Aerosol provision device

Abstract

To provide an aerosol provision device.SOLUTION: The device comprises a plurality of electrical components, a heating assembly comprising a heater component for heating aerosol generating material, and a battery to power the plurality of electrical components and the heating assembly. In use, the power consumption of the plurality of electrical components is less than about 0.25 W.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an aerosol delivery device and an aerosol delivery system.

[0002] Smoking articles, such as cigarettes, cigars, and the like, burn tobacco to produce tobacco smoke during use. Attempts have been made to provide alternatives to these tobacco-burning articles by creating products that release compounds without combustion. Examples of such products include heating devices that release compounds by heating a material without burning it. The material may be, for example, tobacco or other non-tobacco products that may or may not contain nicotine. Overview

[0003] According to a first aspect of the present disclosure, a plurality of electrical components; a heating assembly including a heater component for heating the aerosol-forming material; a battery for powering the plurality of electrical components and the heating assembly; 1. An aerosol delivery device comprising: An aerosol delivery device is provided, wherein, during use, the electrical components consume less than about 0.25 W of power.

[0004] According to a second aspect of the present disclosure, a plurality of electrical components; a heating assembly including a heater component for heating the aerosol-forming material; a battery for powering the plurality of electrical components and the heating assembly; 1. An aerosol delivery device comprising: An aerosol delivery device is provided, wherein, in use, the power consumption of the plurality of electrical components is less than about 1% of the power consumption of the heating assembly.

[0005] According to a third aspect of the present disclosure, an aerosol delivery device according to the first aspect; an article containing an aerosol-forming material; An aerosol delivery system is provided comprising:

[0006] Further features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, made with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 shows a front view of an example of an aerosol generating device. [Figure 2] FIG. 2 shows a front view of the aerosol generating device of FIG. 1 with the outer cover removed. [Figure 3] FIG. 3 shows a cross-sectional view of the aerosol generating device of FIG. [Figure 4] FIG. 4 shows an exploded view of the aerosol generating device of FIG. [Figure 5] Figure 5A shows a cross-sectional view of a heating assembly in an aerosol generating device, and Figure 5B shows an enlarged view of a portion of the heating assembly of Figure 5A. [Figure 6] FIG. 6 shows a schematic diagram of an exemplary induction heating circuit for the aerosol generating device of FIGS. 1 to 5B. [Figure 7A] FIG. 7A shows a schematic diagram of the current through the inductor of the exemplary induction heating circuit of FIG. [Figure 7B] FIG. 7B shows a schematic diagram of the voltage across the current sensing resistor of the exemplary induction heating circuit of FIG. [Figure 8] FIG. 8 shows a schematic diagram of the voltage across the switching arrangement of the circuit of FIG. [Figure 9] FIG. 9 shows another schematic diagram of an exemplary induction heating circuit for the device of FIGS. 1-5B. [Figure 10] 10-13 show various portions of an exemplary control arrangement for the exemplary induction heating circuit represented by the previous figures. [Figure 11]10-13 show various portions of an exemplary control arrangement for the exemplary induction heating circuit represented by the previous figures. [Figure 12] 10-13 show various portions of an exemplary control arrangement for the exemplary induction heating circuit represented by the previous figures. [Figure 13] 10-13 show various portions of an exemplary control arrangement for the exemplary induction heating circuit represented by the previous figures. [Figure 14] FIG. 14 shows a flow chart diagram of an exemplary method for controlling aspects of an exemplary induction heating circuit. [Figure 15] FIG. 15 shows a flow chart diagram of another exemplary method for controlling aspects of an exemplary induction heating circuit. [Figure 16] FIG. 16 shows a schematic diagram of the temperature of the inductor and the target power to be supplied to the inductor during operation of an exemplary induction heating circuit. Detailed Description

[0008] As used herein, the term "aerosol-forming material" includes materials that, when heated, provide volatile components, typically in the form of an aerosol. Aerosol-forming materials include any tobacco-containing material, and may include, for example, one or more of tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco, or tobacco substitutes. Aerosol-forming materials may also include other non-tobacco products, which may or may not contain nicotine, depending on the product. Aerosol-forming materials may be in the form of, for example, a solid, liquid, gel, wax, or the like. Aerosol-forming materials may also be, for example, a combination or mixture of materials. Aerosol-forming materials may also be what is known as "smoking material."

[0009] Devices are known that heat an aerosol-generating material to volatilize at least one component of the aerosol-generating material, typically forming an inhalable aerosol without burning or igniting the aerosol-generating material. Such devices may be described as "aerosol-generating devices," "aerosol-delivery devices," "non-combustion heating devices," "tobacco heating product devices," or "tobacco heating devices," or similar. Similarly, so-called e-cigarette devices exist that typically vaporize aerosol-generating material in liquid form, which may or may not contain nicotine. The aerosol-generating material may be in the form of, or provided as part of, a rod, cartridge, cassette, or the like that can be inserted into the device. A heater for heating and volatilizing the aerosol-generating material may be provided as a "fixed" component of the device.

[0010] The aerosol delivery device can receive an article including an aerosol-forming material for heating. An "article" in this context is a component that includes or contains the aerosol-forming material during use, and optionally other components, that is heated to volatilize the aerosol-forming material. A user may insert the article into the aerosol delivery device before the article is heated to generate an aerosol that the user subsequently inhales. The article may be of a predetermined or specific size, for example, configured to be placed within a heating chamber of a device sized to receive the article.

[0011] The present disclosure describes an aerosol delivery device comprising a plurality of electrical components and a heating assembly including at least one heater component for heating an aerosol-generating material. The heater assembly may use resistive or inductive heating. In certain examples, the heating assembly includes at least one coil. The coil may be, for example, an inductor coil. Thus, the heater component may be a susceptor, and the coil may heat the susceptor, which in turn heats the aerosol-generating material. The coil may be an inductor or an inductor coil.

[0012] The device further comprises a battery for powering the electrical components and the heating assembly, wherein, during use, the electrical components consume less than about 0.25 W.

[0013] Thus, the device includes a heating assembly configured to heat the aerosol-generating material and a number of other electrical components. The electrical components may include a controller, such as a microprocessor, and a visual indicator, such as a number of LEDs. The electrical components do not include a heater assembly, such as a heater component and coil(s).

[0014] The power consumption of the electrical components is preferably less than about 0.1 W. It has been found that keeping the power consumption of the electrical components below 0.1 W can reduce the surface temperature of the device and contribute to overall energy efficiency. For example, it may be desirable to maintain the surface temperature of the device below about 48°C or below about 43°C. Electrical components may be located closer to the surface than heating components and may be less insulated, which can have a greater than expected impact on the surface temperature. Using energy-efficient components can reduce the surface temperature of the device. Additionally, if the electrical components consume less than about 0.1 W, the device can be used for a longer period of time before the battery needs to be recharged.

[0015] The battery may be a DC power supply. The battery may be a battery module or a battery assembly. The battery may be a 3-4V battery.

[0016] The power consumption of the plurality of electrical components may be less than about 0.05W, or less than about 0.04W, or less than about 0.01W.

[0017] In one example, the plurality of electrical components comprises a controller, and when the controller is active, the power consumption of the controller is between about 10 mW and about 20 mW, and when the controller is inactive, the power consumption of the plurality of electrical components is less than about 0.5 mW.

[0018] In one example, the electrical components include a plurality of LEDs, each having a power consumption of less than about 0.01 W at maximum brightness or intensity. In one example, there are four LEDs, and the power consumption of the four LEDs is less than about 0.04 W at maximum brightness. For example, the power consumption of the four LEDs may be about 0.03 W.

[0019] Thus, the plurality of electrical components may include four LEDs and a controller, and when the controller is inactive and the LEDs are switched off, the power consumption of the electrical components is less than about 0.5 mW. When the controller is active and the LEDs are switched on, the power consumption of the electrical components is less than about 0.05 W. For example, when the controller is active and the LEDs are switched on, the power consumption of the electrical components may be between about 0.03 W and about 0.05 W.

[0020] During a heating session, the heating assembly may consume between about 15 W and about 25 W. For example, during use, the power consumption of the heater assembly is between about 15 W and about 25 W. Preferably, the power consumption of the heater assembly is between about 20 W and about 25 W, such as between about 20 W and about 23 W.

[0021] In some examples, the electrical components include a WiFi interface and / or a Bluetooth interface and / or an NFC interface.

[0022] In some examples, the power consumption of the electrical components is less than about 1% of the power consumption of the heating assembly. In other examples, the power consumption of the electrical components is less than about 0.5% of the power consumption of the heating assembly. Preferably, the power consumption of the electrical components is less than about 0.2% of the power consumption of the heating assembly. For example, the power consumption of the electrical components may be about 0.05 W, and the power consumption of the heater assembly may be about 20 W.

[0023] The battery may have a battery capacity of between about 30,000J and 35,000J.

[0024] The heater assembly may be configured to operate for a period of about 3 minutes to about 5 minutes and may be configured to consume about 1000 J to about 1400 J during that period. Thus, the battery may be configured to power the heater assembly for about 20 to about 35 periods, each period may be known as a heating session. During this period, one or more inductor coils may be operated intermittently.

[0025] Preferably, the device is a tobacco heating device, also known as a non-combustion heating device.

[0026] As briefly mentioned above, in some examples, the coil(s) are configured to, during use, cause heating of at least one conductive heating component / element (also known as a heater component / element), thereby enabling thermal energy to be conducted from the at least one conductive heating component to the aerosol-generating material, thereby causing heating of the aerosol-generating material.

[0027] In some examples, the coil(s) are configured to, in use, generate a varying magnetic field for penetrating at least one heating component / element, thereby causing inductive heating and / or magnetic hysteresis heating of the at least one heating component. In such configurations, the or each heating component may be referred to as a "susceptor." A coil configured to, in use, generate a varying magnetic field for penetrating at least one electrically conductive heating component, thereby causing inductive heating of the at least one electrically conductive heating component, may be referred to as an "induction coil" or "inductor coil."

[0028] The device may include heating component(s), such as, for example, conductive heating component(s), which may be suitably positioned or positionable relative to the coil(s) to enable such heating of the heating component(s). The heating component(s) may be in a fixed position relative to the coil(s). Alternatively, at least one heating component, such as, for example, at least one conductive heating component, may be included in an article for insertion into a heating zone of the device, the article further comprising an aerosol-generating material and removable from the heating zone after use. Alternatively, both the device and such article may include at least one respective heating component, such as, for example, at least one conductive heating component, and the coil(s) may be adapted to cause heating of the heating component(s) of each of the device and the article when the article is in the heating zone.

[0029] In some examples, the coil(s) are helical. In some examples, the coil(s) surround at least a portion of a heating zone of a device configured to receive the aerosol-generating material. In some examples, the coil(s) are helical coil(s) surrounding at least a portion of the heating zone. The heating zone may be a container shaped to receive the aerosol-generating material.

[0030] In some examples, the device includes an electrically conductive heating component at least partially surrounding the heating zone, and the coil(s) are helical coil(s) surrounding at least a portion of the electrically conductive heating component. In some examples, the electrically conductive heating component is tubular. In some examples, the coil is an inductor coil.

[0031] 1 shows an example of an aerosol delivery device 100 for generating an aerosol from an aerosol-generating medium / material. Generally, device 100 may be used to heat a replaceable item 110 containing an aerosol-generating medium to generate an aerosol or other inhalable medium that is inhaled by a user of device 100.

[0032] The device 100 comprises a housing 102 (in the form of an outer cover) that surrounds and houses the various components of the device 100. The device 100 has an opening 104 at one end into which an item 110 can be inserted for heating by the heating assembly. In use, the item 110 may be fully or partially inserted into the heating assembly in a position such that it can be heated by one or more components of the heater assembly.

[0033] The device 100 of this example includes a first end member 106 with a lid 108 that is movable relative to the first end member 106 to close the opening 104 when the item 110 is not in place. In Figure 1, the lid 108 is shown in an open position, but the cap 108 may also be moved to a closed position. For example, a user may slide the lid 108 in the direction of arrow "A."

[0034] Device 100 may further include a user-operable control element 112, such as a button or switch, that, when pressed, operates device 100. For example, a user may turn on device 100 by operating switch 112.

[0035] Device 100 may further include electrical components, such as a socket / port 114 capable of receiving a cable for charging a battery of device 100. For example, socket 114 may be a charging port, such as a USB charging port. In some examples, socket 114 may additionally or alternatively be used to transfer data between device 100 and another device, such as a computing device.

[0036] 2 illustrates the device 100 of FIG. 1 with the outer cover 102 removed. The device 100 defines a longitudinal axis 134.

[0037] As shown in FIG. 2, the first end member 106 is disposed at one end of the device 100, and the second end member 116 is disposed at the opposite end of the device 100. The first and second end members 106, 116 together at least partially define an end surface of the device 100. For example, the bottom surface of the second end member 116 at least partially defines the bottom surface of the device 100. An edge of the outer cover 102 may also define a portion of the end surface. In this example, the lid 108 also defines a portion of the top surface of the device 100. FIG. 2 also shows a second printed circuit board 138 associated within the control element 112.

[0038] The end of the device nearest opening 104 may be known as the proximal end (or oral end) of device 100, as it is closest to the user's mouth during use. During use, a user inserts item 110 into opening 104, operates user control 112 to begin heating the aerosol-generating material, and inhales the aerosol generated by the device, causing the aerosol to flow through device 100 along a flow path toward the proximal end of device 100.

[0039] The other end of the device furthest from opening 104 may be known as the distal end of device 100, as it is the end farthest from the user's mouth during use. As the user inhales the aerosol generated by the device, the aerosol flows away from the distal end of device 100.

[0040] Device 100 further includes a power source 118. Power source 118 may be, for example, a battery, such as a rechargeable or non-rechargeable battery. Examples of suitable batteries include, for example, lithium batteries (such as lithium-ion batteries), nickel batteries (such as nickel-cadmium batteries), and alkaline batteries. The battery is electrically coupled to the heating assembly to provide power to heat the aerosol-generating material when needed and under the control of a controller (not shown). In this example, the battery is connected to a central support 120 that holds battery 118 in place. Power source 118 may be a DC voltage source 118.

