is arranged to be inductively coupled to a conductive susceptor, which is in thermal proximity to the aerosol-forming substrate. The inductor generates a varying magnetic field that generates eddy currents and hysteresis losses in the susceptor, heating the susceptor and thereby the aerosol-forming substrate.

[0005] To reduce manufacturing complexity, the heater for the aerosol generating device can be provided as part of a heater module to aid in module assembly. For induction heating devices, the heater module can include an inductor, or a connection to an inductor, and a drive circuit to power the inductor to generate the varying magnetic field. To achieve precise heating of the susceptor, the operating parameters of the heater module must be carefully controlled.

[0006] Aerosol generators also require a power source to operate, but due to the portable nature of aerosol generators, this typically involves some form of battery. Lithium-ion batteries are a popular choice of battery for aerosol generators due to their high energy density. However, there are many different types of lithium-ion batteries with different battery chemistries that affect the battery's characteristics, particularly the battery's output or supply voltage. For example, Lithium Iron Phosphate (LiFePO4 or LFP) batteries typically have an output voltage of 3.7 volts (maximum charge voltage) to 2.5 volts (minimum discharge voltage), with a typical output voltage of 3.2V to 3.0V for the operating range of LFP batteries. Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2 or NMC) batteries, on the other hand, usually have a typical output voltage of around 4.2 volts.

[0007] Typically, manufacturers design aerosol generating devices, and the control electronics of such devices, to operate with a specific supply voltage that depends on the type of battery chemistry selected. Certain components or circuits within the device may be very sensitive to the specified supply voltage and may not operate with other battery chemistries having different supply voltages. This can be problematic in modular systems where certain components or circuits of the aerosol generating device are incorporated into modules, as it may prevent a module designed for one battery chemistry from being used with an aerosol generating device having a different battery chemistry. Indeed, use of such modules with battery chemistries that they were not designed to use may result in undesirable operation.

[0008] It would be desirable to provide an induction heating device that can accommodate different battery chemistries.It would be desirable to provide an induction heating system that can accommodate different battery chemistries. Summary of the Invention

[0009] According to an embodiment of the present disclosure, an induction heating apparatus for heating an aerosol-generating substrate using a susceptor is provided. The induction heating apparatus may comprise a DC power supply for providing a DC supply voltage. The induction heating apparatus may comprise a heater module. The heater module may comprise an inductor arranged to inductively couple to the susceptor. The heater module may include the inductor or may include a DC / AC voltage converter connected to the inductor. The DC / AC converter may be configured to convert a heater module input voltage to an AC voltage for driving the inductor. The induction heating apparatus may further include a DC / DC voltage converter configured to convert the DC supply voltage to the heater module input voltage.

[0010] According to an embodiment of the present disclosure, there is provided an induction heating apparatus for heating an aerosol-generating substrate using a susceptor, the induction heating apparatus comprising: a DC power supply for providing a DC supply voltage; a heater module comprising an inductor arranged to inductively couple to the susceptor; and a DC / AC voltage converter comprising or connected to the inductor and configured to convert the heater module input voltage to an AC voltage for driving the inductor; the induction heating apparatus further comprising a DC / DC voltage converter configured to convert the DC supply voltage to the heater module input voltage.

[0011] Advantageously, the use of a DC / DC voltage converter allows power sources having different battery chemistries to be used with the heater module. The DC / DC voltage converter can convert the output or supply voltage provided by the power source to the input voltage required by the heater module to enable the heater module to operate correctly. This allows the same heater module to be used in a range of devices that may have different supply voltages. This reduces manufacturing complexity and eliminates the need to design a bespoke heater module for each specific battery used to power the heater module in each device.

[0012] Another benefit of using a DC / DC voltage converter is that it helps improve the operational stability of the heater module by providing a constant input voltage to the heater module. Several components and operating parameters of the heater module are voltage dependent, and the use of different battery chemistries can result in certain components of the heater module experiencing different voltages outside of their operating range. Additionally, as the battery is used and its charge gradually depletes, the battery's output or supply voltage may decrease. While the battery's discharge voltage remains relatively constant throughout its operating range, there can be variations that can affect voltage sensitive components and systems. Thus, a DC / DC voltage converter helps keep the voltage supplied to the heater module constant for consistent operation.

[0013] An additional benefit of using a DC / DC voltage converter is that it provides a constant output voltage that can be used as a voltage reference for use in measuring properties such as sensors, analog-to-digital converters, and power. For example, if the heating module input voltage is constant and known, then only the current needs to be determined to calculate the power the heater module is drawing.

[0014] As used herein, the term "inductive heating device" refers to an aerosol-generating device that uses inductive heating to heat an aerosol-forming substrate.

[0015] As used herein, the term "module" refers to a portion or subset of a larger device or electrical circuit. A module may include a collection of related components that are grouped or connected together and arranged for interconnection with other portions of the device or other modules. A module may be an independent part, such as a separate printed circuit board, or may be part of a larger component or circuit, e.g., a larger printed circuit board.

[0016] As used herein, the term "susceptor" refers to an element that includes a material capable of converting magnetic energy into heat. When the susceptor is placed in a varying magnetic field, such as that generated by an inductor, the susceptor heats up. Heating of the susceptor can be the result of at least one of hysteresis losses and eddy currents induced within the susceptor, depending on the electrical and magnetic properties of the susceptor material.

[0017] As used herein, the terms "distal" and "proximal" are used to describe the relative location of a component to a user. The term "distal" refers to a location further or away from the user, and the term "proximal" refers to a location closer to or toward the user.

[0018] The DC / DC voltage converter may be part of the heater module, which reduces the number of separate components in the induction heating device and also ensures that the heater module always receives the correct input voltage because the supply voltage connected to the heater module is converted to the correct and constant heater module input voltage. In other embodiments, the DC / DC voltage converter may be a separate module or unit.

[0019] The heater module input voltage can be in the range of 1 volt to 9 volts, preferably 2 volts to 6 volts, and more preferably 2.5 volts to 5.5 volts. The heater module input voltage can be 2.95 volts.

[0020] The heater module input voltage may be lower than the DC supply voltage. The DC / DC voltage converter may be a step-down voltage converter. For example, the DC / DC voltage converter may be a buck converter. The heater module input voltage may be greater than the DC supply voltage. The DC / DC voltage converter may be a step-up voltage converter. For example, the DC / DC voltage converter may be a boost converter. The DC / DC voltage converter may be a step-up or step-down voltage converter. For example, the DC / DC voltage converter may be a buck-boost converter.

[0021] The DC / DC voltage converter may be configured to accept a range of DC supply voltages. The DC / DC voltage converter may be configured to accept a DC supply voltage in the range of 1 volt to 9 volts, preferably 2 volts to 6 volts, more preferably 2.4 volts to 5.5 volts. The DC / DC voltage converter may be configured to output a constant heater module input voltage.

[0022] The DC / DC voltage converter may be a switch mode voltage converter. The output voltage of the DC / DC voltage converter may be related to a duty cycle of a switching signal generated or received by the DC / DC voltage converter. Using a switching signal having a duty cycle provides a simple way to control the output voltage from the DC / DC voltage converter and the heater module input voltage.

[0023] The DC / DC voltage converter may include a first switching element. The first switching element may be configured to be activated during a first portion of a switching signal. The first switching element may be a bipolar junction transistor (BJT). The first switching element may be a field effect transistor (FET), such as a metal oxide semiconductor field effect transistor (MOSFET) or a metal semiconductor field effect transistor (MESFET). Preferably, the first switching element is a MOSFET. A MOSFET has a low resistance during start-up or power-up, which helps reduce power losses.

[0024] The DC / DC voltage converter may include a second switching element. The second switching element may be configured to be activated during a second portion of the switching signal. The second switching element may be a diode. The second switching element may be a bipolar junction transistor (BJT). The second switching element may be a field effect transistor (FET), such as a metal oxide semiconductor field effect transistor (MOSFET) or a metal semiconductor field effect transistor (MESFET). Preferably, the second switching element is a MOSM.

[0025] When the first switching element is activated, the second switching element may be deactivated, and when the second switching element is activated, the first switching element may be deactivated, which helps prevent undesired short circuits between the DC supply voltage and electrical ground.

[0026] The DC / DC voltage converter may include a controller for generating the switching signals. The controller may be configured to generate a first switching signal for a first switching element. The controller may be configured to generate a second switching signal for a second switching element. The second switching signal may be an inversion of the first switching signal. The inversion of the second switching signal prevents the second switching element from activating or turning on at the same time as the first switching element. As discussed above, this helps to prevent a short circuit between the DC supply voltage and electrical ground. The controller may include logic for inverting the second switching signal.

