Charging coil and terminal device

Abstract

Disclosed in the present application are a charging coil and a terminal device. The charging coil comprises a first coil layer and a second coil layer, which are connected in series, wherein the first coil layer comprises N strands of coils connected in series; each strand of coil of the first coil layer comprises L turns of coils connected in parallel; the second coil layer comprises M strands of coils connected in series; each strand of coil of the second coil layer comprises K turns of coils connected in parallel; and N and M are positive integers greater than or equal to 1, and K and L are positive integers greater than or equal to 2.

Description

Charging coil and terminal equipment

[0001] Cross-references

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on September 26, 2023, with application number 202311257863.2 and invention name “Charging Coil and Terminal Device”. The entire contents of the application are incorporated by reference into this application. Technical Field

[0003] The present application belongs to the field of wireless charging technology, and specifically relates to a charging coil and a terminal device. Background Art

[0004] Portable mobile electronic devices have been trending towards becoming thinner and lighter, which has led to a demand for thinner charging coils. However, the design requirements for wireless charging transmitter coils and receiver coils in related technologies can lead to some problems when thinning the charging coils. For example, simply reducing the thickness of the charging coil will greatly increase the impedance of the charging coil, causing the charging coil to overheat during wireless charging, thereby reducing the user experience of wireless charging.

[0005] Summary of the Invention

[0006] The embodiments of the present application provide a charging coil and a terminal device, which can solve the problem that simply reducing the thickness of the coil will greatly increase the coil impedance, thereby causing the coil to overheat during wireless charging.

[0007] In a first aspect, an embodiment of the present application provides a charging coil, comprising: a first coil layer and a second coil layer connected in series; wherein the first coil layer comprises N coils connected in series; each coil of the first coil layer comprises L turns of coils connected in parallel; the second coil layer comprises M coils connected in series; each coil of the second coil layer comprises K turns of coils connected in parallel; N and M are positive integers greater than or equal to 1, and K and L are positive integers greater than or equal to 2.

[0008] In a second aspect, an embodiment of the present application provides a terminal device, which includes the charging coil as described in the first aspect.

[0009] The charging coil in the embodiment of the present application includes a first coil layer and a second coil layer connected in series; wherein the first coil layer includes N coils connected in series; each coil of the first coil layer includes L turns of coils connected in parallel; the second coil layer includes M coils connected in series; each coil of the second coil layer includes K turns of coils connected in parallel; N and M are positive integers greater than or equal to 1, and K and L are positive integers greater than or equal to 2. When the thickness of the charging coil is reduced, the charging coil provided in the embodiment of the present application can effectively reduce the charging coil impedance increased by the thickness reduction of the charging coil by increasing the number of turns of the parallel coils in each coil, connecting multiple turns of coils in parallel into one coil, and connecting multiple coils in series. This can prevent the charging coil from overheating during wireless charging and improve the user experience of wireless charging. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG1a is a schematic cross-sectional view of a charging coil provided in an embodiment of the present application;

[0011] FIG1b is a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application;

[0012] FIG1c is a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application;

[0013] FIG2 is a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application;

[0014] FIG3a is a schematic diagram showing a current direction trend of a first coil layer of a charging coil provided in an embodiment of the present application;

[0015] FIG3 b is a schematic diagram showing the current direction trend of the second coil layer of a charging coil provided in an embodiment of the present application;

[0016] FIG4 shows the proportion of magnetic loss and line loss in the total loss of a charging coil provided by an embodiment of the present application as the output current increases;

[0017] FIG5 is a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application;

[0018] FIG6 is a schematic diagram of the magnetic field distribution of a charging coil during wireless charging provided by an embodiment of the present application;

[0019] FIG7 a is a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application;

[0020] FIG7 b is a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application;

[0021] FIG8a is a schematic diagram showing the relationship between the number of parallel turns per coil and the coil impedance and magnetic loss of a charging coil provided in an embodiment of the present application;

[0022] FIG8 b is a schematic diagram showing the relationship between the number of parallel turns and inductance of each coil of a charging coil provided in an embodiment of the present application;

[0023] FIG9a is a schematic diagram of a partial layout of a first coil layer of a charging coil provided in an embodiment of the present application;