[0041] The device further includes at least one electronics module 122. The electronics module 122 may include, for example, a printed circuit board (PCB). The PCB 122 may support at least one controller, such as a processor, and a memory. The PCB 122 may further include one or more electrical traces for electrically connecting together various electronic components of the device 100. For example, battery terminals may be electrically connected to the PCB 122 so that power can be distributed throughout the device 100. The socket 114 may also be electrically coupled to the battery via electrical traces.

[0042] In the exemplary device 100, the heating assembly is an induction heating assembly and includes various components for heating the aerosol-generating material of the article 110 by an induction heating process. Induction heating is a process of heating a conductive object (such as a susceptor) by electromagnetic induction. The induction heating assembly may include an induction element, such as one or more inductor coils, and a device for passing a varying current, such as an alternating current, through the induction element. The varying current in the induction element generates a varying magnetic field. The varying magnetic field penetrates a susceptor appropriately positioned relative to the induction element, generating eddy currents within the susceptor. The susceptor has an electrical resistance to the eddy currents, and therefore, the flow of eddy currents against this resistance heats the susceptor by Joule heating. If the susceptor includes a ferromagnetic material, such as iron, nickel, or cobalt, heat may also be generated by magnetic hysteresis losses in the susceptor, i.e., by the magnetic dipole orientation of the magnetic material changing as a result of aligning with the varying magnetic field. In comparison with, for example, conduction heating, induction heating allows for rapid heating by generating heat inside the susceptor, and furthermore does not require any physical contact between the induction heater and the susceptor, allowing for greater flexibility in design and application.

[0043] The induction heating assembly of the exemplary device 100 includes a susceptor structure 132 (referred to herein as a "susceptor"), a first inductor coil 124, and a second inductor coil 126. The first and second inductor coils 124, 126 are made from a conductive material. In this example, the first and second inductor coils 124, 126 are made from litz wire / cable that is helically wound to form the helical inductor coils 124, 126. Litz wire includes multiple individual wires that are individually insulated and twisted together to form a single wire. Litz wire is designed to reduce skin effect losses in the conductor. In the exemplary device 100, the first and second inductor coils 124, 126 are made from copper litz wire having a substantially circular cross-section. In other examples, the litz wire may have a cross-section of other shapes, such as rectangular.

[0044] The first inductor coil 124 is configured to generate a first varying magnetic field for heating a first section of the susceptor 132, and the second inductor coil 126 is configured to generate a second varying magnetic field for heating a second section of the susceptor 132. Here, the first section of the susceptor 132 is referred to as the first susceptor zone 132a, and the second section of the susceptor 132 is referred to as the second susceptor zone 132b. In this example, the first inductor coil 124 is adjacent to the second inductor coil 126 in a direction along the longitudinal axis 134 of the device 100 (i.e., the first and second inductor coils 124, 126 do not overlap). In this example, the susceptor structure 132 comprises a single susceptor having two zones, although in other examples, the susceptor structure 132 may comprise two or more separate susceptors. The ends 130 of the first and second inductor coils 124 , 126 are connected to the PCB 122 .

[0045] It will be appreciated that the first and second inductor coils 124, 126 may have at least one characteristic that differs from one another in some examples. For example, the first inductor coil 124 may have at least one characteristic that differs from the second inductor coil 126. More specifically, in one example, the first inductor coil 124 may have a different inductance value than the second inductor coil 126. In FIG. 2 , the first and second inductor coils 124, 126 are different lengths such that the first inductor coil 124 is wound across a smaller section of the susceptor 132 than the second inductor coil 126. Thus, the first inductor coil 124 may have a different number of turns than the second inductor coil 126 (assuming the spacing between individual turns is substantially the same). In yet another example, the first inductor coil 124 may be made of a different material than the second inductor coil 126. In some examples, the first and second inductor coils 124, 126 may be substantially identical.

[0046] In this example, the inductor coils 124, 126 are wound in the same direction as each other. That is, the first inductor coil 124 and the second inductor coil 126 are both left-handed spirals. In another example, the inductor coils 124, 126 may both be right-handed spirals. In yet another example (not shown), the first inductor coil 124 and the second inductor coil 126 are wound in opposite directions. This can be useful when the inductor coils are active at different times. For example, the first inductor coil 124 may initially operate to heat a first section of the article 110, and then the second inductor coil 126 may operate to heat a second section of the article 110. Winding the coils in opposite directions helps reduce current induced in inactive coils when used in combination with certain types of control circuitry. In one example (not shown) where the coils 124, 126 are wound in different directions, the first inductor coil 124 may be a right-handed spiral and the second inductor coil 126 may be a left-handed spiral. In another such embodiment, the first inductor coil 124 may be a left-handed spiral and the second inductor coil 126 may be a right-handed spiral.

[0047] The susceptor 132 in this example is hollow and thus defines a reservoir in which the aerosol-generating material can be received. For example, the article 110 can be inserted into the susceptor 132. In this example, the susceptor 132 is tubular with a circular cross section.

[0048] 2 further includes an insulating member 128 that may be generally tubular and at least partially surround the susceptor 132. The insulating member 128 may be constructed from any insulating material, such as, for example, a plastic material. In this particular example, the insulating member is constructed from polyetheretherketone (PEEK). The insulating member 128 may help insulate various components of the device 100 from heat generated in the susceptor 132.

[0049] The insulating member 128 may also fully or partially support the first and second inductor coils 124, 126. For example, as shown in FIG. 2 , the first and second inductor coils 124, 126 are positioned around the insulating member 128 and contact a radially outer surface of the insulating member 128. In some examples, the insulating member 128 does not abut the first and second inductor coils 124, 126. For example, a small gap may exist between the outer surface of the insulating member 128 and the inner surfaces of the first and second inductor coils 124, 126.

[0050] In one particular example, the susceptor 132 , the insulating member 128 , and the first and second inductor coils 124 , 126 are coaxial about a central longitudinal axis of the susceptor 132 .

[0051] 3 shows a side view, partially in cross section, of device 100. Outer cover 102 is again not shown in this example. The circular cross-sectional shapes of first and second inductor coils 124, 126 are more clearly visible in FIG.

[0052] The device 100 further comprises a support 136 that engages one end of the susceptor 132 to hold the susceptor 132 in place. The support 136 is connected to the second end member 116.

[0053] The device 100 further includes a second lid / cap 140 and a spring 142 disposed distally of the device 100. The spring 142 allows the second lid 140 to open to provide access to the susceptor 132. A user may, for example, open the second lid 140 to clean the susceptor 132 and / or the support 136.

[0054] The device 100 further includes an expansion chamber 144 that extends away from the proximal end of the susceptor 132 toward the opening 104 of the device. A retaining clip 146 is disposed at least partially within the expansion chamber 144 to abut and retain the article 110 when received within the device 100. The expansion chamber 144 is connected to the end member 106.

[0055] FIG. 4 is an exploded view of the device 100 of FIG. 1, again with the outer cover 102 omitted.

[0056] FIG. 5A illustrates a cross-section of a portion of the device 100 of FIG. 1. FIG. 5B illustrates an enlarged view of a region of FIG. 5A. FIGS. 5A and 5B show the article 110 received within the susceptor 132, with the article 110 sized so that the outer surface of the article 110 abuts the inner surface of the susceptor 132. This ensures the most efficient heating. The article 110 in this example includes an aerosol-forming material 110a. The aerosol-forming material 110a is positioned within the susceptor 132. The article 110 may further include other components, such as a filter, packaging, and / or a cooling structure.

[0057] 5B shows that the outer surface of the susceptor 132 is spaced from the inner surfaces of the inductor coils 124, 126 by a distance 150 measured in a direction perpendicular to the longitudinal axis 158 of the susceptor 132. In one particular example, the distance 150 is about 3 mm to 4 mm, about 3 mm to 3.5 mm, or about 3.25 mm.

[0058] 5B further shows that the outer surface of the insulating member 128 is spaced from the inner surfaces of the inductor coils 124, 126 by a distance 152 measured in a direction perpendicular to the longitudinal axis 158 of the susceptor 132. In one particular example, the distance 152 is approximately 0.05 mm. In another example, the distance 152 is substantially 0 mm such that the inductor coils 124, 126 abut and contact the insulating member 128.

[0059] In one example, the susceptor 132 has a wall thickness 154 of between about 0.025 mm and 1 mm, or about 0.05 mm.

[0060] In one example, the susceptor 132 has a length of about 40 mm to 60 mm, about 40 mm to 45 mm, or about 44.5 mm.

[0061] In one example, the insulating member 128 has a wall thickness 156 of between about 0.25 mm and 2 mm, between 0.25 mm and 1 mm, or about 0.5 mm.

[0062] As described above, the heating assembly of exemplary device 100 is an induction heating assembly that includes various components for heating the aerosol-generating material of article 110 through an induction heating process. In particular, first inductor coil 124 and second inductor coil 126 are used to heat first zone 132a and second zone 132b, respectively, of susceptor 132 to heat the aerosol-generating material and generate an aerosol. The operation of device 100 in inductively heating susceptor structure 132 using first and second inductor coils 124, 126 will now be described in detail with reference to FIGS. 6-12 .

[0063] The induction heating assembly of device 100 comprises an LC circuit. The LC circuit has an inductance L formed by an inductive element and a capacitance C formed by a capacitor. As discussed below, in device 100, inductance L is formed by first and second inductor coils 124, 126, and capacitance C is formed by multiple capacitors. An induction heater circuit having inductance L and capacitance C may, in some cases, be represented as an RLC circuit with resistance R formed by a resistor. In some cases, the resistance is formed by ohmic resistance in the portion of the circuit connecting the inductor and capacitor; thus, the circuit need not necessarily include a resistor in such cases. Such circuits may exhibit electrical resonance, which occurs at a particular resonant frequency when the imaginary parts of the impedances or admittances of the circuit elements cancel each other.

[0064] One example of an LC circuit is a series circuit in which an inductor and a capacitor are connected in series. Another example of an LC circuit is a parallel LC circuit in which an inductor and a capacitor are connected in parallel. Resonance occurs in an LC circuit because the inductor's plummeting magnetic field generates a current in the inductor's winding that charges the capacitor, while the discharging capacitor creates a current that increases the inductor's magnetic field. When a parallel LC circuit is driven at a resonant frequency, the dynamic impedance of the circuit is maximized (as the inductor's reactance equals the capacitor's reactance) and the circuit current is minimized. However, in a parallel LC circuit, the parallel inductor and capacitor loop acts as a current multiplier (effectively multiplying the current in the loop and, therefore, the current passing through the inductor). Therefore, allowing the RLC or LC circuit to operate at a resonant frequency for at least a portion of the time the circuit is operating to heat the susceptor can maximize the value of the magnetic field penetrating the susceptor, resulting in effective and / or efficient induction heating.

[0065] The LC circuit used by the device 100 to heat the susceptor 132 may utilize one or more transistors operating as a switching element, as described below. A transistor is a semiconductor device for switching electronic signals. A transistor typically has at least three terminals for connection to an electronic circuit. A field-effect transistor (FET) is a transistor in which the effect of an applied electric field can be used to vary the effective conductance of the transistor. A field-effect transistor may have a body, a source terminal S, a drain terminal D, and a gate terminal G. A field-effect transistor has an active channel comprising a semiconductor through which electron or hole charge carriers can flow between the source terminal S and the drain terminal D. The conductivity of the channel, i.e., the conductivity between the drain terminal D and the source terminal S, is a function of the potential difference between the gate terminal G and the source terminal S, generated, for example, by a potential applied to the gate terminal G. In an enhancement mode FET, the FET may be OFF (i.e., may substantially prevent current from passing through the FET) when the voltage from the gate G to the source S is substantially zero, and may be ON (i.e., may substantially allow current to flow through the FET) when the voltage from the gate G to the source S is substantially non-zero.

[0066] One type of transistor that may be used in the circuitry of device 100 is an n-channel (or n-type) field-effect transistor (n-FET). An n-FET is a field-effect transistor whose channel includes an n-type semiconductor in which electrons are the majority carriers and holes are the minority carriers. For example, the n-type semiconductor may include an intrinsic semiconductor (such as silicon) doped with a donor impurity (such as phosphorus). In an n-channel FET, the drain terminal D is placed at a higher potential than the source terminal S (i.e., the drain-source voltage is positive, or, in other words, the source-drain voltage is negative). To turn the n-channel FET "on" (i.e., to allow current to pass through the n-channel FET), a switching potential higher than the potential of the source terminal S is applied to the gate terminal G.

[0067] Another type of transistor that can be used in device 100 is a p-channel (or p-type) field-effect transistor (p-FET). A p-FET is a field-effect transistor whose channel includes a p-type semiconductor in which holes are the majority carriers and electrons are the minority carriers. For example, the p-type semiconductor can include an intrinsic semiconductor (such as silicon) doped with an acceptor impurity (such as boron). In a p-channel FET, the source terminal S is placed at a higher potential than the drain terminal D (i.e., the drain-source voltage is negative, or in other words, the source-drain voltage is positive). To turn the p-channel FET "on" (i.e., to allow current to pass through the p-channel FET), a switching potential lower than the potential of the source terminal S (and which may be higher than the potential of the drain terminal D, for example) is applied to the gate terminal G.

[0068] As an example, one or more of the FETs used in device 100 may be metal-oxide-semiconductor field-effect transistors (MOSFETs). A MOSFET is a field-effect transistor whose gate terminal G is electrically isolated from the semiconductor channel by an insulating layer. In some examples, the gate terminal G may be a metal and the insulating layer may be an oxide (e.g., silicon dioxide), and thus a "metal-oxide-semiconductor." However, in other examples, the gate may be made of a material other than a metal, such as polysilicon, and / or the insulating layer may be made of a material other than an oxide, such as a dielectric material. Such devices are still typically referred to as metal-oxide-semiconductor field-effect transistors (MOSFETs), and it should be understood that, as used herein, the terms metal-oxide-semiconductor field-effect transistor or MOSFET should be interpreted to include such devices.