[0027] The first and second switching elements may be arranged in a half-bridge arrangement, which allows each of the first and second switching elements to be alternately connected to the same load.

[0028] The DC / DC voltage converter may include a comparator configured to compare an output voltage of the DC / DC voltage converter to a reference voltage. The comparator may be configured to generate an output signal to adjust the duty cycle of the switching signal based on the comparison, thereby increasing or decreasing the duty cycle to correct the output voltage to a predetermined voltage, e.g., a heater module input voltage. The output signal from the comparator may be sent to a controller of the DC / DC voltage converter to adjust the duty cycle.

[0029] The controller, comparator, and first and second switching elements of the DC / DC voltage converter may be combined as an integrated circuit. This arrangement means that the only additional components required to implement the DC / DC voltage converter are an inductor and a capacitor. This helps to reduce the component count and the required printed circuit board area, and therefore the overall size of the induction heating device.

[0030] The induction heating device may be configured to determine the temperature of the susceptor by determining the resistance or conductance of the susceptor based on a measured current supplied to the heater module by a DC power supply or a DC / DC voltage converter. This has been found to be a convenient and accurate method for determining the temperature of the susceptor, which is otherwise difficult to measure because the susceptor is not part of the heater module circuit. Furthermore, because the susceptor is embedded in the aerosol-forming substrate and may be part of the aerosol-generating article rather than the induction heating device, it is difficult to place a temperature sensor close enough to the susceptor. Determining the resistance or conductance of the susceptor based on a measured current supplied to the heater module by a DC power supply or a DC / DC voltage converter eliminates the need for a dedicated temperature sensor.

[0031] The induction heating device may include a DC current sensor for measuring the current provided by the DC power supply or the DC / DC voltage converter. The current sensor may include a resistor. The resistor may be placed in series with the circuit for driving and powering the inductor.

[0032] The induction heating device may include a DC voltage sensor for measuring a DC voltage provided by a DC power source or a DC / DC voltage converter. The DC voltage sensor may include a voltage divider or a voltage divider. The voltage divider may include two resistors. Each of the two resistors may have an equal value.

[0033] The inductor may comprise a first inductor and the induction heating device may comprise a second inductor. The second inductor may be disposed at an input to a drive circuit for the first inductor. The second inductor may be connected in series with the transistor. The second inductor may include a radio frequency choke.

[0034] The induction heating device may be configured to interrupt or turn off generation of the AC voltage when the determined temperature of the susceptor exceeds or equals a predetermined threshold. The induction heating device may be configured to activate or turn on generation of the AC voltage when the determined temperature of the susceptor is below a predetermined threshold. This provides a simple on / off controller for controlling the temperature of the susceptor.

[0035] The DC power source is configured to provide a DC supply voltage and a DC current. The DC power source may be any suitable DC power source. For example, the DC power source may be a single-use battery or a rechargeable battery. In some embodiments, the DC power source may include a lithium-ion battery. For example, the DC power source may include a lithium polymer battery, a lithium iron phosphate (LiFePO4) battery, a lithium manganese oxide (LiMn2O4 or Li2MnO3) battery, a lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC) battery, or a lithium titanate oxide (LTO) battery. In other embodiments, the DC power source may include a nickel metal hydride battery or a nickel cadmium battery. In some embodiments, the DC power source may include one or more capacitors, supercapacitors, or hybrid capacitors. The DC power source may include one or more lithium-ion hybrid capacitors.

[0036] The DC power source may have a capacity that allows for storage of sufficient energy for one or more user actions. For example, the power source may have a capacity sufficient to allow continuous heating of the aerosol-forming substrate for approximately six minutes, or a multiple of six minutes, corresponding to the typical time it takes to smoke one conventional cigarette. In another embodiment, the power source may have a capacity sufficient to allow a predetermined number of puffs or discontinuous activations of the induction heating device. In another embodiment, the power source may have a capacity sufficient to allow a predetermined number of uses or discontinuous activations of the device.

[0037] The DC supply voltage may be in the range of about 1 volt to about 9 volts, preferably about 2 volts to about 6 volts, and more preferably about 2.4 volts to about 5.5 volts. The DC supply voltage may be about 3.2 volts or about 3.6 volts or about 4.2 volts. In one embodiment, the DC power source has a DC supply voltage in the range of about 2.5 volts to about 4.5 volts, and a DC supply current in the range of about 1 ampere to about 10 amperes (corresponding to a DC power supply in the range of about 2.5 watts to about 45 watts).

[0038] The induction heating device may include a driving circuit for driving the inductor or the DC / AC voltage converter. The driving circuit may include a transistor. The driving circuit may be configured to receive a switching signal and drive the DC / AC voltage converter based on the switching signal.

[0039] The DC / AC voltage converter may include an inductor, which helps reduce the number of components required for the heater module.

[0040] The DC / AC converter may be configured to operate at high frequencies. As used herein, the term "high frequency" is used to describe frequencies in the ranges of about 1 megahertz (MHz) to about 30 megahertz (MHz), about 1 megahertz (MHz) to about 10 MHz (including the range of about 1 MHz to about 10 MHz), and about 5 megahertz (MHz) to about 7 megahertz (MHz) (including the range of about 5 MHz to about 7 MHz).

[0041] The DC / AC voltage converter may include an inductor-capacitor (LC) load network. The LC load network may be configured to operate with a low ohmic load. The LC load network may include an inductor and a capacitor connected in series with the inductor. The LC load network may include a shunt capacitor. The capacitor may be tuned or configured to reduce the ohmic resistance of the inductor. The series connected capacitor may include multiple capacitors. The shunt capacitor may include multiple capacitors.

[0042] The DC / AC voltage converter may include a resonator including an inductor and a series capacitor. The resonator may act as a bandpass filter that allows only a predetermined range of frequencies to pass through the DC / AC voltage converter. The predetermined range of frequencies may include the frequency of a switching signal provided to a drive circuit of the induction heating device.

[0043] The heater module may include a power amplifier for powering the inductor. The power amplifier may include a Class E power amplifier. Class E power amplifiers have very high efficiency compared to other classes of power amplifiers and require only a single switching element or transistor.

[0044] The inductor may include a coil. The coil may be a spirally wound cylindrical inductor coil. In some embodiments, the inductor coil may have an elliptical shape and may be approximately 0.15 cm. 3 ~approx. 1.10cm 3 For example, the inner diameter of the helically wound cylindrical inductor coil may be about 5 mm to about 10 mm, or about 7 mm, and the length of the helically wound cylindrical inductor coil may be about 8 mm to about 14 mm. The diameter or thickness of the wire of the inductor coil may be about 0.5 mm to about 1 mm depending on whether a circular cross-section coil wire or a flat rectangular cross-section coil wire is used. The inductor coil may be positioned on or adjacent to an interior surface of a cavity of the induction heating device for receiving the aerosol-generating article. The coil may surround the cavity. The inductor may include one coil or two or more coils.

[0045] The induction heating device may include a susceptor. The susceptor may include any suitable material. The susceptor may be formed of any material that can be inductively heated to a temperature sufficient to release the volatile compound from the aerosol-forming substrate. A preferred susceptor may be heated to a temperature greater than about 250 degrees Celsius. A preferred susceptor may be formed of an electrically conductive material. Suitable materials for the susceptor include graphite, molybdenum, silicon carbide, stainless steel, niobium, aluminum, nickel, nickel-containing compounds, titanium, and composites of metallic materials. A preferred susceptor includes metal or carbon. Some preferred susceptors include ferromagnetic materials, such as, for example, ferritic iron, ferromagnetic alloys, such as ferromagnetic steel or stainless steel, ferromagnetic particles, and ferrites. Some preferred susceptors are made of ferromagnetic materials. A suitable susceptor may include aluminum. A suitable susceptor may be made of aluminum. The susceptor may include at least about 5 percent, at least about 20 percent, at least about 50 percent, or at least about 90 percent of a ferromagnetic or paramagnetic material.

[0046] The susceptor of the induction heating device may have any suitable shape. For example, the susceptor may be elongated. The susceptor may have any suitable cross-section. For example, the susceptor may have a circular, oval, square, rectangular, triangular, or other polygonal cross-section. The susceptor may be tubular.

