An aerosol generating device

Abstract

An aerosol generating device is described. The aerosol generating device includes an air passage (38) extending from an air inlet (40) of the aerosol generating device, a microcontroller unit, and a sensor assembly (42). The sensor assembly (42) includes a temperature sensor (44) located in the air passage (38) and adapted to measure the temperature in the air passage (38) and to provide temperature measurements to the MCU, and a heater (46) located in the air passage (38) upstream of the temperature sensor (44) and adapted to heat air flowing past the heater (46) from the air inlet (38). The MCU is adapted to use the temperature measurements from the temperature sensor (44) to determine one or more characteristics of a puff taken by a user of the aerosol generating device when air flows through the air passage (38).

Description

[0001] AN AEROSOL GENERATING DEVICE

[0002] Technical Field

[0003] The present disclosure relates generally to an aerosol generating device, and in particular a device that is adapted to heat aerosol generating material to generate an aerosol for inhalation by a user.

[0004] The present disclosure is particularly applicable to a portable (hand-held) aerosol generating device.

[0005] Technical Background

[0006] Devices which heat, rather than bum, an aerosol generating material to produce an aerosol for inhalation have become popular with consumers in recent years. A commonly available reduced-risk or modified-risk device is the heated material aerosol generating device, or so-called heat-not-bum device. Devices of this type generate an aerosol or vapour by heating an aerosol generating material to a temperature typically in the range 150°C to 300°C, and in some cases as high as 350°C. This temperature range is quite low compared to an ordinary cigarette. Heating the aerosol generating material to a temperature within this range, without burning or combusting the aerosol generating material, generates a vapour which typically cools and condenses to form an aerosol for inhalation by a user of the device.

[0007] The aerosol generating material may be a solid or liquid. For example, an aerosol generating article that is received in the aerosol generating device in use may include aerosol generating material in the form of solid or semi-solid substrate of plant derived material, such as tobacco.

[0008] The aerosol is inhaled by the user in one or more puffs. Each puff may be characterised by its start time, its end time, its instantaneous flow rate, its maximum flow rate, total volume etc. It may be important to measure one or more of these characteristics to control the operation of the aerosol generating device. There is a need for an improved aerosol generating device where one or more characteristics of a puff taken by a user are accurately determined.

[0009] Summary of the Disclosure

[0010] According to a first aspect of the disclosure, there is provided an aerosol generating device comprising: an air passage extending from an air inlet of the aerosol generating device; a microcontroller unit (or MCU); and a sensor assembly comprising: a temperature sensor located in the air passage and adapted to measure the temperature in the air passage and to provide temperature measurements to the MCU, and a heater located in the air passage upstream of the temperature sensor (i.e., between the air inlet and the temperature sensor) and adapted to heat air flowing past the heater from the air inlet, e.g., so that when a puff is taken by a user, heat is transferred from the heater to the temperature sensor by forced air convection; wherein the MCU is adapted to use the temperature measurements from the temperature sensor to determine one or more characteristics of a puff taken by a user of the aerosol generating device when air flows through the air passage.

[0011] The device may comprise a heating chamber for receiving at least part of an aerosol generating article that comprises aerosol generating material, and a primary heater (or heating assembly) configured to heat the aerosol generating material to generate an aerosol. The primary heater may be an induction heater with an induction coil disposed around or adjacent to the heating chamber, or may comprise one or more resistive heaters, e.g., a low power thin film heater, printed heater etc.

[0012] The aerosol generating material may comprise any type of solid or semi-solid material. Example types of aerosol generating solids include powder, granules, pellets, shreds, strands, particles, gel, strips, loose leaves, cut filler, porous material, foam material or sheets. The aerosol generating material may comprise plant derived material and in particular, may comprise tobacco. It may advantageously comprise reconstituted tobacco, for example including tobacco and any one or more of cellulose fibres, tobacco stalk fibres and inorganic fillers such as CaCO3.

[0013] Consequently, the aerosol generating device may be referred to as a “heated tobacco device”, a “heat- not-bum tobacco device”, a “device for vaporising tobacco products”, and the like, with this being interpreted as a device suitable for achieving these effects. The features disclosed herein are equally applicable to devices which are designed to vaporise any aerosol generating material, including a liquid material or substrate.

[0014] The aerosol generating article may be formed substantially in the shape of a stick, and may broadly resemble a cigarette, having a tubular region with an aerosol generating material or substrate arranged in a suitable manner. The aerosol generating article may include a filter segment, for example comprising cellulose acetate fibres, at a proximal end of the aerosol generating article. The filter segment may constitute a mouthpiece filter and may be in coaxial alignment with the aerosol generating material. One or more vapour collection regions, cooling regions, and other structures may also be included in some designs. For example, the aerosol generating article may include at least one tubular segment upstream of the filter segment. The tubular segment may act as a vapour cooling region. The vapour cooling region may advantageously allow the heated vapour generated by heating the aerosol generating material to cool and condense to form an aerosol with suitable characteristics for inhalation by a user, for example through the filter segment. The aerosol generating material may comprise an aerosol-former. Examples of aerosol-formers include polyhydric alcohols and mixtures thereof such as glycerine or propylene glycol. Typically, the aerosol generating material may comprise an aerosol-former content of between approximately 5% and approximately 50% on a dry weight basis. In some embodiments, the aerosol generating material may comprise an aerosol-former content of between approximately 10% and approximately 20% on a dry weight basis, and possibly approximately 15% on a dry weight basis.

[0015] Upon being heated, the aerosol generating material may release volatile compounds. The volatile compounds may include nicotine or flavour compounds such as tobacco flavouring.

[0016] The aerosol generating device may be configured to heat an aerosol generating material or substrate, without burning the aerosol generating material, to volatise at least one component of the aerosol generating material and thereby generate a heated vapour which cools and condenses to form an aerosol for inhalation by a user of the aerosol generating device.

[0017] In general terms, a vapour is a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapour may be condensed to a liquid by increasing its pressure without reducing the temperature, whereas an aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. It should, however, be noted that the terms ‘aerosol’ and ‘vapour’ may be used interchangeably in this specification, particularly with regard to the form of the inhalable medium that is generated for inhalation by a user.

