A method of winding a flyback transformer with very low leakage inductance

Abstract

The application discloses a method for winding of a flyback transformer with extremely low leakage inductance, wherein the primary winding is wired on the same layer and the same side, and the secondary winding is wired on the same side but different layers, so that the loop area of the wired end is greatly reduced, the coil loop is more complete, the coupling degree of the primary winding and the secondary winding is enhanced, the leakage inductance of the transformer can be reduced to an extremely low value, the primary winding and the secondary winding are wound on the magnetic core in an interlaced and stacked manner, the leakage inductance of the transformer is reduced, the magnetic loss is reduced, and meanwhile, the copper loss and the parasitic capacitance between turns are not increased.

Description

Technical Field

[0001] This invention relates to the field of circuit design technology, specifically to a method for winding a flyback transformer with extremely low leakage inductance. Background Technology

[0002] With the continuous upgrading of semiconductor devices and the rapid development of power electronics technology, switching power supply technology is moving towards miniaturization, low profile, and high integration. Whether in computer chip power supplies, radar power supplies, or military shipborne power supplies, there is an urgent need for smaller, lower-loss, high-performance power supplies. Flyback transformers are widely used in switching power supplies due to their energy efficiency, high performance, stability, and reliability. Switching power supplies mainly operate at high frequencies, which presents transformers with problems not encountered in low-frequency designs, such as increased and unpredictable losses. Traditional high-frequency wire-wound transformers are affected by the skin effect and proximity effect, resulting in significant losses and requiring special cooling devices, thus increasing their size and hindering the miniaturization and high power density trends of modern integrated circuits. Furthermore, the errors introduced by manual winding in wire-wound transformers are difficult to estimate, and inconsistencies in parameters within the same batch of components can occur. Excessive leakage inductance can cause the switching transistors in the circuit to experience significant voltage stress, potentially damaging the circuit. The wire-wound magnetic components in traditional transformers limit the development of switching power supplies towards high frequency, high efficiency, and high power density. Therefore, the design and research of flyback transformer windings with low leakage inductance under high-frequency operating conditions is of practical significance.

[0003] In recent years, planar magnetism has been widely used in industry and academia. Planar magnetic core and PCB technology have proven to be an effective means of reducing the size, weight, and cost of DC / DC converters and improving converter efficiency. Planar magnetic components are more suitable for high-frequency, high-power converters than traditional wire-wound magnetic components. The issues of reducing leakage inductance in planar magnetic components include the following: 1) When edge effects are ignored, the leakage inductance is proportional to the square of the number of transformer turns; however, reducing the number of coil turns may lead to magnetic saturation and higher magnetic losses; 2) Reducing the distance between the copper foils in the windings and the thickness between the copper layers on the PCB can reduce leakage inductance, but it will increase copper losses and inter-turn parasitic capacitance. Summary of the Invention

[0004] The purpose of this invention is to provide a flyback transformer winding method with extremely low leakage inductance, in order to overcome the problems in the prior art where, when the edge effect is ignored, reducing the number of coil turns may lead to easy magnetic saturation and high magnetic loss; reducing the distance between the copper foils in the winding and reducing the thickness between the copper layers of the PCB can reduce leakage inductance, but will increase copper loss and inter-turn parasitic capacitance.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for winding a flyback transformer with extremely low leakage inductance involves winding multiple sets of primary and secondary windings on a magnetic core. The primary and secondary windings are wound in an alternating layered manner on the magnetic core. The primary windings have wires exiting from the same layer and side, while the secondary windings have wires exiting from different layers on the same side.

[0007] Preferably, the secondary windings are connected to different layers on the same side via vias.

[0008] Preferably, the primary winding and the secondary winding are connected in parallel in an alternating manner.

[0009] Preferably, the magnetic core is an ELP220616 magnetic core.

[0010] Preferably, the magnetic permeability of the magnetic core is 1500.

[0011] Preferably, the secondary winding is located at the top of the wound winding.

[0012] Preferably, the input and output terminals of the primary and secondary windings are on the same side of the magnetic core.

[0013] Preferably, the number of primary windings and secondary windings are the same.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for winding a flyback transformer with extremely low leakage inductance. The primary winding is led out on the same layer and side, while the secondary winding is led out on the same side but different layers, which greatly reduces the loop area at the lead-out end, makes the coil loop more complete, and enhances the coupling between the primary and secondary sides. This can reduce the leakage inductance of the transformer to an extremely low value. The primary and secondary windings are wound on the magnetic core in an alternating layered manner, which reduces the leakage inductance of the transformer and reduces magnetic loss, while not increasing copper loss and inter-turn parasitic capacitance.