[0047] In some preferred embodiments, the susceptor may include a susceptor layer provided on a support. Placing the susceptor in a fluctuating magnetic field induces eddy currents adjacent to the susceptor surface, resulting in an effect called the skin effect. Thus, the susceptor can be formed from a relatively thin layer of susceptor material while ensuring that the susceptor is effectively heated in the presence of the fluctuating magnetic field. Making the susceptor from a support and a relatively thin susceptor layer can facilitate the manufacture of aerosol-generating articles that are simple, inexpensive, and robust.

[0048] When the susceptor is a tubular susceptor, the tubular susceptor may at least partially define a cavity for receiving the aerosol-generating article or the aerosol-forming substrate. When the susceptor comprises a support, the support may be a tubular support and the susceptor layer may be provided on an inner surface of the tubular support. By providing the susceptor layer on the inner surface of the support, the susceptor layer may be positioned adjacent to the aerosol-generating article or the aerosol-forming substrate within the cavity for receiving the aerosol-generating article or the aerosol-forming substrate, improving heat transfer between the susceptor layer and the aerosol-forming substrate.

[0049] The support may be formed from a material that is not susceptible to inductive heating, which may advantageously reduce heating of the surface of the susceptor that is not in contact with the aerosol-forming substrate, where the surface of the support forms the surface of the susceptor that is not in contact with the aerosol-forming substrate.

[0050] The support may comprise an electrically insulating material. As used herein, "electrically insulating" means having a thermal conductivity of at least 1×10 at 20 degrees Celsius. 4 Refers to a material that has an electrical resistivity in ohmmeters (Ωm).

[0051] The support may be formed from a thermally insulating material to provide an insulating barrier between the susceptor layer and other components of the induction heater assembly, such as the inductor coil that surrounds the susceptor, which may advantageously reduce heat transfer between the susceptor and other components of the induction heating device.

[0052] Insulating materials also have a thermal conductivity of approximately 0.01 square centimeters per second (cm) when measured using the laser flash method. 2 / s) or less. Providing a support with such a thermal diffusivity may result in a support with high thermal inertia, which may reduce heat transfer between the susceptor layer and the support and reduce fluctuations in temperature of the support.

[0053] The susceptor may have any suitable dimensions. The susceptor may have a length of about 5 millimeters to about 15 millimeters, for example, about 6 millimeters to about 12 millimeters, or about 8 millimeters to about 10 millimeters. The susceptor may have a width of about 1 millimeter to about 8 millimeters, for example, about 3 millimeters to about 5 millimeters. The susceptor may have a thickness of about 0.01 millimeters to about 2 millimeters. When the susceptor has a constant cross-section, for example a circular cross-section, the susceptor may have a preferred width or diameter of about 1 millimeter to about 5 millimeters.

[0054] The induction heating device may include at least one external heating element. The at least one external heating element may comprise a susceptor. As used herein, the term "external heating element" refers to a heating element configured to heat an outer surface of the aerosol-forming article or substrate. The at least one external heating element may at least partially surround the recess for receiving the aerosol-generating article or substrate.

[0055] The induction heating device may comprise at least one internal heating element. The internal heating element may comprise a susceptor. As used herein, the term "internal heating element" refers to a heating element configured to be inserted into the aerosol-forming substrate. The internal heating element may be in the form of a blade, a pin, and a cone. The at least one internal heating element may extend into a recess for receiving the aerosol-generating article or the aerosol-forming substrate.

[0056] In some embodiments, the induction heating device comprises at least one internal heating element and at least one external heating element.

[0057] The induction heating device may include one or more of the susceptors described above.

[0058] The induction heating device may comprise a device housing. The device housing may at least partially define a cavity for receiving the aerosol-generating article or the aerosol-forming substrate. The cavity for receiving the aerosol-generating article or the aerosol-forming substrate is preferably at a proximal end of the device.

[0059] The device housing may be elongated. The device housing is preferably cylindrical in shape. The device housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics, or composites containing one or more of these materials, or thermoplastics suitable for food or pharmaceutical applications, such as polypropylene, polyetheretherketone (PEEK), and polyethylene. Preferably, the material is light and not brittle.

[0060] The induction heating device is preferably portable. The induction heating device may have a size comparable to a conventional cigar or cigarette. The induction heating device may have an overall length of about 30 millimeters to about 150 millimeters. The induction heating device may have an outer diameter of about 5 millimeters to about 30 millimeters. The induction heating device may be a handheld device. In other words, the induction heating device may be sized and shaped to be held in a user's hand.

[0061] The aerosol generating device may comprise a control circuit or controller connected to the at least one inductor coil and a power source. The control circuit may be configured to control the supply of power from the power source to the at least one inductor coil. The control circuit may comprise a microprocessor, which may be a programmable microprocessor, a microcontroller, or an application specific integrated circuit chip (ASIC) or other electronic circuit capable of providing control. The control circuit may comprise further electronic components. The control circuit may be configured to regulate the supply of current to the at least one inductor coil. The current may be supplied to the at least one inductor coil continuously after activation of the aerosol generating device, or may be supplied intermittently (such as after every puff).

[0062] The control circuitry may include a first microcontroller and the heater module may include a second microcontroller. The second microcontroller may be part of the heater module and may be dedicated to controlling the power supply to the heater module, in particular the inductor. The second microcontroller may be connected to the first microcontroller 202. The second microcontroller may control the power supply to the inductor in response to a signal received from the first microcontroller. The advantage of a heater module having its own microcontroller is that it can be programmed with its own firmware for controlling the heating process and does not need to include firmware related to heating in other components such as the first microcontroller, which helps make the heater module reusable in different devices. This allows the heater module to be a standalone unit or module that can be incorporated into a variety of different devices.

[0063] The induction heating device may include a user interface for activating the device, e.g., a button to initiate heating of the aerosol-generating article. The induction heating device may include a display that indicates the status of the device or the aerosol-forming substrate. The induction heating device may include a sensor for detecting when a user has puffed on the aerosol-generating article.

[0064] The induction heating device of the present disclosure is configured to heat an aerosol-forming substrate. As used herein, the term "aerosol-forming substrate" relates to a substrate capable of releasing volatile compounds capable of forming an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate.

[0065] The aerosol-forming substrate may comprise nicotine. The nicotine-containing aerosol-forming substrate may be a nicotine salt matrix.

[0066] The aerosol-forming substrate may be a liquid. The aerosol-forming substrate may comprise a solid component and a liquid component. The aerosol-forming substrate is preferably a solid.

[0067] The aerosol-forming substrate may comprise a plant-derived material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material comprising volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. The aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may comprise a homogenised plant-derived material. The aerosol-forming substrate may comprise a homogenised tobacco material. The homogenised tobacco material may be formed by agglomerating particulate tobacco. In a particularly preferred embodiment, the aerosol-forming substrate comprises an assembly of crimped sheets of homogenised tobacco material. As used herein, the term "crimped sheet" means a sheet having a plurality of substantially parallel ridges or corrugations.

[0068] The aerosol-forming substrate may include at least one aerosol former. The aerosol former is any suitable known compound or mixture of compounds that facilitates the formation of a dense, stable aerosol during use and is substantially resistant to thermal decomposition at the operating temperature of the system. Suitable aerosol formers are known in the art and include, but are not limited to, polyhydric alcohols (such as triethylene glycol, 1,3-butanediol, glycerin, etc.), esters of polyhydric alcohols (such as glycerol monoacetate, diacetate, or triacetate, etc.), and aliphatic esters of mono-, di-, or polycarboxylic acids (such as dimethyl dodecanedioate, dimethyl tetradecanedioate, etc.). A preferred aerosol former may include a polyhydric alcohol or mixtures thereof (such as triethylene glycol, 1,3-butanediol, etc.). Preferably, the aerosol former is glycerin. When present, the homogenized tobacco material may have an aerosol former content of 5 weight percent or more on a dry weight basis (e.g., from about 5 weight percent to about 30 weight percent on a dry weight basis). The aerosol-forming substrate may contain other additives and ingredients, such as flavourants.

[0069] The aerosol-forming substrate may be part of an aerosol-generating article. As used herein, the term "aerosol-generating article" refers to an article that includes an aerosol-forming substrate that releases a volatile compound capable of forming an aerosol when heated in an induction heating device. The aerosol-generating article is separate from and configured to be combined with an induction heating device for heating the aerosol-generating article.

[0070] The aerosol-generating article may be in the form of a rod that includes two ends, an oral end (i.e., the proximal end, through which the aerosol exits the aerosol-generating article and is delivered to the user) and a distal end. In use, a user may suck on the oral end to inhale the aerosol generated by the aerosol-generating article. The oral end is downstream of the distal end. The distal end may also be referred to as the upstream end, and is upstream of the oral end.

