CN117277598A - Charging coils and terminal equipment - Google Patents

Abstract

The application discloses charging coil and terminal equipment, this charging coil includes: a first coil layer and a second coil layer 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 coil of the second coil layer comprises K 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 coils and terminal equipment

Technical field

This application belongs to the field of wireless charging technology, and specifically relates to a charging coil and terminal equipment.

Background technique

Portable mobile electronic devices have always been developing in a lighter and lighter direction. Among them, there are also requirements for the thickness of charging coils to be thinner. However, in related technologies, the design requirements for the transmitter coil and the receiving end coil of wireless charging will make Some problems arise when thinning the charging coil. For example, simply thinning the thickness of the charging coil will greatly increase the impedance of the charging coil, causing the charging coil to overheat during the wireless charging process and reducing the wireless charging experience. .

Contents of the invention

Embodiments of the present application provide a charging coil and terminal equipment, which can solve the problem that simply thinning the thickness of the coil will greatly increase the coil impedance, thereby causing the coil to overheat during the wireless charging process.

In a first aspect, an embodiment of the present application provides a charging coil. The charging coil 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 a coil layer includes L turns of coils connected in parallel; the second coil layer includes M coils of series connection; each coil of the second coil layer includes K turns of coils connected in parallel; the N and the M is a positive integer greater than or equal to 1, and the K and L are positive integers greater than or equal to 2.

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.

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 in parallel The coil; 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; the N and the M are positive integers greater than or equal to 1, so The K and the L are positive integers greater than or equal to 2. When thinning the thickness of the charging coil, the charging coil provided in the embodiment of the present application can effectively reduce the charge due to thinning by increasing the number of turns of the parallel coil in each coil. The thickness of the coil increases the impedance of the charging coil, thereby preventing the charging coil from overheating during the wireless charging process and improving the wireless charging experience.

Description of the drawings

Figure 1a is a schematic cross-sectional view of a charging coil provided by an embodiment of the present application;

Figure 1b is a schematic cross-sectional view of another charging coil provided by an embodiment of the present application;

Figure 1c is a schematic cross-sectional view of yet another charging coil provided by an embodiment of the present application;

Figure 2 is a schematic cross-sectional view of another charging coil provided by an embodiment of the present application;

Figure 3a is a schematic diagram of the current direction trend of the first coil layer of a charging coil provided by an embodiment of the present application;

Figure 3b is a schematic diagram of the current direction trend of the second coil layer of a charging coil provided by an embodiment of the present application;

Figure 4 shows the proportion of magnetic loss and line loss in the overall loss caused by the increase in output current of a charging coil provided by the embodiment of the present application;

Figure 5 is a schematic cross-sectional view of another charging coil provided by an embodiment of the present application;

Figure 6 is a schematic diagram of the coil magnetic field distribution of a charging coil during wireless charging provided by an embodiment of the present application;

Figure 7a is a schematic cross-sectional view of another charging coil provided by an embodiment of the present application;

Figure 7b is a schematic cross-sectional view of another charging coil provided by an embodiment of the present application;

Figure 8a is a schematic diagram of the relationship between the number of parallel turns of each coil of a charging coil, coil impedance, and magnetic loss according to an embodiment of the present application;

Figure 8b is a schematic diagram of the relationship between the number of parallel turns and the inductance of each coil of a charging coil provided by an embodiment of the present application;

Figure 9a is a partial layout diagram of the first coil layer of a charging coil provided by an embodiment of the present application;

Figure 9b is a partial layout schematic diagram of the second coil layer of a charging coil provided by an embodiment of the present application;

Figure 9c is a partial layout diagram of the second coil layer of another charging coil provided by an embodiment of the present application;

Figure 10a is a schematic layout diagram of the first coil layer of another charging coil provided by an embodiment of the present application;

Figure 10b is a schematic layout diagram of the second coil layer of another charging coil provided by an embodiment of the present application;

Figure 11 is a schematic cross-sectional view of another charging coil provided by an embodiment of the present application;

