Electromagnetic heating smoking device

Abstract

The present invention discloses an electromagnetically heated smoking device capable of heating an aerosol-generating product through induction heating to produce an aerosol for inhalation. The electromagnetically heated smoking device comprises a heating chamber for receiving the aerosol-generating product; a first coil and a second coil circumferentially disposed outside the heating chamber, the first and second coils being configured to generate an induction field; a control system comprising a coil switching switch, a switch control circuit, a coil oscillation circuit, and a temperature detection unit. The temperature detection unit is configured to detect a physical quantity related to the temperature of the susceptor; the control system controls the heating operation of the electromagnetically heated smoking device based on signals received from the temperature detection unit. The present invention utilizes a multi-stage coil configuration to adjust the oscillation frequency of the entire coil, thereby adjusting the coil power and reducing EMI radiation output.

Description

Technical Field

[0001] The present invention relates to the field of novel tobacco product smoking articles, in particular to an electromagnetic heating smoking article. Background Art

[0002] In existing electromagnetic heat-not-burn smoking devices, the coils used for energy output all have a fixed number of turns and a fixed turn spacing. This offers the advantage of lower cost, and the power applied to the coils can be adjusted by reducing the operating voltage or intermittently operating the electromagnetic oscillator circuit. However, this also comes with significant disadvantages.

[0003] First, coil power adjustment can be achieved by lowering the operating voltage, that is, lowering the voltage on the coil and the driving circuit voltage. However, since the coil simulates the AC state, it requires a switching tube (usually MOS) for cooperative driving. The on-resistance of the switching tube is related to the voltage. The higher the voltage (within the allowable voltage range of the component, exceeding it will cause damage), the lower its on-resistance. The lower the impedance, the smaller the loss on the line. Therefore, lowering the voltage will reduce the efficiency of the entire circuit, resulting in increased power consumption.

[0004] Secondly, adopt intermittent operation. Intermittent operation has two states: active and inactive. Although intermittent operation causes the average current to decrease, the current remains high during operation, placing relatively stringent requirements on the battery-powered system (battery discharge capacity is related to discharge current; the higher the discharge current, the lower the total charge that can be discharged). Furthermore, due to intermittent operation, the switching tube must be turned on and off during operation. This switching introduces high-order harmonic components, resulting in poor EMI performance.

[0005] Therefore, in view of the characteristics of the existing fixed coil electromagnetic heating method, in order to reduce the peak power in the constant temperature stage and at the same time reduce the EMI radiation problem caused by excessive high-order harmonics generated during switching, it is necessary to develop a new type of electromagnetic heating smoking device. Summary of the Invention

[0006] The purpose of the present invention is to reduce the peak power in the constant temperature stage and, at the same time, reduce the EMI radiation problem caused by excessive high-order harmonics generated during switching.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] An electromagnetic heating smoking device, which can heat an aerosol-generating product by induction heating to generate an aerosol for a user to inhale; the electromagnetic heating smoking device comprises: a heating chamber for receiving the aerosol-generating product; a first coil and a second coil, circumferentially arranged outside the heating chamber, the first coil and the second coil being used to generate an induction field, the first coil and the second coil having at least a portion overlapping in axial projection; a power supply, which is configured to provide a high-frequency current to the first coil or the second coil, and in use, the first coil or the second coil generates a fluctuating electromagnetic field to heat a susceptor in thermal contact with the aerosol-generating product and thereby heat an aerosol-generating substrate of the aerosol-generating product; a control system, the control system comprising a coil switching switch and a temperature detection unit, the temperature detection unit being used to detect a physical quantity related to the temperature of the susceptor, and the control system controlling the heating action of the electromagnetic heating smoking device according to a signal received from the temperature detection unit.

[0009] Furthermore, the coil switching switch is used to switch the connection between the power supply and the first coil or the second coil.

[0010] Furthermore, the first coil and the second coil are configured in an axially nested relationship, the diameter of the first coil is larger than that of the second coil, and the first coil is nested outside the second coil.

[0011] Further, the length of the first coil in the axial direction is equal to the length of the second coil in the axial direction.

[0012] Furthermore, the number of turns of the second coil is greater than the number of turns of the first coil.

[0013] Furthermore, the ratio of the number of turns of the second coil to the number of turns of the first coil is at least 1.5:1.