[0024] FIG9 b is a schematic diagram of a partial layout of a second coil layer of a charging coil provided in an embodiment of the present application;

[0025] FIG9c is a schematic diagram of a partial layout of a second coil layer of another charging coil provided in an embodiment of the present application;

[0026] FIG10a is a schematic diagram of the layout of the first coil layer of another charging coil provided in an embodiment of the present application;

[0027] FIG10 b is a schematic diagram of the layout of the second coil layer of another charging coil provided in an embodiment of the present application;

[0028] FIG11 is a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application;

[0029] FIG12a is a schematic diagram of a basic circuit model of a charging coil provided in an embodiment of the present application;

[0030] FIG12 b is a schematic diagram of an equivalent circuit model of a charging coil provided in an embodiment of the present application. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0032] The terms "first," "second," and the like in the specification and claims of this application are used to distinguish similar objects, and are not used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of this application can be implemented in an order other than that illustrated or described herein, and that the objects distinguished by "first," "second," and the like are generally of the same type, and do not limit the number of objects; for example, the first object can be one or more. In addition, the term "and / or" in the specification and claims refers to at least one of the connected objects, and the character " / " generally indicates that the objects connected are in an "or" relationship.

[0033] The following describes in detail the charging coil and terminal device provided in the embodiments of the present application through specific embodiments and their application scenarios in conjunction with the accompanying drawings.

[0034] Figure 1 shows a cross-sectional schematic diagram of a charging coil provided in an embodiment of the present application. Referring to Figure 1 , the charging coil 1 includes: a first coil layer 11 and a second coil layer 12 connected in series; wherein, the first coil layer 11 includes N coils 110 connected in series; each coil 110 of the first coil layer 11 includes L turns of coils 1101 connected in parallel; the second coil layer 12 includes M coils 120 connected in series; each coil 120 of the second coil layer 12 includes K turns of coils 1201 connected in parallel; N and M are positive integers greater than or equal to 1, and K and L are positive integers greater than or equal to 2.

[0035] The number of coil strands N in the first coil layer 11 and the number of coil strands M in the second coil layer 12 may be the same or different. The number of turns L per coil 110 in the first coil layer 11 and the number of turns K per coil 120 in the second coil layer 12 may be the same or different.

[0036] For example, Figure 1b shows a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application. Referring to Figure 1b , in the charging coil 1 provided in this embodiment, N=2, M=3, and L=K=2. The first coil layer 11 includes coils 101 and 102 connected in series, and the second coil layer 12 includes coils 103, 104, and 105 connected in series. Coil 102, located at the innermost turn of the first coil layer 11 of the charging coil 1, is connected in series with coil 105, located at the innermost turn of the second coil layer 12 of the charging coil 1, thereby achieving a series connection between the first coil layer 11 and the second coil layer 12 of the charging coil 1.

[0037] For example, Figure 1c shows a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application. Referring to Figure 1c, in the charging coil 1 provided in this embodiment, N = 2, M = 3, L = 3, and K = 2. The first coil layer 11 includes coils 101 and 102 connected in series, and the second coil layer 12 includes coils 103, 104, and 105 connected in series. The innermost coil 102 of the first coil layer 11 of the charging coil 1 is connected in series with the innermost coil 105 of the second coil layer 12 of the charging coil 1, thereby achieving a series connection between the first coil layer 11 and the second coil layer 12 of the charging coil 1.

[0038] When reducing the thickness of the charging coil, the charging coil provided in the embodiment of the present application increases the number of turns of the parallel coils in each coil, connects multiple turns of coils in parallel into one strand, and connects multiple strands of coils in series, thereby reducing the charging coil impedance increased due to the thinning of the charging coil, thereby preventing the charging coil from overheating during the wireless charging process and improving the user experience of wireless charging.

[0039] Figure 2 shows a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application, in one implementation. Referring to Figure 2 , each coil 110 of the first coil layer 11 includes L parallel turns of coils 1101, which may include a first coil 21 and a second coil 22. The width of the first coil 21 is greater than the width of the second coil 22. The first coil 21 is located on the outer turn of the second coil 22. Each coil 120 of the second coil layer 12 includes K parallel turns of coils 1201, which may include a third coil 23 and a fourth coil 24. The width of the third coil 23 is greater than the width of the fourth coil 24. The third coil 23 is located on the outer turn of the fourth coil 24.