Figure 12a is a schematic diagram of a basic circuit model of a charging coil provided by an embodiment of the present application;

Figure 12b is a schematic diagram of an equivalent circuit model of a charging coil provided by an embodiment of the present application.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

The terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects and are not used to describe a specific order or sequence. It is to be understood that the figures so used are interchangeable under appropriate circumstances so that the embodiments of the present application can be practiced in orders other than those illustrated or described herein, and that "first," "second," etc. are distinguished Objects are usually of one type, and the number of objects is not limited. For example, the first object can be one or multiple. In addition, "and/or" in the description and claims indicates at least one of the connected objects, and the character "/" generally indicates that the related objects are in an "or" relationship.

The charging coil and terminal equipment provided by the embodiments of the present application will be described in detail below with reference to the accompanying drawings through specific embodiments and application scenarios.

Figure 1 shows a schematic cross-sectional view of a charging coil provided by 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 The layer 11 includes N coils 110 connected in series; each coil 110 of the first coil layer 11 includes L turns of parallel coils 1101; the second coil layer 12 includes M coils 120 connected in series; the second coil Each coil 120 of layer 12 includes K turns of parallel-connected coils 1201; the N and the M are positive integers greater than or equal to 1, and the K and L are positive integers greater than or equal to 2.

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

For example, FIG. 1 b shows a schematic cross-sectional view of another charging coil provided by an embodiment of the present application. Referring to FIG. 1 b, N=2, M=3, and L=K=2 in the charging coil 1 provided by this embodiment. The first coil layer 11 includes a coil 101 and a coil 102 connected in series, and the second coil layer 12 includes a coil 103 and a coil 104 and a coil 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 to realize the connection between the first coil layer 11 of the charging coil 1 and the second coil layer 12 of the charging coil 1 . Series connection of coil layers 12.

As another example, Figure 1c shows a schematic cross-sectional view of yet another charging coil provided by an embodiment of the present application. Referring to Figure 1c, N=2, M=3, L=3, K in the charging coil 1 provided by this embodiment. =2. The first coil layer 11 includes a coil 101 and a coil 102 connected in series, and the second coil layer 12 includes a coil 103 and a coil 104 and a coil 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 to realize the connection between the first coil layer 11 of the charging coil 1 and the second coil layer 12 of the charging coil 1 . Series connection of coil layers 12.

When thinning the thickness of the charging coil, the charging coil provided by the embodiment of the present application increases the number of turns of the parallel coil in each coil. The impedance of the charging coil increases due to the thickness, thereby preventing the charging coil from overheating during the wireless charging process and improving the wireless charging experience.

FIG. 2 shows a schematic cross-sectional view of another charging coil provided by an embodiment of the present application in an implementation manner. Referring to FIG. 2 , each coil 110 of the first coil layer 11 includes L turns of parallel coils 1101 , which may include a first coil 21 and a second coil 22 . The width of the first coil 21 is larger than that of the second coil. 22 width. Wherein, the first coil 21 is located on the outer circle of the second coil 22 . Each coil 120 of the second coil layer 12 includes K turns of parallel coils 1201 that 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 turn coil 24. . Wherein, the third coil 23 is located on the outer circle of the fourth coil 24 .

Wherein, the first coil 21 is located in the outer circle of the second coil 22, which can be understood as the distance between the first coil 21 and the center of the charging coil is greater than the distance between the second coil 22 and the center of the charging coil. The third coil 23 is located in the outer circle of the fourth coil 24. It can be understood that the distance between the third coil 23 and the center of the charging coil is greater than the distance between the fourth coil 24 and the center of the charging coil.

In the embodiment of the present application, for each turn of each coil of the first coil layer 11 and the second coil layer 12, the coil width is set to decrease from the outer coil to the inner coil, so that the outer coil with a wider coil width is The inner coil can reduce the impedance of the coil, and the inner coil with a narrow coil width can avoid the heat loss caused by the eddy current generated by the strong alternating magnetic field on the coil.