[0069] The MOSFET may be an n-channel (or n-type) MOSFET, in which the semiconductor is n-type. The n-channel MOSFET (n-MOSFET) may be operated in the same manner as described above for the n-channel FET. As another example, the MOSFET may be a p-channel (or p-type) MOSFET, in which the semiconductor is p-type. The p-channel MOSFET (p-MOSFET) may be operated in the same manner as described above for the p-channel FET. An n-MOSFET typically has a lower source-drain resistance than a p-MOSFET. Therefore, in the “on” (i.e., current passing) state, an n-MOSFET may generate less heat compared to a p-MOSFET and therefore consume less energy during operation than a p-MOSFET. Furthermore, an n-MOSFET typically has a shorter switching time (i.e., the characteristic response time from a change in the switching potential supplied to the gate terminal G to the time the MOSFET changes whether or not it passes current) compared to a p-MOSFET. This can enable faster switching rates and improved switching control.

[0070] Referring now to FIG. 6 , a circuit for inductive heating by the device 100 will be described. FIG. 6 shows a simplified schematic diagram of a portion of an inductive heating circuit 600 of the aerosol generation device 100. FIG. 6 shows a portion of the inductive heating circuit 600 including a first inductor coil 124 for heating a first susceptor zone 132 a when a fluctuating current flows through the first inductor coil 124. The first susceptor zone 132 a is represented in FIG. 6 as having an inductive element and a resistive element to illustrate how the susceptor 132 is inductively coupled with the first inductor 124 and heated by the generation of eddy currents. It will be noted that the device 100 additionally includes a second inductor coil 126, not shown in FIG. 6 . The second inductor coil 126 is also part of the inductive heating circuit 600 and is controlled to heat a second susceptor zone 132 b, as described below. However, for clarity, the circuit 600 will first be described with respect to the features shown in FIG. 6 .

[0071] The circuit 600 comprises a first resonator section 601, a DC voltage supply 118 for supplying a DC voltage to the first resonator section 601, and a control arrangement for controlling the circuit 600. The first resonator section 601 includes a first inductor 124 and a switching arrangement comprising a first FET 608, the control arrangement being configured to switch the FET 608 between a first state and a second state to operate the first inductor 124 in response to voltage conditions detected in the circuit 600, as described in more detail below. The circuit 600, excluding the susceptor 132, is disposed on the PCB 122 of the device 100, and the inductor coil 124 is connected to the PCB 122 at a first end 130 a and a second end 130 b.

[0072] The first resonator section 601 includes a first capacitor 606 and a second capacitor 610, both of which are arranged in parallel with the first inductor 124 so that when the first resonator section 601 is allowed to resonate, an alternating current flows between the first capacitor 606 and the second capacitor 610 and through the inductor 124. As mentioned above, the first FET 608, in this example an n-channel MOSFET, is arranged to operate as a switching element in the first resonator section 601.

[0073] It should be noted that in other examples, the resonator section 601 may include only one capacitor, for example, in the position of the first capacitor 606 or in the position of the second capacitor 610. In other examples, the resonator section 601 may include any other number of capacitors, such as three or more capacitors. For example, either or both of the first capacitor 606 and the second capacitor 610 may be replaced by two or more capacitors arranged in parallel with each other. As will be appreciated, the resonator section 601 has a resonant frequency that depends on the inductance L and capacitance C of the resonator section 601. The number, type, and placement of capacitors in the resonator section 601 may be selected based on considerations of the power level used in the circuit 600 and the desired operating frequency of the circuit 600. For example, it will be appreciated that each capacitor and its placement may be considered to have an equivalent series resistance (ESR) in addition to limitations on the capacitor's ability to handle current. Such characteristics may be considered when determining the placement of the capacitors that form the capacitance in the resonator section 601. For example, depending on the desired power level and operating frequency, it may be advantageous to have multiple capacitors in parallel to provide higher capacitance or lower ESR. In this example, the first and second capacitors 606, 610 are both ceramic C0G capacitors, each having a capacitance on the order of 100 nF. In other examples, other types of capacitors and / or capacitors having other capacitance values, such as capacitors with unequal capacitance values, may be used, subject to the considerations outlined in this paragraph.

[0074] A DC voltage, such as the voltage supplied by a battery as described above, is supplied to the first resonator section 601 by a DC voltage supply 118. As shown in FIG. 6, the DC voltage supply 118 has a positive terminal 118a and a negative terminal 118b. In one example, the DC voltage supply 118 supplies a DC voltage of approximately 4.2 V to the first resonator section 601. In other examples, the DC voltage supply 118 may supply a voltage of approximately 2 to 10 V, or 3 to 5 V, for example.

[0075] Controller 1001 is configured to control the operation of circuit 600. Controller 1001 may comprise a microcontroller, such as a microprocessing unit (MPU), having multiple inputs and outputs. In one example, controller 1001 is an STM32L051C8T6 model MPU. In some examples, DC voltage supply 118 provided in circuit 600 is provided by an output from controller 1001, which itself receives power from a battery or other power source.

[0076] The positive terminal 118a of the DC voltage source 118 is electrically connected to a first node 600A. In one example, the DC voltage source 118 is connected to the node 600A via a controller 1001, which receives power from the DC voltage source 118 and supplies the voltage provided by the DC voltage source to the components of the device, including the circuit 600. The first node 600A is electrically connected to a first end 606a of a first capacitor 606 and a first end 130a of a first inductor 124. The second end 130b of the first inductor 124 is electrically connected to a second node 600B, which is represented in FIG. 6 as two electrically equivalent points on the circuit diagram. The second node 600B is electrically connected to a drain terminal 608D of the FET 608. In this example, the second node 600B is also electrically connected to a first end 610a of a second capacitor 610. Continuing through the circuit, the source terminal 608S of the first FET 608 is electrically connected to a third node 600C. The third node 600C is electrically connected to ground 616 and, in this example, to the second end 610b of the second capacitor 610. The third node 600C is electrically connected to a fourth node 600D through a current sense resistor 615, which is electrically connected to the negative terminal 118b of the DC voltage source 118, which, like the positive terminal, is supplied through the controller 1001 in one example.

[0077] Note that in an example where the second capacitor 610 is not present, the third node 600C may have only three electrical connections: to the first FET source terminal 608S, ground 616, and the current sensing resistor 615.

[0078] As discussed above, the first FET 608 operates as a switching component in the first resonator section 601. The first FET 608 is configurable between a first or “ON” state and a second or “OFF” state. As will be well understood by those skilled in the art, an n-channel FET effectively operates as a diode when in the OFF state (i.e., when an appropriate control voltage is not applied to its gate). In FIG. 6, the diode function that the first FET 608 exhibits when in the OFF state is represented by the first diode 608a. That is, when the FET 608 is in the OFF state, the first diode 608a primarily operates to prevent current from flowing from the drain terminal 608D to the source terminal 608S, but allows current to flow from the source terminal 608S to the drain terminal 608D when the diode 608a is appropriately forward biased. The n-channel FET is in the ON state when an appropriate control voltage is applied to the gate, creating a conductive path between the drain D and the source S. Therefore, when the first FET 608 is in the ON state, it acts like a closed switch in the first resonator section 601 .

[0079] As discussed above, circuit 600 may be considered to comprise first resonator section 601 and additional control structure. The control structure comprises comparator 618, zero voltage detector 621, and flip-flop 622, and is configured to detect voltage conditions within first resonator section 601 and to control first FET 608 in response to the detected voltage conditions. This control of first FET 608 by the control structure will now be described in more detail.

[0080] A zero voltage detector 621 is electrically connected to the second node 600B, the zero voltage detector 621 being configured to detect a voltage condition at the point of the circuit 600 to which the zero voltage detector 621 is connected, i.e., a voltage of 0V or near 0V with respect to ground. The zero voltage detector 621 is configured to output a signal for controlling the switching of the state of the FET 608. That is, the zero voltage detector 621 is configured to output a signal to a flip-flop 622. The flip-flop 622 is an electrical circuit that can be set between two stable states. The flip-flop 622 is electrically connected to a first gate driver 623 configured to supply a voltage to the first FET gate terminal 608G depending on the state of the flip-flop. That is, the first gate driver 623 is configured to supply an appropriate voltage to the first FET gate terminal 608G to switch the FET 608 to an ON state when the flip-flop 622 is in one state, but is configured not to supply an appropriate voltage to maintain the FET 608 in an ON state when the flip-flop 622 is in the other state. For example, the first gate driver 623 may be configured to provide an appropriate gate-source voltage to the first FET gate 608G to switch the FET 608 ON when the flip-flop 622 is in the "1" state, and the first gate driver 623 may be configured to not provide this gate-source voltage when the flip-flop 622 is in the "0" state. Thus, the state of the flip-flop means 622 controls whether the first FET 608 is ON or OFF.

[0081] In this example, the zero voltage detector 621 and the first gate driver 623 of the control arrangement are configured to receive respective signals 1011, 1021 from the controller 1001, which enable the controller 1001 to initiate and control the operation of the circuit 600, as discussed in more detail below.

[0082] A control voltage line 619 is electrically connected to the fourth node 600D. The control voltage line 619 is electrically connected to a fifth node 600E via a resistor 617a, and the fifth node 600E is electrically connected to a voltage comparator 618 (hereinafter referred to as comparator 618). The fifth node 600E is electrically connected to a positive terminal of the comparator 618. A negative terminal of the comparator 618 is connected to ground 616. In this example, the comparator 618 is configured to output a signal based on a comparison of the voltage at the fifth node 600E with the ground voltage. The output signal of the comparator 618 is sent to a flip-flop 622. A control voltage 1031 is supplied to the control voltage line 619 via a second resistor 617b from the controller 1001 in this example.

[0083] As discussed above, comparator 618 is electrically connected to provide an output to flip-flop 622. Flip-flop 622 is configured such that the output signal from comparator 618 can cause flip-flop 622 to change state, thereby causing first driver 623 to change the state of first FET 608.

[0084] The operation of the exemplary circuit 600 will now be described in more detail with respect to the first resonator section 601 being activated by the controller 1001 such that the first inductor coil 124 is operated to heat the first susceptor zone 132a.

[0085] Initially, the first FET 608 is set to an OFF state, thereby acting as a diode 608a that prevents current from flowing through the inductor 124. The controller 1001 initiates operation of the circuit 600 to heat the first susceptor zone 132a by switching the FET 608 from an OFF state to an ON state. In this example, the controller initiates operation of the circuit 600 by providing a START signal 1011 to the zero voltage detector 621. This causes the flip-flop 622 to change state, causing the first gate driver 623 to provide a signal to the FET gate terminal 608G to switch the FET to an ON state.

[0086] Switching FET 608 to the ON state initiates what may be referred to as a self-oscillating heating cycle of circuit 600. The ON state of FET 608 then acts as a closed switch, allowing DC current to begin flowing from DC voltage source positive terminal 118a through first inductor 124, via current-sensing resistor 615, and back to DC voltage source negative terminal 118b. First inductor 124, as is well known, generates a back-EMF in accordance with Faraday's Law and Lenz's Law, opposing this initial increase in current. In the ON state, the voltage between drain terminal 608D and source terminal 608S is substantially zero.

[0087] 7A shows a schematic graphical representation of current flowing through first inductor 124 versus time t, beginning when FET 608 is switched on at time t0. At time t0, DC current begins to increase in inductor 124 from zero at a rate that depends on the inductance L1 of inductor 124 and the DC resistance of circuit 600. In one example, current sense resistor 615 has a resistance on the order of 2 mΩ, while inductor 124 has a DC resistance on the order of 2-15 mΩ, or 4-10 mΩ, or in this example, 5.2 mΩ. This increase in current in the inductor corresponds to the storage of magnetic energy by inductor 124, and the amount of magnetic energy that can be stored by inductor 124 depends on its inductance L1, as will be appreciated.

[0088] FIG. 7B also shows a simplified representation of the voltage across current sense resistor 615 versus time t from time t0, when FET 608 is turned on. Shortly after FET 608 is turned on, a large voltage appears across inductor 124, which is the back-EMF generated by inductor 124 as it resists the increasing current. Therefore, at this time, as shown in FIG. 7B, the voltage across current sense resistor 615 is small. This is because nearly all of the voltage difference provided by DC supply 118 is dropped across inductor 124. Then, as the current through inductor 124 increases and the back-EMF of inductor 124 decays, the voltage across current sense resistor 615 increases. This is seen as the appearance of a negative voltage across current sense resistor 615, as shown in FIG. 7B. That is, the voltage across current sense resistor 615 increases in a negative direction with the length of time that FET 608 is on.

[0089] A negative increase in the voltage across current sense resistor 615 corresponds to an increase in the current through inductor 124, and so the magnitude of the voltage across current sense resistor 615 is an indication of the current flowing through inductor 124. While FET 608 remains on, the current through inductor 124 and the voltage across current sense resistor 615 reach their respective maximum values I (which depend on the DC voltage supplied by DC supply 118 and the DC resistance of circuit 600) with a time constant that depends on inductance L1 and the DC resistance of circuit 600. max , V max It should be noted that as the current through the inductor 124 varies after time t, some inductive heating of the susceptor 132 may occur while the DC current through the first inductor 124 increases.

[0090] Circuit 600 is configured so that the amount of energy stored in first inductor 124 during the time FET 608 is switched on can be determined by a control arrangement and controlled by controller 1001. That is, controller 1001 controls the amount of DC current (and thus the amount of magnetic energy) that is allowed to build up in inductor 124, as will now be described.

[0091] As explained above, the control voltage 1031 is applied to the control voltage line 619. In this example, the control voltage 1031 is a positive voltage, and the voltage input to the positive terminal of the comparator 618 (i.e., the voltage at the fifth node 600E) always depends on the value of the control voltage 1031 and the voltage at the fourth node 600D. When the negative voltage across the current sense resistor 615 reaches a certain value, it cancels the positive control voltage 1031 at the fifth node 600E, causing a voltage of 0V (i.e., ground voltage) at the fifth node 600E. In this example, the resistor 617a has a resistance of 2 mΩ. The resistor 617b represents an effective resistance to the controller 1001 of 70 kΩ. The voltage at the fifth node 600E reaches 0V when the negative voltage across the current sense resistor 615 has the same magnitude as the control voltage 1031.