[0018] It is known to use the temperature drop of the primary heater to determine generally when the user takes a puff. In other words, by monitoring the temperature of the primary heater it may be possible to determine when a puff is happening and when a puff is not happening. But it is not possible to determine the characteristics of the puff such as its start time, its end time, its instantaneous flow rate, its maximum flow rate, total volume etc. Using a temperature drop of the primary heater to try and determine when the user takes a puff may be negatively affected by any degradation of the primary heater, including if the primary heater gets dirty, for example, as well as changes in environmental factors such as humidity and ambient temperature. Using a sensor assembly comprising a temperature sensor and a separate heater (i.e., not the primary heater) allows for precise determination of one or more puff characteristics, not just a general determination of whether the user is taking a puff or not. Because the heater is located in the air passage upstream of the temperature sensor, an output value of the temperature sensor is indicative of the heat that is transferred from the heater. The amount of heat transferred from the heater per unit of time depends on the puff. Consequently, the MCU may determine one or more characteristics of the puff by analysing an instantaneous value or a time-varying value of the temperature sensor (e.g., an instantaneous output voltage or time-varying voltage that is provided by the temperature sensor and which is indicative of the measured temperature). Because the heater and the temperature sensor are implemented in the same sensor assembly, they are separated by a short distance. It therefore means that the distance over which the heat from the heater is transferred to the temperature sensor is also short. Such an arrangement is not easily affected by changes in environmental factors such as humidity and ambient temperature, for example. It may also be noted that the thermal mass of the heater of the sensor assembly will typically be an order of magnitude smaller than the thermal mass of the primary heater and any delay in detecting the start of a puff is therefore minimised.

[0019] The heater may be adapted to heat the air flowing past the heater based on a target temperature set by the MCU.

[0020] The MCU may be adapted to set the target temperature based on a constant or time-varying value. In this arrangement, the target temperature does not depend on the temperature measurements from the temperature sensor but is set by the MCU to an appropriate value. The value may be a constant or fixed value or may be a value that varies, e.g., during the course of the vaping session or depending on an operating condition of the aerosol generating device, for example.

[0021] When the user takes a puff, air is drawn into the air passage through the air inlet, is pre-heated by the heater and flows through the air passage past the downstream temperature sensor. The air may flow out of the air passage into the heating chamber, where it may then flow through the aerosol generating material. When the sensor assembly is operating, e.g., during a vaping session where the user is actively taking puffs, the temperature sensor may continuously measure the temperature of the air passage and provide the measurements to the MCU. Initially, the nominal temperature of the air passage will be substantially the same as the external ambient temperature. It will be understood that in the present description, the term “nominal temperature” is used to refer to the temperature of the air passage between puffs - i.e., when air is not flowing through the air passage and heat is not being transferred from the heater to the temperature sensor by forced air convection. Because the time between puffs when air is not flowing through the air passage is normally significantly longer than the times when the user is taking a puff, it will be understood that the temperature sensor will normally measure the nominal temperature and that any rapid deviation from the nominal temperature will normally indicate that a puff is being taken by the user. In a typical vaping session, the time between puffs may be about 20-30 seconds, whereas an individual puff may last about 2 seconds, for example. It is only when air is flowing through the air passage that heat is transferred from the heater to the temperature sensor by forced air convection, which will result in a rapid and temporary increase in the temperature measured by the temperature sensor. As described in more detail below, the temperature measurements may therefore be used by the MCU to determine one or more characteristics of a puff, such as the start time of the puff, the end time of the puff, the instantaneous flow rate of the puff, the maximum flow rate of the puff, and the total volume of the puff, for example. The start time of the puff may be indicated by the time when the temperature measured by the temperature sensor starts to increase rapidly from the nominal temperature or where the rate of change of the temperature measured by the temperature sensor exceeds a threshold, for example. It will be understood that heat starts to be transferred from the heater to the temperature sensor at the start of a puff. The end time of the puff may be indicated by the time when the temperature measured by the temperature sensor returns substantially the nominal temperature, i.e., the temperature measured before the start of the puff, or when the rate of change of the temperature measured by the temperature sensor falls below a threshold, for example. It will be understood that heat stops being transferred from the heater to the temperature sensor at the end of a puff because air stops flowing through the air passage. The instantaneous flow rate of the puff may be estimated or determined based on the deviation of the measured temperature from the nominal temperature, for example. The maximum flow rate of the puff may be estimated or determined based on the maximum deviation of the measured temperature from the nominal temperature, for example. The total volume of the puff may be estimated or determined using an integrating process as described in more detail below. Determining the one or more puff characteristics may allow improved dynamic haptic and / or auditory feedback to be provided to the user - i.e., where the feedback depends on the one or more puff characteristics. The one or more puff characteristics may also be used to control an operation or function of the aerosol generating device, e.g., adjusting the heating or calculating the remaining amount of aerosol generating material or substrate.

[0022] At the start of a vaping session, the nominal temperature of the air passage will normally be the substantially the same as the external ambient temperature. As the primary heater starts to heat up, the nominal temperature will gradually increase as a result of thermal transfer from the primary heater of the aerosol generating device that is used to heat the aerosol generating material. This gradual increase (or “drift”) in the nominal temperature of the air passage may negatively affect the determination of the puff characteristics unless it is compensated for. The MCU may be adapted to set the target temperature for the heater of the sensor assembly to be higher than the measured nominal temperature. This makes sure that the air that enters the air passage through the air inlet is pre-heated by the heater to a temperature that is higher than the measured nominal temperature before it reaches the downstream temperature sensor. Otherwise, the measurements provided by the temperature sensor will not be influenced by the temperature of the air flowing through the air passage during a puff, but only by the thermal transfer of heat from the primary heater of the aerosol generating device. Put another way, the MCU may not be able to use the temperature measurements from the temperature sensor to determine one or more puff characteristics if the temperature of the air flowing through the air passage is about the same as, or less than, the measured nominal temperature of the air passage.

[0023] The aerosol generating device may further comprise an operational amplifier. The operational amplifier may include a non-inverting input terminal, an inverting input terminal, and an output terminal. The non-inverting input terminal may be adapted to receive one of:

[0024] (a) an output voltage from the heater, and

[0025] (b) an output voltage from the temperature sensor that is indicative of the temperature measurements.

[0026] The inverting input terminal may be adapted to receive the other one of:

[0027] (a) an output voltage from the heater, and

[0028] (b) an output voltage from the temperature sensor that is indicative of the temperature measurements.

[0029] In other words, the non-inverting input terminal of the operational amplifier may be electrically connected to one of the heater and the temperature sensor of the sensor assembly, and the inverting input terminal of the operational amplifier may be electrically connected to the other one of the heater and the temperature sensor.