Figure 3a shows a schematic diagram of the current direction trend of the first coil layer of a charging coil provided by an embodiment of the present application. Figure 3b shows a current direction trend of the second coil layer of a charging coil provided by an embodiment of the present application. Schematic diagram; see Figure 3a and Figure 3b. The embodiment of the present application provides an example of a charging coil with two turns connected in parallel to form one coil, and each layer is composed of one coil. The first coil layer and the third coil layer of the charging coil are shown. The trend of the current direction in the second coil layer. The current flows from the first outlet terminal 31 of the first coil layer through the parallel coil L1 and coil L2 to the through hole, and then passes through the parallel coil L3 and coil L4 of the second coil layer to the third coil layer. Two outlet terminals 32, in which the coil L1 is located on the outer ring of the coil L2, the width of the coil L1 is greater than the width of the coil L2, the coil L4 is located on the outer ring of the coil L3, the width of the coil L4 is greater than the width of the coil L3, realizing parallel connection within each strand The width of the multi-turn coil decreases from the outer ring to the inner ring, reducing the impedance of the charging coil while ensuring the inductance of the charging coil.

Figure 4 shows the proportion of magnetic loss and line loss in the overall loss caused by an increase in output current of a charging coil provided by an embodiment of the present application. The charging coil provided by the 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 sending end will interact with magnetic shielding materials such as nanocrystals to produce Stronger magnetic loss, as shown in Figure 4. 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, and when magnetic loss accounts for the main loss, the charging coil provided by the embodiment of the present application will The significant increase in magnetic losses leads to temperature rise and deterioration in losses. It can be seen from Figure 4 that when the effective current value reaches 2.09A and above, the charging coil provided by the embodiment of the present application can gain benefits in terms of temperature rise and loss under the working condition of more than 36W. The performance of the thinned charging coil It can support working under working conditions up to around 36W.

With the charging coil provided by the embodiment of the present application, when the charging coil is thinned and the available area is the same, the charging coil at this time will require fewer winding strands. By increasing the number of turns of the parallel coil, Increasing the wire diameter can reduce the impedance of the charging coil, thereby compensating for the increased impedance caused by thinning the charging coil, effectively reducing the impedance of the charging coil while ensuring the inductance. And after thinning the charging coil, fewer nanocrystals are needed to achieve the target sensitivity, which can reduce the number of nanocrystals from three layers to two layers, thereby further reducing the thickness of the charging coil structure.

Figure 5 shows a schematic cross-sectional view of another charging coil provided by the embodiment of the present application in an implementation manner; referring to Figure 5, the N series coils include a fifth coil 51 and a sixth coil 52, so 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 circle of the sixth coil 52; the M series coils include a seventh coil 53 and a Eight coils 54, 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 circle of the eighth coil 54.

In the charging coil in the embodiment of the present application, the coil width is set to decrease from the outer ring to the inner ring. During the wireless charging process, generally due to the superposition of the magnetic field generated by each turn of the coil, the intensity of the magnetic field of the coil located in the inner ring decreases. The intensity of the magnetic field is higher than that of the coil located on the outer coil, as shown in Figure 6; therefore, the impedance of the coil can be reduced by setting the width of the coil located on the outer coil to be greater than the width of the coil located on the inner coil. At the same time, due to the large intensity of the coil magnetic field in the inner coil, the width of the coil located in the inner coil is set smaller to avoid heat loss caused by eddy currents generated by the strong alternating magnetic field on the coil surface, that is, a large impedance is generated. In addition, the charging coil provided by the embodiment of the present application has a reduced coil width from the outer ring to the inner ring, which can also ensure a larger coil inner diameter, so that fewer coils work in the strongest magnetic field area, thereby reducing the influence of the skin effect. .