[0071] The terms "upstream" and "downstream" as used herein are used to describe the relative position of an element or portion of an element of an aerosol-generating article with respect to the direction in which a user draws on the aerosol-generating article during their use.

[0072] The aerosol-generating article may have any suitable shape. The aerosol-generating article may be substantially cylindrical in shape. The aerosol-generating article may be substantially elongated.

[0073] In some preferred embodiments, the aerosol-generating article may have an overall length of about 30 millimeters to about 100 millimeters. In some embodiments, the aerosol-generating article has an overall length of about 45 millimeters. The aerosol-generating article may have an outer diameter of about 5 millimeters to about 12 millimeters. In some embodiments, the aerosol-generating article may have an outer diameter of about 7.2 millimeters.

[0074] The aerosol-forming substrate may be provided as an aerosol-generation segment containing the aerosol-forming substrate. The aerosol-generation segment may have a length of about 7 millimeters to about 15 millimeters. In some embodiments, the aerosol-generation segment may have a length of about 10 millimeters or about 12 millimeters.

[0075] The aerosol-generation segment preferably has an outer diameter approximately equal to the outer diameter of the aerosol-generating article. The outer diameter of the aerosol-generation segment may be from about 5 millimeters to about 12 millimeters. In one embodiment, the aerosol-generation segment may have an outer diameter of about 7.2 millimeters.

[0076] The aerosol-generating article may comprise a susceptor. The susceptor may be disposed in thermal proximity to the aerosol-forming substrate. Thus, as the temperature of the susceptor increases, the aerosol-forming substrate is heated and an aerosol is formed. The susceptor may be arranged in direct physical contact or in intimate contact with the aerosol-forming substrate, for example within the aerosol-forming substrate.

[0077] The susceptor may comprise any suitable material. The susceptor may be formed from any material that can be inductively heated to a temperature sufficient to release the volatile compound from the aerosol-forming substrate. A preferred susceptor may be heated to a temperature greater than about 250 degrees Celsius. A preferred susceptor may be formed from an electrically conductive material. Suitable materials for the susceptor include graphite, molybdenum, silicon carbide, stainless steel, niobium, aluminum, nickel, nickel-containing compounds, titanium, and composites of metallic materials. A preferred susceptor comprises a metal or carbon. Some preferred susceptors include ferromagnetic materials, such as, for example, ferritic iron, ferromagnetic alloys such as ferromagnetic steel or stainless steel, ferromagnetic particles, and ferrites. Some preferred susceptors are made of ferromagnetic materials. A preferred susceptor may comprise aluminum. A preferred susceptor may be made of aluminum. A susceptor may comprise at least about 5 percent, at least about 20 percent, at least about 50 percent, or at least about 90 percent of ferromagnetic or paramagnetic material.

[0078] The susceptor may be in the form of a pin, rod, or blade. The length of the susceptor may be about 5 mm to about 15 mm, about 6 mm to about 12 mm, or about 8 mm to about 10 mm. The width of the susceptor may be about 1 mm to 6 mm, and the thickness may be about 10 micrometers to about 500 micrometers, or about 10 to about 100 micrometers. If the susceptor has a constant cross-section (e.g., a circular cross-section), the width or diameter may be about 1 mm to 5 mm.

[0079] The susceptor may have a length dimension that is greater than its width dimension or its thickness dimension, e.g., greater than twice its width dimension or its thickness dimension. Thus, the susceptor may be described as an elongated susceptor. The susceptor may be substantially longitudinally aligned within the rod. This means that the length dimension of the elongated susceptor is aligned approximately parallel to the longitudinal axis of the rod, e.g., within ±10 degrees of parallel to the longitudinal axis of the rod. The elongated susceptor element may be positioned at a radially central location within the rod, or may extend along the longitudinal axis of the rod.

[0080] In some embodiments, the aerosol-generating article may comprise a single susceptor. In other embodiments, the aerosol-generating article may comprise two or more susceptors. The aerosol-generating article may comprise two or more elongated susceptors. In this way, heating may be achieved effectively at different portions of the aerosol-forming substrate.

[0081] In some preferred embodiments, the susceptor comprises a first susceptor material and a second susceptor material. The first susceptor material is disposed in thermal proximity to the second susceptor material. The first susceptor material may be disposed in intimate physical contact with the second susceptor material.

[0082] The aerosol-generating article may include a mouthpiece filter. The mouthpiece filter may be located at a proximal end of the aerosol-generating article. The mouthpiece filter plug may be a cellulose acetate filter plug. In some embodiments, the mouthpiece filter may have a length of about 5 millimeters to about 10 millimeters. In some preferred embodiments, the filter plug may have a length of about 7 millimeters.

[0083] The aerosol-generating article may comprise one or more hollow tubes.The aerosol-generating article may comprise two hollow tubes.The hollow tubes may be made from cellulose acetate.

[0084] The aerosol-generating article may include an end plug, which may be located at a distal end of the aerosol-generating article, which serves to prevent a user from contacting the heated susceptor at any time, such as after use.

[0085] The aerosol-generating article may include an outer wrapper. The outer wrapper may be formed from paper. The outer wrapper may be gas permeable in the aerosol-generation segment. This may improve the characteristics of the aerosol generated from the aerosol-forming substrate.

[0086] According to an embodiment of the present disclosure, an induction heating system is provided that includes a first induction heating device. The first induction heating device may include a first DC power supply for providing a first DC supply voltage. The first induction heating device may include a first heater module. The first heater module may include an inductor for providing induction heating. The first heater module may have a first heater module input voltage. The first heater module input voltage may be substantially equal to the first DC supply voltage. The induction heating system may include a second induction heating device. The second induction heating device may include a second DC power supply for providing a second DC supply voltage. The second DC power supply may be different from the first DC supply voltage. The second induction heating device may include a second heater module. The second heater module may include an inductor for providing induction heating. The second heater module may have a first heater module input voltage. The second induction heating device may include a DC / DC voltage converter for converting the second DC supply voltage to the first heater module input voltage.

[0087] According to an embodiment of the present disclosure, there is provided an induction heating system comprising: a first induction heating device comprising: a first DC power source for providing a first DC supply voltage; a first heater module including an inductor for providing induction heating, the first heater module having a first heater module input voltage substantially equal to the first DC supply voltage; a second induction heating device comprising: a second DC power source for providing a second DC supply voltage different from the first DC supply voltage; a second heater module including an inductor for providing induction heating, the second heater module having the first heater module input voltage; and a DC / DC voltage converter for converting the second DC supply voltage to the first heater module input voltage.

[0088] The first heater module input voltage may be less than the second DC supply voltage. The DC / DC voltage converter may be a step-down voltage converter. The DC / DC voltage converter may be a buck converter. The first heater module input voltage may be greater than the second DC supply voltage. The DC / DC voltage converter may be a step-up voltage converter. The DC / DC voltage converter may be a boost converter. The DC / DC voltage converter may be a step-up or step-down voltage converter. The DC / DC voltage converter may be a buck-boost converter.

[0089] The first and second induction heating devices of the induction heating system may include any of the induction heating devices and heater modules described above.

[0090] Features described with respect to one of the above embodiments may equally be applied to other embodiments of the present disclosure.

[0091] The invention is defined in the claims. However, below is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of any other example, embodiment, or aspect described herein.

