A planar transformer winding method with low leakage inductance and a planar transformer

Abstract

The present invention relates to a method for winding planar transformer windings with low leakage inductance and a planar transformer. The method comprises calculating grouping parameters based on the relationship between the number of turns of the primary and secondary windings, performing grouping based on the grouping parameters, and obtaining a low-leakage inductance planar transformer through interleaved winding. By rationally arranging the positions of the primary and secondary windings, the present invention enables a planar transformer with any turns ratio to achieve minimum leakage inductance, thereby reducing transformer losses and improving system efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a method for winding a planar transformer with low leakage inductance and a planar transformer. Background Art

[0002] In a switching power supply, the transformer's leakage inductance increases power losses and reduces system efficiency. Furthermore, the energy stored in the leakage inductance can cause voltage spikes when the switch switches between states, potentially leading to excessive voltage across the switch and causing it to break down. Therefore, when designing a transformer, it's important to minimize the transformer's leakage inductance to mitigate its negative effects.

[0003] The primary leakage inductance of the transformer L leakage Determined by the energy E in the transformer, the relationship between the two is Among them, I p is the current in the primary winding. The relationship between energy E and the magnetic induction intensity B and magnetic field intensity H of the transformer is: Then we can get the leakage inductance L leakage The relationship between the magnetic induction intensity B and the magnetic field intensity H is: If the distribution of magnetic field strength and magnetic induction strength in the transformer can be changed to reduce the value of ∫B·H·dV, the leakage inductance of the transformer can be reduced.

[0004] Since the leakage flux that generates leakage inductance dissipates quickly after leaving the winding, and the magnetic resistance of the core is much smaller than the magnetic resistance of the winding and the window, the contribution of the path inside the core can be ignored in the closed loop integrated in Ampere's loop law, and it can be simplified to NI = H·b, where b is the winding width. If the influence of the current skin effect is further ignored and the current density in the winding is assumed to be uniformly distributed, the magnetic field intensity in the primary winding can be obtained as Where H(0) is the magnetic field strength at the top of the primary winding of this layer, n p is the number of turns of each layer of primary winding, h p is the thickness of each layer of primary winding; the magnetic field strength in the secondary winding Where H(0) is the magnetic field strength at the top of the primary winding of this layer, n s is the number of turns of each secondary winding, h s is the thickness of each primary winding; since no current flows through the isolation layer, the magnetic field strength in the isolation layer is ideally equal everywhere.

[0005] Currently, the most commonly used winding method to reduce transformer leakage inductance is the fully interleaved winding method. Taking the case of 16 turns of primary winding, 12 turns of secondary winding, and one turn of coil per layer as an example, the winding arrangement and magnetomotive force (MMF) distribution of the fully interleaved transformer are as follows:Figure 1 As shown. In this winding method, the primary winding and the secondary winding are placed alternately, which reduces the leakage of magnetic flux, so the leakage inductance is small. The leakage inductance can be calculated by the following formula:

[0006]

[0007] It is generally believed that a fully interleaved winding method can achieve the minimum leakage inductance because the primary and secondary windings are most tightly coupled in this winding method, resulting in very little leakage flux. However, in reality, a fully interleaved winding method only achieves the minimum leakage inductance when the difference in the number of turns between the primary and secondary windings is less than or equal to 1. If the difference in the number of turns between the primary and secondary windings is greater than 1, there will be redundant primary or secondary windings that cannot be paired. From the perspective of leakage flux, there will be more leakage flux at the unpaired redundant windings; from the perspective of energy, the square value of the magnetic field strength at the unpaired redundant windings (H 2 ) is large, which increases the energy in the transformer and leads to a large leakage inductance. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a planar transformer winding method with low leakage inductance and a planar transformer, which can enable a planar transformer with any turns ratio to obtain minimum leakage inductance.