[0014] Furthermore, an isolation device is provided between the first coil and the second coil, and the isolation device can shield the current but not the magnetic field.

[0015] Furthermore, the first port of the first coil and the first port of the second coil are directly electrically connected, and the second port of the first coil and the second port of the second coil are electrically insulated from each other.

[0016] Furthermore, the second coil includes at least one tap, and the coil switching switch is used to switch the connection between the power supply and the first port, the second port and the tap of the second coil.

[0017] Furthermore, when the electromagnetic heating smoking device is started, the control system drives the first coil until the sensor reaches the preheating target temperature; after the sensor reaches the preheating target temperature, the control system turns off the first coil and drives the second coil to maintain the sensor at the working target temperature.

[0018] Among them, the aerosol-generating article is a smoking article comprising an aerosol-forming substrate which, upon heating, generates an aerosol which is directly inhalable into the lungs of a user through the user's mouth.

[0019] Preferably, the aerosol-forming substrate is a solid aerosol-forming substrate.The aerosol-forming substrate may comprise both solid and liquid components.

[0020] Preferably, the aerosol-forming substrate comprises nicotine. In some preferred embodiments, the aerosol-forming substrate comprises tobacco. For example, the aerosol-forming material may be formed from a sheet of homogenized tobacco.

[0021] Alternatively or additionally, the aerosol-forming substrate may comprise a tobacco-free aerosol-forming material.For example, the aerosol-forming material may be a sheet comprising nicotine salt and an aerosol-former.

[0022] If the aerosol-forming substrate is a solid aerosol-forming substrate, the solid aerosol-forming substrate may comprise one or more of a powder, granules, pellets, shreds, strips, rods or sheets containing one or more of herb leaves, tobacco leaves, tobacco ribs, flat tobacco and homogenised tobacco.

[0023] Optionally, the solid aerosol-forming substrate may comprise tobacco volatile aroma compounds or non-tobacco volatile aroma compounds that are released upon heating the solid aerosol-forming substrate. The solid aerosol-forming substrate may also comprise one or more capsules comprising, for example, additional tobacco volatile aroma compounds or non-tobacco volatile aroma compounds, and such capsules may melt during heating of the solid aerosol-forming substrate.

[0024] Optionally, the solid aerosol-forming substrate may be disposed on or embedded in a thermally stable carrier. The carrier may be in the form of a powder, granules, pellets, chips, strips, bars, or sheets. The solid aerosol-forming substrate may be disposed on the surface of the carrier in the form of, for example, a sheet, foam, gel, or slurry. The solid aerosol-forming substrate may be placed over the entire surface of the carrier, or alternatively, may be arranged in a pattern to provide uneven flavor delivery during use.

[0025] In the present invention, the homogenized tobacco material means a material formed by agglomerating particulate tobacco.

[0026] In the present invention, a sheet means a laminar element having a width and a length that are substantially greater than its thickness.

[0027] In the present invention, gathered is used to describe a sheet that is rolled, folded or compressed or shrunk substantially transversely to the longitudinal axis of the aerosol-generating article.

[0028] Preferably, the aerosol-forming substrate comprises a gathered textured sheet of homogenised tobacco material.

[0029] In the present invention, textured sheet material refers to a sheet material that has been curled, embossed, embossed, perforated or otherwise deformed. The aerosol-forming substrate can include a textured sheet material of the aggregation of homogenous tobacco material, which includes a plurality of spaced-apart notches, protrusions, perforations or a combination thereof. Preferably, the aerosol-forming substrate includes a gathered curled sheet of homogenous tobacco material. The use of the textured sheet material of homogenous tobacco material can advantageously promote the aggregation of the homogenous tobacco material sheet material, to form an aerosol-forming substrate.

[0030] In the present invention, a curled sheet is a sheet having a plurality of substantially parallel ridges or folds. Preferably, when the aerosol-generating article is assembled, the substantially parallel ridges or folds extend along or parallel to the longitudinal axis of the aerosol-generating article. This advantageously facilitates the aggregation of the curled sheet of homogenized tobacco material to form an aerosol-forming substrate. However, it will be appreciated that the curled sheet of homogenized tobacco material for inclusion in an aerosol-generating article may alternatively or additionally have a plurality of substantially parallel ridges or folds which, when the aerosol-generating article is assembled, are arranged at an acute angle or an obtuse angle to the longitudinal axis of the aerosol-generating article.