[0092] Comparator 618 is configured to compare the voltage at its positive terminal with the voltage of ground 616 connected to its negative terminal and output a resulting signal. In one example, the comparator is a standard part FAN156 available from On-Semiconductor. Thus, when the voltage at fifth node 600E reaches 0V, comparator 618 receives a 0V signal at its positive terminal, and the result of the comparison by comparator 618 is that the voltage at the positive terminal is equal to the voltage at the negative terminal. Comparator 618 outputs a resulting signal to flip-flop 622, switching off FET 608. Therefore, switching off FET 608 depends on the voltage condition detected in circuit 600. That is, in this example, FET 608 is switched off when comparator 618 detects, by comparing the voltages across its terminals, that the negative voltage across current sense resistor 615 reaches the same magnitude as control voltage 1031, which occurs at time t1. In FIG. 7A, the DC current flowing through inductor 124 at time t1 when FET 608 is switched off is labeled I1.

[0093] When FET 608 is turned off at time t1, FET 608 switches from behaving like a closed switch in resonator section 601 to behaving like diode 608a and effectively like an open switch with respect to the supply from DC supply 118. At time t1, the DC current path through inductor 124 to ground 616 is blocked by FET 608. This causes a decrease in current through first inductor 124 (not shown in FIG. 7A ), and inductor 124 opposes this change in current by creating an induced voltage. Thus, current begins to oscillate back and forth between inductor 124 and capacitors 606, 608 at the resonant frequency of first resonator section 601.

[0094] Similarly, the voltage across inductor 124, and consequently the voltage between drain terminal 608D and source terminal 608S of the first FET, begins to oscillate at the resonant frequency of first resonator section 601. As the current through and voltage across inductor 124 begin to oscillate, susceptor 132 is inductively heated. Thus, switching FET 608 to the OFF state serves to release the magnetic energy stored in inductor 124 at time t1, heating susceptor 132.

[0095] 8 shows a waveform 800 of the voltage across the first FET 608, starting when the FET 608 is in the ON state from time t0 to t1. Over the time period shown in FIG. 8, the first FET 608 is turned off and on twice.

[0096] Voltage waveform 800 includes a first section 800a between times t0 and t1 during which first FET 608 is ON, and second sections 800b-800d during which first FET 608 is switched off. At 800e, FET 608 is switched on again, commencing a third section 800f, corresponding to first section 800a, during which the first FET 608 remains on, and the above-described process of increasing DC current through inductor 124 repeats. Figure 8 further shows a fourth section 800g during which first FET 608 is switched off again, allowing the voltage across FET 608 to oscillate, and a fifth section 800h during which first FET 608 is then switched on again.

[0097] When the first FET 608 is on in sections 800a, 800f, and 800h, the voltage across the first FET 608 is zero. As shown by sections 800b-800d and then section 800g, when the first FET 608 is turned off, the first inductor 124 uses the energy stored in the magnetic field (which is a result of the increased DC current when the first FET 608 was on) to induce a voltage that opposes the drop in current flowing through the first inductor 124 as a result of the first FET 608 being turned off. The voltage induced in the first inductor 124 causes a corresponding fluctuation in the voltage across the first FET 608. During this voltage fluctuation, the first inductor 124 and the capacitors 606, 610 begin to resonate with each other in a sinusoidal waveform. The voltage shown by voltage waveform 800 initially increases (see, e.g., 800b) as the induced voltage in the first inductor 124 increases to counter the drop in current caused by the first FET 608 being turned off, reaches a peak (see, e.g., 800c), and then decreases again to zero (see, e.g., 800d) as the energy stored in the magnetic field of the first inductor 124 gradually decreases.

[0098] The fluctuating voltages 800b-800d and 800g cause corresponding fluctuating currents (not shown), and during the off-time of the first FET 608, the capacitors 606, 610 and the first inductor 124 operate as a resonant LC circuit, so that the total impedance of the combination of the first inductor 124 and the capacitors 606, 610 is at a minimum during this time. It will be appreciated, therefore, that the maximum magnitude of the fluctuating current flowing through the first inductor 124 is relatively large. This relatively large fluctuating current, in turn, causes a relatively large fluctuating magnetic field in the first inductor 124, which generates heat in the susceptor 132. The duration of the fluctuating voltage across the first FET 608, as shown in this example by sections 800b-800d and section 800g, depends on the resonant frequency of the first resonator section 601.

[0099] 6 and 8 , circuit 600 is configured such that when first FET 608 turns off and the voltage across first FET 608 decreases again toward 0V, zero voltage detector 621 detects this voltage condition and outputs a signal to flip-flop 622 to switch first FET 608 back to the ON state. That is, in response to this voltage condition detected in first resonator section 601, FET 608 is switched from the OFF state to the ON state. Zero voltage detector 621 may be thought of as detecting a voltage condition that indicates that a given percentage of a cycle of current oscillation between the inductive and capacitive elements has been completed since FET 608 was switched off. That is, by detecting that the voltage across FET 608 has returned to 0V or nearly 0V, zero voltage detector 621 detects that a half-cycle of current (and voltage) oscillation at the resonant frequency of first resonator section 601 has been completed.

[0100] In some examples, the zero voltage detector 621 may detect when the voltage across the first FET 608 returns to or below the voltage level 801, and in such a case may output a signal that causes the state of the FET 608 to switch before the voltage across the FET 608 reaches exactly 0V. As shown by FIG. 8, the operation of the zero voltage detector 621 shortens the voltage oscillation in the resonator section 601 after a half cycle, thus resulting in a substantially half-sine wave voltage profile across the first FET 608. Further details of the operation of the zero voltage detector 621 are described below with reference to FIG. 9.

[0101] When the first FET 608 is switched on again at point 800e, the DC current driven by the DC source 118 again increases through the first inductor 124. The first inductor 124 may then again store energy in the form of a magnetic field that will be released when the first FET 608 is next switched off to begin resonance within the first resonator section 601. In this manner, the above process is continuously repeated to heat the susceptor 132 as the first FET 608 is repeatedly switched on and off.

[0102] 7A and 7B occurs both when FET 608 is initially turned on in response to START signal 1011 from controller 1001 and when FET 608 is subsequently switched on due to a zero-voltage condition detected by zero-voltage detector 621. In the first case, the current in inductor 124 increases substantially linearly from zero in response to START signal 1011. In the second case, when FET 608 is turned on again in response to the detection of the zero-voltage condition at point 800e, some excess current (e.g., from the previous cycle of switching FET 608 on and off) is circulating through circuit 600. With FET 608 being turned on again after the detection of the zero-voltage condition, the recirculating current causes an initial negative current to flow through FET 608. Then, while FET 608 remains on, the current through FET 608 and inductor 124 increases substantially linearly from the initial negative current value caused by the recirculating current. As the current through inductor 124 increases, the voltage across current sense resistor 615 correspondingly increases in the negative direction, as explained above.

[0103] In examples, the switching on and off of FET 608 may occur at frequencies on the order of 100 kHz to 2 MHz, or on the order of 500 kHz to 1 MHz, or on the order of 300 kHz. The frequency at which FET 608 switches on and off depends on the inductance L, the capacitance C, the DC supply voltage provided by supply 618, as well as the degree to which current continues to recirculate through resonator section 601 and the loading effect of susceptor 132. For example, if the DC supply voltage is equal to 3.6 V, the inductance of inductor 124 is 140 nH, and the capacitance of resonator section 601 is 100 nF, the time FET 608 remains on may be on the order of 2700 ns, and the time it takes to complete a half-cycle of oscillation in which FET 608 turns off may be on the order of 675 ns. These values correspond to a power of on the order of 20 W being supplied to resonator section 601 from DC voltage supply 118. The above value for the time that FET 608 remains on is affected by the amount of current recirculating through the circuit because, as explained above, this recirculating current causes an initial negative current through the inductor when FET 608 switches on. Note also that the time it takes for the current to increase to a value that causes FET 608 to switch off depends at least in part on the resistance of inductor 124, but this has a relatively minor effect on that time compared to the effect of the inductance of resonator section 601. The time it takes to complete a half-cycle of oscillation (675 ns in this example) depends on the resonant frequency of resonator section 601, which is affected not only by the inductance and capacitance values of inductor 124 and capacitors 606 and 610, respectively, but also by the effective resistance formed by the loading of inductor 124 by susceptor 132.

[0104] Thus far, circuit 600 has been described with respect to its operation for heating susceptor 132 with one inductor, namely, first inductor 124, and thus only a portion of circuit 600 used by device 100 has been described. However, as explained above, device 100 further includes a second inductor 126 for heating second zone 132b of susceptor 132. Figure 9 shows a simplified schematic diagram of circuit 600 including second inductor 126 in addition to first inductor 124.

[0105] As shown in FIG. 9 , in addition to the features described with reference to FIGS. 6-8 , circuit 600 includes a second resonator section 701 including a second inductor coil 126, a third capacitor 706, a fourth capacitor 710, and a second FET 708 having a drain terminal 708D, a source terminal 708S, and a gate terminal 708G. Additionally, circuit 600 includes a second gate driver 723 configured to provide a gate-source voltage to second FET gate terminal 708G. Although controller 1001 is not shown in FIG. 9 , controller 1001 controls circuit 600 as described with reference to FIGS. 6-8 and is additionally configured to provide a control signal 1012 to second gate driver 723. For clarity, reference numerals for some of the features of circuit 600 already described with reference to FIG. 6 have been omitted in FIG. 9 .

[0106] As described above, the first inductor 124 is positioned to heat the first zone 132a of the susceptor 132, and the second inductor 126 is positioned to heat the second zone 132b of the susceptor 132. The second inductor 126, the third and fourth capacitors 706, 710, and the second FET 708 are positioned to form the second resonator section 701 in the same manner as the first inductor 124, the first and second capacitors 606, 610, and the first FET 608 are positioned to form the first resonator section 601. In one example, the third and fourth capacitors 706, 710 are also C0G capacitors and may have a capacitance on the order of 100 nF. In one example, the second inductor 126 has a DC resistance on the order of 8 mΩ. When active, the second resonator section 701 operates to heat the susceptor 132 in a manner similar to that described above for the first resonator section 601, and this description will not be repeated here.

[0107] It will be appreciated that the value of the DC resistance of the inductors 124, 126 will affect the efficiency of the circuit 600, as higher DC resistance results in higher resistive losses. Therefore, it may be desirable to minimize the inductor DC resistance, for example, by varying the number of turns, or the cross-section of the inductors 124, 126. Furthermore, it will be appreciated that the AC resistance of the inductor 124 will be large compared to the DC resistance due to the skin effect. Therefore, using litz wire, for example, can reduce the skin effect, thereby reducing the AC resistance and associated resistive losses from the inductors 124, 126. By way of example, if the first inductor 124 has a DC resistance of approximately 5 mΩ, the second inductor 126 has a DC resistance of approximately 8 mΩ, and the circuit operates at approximately 300 kHz, the particular arrangement of the litz wire forming the coils will result in the effective resistance of the inductors 124, 126 being approximately 1.14 times their DC resistance.

[0108] Node 700A in the second resonator section 701 corresponds to the first node 600A in the first resonator section 601 and is electrically connected to the first node 600A and, consequently, to the positive terminal 118a of the DC supply 118. Node 700C is at a position in the second resonator section 701 equivalent to the third node 600C in the first resonator section 601, and node 700C is similarly connected to ground 616.

[0109] It is important to note that the circuit 600 is configured to be operated by the controller 1001 such that only one of the resonator sections 601, 701 is active at any one time. An example of this operation is described in more detail below.

[0110] During activation of one of the resonator sections 601, 701, the zero voltage detector 621 is configured to detect a zero voltage situation in the active resonator section 601, 701 and therefore control the switching of the respective FET 608, 708 of the active resonator section 601, 701. The zero voltage detector 621 controls when the respective FET 608, 708 of the active resonator section 601, 701 is switched on again (such as at point 800e), an example of which will now be described in more detail with reference to Figures 8-10.

[0111] In circuit 600, zero voltage detector 621 is configured to detect a zero voltage condition at second node 600B of first resonator section 601 or at equivalent node 700B of second resonator section 701. When one of first resonator section 601 and second resonator section 701 is active, zero voltage detector 621 detects that the voltage across the respective FET 608, 708 has returned to zero (e.g., point 800e in FIG. 8 ) or is close to zero, e.g., below level 801, each time that FET is switched off. In response to this detection, zero voltage detector 621 outputs a signal to change the state of flip-flop 622. The respective gate driver 623, which is active, then outputs a gate-source voltage to switch the respective FET back on.

[0112] A first small signal diode 725 connects the zero voltage detector 621 to the second node 600B of the first resonator section, and a second small signal diode 726 connects the zero voltage detector 621 to an equivalent node 700B of the second resonator section 701. Specifically, the anodes of the first small signal diode 725 and the second small signal diode are connected to the input of the zero voltage detector 621 via a common node 701B, while the cathodes of diodes 725, 726 are connected to nodes 600B, 700B, respectively.

[0113] The operation of the zero voltage detector 621 in a specific example will now be described with reference to Figure 10. Figure 10 shows the zero voltage detector 621 and the flip-flop 622. In Figure 10, the components that make up the zero voltage detector 621 are enclosed in a dotted box. Node 701B is shown, which is connected to the anodes of first and second small signal diodes 725, 726. Also visible in Figure 13 is a start signal 1011 from the controller 1001 to the zero voltage detector 621.