[0030] The heater and the temperature sensor may have a temperature coefficient characteristic where the resistance of the heater and the temperature sensor vary as a function of temperature. The resistance of the heater and the temperature sensor may be measured from a respective voltage across the heater and the temperature sensor. It means that the voltage across the heater and the temperature sensor is indicative of the temperature. The operational amplifier subtracts the value provided to the inverting input terminal from the value provided to the non-inverting input terminal. It means that the operational amplifier subtracts the output voltage from the temperature sensor from the output voltage from the heater or vice versa. The operational amplifier outputs the result of that subtraction, or an amplified result of that subtraction, at the output terminal. For precise determination of puff characteristics, it is important to extract a component from the output voltage of the temperature sensor that relates only to the heat transferred from the heater to the temperature sensor. It will be understood that the output voltage of the temperature sensor will include a component that relates to the nominal temperature. This nominal temperature may be affected by heat that is transferred to the temperature sensor from the primary heater, so it may be time-varying value - e.g., it may increase as the aerosol generating device gradually heats up. The output voltage of the heater will also include a component that relates to the nominal temperature. Consequently, subtracting the output voltage from the temperature sensor from the output voltage from the heater or vice versa will therefore cancel the component that relates to the nominal temperature. If this component is properly cancelled, the output voltage provided by the operational amplifier may be substantially constant unless the user takes a puff. Put another way, the output terminal of the operational amplifier may be adapted to provide an output voltage that is indicative of compensated temperature measurements (i.e., where the component of the output voltage of the temperature sensor that relates to the nominal temperature has been properly compensated for). The MCU may be further adapted to receive the output voltage from the temperature sensor that is indicative of the temperature measurements, and the output voltage from the operational amplifier that is indicative of compensated temperature measurements. For example, the temperature sensor and the output terminal of the operational amplifier may be electrically connected to respective input terminals of the MCU so that output voltages from the temperature sensor and the operational amplifier are provided to the MCU.

[0031] The MCU may be further adapted to use the output voltage from the temperature sensor that is indicative of the temperature measurements to set the target temperature for the heater of the sensor assembly.

[0032] The MCU may be further adapted to use the output voltage of the operational amplifier that is indicative of the compensated temperature measurements to determine the one or more characteristics of the puff.

[0033] The MCU may be further adapted to determine the volume of the puff if the output voltage of the operational amplifier increases in response to the puff (e.g., a positive deviation) by:

[0034] (a) integrating only the part of the output voltage of the operational amplifier that is greater than a threshold voltage, or

[0035] (b) integrating the output voltage of the operational amplifier to obtain a first value, integrating a threshold voltage to obtain a second value, and subtracting the second value from the first value.

[0036] Alternatively or additionally, the MCU may be further adapted to determine the volume of the puff if the output voltage of the operational amplifier decreases in response to the puff (e.g., a negative deviation) by:

[0037] (a) inverting the output voltage of the operational amplifier and integrating only the part of the inverted output voltage of the operational amplifier that is greater than a threshold voltage, or

[0038] (b) inverting the output voltage of the operational amplifier, integrating the inverted output voltage of the operational amplifier to obtain a first value, integrating a threshold voltage to obtain a second value, and subtracting the second value from the first value.

[0039] As explained above, if the component that relates to the nominal temperature is cancelled or properly compensated for, the output voltage provided by the operational amplifier may be a substantially constant value (e.g., a “baseline” value) unless the user takes a puff. The temperature of the heater of the sensor assembly is normally higher than the temperature of the temperature sensor, so the “baseline” value may be a non-zero value. In the output voltage of the operational amplifier, the puff may be identified as a positive or negative deviation from the “baseline” value depending on how the operational amplifier is electrically connected to the heater and the temperature sensor, i.e., if the noninverting terminal is electrically connected to the heater and the inverting terminal is electrically connected to the temperature sensor or vice versa. The threshold voltage used in option (a) above may be set based on the “baseline” value and it may move the baseline value to the zero-crossing line. The threshold voltage used in option (b) may be set based on the “baseline” value (or more particularly, on an integration of the “baseline” value), and it may extract an integrated value coming from only the positive or negative deviation of the output voltage of the operational amplifier.

[0040] The aerosol generating device may further comprise a voltage regulator adapted to output a constant voltage, and a npn bipolar transistor.

[0041] The npn bipolar transistor may include:

[0042] - a base terminal adapted to receive the output voltage from the operational amplifier, e.g., wherein the base terminal is electrically connected to the output terminal of the operational amplifier,

[0043] - a collector terminal adapted to receive the constant output voltage from the voltage regulator, e.g., where the collector terminal is electrically connected to the voltage regulator, and

[0044] - an emitter terminal adapted to provide an output voltage indicative of compensated and amplified temperature measurements.

[0045] The MCU may be further adapted to use the output voltage from the npn bipolar transistor that is indicative of the compensated and amplified temperature measurements to determine the one or more characteristics of the puff. For example, the emitter terminal of the npn bipolar transistor may be electrically connected to an input terminal of the MCU. In this arrangement, the npn bipolar transistor may amplify an output current from the emitter terminal of the npn bipolar transistor itself based on the output voltage of the operational amplifier. More particularly, the output current from the emitter terminal is further amplified as the output voltage of the operational amplifier increases. Since the output voltage of the npn bipolar transistor has a correlation with the output voltage of the operational amplifier, the output voltage of the npn bipolar transistor may be used in preference to the output voltage of the operational amplifier that is indicative of the compensated temperature measurements.

[0046] The aerosol generating device may further comprise a current limiting resistor. The current limiting resistor may include:

[0047] - a first end adapted to receive the output voltage from the voltage regulator, e.g., where the first end is electrically connected to the voltage regulator, and

[0048] - a second end adapted to provide a voltage to the temperature sensor, e.g., where the second end is electrically connected to the temperature sensor. The current limiting resistor may be electrically connected in parallel with the npn bipolar transistor.

[0049] The second end of the current limiting resistor may also be adapted to provide a voltage to the heater, e.g., where the second end is also electrically connected to the heater. In this arrangement, the voltage regulator is used to output voltage from the temperature sensor and / or the heater in addition to amplifying the output voltage from the operational amplifier.

[0050] The aerosol generating device may further comprise a power supply path adapted to supply a voltage for heating the heater of the sensor assembly (e.g., the power supply path may be electrically connected to the heater). The power supply path may be electrically connected in parallel with the current limiting resistor and the npn bipolar transistor. Since the constant output voltage from the voltage regulator is provided to the MCU, a high regulated voltage is not suitable. On the other hand, a high voltage is beneficial for efficient and rapid heating of the heater. In this arrangement, a dedicated voltage is therefore supplied to the heater through the power supply path for efficient and rapid heating of the heater.