[0031] The aerosol-forming substrate may be in the form of a plug comprising the aerosol-forming material circumscribed by paper or other wrapping material.Where the aerosol-forming substrate is in the form of a plug, the entire plug including any wrapping paper is considered to be the aerosol-forming substrate.

[0032] Preferably, the aerosol-forming substrate comprises a plug comprising a gathered sheet of homogenised tobacco material or other aerosol-forming material surrounded by a wrapper.Preferably, the or each elongate susceptor is located within the plug in direct contact with the aerosol-forming material.

[0033] Susceptors are materials that can convert electromagnetic energy into heat. When exposed to a fluctuating electromagnetic field, eddy currents induced in the susceptor result in heating of the susceptor. When the elongated susceptor is positioned in thermal contact with the aerosol-forming substrate, the aerosol-forming substrate is heated by the susceptor.

[0034] The susceptor is preferably needle-shaped, bar-shaped, or leaf-shaped. The susceptor may be made of any material that can be heated by induction to a temperature sufficient to cause the aerosol-forming substrate to generate an aerosol. Preferred susceptors include metal or carbon. Preferred susceptors may include ferromagnetic materials, such as ferrite, ferromagnetic steel, or stainless steel. Suitable susceptors may be or may include aluminum. Preferred susceptors may be made of 400 series stainless steel, such as 410 grade, 420 grade, or 430 grade stainless steel. Different materials will consume different amounts of energy when placed in an electromagnetic field with similar frequency and field strength values. Therefore, the parameters of the susceptor, such as material type, length, width, and thickness, can be varied within a known electromagnetic field to provide the desired energy consumption.

[0035] It is possible to heat the preferred susceptor to temperatures exceeding 250 degrees C. Suitable susceptors may include a non-metallic core having a metal layer disposed on the non-metallic core, such as metal tracks formed on the surface of a ceramic core.

[0036] The susceptor may have an outer protective layer, such as a ceramic or glass protective layer that encapsulates the elongated susceptor to form a complete heating body. The susceptor may include a protective coating formed of glass, ceramic, or inert metal formed on a core of the susceptor material.

[0037] The susceptor is arranged in thermal contact with the aerosol-forming substrate. Thus, when the susceptor is heated, the aerosol-forming substrate is heated and an aerosol is formed. In one embodiment, a heating element comprising a susceptor is inserted into the aerosol-forming substrate. The aerosol-generating device may comprise a single or multiple elongated heating elements. In another embodiment, the aerosol-generating substrate may comprise a susceptor. Alternatively, the aerosol-generating substrate may comprise a plurality of susceptors. The susceptors may have an elongated shape, a granular shape, a mesh shape, a radial shape, a tubular shape, an hourglass shape, a spiral shape, or the like.

[0038] The coil material should be a material with good electrical conductivity, such as metal. In addition, in the present invention, the coil material should also have good elastic deformation ability, and metals such as spring steel, gold, and silver can be used.

[0039] The present invention adjusts the oscillation frequency of the entire coil by setting a multi-stage coil, thereby adjusting the coil power. It has the following technical effects:

[0040] 1. Stable and adjustable control of coil peak power.

[0041] 2. Reduce the long-term peak output of the power supply, reduce the operating burden of the power supply, and increase the battery life and life of the product.

[0042] 3. Reduce EMI radiation output. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The above technical content of the present invention and the following detailed description will be better understood when read in conjunction with the accompanying drawings. It should be noted that the accompanying drawings are only examples of the technical solutions claimed. In the accompanying drawings, the same reference numerals represent the same or similar elements.

[0044] Figure 1 is a cross-sectional view of an electromagnetic heating smoking device according to an embodiment of the present invention;

[0045] Figure 2-A is a schematic diagram of a first coil according to an embodiment of the present invention;

[0046] Figure 2-B is a schematic diagram of a second coil according to an embodiment of the present invention;

[0047] Figure 3 is a circuit diagram of a control system according to an embodiment of the present invention;

[0048] Figure 4 This is a flow chart of a control method for an electromagnetic heating smoking device according to an embodiment of the present invention.

