CN110164664A - A kind of inductive type network transformer based on flexible circuit board - Google Patents

Abstract

The invention relates to the field of transformers. The present invention is an inductive network transformer based on a flexible circuit board. The transformer includes a primary side flexible circuit board and a secondary side flexible circuit board. The primary side flexible circuit board encapsulates the primary side coil winding, and the secondary side The flexible circuit board encapsulates the secondary side coil winding, the primary side flexible circuit board and the secondary side flexible circuit board are combined up and down in a detachable manner, and there are at least two pads connected to the starting point of the inner turn and the outer turn of the coil winding The termination point can be used to connect the front and rear circuits. The primary side coil and the secondary side coil are copper wires with a planar circular spiral structure, and they are alternately staggered up and down. Improve the problem of large volume, high cost, complicated assembly and disassembly of existing transformers, and the inability to perform parameter design multiple times, realize flattening of the device, make it lighter and thinner, reduce manufacturing costs, simplify disassembly and welding, and facilitate parameter design.

Description

An Inductive Network Transformer Based on Flexible Circuit Board

technical field

The invention relates to the technical field of transformers, in particular to an inductive network transformer based on a flexible circuit board.

Background technique

In the SPI communication circuit, a small high-frequency transformer is required for electrical isolation. The isolation network transformer traditionally used in the SPI communication circuit has a large volume and high frequency loss and cannot meet the miniaturization and low-loss requirements of modern electronic circuits. The manufacturing cost is high, and the assembly and disassembly welding process is complicated. Therefore, planar transformers based on printed circuit boards (PCBs) are widely used, but the PCB boards cannot be bent and are not easy to disassemble, and the transformers made of them cannot flexibly meet the requirements of different parameters. The hard material properties make it impossible to make full use of the space and increase the volume of the device. As a flexible printed circuit board with high reliability, the flexible circuit board (FPC) can overcome these shortcomings of the PCB board, and is thinner, lighter, and smaller than the PCB board, and can better meet the modern requirements. electronic circuit requirements.

Contents of the invention

(1) Technical problems to be solved

Based on the above problems, the present invention provides an inductive network transformer based on a flexible circuit board, which realizes a flatter, lighter and thinner device, reduces manufacturing costs, simplifies disassembly and welding, and facilitates parameter design.

(2) Technical solutions

Based on the above technical problems, the present invention provides an inductive network transformer based on a flexible circuit board, which is characterized in that the transformer includes a primary-side flexible circuit board and a secondary-side flexible circuit board, and the primary-side flexible circuit board is packaged The primary side coil winding, the secondary side flexible circuit board encapsulates the secondary side coil winding, the primary side flexible circuit board and the secondary side flexible circuit board are combined up and down, and the primary side coil winding and the secondary side coil winding are both planar Spiral structure, that is, each turn of the coil is helically wound in the same plane, and the middle is hollow, that is, the starting point inside the coil is a certain distance from the center point of the outermost turn of the coil, and there is a distance between each turn of the coil and the coil.

Further, the primary-side flexible circuit board and the secondary-side flexible circuit board have the same area and are combined up and down in a detachable manner through gluing, filling or process pressing to form a whole.

Further, there are at least two pads on both the primary-side flexible circuit board and the secondary-side flexible circuit board connected to the start point of the inner turn and the end point of the outer turn of the coil winding, for connecting the front and rear circuits.

Preferably, the primary-side coil windings and the secondary-side coil windings are alternately staggered from each other in a top view, that is, there is a certain offset in the lateral direction.

Preferably, both the primary coil winding and the secondary coil winding have a planar spiral circular structure.

Further, the formula for calculating the inductance of the coil winding is

Among them, μ is the magnetic permeability of the coil, N is the number of turns of the coil, ρ is the filling ratio of the coil, which represents the hollowness of the inductor, c ₁ , c ₂ , c ₃ , and c ₄ are the coupling coefficients related to the layout of the circular spiral coil , d _out is the diameter of the outermost turn of the coil, d _in is the diameter of the innermost turn of the coil, s is the distance between each turn of the coil and the coil, and w is the line width.

Preferably, the coils are made of copper wires.

Preferably, the cross section of the coil is rectangular, the line width is greater than the line height, the ratio of the line width to the line height is greater than or equal to 3, and the ratio of the distance between each coil and the coil to the line width is greater than or equal to 1 and less than or equal to 3 , the ratio of the diameter of the innermost turn of the coil to the diameter of the outermost turn of the coil is greater than or equal to 0.2 and less than or equal to 0.8.

Preferably, the range of the line width of the coil is 0.1mm-0.5cm.