[0092] Example 1: 1. An induction heating apparatus for heating an aerosol-generating substrate using a susceptor, the induction heating apparatus comprising: a DC power supply for providing a DC supply voltage; and a heater module comprising an inductor arranged to inductively couple to the susceptor, the heater module having a heater module input voltage, the induction heating apparatus further comprising a DC / DC voltage converter configured to convert the DC supply voltage to the heater module input voltage. Example 2: The induction heating device of embodiment Ex1, wherein the heater module includes an inductor or is connected to the inductor and further comprises a DC / AC voltage converter configured to convert the heater module input voltage into an AC voltage for driving the inductor. Example 3: The induction heating device according to embodiment Ex1 or 2, wherein the DC / DC voltage converter is part of the heater module. Example 4: The induction heating apparatus of any of embodiments Ex1 to Ex3, wherein the heater module input voltage is less than the DC supply voltage and the DC / DC voltage converter is a step-down voltage converter. Example 5: The induction heating apparatus of any of embodiments Ex1-Ex4, wherein the DC / DC voltage converter is configured to accept a range of DC supply voltages and output a constant heater module input voltage. Example 6: The induction heating device according to any of embodiments Ex1 to Ex5, wherein the output voltage of the DC / DC voltage converter is related to the duty cycle of a switching signal generated or received by the DC / DC voltage converter. Example 7: The induction heating apparatus according to any of embodiments Ex1 to Ex6, wherein the DC / DC voltage converter comprises a first switching element configured to be activated during a first portion of a switching signal. Example 8: The induction heating apparatus of embodiment Ex7, wherein the DC / DC voltage converter includes a second switching element configured to be activated during a second portion of the switching signal. Example 9: An induction heating device according to embodiment Ex8, wherein when the first switching element is activated, the second switching element is deactivated, and when the second switching element is activated, the first switching element is deactivated. Example 10: The induction heating apparatus of embodiment Ex8 or Ex9, wherein the first and second switching elements are arranged in a half-bridge arrangement. Example 11: The induction heating apparatus of any of embodiments Ex1 to Ex10, wherein the DC / DC voltage converter includes a comparator configured to compare an output voltage of the DC / DC voltage converter with a reference voltage and generate an output signal for adjusting a duty cycle of the switching signal based on the comparison. Example 12: The induction heating apparatus according to any of embodiments Ex8 to Ex11, wherein the DC / DC voltage converter includes a converter driver for driving the first and second switching elements based on a switching signal. Example 13: The induction heating apparatus of any of embodiments Ex1 to Ex12, wherein the induction heating apparatus is configured to determine the temperature of the susceptor by determining a resistance or conductance of the susceptor based on a measured current supplied to the heater module by a DC power supply or a DC / DC voltage converter. Example 14: The induction heating apparatus of embodiment Ex13, further comprising a DC current sensor for measuring the current supplied by the DC power supply. Example 15: The induction heating apparatus of embodiment Ex14, wherein the DC current sensor comprises a resistor. Example 16: The induction heating apparatus of embodiment Ex13 or Ex14, further comprising a DC voltage sensor for measuring a DC voltage of the DC power source. Example 17: The induction heating apparatus of any one of embodiments Ex13 to Ex16, wherein the DC voltage sensor comprises a voltage divider. Example 18: The induction heating apparatus of any of embodiments Ex1-Ex17, wherein the DC / AC voltage converter includes an LC load network configured to operate with a low ohmic load. Example 19: The induction heating apparatus of embodiment Ex18, wherein the LC load network includes an inductor and a capacitor connected in series with the inductor. Example 20: The induction heating apparatus of embodiment Ex18 or Ex19, wherein the LC load network includes a shunt capacitor. Example 21: The induction heating apparatus of embodiment Ex19 or Ex20, wherein one or more of the series capacitor or the shunt capacitor is adjusted or configured to reduce the ohmic resistance of the inductor. Example 22: The induction heating apparatus of any of embodiments Ex19 to Ex21, wherein the series capacitor includes multiple capacitors. Example 23: The induction heating apparatus of any of embodiments Ex20 to Ex22, wherein the shunt capacitor comprises a plurality of capacitors. Example 24: The induction heating apparatus of any of embodiments Ex19 to Ex23, wherein the inductor and the series capacitor form a resonator that acts as a bandpass filter to allow only a predetermined range of frequencies to pass through the DC / AC voltage converter. Example 25: The induction heating apparatus of embodiment Ex24, wherein the predetermined range of frequencies includes a frequency of a switching signal provided to the DC / AC voltage converter. Example 26: The induction heating apparatus of any of embodiments Ex13 to Ex25, wherein the induction heating apparatus is configured to interrupt generation of the AC voltage when the determined temperature of the susceptor exceeds or is equal to a predetermined threshold. Example 27: 1. An induction heating system comprising: a first induction heating apparatus comprising a first DC power source for providing a first DC supply voltage and a first heater module including an inductor for providing induction heating, the first heater module having a first heater module input voltage substantially equal to the first DC supply voltage; a second DC power source for providing a second DC supply voltage different from the first DC supply voltage; a second heater module including an inductor for providing induction heating, the heater module having the first heater module input voltage; and a DC / DC voltage converter for converting the second DC supply voltage to the first heater module input voltage. Example 28: The system of embodiment Ex27, wherein the first heater module input voltage is less than the second DC supply voltage and the DC / DC voltage converter is a step-down voltage converter.

[0093] The embodiments will now be further described with reference to the figures. [Brief description of the drawings]

[0094] [Figure 1] FIG. 1 is a schematic longitudinal cross-sectional view of an induction heating device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic longitudinal cross-sectional view of an aerosol-generating article for use with the induction heating apparatus of FIG. [Diagram 3] 3 is a schematic longitudinal cross-sectional view showing the aerosol-generating article of FIG. 2 received in the induction heating apparatus of FIG. [Figure 4] FIG. 4 is a schematic block diagram of a control circuit for an induction heating device according to an embodiment of the present disclosure. [Diagram 5] FIG. 5 is a schematic circuit diagram of a heater module of the control circuit of FIG. [Figure 6] FIG. 6 is a schematic circuit diagram of a DC / DC voltage converter for use in an induction heating device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0095] Referring to Figure 1, this shows a schematic longitudinal cross-sectional view of an induction heating device 1 including a housing 2, a rechargeable lithium ion battery 4, control circuitry 6, and an inductor in the form of an induction coil 8. In this example, the battery is a lithium iron phosphate battery having an output or supply voltage of about 3.2 volts, although it will be understood that other types of batteries may be used. Control circuitry 6 is connected to battery 4 and induction coil 8 and configured to control the supply of power from battery 4 to induction coil 8. The proximal end of housing 2 of induction heating device 1 has a chamber or recess 10 for receiving at least a portion of an aerosol-generating article (an example of which is shown in Figure 2). Induction coil 8 is mounted within housing 2 surrounding chamber 10.

[0096] Figure 2 shows an aerosol-generating article 100 for use with the induction heating device 1 of Figure 1. The aerosol-generating article 100 comprises a mouthpiece filter 102, a first hollow tube 104, a second hollow tube 106, an aerosol-forming substrate 108 and an end plug 110. Each component of the aerosol-generating article 100 is a substantially cylindrical element, each having substantially the same diameter. The components are disposed consecutively in adjacent coaxial alignment and surrounded by an outer wrapper 112 to form a cylindrical rod.

[0097] The aerosol-forming substrate 108 is a tobacco rod or plug comprising an assembly of crimped sheets of homogenized tobacco material surrounded by a wrapper. The crimped sheets of homogenized tobacco material contain glycerin as an aerosol former. An electrically conductive susceptor 114 is embedded within the aerosol-forming substrate 108 in intimate physical contact with the homogenized tobacco material. The susceptor 114 extends along substantially the entire length of the central longitudinal axis of the aerosol-forming substrate 108.

[0098] The first hollow tube 104 and the second hollow tube 106, the mouthpiece filter 102 and the end plug 110 are all made from cellulose acetate. The end plug 110 is disposed at a distal end 116 of the aerosol-generating article 100 and the mouthpiece filter 102 is disposed at a proximal end of the aerosol-generating article 100. The end plug 110 is provided to prevent contact with the heating susceptor 114 at any time, such as after use. The first hollow tube 104 may have a vent formed through the thickness of the tube to allow air to be drawn through the vent to dilute the aerosol generated from the aerosol-forming substrate before the aerosol is drawn into the user's mouth.

[0099] Figure 3 shows the aerosol-generating article 100 of Figure 2 received within the induction heating device 1 of Figure 1. The distal end 116 of the aerosol-generating article 100 is inserted into the cavity 10 of the induction heating device 1 until the end plug 100 abuts the closed end of the cavity 10. In this position, the aerosol-forming substrate 108 is disposed within the induction coil 8 such that the susceptor 114 may be inductively coupled to the varying magnetic field generated by the induction coil during use. The distal portion of the aerosol-generating article 100 extends outside the cavity 10 to allow a user to receive the mouthpiece filter 102 between their lips.

