CN116246880A

CN116246880A - Flyback transformer winding method with extremely low leakage inductance

Info

Publication number: CN116246880A
Application number: CN202310405214.6A
Authority: CN
Inventors: 汪洋; 周翔; 李超杰; 史海林; 付翀丽; 王俊峰
Original assignee: Xian Microelectronics Technology Institute
Current assignee: Xian Microelectronics Technology Institute
Priority date: 2023-04-14
Filing date: 2023-04-14
Publication date: 2023-06-09

Abstract

The invention discloses a flyback transformer winding method with extremely low leakage inductance, which is characterized in that a primary winding is connected with an outgoing line on the same side of a layer, a secondary winding is connected with an outgoing line on different layers on the same side of the secondary winding, the loop area of an outgoing line end is greatly reduced, a coil loop is more complete, the coupling degree of the primary side and the secondary side is enhanced, the leakage inductance of a transformer can be reduced to an extremely low value, the primary winding and the secondary winding are wound on a magnetic core in a staggered lamination mode, the leakage inductance of the transformer is reduced, the magnetic loss is reduced, and copper loss and inter-turn parasitic capacitance are not increased.

Description

Flyback transformer winding method with extremely low leakage inductance

Technical Field

The invention relates to the technical field of circuit design, in particular to a flyback transformer winding method with extremely low leakage inductance.

Background

With the continuous upgrading of semiconductor devices and the rapid development of the power electronics technology, the technology of switching power supplies is developed towards miniaturization, low profile and high integration. Both chip power supplies in the computer field and radar power supplies or military ship-based power supplies are in urgent need for high performance power supplies with smaller size and lower loss. Flyback transformers are widely used in switching power supplies due to the advantages of energy conservation, high efficiency, stability, reliability and the like. The switching power supply mainly works in a high frequency state, so that the transformer faces the problems which are not encountered when designing in a low frequency state, such as increased loss and difficult estimation. The traditional high-frequency winding type transformer is influenced by skin effect and proximity effect, so that the loss of the transformer becomes large, a special cooling device is needed, the volume is increased, and the development trend of miniaturization and high power density of modern integrated circuits is not facilitated. Meanwhile, the winding type transformer is difficult to estimate due to errors caused by manual winding, and the parameters of the devices in the same batch are inconsistent. If leakage inductance is too large, the switching tubes in the circuit are subjected to great voltage stress, so that the circuit is damaged. The wire wound magnetic elements in conventional transformers limit the development of switching power supplies to high frequency efficiency and high power densities. Therefore, the method has practical significance for the design and research of the flyback transformer winding with low leakage inductance in a high-frequency working state.

Planar magnetic integration of planar magnetic cores with PCB technology has proven to be an effective means of reducing the size, weight, cost of DC/DC converters and improving the efficiency of the converters, as planar magnetic technology has been widely used in industry and academia in recent years. The planar magnetic member is more suitable for high-frequency high-power converters than the traditional wire-wound magnetic member. The problem of reducing leakage inductance in planar magnetic members includes the following: 1) When the edge effect is ignored, the magnitude of the leakage inductance is proportional to the square of the turns of the transformer, but the reduction of the turns of the coil can lead to easy saturation of magnetism and higher magnetic loss; 2) Reducing the distance between the copper foils of the windings, and reducing the thickness between the copper layers of the PCB, reduces leakage inductance, but increases copper losses and inter-turn parasitic capacitance.

Disclosure of Invention

The invention aims to provide a flyback transformer winding method with extremely low leakage inductance, which is used for overcoming the defect that the magnetic property is easy to saturate and the magnetic property loss is high due to the fact that the number of turns of a coil is reduced when the edge effect is ignored in the prior art; reducing the distance between the copper foils of the windings and the thickness between the copper layers of the PCB can reduce leakage inductance, and can increase copper loss and inter-turn parasitic capacitance.

In order to achieve the above purpose, the present invention provides the following technical solutions:

a flyback transformer winding method with extremely low leakage inductance comprises the steps of winding a plurality of groups of primary side windings and secondary side windings on a magnetic core, wherein the primary side windings and the secondary side windings are wound on the magnetic core in a staggered lamination mode, the primary side windings are outgoing lines on the same layer, and the secondary side windings are outgoing lines on different layers on the same side.

Preferably, the secondary winding realizes the same-side different-layer wire outlet through the via hole.

Preferably, the primary winding and the secondary winding are connected in parallel in a staggered manner.

Preferably, the core is an ELP220616 core.

Preferably, the magnetic core has a permeability of 1500.

Preferably, the secondary winding is disposed at the very top of the wound winding.

Preferably, the inlet and outlet ends of the primary and secondary windings are on the same side as the core.

Preferably, the number of primary and secondary windings is the same.