[0015] Furthermore, the primary and secondary windings are connected in parallel in an alternating manner, which can enhance the current carrying capacity of the transformer in low-voltage, high-current applications, while reducing the winding losses and further reducing the leakage inductance of the transformer. Attached Figure Description

[0016] Figure 1 It is the existing method of outputting wires from both sides of the primary winding;

[0017] Figure 2 This is the same-side output method of the secondary winding of the present invention;

[0018] Figure 3 This is the parallel connection method of the two-phase windings in this invention;

[0019] Figure 4 This is the winding interleaved stacking method of the present invention;

[0020] Figure 5 This is a cross-sectional view of the winding of the present invention;

[0021] Figure 6 This invention relates to the ELP220616 magnetic core structure;

[0022] Figure 7 This is the same-side lead-out method of the primary winding of the present invention;

[0023] Figure 8 This is the parallel connection method of the two-phase windings in this invention;

[0024] Figure 9 This is the method of alternating stacking of primary and secondary windings in this invention;

[0025] Figure 10 This is the high-frequency DC-ZVS circuit topology in the embodiments of the present invention;

[0026] Figure 11 This is the voltage oscillation waveform of the clamping capacitor in this invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0028] Figure 1 The diagram shows a traditional primary winding with leads on both sides. Taking a transformer winding designed with one turn on each side as an example, the input and output ends are on opposite sides, resulting in loose coupling between the primary and secondary windings and a large leakage flux. With this winding method, the transformer leakage inductance can reach 33nH when the magnetizing inductance is 300nH, which is difficult to meet the application requirements in many situations.

[0029] This invention proposes a flyback transformer winding with extremely low leakage inductance, which can significantly reduce the leakage inductance of the transformer. The primary winding has a same-side lead-out configuration as follows: Figure 2 As shown, the two-phase windings are connected in parallel as follows: Figure 3 As shown, the primary and secondary windings are interleaved as follows: Figure 4 As shown. For Figure 2 The primary windings are routed out on the same side, with the red coil representing the primary winding and the blue and yellow coils representing the secondary windings. The PCB winding configuration consists of one turn for the primary winding and one turn for the secondary winding. The primary windings are routed out on the same layer and side, while the secondary windings are routed out on different layers on the same side via vias. This significantly reduces the loop area at the route terminals, resulting in a more complete coil loop and enhanced coupling between the primary and secondary windings. This reduces the transformer leakage inductance to an extremely low level.

[0030] (1) In applications with high power density, when the module power supply is small in size, the transformer winding occupies less than half of the board area, and the line width of the primary and secondary coils is less than 2mm, this will result in a large AC / DC resistance of the transformer winding and a large copper loss in the case of a single-layer winding; therefore, further design is needed, such as Figure 3 The two-phase parallel winding method shown here, with the primary and secondary windings connected in parallel based on the primary winding's same-side output, enhances the transformer's current-carrying capacity and reduces winding losses in low-voltage, high-current applications, further reducing leakage inductance. PCB winding method: 2 turns in parallel on the primary side, 2 turns in parallel on the secondary side, with the primary side output from the same layer, and the secondary side output from upper and lower layers. The layer sequence is: upper secondary - upper primary - lower secondary - lower primary.

[0031] (2) The staggered layering of primary and secondary windings can reduce leakage inductance to a certain extent. Therefore, based on the same-side lead-out method of the primary winding, a multi-winding parallel connection method is adopted, and the design is as follows: Figure 4 The winding method shown, under the condition that the PCB board thickness or copper strip thickness and the core window cross-sectional area are satisfied, should select as many turns as possible for parallel connection. Taking the PCB winding method of 6 turns on the primary side and 6 turns on the secondary side as an example, the primary and secondary sides are alternately connected in parallel. Figure 4 To build a winding model for the ANSYS simulation platform, Figure 5 The winding is divided into three groups, each with four turns. Within each group, the windings are alternately wound in the manner of upper secondary, upper primary, lower secondary, and lower primary. The layer sequence is as follows: upper secondary 1 - upper primary 1 - lower secondary 1 - lower primary 1 - upper secondary 2 - upper primary 2 - lower secondary 2 - lower primary 2 - upper secondary 3 - upper primary 3 - lower secondary 3 - lower primary 3. The primary side is the same layer of output wire, and the secondary side is the upper and lower layers of output wire.

[0032] Example:

[0033] This invention uses an ELP220616 magnetic core and N49 magnetic material for practical verification. A simulation model is built on the ANSYS platform, and its structural diagram is shown below. Figure 6 As shown, Figure 7 This is a simulation diagram of the same-side output configuration of the primary winding. Figure 8 This is a simulation diagram of a two-phase winding in parallel configuration. Figure 9 This is a simulation diagram of the primary and secondary windings being stacked alternately. Figure 10 This is a circuit example of a topology for a high-frequency DC-ZVS circuit using a flyback transformer wound according to the present invention.

[0034] (1) Magnetic core ELP220616, magnetic material N49, PCB winding method: one turn on the primary side, one turn on the secondary side, no parallel connection.