[0051] The voltage supplied through the power supply path for heating the heater may be greater than the constant output voltage of the voltage regulator. The voltage supplied through the power supply path may be generated by boosting the output voltage of a power supply (e.g., a battery or other energy storage device). The output voltage may be boosted by a power converter, for example.

[0052] The MCU may be adapted to set the target temperature for the heater of the sensor assembly based on the temperature measurements from the temperature sensor plus a temperature offset. For the precise determination of one or more puff characteristics, a temperature of the temperature sensor typically needs to be increased by the transfer of heat from the heater, e.g., by forced air convection. This means that the temperature of the heater is preferably higher than the temperature of the temperature sensor. In this arrangement, the target temperature of the heater is set to be higher than the temperature that is measured by the temperature sensor by an appropriate temperature offset. This may ensure that the actual temperature of the heater is always higher than an actual temperature of the temperature sensor.

[0053] The MCU may be adapted to smooth the temperature measurements from the temperature sensor, e.g., to determine a moving average of the temperature measurements. Alternatively, the aerosol generating device may further comprise a smoothing circuit (e.g., an analog circuit) adapted to smooth the temperature measurements. The smoothing circuit may be electrically connected between the temperature sensor and an input terminal of the MCU. The smoothing carried out by the MCU or the smoothing circuit effectively removes the deviations in the temperature measurements from the temperature sensor that are caused when the user takes a puff and heat is transferred from the upstream heater. The MCU may be adapted to set the target temperature based on the smoothed temperature measurements plus a temperature offset. This means that the deviations of the temperature measurements from the temperature sensor caused by the puffs are not used to set the target temperature.

[0054] The temperature offset may be in the range of from about 10°C to about 40°C, for example. If the temperature offset is too small, not enough heat may be transferred from the heater to the temperature sensor when the user takes a puff. However, if the temperature offset is too large it may result in too much power being supplied to the heater. A temperature offset of between about 10°C to about 40°C may be considered to be preferred because it may ensure that enough heat is transferred for precise determination of one or more puff characteristics without excessive power being supplied to the heater. Alternatively, a narrower range (e.g., from about 20°C to about 30°C) or a wider range (e.g., from about 10 °C to about 50 °C) may be preferred.

[0055] The aerosol generating device may further comprise a printed circuit board assembly (PCBA) comprising a first printed circuit board, and a second printed circuit board physically separated from the first printed circuit board. The MCU may be mounted on the first printed circuit board. The temperature sensor and the heater may be mounted on the second printed circuit board. The MCU may therefore be spaced apart from the heater. This arrangement may be beneficial to protect the MCU from the heat that is generated by the heater.

[0056] The aerosol generating device may further comprise a heating chamber adapted to receive an aerosol generating article, in use, and a primary heater positioned adjacent the heating chamber and adapted to heat the aerosol generating article. The primary heater may therefore be physically separated from the heater of the sensor assembly. The aerosol generating article may comprise aerosol generating material.

[0057] According to a second aspect of the disclosure, there is provided a method of determining one or more characteristics of a puff taken by a user of an aerosol generating device, the aerosol generating device comprising: an air passage extending from an air inlet of the aerosol generating device; and a sensor assembly comprising: a temperature sensor located in the air passage and adapted to measure the temperature in the air passage, and a heater located in the air passage upstream of the temperature sensor (i.e., between the air inlet and the temperature sensor) and adapted to heat air flowing past the heater from the air inlet, e.g., so that when a puff is taken by a user, heat is transferred from the heater to the temperature sensor by forced air convection; wherein the method comprises using the temperature measurements from the temperature sensor to determine one or more characteristics of a puff taken by a user of the aerosol generating device when air flows through the air passage.

[0058] The heater may be adapted to heat the air flowing past the heater based on a target temperature which is set to be higher than a measured nominal temperature.

[0059] The target temperature may be set based on the temperature measurements from the temperature sensor plus a temperature offset, e.g., from about 10°C to about 40°C, but see the description above for alternative narrower and wider ranges.

[0060] The method may further comprise smoothing the temperature measurements from the temperature sensor to provide smoothed temperature measurements. The target temperature may be set based on the smoothed temperature measurements.

[0061] The working principle of the present disclosure may be understood with reference to Figure 1 A which shows the following temperature profiles:

[0062] - the temperature measurements provided by the temperature sensor of the sensor assembly (indicated by solid line),

[0063] - the smoothed temperature measurements (indicated by dashed line), and

[0064] - a target temperature for the heater of the sensor assembly which is set based on the smoothed temperature measurements plus a temperature offset, e.g., 20°C (indicated by dash-dotted line).

[0065] Figure 1A shows how the profile of the temperature measurements provided by the temperature sensor of the sensor assembly gradually increases as the aerosol generating device heats up, i.e., the measured nominal temperature of the air passage increases as a result of thermal transfer from the primary heater of the aerosol generating device. The rapid and temporary increases in the temperature measurements are caused by puffs taken by the user, which is when heat is transferred from the heater to the temperature sensor by forced air convection.

[0066] The smoothed temperature measurements effectively remove the rapid and temporary increases in the temperature measurements caused by the puffs.

[0067] The profile of the target temperature is based on the smoothed temperature measurements plus a temperature offset, e.g., 20°C. The actual temperature of the heater of the sensor assembly closely matches the target temperature. The target temperature is set higher than the smoothed temperature measurements (i.e., to be higher than the measured nominal temperature) for the reasons explained above.

[0068] Figure IB shows typical puff characteristics that may be determined. The puff characteristics include the start time of the puff, the end time of the puff, the instantaneous flow rate of the puff, the maximum flow rate of the puff, and the total volume of the puff.

[0069] Brief Description of the Drawings

[0070] Figure 1 A is a graphical representation of various temperature profiles that show the working principal of the present disclosure;

[0071] Figure IB is a graphical representation of puff characteristics;

[0072] Figure 2 is a diagrammatic view of an aerosol generating system with an aerosol generating device and an aerosol generating article;

[0073] Figure 3 is a diagrammatic view of part of the aerosol generating device of Figure 2;

[0074] Figure 4 is a diagrammatic view of an electric circuit and controller of the aerosol generating device of Figure 2;

[0075] Figure 5 is a graphical representation of output voltage profiles indicative of compensated and uncompensated temperature measurements;

[0076] Figure 6 is a graphical representation of voltage measurements during a puff; and Figure 7 is a flow diagram.

[0077] Detailed Description of Embodiments

[0078] Embodiments of the present disclosure will now be described by way of example only and with reference to the accompanying drawings.