Figure 7a shows a schematic cross-sectional view of another charging coil provided by an embodiment of the present application in an implementation manner. Referring to Figure 7a, the charging coil also includes: a connecting coil 13. The connecting coil 13 includes J turns of a coil 130 connected in parallel. The number J of the coil turns of the connecting coil 13 can be the same as the above-mentioned L and the above-mentioned K. , can also be different. As shown in Figure 7b, in the charging coil provided by this embodiment, N=2, M=3, L=3, K=2, J=4; in the first coil layer 11 The ninth coil 111 is connected in series with the connecting coil 13; the connecting coil 13 is connected in series with the tenth coil 121 in the second coil layer 12, and the ninth coil 111 is located in the N-strand coil. The coil in the first preset position of the first coil layer 11, and the tenth coil 121 is the coil in the second preset position of the second coil layer 12 among the M-strand coils, wherein the first preset position The position includes the innermost circle of the first coil layer 11 ; the second preset position includes the innermost circle of the second coil layer 12 .

In one implementation, the K, the L and the J are 6.

Figure 8a shows a schematic diagram of the relationship between the number of parallel turns of each coil, coil impedance and magnetic loss of a charging coil provided by an embodiment of the present application; Figure 8b shows a charging coil provided by an embodiment of the present application. The schematic diagram of the relationship between the number of parallel turns of each coil and the coil inductance; see Figure 8a, as the number of parallel turns of each coil increases, the impedance of the charging coil decreases, so the line loss of the charging coil also decreases. Correspondingly, see Figure 8b, as the number of parallel turns of each coil increases, the inductance of the charging coil decreases, so that to meet the preset output power, the current at the sending end needs to be increased, thus increasing the charging due to the high current. Magnetic losses in the coil. When the design requirements of the charging coil are to have as low impedance and as low magnetic loss as possible, determining the number of parallel turns of each coil should comprehensively consider the relationship between the coil impedance and the magnetic loss generated at the preset output power. It can be seen from Figure 8a that as the number of parallel turns of each coil increases to around 6 turns, the impedance of the charging coil decreases slowly and the magnetic loss increases. Therefore, the number of parallel turns of each coil is set to 6 turns. The optimal value is that the corresponding inductance of the charging coil is 3.75uH.

In one implementation, FIG. 9a shows a partial layout diagram of the first coil layer of a charging coil provided by an embodiment of the present application, and FIG. 9b shows a first layer of a charging coil provided by an embodiment of the present application. Schematic diagram of partial layout of coil layers. Referring to Figures 9a and 9b, the connection coil includes a first connection coil 91 and a second connection coil 92 connected in parallel; each turn of the connection 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 and the first The first port 95 of the connecting coil 91 is connected, 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 of the second connecting coil 92. The port 97 is connected, and the fourteenth coil 90 is connected to the second port 98 of the first connection coil 91 .

In the embodiment of the present application, the first coil layer and the second coil layer included in the charging coil are connected in series through the connecting coil. The connecting coil can be divided into two parts of coils, one part of which is located on the first coil layer. The first coil layer and the second coil layer are connected in series. The second coil layer is connected in series, and the other part is located in the second coil layer. The first coil layer and the second coil layer are connected in series, which can reduce the first coil layer and the second coil layer on the premise of ensuring that the first coil layer and the second coil layer are connected in series. The winding area of the second coil layer increases the inner diameter of the charging coil, allowing fewer coils to work in the strongest magnetic field area, thus reducing the impact of the skin effect.

FIG. 9c shows a partial layout diagram of the second coil layer of another charging coil provided by an embodiment of the present application in one implementation. In the charging coil in the embodiment of the present application, the eleventh coil 93 is located on the outer circle of the twelfth coil 94 , and the thirteenth coil 99 is located on the outer circle of the fourteenth coil 90 .