[0100] In use, a user inserts an aerosol-generating article 100 into the cavity 10 of the induction heating device 1, as shown in FIG. 3. The user then initiates a heating cycle by activating the induction heating device 1, for example by pressing a switch that turns the device on. The induction heating device 1 activates the induction coil 8 by providing power to the induction coil 8 from the battery 4 via a control circuit 6. The control circuit 6 passes an alternating current through the induction coil 8, causing the induction coil 8 to generate a varying magnetic field. The varying magnetic field penetrates the susceptor 114 located within the aerosol-forming substrate 108, causing it to heat up. During the heating cycle, the induction coil 8 heats the susceptor 114 in the article to a predetermined temperature, or to a range of predetermined temperatures according to a temperature profile. The heating cycle may last for approximately 6 minutes. Heat from the susceptor 114 is transferred to the aerosol-forming substrate 108, releasing volatile compounds from the aerosol-forming substrate 108. The volatile compounds form an aerosol within an aerosolization chamber formed by the hollow spaces within the first hollow tube 104 and the second hollow tube 106. During the heating cycle, the user places the mouthpiece filter 102 of the aerosol-generating article 100 between their lips and puffs or inhales through the mouthpiece filter 102. The generated aerosol is drawn through the mouthpiece filter 102 and into the user's mouth.

[0101] It should be noted that Figures 1, 2, and 3 are schematic and not to scale. For clarity, the drawings have been simplified by omitting certain irrelevant features and by varying the size or number of other features.

[0102] 4 is a schematic block diagram illustrating an example of a control circuit 200 for an induction heating device connected to a battery 201. The control circuit 200 includes a first microcontroller 202 and a heater engine or heater module 204. In this embodiment, the first microcontroller 202 is mounted on the same printed circuit board (not shown) together with other electronic components and the heater module 204, although it will be appreciated that the heater module 204 could be provided on a separate dedicated printed circuit board.

[0103] A first microcontroller 202 is provided for controlling the general operation of the induction heating apparatus and is connected to various other electronic components to enable this. For clarity and to simplify the diagram, these various other electronic components have been omitted from Figure 4. For example, such other electronic components may include sensors, a user interface such as an LED or LCD screen for displaying information to a user for activating the induction heating apparatus and switches, means for providing data connections with external devices and charging circuitry for recharging the battery of the induction heating apparatus.

[0104] The control circuit 200 comprises a second microcontroller 208, the purpose of which is to control the power delivered to the heater module 204, in particular the induction coil of the heater module 204, which is inductively coupled to the susceptor in the aerosol-generating article when the aerosol-generating article is received in the induction heating device (shown in FIG. 3). For clarity, the second microcontroller 208 is shown as a separate component in this example, but is preferably part of the heater module 204 and is dedicated to controlling the heater module 204. In this example, the induction coil is connected to and part of the heater module 204. The second microcontroller 208 is connected to the first microcontroller 202 and controls the power supply to the induction coil in response to a signal received from the first microcontroller 202 to initiate a heating cycle. The advantage of a heater module having its own microcontroller is that it can be programmed with its own firmware for controlling the heating process, which helps make the heater module reusable in different devices, since there is no need to include firmware related to heating in other components such as the first microcontroller 202. This allows the heater module to be a stand-alone unit or module that can be incorporated into a variety of different devices.

[0105] As discussed in more detail below with reference to FIG. 5, the heater module 204 includes a drive circuit (not shown in FIG. 4) for driving the induction coil to heat the susceptor in the aerosol-generating article. The heater module 204 also includes a DC / AC voltage converter (not shown in FIG. 4) connected to the drive circuit and converting a DC voltage supplied to the drive circuit into an AC voltage to generate an alternating current in the induction coil, which in turn generates a fluctuating or alternating magnetic field in the induction coil. In this example, the induction coil is part of the DC / AC voltage converter. This arrangement helps to reduce the number of electrical components required. However, it will be appreciated that the induction coil may be separate from the DC / AC voltage converter, which may require additional components to generate the AC voltage. The DC / AC voltage converter may also include a matching network (not shown in FIG. 4) configured to operate with a low ohmic load, which helps to match the output impedance of the DC / AC converter to the load represented by the resistive losses of the induction coil and the apparent or equivalent resistance of the susceptor.

[0106] The control circuit receives a DC supply voltage V from the induction heater battery. supplyand outputting a constant voltage of 2.95 volts at a voltage converter output 207. The voltage converter output 207 is connected to the heater module 204 and provides a voltage input to the heater module 204. Thus, the output voltage from the DC / DC voltage converter 206 constitutes the heater module input voltage Vin. The heater module input voltage Vin is used to power the heater module 204. This heater module input voltage is selected to provide a predetermined heating performance based on the particular components of the heater module. It will be appreciated that different heater module input voltages can be used to provide different heating performances and the DC / DC voltage converter 206 can be configured to output different voltages. However, once the heater module input voltage Vin is set, significant changes in the heater module input voltage Vin can change the power delivered to the induction coil, leading to undesirable changes in heating performance. Additionally, some component parameters of the heater module 204 are sensitive to input voltage and may become unstable when changing the heater module input voltage Vin. Thus, the DC / DC voltage converter 206 helps reduce variability and improve stability by providing a constant heater module input voltage Vin. For clarity, the DC / DC voltage converter 206 is shown as a separate component in this example, but may also be part of the heater module 204.

[0107] When the control circuit 200 of FIG. 4 is used with the induction heating device 1 of FIG. 1, it converts a 3.2 volt DC supply voltage of a lithium iron phosphate battery to a constant heater module input voltage of 2.95 volts. In this case, the DC / DC voltage converter 206 helps to maintain a constant heater module input voltage, but the heater module 204 can function relatively normally even without the DC / DC voltage converter 206 because the 3.2 volt supply from the lithium iron phosphate battery is not significantly different from the heater module input voltage of 2.95 volts. However, it will be appreciated that the heater module 204 can be used in different induction heating devices using batteries having different battery chemistries. For example, the induction heating device 1 of FIG. 1 can use a lithium nickel manganese cobalt oxide battery with a DC supply voltage of 4.2 volts. In this case, the DC / DC voltage converter 206 allows the heater module 204 to operate similarly to how it operates using lithium iron phosphate batteries, by converting this higher DC supply voltage to 2.95 volts, providing the voltage directly without the use of the DC / DC voltage converter 206. In effect, the DC / DC voltage converter 206 is configured to accept a range of DC supply voltages and output a constant heater module input voltage. Thus, the DC / DC voltage converter 206 of the heater module 204 allows the use of different types of batteries having a range of DC supply voltages.

[0108] The control circuit 200 may also include a voltage controller 210, such as a low dropout controller, that provides a low voltage, for example 2.5 volts, for powering logic circuitry, such as the second microcontroller 208. The advantage of using such a low logic voltage is that it reduces power consumption of the control circuit 200, helping to preserve long term battery life.

[0109] FIG. 5 shows a portion of the control circuit 200 of FIG. 4 in more detail, in particular the heater module 204 of FIG. 4. The circuit of FIG. 5 is powered by the output voltage from the DC / DC voltage converter 206 of FIG. 4, i.e., the heater module input voltage Vin, received at point X of FIG. 5. The heater module 204 includes a transistor switch Q1 and a first inductor L1, which function as a drive circuit for driving the induction heating coil and the DC / AC voltage converter. The transistor switch Q1 includes a field effect transistor (FET), e.g., a metal oxide semiconductor field effect transistor (MOSFET), and the first inductor L1 includes a radio frequency choke. The heater module input voltage Vin is supplied to the transistor switch Q1 through a resistor R3 (described in more detail below) and the first inductor L1. The first inductor L1 serves to reduce radio frequencies that may be present at the input X upon entering the circuit. A gate G of the transistor switch Q1 is connected to the second microcontroller 208 of FIG. 4 and receives switching signals from the second microcontroller 208 to turn the transistor switch Q1 on and off. The switching signal is substantially a square wave with a 50% duty cycle.

[0110] The heater module 204 further comprises a first capacitor C1 connected in series with a second inductor L2, which corresponds to an inductive coil inductively coupled to a susceptor in an aerosol-generating article (an example of which is shown in FIG. 2). The second capacitor C2 is connected between the drain D of the transistor switch Q1 and electrical ground and functions as a shunt capacitor. The first capacitor C1, the second inductor L2 and the second capacitor C2 define a DC / AC voltage converter for converting the switching signal passed to the transistor switch Q1 into an AC voltage across a load resistor R4. Resistor R4 represents the total ohmic load connected to the DC / AC voltage converter, and the ohmic resistance R of the second inductor L2 coiland the apparent ohmic resistance Ra of the susceptor. Resistor R4 is shown in dotted lines in Figure 5 to indicate that it is not an actual resistor in the circuit, but is the equivalent resistance of the second inductor L2 and the susceptor. Resistor R4 is the sum of the apparent ohmic resistance Ra of the susceptor and the equivalent resistance R of the second inductor L2 in series. coil is equivalent to

[0111] Together, the first inductor L1, the transistor switch Q1, the first capacitor C1, the second inductor L2, and the second capacitor C2 form a Class E power amplifier. The general operating principles of Class E power amplifiers are well known and are described in detail in the article "Class-E RF Power Amplifiers" by Nathan O. Sokal, published in the January / February 2001 issue of QEX, a bimonthly magazine of the American Radio Relay League (ARRL), Newington, Connecticut, USA, pages 9-20.