[0079] Referring initially to Figure 2, there is shown diagrammatically an example of an aerosol generating system 1. The aerosol generating system 1 comprises an aerosol generating device 10 and an aerosol generating article 100 for use with the device 10. The aerosol generating device 10 comprises a main body 12 housing various components of the aerosol generating device 10. The main body 12 may have any shape that is sized to fit the components described in the various embodiments set out herein and to be comfortably held by a user unaided, in a single hand.

[0080] A first end 14 of the aerosol generating device 10, shown towards the bottom of Figure 2, is described for convenience as a distal, bottom, base or lower end of the aerosol generating device 10. A second end 16 of the aerosol generating device 10, shown towards the top of Figure 2, is described as a proximal, top or upper end of the aerosol generating device 10. During use, the user typically orients the aerosol generating device 10 with the first end 14 downward and / or in a distal position with respect to the user’s mouth and the second end 16 upward and / or in a proximate position with respect to the user’s mouth.

[0081] The aerosol generating device 10 comprises a heating chamber 18 positioned in the main body 12. The heating chamber 18 defines an interior volume in the form of a cavity 20 having a substantially cylindrical cross-section for receiving an aerosol generating article 100. The heating chamber 18 has a longitudinal axis defining a longitudinal direction and is formed of a heat-resistant plastics material, such as polyether ether ketone (PEEK). The aerosol generating device 10 further comprises a power source (not shown), for example one or more batteries which may be rechargeable, and a controller such as a microcontroller unit (or MCU) 50 that is described in more detail below.

[0082] The heating chamber 18 is open towards the second end 16 of the aerosol generating device 10. In other words, the heating chamber 18 has an open first end 26 towards the second end 16 of the aerosol generating device 10. The heating chamber 18 is typically held spaced apart from the inner surface of the main body 12 to minimise heat transfer to the main body 12.

[0083] The aerosol generating device 10 may optionally include a sliding cover 28 movable transversely between a closed position (shown in Figure 2) in which it covers the open first end 26 of the heating chamber 18 to prevent access to the heating chamber 18 and an open position (not shown) in which it exposes the open first end 26 of the heating chamber 18 to provide access to the heating chamber 18. The sliding cover 28 may be biased to the closed position in some embodiments.

[0084] The heating chamber 18, and specifically the cavity 20, is arranged to receive a correspondingly shaped generally cylindrical or rod-shaped aerosol generating article 100. Typically, the aerosol generating article 100 comprises a pre-packaged aerosol generating material or substrate 102. The aerosol generating article 100 is a disposable and replaceable article (also known as a “consumable”) which may, for example, contain tobacco as the aerosol generating material 102. The aerosol generating article 100 has a proximal end 104 (or mouth end) and a distal end 106. The aerosol generating article 100 further comprises a mouthpiece segment 108 positioned downstream of the aerosol generating material 102. The aerosol generating material 102 and the mouthpiece segment 108 are arranged in coaxial alignment inside a wrapper 110 (e.g., a paper wrapper) to hold the components in position to form the rod-shaped aerosol generating article 100.

[0085] The mouthpiece segment 108 may comprise one or more of the following components (not shown in detail) arranged sequentially and in co-axial alignment in a downstream direction, in other words from the distal end 106 towards the proximal (mouth) end 104 of the aerosol generating article 100: a cooling segment, a centre hole segment and a filter segment. The cooling segment typically comprises a hollow paper tube having a thickness which is greater than the thickness of the wrapper 110. The centre hole segment may comprise a cured mixture containing cellulose acetate fibres and a plasticizer, and functions to increase the strength of the mouthpiece segment 108. The filter segment typically comprises cellulose acetate fibres and acts as a mouthpiece filter. As heated vapour flows from the aerosol generating material 102 towards the proximal (mouth) end 104 of the aerosol generating article 100, the vapour cools and condenses as it passes through the cooling segment and the centre hole segment to form an aerosol with suitable characteristics for inhalation by a user through the filter segment.

[0086] The heating chamber 18 has a side wall (or chamber wall) 30 extending between a base 32, located at a second end 34 of the heating chamber 18, and the open first end 26. The side wall 30 and the base 32 are connected to each other and may be integrally formed as a single piece. In the illustrated embodiment, the side wall 30 is tubular and, more specifically, cylindrical. In other embodiments, the side wall 30 may have other suitable shapes, such as a tube with an elliptical or polygonal cross section. In yet further embodiments, the side wall 30 may be tapered.

[0087] In the illustrated embodiment, the base 32 of the heating chamber 18 is cup-shaped. It may ensure that a user inserts the aerosol generating article 100 into the heating chamber 18 an intended distance and no further.

[0088] The device 10 includes a primary heater (or heater assembly 36), which is configured to heat the aerosol generating material 102 when the aerosol generating article 100 is received in the heating chamber 18.

[0089] Figure 3 shows a detail view of the upper part of the heating chamber 18 with the aerosol generating article 100 inserted. An air passage 38 extends from an air inlet 40.

[0090] A sensor assembly 42 comprises a temperature sensor 44 and a heater 46. The temperature sensor 44 and the heater 46 are mounted on a printed circuit board 48 and are positioned in the air passage 38 at a part of the side wall 30 that acts as a guide for the aerosol generating article 100 (e.g., a “stick guide”). Preferably, the air passage 38 includes a concave portion or recess in which the sensor assembly 42 is positioned so that the temperature sensor 44 and the heater 46 are not in contact with the aerosol generating article 100. The temperature sensor 44 is adapted to measure the temperature in the air passage and to provide temperature measurements to a MCU 50 (Figure 4) which is mounted on a separate printed circuit board (not shown) and located away from the primary heater 36 and / or the heater 46. The heater 46 is also located upstream of the temperature sensor 44 - i.e., between the air inlet 40 and the temperature sensor 44. The heater 46 is adapted to heat air flowing past the heater 46 from the air inlet 40, e.g., so that when a puff is taken by a user, heat is transferred from the heater 46 to the downstream temperature sensor 44 by forced air convection. In Figure 3, the flow of air through the air passage is indicated by the arrow.

[0091] The MCU 50 is shown in Figure 4 and includes:

[0092] - a first input terminal 52,

[0093] - a second input terminal 54, and

[0094] - an output terminal 56.

[0095] An electric circuit 58 of the aerosol generating device 10 is also shown in Figure 4 and includes the sensor assembly 42 (i.e., the temperature sensor 44 and the heater 46). The other components of the electric circuit 58 may also be mounted on the printed circuit board 48 so that the electric circuit 58 is implemented as a printed circuit board assembly. The electric circuit 58 includes:

[0096] - an operational amplifier 60,

[0097] - a npn bipolar transistor 62,

[0098] - current limiting resistor 64, and

[0099] - resistors 66, 68.