[0114] The zero voltage detector 621 in this example comprises an inverter gate U103 having input 2 from node 701B and output 4 connected to the input of flip-flop 622. Inverter gate U103 is powered by connections 5 and 3, with capacitor C108 isolating connection 5 from ground. A logic power supply 621a, in this example 2.5V, is applied to input 5 and via pull-up resistor R111 to input 2 of inverter gate U103. The logic power supply 621a, in this example, is provided by controller 1001. Inverter gate U103 is configured to operate as an OR gate for the START signal 1011 and the zero voltage detect signal from node 701B. That is, inverter gate U103 is configured to receive a logic low signal in the form of the START signal 1011 from controller 1001 to initiate operation of circuit 600a. The START signal 1011 may be provided by an "open-drain" signal pin of controller 1001. Inverter gate U103 is further configured to receive a logic low signal from node 701B when one of first and second signal diodes 725, 726 is forward biased due to one of nodes 600B, 700B being at or near zero volts, as described below. When one or both of these logic low signals are received by inverter gate Input 2, inverter gate U103 inverts the received signal and outputs a logic high signal to flip-flop 622.

[0115] The second FET 708 remains off when the first inductor 124 is operated to heat the susceptor 132. When the second FET 708 remains off, the second small signal diode 726 is either unbiased or reverse biased, depending on the voltages at the logic power source and the DC supply 118, i.e., the voltage at the cathode end (closest to node 700B) of the second small signal diode 726 is either substantially the same as or higher than the voltage at the anode end (closest to the zero voltage detector 621) of the second small signal diode 726.

[0116] During operation of the first resonator section 601, when the first FET 608 is off and the voltage across it swings as shown by 800b-d in FIG. 8, the first small signal diode 725 is reverse biased. At the end of this voltage swing, when the voltage reaches or approaches 0V (e.g., at or below level 801) as shown by 800e, the first small signal diode 725 becomes forward biased. Thus, when the first small signal diode 725 is forward biased at 800e, there is a voltage drop across resistor R111 from signal 621a, causing the signal provided to input 2 of inverter gate U103 to be a logic low signal. Therefore, when this logic low signal is inverted by inverter gate U103, a logic high signal is provided at output 4 of inverter gate U103.

[0117] Although the above description describes the operation of zero voltage detector 621 with respect to controlling the switching of first FET 608, it will be understood that zero voltage detector 621 functions similarly using second small signal diode 726 instead of first small signal diode 725 to control second FET 708.

[0118] 10, flip-flop 622 has a clock input CLK, a reset input / RST, and an output Q. Flip-flop 622 further has further inputs D and VCC for supplying power, and in this example the flip-flop receives the same 2.5V logic power supply 621a from controller 1001 as does inverter gate U103. Clock input CLK is connected to output 4 of inverter gate U103 and is configured to receive a signal therefrom. When output 4 of inverter gate U103 switches from a logic low to a logic high (due to a detected zero voltage condition or the receipt of a START signal 1011 at input 2 of inverter gate U103, as explained above), clock input CLK of flip-flop 622 receives a logic high rising edge signal which "clocks" flip-flop 622 and causes flip-flop output Q to go to a high state. Flip-flop 622 has a further input / RST arranged to receive a signal from the output of comparator 618 that causes comparator 618 to change state of flip-flop 621 and drive flip-flop output Q high. Flip-flop output Q is connected to first and second gate drivers 623, 723 which, upon receiving a high output from flip-flop output Q, provide a gate driver signal to their respective FETs 608, 708, whichever gate driver 623, 723 is active (due to receiving signals 1021, 1022 as explained above).

[0119] In one particular example, flip-flop 622 may switch at half the voltage of logic power source 621a, i.e., 1.25V in this example. This means that the sum of the forward bias voltage of first small signal diode 725 and the voltage at first FET drain 608D must be 1.25V for first FET 608 to switch on. Thus, in this example, first FET 608 switches on when its drain 608D is at 0.55V, not exactly 0V. Note that, in the ideal case, switching may occur with 0V across FET 608 to maximize efficiency. This zero-voltage switching is advantageous in that it prevents first FET 608 from discharging capacitors 606, 610 and thereby consuming the energy stored in them.

[0120] 11 shows in more detail the first and second gate drivers 623, 723 and their connections to the gates 608G, 708G of the respective FETs 608, 708. Each of the gate drivers 623, 723 has an input IN configured to receive a signal that depends on the heater activation signals 1021, 1022 provided by the controller 1001. In addition, the signal received by the input IN of the gate drivers 623, 723 depends on whether the signal output by the flip-flop output Q is high or low. The input IN is connected to the output Q of the flip-flop 622 via respective resistors R125, R128, each having a value of 2 kΩ in this example.

[0121] Each of the gate drivers 623, 723 has two further inputs, VDD and XREF, where each input VDD receives a 6V power supply from the controller 1001, and XREF receives a 2.5V logic voltage, in this example, which is the same logic voltage supplied by the controller 1001 to the flip-flop 622 and the inverter gate U103. The input VDD of each of the first and second gate drivers 623, 723 is connected to the 6V supply voltage, and the input VDD is connected to ground via two buffer capacitors C120, C121. Each of the gate drivers 623, 723 further has a terminal GND connected to ground, and the terminals VDD and GND operate to supply power to the gate drivers 623, 723. In this example, the capacitors C120, C121 each have a value of 1 μF. The gate drivers 623, 723 are configured to output a gate drive voltage from their respective outputs OUT. The outputs OUT of gate drivers 623, 723 are connected to FET gates 608G, 708G, respectively, via resistors R114, R115, each having a resistance of 4.99 Ω in this example.

[0122] Each gate driver 623, 723 is configured to receive at its input IN a signal that activates the gate driver only while a logic high signal is provided from the flip-flop output Q and a heater activation signal 1021, 1022 is received from the controller 1001. An "open drain" signal pin may be provided on the controller 1001 that is configured to provide the signal 1021, 1022. In one example,

[0123] By way of example, starting the circuit 600 for heating by one of the resonator sections 601, 701 proceeds by the controller 1001 first starting the desired one of the gate drivers 623, 723 with a respective one of the heater start signals 1021, 1022. The controller 1001 then provides a START signal 1011 to the zero voltage detector 621. The duration of the START signal 1011 should be less than half a cycle of oscillation by the active resonator section 601, 701 (this period may be referred to as the "resonant flyback period"), allowing the circuit to properly begin self-oscillation in response to a detected zero voltage condition. In another example, the order of the START signal 1011 and the respective heater enable signals 1021, 1022 may be reversed so that the START signal 1011 is first applied to set the flip-flop Q output high, and then one of the heater start signals 1021, 1022 is applied to initiate self-oscillation of the resonator section 601, 701 corresponding to the heater to which the signal 1021, 1022 is supplied.

[0124] Continuing with a more detailed description of the control structure for controlling circuit 600, FIG. 12 shows a portion of the control structure including comparator 618 and associated components. In FIG. 12, the positive terminal 118a of DC power supply 118 is shown connected to node 1500A, which is connected to nodes 600A and 700A of first and second resonator sections 601 and 701, respectively. The negative terminal 118b of the DC power supply is connected to node 1500B, which corresponds to node 600D shown in FIG. 6. Node 1500B is connected to ground 616 through current sense resistor 615. A parallel arrangement of capacitors C111, C112, C115, and C116, each having a capacitance of 100 μF in this example, is connected between nodes 1500A and 1500B to provide buffering between nodes 1500A and 1500B.

[0125] FIG. 12 shows in more detail the components involved in the operation of comparator 618 to detect when the current through the active inductor 124 or 126 reaches a given level. As explained with reference to the previous figures, comparator 618 operates to compare a voltage indicative of the amount of DC current flowing through the active inductor (124 or 126) with a control voltage 1031 generated by controller 1001. Comparator 618 receives power via input 6, which in this example is connected via a 100 Ω resistor R116 to a logic power signal of 2.5 V provided by controller 1001 and to the same logic signal as signal 621 a received by flip-flop 622. Comparator power input 6 is connected to ground via a 10 nF capacitor C119. A further terminal 2 of comparator 618 is connected directly to ground.

[0126] In some examples, the controller 1001 is a microprocessing unit that includes a timer (not shown) for generating a signal that produces the control voltage 1031. In this example, the control voltage 1031 is produced by a pulse-width modulated signal PWM_DAC generated by the controller 1001. The timer of the controller 1001 generates a pulse-width modulated square wave having a magnitude of, for example, about 2.5 V and a frequency of, for example, about 20 kHz, and a particular duty cycle. The pulse-width modulated signal PWM_DAC is filtered by 10 nF capacitors C127 and C128 and two 49.9 kΩ resistors R121, R123, and a 10 kΩ resistor R124 to produce a substantially constant control voltage 1031 at the frequency at which the controller 1001 controls the control voltage 1031 (for example, about 64 Hz). To adjust the control voltage 1031, the controller 1001 is configured, for example, to adjust the duty cycle of the pulse-width modulated signal PWM_DAC applied to the circuit 600. Therefore, the components positioned between the input PWM_DAC and the positive terminal of the comparator 618 effectively enable the control voltage 1031 to be generated by a pulse-wave modulated signal, and the magnitude of the control voltage 1031 to be adjusted by adjusting the duty cycle of this pulse-wave modulated signal. Thus, the control voltage line 619 shown in FIGS. 6 and 9 may be replaced by these components. However, in other examples, the control voltage 1031 may be generated by a substantially constant voltage, for example, provided by the controller 1001. In such examples, some or all of the components shown in FIG. 12 for filtering the signal PWM_DAC may not be present.

[0127] Node 1500B, which is input to the positive input of comparator 618, corresponds to node 600D of circuit 600, as discussed above. As discussed with reference to the simplified schematic diagram shown in FIG. 6, it can be seen from FIG. 12 that node 1500B is connected to the positive input of comparator 618 through resistor 617a. Thus, the operation of comparator 618 is to receive at its positive terminal an input that depends on control voltage 1031 and the voltage across current sense resistor 615, as discussed above. When the voltage at the positive terminal of comparator 618 reaches ground, a signal / FF RST is output via resistor R118 to the input / RST of flip-flop 622, causing flip-flop 622 to change state, thereby switching off active FET 608 / 708.

[0128] Figure 13 shows further components of a particular example of a control structure for circuit 600. The components shown in Figure 13 define a current sensing device 1300 for providing a signal I_SENSE indicative of the amount of current drawn from DC voltage supply 118 during operation of circuit 600. From this signal, controller 1001 may determine the current drawn from voltage supply 118 and may use this, along with the value of the voltage provided by DC voltage supply 118, to determine a value for the power supplied to circuit 600. In some examples, the determined value of power may be used by controller 1001 to control circuit 600, as described below.

[0129] Input 1301 to current sensing device 1300 is provided via resistor R120 as shown in FIG. 12. The input is therefore connected to node 1500B via resistor R120 and receives a voltage indicative of the voltage across current sensing resistor 615. Current sensing device 1300 operates as a low-side current sensing device for circuit 600. In that regard, current sensing device 1300 comprises an operational amplifier U110 (part type TS507) operating with a voltage of 3.8V supplied to input 5 of the operational amplifier U110 configured for low-side current sensing using current sensing resistor 615, as will be appreciated. Transistor U109 (part type RN4986) with an internal bias resistor operates to switch up the 2.5V supplied by controller 1001 to the 3.8V supply for operational amplifier U110. The power supply line from transistor component U109 is connected to ground via a 10nF capacitor C132. Additionally, a 1 kΩ resistor R130 is connected between the positive input of operational amplifier U110 and ground, and a 412 kΩ resistor R129 is connected between the 2.5 V input from controller 1001 and the positive input of comparator U110. The negative terminal of operational amplifier U110 receives a voltage that depends on the voltage across current sense resistor 615. Resistor R131 and capacitor C133 in series provide filtering of the voltage signal received via input 1301. A further resistor R133 (having a resistance of 97.6 kΩ in this example) and a 10 nF capacitor C134 are connected in parallel between the input to the negative terminal of operational amplifier U110 and the output of operational amplifier U110 so that the operational amplifier operates in closed-loop mode.

[0130] Op-amp U110 operates to output a voltage signal I_SENSE to controller 1001 that is indicative of the current through current sense resistor 615, thereby enabling controller 1001 to determine the current drawn from DC voltage supply 118 through circuit 600.

[0131] It should be noted that, taking into account the first and second FETs 608 and 708 and the topology of circuit 600, the phase relationship of the first and second inductor coils 124 and 126 relative to each other may be selected such that when the first inductor coil 124 is operated, a current sufficient to cause significant heating of the susceptor 132 is prevented from flowing through the second inductor coil 126, and when the second inductor coil 126 is operated, a current sufficient to cause significant heating of the susceptor 132 is prevented from flowing through the first inductor coil 124.

[0132] As explained above, when the first FET 608 and the second FET 708 are switched off, they effectively act as diodes 608 a, 708 a and, therefore, may conduct current when forward biased (i.e., the FETs are not perfect switches). Thus, by way of example, the circuit 600 may be configured such that when one of the first inductor coil 124 and the inductor coil 126 is active to heat the susceptor 132, the voltage induced across the other, inactive inductor coil reverse biases the intrinsic diode of the FET associated with that inactive inductor coil without forward biasing it.

[0133] The effect of the above-described control arrangement being configured to control the switching arrangements 608, 708 of circuit 600 in response to detected voltage conditions is that when one of the first and second resonator sections 601, 701 is active (i.e., its gate driver 623, 723 is activated by controller 1001), that resonator section will "self-oscillate" while the other section remains inactive. That is, the switching of each FET 608, 708 in resonator section 601, 701 occurs repeatedly at a high frequency as a first voltage condition (detected by comparator 618) switches the FET from on to off and a second voltage condition (detected by zero voltage detector 621) switches the FET from off to on.

[0134] The controller 1001 is configured to control the induction heating circuit 600 of the device 100 such that only one of the first inductor 124 and the second inductor 126 is active at any one time. The controller 1001 is configured to determine which of the first inductor 124 and the second inductor 126 to activate at a predetermined frequency.