Compared with the prior art, the invention has the following beneficial effects: the invention provides a flyback transformer winding method with extremely low leakage inductance, which is characterized in that a primary winding is connected with an outgoing line on the same side of a layer, a secondary winding is connected with an outgoing line on different layers on the same side of the secondary winding, the loop area of an outgoing line end is greatly reduced, a coil loop is more complete, the coupling degree of the primary side and the secondary side is enhanced, the leakage inductance of a transformer can be reduced to an extremely low value, the primary winding and the secondary winding are wound on a magnetic core in a staggered lamination mode, the leakage inductance of the transformer is reduced, the magnetic loss is reduced, and copper loss and inter-turn parasitic capacitance are not increased.

Furthermore, the primary winding and the secondary winding are connected in parallel in a staggered manner, so that the current carrying capacity of the transformer can be enhanced in the application occasion of low voltage and high current, the winding loss of the transformer is reduced, and the leakage inductance of the transformer is further reduced.

Drawings

FIG. 1 is a prior art primary winding two-sided wire outlet;

FIG. 2 is a side-by-side wire outlet of the secondary winding of the present invention;

FIG. 3 is a two-phase winding parallel arrangement of the present invention;

FIG. 4 is a cross-lamination of windings in accordance with the present invention;

FIG. 5 is a cross-sectional view of a winding of the present invention;

FIG. 6 is an ELP220616 core structure of the present invention;

FIG. 7 shows the same-side wire outlet mode of the primary winding of the invention;

FIG. 8 is a two-phase winding parallel arrangement of the present invention;

FIG. 9 shows a staggered stack of primary and secondary windings in accordance with the present invention;

FIG. 10 is a high frequency DC-ZVS circuit topology in an embodiment of the invention;

FIG. 11 is a waveform of the voltage oscillation of the clamping capacitor according to the present invention.

Detailed Description

The invention will now be described in further detail with reference to specific examples, which are intended to illustrate, but not to limit, the invention.

Fig. 1 shows a conventional primary winding two-side wire outlet manner: for the primary side winding two-side wire-outgoing mode, taking the design of the transformer winding that the primary side and the secondary side are 1 turn as an example, under the winding mode, the wire inlet end and the wire outlet end are respectively arranged on two sides, the primary side and the secondary side are not tightly coupled, so that leakage magnetic flux is larger, under the winding mode, under the condition that the excitation inductance is 300nH, the leakage inductance of the transformer can reach 33nH, and the application requirements of many occasions are difficult to meet.

The invention provides a flyback transformer winding with extremely low leakage inductance, which can greatly reduce the leakage inductance of a transformer, wherein the same-side outgoing line mode of a primary winding is shown in figure 2, the parallel mode of two-phase windings is shown in figure 3, and the staggered lamination mode of primary and secondary windings is shown in figure 4. For the same-side wire outlet mode of the primary winding in fig. 2, the red coil is the primary winding, and the blue and yellow coils are the secondary windings; PCB winding mode: one turn on the primary side and one turn on the secondary side. The primary winding is connected with the same-layer same-side wire outlet, the secondary winding is connected with different-layer wire outlet at the same side through the through holes, the loop area of the wire outlet end is greatly reduced, the loop is more complete, the coupling degree of the primary and secondary sides is enhanced, and the leakage inductance of the transformer can be reduced to an extremely low value.

(1) When the power density is higher, the volume of the module power supply is smaller, the occupied area of the transformer winding is less than half, the line width of the primary and secondary side coils is less than 2mm, so that the alternating current-direct current resistance of the transformer winding is larger, and the copper loss of the transformer is larger under the condition of single-layer winding; therefore, the parallel winding mode of the two-phase windings is further designed as shown in fig. 3, and the winding of the primary side and the secondary side adopts the parallel winding mode of the two-phase windings under the mode of leading out wires on the same side of the primary side winding, so that the current carrying capacity of the transformer can be enhanced in the application occasion of low voltage and high current, the winding loss of the transformer is reduced, and the leakage inductance of the transformer is further reduced. PCB winding mode: 2 turns of primary sides are connected in parallel, 2 turns of secondary sides are connected in parallel, the primary sides are outgoing lines on the same layer, and the secondary sides are outgoing lines on the upper layer and the lower layer. The interlayer sequence is as follows: superior-inferior.

(2) The staggered lamination mode of the primary and secondary windings can reduce leakage inductance to a certain extent, so that a multi-winding parallel connection mode is adopted based on the same-side wire outlet mode of the primary windings, a winding mode shown in fig. 4 is designed, more turns are selected as much as possible for parallel connection under the conditions that the thickness of a PCB (printed circuit board) board or a copper strip and the cross section area of a window of a magnetic core are met, the winding mode of the PCB winding is taken as 6 turns of the primary side, and 6 turns of the secondary side are taken as an example, and the staggered parallel connection of the primary side and the secondary side is adopted. Wherein fig. 4 is an ANSYS simulation platform building winding model, fig. 5 is a winding section view, the winding groups are divided into three groups, each group is four turns, the winding is staggered in the groups according to the upper pair, the lower pair and the lower pair, and the interlayer sequence is as follows: the primary side is the same layer outgoing line, and the secondary side is the upper layer outgoing line.