[0100] The temperature sensor 44 is electrically connected to a ground plane of the printed circuit board 48 by the resistor 66 - i.e., the temperature sensor 44 and the resistor 66 are electrically connected in series. The heater 46 is electrically connected to the ground plane by the resistor 68 - i.e., the heater 46 and the resistor 68 are electrically connected in series. The temperature sensor 44 and the heater 46 form respective voltage divider circuits with the resistors 66 and 68.

[0101] The operational amplifier 60 includes:

[0102] - a non-inverting input terminal,

[0103] - an inverting input terminal,

[0104] - an output terminal,

[0105] - a positive power supply terminal, and

[0106] - a negative power supply terminal.

[0107] In the electric circuit 58 shown in Figure 4, the non-inverting input terminal is electrically connected the junction between the heater 46 and the resistor 68. The non-inverting input terminal is therefore adapted to receive the output voltage 70 from the heater 46 as a mid-point voltage of the voltage divider circuit the includes the heater 46 and the resistor 68. However, in an alternative electric circuit, the non- inverting input terminal is electrically connected to the junction between the temperature sensor 44 and the resistor 66 and is adapted to receive the output voltage from the temperature sensor 44 as a mid-point voltage of the voltage divider circuit that includes the temperature sensor 44 and the resistor 66. The inverting input terminal is electrically connected to the junction between the temperature sensor 44 and the resistor 66. The inverting input terminal is therefore adapted to receive the output voltage 72 from the temperature sensor 44 as a mid-point voltage of the voltage divider circuit that includes the temperature sensor 44 and the resistor 66. However, in an alternative electric circuit, the inverting input terminal is electrically connected to the junction between the heater 46 and the resistor 68 and is adapted to receive the output voltage from the heater 46 as a mid-point voltage of the voltage divider circuit that includes the heater 46 and the resistor 68.

[0108] The temperature sensor 44 and the heater 46 may have a temperature coefficient characteristic where the resistance of the temperature sensor 44 and the heater 46 vary as a function of temperature. The resistance of the temperature sensor 44 and the heater 46 may be measured from a respective voltage across the temperature sensor 44 and the heater 46, or more particularly as the mid-point voltage from the respective voltage divider circuit that also includes the resistor 66 or the resistor 68. The mid-point voltages that are provided to the non-inverting and inverting terminals of the operational amplifier 60 vary with temperature. The temperature coefficient characteristic may be a positive temperature coefficient (PTC) or a negative temperature coefficient (NTC). As described in more detail below, the operational amplifier 60 subtracts the output voltage 72 from the output voltage 70 or vice versa in order to provide compensated temperature measurements. It is therefore preferred that the temperature coefficient characteristics of the temperature sensor 44 and the heater 46 are selected to that the output voltages 70, 72 vary in the same way with changes in temperature. For example, if the output voltages 70, 72 decrease in accordance with temperature increases, both the temperature sensor 44 and the heater 46 may have PTC characteristics. Alternatively, both the temperature sensor 44 and the heater 46 may have NTC characteristics and the respective position of the temperature sensor 44 and the heater 46 and the resistors 66, 68 may be swapped - i.e., so that the temperature sensor 44 and the heater 46 are electrically connected at the low potential side of the resistors 66, 68. Further alternatively, the temperature sensor 44 may have a PTC characteristic and may be electrically connected at the high potential side of the resistor 66 and the heater 46 may have an NTC characteristic and may be electrically connected at the low potential side of the resistor 68 or vice versa.

[0109] In the following description, it will be assumed that the temperature sensor 44 and the heater 46 have PTC characteristics such that the output voltages 70, 72 decrease when the temperature increases.

[0110] The output terminal of the operational amplifier 60 is adapted to provide an output voltage 74 indicative of compensated temperature measurements. An example of the output voltage 74 is shown in Figure 5. Figure 5 also shows an example of an uncompensated output voltage, which shows a gradual decrease in the output voltage as the aerosol generating device 2 heats up and also a reduction in the amplitude of the individual puff measurements. Figure 1A shows how the nominal temperature gradually increases as the aerosol generating device 2 heats up. Following the trend of the nominal temperature, the target temperature, to which the actual temperature of the heater 46 corresponds closely, will also gradually increase. Because the temperature sensor 44 has PTC characteristics and is connected at the high potential side of resistor 66, this gradual increase in temperature appears as a gradual decrease in the uncompensated output voltage. For precise determination of puff characteristics, these trends in the nominal temperature and the output voltage are preferably removed or compensated for. As described above, this compensation may be carried out by subtracting the output voltage 72 from the output voltage 70 (or vice versa). Figure 5 shows a completely compensated output voltage which is substantially constant and defines a “baseline” value. Each puff appears as a positive deviation from the “baseline” value. This is because the output voltage 70 is provided to the non-inverting input terminal of the operational amplifier 60 and the output voltage 72 is provided to the inverting input terminal of the operational amplifier. If this is reversed, each puff would appear as a negative deviation from the “baseline” value.

[0111] The positive power supply terminal of the operational amplifier 60 receives a constant voltage from a voltage regulator (not shown). In Figure 4 the constant voltage is labelled “Vin”. Alternatively, the positive power supply terminal may be directly or indirectly electrically connected to the power supply without using a voltage regulator.

[0112] The negative power supply terminal of the operational amplifier 60 is electrically connected to the ground plane of the printed circuit board 48.

[0113] The npn bipolar transistor 62 includes:

[0114] - a base terminal electrically connected to the output terminal of the operational amplifier 60 and adapted to receive the output voltage 74 indicative of compensated temperature measurements,

[0115] - a collector terminal electrically connected to the voltage regulator (not shown) and adapted to receive the constant voltage from the voltage regulator, and

[0116] - an emitter terminal adapted to provide an output voltage 76 indicative of compensated and amplified temperature measurements.

[0117] The npn bipolar transistor 62 may amplify an output current from the emitter terminal of the npn bipolar transistor 62 itself based on the output voltage 74 of the operational amplifier 60. More particularly, the output current from the emitter terminal is further amplified as the output voltage 74 of the operational amplifier 60 increases. The emitter terminal of the npn bipolar transistor 62 is electrically connected to the temperature sensor 44 and the heater 46. The temperature sensor 44 and the heater 46 therefore receive the output voltage 76 indicative of compensated and amplified temperature measurements.