[0040] The first coil 21 is located outside the second coil 22, which means the distance from the first coil 21 to the center of the charging coil is greater than the distance from the second coil 22 to the center of the charging coil. The third coil 23 is located outside the fourth coil 24, which means the distance from the third coil 23 to the center of the charging coil is greater than the distance from the fourth coil 24 to the center of the charging coil.

[0041] In the embodiment of the present application, the coil width of each turn of the coil in each coil of the first coil layer 11 and the second coil layer 12 is set to decrease from the outer circle to the inner circle, so that the outer circle coil with a wider coil width can reduce the impedance of the coil, and at the same time, the inner circle coil with a narrower coil width can avoid heat loss caused by eddy currents generated in the coil by the strong alternating magnetic field.

[0042] FIG3 a schematically illustrates the current direction trend in the first coil layer of a charging coil provided in an embodiment of the present application, and FIG3 b schematically illustrates the current direction trend in the second coil layer of a charging coil provided in an embodiment of the present application. Referring to FIG3 a and FIG3 b , the embodiment of the present application provides a charging coil in which two turns are connected in parallel to form a strand, with each layer consisting of one strand of coil. The current direction trends in the first and second coil layers of the charging coil are illustrated. Current flows from a first output terminal 31 of the first coil layer through parallel coils L1 and L2 to a through-hole, and then through parallel coils L3 and L4 of the second coil layer to a second output terminal 32. Coil L1 is located on the outer coil of coil L2, and its width is greater than that of coil L2. Coil L4 is located on the outer coil of coil L3, and its width is greater than that of coil L3. This reduces the width of the multiple turns of coils connected in parallel within each strand from the outer to the inner coil, thereby reducing the impedance of the charging coil while ensuring the inductance of the charging coil.

[0043] FIG4 shows the proportion of magnetic loss and line loss in the total loss of a charging coil provided by an embodiment of the present application as the output current increases. The charging coil provided by an embodiment of the present application reduces the impedance of the charging coil, thereby reducing the line loss of the charging coil. However, the increased magnetic field generated by the increased current at the transmitting end interacts with magnetic shielding materials such as nanocrystals to produce stronger magnetic loss, as shown in FIG4 . Therefore, when line loss accounts for the main loss, the charging coil provided by the embodiment of the present application can bring benefits in terms of temperature rise and loss, while when magnetic loss accounts for the main loss, the charging coil provided by the embodiment of the present application will cause a deterioration in temperature rise and loss due to the significant increase in magnetic loss. As can be seen from FIG4 , when the effective value of the current reaches 2.09A and above, the charging coil provided by the embodiment of the present application can achieve benefits in terms of temperature rise and loss under working conditions above 36W, and the performance of the thinned charging coil can best support working under working conditions near 36W.

[0044] The charging coil provided by the embodiments of the present application requires fewer winding strands when the charging coil is thinned, maintaining the same available area. By increasing the number of turns in parallel and increasing the wire diameter, the impedance of the charging coil can be reduced, compensating for the increased impedance caused by thinning the charging coil. This effectively reduces the impedance of the charging coil while ensuring the desired inductance. Furthermore, thinning the charging coil requires fewer nanocrystals to achieve the target inductance, allowing the number of nanocrystal layers to be reduced from three to two, further reducing the thickness of the charging coil structure.

[0045] Figure 5 shows a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application in one implementation; referring to Figure 5, the N coils connected in series include a fifth coil 51 and a sixth coil 52, and the width of the fifth coil 51 is greater than the width of the sixth coil 52; wherein, the fifth coil 51 is located on the outer ring of the sixth coil 52; the M coils connected in series include a seventh coil 53 and an eighth coil 54, and the width of the seventh coil 53 is greater than the width of the eighth coil 54; wherein, the seventh coil 53 is located on the outer ring of the eighth coil 54.