In the embodiment of the present application, the first coil layer and the second coil layer are connected in series through the connecting coil. When the connecting coil is divided into a first connecting coil and a second connecting coil, the first coil layer and the second coil layer are connected. The connecting coil 91 is connected to the eleventh coil 93 located in the outer circle relative to the twelfth coil 94 at the first coil layer, and is connected to the fourteenth coil located in the inner circle relative to the thirteenth coil 99 at the second coil layer. 90 connections. The second connecting coil 92 is connected to the twelfth coil 94 located on the inner circle relative to the eleventh coil 93 at the first coil layer, and is connected to the tenth coil 94 located on the outer circle relative to the fourteenth coil 90 at the second coil layer. The three-coil 99 connection realizes that on the premise of ensuring that the first coil layer and the second coil layer are connected in series, the first coil layer is connected in series with the second coil layer in reverse through the first connecting coil and the second connecting coil, reducing the The space occupied by the series connection of one coil layer and the second coil layer enables the terminal device including the charging coil to be further thinned.

In one implementation, Figure 10a shows a schematic layout diagram of the first coil layer of another charging coil provided by an embodiment of the present application, and Figure 10b shows a third coil layer of another charging coil provided by an embodiment of the present application. Schematic diagram of the layout of the two coil layers. In the embodiment of the present application, the number of coil turns L of each coil of the first coil layer of the charging coil, the number of coil turns K of each coil of the second coil layer, and the coil turns of the connecting coil The numbers J are all 6. Among them, the charging coil includes a first coil layer and a second coil layer, with a total of 42 turns, 6 turns are arranged in parallel to form one strand, and each layer is provided with a total of 21 turns, that is, 3.5 strands. The fourth strand coil is formed by connecting coils L19 to L24 in parallel and serves as a connecting coil between the first coil layer and the second coil layer. Three turns of the fourth coil are distributed in the first coil layer. As shown in Figure 10a, one end of the coil L19 to coil L21 is connected in series with the three turns of the third coil in the first coil layer. The coils L19 to L21 are connected in series. The other end of L21 is connected in series with the 3-turn coil of the 5th coil of the second coil layer through through hole 1 to through hole 3. The remaining 3 turns of the 4th 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 3 turns of the 5th coil in the second coil layer. Coils 22 to 24 are connected in series. The other end of 24 is connected in series with the 3-turn coil of the 3rd strand coil in the first coil layer through the through hole 4 to the through hole 6.

Figure 11 shows a schematic cross-sectional view of another charging coil provided by an embodiment of the present application. Referring to Figure 11, the coil width of the charging coil provided by this embodiment is reduced from the outermost coil width of 1.2mm to the innermost coil width. The coil width is 0.3mm. This setting of the coil width can ensure that under the terminal design conditions of 48mm outer diameter and 22mm inner diameter, the charging coil can reach an inductance of 3.5uH and reduce the impedance of the charging coil. Therefore, the charging coil provided by the embodiment of the present application can use the thinnest mass-produced copper wire, that is, the thickness of the single-layer coil layer is 0.022mm, and can only use two layers of nanocrystals to meet the above-mentioned inductance value. The overall charging coil The thickness can also be further reduced, achieving a thinner charging coil while ensuring the wireless charging performance of the charging coil.

Figure 12a shows a schematic diagram of a basic circuit model of a charging coil provided by an embodiment of the present application; Figure 12b shows a schematic diagram of an equivalent circuit model of a charging coil provided by an embodiment of the present application; wherein, the transmitter (Transport, The current expression I ₁ of Tx) and the current expression I ₂ of the receiving end (Receive, Rx) are respectively:

Among them, M is the mutual inductance value of Tx and Rx charging coils, Z ₁₁ is the input impedance of the wireless charging system when viewed from the feed end, Y ₂₂ is the admittance of the wireless charging system when viewed from the load end, L _s , C _s , R _s are the inductance, capacitance, and resistance of the secondary coil, that is, the inductance, capacitance, and resistance of the Rx charging coil. L _p , C _p , and R _p are the inductance, capacitance, and resistance of the primary coil, that is, the inductance, capacitance, and resistance of the Tx charging coil. R _L is the load resistance, V _p is the feed voltage, ω = 2πf, and f is the operating frequency. According to formulas (1) and (2), it can be seen that when the output voltage and current remain unchanged, reducing the inductance of the Rx charging coil causes the mutual inductance value M to decrease. That is, in order to achieve the output power before the inductance is reduced, the current of the Tx coil needs to be Increase can generate enough induced electromotive force, which leads to an increase in 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 The problem of excessive heating of Rx coil during wireless charging.