[0118] The current limiting resistor 64 includes:

[0119] - a first end electrically connected to the voltage regulator (not shown) and adapted to receive the constant voltage from the voltage regulator, and

[0120] - a second end electrically connected to the temperature sensor 44 and the heater 46.

[0121] The current limiting resistor 64 is electrically connected in parallel with the npn bipolar transistor 62. The current limiting resistor 64 may supply the constant voltage from the voltage regulator when the electric circuit 58 first starts to operate. The current limiting resistor 64 may also isolate the current voltage from the output voltage 76 after the operational amplifier 60 starts to provide the output voltage 74.

[0122] The output voltage 76 indicative of compensated and amplified temperature measurements is provided to the first input terminal 52 of the MCU 50. (In an alternative arrangement, the output voltage 74 indicative of compensated temperature measurements is provided to the first input terminal 52 of the MCU 50 instead of the output voltage 76.) The MCU 50 is adapted to use the output voltage 76 (or the output voltage 74) to determine the one or more characteristics of the puff, such as the start time of the puff, the end time of the puff, the instantaneous flow rate of the puff, the maximum flow rate of the puff, and the total volume of the puff, for example. For example, Figure 6 shows an example of output voltages indicative of compensated and amplified temperature measurements when a puff is being taken. It is possible to determine the start time of the puff, i.e., when the output voltage starts to increase rapidly, the end time of the puff, the instantaneous and maximum flow rate which are related to the magnitude of the output voltage, and the total volume of the puff. Determining the one or more puff characteristics may allow improved dynamic haptic and / or auditory feedback to be provided to the user - i.e., where the feedback depends on the one or more puff characteristics. The one or more puff characteristics may also be used to control an operation or a function of the aerosol generating device, e.g., adjusting heating of the aerosol generating material or substrate, or calculating the remaining amount of aerosol generating material or substrate.

[0123] If the output voltage 76 increases in response to a puff as shown in Figure 6, the MCU 50 may determine the total volume of the puff by :

[0124] - integrating only the part of the output voltage of the operational amplifier that is greater than a threshold voltage, or integrating the output voltage of the operational amplifier to obtain a first value, integrating a threshold voltage to obtain a second value, and subtracting the second value from the first value.

[0125] The threshold voltage may be a constant value that is set in advance or a variable value that may be based on other measurements, for example. If the “baseline” value of the output voltage 76 (or output voltage 74) is substantially constant - for example, as shown in Figure 5 - the threshold voltage may be set to correspond to the “baseline” value. The “baseline” value may be easily calculated by continuously measuring the output voltage 76 (or output voltage 74). If the output voltage 76 (or the output voltage 74) changes linearly or non-linearly as shown in Figure 6, the “baseline” value may be described as a function of time. The function may be expressed by linear or non-linear approximation based on the previous measurements of the output voltage 76 (or output voltage 74). This means that the threshold voltage may be a time-varying value which may be calculated using the function by inputting time as a variable.

[0126] The output voltage 72 of the temperature sensor 44 is provided to the second input terminal 54 of the MCU 50. The heater 46 is adapted to heat the air flowing past the heater 46 based on a target temperature set by the MCU 50. The MCU 50 is adapted to use the output voltage 72 from the temperature sensor 44 to set the target temperature. In particular, the MCU 50 is adapted to smooth the output voltage 72 that is indicative of the temperature measurements, e.g., to determine a moving average of the output voltage. The target temperature is then set by the MCU 50 based on the smoothed output voltage indicative of smoothed temperature measurements plus a temperature offset (e.g., from about 10°C to about 40°C). Alternatively, a smoothing circuit (e.g., an analog circuit) that is adapted to smooth the output voltage 72 may be electrically connected between the temperature sensor 44 and the second input terminal 54 of the MCU 50. The smoothed output voltage from the smoothing circuit would be provided to the second input terminal 54 of the MCU 50 and this may reduce the calculation load of the MCU 50.

[0127] The electric circuit 58 includes a power supply path 78 electrically connected to the heater 46. The power supply path 78 is electrically connected in parallel with the npn bipolar transistor 62 and the current limiting resistor 64. The power supply path 78 includes a semiconductor switch 80 (e.g., a npn bipolar transistor or a p-channel MOSFET) that may be switched on and off by a control signal 82 provided by the output terminal 56 of the MCU 50. The semiconductor switch 80 is switched on and off to control the supply of power to the heater 46 so that the temperature of the heater 46 closely matches the target temperature set by the MCU 50. The voltage supplied through the power supply path 78 for heating the heater 46 (labelled “Vhtr”) is greater than the constant voltage (i.e., Vin) of the voltage regulator (not shown). Figure 7 shows a flow diagram with the following steps:

[0128] - Step 1 : Read the output voltage 72 from the temperature sensor 44, e.g., provide the output voltage 72 to the second input terminal 54 of the MCU 50,

[0129] - Step 2: Smooth the output voltage 72, e.g., smooth the received output voltage 72 within the MCU 50 (or alternatively, the output voltage 72 is provided to a smoothing circuit and the smoothed output voltage is provided to the second input terminal 54 of the MCU 50),

[0130] - Step 3: Set the target temperature, e.g., where the MCU 50 uses the smoothed output voltage to set the target temperature of the heater 46,

[0131] - Step 4: Read output voltage 76 indicative of the compensated and amplified temperature measurements, i.e., provide the output voltage 76 to the first input terminal 52 of the MCU 50 (or alternatively provide the output voltage 74 indicative of the compensated temperature measurements to the first input terminal 52 of the MCU 50), and

[0132] - Step 5: If the output voltage 76 is above a threshold voltage, integrate the output voltage 76 and sum with previous values, otherwise, return to Step 1.

[0133] The flow diagram shows how to determine the total puff volume.

[0134] The output voltage 76 (or output voltage 74) may also be used to determine one or more of the start time of the puff, the end time of the puff, the instantaneous flow rate of the puff, and the maximum flow rate of the puff. The start and end time of the puff may be determined respectively based on the time when the deviation in the output voltage 74 (or output voltage 76) starts and ends. The instantaneous flow rate of the puff may be determined based on an instantaneous value of the output voltage 76 (or output voltage 74). The maximum flow rate of the puff may be determined based on a maximum value (or for negative deviations, a minimum value) of the output voltage 76 (or output voltage 74). The MCU 50 may use a table (e.g., a look-up table) or a suitable equation or other function to convert the determined voltage values to flow rate.