Preferably, the height of the insulating layer on one side of the flexible circuit board ranges from 20um to 0.5cm.

(3) Beneficial effects

The technical scheme of the present invention has the following advantages:

(1) The transformer is made of flexible circuit board, so it has the advantages of extremely high wiring density, extremely light weight, extremely thin thickness, folding resistance, easy disassembly and assembly of the flexible circuit board;

(2) The transformer cancels the magnetic core and the primary and secondary coils face each other up and down, and the distance is extremely close. The coupling coefficient of the coil is large, and the leakage inductance is reduced. It is suitable for high-frequency bands and has good characteristics in high-frequency bands;

(3) The primary-side flexible circuit board and the secondary-side flexible circuit board of the transformer are combined up and down in a detachable way through gluing or filling, and process pressing, which is easy to disassemble, and the upper and lower distances are easy to adjust, thus facilitating the installation of the transformer. Parameter adjustment, while the primary and secondary coils of the coreless PCB transformer cannot be disassembled, and the upper and lower distances are fixed;

(4) The transformer has reserved pads for connecting the front and rear circuits for parameter design, and is different from the transformer in the traditional communication circuit. The FPC transformer of the present invention can be freely designed infinitely according to the change of the demand without changing the transformer. , also saves cost;

(5) The primary side coil winding and the secondary side coil winding are alternately staggered from each other in the top view, compared with when the coils are facing each other, the influence of the capacitance effect between the coils can be reduced, and the performance is better;

(6) Compared with the planar rectangular helical structure, the planar circular spiral structure does not have a sudden change in current, and the resistance of the coil is smaller, and the capacitance between the coils is also smaller;

(7) The transformer has canceled the magnetic core, so the transformer is small in size, light in weight, has no magnetic core loss, and the energy loss is mainly the winding loss, so its loss is relatively low.

Description of drawings

The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the accompanying drawings:

FIG. 1 is a schematic top view of a primary-side flexible circuit board according to an embodiment of the present invention;

2 is a schematic top view of a secondary-side flexible circuit board according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of the overall left view of the flexible circuit board of the transformer according to the embodiment of the present invention;

Fig. 4 is an overall top view schematic diagram of the primary and secondary coil windings of the embodiment of the present invention;

FIG. 5 is an enlarged schematic view of the details of the overall top view of the primary and secondary coil windings of the embodiment of the present invention;

Fig. 6 is the equivalent circuit diagram of the voltage on both sides of the primary and secondary coils of the transformer after measuring the external resistance with an oscilloscope in an embodiment of the present invention;

Figure 7 is the waveform diagram displayed by the oscilloscope when the external resistance is 500Ω;

Figure 8 is a waveform diagram displayed by the oscilloscope when the external resistance is 120Ω.

Detailed ways

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

The present invention is an inductive network transformer based on a flexible circuit board, including a primary side flexible circuit board and a secondary side flexible circuit board, as shown in Figures 1 and 2, the primary side flexible circuit board encapsulates the primary side coil winding , the secondary-side flexible circuit board encapsulates the secondary-side coil winding. The area of the primary side flexible circuit board and the secondary side flexible circuit board are equal in size, and they are combined up and down in a detachable way by gluing, filling or process pressing, as shown in Figure 3.

The primary side coil winding and the secondary side coil winding are copper wires with a planar circular spiral coil structure, and there is a hollow circle in the middle, and there is a space between each turn of the coil. The hollow circle refers to the distance between the starting point inside the coil and the outermost turn of the coil. There is a certain distance from the center of the circle, and the plane circular spiral structure means that each turn of the coil is wound in a helical circle in the same plane. Since the connecting parts of the adjacent sides of the planar rectangular spiral coil are at an angle of 90°, there is a sudden change in current, so the embodiment of the present invention adopts a planar circular spiral structure, and the circular path is shorter and the overlapping area is smaller, so the resistance of the coil Smaller, the capacitance between each turn of the coil is also smaller.

The primary side coil windings and the secondary side coil windings are alternately staggered from each other in a top view, as shown in FIG. There is a certain offset between the winding and the secondary coil winding in the lateral direction, and the offset distance can be an integer multiple of the line width. As shown in Figure 4 or Figure 5, the primary coil winding and the secondary coil winding alternately stagger each other. When the coils are facing each other, the influence of the capacitance effect between the coils can be reduced, and the performance is better.