[0049] The description of the accompanying drawings is as follows:

[0050] Aerosol-generating products

[0051] Heating chamber

[0052] receptors

[0053] First coil

[0054] Second coil

[0055] Electric shielding device

[0056] A The first port of the first coil

[0057] B The first port of the second coil

[0058] C The second port of the first coil

[0059] D The second port of the second coil

[0060] N-tap DETAILED DESCRIPTION

[0061] The detailed features and advantages of the present invention are described below in the specific embodiments, and the content is sufficient to enable those skilled in the art to understand the technical content of the present invention and implement it accordingly. Based on this specification, claims and drawings, those skilled in the art can easily understand the relevant purposes and advantages of the present invention.

[0062] Existing electromagnetic heat-not-burn (HNB) smoking devices use coils with a fixed number of turns and fixed turn spacing as the energy output. This offers the advantage of lower costs, but also has significant drawbacks. During the constant temperature control phase, the average power applied to the coil can only be adjusted through duty cycle control, resulting in consistently high peak power levels. This is detrimental to battery-powered systems and places higher demands on battery performance.

[0063] This invention provides a targeted solution to the challenges of existing fixed-coil electromagnetic heating methods. By configuring multiple coils and adjusting the coil's oscillation frequency, coil power can be adjusted. This reduces peak power during the constant temperature phase while also minimizing EMI emissions caused by excessive high-order harmonics generated during switching.

[0064] The present invention adopts a multi-stage coil, and by selecting or adjusting the number of turns of the coil, the coil power is adjusted, and the heating power on the electromagnetic susceptor is adjusted to achieve the purpose of adjusting the peak power of the coil, thereby achieving the purpose of adjusting the heating power.

[0065] like Figure 1 As shown, an electromagnetic heating smoking device is used to heat an aerosol generating product 1, including a heating chamber 2, a power supply, a first coil 4 and a second coil 5, a power supply and a control system.

[0066] The heating chamber 2 is used to receive the aerosol-generating product 1 (such as a cigarette).

[0067] A power supply is configured to provide a high-frequency current to the first coil 4 or the second coil 5, and in use, the first coil 4 or the second coil 5 generates a fluctuating electromagnetic field to heat the susceptor 3 in thermal contact with the aerosol-forming article 1 and thereby heat the aerosol-generating substrate of the aerosol-generating article 1.

[0068] Receptor 3 is used to heat aerosol-generating article 1. Receptor 3 generates heat due to the induction field. Receptor 3 can be disposed within heating chamber 2 or within aerosol-generating article 1. Receptor 3 should be disposed within first coil 4 and second coil 5 when the electromagnetic heating device is operating.

[0069] The schematic diagram does not take into account the thickness of the coils. The first coil 4 and the second coil 5 are circumferentially arranged outside the heating chamber 2 to generate an induction field. The first coil 4 and the second coil 5 overlap at least partially in their axial projections. During assembly, the first coil 4 and the second coil 5 are aligned on the same axis. Furthermore, the electromagnetic heating smoking device can include more nested (or partially overlapping) coils. Their circuitry and assembly procedures refer to those for the first coil 4 and the second coil 5.

[0070] like Figure 2-A and Figure 2-B As shown, the first coil 4 and the second coil 5. The number of turns of the second coil 5 may be greater than the number of turns of the first coil 4. Preferably, the ratio of the number of turns of the second coil 5 to the number of turns of the first coil 4 is at least 1.5:1.

[0071] In one embodiment, the first coil 4 and the second coil 5 are arranged in an axially nested relationship, the first coil 4 has a larger diameter than the second coil 5 , and the first coil 4 is nested outside the second coil 5 .

[0072] In one embodiment, the length of the first coil 4 in the axial direction is equal to the length of the second coil 5 in the axial direction, that is, the projections of the first coil 4 and the second coil 5 in the axial direction completely overlap.

[0073] In one embodiment, the first port of the first coil 4 is directly electrically connected to the first port of the second coil 5, and the second port of the first coil 4 and the second port of the second coil 5 are electrically insulated from each other. An electric shielding device 6 is provided between the first coil 4 and the second coil 5. The electric shielding device 6 can shield current but not magnetic field.

[0074] In one embodiment, the second coil 5 is a multi-tap coil, and the second coil 5 includes at least one tap N that is not located at an end.