[0135] Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments. According to above-described exemplary embodiments, heat transferred from a heater to a temperature sensor is used to determine puff characteristics. However, instead of a heater, the sensor assembly may comprise a cooler (e.g., a Peltier device) so that cold is transferred from the cooler to the temperature sensor optionally using forced air convection, for example. The present disclosure should therefore be considered to include such a modification to determine one or more puff characteristics where the disclosure is considered to refer to “cold” instead of “heat”, “cooling” instead of “heating” etc. Any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0136] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

Claims

Claims1. An aerosol generating device (10) comprising: an air passage (38) extending from an air inlet (40) of the aerosol generating device (10); a microcontroller unit MCU (50); and a sensor assembly (42) comprising: a temperature sensor (44) located in the air passage (38) and adapted to measure the temperature in the air passage (38) and to provide temperature measurements to the MCU (50), and a heater (46) located in the air passage (38) upstream of the temperature sensor (44) and adapted to heat air flowing past the heater (46) from the air inlet (40); wherein the MCU (50) is adapted to use the temperature measurements from the temperature sensor (44) to determine one or more characteristics of a puff taken by a user of the aerosol generating device (10) when air flows through the air passage (38).

2. An aerosol generating device (10) according to claim 1, wherein the heater (44) is adapted to heat the air flowing past the heater (44) based on a target temperature set by the MCU (50); and wherein the MCU (50) is adapted to set the target temperature based on a constant or timevarying value.

3. An aerosol generating device according to claim 1, wherein the heater (44) is adapted to heat the air flowing past the heater (44) based on a target temperature set by the MCU (50); and wherein the MCU (50) is adapted to set the target temperature to be higher than a measured nominal temperature.

4. An aerosol generating device (10) according to claim 3, further comprising an operational amplifier (60), wherein the operational amplifier (60) includes: a non- inverting input terminal adapted to receive one of: (a) an output voltage (70) from the heater (46), and (b) an output voltage (72) from the temperature sensor (44) that is indicative of the temperature measurements, an inverting input terminal adapted to receive the other one of: (a) an output voltage (70) from the heater (46), and (b) an output voltage (72) from the temperature sensor (44) that is indicative of the temperature measurements, and an output terminal adapted to provide an output voltage (74) indicative of compensated temperature measurements; wherein the MCU (50) is further adapted to receive the output voltage (72) from the temperature sensor (44) that is indicative of the temperature measurements, and the output voltage (74) from the operational amplifier (60) that is indicative of compensated temperature measurements; andwherein the MCU (50) is further adapted to use the output voltage (72) from the temperature sensor (44) that is indicative of the temperature measurements to set the target temperature, and is further adapted to use the output voltage (74) of the operational amplifier (60) that is indicative of the compensated temperature measurements to determine the one or more characteristics of the puff.

5. An aerosol generating device (10) according to claim 4, wherein the MCU (50) is further adapted to determine the total volume of the puff if the output voltage (74) of the operational amplifier (60) increases in response to the puff by:(a) integrating only the part of the output voltage (74) of the operational amplifier (60) that is greater than a threshold voltage, or(b) integrating the output voltage (74) of the operational amplifier (60) to obtain a first value, integrating a threshold voltage to obtain a second value, and subtracting the second value from the first value; and / or wherein the MCU (50) is further adapted to determine the total volume of the puff if the output voltage (74) of the operational amplifier (60) decreases in response to the puff by :(a) inverting the output voltage (74) of the operational amplifier (60) and integrating only the part of the inverted output voltage of the operational amplifier (60) that is greater than a threshold voltage, or(b) inverting the output voltage (74) of the operational amplifier (60), integrating the inverted output voltage of the operational amplifier (60) to obtain a first value, integrating a threshold voltage to obtain a second value, and subtracting the second value from the first value.

6. An aerosol generating device (10) according to claim 4 or claim 5, further comprising: a voltage regulator adapted to output a constant voltage; and a npn bipolar transistor (62), wherein the npn bipolar transistor (62) includes: a base terminal adapted to receive the output voltage (74) from the operational amplifier, a collector terminal adapted to receive the constant output voltage from the voltage regulator, and an emitter terminal adapted to provide an output voltage (76) indicative of compensated and amplified temperature measurements; wherein the MCU (50) is further adapted to use the output voltage (76) from the npn bipolar transistor (62) that is indicative of the compensated and amplified temperature measurements to determine the one or more characteristics of the puff.

7. An aerosol generating device (10) according to claim 6, further comprising a current limiting resistor (64), wherein the current limiting resistor (64) includes: a first end adapted to receive the output voltage from the voltage regulator, and a second end adapted to provide a voltage to the temperature sensor (44); and wherein the current limiting resistor (64) is electrically connected in parallel with the npn bipolar transistor (62).

8. An aerosol generating device (10) according to claim 7, wherein the second end of the current limiting resistor (64) is also adapted to provide a voltage to the heater (46).

9. An aerosol generating device (10) according to claim 8, further comprising a power supply path (78) adapted to supply a voltage for heating the heater (46), wherein the power supply path (78) is electrically connected in parallel with the current limiting resistor (64) and the npn bipolar transistor (62).

10. An aerosol generating device (10) according to claim 9, wherein the voltage supplied through the power supply path (78) for heating the heater (46) is greater than the constant output voltage of the voltage regulator.

11. An aerosol generating device (10) according to any of claims 3 to 10, wherein the MCU (50) is adapted to set the target temperature based on the temperature measurements from the temperature sensor (44) plus a temperature offset.

12. An aerosol generating device (10) according to claim 11, wherein:(a) the MCU (50) is adapted to smooth the temperature measurements, or(b) the aerosol generating device (10) further comprises a smoothing circuit adapted to smooth the temperature measurements, wherein the smoothing circuit is electrically connected between the temperature sensor (44) and an input terminal (54) of the MCU (50); and wherein the MCU (50) is adapted to set the target temperature based on the smoothed temperature measurements plus a temperature offset.

13. An aerosol generating device (100 according to claim 11 or claim 12, wherein the temperature offset is in the range of from about 10°C to about 40°C.

14. An aerosol generating device (10) according to any preceding claim, further comprising a printed circuit board assembly comprising a first printed circuit board, and a second printed circuit board (48) physically separated from the first printed circuit board; wherein the MCU (50) is mounted on the first printed circuit board; andwherein the temperature sensor (44) and the heater (46) are mounted on the second printed circuit board (48).

15. An aerosol generating device (10) according to any preceding claim, further comprising: a heating chamber (18) adapted to receive an aerosol generating article (100), in use; and a primary heater (36) positioned adjacent the heating chamber (18) and adapted to heat the aerosol generating article (100), wherein the primary heater (36) is physically separated from the heater

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