The actual transformer is designed by the following method: First, according to the actual needs, such as area, height, inductance size, signal voltage transmission ratio, delay and other parameters, the inductance, parasitic capacitance, and resistance of the inductance coil winding are designed and calculated according to the formula Calculate the relevant parameters:

μ=1.2566×10 ^-6 H/m, d _avg =0.5(d _out +d _in ),

c ₁ =1.00, c ₂ =2.46, c ₃ =0.00, c ₄ =0.20,

Among them, L is the inductance of the coil winding, μ is the magnetic permeability of the copper wire, N is the number of turns of the coil, ρ is the filling ratio of the coil, which represents the hollowness of the inductor, c ₁ , c ₂ , c ₃ , and c ₄ are circular The coupling coefficient related to the layout of the spiral coil, d _out is the diameter of the outermost turn of the coil, d _in is the diameter of the innermost turn of the coil, s is the distance between each turn of the coil and the coil, and w is the line width.

Build the model in Q3D software according to actual needs and calculation parameters, adjust the copper wire cross-section parameters, line spacing, flexible circuit board insulation layer height, and the lateral offset distance of the primary side and secondary side coil windings on the primary side and secondary side for simulation Analyze and obtain the required inductance, coupling coefficient, parasitic capacitance and mutual capacitance of the primary and secondary coil windings, adjust the independent variables, carry out parameter design, and bring the obtained high-frequency parameters into the circuit model simulation, according to the actual project Or project needs to optimize the design, connect to the front and rear circuits, connect capacitors, resistors and inductors in series and parallel, optimize the transmission characteristics, and guide the next step of physical manufacturing based on the simulation results.

The cross-section of the coil is rectangular, the line width is greater than the line height, the ratio of the line width to the line height is greater than or equal to 3, and the value range of the line width is 0.1mm-0.5cm, which is subject to the actual demand; each turn of the coil and the coil The ratio of the spacing between them to the line width is greater than or equal to 1 and less than or equal to 3, depending on the distributed capacitance, AC resistance, etc.; the ratio of the diameter of the innermost turn of the coil to the diameter of the outermost turn of the coil is greater than or equal to 0.2 and less than or equal to 0.8; the coil The value range of the line width is 0.1mm-0.5cm. The height range of the single-sided insulation layer of the flexible circuit board is 20um-0.5cm.

Both the primary side flexible circuit board and the secondary side flexible circuit board have at least two pads connected to the starting point of the inner turn and the termination point of the outer turn of the coil winding, which can be used to connect the front and back stages of the circuit, or freely connect the series and parallel resistors and capacitors. Adjust and design parameters of network transformers.

Connect a resistor R externally to the pad of the flexible circuit board on the secondary side of the transformer of the present invention, and then use two probes of an oscilloscope to connect the two ends of the primary side and the secondary side respectively, give pulse power, and display on the oscilloscope display screen respectively The input and output terminal voltage of the designed transformer. Its equivalent circuit is shown in Figure 6, the power supply Vin is a narrow pulse with a frequency of plus or minus 2V and a frequency of 10MHz, R ₀ =50Ω, L ₀ =300nH, respectively the resistance and inductance of the pulse signal line, C ₀₁ =8pF, C ₀₂ ＝8pF, which are the capacitances of the two probes, L ₁ ＝39.79uH, L ₂ ＝39.79uH, which are the inductances of the primary coil and the secondary coil, and the mutual inductance M ₁₂ ＝36uH generated by the same direction coupling, R ₁ ＝ 8.513Ω, R ₂ =8.513Ω, which are the high-frequency internal resistance generated by the primary coil and the secondary coil respectively, C ₁ =1.0062pF, C ₂ =1.0062pF, which are the distributed capacitance generated by the primary coil and the secondary coil respectively , V ₁ is a voltmeter for measuring the input voltage, V ₂ is a voltmeter for measuring the output voltage, and R is an external resistor.

When the external resistance R=500Ω, the voltage at both ends of the transformer coil measured by the oscilloscope is shown in Figure 7, and the voltage transmission ratio of the transformer is 2:1.55; when the external resistance R=120Ω, the voltage at both ends of the transformer coil measured by the oscilloscope See Figure 8 for the voltage, and the voltage transfer ratio of the transformer is 2:1. Therefore, the transfer characteristics of the network transformer can be freely adjusted and designed by connecting the front and back stage circuits, or series and parallel resistors and capacitors, and the number of times is not limited.