[0135] As an example, during use of the device 100, the controller 1001 determines which of the first resonator section 601 and the second resonator section 701 to activate at a predetermined frequency, i.e., once every multiple predetermined time intervals. In one example, each time the controller 1001 determines which of the first resonator section 601 and the second resonator section 701 to activate, the controller 1001 may determine which of the resonator sections to activate to heat the susceptor 132 for the duration of the next predetermined interval. That is, if the predetermined frequency (sometimes referred to as the "shutdown rate") is, for example, 64 Hz, the controller 1001 may determine, at predetermined intervals of 1 / 64 s, which of the resonator sections 601 and 701 to activate for the duration of the subsequent 1 / 64 s until the controller makes a next decision regarding which of the resonator sections 601 and 701 to activate at the end of the subsequent 1 / 64 s interval. In another example, the shutoff rate may be, for example, 20 Hz to 80 Hz, or the predetermined interval may be correspondingly long, for example, 1 / 80 s to 1 / 20 s. To determine which inductors 124, 126 should be activated for the predetermined interval, the controller 1001 determines which susceptor zones 132 a, 132 b should be heated for the predetermined interval. For example, the controller 1001 determines which susceptor zones 132 a, 132 b should be heated by reference to the measured temperatures of the susceptor zones 132 a, 132 b, as described below.

[0136] 14 shows a flowchart of an exemplary method for determining which of the two resonator sections 601, 701 should be activated for a particular predetermined interval. In this example, the controller 1001 determines which of the first resonator section 601 and the second resonator section 701 to activate for a particular predetermined interval based on the current temperature T1 of the first susceptor zone 132a heated by the first inductor 124 and the current temperature T2 of the second susceptor zone 132b heated by the second inductor 126. In one example, the current temperatures T1 and T2 of the first susceptor zone 132a and the second susceptor zone 132b may be measured by respective thermocouples (not shown) attached to each zone of the susceptor 132. The thermocouples provide input to the controller 1001 that enables the controller 1001 to determine the temperatures T1 and T2. In other examples, other suitable means may be used to determine the temperature of each of the susceptor zones 132a, 132b.

[0137] In block 1051, the controller 1001 determines the current value of the temperature T1 and compares it to a target temperature target1 for the first zone 132a arranged to be heated by the first inductor 124. The target temperature target1 for the first zone 132a has a value that can vary throughout a usage session of the device using the circuit 600. For example, a temperature profile may be defined for the first zone that defines a value for target1 throughout a usage session of the device 100.

[0138] In block 1052, the controller 1001 performs the same operation as was performed for the first inductor 124 in block 1051, determining whether the current temperature T2 of the second zone 132b is less than the target temperature target2 for the second zone 132b at this time. Again, the target temperature of the second zone 132b may be defined by a temperature profile that defines the value of target2 throughout the use session. The temperature of the second zone 132b, like the first zone 132a, may be measured by any suitable means, such as a thermocouple.

[0139] If the answer in both blocks 1051 and 1052 is "No", i.e., if both susceptor zones 132a, 132b are currently at or above their respective target temperatures target1, target2, the controller 1001 determines that neither the first nor second resonator sections 601, 701 should be activated for the next predetermined interval.

[0140] If the answer in block 1051 is "No" and the answer in block 1052 is "Yes", i.e., if the first zone 132a is at or above its target temperature target1 but the second zone 132b is below its target temperature target2, the controller 1001 determines that the second resonator section 701 should be activated to heat the second zone 132b for the next predetermined interval.

[0141] If the answer in block 1051 is "yes" and the answer in block 1052 is "no", i.e., if the first zone 132a is below its target temperature target1 and the second zone 132b is at or above its target temperature target2, the controller 1001 determines that the first resonator section 601 should be activated to heat the first zone 132a for the next predetermined interval.

[0142] If the answer at block 1051 is "Yes" and the answer at block 1052 is "Yes", i.e., if both the first zone 132a and the second zone 132b are below their respective target temperatures target1, target2, the controller 1001 proceeds to block 1053. At block 1053, the controller 1001 effectively operates to alternate between activating the first resonator section 601 and the second resonator section 701 for each predetermined interval that both zones 132a, 132b remain below their respective target temperatures.

[0143] In one example, to alternately activate the first resonator section 601 and the second resonator section 701, in block 1053, the controller 1001 determines whether an even number of predetermined intervals have elapsed since the start of the session, in some examples. If an even number of predetermined intervals have elapsed since the start of the session, the controller 1001 determines that the first resonator section 601 should be activated for the next interval. If an odd number of predetermined intervals have elapsed since the start of the session, the controller 1001 determines that the second resonator section 701 should be activated for the next interval. It should be understood that in other examples, the controller 1001 may instead activate the second resonator section 701 when an even number of intervals have elapsed and activate the first resonator section 601 when an odd number of intervals have elapsed.

[0144] In a particular example, circuit 600 is configured such that once one of resonator sections 601, 701 is activated by receipt of signal 1021 or 1022 at one of gate drivers 623, 624, that resonator section 601 / 701 continues to operate, i.e., self-oscillate, until that resonator section 601 / 701 is deactivated by controller 1001, for example, by providing a different signal to the gate driver for that resonator section 601 / 701. Thus, upon determining which of resonator sections 601, 701 to activate during a given interval, controller 1001 may deactivate one of resonator sections 601, 701 that was active during the previous interval to initiate this activation.

[0145] To give an example of block 1053 of method 1050 shown in FIG. 14 being performed at 1 / 64 s intervals, if controller 1001 determines that both zones 132a, 132b are below their respective target temperatures target1, target2 and an even number of 1 / 64 s intervals have elapsed since the start of a usage session of device 100, controller 1001 activates first resonator section 601 for the next 1 / 64 s interval while deactivating second resonator section 701, which, by way of example, requires controller 1001 to deactivate second resonator section 701. If after this next 1 / 64 s interval both zones 132a, 132b remain below their respective target temperatures target1, target2, then for the subsequent 1 / 64 s interval the controller 1001 activates the second resonator section 701 while the first resonator section 601 is deactivated, which, by way of example, requires the controller 1001 to deactivate the second resonator section 701. This alternating activation of the first resonator section 601 and the second resonator section 701 continues for each interval that both zones 132a, 132b remain below their respective target temperatures.

[0146] Overall, method 1050 has the effect that the two inductors 124, 126 are never activated simultaneously. If it is determined that both inductors 124, 126 require activation to bring their respective zones 132a, 132b to their target temperatures, controller 1001 alternates between supplying power to inductors 124, 126 at a predetermined frequency to bring both zones 132a, 132b up to their respective target temperatures. Thus, for example, during a use session that includes multiple intervals during which first zone 132a is substantially below its target temperature and second zone 132b is at or above its target temperature, method 1050 can be seen to have the effect that power can be supplied to first resonator section 601 for nearly 100% of this period. However, during a use session that includes multiple intervals during which both zones 132a, 132b are below their target temperatures, each inductor may receive power for approximately 50% of this period.

[0147] As noted, when both zones 132a, 132b are at their target temperatures, power may not be supplied to either inductor. In a particular example, during a heating session lasting a predetermined period of time (e.g., 3, 3.5, 4, or 4.5 minutes), either inductor may receive power for more than about 75% of the time or more than about 80% of the time. In other words, both inductors may be at the target temperature for more than 75% of the time or more than 80% of the time, so that a constant supply of power is not required. Instead, power is supplied only when the temperatures of zones 132a, 132b are below their respective target temperatures. In a particular example, the heating session lasts for a period of 260 seconds, with the first inductor 124 receiving power for a total of about 25 seconds during the heating session and the second inductor coil 126 receiving power for a total of about 19 seconds during the heating session. More generally, each inductor may receive power for approximately 7% to 15% of the time during a heating session, meaning that the inductor is operational for approximately 14% to 30% of the time.

[0148] The power supplied over each 1 / 64 second interval can be determined as the product of the DC voltage across DC supply 118 during that interval and the average DC current drawn from DC supply 118 during that interval. In a particular example, when the inductor is operated during an interval, the power may be between about 15 W and about 25 W, or more preferably between about 20 W and about 23 W.

[0149] The energy consumed by the inductor during that interval is determined by the power multiplied by the length of the interval. Thus, the energy consumed by the inductor during that interval may be between about 0.31 J and about 0.36 J. When the inductor is not operating (because zones 132a, 132b are at the target temperature), the power supplied to the inductor and the energy consumed by the inductor may be negligible. For example, the energy consumed by the inductor may be less than about 0.01 J.

[0150] The first and second inductors 124, 126 may be collectively referred to as a heater / heating assembly. Assuming the inductors are activated for only about 25% of the time during a heating session, as discussed above, the total energy consumed by the inductors during that session is between about 1200 J and about 1400 J. Assuming the inductors are activated for only about 20% of the time during a heating session, the total energy consumed by the inductors is between about 1000 J and about 1150 J. Depending on the characteristics of the heater assembly, the environment, and the items received by the device, the total energy consumed by the inductors may be between about 1000 J and about 1400 J.

[0151] In one example, the DC supply 118 (i.e., battery) has a battery capacity of approximately 3000 mAh and a voltage of approximately 3-4 V, which results in a capacity of between approximately 30,000 J and approximately 35,000 J. In a specific example, the battery capacity is approximately 33,000 J. This allows the DC supply 118 to provide power for approximately 25-30 heating sessions.

[0152] In a specific example, when the device is inactive, the current draw is approximately 0.1 mA. Most of this current draw is quiescent current drawn by the voltage regulator of the DC supply 118. In one example, the regulator is a 2.5 V regulator. Some of this current may be due to small leakage currents in any additional powered integrated circuits present in the device, such as those associated with the charging socket 114. Assuming the battery has a voltage of approximately 3.7 V, the power consumed by the device when inactive may be approximately 0.370 mW. Preferably, an inactive device 100 consumes less than approximately 1 mW, or less than approximately 0.5 mW, or less than approximately 0.4 mW.

[0153] When the controller 1001 is active, the current draw may be approximately 3 mA. Therefore, the controller 1001 consumes approximately 0.01 W during use. In one example, the controller 1001 has a 16 MHz clock. Preferably, the controller 1001 consumes less than approximately 0.05 W, or less than approximately 0.03 W, or less than approximately 0.01 W.

[0154] Device 100 may further include visual indicators, such as a plurality of LEDs. As briefly mentioned above, FIG. 2 shows second printed circuit board 138. Four LEDs are mounted on second printed circuit board 138. The LEDs may be illuminated to indicate certain events to the user, such as when the device is ready for use. Each LED may draw approximately 2 mA of current at maximum brightness or intensity. The four LEDs collectively consume approximately 0.03 W of power when all at maximum brightness. Preferably, the visual indicators consume less than approximately 0.05 W, or less than approximately 0.04 W, or less than approximately 0.03 W. The LEDs may be illuminated, for example, during a heating session.

[0155] Thus, during a heating session, the heating assembly may consume between about 15 W and about 25 W. The other electrical components in the device (i.e., all components except for inductors 124, 126) may consume a total power of about 0.04 W (about 0.03 W for the LEDs and about 0.01 W for the voltage regulator, controller 1001, and other leakage currents). Preferably, the power consumption of the electrical components is less than about 0.1 W, or less than about 0.05 W.

[0156] It will be appreciated that in the above example, the power will vary depending on the voltage of the battery 118. In the above example, it is assumed that the voltage of the battery 118 is approximately 3.7V.

[0157] In one example, the power consumption of the electrical components is less than about 0.5% of the power consumption of the heating assembly (i.e., the inductor). Preferably, the power consumption of the electrical components is less than about 0.2% of the power consumption of the heating assembly. For example, the power consumption of the heater assembly (i.e., the inductor) may be about 20 W, while the power consumption of the other electrical components is about 0.04 W. Thus, the power consumption of the electrical components is about 0.2% of the power consumption of the heating assembly.

[0158] For example, the controller 1001 is further configured to determine the power being supplied to one of the resonator sections 601, 701 from the DC supply 118 at predetermined intervals that correspond, for example, to the predetermined intervals at which the method 1050 is performed.

[0159] As explained above, particularly with reference to Figures 9 to 11, in order to control whether the first resonator section 601 or the second resonator section 701 is active at any one time, the controller 1001 is configured to selectively send a first heater operating signal 1011 to the first gate driver 623 to activate the first resonator section 601 or a second heater operating signal 1012 to the second gate driver 723 to activate the second resonator section 701, in addition to sending a START signal 1001 to initiate operation of the circuit 600.

[0160] For example, when the controller 1001 initiates operation of the circuit 600 and the controller 1001 sends a first heater operating signal 1011, the circuit 600 operates to activate the first inductor 124 to heat the first susceptor zone 132a, as described above. When the controller 1001 sends a second heater operating signal 1012, the circuit 600 operates to activate the second inductor 126 to heat the second susceptor zone 132b. If the controller 1001 does not send either the first heater signal 1011 or the second heater signal 1012, then neither the inductors 124, 126 are activated and the susceptor 132 is not heated.

[0161] The controller 1001 is configured to control the power supplied from the DC voltage supply 118 to the circuit 600 for inductive heating of the susceptor 132 based on a comparison of a measured value of the power supplied to the circuit 600 with a target power. The controller 1001 is configured to control the power supplied to the circuit 600 by controlling the switching components of the circuit 600, i.e., by controlling the switching of the FETs 608, 708. The controller 1001 may control the switching of the FETs 608, 708 by setting a control voltage 1031. The control voltage 1031 determines the DC current that is allowed to build in the inductor 124, 126 corresponding to the FET 608, 708 before the FET 608, 708 is switched off.

[0162] 15 shows an example method 1100 performed by the controller 1001 to control the power supplied to the circuit 600. In block 1101, the controller 1001 determines the power P supplied to the circuit 600 from the DC supply 118. For example, the controller 1001 may determine the average value of the power supplied to the circuit 600 during a previous predetermined interval. As an example, the power P supplied to the circuit 600 during an interval may be determined by measuring the voltage across and the DC current driven through a given one of the resonator sections 601, 701. The controller 1001 may then determine the product of the voltage across and the DC current through a given one of the resonator sections 601, 701 to determine the power P supplied to that resonator section.

[0163] By way of example, the determined power P is the average power supplied from the DC supply 118 over a given interval, which may be determined by determining the product of the average DC voltage across the DC supply 118 and the average DC current drawn from the DC supply 118 over the previous interval.