[0075] The control system includes a coil switching switch, a switch control circuit, a coil oscillation circuit, and a temperature detection unit. The temperature detection unit is used to detect the temperature of the sensor 3. The control system controls the heating action of the electromagnetic heating device based on the signal received from the temperature detection unit. The control system uses the inductance selection control signal from the MCU to control the coil switching switch to select different coils. Together with the oscillation circuit, it forms an oscillator to realize the operation of different working coils. Figure 3 An example of a coil switch switching between two heating modes is provided. For example, when the coil switch's switching path is selected as bc and connected, the power supply current flows through the inductor's ab segment, heating the susceptor in the first heating mode. When the coil switch's switching path is selected as ba and connected, the power supply current flows through the inductor's ac segment, heating the susceptor in the second heating mode. The power supply current can be selectively delivered to the induction coil as needed. Furthermore, the coil switch can switch between at least three heating modes, primarily differing in the choice of at least three switching paths. Since the various switching paths of a switch are common knowledge, they will not be discussed in detail here.

[0076] Specifically, in one embodiment, the coil switching switch can be used to switch the connection between the power supply and the first coil 4 and / or the second coil 5. Further, it can be switched so that the power supply is only connected to the first coil 4 or the power supply is only connected to the second coil 5. For example, when Figure 3When the coil switch in the circuit is connected to the circuit bc, the ab section of the inductance represents that the power supply is only connected to the first coil 4, which is used for rapid heating; Figure 3 When the coil switch is set to ba, the inductor's ac segment represents the power supply connected to the series-connected first coil 4 and second coil 5. At this point, the winding directions of the first and second coils are opposite, reducing power consumption and maintaining the operating temperature. Furthermore, the coil switch can include a third switching path, connecting the power supply only to the second coil 5, to quickly replenish energy lost during puffing.

[0077] In another embodiment, Figure 3 As shown, the coil switching switch can be used to switch the connection between the power supply and the internal tap / port of the second coil 5. Figure 3 When the coil switch in the circuit is turned on, the current flows through the ab section of the inductor, which means that the power supply is connected to the BN section of the second coil 5 with fewer turns. Figure 3 When the coil switching switch in is selected to be connected at ba, the current passes through the ac segment of the inductor, which means that the power supply is connected to the BD segment of the second coil 5 with more turns.

[0078] Preferably, by setting the switching path of the coil switching switch, the switching switch can simultaneously realize the functional operations of at least the above two embodiments, that is, to realize the selectable connection between the power supply and the first coil 4, the second coil 5, the tap / port of the second coil 5, etc.

[0079] In one embodiment, the electromagnetic heating smoking device is as follows Figure 4 The control method of electromagnetic heating smoking device includes the following steps:

[0080] S101: The coil switch selects the first coil and enters S102;

[0081] S102: Start the oscillation circuit and enter S103;

[0082] S103: Detect temperature feedback and proceed to S104;

[0083] S104: Determine whether the preheating target temperature has been reached. If so, proceed to S105; if not, return to S103.

[0084] S105: Turn off the oscillation circuit and enter S106;

[0085] S106: The coil switching switch switches the second coil and enters S107;

[0086] S107: Start the oscillation circuit and enter S108;

[0087] S108: Detect temperature feedback and proceed to S109;

[0088] S109: Determine whether the temperature is higher than the target operating temperature. If it is higher, proceed to S110; if it is lower, return to S108; if the time has expired or a shutdown command has been received, terminate the smoking device operation.

[0089] S110: Turn off the oscillation circuit and enter S111;

[0090] S111: Detect temperature feedback and proceed to S112;

[0091] S112: Determine whether the temperature is lower than the target operating temperature. If it is lower, proceed to S107; if it is higher, return to S111.

[0092] In operations S101-S104, when the electromagnetic heating device is activated, the control system activates the first coil until the susceptor reaches the preheating target temperature. Because the first coil has fewer turns and a higher oscillation frequency, this allows for a higher oscillation frequency and a higher power value, resulting in higher heating power to the susceptor, achieving rapid heating of the susceptor.

[0093] In operations S105-S107, when the temperature of the susceptor reaches the preheating target temperature, the heating power required to maintain the operating target temperature is low, the oscillation frequency is reduced, and thus the coil power is reduced. At the same time, the heating power of the susceptor is also reduced, and the control system turns off the first coil 4 and starts the second coil 5.