In summary, through the above-mentioned inductive network transformer based on the flexible circuit board, the above-mentioned technical solution of the present invention has the following advantages:

(1) The transformer is made of flexible circuit board, so it has the advantages of extremely high wiring density, extremely light weight, extremely thin thickness, folding resistance, easy disassembly and assembly of the flexible circuit board;

(2) The transformer cancels the magnetic core and the primary and secondary coils face each other up and down, and the distance is extremely close. The coupling coefficient of the coil is large, and the leakage inductance is reduced. It is suitable for high-frequency bands and has good characteristics in high-frequency bands;

(3) The primary-side flexible circuit board and the secondary-side flexible circuit board of the transformer are combined up and down in a detachable way through gluing or filling, and process pressing, which is easy to disassemble, and the upper and lower distances are easy to adjust, thus facilitating the installation of the transformer. Parameter adjustment, while the primary and secondary coils of the coreless PCB transformer cannot be disassembled, and the upper and lower distances are fixed;

(4) The transformer has reserved pads for connecting the front and rear circuits for parameter design, and is different from the transformer in the traditional communication circuit. The FPC transformer of the present invention can be freely designed infinitely according to the change of the demand without changing the transformer. , also saves cost;

(5) The primary side coil winding and the secondary side coil winding are alternately staggered from each other in the top view, compared with when the coils are facing each other, the influence of the capacitance effect between the coils can be reduced, and the performance is better;

(6) Compared with the planar rectangular helical structure, the planar circular spiral structure does not have a sudden change in current, and the resistance of the coil is smaller, and the capacitance between the coils is also smaller;

(7) The transformer has canceled the magnetic core, so the transformer is small in size, light in weight, has no magnetic core loss, and the energy loss is mainly the winding loss, so its loss is relatively low.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can Various modifications and variations are made within the scope and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims (10)

1. An inductive network transformer based on a flexible circuit board, characterized in that the transformer includes a primary side flexible circuit board and a secondary side flexible circuit board, the primary side flexible circuit board encapsulates the primary side coil winding, and the The secondary side flexible circuit board encapsulates the secondary side coil winding, and the primary side flexible circuit board and the secondary side flexible circuit board are combined up and down. The primary side coil winding and the secondary side coil winding are both planar spiral structures, that is, each turn of the coil They are all helically wound in the same plane, and the middle is hollow, that is, there is a certain distance between the starting point inside the coil and the center point of the outermost turn of the coil, and there is a gap between each coil and the coil. 2. A kind of inductive network transformer based on flexible circuit board according to claim 1, it is characterized in that, the area size of described primary side flexible circuit board and secondary side flexible circuit board is equal, through gluing, filling Or the detachable method of craft pressing is facing up and down, and combined into one. 3. An inductive network transformer based on a flexible circuit board according to claim 1 or 2, wherein there are at least two pad connections on the primary side flexible circuit board and the secondary side flexible circuit board To the starting point of the inner turn and the ending point of the outer turn of the coil winding, it is used to connect the front and rear circuits. 4. The inductive network transformer based on a flexible circuit board according to claim 1, wherein the primary side coil winding and the secondary side coil winding are alternately staggered from each other in a top view, that is, there are Must be offset. 5 . The inductive network transformer based on a flexible printed circuit according to claim 1 , wherein the primary coil winding and the secondary coil winding are both planar spiral circular structures. 6 . 6. A kind of inductive network transformer based on flexible circuit board according to claim 1, is characterized in that, the inductance calculation formula of described coil winding is d _avg =0.5(d _out +d _in ), Among them, μ is the magnetic permeability of the coil, N is the number of turns of the coil, ρ is the filling ratio of the coil, which represents the hollowness of the inductor, c ₁ , c ₂ , c ₃ , and c ₄ are the coupling coefficients related to the layout of the circular spiral coil , d _out is the diameter of the outermost turn of the coil, d _in is the diameter of the innermost turn of the coil, s is the distance between each turn of the coil and the coil, and w is the line width. 7. An inductive network transformer based on a flexible printed circuit according to claim 1 or 6, wherein the coil is made of copper wire. 8. An inductive network transformer based on a flexible circuit board according to claim 1 or 6, wherein the cross section of the coil is rectangular, the line width is greater than the line height, and the ratio of the line width to the line height is greater than Equal to 3, the ratio of the spacing between each coil and the coil to the line width is greater than or equal to 1 and less than or equal to 3, and the ratio of the diameter of the innermost turn of the coil to the diameter of the outermost turn of the coil is greater than or equal to 0.2 and less than or equal to 0.8. 9. An inductive network transformer based on a flexible printed circuit according to claim 1 or 6, wherein the line width of the coil ranges from 0.1 mm to 0.5 cm. 10 . The inductive network transformer based on a flexible circuit board according to claim 1 , wherein the height of the insulating layer on one side of the flexible circuit board ranges from 20 um to 0.5 cm. 11 .