[0164] In the exemplary device 100, the DC supply 118 is a battery connected to a controller 1001, which outputs the voltage of the DC supply 118 to the circuit 600. The controller 1001 is configured to determine the DC voltage provided by the battery 118. The current drawn from the battery 118 is determined by operation of a current sensing device 1300. The controller 1001 determines the DC voltage and DC current once every 1 / 64 second interval. The DC voltage can be considered substantially constant over this short period of time. However, the current is fluctuating at a rate that depends on the rapid rate at which the circuit switches on and off. As explained above, this is on the order of 300 kHz in some examples. The current sensing device 1300 outputs a signal I_SENSE that is filtered to remove this 300 kHz signal, as explained above with reference to FIG. 13 . Thus, the average DC current over a 1 / 64 second interval is obtained by taking a measurement of this filtered signal I_SENSE, which is taken just before the end of the 1 / 64 second interval to allow the signal from the filter to settle. As a result, controller 1001 can obtain measurements of DC voltage and DC current over the 1 / 64 second interval and multiply these values to obtain the determined power P. This determined power P may be considered to be the average value of the power supplied by DC supply 118 over the 1 / 64 second interval.

[0165] In block 1102, the supplied power P determined in block 1101 is compared to a target power. If the determined power P is the average power over a predetermined interval, the target power is the target average power over the same interval. In one example, the target power is a target value for the average power supplied over the predetermined interval and may have a value between 10 and 25 W, or between 15 and 23 W, or about 20 W. In this example, the target power is, for example, in the range of 20 to 21 W or 15 to 25 W. Thus, in block 1102, the controller 1001 may compare the supplied power value P determined in block 1101 with a target range and determine whether the supplied power is below the range, within the target range, or above the target range. For example, if the target range is 20 to 21 W, then in block 1102 the controller 1001 determines whether P<20 W, 20 W≦P≦21 W, or P>21 W.

[0166] Based on a comparison of the supplied power P with the target range, the controller 1001 determines whether and how to adjust the power over the next predetermined interval in order to bring the actual power supplied to the active inductor 124 or 126 over the next predetermined interval closer to the target power range. That is, if the supplied power P is less than the target range, the controller 1001 determines to increase the power supplied to the circuit 600 over the next predetermined interval. If the supplied power P exceeds the target range, the controller 1001 determines to decrease the power supplied to the circuit 600 over the next predetermined interval. If the supplied power P is less than the target range, the controller 1001 determines not to adjust the power supplied to the circuit 600 over the next predetermined interval.

[0167] Due to the configuration of circuit 600 described above, the delivered power P over a given interval depends on the value of control voltage 1031 over that interval. Taking one 1 / 64 s interval during which first resonator section 601 is active as an example, this 1 / 64 s interval includes multiple repeating cycles of sections 800a-800e of voltage waveform 800 and their repetitions. During each cycle between times t1 and t0, resonator section 601 is allowed to resonate, and because FET 608 is off during this period, no power is drawn from DC supply 118 through first resonator section 601. Thus, substantially all of the power drawn from DC supply 118 during a given 1 / 64 s interval to power resonator section 601 is drawn during the time period between t0 and t1 when current is “conducting” in inductor 124, i.e., FET 608 is on. The time between t1 and t0 is determined by the resonant frequency of the first resonator section 601. This resonant frequency may remain substantially constant at least throughout a given 1 / 64 s interval (although it may vary over the duration of operation of the circuit 600 due to dependence on coil and susceptor temperatures and battery voltage). The length of time t0 to t1 is determined by the value of the control voltage 1031, as well as the DC voltage supplied by the DC supply 118 and the resistance and inductance of the first resonator section 601 (and similarly for the second resonator section 701). That is, for a given DC supply voltage, the control voltage 1031 sets the current I1 that is allowed to increase in the inductor 124 between t0 and t1; however, if the DC supply voltage decreases, the time required to increase to a given value of I1 increases. Therefore, the average power delivered during the 1 / 64 s interval depends on the value of the control voltage 1031.

[0168] Thus, by way of example, to control the power delivered to the circuit 600 during the next interval, the controller 1001 sets the value of the control voltage 1031 for the next interval. By way of example, for a given DC supply 118 over a given interval in which one of the resonator sections 601, 701 is active, the more positive the value of the control voltage 1031, the greater the value of the power P delivered to the circuit 600. Thus, in such an example, if the controller 1001 determines that the delivered power P was above the target range over the previous interval, the controller 1001 reduces the control voltage 1031 for the next interval. If the controller 1001 determines that the delivered power P was below the target range over the previous interval, the controller 1001 increases the control voltage 1031 for the next interval. If the controller 1001 determines that the delivered power P was above the target range over the previous interval, the controller 1001 leaves the control voltage 1031 unchanged for the next interval.

[0169] It should be noted that in one example of the above method 1100, the delivered power P determined in block 1101 is the power delivered to a particular one of the resonator sections 601, 701. For example, the power P may be determined by measuring the voltage across and the DC current through the first resonator section 601. In one such example, the power P delivered to the first resonator section 601 is used to control the control voltage 1031. It should also be noted that for a given control voltage 1031, in some examples, the power delivered to each of the inductors 124, 126 when the respective resonator section 601, 701 is active may be different. This may be because, for example, the inductors 124, 126 have different values of inductance or DC resistance, or because the capacitances of the two resonator sections 601, 701 are unequal. Therefore, in this example, during a given predetermined interval, a target power outside the target power range may be supplied to the second resonator section 701, but since the control voltage 1031 is controlled based on the power P supplied to the first resonator section 601, in this example the controller 1001 does not have to adjust the control voltage 1031.

[0170] For example, for a given value of the control voltage 1031, the controller 1001 may determine in block 1101 that an average power of 20 W was delivered to the first resonator section 601 over a given interval, with the target voltage being 20-21 W in this example. In block 1102, the controller 1001 determines that the delivered voltage was within the target range, and thus the controller 1001 decides not to adjust the control voltage 1031. Consider that over the next predetermined interval, the controller 1001 determines (via exemplary method 1050) that the second resonator section 701 should be activated and the first resonator section 601 should not be activated. For the given value of the control voltage 1031, in this example, 22.5 W is delivered due to the difference in the electrical properties of the first resonator section 601 and the second resonator section 701. However, in this example, in block 1102, the controller 1001 compares the last measured value of the power P delivered to the first resonator section 601 and therefore decides not to adjust the control voltage 1031 in block 1103. As such, in one example of method 1100, the power delivered to the circuit 600 may be outside of a target range. However, this may make it possible to control the power delivered to the inductors 124, 126 by measuring only the power P delivered to one of the resonator sections 601, 701. This may provide a simple and useful solution for maintaining the power delivered to the circuit 600 within an acceptable range, for example, when the resonator sections 601, 701 and their components have roughly similar electrical characteristics.

[0171] As noted above, in some examples, DC supply 118 is a battery having a voltage on the order of 2-10 V, or 3-5 V, or in one example, on the order of 4.2 V. In some examples, the DC voltage produced by DC supply 118 may change, e.g., decrease, over the time that circuit 600 is operated. For example, if DC voltage source 118 is a battery, the battery may initially provide a voltage of 4.2 V, but the voltage provided by the battery may decrease as the battery depletes. Thus, after a given period of time, DC voltage source 118 may provide, for example, 3.5 V rather than the initial 4.2 V.

[0172] As explained above, for a given supply voltage, the value of control voltage 1031 controls the amount of current allowed to build in the active inductor 124 / 126 before the respective FET 608 / 708 is switched off. Power is provided by DC voltage supply 118 to "fire" the active inductor 124 / 126 by allowing a DC current to build when FET 608, 708 is on. Also as explained above, the time t1 it takes for the current to build up to a value that causes FET 608 / 708 to switch depends on the DC voltage supply. Thus, for example, if the voltage provided by DC supply 118 is reduced, the rate at which current builds up in inductor coil 124 will decrease, resulting in a reduction in power P supplied to circuit 600.

[0173] The exemplary method 1100 may allow the target power to be maintained even if the supply voltage from the DC supply 118 changes. That is, because the actual supplied power P is determined and used to control the control voltage 1031, the controller 1001 may operate to maintain the target power by adjusting the control voltage 1031. For example, if the battery level is depleted, the controller 1001 may measure a decrease in the power P supplied to the circuit 600 at a given control voltage 1031 and operate to increase the power P supplied to the circuit by increasing the control voltage 1031. Thus, the target power level may be maintained while the battery used to power the circuit 600 is depleted. This is advantageous because maintaining the target power level may optimize the efficiency of operation of the induction heating circuit 600. For example, maintaining the supplied power substantially constant may enable stable heating of the aerosolizable material 110a regardless of the supply voltage. Similarly, the exemplary method 1100 allows for a substantially constant power supply regardless of other changing factors in the circuit that may affect the amount of power delivered, such as a different load on the circuit 600 presented by the susceptor 132 as the temperature of the susceptor 132 increases. This provides a consistent and good consumer experience, for example, by providing a consistent time to first draw, i.e., a consistent time from when the device 100 is activated to when it is ready to provide aerosol to be inhaled by the user.

[0174] In another example, the measured power value P based on which the control voltage 1031 is controlled is varied throughout a use session. For example, during a particular use session, during a first portion of the use session (e.g., approximately the first 60 seconds of the use session), the temperature profile may be such that the first inductor 124 is primarily active, while the second inductor 126 is inactive. During this first portion of the use session, it may be appropriate to base the control of the control voltage 1031 on a measurement of the power delivered to the first resonator section 601. However, later in the session, again due to, for example, the temperature profile of the session, the second inductor 126 may be primarily active, while the first inductor 124 is active for a lesser amount of time. Thus, during a second portion of the use session (e.g., after approximately 60 seconds), it may be advantageous to control the control voltage 1031 based on a measurement of the power delivered to the second resonator section 701. Thus, the controller 1001 may switch from basing control of the control voltage 1031 on a measurement of the power supplied to the first resonator section 601 to basing control of the control voltage 1031 on a measurement of the power supplied to the second resonator section 701. In this way, for example, the target power may be more closely adhered to throughout a usage session because the control voltage 1031 is set based on a comparison of the actual power being delivered to the active inductors 124, 126 with a target power range.

[0175] In some examples, if the controller 1001 determines in block 1103 that the power should be adjusted, the controller 1001 may adjust the control voltage 1031 in predetermined steps. For example, the controller 1001 may be configured to adjust the control voltage 1031 by a predetermined amount at each predetermined time interval. If the controller 1001 determines in block 1102 that the supplied power P was below the target power range, the controller 1001 may increase the control voltage 1031 by a predetermined number of volts at the next predetermined interval. Conversely, if the controller 1001 determines in block 1102 that the supplied power was above the target power range, the controller 1001 may increase the control voltage 1031 by a predetermined amount at the next predetermined interval.

[0176] In the example described above, particularly with reference to FIG. 12 , the control voltage 1031 is generated by a pulse wave modulated signal PWM_DAC. As described above, the signal PWM_DAC has a rectangular waveform of 2.5 V. The duty cycle of the signal PWM_DAC is controllable by the controller 1001, which sets a value between 0 and 800 for the duty cycle of the PWM_DAC, where 0 corresponds to a 0% duty cycle and 800 corresponds to a 100% duty cycle. The filtered signal PWM_DAC provides a substantially constant control voltage 1031, so that a setting of the duty cycle of the PWM_DAC signal between 0 and 800 results in the control voltage 1031 having a magnitude between 0 and 2.5 V. In this example, the controller 1031 may adjust the duty cycle setting of the PWM_DAC signal by a set amount, such as 8 out of 800, for each predetermined interval, or leave the setting unchanged. In another example, the controller 1001 may allow the control voltage 1031 to be adjusted by some other means, and if the controller 1001 determines that the control voltage 1031 should be adjusted, the controller 1001 may adjust the control voltage 1031 by, for example, 1%, or 2%, or 5% of the maximum value of the control voltage 1031 for the next predetermined interval.

[0177] In some examples, when operation of circuit 600 is initiated by controller 1001, e.g., when a usage session of device 100 including circuit 600 is initiated, control voltage 1031 is set to a predetermined initial value. In one example, a value of control voltage 1031 corresponding to a target power level (e.g., a duty cycle setting of signal PWM_DAC that results in this value of control voltage 1031) is determined during configuration of circuit 600. That is, the power delivered to circuit 600 may be determined (e.g., measured or theoretically determined) for multiple values of control voltage 1031, e.g., to create a calibration curve. The value of control voltage 1031 corresponding to the target power may then be determined. In one example, DC supply 118 may supply 4.2 V, and to achieve a target power of 20 W, controller 1001 may determine a calibration value for the duty cycle of the PWM_DAC signal setting of, e.g., 344 out of 800.

[0178] In one example, the controller 1001 is configured to set the control voltage 1031 to an initial value based on this determined value of the control voltage 1031. For example, the initial value of the duty cycle of the PWM_DAC that determines the control voltage 1031 may be set to half of the determined value that corresponds to the target power. For example, if the duty cycle setting for the control voltage 1031 that is known to correspond to the target power is 344 out of 800, the controller 1001 may begin a session with the setting set to 152 out of 800 and increase the setting by a predetermined amount at predetermined intervals until the measured power P is within the target range. This may have the effect that at the beginning of a use session, the delivered power may be well below the target power, and then the delivered power may be increased (by the controller 1001 increasing the control voltage 1031) until it reaches the target power range. This initial increase in delivered power provides improved safety in the operation of the circuit 600, preventing overheating of the susceptor at the beginning of a session and allowing the circuit 600 to respond to the actual supplied power determined by the controller 1001.