[0035] The results are as follows: the air gap is 0.2 mm, Lm = 308 nH, and Ls = 4 nH.

[0036] (2) Magnetic core ELP220616, magnetic material N49, PCB winding method: 2 turns of primary side in parallel, 2 turns of secondary side in parallel, the layer sequence is: upper secondary-upper primary-lower secondary-lower primary, and the primary side is the same layer output, and the secondary side is the upper and lower layers output.

[0037] The results are as follows: air gap is 0.2 mm, Lm = 295 nH, Ls = 3 nH.

[0038] (3) Magnetic core ELP220616, magnetic material N49, PCB winding method: 6 turns of primary side in parallel, 6 turns of secondary side in parallel, the layer sequence is: upper secondary 1-upper primary 1-lower secondary 1-lower primary 1-upper secondary 2-upper primary 2-lower secondary 2-lower primary 2-upper secondary 3-upper primary 3-lower secondary 3-lower primary 3, and the primary side is the same layer of wire output, and the secondary side is the upper and lower layers of wire output.

[0039] The results are as follows: air gap is 0.2 mm, Lm = 298.6 nH, Ls = 1.3 nH

[0040] The overall simulation results are shown in Table 1.

[0041] Table 1. Winding results of planar transformers

[0042]

[0043] Figure 10 This invention relates to a topology of a high-frequency DC-ZVS circuit.

[0044] The DC-ZVS topology employs a primary-side feedback control structure, specifically primary-side clamping capacitor voltage feedback control. Therefore, the clamping capacitor voltage must not fluctuate significantly. However, the transformer leakage inductance resonates with the clamping capacitor during secondary-side freewheeling. When the leakage inductance is large, the capacitor voltage fluctuates violently, making primary-side feedback control impossible. Furthermore, at high frequencies, a large leakage inductance and clamping capacitor oscillation can significantly increase the effective value of the primary-side current, leading to increased switching losses and reduced efficiency.

[0045] The simulation results of clamping capacitor voltage ripple and effective value of switching transistor current under different leakage inductance conditions are shown in Table 2.

[0046] Table 2. Influence of leakage inductance on the effective values ​​of clamping capacitor voltage and current.

[0047] Leakage inductance / nH Clamping capacitor voltage ripple / V <![CDATA[I 1,rms / A]]> <![CDATA[I 4,rms / A]]> <![CDATA[I 2,rms / A]]> <![CDATA[I 3,rms / A]]> 1 0.6 12.9 13.2 7.3 6.7 5 2.64 12.8 13.1 14.1 13 20 3.6 12.8 13.6 17.8 17.2 40 4.5 12.9 14.7 18.1 16.6

[0048] Figure 11 The circuit waveform is shown when the sum of the transformer leakage inductance and the line parasitic inductance reaches 40nH. The voltage waveform under a clamping capacitor input of 48V and a 1A load shows a voltage fluctuation of 5.6V.

[0049] Because of the large leakage inductance, the effective value of the current increases significantly. Therefore, the first thing to do in the magnetic integration design of planar transformers is to solve the problems caused by excessive leakage inductance and line parasitic inductance.

[0050] After adopting the primary and secondary side interleaved stacking method in this invention, under the same magnetic core and magnetic material conditions, with an excitation inductance of 308nH, an air gap of 0.2mm, and a simulated leakage inductance value of 1.3nH, the requirements for transformer leakage inductance can be well met.

[0051] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art, guided by the specification, can make many other modifications without departing from the scope of the claims of the present invention, and all of these modifications are within the scope of protection of the present invention.

Claims

1. A method for constructing a flyback transformer winding with extremely low leakage inductance, characterized in that, Multiple sets of primary and secondary windings are wound on the magnetic core. The primary and secondary windings are wound on the magnetic core in an alternating layered manner. The primary windings have wires exiting from the same layer and side, while the secondary windings have wires exiting from different layers on the same side. The secondary winding achieves different layers of wire output on the same side through vias; The primary winding and secondary winding are connected in parallel and alternately.

2. The method for constructing a flyback transformer winding with extremely low leakage inductance according to claim 1, characterized in that, The magnetic core used is an ELP220616 magnetic core.

3. The method for constructing a flyback transformer winding with extremely low leakage inductance according to claim 1, characterized in that, The magnetic core has a permeability of 1500.

4. The method for constructing a flyback transformer winding with extremely low leakage inductance according to claim 1, characterized in that, The secondary winding is located at the very top of the winding.

5. The method for constructing a flyback transformer winding with extremely low leakage inductance according to claim 1, characterized in that, The input and output terminals of the primary and secondary windings are on the same side of the magnetic core.

6. The method for constructing a flyback transformer winding with extremely low leakage inductance according to claim 1, characterized in that, The number of primary windings and secondary windings are the same.

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