An embodiment of the present application also provides a terminal device, which includes the charging coil as described in the above embodiments. The terminal device can be a sending device or a receiving device. Wherein, when the terminal device performs wireless charging, since the charging coil in the terminal device increases the number of parallel coil turns in each coil, multiple coils are connected in parallel to form one coil, and the coils are connected in series. , effectively reducing the charging coil impedance increased by thinning the thickness of the charging coil, thereby preventing the charging coil from overheating during the wireless charging process and improving the wireless charging experience.

It should be noted that, in this document, the terms "comprising", "comprises" or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article or device that includes a series of elements not only includes those elements, It also includes other elements not expressly listed or inherent in the process, method, article or apparatus. Without further limitation, an element defined by the statement "comprises a..." does not exclude the presence of additional identical elements in a process, method, article or apparatus that includes that element. In addition, it should be pointed out 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, but may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved. Functions may be performed, for example, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus the necessary general hardware platform. Of course, it can also be implemented by hardware, but in many cases the former is better. implementation. Based on this understanding, the technical solution of the present application can be embodied in the form of a software product in essence or that contributes to the existing technology. The computer software product is stored in a storage medium (such as ROM/RAM, disk, CD), including several instructions to cause a terminal (which can be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in various embodiments of this application.

The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above-mentioned specific implementations. The above-mentioned specific implementations are only illustrative and not restrictive. Those of ordinary skill in the art will Inspired by this application, many forms can be made without departing from the purpose of this application and the scope protected by the claims, all of which fall within the protection of this application.

Claims (10)

1. A charging coil, comprising: a first coil layer and a second coil layer 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 coil of the second coil layer comprises K 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.

2. The charging coil of claim 1, wherein the charging coil comprises a coil,

the L-turn parallel coil comprises a first coil and a second coil, and the width of the first coil is larger than that of the second coil; wherein the first coil is positioned on the outer ring of the second coil;

the K-turn parallel coil comprises a third coil and a fourth coil, and the width of the third coil is larger than that of the fourth coil; wherein the third coil is located at an outer ring of the fourth coil.

3. The charging coil of claim 1, wherein the charging coil comprises a coil,

the N strands of coils connected in series comprise a fifth coil and a sixth coil, and the width of the fifth coil is larger than that of the sixth coil; wherein the fifth coil is positioned on the outer ring of the sixth coil;

the M strands of coils connected in series comprise a seventh coil and an eighth coil, and the width of the seventh coil is larger than that of the eighth coil; wherein the seventh coil is located at an outer ring of the eighth coil.

4. The charging coil of claim 1, further comprising: a connecting coil, wherein the connecting coil comprises J turns connected in parallel;

a ninth coil of the first coil layer is connected in series with the connecting wire;

the connecting wire is connected with a tenth coil of the second coil layer in series;

the ninth coil is a coil located at a first preset position of the first coil layer in the N-strand coil, and the tenth coil is a coil located at a second preset position of the second coil layer in the M-strand coil;

wherein the first preset position includes an innermost ring of the first coil layer; the second preset position includes an innermost ring of the second coil layer.

5. The charging coil of claim 4, wherein K, L and J are 6.

6. The charging coil of claim 4, wherein the connecting coil comprises a first connecting coil and a second connecting coil connected in parallel; each turn of the connecting wire comprises 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 with the first port of the first connection coil, and the twelfth coil is connected with the first port of the second connection 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 of claim 6, wherein the eleventh coil is located on an outer ring of the twelfth coil; the thirteenth coil is located on an outer ring of the fourteenth coil.

8. The charging coil of claim 1, wherein N is the same as M.

9. The charging coil of claim 1, wherein L is the same as K.

10. Terminal device, characterized by comprising a charging coil according to any of claims 1 to 9.