Examples:

the embodiment of the invention uses an ELP220616 magnetic core and N49 magnetic materials for instance verification, and builds a simulation model based on an ANSYS platform, wherein the structure diagram is shown in FIG. 6, FIG. 7 is a simulation diagram of a primary winding on the same side in a wire outlet mode, FIG. 8 is a simulation diagram of a two-phase winding parallel mode, and FIG. 9 is a simulation diagram of a primary and secondary winding staggered lamination mode. Fig. 10 is a circuit example of a topology for a high frequency DC-ZVS circuit employing the wound flyback transformer of the present invention.

(1) Magnetic core ELP220616, magnetic material N49, PCB wire winding mode: one turn on the primary side and one turn on the secondary side, and no parallel connection exists.

The results were as follows: the air gap was 0.2mm, lm=308 nH, ls=4 nH.

(2) Magnetic core ELP220616, magnetic material N49, PCB wire winding mode: 2 turns of the primary side are connected in parallel, 2 turns of the secondary side are connected in parallel, and the interlayer sequence is as follows: the primary side is the same layer of outgoing line, and the secondary side is the upper layer of outgoing line and the lower layer of outgoing line.

The results were as follows: the air gap was 0.2mm, lm=5nh, ls=3nh.

(3) Magnetic core ELP220616, magnetic material N49, PCB wire winding mode: the primary side is connected with 6 turns in parallel, the secondary side is connected with 6 turns in parallel, and the interlayer sequence is as follows: the primary side is the same layer outgoing line, and the secondary side is the upper layer outgoing line.

The results were as follows: the air gap was 0.2mm, lm=298.6nh, ls=1.3 nH

The overall simulation results are shown in table 1.

Table 1 planar transformer winding results

Fig. 10 is a topology of a high frequency DC-ZVS circuit to which the present invention applies.

The DC-ZVS topological structure adopts a primary side feedback control structure, namely, primary side clamping capacitor voltage feedback control is adopted, so that the voltage of the clamping capacitor cannot be required to have larger fluctuation, leakage inductance of the transformer resonates with the clamping capacitor during secondary side follow current, and when the leakage inductance is larger, the fluctuation of the capacitor voltage is severe, and the primary side feedback control cannot be implemented; in addition, under high frequency, larger leakage inductance and clamping capacitance oscillation can cause the effective value of primary current to be greatly increased, so that the loss of a switching tube is increased, and the efficiency is reduced.

The simulation results of the clamping capacitor voltage ripple and the effective value of the switching tube current under different leakage inductance conditions are shown in table 2.

TABLE 2 influence of leakage inductance on effective value of clamping capacitor voltage and current

Leakage inductance/nH	Clamping capacitor voltage ripple/V	I _1,rms /A	I _4,rms /A	I _2,rms /A	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

Fig. 11 is a circuit waveform when the sum of the leakage inductance of the transformer and the parasitic inductance of the line reaches 40 nH. When the clamping capacitor is input at 48V and the voltage waveform is under the condition of 1A load, the voltage fluctuation can be seen to reach 5.6V.

Because the leakage inductance is larger, the effective value of the current is obviously increased, and therefore, the problems caused by overlarge leakage inductance and line parasitic inductance are needed to be solved firstly when the planar transformer is designed in a magnetic integration way.

After the primary side and secondary side staggered lamination mode is adopted, under the condition of the same magnetic core and magnetic material, under the condition that the excitation inductance is 308nH, the air gap is 0.2mm, the leakage inductance simulation value is 1.3nH, and the requirement of the leakage inductance of the transformer can be well met.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described specific embodiments and application fields, which are merely illustrative, instructive, and not restrictive. Those skilled in the art, having the benefit of this disclosure, may make many forms without departing from the scope of the invention as claimed.

Claims

1. A flyback transformer winding method with extremely low leakage inductance is characterized in that a plurality of groups of primary windings and secondary windings are wound on a magnetic core, the primary windings and the secondary windings are wound on the magnetic core in a staggered lamination mode, the primary windings are outgoing lines on the same layer and the same side, and the secondary windings are outgoing lines on different layers on the same side.

2. The method of claim 1, wherein the secondary winding is configured to provide different layers of outgoing lines on the same side through vias.

3. The method of winding a flyback transformer with very low leakage inductance according to claim 1, wherein the primary winding and the secondary winding are connected in parallel in a staggered manner.

4. A flyback transformer winding method with very low leakage inductance according to claim 1, wherein the core is ELP220616 core.

5. A flyback transformer winding method with very low leakage inductance according to claim 1, wherein the magnetic core has a permeability of 1500.

6. A method of winding a flyback transformer with very low leakage inductance according to claim 1, wherein the secondary winding is disposed at the very top of the wound winding.

7. A method of winding a flyback transformer with very low leakage inductance according to claim 1, wherein the primary winding and secondary winding are on the same side as the inlet and outlet core.

8. A method of winding a flyback transformer with very low leakage inductance according to claim 1, wherein the number of primary and secondary windings is the same.