[0094] In operations S107-S112, the control system drives the second coil 5 to maintain the target operating temperature of the susceptor (constant temperature phase). Because a decrease in coil power reduces the current flowing through the coil, the power supply's output power can be reduced, lowering the battery discharge rate. Based on power supply characteristics, operating at a low discharge rate can effectively extend the cycle life and increase the discharge capacity. Furthermore, switching to low power operation reduces the switching frequency, effectively suppressing higher harmonics and reducing EMI radiation.

[0095] In one embodiment, to achieve further step-by-step heating during the constant temperature phase, the control system can control the power of the second coil 5 by driving taps. Different taps (ends) are connected to the coil drive circuit, driving the coils with different taps at different times to achieve heating. Preferably, when rapid heating is required, the control system selects the BN coil, which has fewer turns and achieves higher coil power. When a small amount of heating or a constant temperature is required, the control system switches to the BD coil, reducing the coil power.

[0096] The terms and expressions used herein are for descriptive purposes only, and the present invention is not limited to these terms and expressions. The use of these terms and expressions does not exclude any equivalent features shown and described (or portions thereof), and it should be recognized that various modifications that may exist are also intended to be included within the scope of the claims. Other modifications, variations, and substitutions are also possible. Accordingly, the claims should be deemed to cover all such equivalents.

[0097] Similarly, it should be pointed out that although the present invention has been described with reference to the current specific embodiments, ordinary technicians in this technical field should realize that the above embodiments are only used to illustrate the present invention, and various equivalent changes or substitutions can be made without departing from the spirit of the present invention. Therefore, as long as the changes and modifications to the above embodiments are within the scope of the essential spirit of the present invention, they will fall within the scope of the claims of the present invention.

Claims

1. An electromagnetic heating smoking device capable of heating an aerosol generating product (1) by induction heating to generate an aerosol for a user to inhale; characterized in that: The electromagnetic heating smoking device comprises: a heating chamber (2) for receiving the aerosol-generating article; The first coil (4) and the second coil (5) are circumferentially arranged outside the heating chamber (2); the first coil (4) and the second coil (5) are used to generate an induction field; the projections of the first coil (4) and the second coil (5) on the axis completely overlap; the number of turns of the second coil (5) is greater than the number of turns of the first coil (4); a power supply configured to supply a high-frequency current to the first coil (4) or the second coil (5), wherein in use the first coil (4) or the second coil (5) generates a fluctuating electromagnetic field to heat a susceptor (3) in thermal contact with the aerosol-generating article (1) and thereby heat an aerosol-generating substrate of the aerosol-generating article; A control system, comprising a coil switching switch and a temperature detection unit, wherein the coil switching switch is used to switch the connection between the power supply and the first coil (4) or the second coil (5), and the temperature detection unit is used to detect a physical quantity related to the temperature of the sensor (3). The control system controls the heating action of the electromagnetic heating smoking device according to a signal received from the temperature detection unit. When the electromagnetic heating smoking device is started, the control system drives the first coil (4) until the sensor (3) reaches a preheating target temperature; after the sensor (3) reaches the preheating target temperature, the control system turns off the first coil (4) and reduces the oscillation frequency to drive the second coil to maintain the sensor (3) at the working target temperature.

2. The electromagnetic heating smoking device according to claim 1, characterized in that: The first coil (4) and the second coil (5) are arranged in an axial sleeve relationship, the diameter of the first coil (4) is larger than that of the second coil (5), and the first coil (4) is sleeved outside the second coil (5).

3. The electromagnetic heating smoking device according to claim 1, characterized in that: The ratio of the number of turns of the second coil (5) to the number of turns of the first coil (4) is at least 1.5:

1.

4. The electromagnetic heating smoking device according to claim 1, characterized in that: An isolation device is provided between the first coil (4) and the second coil (5), and the isolation device is capable of shielding current but not shielding magnetic field.

5. The electromagnetic heating smoking device according to claim 1, characterized in that: The first port of the first coil (4) and the first port of the second coil (5) are directly electrically connected, and the second port of the first coil (4) and the second port of the second coil (5) are electrically insulated from each other.

6. The electromagnetic heating smoking device according to claim 5, characterized in that: The second coil (5) includes at least one tap, and the coil switching switch is used to switch the connection between the power supply and the first port of the second coil (5), and the second port of the second coil (5) and the tap.

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