[0179] In one example, the predetermined interval is the same predetermined interval used by the controller 1001 in the method 1050 for determining whether to activate the first inductor 124 or the second inductor 126. In one such example, as described above, the predetermined interval is 1 / 64 seconds long. The length of the predetermined interval (i.e., the shutoff rate) may be selected to provide an advantageous time interval during which the controller can monitor the circuit and adjust parameters accordingly. For example, a shutoff rate of 64 Hz or within a range of approximately 10-100 Hz may be used. At these exemplary shutoff rates, the controller 1001 may measure the increase in temperature of a susceptor zone at a rate high enough to determine to stop heating by a particular inductor 124, 126 before the zones 132a, 132b of the susceptor 132 can increase significantly above their target temperature. Similarly, the examples given for the shutoff rate may provide advantageous frequencies at which the control voltage 1031 may be adjusted to enable the power supplied to the inductors 124, 126 to be appropriately controlled within a safe target range.

[0180] In an exemplary method of operation of circuit 600, a target power for use by controller 1001 in controlling power delivered to circuit 600 is predetermined based on characteristics of the intended use session. For example, the target power range may be adjusted throughout the use session.

[0181] 16 shows a schematic example of a temperature profile, target1, for a portion of a use session, in this example a target temperature for a single susceptor zone 132a. In this example, initially, in a first portion 1201 of the use session, the first zone 132a is substantially below its target temperature, target1. In this first portion 1201, the circuit 600 operates to raise the first zone 132a to the target temperature, target1. In such an exemplary portion of a use session, the target power, P1, may have a value ranging from, for example, 20 to 21 W. The target power during the first portion 1201 of the session may be relatively high to quickly raise the susceptor 132, and therefore the aerosolizable material 110a, to a temperature appropriate for generating an aerosol for inhalation by the user.

[0182] As the use session progresses, the first zone 132a substantially reaches its target temperature, target1. A second portion 1202 of the use session may be defined as beginning shortly after the first zone 132a reaches its target temperature, target1. By way of example, throughout this portion 1202 of the use session, the first zone 132a may be substantially at its target temperature, target1, e.g., 250°C, and may be maintained at target temperature, target1, in accordance with method 1050. Similarly, although this is not shown in FIG. 16 , the second zone 132b may be maintained at its target temperature, target2, in accordance with method 1050 (the target temperature, target2, of the second zone 132b may define a different temperature profile than that defined by target1).

[0183] Portion 1202 of the use session, after first zone 132a has substantially reached temperature target1, may be characterized by controller 1001 operating to maintain the temperature of first zone 132a (or both zones 132a and 132b) rather than increasing the temperature of first zone 132a to its target temperature, target1, as in first portion 1201. As such, relatively less power may need to be supplied to susceptor zone 132a to maintain target temperature, target1, during portion 1202 of the use session compared to the power required to increase susceptor zone 132a to target temperature, target1. In second portion 1202 of the use session, it may be advantageous to reduce the value of target power P1 compared to the value of target power P1 in portion 1201. In one example, target power level P1 may be reduced during portion 1202 of the use session from 20-21 W in portion 1201 to approximately 15 W. Reducing the target power P1 in this manner may be advantageous in some instances because using a lower level of power energy may reduce losses in the circuit, thus increasing efficiency.

[0184] During the third portion 1203 of the use session, the value of target temperature target1 is 0, i.e., the first inductor 124 is not activated. At this point, if the use session has ended, the target power P1 may also be reduced to 0, or, if the second inductor 126 is still activated, the target power P1 may remain at a non-zero value while the second inductor 126 is activated. Thus, the target power may take into account the temperature profiles of both zones 132a, 132b at any point during the use session. If a portion of the use session requires, for example, a significant increase in the temperature of one zone, a relatively high target power may be appropriate. Conversely, a relatively low target power may be used during portions of the use session that do not require significant heating of either zone 132a, 132b.

[0185] As noted above, using a lower power level during a particular period of a usage session can provide the advantage that energy savings can be realized over the duration of the session. For example, if the target power level is reduced from 20-21 W in the first period to approximately 15 W in the second period, energy savings of approximately 5-10% can be realized in some instances due to reduced energy losses in the circuit 600 operating at the lower power. In one example, over the course of a typical session approximately 260 seconds in length, maintaining the target power at approximately 20 W for the entire duration of the session can result in energy usage of approximately 1000 J. However, reducing the target power to approximately 15 W once the first zone 132a initially reaches its set temperature and maintaining the target power level at 15 W for the remainder of the session of substantially the same length can result in energy usage of between 900-950 J. By way of example, nearly all of the power used by the device is attributable to the energy supplied to heat the susceptor 132. The power usage of electrical components other than the heating circuit, such as the LED indicators and microcontroller, may be on the order of less than 0.1 W, and in some instances may be on the order of less than 0.01 W.

[0186] Certain methods described herein may be implemented as non-transitory computer program code that may be stored on a non-transitory storage medium. For example, in certain examples, the controller 1001 may include a non-transitory computer-readable storage medium having a set of computer-readable instructions stored thereon and a processor that, when executed by the controller 1001, performs the methods described herein. The controller 1001 may include one or more processors. For example, in some examples, the controller 1001 is a programmable microprocessing unit, as described above. The controller 1001 may include a storage medium that includes a set of machine-readable instructions, e.g., in the form of computer code, that, when executed by the controller 1001, causes the controller 1001 to perform the methods described herein.

[0187] While circuits including two inductor coils are described above, it should be noted that the aspects described above, such as those for controlling the power supplied to the induction heating circuit, may apply to circuits having a different number of coils, such as one or more than two coils. Furthermore, while the description herein describes induction circuits including inductor coils, the aspects described herein may equally apply to induction circuits using other types of inductive elements having inductance and suitable for generating a varying magnetic field for heating the susceptor structure. Additionally, while the circuits above are described with respect to induction heating, features related to the electrical components and power consumption of the heating components apply equally to embodiments using resistive heating.

[0188] The above-described embodiments should be understood as illustrative examples of the present invention. Further embodiments of the present invention are contemplated. It should be understood that any feature described with respect to any one embodiment may be used alone or in combination with other described features, and may also be used in combination with one or more features of any other embodiment or any combination of any other embodiments. Furthermore, equivalents and variations not described above may be employed without departing from the scope of the present invention, as defined in the appended claims. [Item of invention] [Item 1] 1. An aerosol delivery device comprising: a plurality of electrical components; a heating assembly including a heater component for heating the aerosol-forming material; a battery for powering the plurality of electrical components and the heating assembly; Equipped with An aerosol delivery device, wherein, during use, the electrical components consume less than about 0.25 W of power. [Item 2] Item 10. The aerosol delivery device of item 1, wherein the power consumption of the electrical components is less than about 50 mW. [Item 3] 3. The aerosol delivery device of claim 2, wherein the power consumption of the electrical components is less than about 40 mW. [Item 4] 4. The aerosol delivery device of any one of items 1 to 3, wherein the plurality of electrical components comprises a controller, and when the controller is active, the power consumption of the controller is between about 10 mW and about 20 mW, and when the controller is inactive, the power consumption of the plurality of electrical components is less than about 0.5 mW. [Item 5] 5. The aerosol delivery device of any one of items 1 to 4, wherein the plurality of electrical components comprises a plurality of LEDs, each LED having a power consumption of less than about 10 mW at maximum intensity. [Item 6] 1. An aerosol delivery device comprising: a plurality of electrical components; a heating assembly including a heater component for heating the aerosol-forming material; a battery for powering the plurality of electrical components and the heating assembly; Equipped with An aerosol delivery device, wherein, during use, the power consumption of the plurality of electrical components is less than about 1% of the power consumption of the heating assembly. [Item 7] 7. The aerosol delivery device of any one of items 1 to 6, wherein the power consumption of the heater assembly during use is between about 15 W and about 25 W. [Item 8] 8. The aerosol delivery device of any one of items 1 to 7, wherein the battery has a battery capacity of between about 30,000 J and 35,000 J. [Item 9] 9. The aerosol delivery device of any one of items 1 to 8, wherein the heater assembly is configured to operate for a period of about 3 minutes to about 5 minutes and to consume about 1000 J to about 1400 J during said period. [Item 10] 10. The aerosol delivery device of any one of items 1 to 9, wherein the heater assembly further comprises at least one coil configured to heat the heater component. [Item 11] Item 11. The aerosol delivery device of item 10, wherein the heater assembly comprises a first coil and a second coil configured to heat the heater component. [Item 12] 12. The aerosol delivery device of any one of items 1 to 11, wherein the exterior surface of the aerosol delivery device remains below about 48°C during use. [Item 13] The aerosol delivery device according to any one of items 1 to 12, an article containing an aerosol-forming material; An aerosol delivery system comprising:

Claims

1. 1. An aerosol delivery device comprising: a plurality of electrical components; a heating assembly including an induction heating circuit and a heater component for heating the aerosol-generating material over a heating session; a battery for powering the plurality of electrical components and the heating assembly, the battery providing a supply voltage; Equipped with the plurality of electrical components comprises a controller; the controller is configured to control the supply of power to the induction heating circuit; when the supply voltage varies, the controller is configured to vary a control voltage supplied to the induction heating circuit to maintain a supply of power equal to a target power; the aerosol delivery device is configured such that during a first portion of a use session, a first inductor coil of the heating assembly is primarily active while a second inductor coil of the heating assembly remains substantially inactive; the controller is configured to control the control voltage based on a measurement of power delivered to the first inductor coil; during a second portion of the use session, the second inductor coil is primarily active while the first inductor coil is active less of the time; the controller is configured to switch control of the control voltage based on a measurement of power delivered to the second inductor coil; the first inductor coil and the second inductor coil are not activated simultaneously; An aerosol delivery device in which, when it is determined that both inductor coils require activation to reach their target temperatures, a controller alternates between supplying power to the first inductor coil and the second inductor coil according to a predetermined interval.

2. 1. An aerosol delivery device comprising: a plurality of electrical components; a heating assembly including an induction heating circuit and a heater component for heating the aerosol-generating material over a heating session; a battery for powering the plurality of electrical components and the heating assembly, the battery providing a supply voltage; Equipped with the plurality of electrical components comprises a controller; the controller is configured to control the supply of power to the induction heating circuit; when the supply voltage varies, the controller is configured to vary a control voltage supplied to the induction heating circuit to maintain a supply of power equal to a target power; The aerosol delivery device, wherein the controller is configured to maintain the supply of power equal to a target power regardless of changes in load caused by a susceptor changing temperature, so as to provide a stable time between when the aerosol delivery device is activated and when it is ready to provide aerosol to be inhaled by a user.

3. The aerosol delivery device of claim 1 or 2, wherein the target power is constant over the heating session.

4. 3. The aerosol delivery device of claim 1, wherein the target power decreases from a first constant value in a first period to a second constant value in a second period.

5. 3. The aerosol delivery device of claim 1, wherein the current drawn from the battery is measured by the controller and used to determine the power supply.

6. the aerosol delivery device is configured such that during a first portion of a use session, a first inductor coil of the heating assembly is primarily active while a second inductor coil of the heating assembly remains substantially inactive; The aerosol delivery device of claim 2 , wherein the controller is configured to control the control voltage based on a measurement of power delivered to the first inductor coil.

7. during a second portion of the use session, the second inductor coil is primarily active while the first inductor coil is active less of the time; The aerosol delivery device of claim 6 , wherein the controller is configured to switch control of the control voltage based on a measurement of power delivered to the second inductor coil.

8. 3. The aerosol delivery device of claim 1, wherein the controller is configured to adjust the control voltage by a predetermined amount over a predetermined time interval to adjust the power supply to the target power when the power supply is not equal to the target power.

9. The aerosol delivery device of claim 8 , wherein the control voltage is generated by a pulse-wave modulated signal, and adjusting the control voltage includes adjusting a duty cycle of the pulse-wave modulated signal.

10. 9. The aerosol delivery device of claim 8, wherein the control voltage is generated by a pulse wave modulated signal, and adjusting the control voltage includes adjusting a maximum voltage of the pulse wave modulated signal.

11. the controller is configured to set a control voltage supplied to the induction heating circuit to a predetermined initial value at the start of a heating session; 9. The aerosol delivery device of claim 8, wherein the controller is configured to repeatedly increase the control voltage by a predetermined amount over the predetermined time interval until the delivery of power reaches the target power.

12. 9. The aerosol delivery device of claim 8, wherein the predetermined time interval is the same as the predetermined interval used by the controller to determine whether to activate the first inductor coil or the second inductor coil of the heating assembly.

13. 3. The aerosol delivery device of claim 1, wherein one or more inductor coils of the induction heating circuit are operated intermittently during a heating session, with each inductor coil receiving power for less than 30% of the time of the heating session.

14. 3. The aerosol delivery device of claim 1, wherein the battery is a DC power supply configured to provide a voltage of 2 to 10V.

15. 3. The aerosol delivery device of claim 1, wherein, during use, the electrical components consume less than about 0.25 W of power.

16. 3. The aerosol delivery device of claim 1, wherein, during use, the power consumption of the plurality of electrical components is less than about 1% of the power consumption of the heating assembly.

17. 3. The aerosol delivery device of claim 1, wherein the electrical components consume less than about 50 mW of power.

18. 3. The aerosol delivery device of claim 1, wherein the electrical components consume less than about 40 mW of power.

19. 3. The aerosol delivery device of claim 1, wherein the power consumption of the controller is between about 10 mW and about 20 mW when the controller is active, and the power consumption of the plurality of electrical components is less than about 0.5 mW when the controller is inactive.

20. 3. The aerosol delivery device of claim 1, wherein the plurality of electrical components includes a visual indicator, the visual indicator consuming less than about 0.05 W when active.

21. 3. The aerosol delivery device of claim 1, wherein the power consumption of the heating assembly during use is between about 15 W and about 25 W.

22. The aerosol delivery device of claim 1 or 2, wherein the induction heating circuit further comprises at least one coil configured to heat the heater component.

23. 3. The aerosol delivery device of claim 1, wherein the heating assembly comprises a first inductor coil and a second inductor coil configured to heat the heater component.

24. 3. The aerosol delivery device of claim 1, wherein the exterior surface of the aerosol delivery device remains below about 48°C during use.

25. The aerosol delivery device of claim 1 or 2; an article containing an aerosol-forming material; An aerosol delivery system comprising:

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