[0046] In the charging coil of the embodiment of the present application, the coil width is configured to decrease from the outer circle to the inner circle. During wireless charging, due to the superposition of magnetic fields generated by each turn of the coil, the strength of the magnetic field of the coil located in the inner circle is generally higher than that of the magnetic field of the coil located in the outer circle, as shown in Figure 6. Therefore, by setting the width of the coil located in the outer circle to be larger than the width of the coil located in the inner circle, the impedance of the coil can be reduced. At the same time, since the magnetic field strength of the coil in the inner circle is relatively strong, by setting the width of the coil located in the inner circle to be smaller, the heat loss caused by eddy currents generated on the coil surface by the strong alternating magnetic field, that is, the generation of a larger impedance, can be avoided. In addition, the coil width of the charging coil provided in the embodiment of the present application decreases from the outer circle to the inner circle, which can also ensure a larger coil inner diameter, so that fewer coils operate in the strongest magnetic field area, thereby reducing the impact of the skin effect.

[0047] Figure 7a shows a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application, in one implementation. Referring to Figure 7a, the charging coil further includes: a connecting coil 13 comprising J parallel turns of a coil 130, wherein the number of turns J of the connecting coil 13 may be the same as or different from the aforementioned L and K. As shown in Figure 7b, in the charging coil provided in this embodiment, N = 2, M = 3, L = 3, K = 2, and J = 4; a ninth coil 111 in the first coil layer 11 is connected in series with the connecting coil 13; and the connecting coil 13 is connected in series with the tenth coil 121 in the second coil layer 12. The ninth coil 111 is the coil located at a first preset position in the first coil layer 11 among the N coils, and the tenth coil 121 is the coil located at a second preset position in the second coil layer 12 among the M coils. The first preset position includes the innermost turn of the first coil layer 11, and the second preset position includes the innermost turn of the second coil layer 12.

[0048] In one implementation, K, L, and J are all 6.

[0049] Figure 8a illustrates the relationship between the number of parallel turns per coil and the coil impedance and magnetic loss of a charging coil provided in an embodiment of the present application; Figure 8b illustrates the relationship between the number of parallel turns per coil and the coil inductance of a charging coil provided in an embodiment of the present application. Referring to Figure 8a , as the number of parallel turns per coil increases, the impedance of the charging coil decreases, thereby reducing the line loss of the charging coil. Correspondingly, referring to Figure 8b , as the number of parallel turns per coil increases, the inductance of the charging coil decreases, requiring an increase in the current at the transmitting end to meet the preset output power. This high current, in turn, increases the magnetic loss of the charging coil. When the design requirements for the charging coil are to minimize impedance and magnetic loss, determining the number of parallel turns per coil requires comprehensive consideration of the relationship between the coil impedance and the magnetic loss generated at the preset output power. As shown in Figure 8a, as the number of parallel turns per coil increases to approximately 6, the impedance of the charging coil decreases more slowly and the magnetic loss increases more rapidly. Therefore, setting the number of parallel turns per coil to 6 is an optimal value, and the corresponding charging coil inductance is 3.75uH.

[0050] In one implementation, Figure 9a shows a schematic diagram of a partial layout of the first coil layer of a charging coil provided in an embodiment of the present application, and Figure 9b shows a schematic diagram of a partial layout of the first coil layer of a charging coil provided in an embodiment of the present application. Referring to Figures 9a and 9b, the connecting coil includes a first connecting coil 91 and a second connecting coil 92 connected in parallel; each turn of the connecting coil includes a first port and a second port. The first coil layer includes an eleventh coil 93 and a twelfth coil 94; the second coil layer includes a thirteenth coil 99 and a fourteenth coil 90; the eleventh coil 93 is connected to the first port 95 of the first connecting coil 91, the twelfth coil 94 is connected to the first port 96 of the second connecting coil 92; the thirteenth coil 99 is connected to the second port 97 of the second connecting coil 92, and the fourteenth coil 90 is connected to the second port 98 of the first connecting coil 91.

[0051] In an embodiment of the present application, the first coil layer and the second coil layer included in the charging coil are connected in series through a connecting coil, and the connecting coil can be divided into two parts of coils, one part of the coils is located in the first coil layer and the first coil layer and the second coil layer are connected in series, and the other part is located in the second coil layer and the first coil layer and the second coil layer are connected in series. On the premise of ensuring that the first coil layer and the second coil layer are connected in series, the winding area of ​​the first coil layer and the second coil layer can be reduced, the inner diameter of the charging coil can be increased, and fewer coils can operate in the strongest magnetic field area, thereby reducing the influence of the skin effect.