[0112] It has been found that using a class E amplifier to power the second inductor L2 is very efficient. This is because, due to the configuration of the circuit, no current flows through the transistor switch Q1 at the same time that a voltage is applied to the transistor switch Q1. Thus, practically no energy is consumed in the transistor switch Q1, and instead practically all the power is delivered to the load R4. Furthermore, the first capacitor C1 and the second inductor L2 form a series resonant circuit tuned to the switching frequency of the switching signal. The first capacitor C1 and the second inductor L2 act as a bandpass filter that allows the AC voltage signal to be transferred to the load R4 only at the desired operating frequency of the second inductor L2. This means that power is transferred to the load R4 only at the switching frequency of the switching signal, and harmonic frequencies are significantly suppressed, which helps to further improve efficiency.

[0113] Additionally, the second inductor L2 and the capacitors C1 and C2 form an LC load or matching network configured to operate with a low ohmic load and help match the output impedance of the DC / AC converter with the load resistor R4. In particular, the capacitors C1 and C2 are tuned to reduce the ohmic loading of the second inductor L2 to the susceptor, and thus more heat is dissipated at the susceptor compared to the inductor L2, which is desirable for heating the aerosol-forming substrate.

[0114] The heater module 204 includes relatively few components compared to other power electronics for the induction heating device, thus keeping the printed circuit board area required to mount these components small, which helps reduce the overall size of the induction heating device. Additionally, the use of the second inductor L2 for DC / AC conversion further reduces the number of components.

[0115] During operation of the induction heating apparatus, the second inductor L2 generates a high frequency alternating magnetic field that induces eddy currents in the susceptor of the aerosol-generating article (an example of which is shown in FIG. 2). As the susceptor of the aerosol-generating article heats up during operation, the apparent resistance Ra of the susceptor increases as the temperature of the susceptor increases. This increase in apparent resistance Ra is remotely detected by the control circuitry of the heater module 204 through measurement of the DC current drawn by the heater module, as discussed in more detail below. The DC current drawn by the heater module 204 at a constant voltage decreases as the temperature and apparent resistance Ra of the susceptor increase.

[0116] 5 further includes two sensor circuits, a current sensor circuit 222 and a voltage sensor circuit 224, for determining the apparent resistance Ra or conductance G of the susceptor. The current sensor circuit 222 includes a current sensor in the form of a resistor R3 having a known value. Resistor R3 is connected in series between point X (which receives the heater module input voltage Vin) and the first inductor L1. Thus, during operation, a DC current I passing through resistor R3 is DC is substantially the same as the current drawn by the heater module 204. As mentioned above, the circuit of FIG. 5 is powered by the output voltage from the DC / DC voltage converter 206 of FIG. 4. Thus, the DC current I flowing through resistor R3 DC is equal to the DC current supplied by the DC / DC voltage converter. The resistance of resistor R3 is appropriately low to help reduce resistive losses.

[0117] The current sensor circuit 222 further comprises a differential amplifier 226 having two inputs 226a and 226b, which are connected to either side of resistor R3 and thus receive a voltage signal from either side of resistor R3. The differential amplifier 226 calculates the voltage received at its inputs 226a and 226b, i.e., the voltage drop V across resistor R3. R3 The output 226c of the differential amplifier 226 is connected to an analog-to-digital converter (ADC) input of a microcontroller (MCU), i.e., the second microcontroller 208 of FIG. 4. Thus, based on the signal received from the output 226c of the differential amplifier 226, the microcontroller 208 determines the voltage drop V across resistor R3. R3 Since resistor R3 has a known value, the DC current I through resistor R3 supplied to the heater module 204 can be determined. DC can be determined by the second microcontroller 208 by a simple application of Ohm's law, as shown in equation (1). I DC =V R3 / R3(1)

[0118] The voltage sensor circuit 224 comprises a first resistor R1 and a second resistor R2 connected in series between point X in FIG. 5, where the heater module input voltage Vin is received and electrically grounded. The resistors R1 and R2 form a voltage divider or divider and have equal resistance values ​​such that the voltage at point Y between resistors R1 and R2 is equal to half the heater module input voltage Vin. Point Y is connected to an analog-to-digital converter (ADC) input of a microcontroller (MCU), i.e., the second microcontroller 208 in FIG. 4, and provides the second microcontroller 208 with a voltage signal corresponding to the voltage at point Y. This allows the second microcontroller 208 to determine the heater module input voltage Vin by simply doubling the voltage signal received from point Y. Of course, other resistance values ​​can be used for resistors R1 and R2, with corresponding adjustments to the voltage calculations performed by the microcontroller. The resistors R1 and R2 have relatively high resistance values ​​to reduce the current flowing through the voltage divider.

[0119] As mentioned above, the voltage sensor circuit 224 is optional because the heater module input voltage Vin corresponds to a constant voltage output from the DC / DC voltage converter 206 of FIG. 4. Therefore, the heater module input voltage Vin is already known and constant, and therefore can be stored as a value in the memory of the second microcontroller 208 or the first microcontroller 202. However, by providing the voltage sensor circuit 224, it is possible to verify that the heater module input voltage Vin is the same as that stored in the memory. Furthermore, by providing the voltage sensor circuit 224, it is actually unnecessary to store the heater module input voltage Vin in memory, thereby simplifying the programming of the second microcontroller 208 or the first microcontroller 202.

[0120] As mentioned above, a Class E power amplifier has been found to be a very efficient means for transferring power to a load resistor R4, which, as mentioned above, is achieved by incorporating the ohmic resistance R of the second inductor L2 in series with the apparent ohmic resistance Ra of the susceptor (not shown). coil As a result, the DC current I DC indicates the current supplied to the load resistor R4. Furthermore, since the resistance value of the resistor R3 is relatively small, the voltage drop across the resistor R3 is substantially negligible. Therefore, the value of the load resistor R4 can be determined by the second microcontroller 208 by another simple application of Ohm's law, as shown in equation (2). R4=Vin / I DC (2)

[0121] Equation (2) above can be rewritten to give the conductance G of the load resistor R4 as shown in equation (3) below. G=I DC / Vin(3)

[0122] The conductance G is simply the inverse of the resistance R4. The advantage of determining the conductance G according to equation (3) is that when the voltage Vin is constant, the conductance is proportional to the DC current I DC 4. Therefore, the current provided by the DC / DC voltage converter and measured by the current sensor circuit 222 is a direct indication of the conductance of the susceptor. Therefore, the DC current I determined above is directly related to the conductance of the susceptor. DC The value of can be used by the second microcontroller 208 as a proxy for the value of conductance G without actually determining the conductance G or resistance R4, thereby reducing and simplifying the calculations that need to be performed.

[0123] The second microcontroller 208 determines the ohmic resistance R of the second inductor L2 as shown in equation (4). coilFrom the value of the load resistor R4, the apparent ohmic resistance Ra of the susceptor can be determined. Ra=R4-R coil (4)

[0124] As mentioned above, the temperature of the susceptor (not shown) is related to its apparent ohmic resistance Ra or its conductance G. Thus, determining the apparent ohmic resistance Ra or conductance G of the susceptor allows the temperature of the susceptor to be determined by the second microcontroller 208, for example, using a known relationship between the resistance Ra or conductance G and the susceptor temperature. Alternatively, a look-up table may be used. Also, by determining the apparent ohmic resistance Ra or conductance G of the susceptor, the temperature of the susceptor can be controlled by controlling the amount of power supplied to the second inductor L2. The temperature of the susceptor needs to be carefully controlled to ensure that volatile components are vaporized from the aerosol-forming substrate of the aerosol-generating article without combustion or thermal decomposition of the aerosol-forming substrate. To do this, the second microcontroller 208 of FIG. 4 monitors the temperature of the susceptor using the method described above. When the temperature of the susceptor is equal to or exceeds the desired temperature for heating the aerosol-forming substrate, the second microcontroller interrupts or turns off the power supply to the second inductor L2. When the temperature of the susceptor falls below the desired temperature for heating the aerosol-forming substrate, the second microcontroller turns on the power supply to the second inductor L2. Thus, the second microcontroller 208 implements an on / off controller for controlling the temperature of the susceptor. However, it will be appreciated that other control schemes, such as proportional-integral-derivative (PID) control, may be used.

[0125] 6 shows a schematic circuit diagram of a DC / DC voltage converter 300 for use in an induction heating device. The DC / DC voltage converter 300 converts a DC supply voltage V supplyThe DC / DC voltage converter 300 has an input 301 for receiving a DC supply voltage V at an output 308 of the DC / DC voltage converter 300. supply 6 is configured to convert a constant output voltage Vo into a constant output voltage Vo that can be used to power a heater module and is therefore substantially equal to the heater module input voltage Vin used to power the heater module 204 of FIG 5. In FIG 6, the components of the heater module include a load resistor R connected between the output 308 and electrical ground. L The DC / DC voltage converter 300 is capable of receiving a range of different DC supply voltages from different batteries having different battery chemistries.

[0126] The DC / DC voltage converter 300 includes a controller 302 connected to a first switching element Q1 and a second switching element Q2, both of which are metal oxide semiconductor field effect transistors. The controller 302 is configured to generate a first switching signal 304 and output the first switching signal 304 to the first switching element Q1 to turn the first switching element Q1 on and off. The first switching signal 304 is pulse width modulated with a controllable duty cycle, i.e., the percentage of one cycle of the switching signal that the signal is on or high. The controller 302 also generates a second switching signal 306 and output the second switching signal 306 to the second switching element Q2 to turn the second switching element Q2 on and off. The second switching signal 306 is an inverted version of the first switching signal 304, such that when the first switching element Q1 is on, the second switching element Q2 is off, and vice versa. Therefore, the controller 302 turns on the first switching element Q1 at the same time that the second switching element Q2 turns on, and the supply voltage V supply This prevents the device from being shorted to electrical ground.

[0127] The DC / DC voltage converter 300 further includes an inductor L1. A first side of the inductor L1 is connected to a point between the first switching element Q1 and the second switching element Q2, and a second side of the inductor L1 is connected to an output 308 of the DC / DC voltage converter 300. The first switching element Q1 and the second switching element Q2 are arranged in a half-bridge arrangement with the first side of the inductor L1 connected to the midpoint of the bridge. A capacitor C1 is arranged between the output 308 and electrical ground.

[0128] When the first switching element Q1 is turned on or activated, the DC supply voltage Vsupply The load R connected at output 308 L Current flows through inductor L1, charging capacitor C1. As the changing current flows through inductor L1, it creates a voltage that resists the flow of current, generating a magnetic field around inductor L1 until a steady state is reached. This situation continues as long as the first switching element is on. During this time, the second switching element Q2 is off, so no current flows.

[0129] When the first switching element Q1 is turned off, the DC voltage supply V supply is disconnected from the inductor L1, causing the magnetic field around the inductor L1 to collapse and inducing a reverse voltage across the inductor L1. This reverse voltage causes a current generated by the collapsed magnetic field to flow through the load R in the same direction as the current flowed when the first switching element Q1 was on. L and returns through the second switching element Q2 that is turned on or activated. During this time, the capacitor C1 also L The inductor L1 discharges and supplies current to the output 308, smoothing out ripples in the output voltage generated by the switching action of the first switching element Q1 and the second switching element Q2. The current through the inductor L1 always flows in the same direction, resulting in a DC voltage being generated at the output 308.

[0130] As the first switching element Q1 is turned on and off continuously, the average output voltage value seen at the output 308 is related to the duty cycle, which is related to the percentage of time that the first switching element Q1 is on during one complete switching cycle. Thus, the output voltage Vo from the DC / DC voltage converter 300 can be determined from equation (5): Vo = Duty cycle x V supply (5)

[0131] For example, a 50 percent duty cycle is a DC supply voltage of V supply A duty cycle of 25 percent produces an output voltage Vo of 50 percent or half of the DC supply voltage Vsupply The output voltage Vo is 25 percent or one-quarter of the input voltage.

[0132] If no load is connected to the voltage converter, maintaining a constant duty cycle will maintain a constant output voltage Vo. However, if the load R L Variations in the load current through the output 308 will result in some variation in the output voltage Vo at the output 308. Therefore, to address this, the DC / DC voltage converter 300 adjusts the output voltage Vo and the reference voltage V ref and outputs a signal to adjust the duty cycle of the first switching signal 304 to compensate for variations in the output voltage Vo. ref indicates the desired output voltage Vo. The output voltage Vo is compared to the reference voltage V ref If it is less than 1 V, the comparator 310 outputs a signal to increase the duty cycle, and vice versa. The output 308 of the DC / DC voltage converter 300 is connected to one input of the comparator, and the other input of the comparator 310 is connected to a reference voltage V ref The output of the comparator is connected to a controller 302, which receives the output signal from the comparator 310 and adjusts the duty cycle of the first switching signal 304 accordingly.

[0133] For purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like, should be understood in all instances as modified by the term "about." Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein. Thus, in this context, the number A is understood as A ± five percent (5%) of A. Within this context, the number A may be considered to include values ​​that are within the typical standard error for the measurement of the property that the number A modifies. The number A may, in some cases, as used in the appended claims, deviate by the percentages recited above, provided that the amount by which A deviates does not materially affect the basic and novel properties of the claimed invention. Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein.

Claims

1. 1. An induction heating system comprising: A first induction heating device, a first DC power source for providing a DC supply voltage; a first induction heating apparatus comprising: a first heater module having an inductor for providing induction heating, the first heater module having a first heater module input voltage substantially equal to the first DC supply voltage; A second induction heating device, a second DC power supply for providing a second DC supply voltage different from the first DC supply voltage; a second heater module having an inductor for providing inductive heating, the second heater module having an input voltage to the first heater module; a second induction heating device comprising a DC / DC voltage converter for converting the second DC supply voltage to the first heater module input voltage.

2. The induction heating system of claim 1 , wherein the DC / DC voltage converter is part of the second heater module.

3. 3. The induction heating system of claim 1, wherein the first heater module input voltage is less than the second DC supply voltage, and the DC / DC voltage converter is a step-down voltage converter.

4. An induction heating system according to any preceding claim, wherein the DC / DC voltage converter is configured to accept a range of DC supply voltages and to output a constant first heater module input voltage.

5. An induction heating system according to any preceding claim, wherein the output voltage of the DC / DC voltage converter is related to the duty cycle of a switching signal generated or received by the DC / DC voltage converter.

6. An induction heating system according to any preceding claim, wherein the DC / DC voltage converter comprises a first switching element configured to be activated during a first portion of the switching signal.

7. 7. The induction heating system of claim 6, wherein the DC / DC voltage converter comprises a second switching element configured to be activated during a second portion of the switching signal.

8. 8. The induction heating system of claim 7, wherein when the first switching element is activated, the second switching element is deactivated, and when the second switching element is activated, the first switching element is deactivated.

9. 9. The induction heating system of claim 7 or 8, wherein the first and second switching elements are arranged in a half-bridge configuration.

10. 10. The induction heating system of claim 1, wherein the DC / DC voltage converter includes a comparator configured to compare an output voltage of the DC / DC voltage converter with a reference voltage and generate an output signal for adjusting the duty cycle of the switching signal based on the comparison.

11. 11. The induction heating system of claim 1, wherein the first and second induction heating devices are configured to heat the aerosol-forming substrate using a susceptor, and an inductor in each of the first and second induction heating devices is positioned to be inductively coupled with its respective susceptor.

12. 12. The induction heating system of claim 11, wherein the first and second induction heating devices are configured to determine a temperature of their respective susceptors by determining a resistance or conductance of the susceptor based on a measured current supplied by the first and second DC power sources, respectively, or by the DC / DC voltage converter.

13. 13. The induction heating system of claim 12, wherein the first and second induction heating devices further comprise DC current sensors for measuring current supplied by the first and second DC power sources, respectively.

14. 14. The induction heating system of any of claims 1 to 13, wherein the first and second induction heating devices comprise or are connected to their respective inductors, and further comprise a DC / AC voltage converter configured to convert the first heater module input voltage to an AC voltage for driving the inductors.

15. 15. The induction heating system of claim 14, wherein the first and second induction heating devices are configured to discontinue generation of the AC voltage when the determined temperature of the susceptor exceeds or equals a predetermined threshold.

Images