[0052] Figure 9c shows a partial schematic layout diagram of the second coil layer of another charging coil provided in an embodiment of the present application, in one implementation. In the charging coil of this embodiment of the present application, the eleventh coil 93 is located outside the twelfth coil 94, and the thirteenth coil 99 is located outside the fourteenth coil 90.

[0053] In the embodiment of the present application, the first coil layer and the second coil layer are connected in series via a connecting coil, which is divided into a first connecting coil and a second connecting coil. When connecting the first coil layer and the second coil layer, the first connecting coil 91 is connected to the eleventh coil 93 located on the outer circle relative to the twelfth coil 94 in the first coil layer, and to the fourteenth coil 90 located on the inner circle relative to the thirteenth coil 99 in the second coil layer. The second connecting coil 92 is connected to the twelfth coil 94 located on the inner circle relative to the eleventh coil 93 in the first coil layer, and to the thirteenth coil 99 located on the outer circle relative to the fourteenth coil 90 in the second coil layer. This ensures that the first coil layer is connected in series with the second coil layer in the opposite direction via the first connecting coil and the second connecting coil. This reduces the space occupied by the series connection between the first and second coil layers, allowing for further reduction in the thickness of the terminal device including the charging coil.

[0054] In one implementation, Figure 10a shows a schematic layout diagram of the first coil layer of another charging coil provided in an embodiment of the present application, and Figure 10b shows a schematic layout diagram of the second coil layer of another charging coil provided in an embodiment of the present application. In this embodiment of the charging coil, the number of turns L per coil in the first coil layer, the number of turns K per coil in the second coil layer, and the number of turns J of the connecting coil are all 6. The charging coil comprises a first and second coil layer, totaling 42 turns, with 6 turns arranged in parallel as a strand, for a total of 21 turns per layer, or 3.5 strands. A fourth strand, formed by connecting four turns of coils L19 through L2 in parallel, serves as a connecting coil between the first and second coil layers. Three turns of the fourth strand are located in the first coil layer. As shown in Figure 10a, one end of coils L19 through L21 is connected in series with the three turns of the third strand in the first coil layer. The other ends of coils L19 through L21 are connected in series with the three turns of the fifth strand in the second coil layer via through-holes 1 through 3. The remaining three turns of the fourth coil are distributed in the second coil layer, as shown in Figure 10b. One end of coils 22 to 24 is connected in series with the three turns of the fifth coil in the second coil layer, and the other end of coils 22 to 24 is connected in series with the three turns of the third coil in the first coil layer through through holes 4 to 6.

[0055] FIG11 shows a cross-sectional schematic diagram of another charging coil provided in an embodiment of the present application. Referring to FIG11 , the coil width of the charging coil provided in this embodiment is reduced from 1.2 mm in the outermost coil to 0.3 mm in the innermost coil. Setting the coil width in this way ensures that the charging coil can achieve an inductance of 3.5 uH under the terminal design conditions of 48 mm outer diameter and 22 mm inner diameter, and reduces the impedance of the charging coil. Therefore, the charging coil provided in the embodiment of the present application can use the thinnest mass-produced copper wire, that is, the thickness of a single coil layer is 0.022 mm, and only two layers of nanocrystals can be used to meet the above-mentioned inductance value. The overall thickness of the charging coil can also be further reduced, achieving a thinning of the charging coil while ensuring the wireless charging performance of the charging coil.

[0056] FIG12a shows a schematic diagram of a basic circuit model of a charging coil provided in an embodiment of the present application; FIG12b shows a schematic diagram of an equivalent circuit model of a charging coil provided in an embodiment of the present application; wherein, the current expression I1 at the transmitting end (Transport, Tx) and the current expression I2 at the receiving end (Receive, Rx) are respectively:

[0057] Among them, M is the mutual inductance of the Tx and Rx charging coils, Z11 is the input impedance of the wireless charging system from the feed end, Y22 is the admittance of the wireless charging system from the load end, Ls, Cs, Rs are the inductance, capacitance, and resistance of the secondary coil, that is, the inductance, capacitance, and resistance of the Rx charging coil. Lp, Cp, Rp are the inductance, capacitance, and resistance of the primary coil, that is, the inductance, capacitance, and resistance of the Tx charging coil. RL is the load resistance, Vp is the feed voltage, and f is the operating frequency. According to formulas (1) and (2), when the output voltage and current remain unchanged, reducing the inductance of the Rx charging coil will result in a decrease in the mutual inductance M. That is, in order to achieve the output power before the inductance is reduced, the current of the Tx coil needs to be increased to generate sufficient induced electromotive force, which will increase the line loss of the Tx coil. It can be considered that the heat loss is transferred from the Rx coil to the Tx coil, thereby improving the wireless charging performance of the Rx coil, reducing the impedance of the Rx coil, and solving the problem of excessive heating of the Rx coil during wireless charging.

[0058] The present application also provides a terminal device, which includes a charging coil as described in the above embodiments. The terminal device can be a transmitting device or a receiving device. When the terminal device is wirelessly charging, because the charging coil in the terminal device increases the number of turns of the parallel coils in each coil, the multiple turns of the coil are connected in parallel into one coil, and the multiple coils are connected in series. This effectively reduces the impedance of the charging coil that increases due to the thinning of the charging coil, thereby preventing the charging coil from overheating during the wireless charging process and improving the user experience of wireless charging.

[0059] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0060] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus the necessary general hardware platform, and of course can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes a number of instructions for enabling a terminal (which can be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in each embodiment of the present application.

[0061] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are within the protection of this application.

Claims

1. A charging coil, comprising: A first coil layer and a second coil layer connected in series; wherein, The first coil layer includes N coils connected in series; each coil of the first coil layer includes L turns of coils connected in parallel; the second coil layer includes M coils connected in series; each coil of the second coil layer includes K turns of coils connected in parallel; N and M are positive integers greater than or equal to 1, and K and L are positive integers greater than or equal to 2.

2. The charging coil according to claim 1, wherein: The L turns of coils connected in parallel include a first coil and a second coil, the width of the first coil is greater than the width of the second coil; wherein the first coil is located on the outer coil of the second coil; The K turns of coils connected in parallel include a third coil and a fourth coil, the width of the third coil is greater than the width of the fourth coil; wherein the third coil is located on the outer turn of the fourth coil.

3. The charging coil according to claim 1, wherein: The N coils connected in series include a fifth coil and a sixth coil, the width of the fifth coil is greater than the width of the sixth coil; wherein the fifth coil is located in the outer coil of the sixth coil; The M coils connected in series include a seventh coil and an eighth coil, the width of the seventh coil is greater than the width of the eighth coil; wherein the seventh coil is located in the outer coil of the eighth coil.

4. The charging coil according to claim 1, wherein: The charging coil further comprises: a connecting coil, wherein the connecting coil comprises a coil having J turns connected in parallel; The ninth coil of the first coil layer is connected in series with the connecting coil; The connecting coil is connected in series with the tenth coil of the second coil layer; The ninth coil is a coil located at a first preset position of the first coil layer among the N coils, and the tenth coil is a coil located at a second preset position of the second coil layer among the M coils. lock up; Wherein, the first preset position includes the innermost circle of the first coil layer; and the second preset position includes the innermost circle of the second coil layer.

5. The charging coil according to claim 4, wherein: The K, L and J are 6.

6. The charging coil according to claim 4, wherein: The connecting coil includes a first connecting coil and a second connecting coil connected in parallel; each turn of the connecting coil includes a first port and a second port; the first coil layer includes an eleventh coil and a twelfth coil; the second coil layer includes a thirteenth coil and a fourteenth coil; The eleventh coil is connected to the first port of the first connecting coil, and the twelfth coil is connected to the first port of the second connecting coil; The thirteenth coil is connected to the second port of the second connection coil, and the fourteenth coil is connected to the second port of the first connection coil.

7. The charging coil according to claim 6, wherein: The eleventh coil is located on the outer circle of the twelfth coil; the thirteenth coil is located on the outer circle of the fourteenth coil.

8. The charging coil according to claim 1, wherein: The N is the same as the M.

9. The charging coil according to claim 1, wherein: The L is the same as the K.

10. A terminal device, comprising the charging coil according to any one of claims 1 to 9.

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