[0009] The technical solution adopted by the present invention to solve the technical problem is to provide a method for winding a planar transformer with low leakage inductance, comprising the following steps:

[0010] (1) Compare the number of turns of the primary winding and the number of turns of the secondary winding. If the number of turns of the primary winding is less than that of the secondary winding, swap the number of turns of the primary winding with the number of turns of the secondary winding to ensure that the number of turns of the primary winding is not less than that of the secondary winding; if the number of turns of the primary winding is greater than that of the secondary winding, proceed to the next step;

[0011] (2) Determine whether the number of turns of the secondary winding is 0. If so, arrange the primary windings in order from top to bottom. If not, proceed to the next step.

[0012] (3) calculating the difference between the number of turns of the primary winding and the number of turns of the secondary winding; if the difference is less than or equal to 1, completely interleaving the primary winding and the secondary winding; otherwise, calculating the grouping parameters;

[0013] (4) dividing the windings into a first subgroup and a second subgroup according to the grouping parameters, wherein the primary and secondary windings in each subgroup are completely interlaced;

[0014] (5) The original transformer is regarded as a new transformer with a turns ratio of the number of the first subgroup: the number of the second subgroup, the primary winding is the first subgroup, and the secondary winding is the second subgroup; return to step (1) until the conditions in step (2) or step (3) are met.

[0015] In the step (3), Calculate the grouping parameters, where floor() represents the rounding down operation, mod() represents the modulus operation, and N p is the number of turns of the primary winding, N s is the number of turns of the secondary winding, n=N p -N s .

[0016] The turns ratio of the first subgroup in step (4) is n p1 :n s1 , the turns ratio of the second subgroup is n p1 +1:n s1 +1, the number of the first subgroup is n1, and the number of the second subgroup is n2.

[0017] The technical solution adopted by the present invention to solve its technical problem is: providing a planar transformer, including a primary winding and a secondary winding, wherein the primary winding and the secondary winding are wound using the above-mentioned low leakage inductance planar transformer winding winding method.

[0018] Beneficial effects

[0019] Due to the adoption of the above-mentioned technical solution, the present invention has the following advantages and positive effects compared to the prior art: The present invention creates a low-leakage inductance transformer, wound in groups and staggered according to the number of turns of the primary and secondary windings. By rationally arranging the positions of the primary and secondary windings, the energy within the transformer is minimized, enabling planar transformers with any turns ratio to achieve minimum leakage inductance. Compared to traditional winding methods, transformers wound using the present invention have lower leakage inductance, reducing transformer losses and improving system efficiency. It also mitigates the negative impact of voltage spikes caused by energy stored in the leakage inductance when switching between switching states. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the transformer winding arrangement and magnetomotive force distribution of a fully interleaved winding in the prior art;

[0021] Figure 2 is a flow chart of an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of transformer winding arrangement and magnetomotive force distribution obtained by using this embodiment;

[0023] Figure 4 This is a comparison diagram of the distribution of the square value of the magnetic field intensity in the transformer obtained by using the fully interleaved winding method and the method of this embodiment. DETAILED DESCRIPTION

[0024] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0025] The embodiment of the present invention relates to a winding method for a planar transformer with low leakage inductance. By rationally arranging the positions of the primary winding and the secondary winding, the energy in the transformer is minimized, and the leakage inductance of a planar transformer with any turns ratio can be minimized. p , the number of turns of the secondary winding is N s , and each layer of winding contains only one turn of coil, such as Figure 2 As shown, the specific steps include:

[0026] Step 1, if N p <N s , then swap the primary winding and the secondary winding, swap N p and N s That is, in the following process, the transformer is considered to have a primary winding with N turns. s , the number of turns of the secondary winding is N p Analyze the transformer to ensure that the number of turns of the primary winding is not less than the number of turns of the secondary winding;

[0027] Step 2, if N s =0, that is, there is no secondary winding, then the primary windings can be arranged from top to bottom to exit the iteration and obtain the winding arrangement with minimum leakage inductance;

[0028] Step 3: Let n = N p -N s If n≤1, the iteration can be exited by completely interleaving the primary winding and the secondary winding to obtain the winding arrangement with minimum leakage inductance; otherwise, let Among them, floor() represents the rounding down operation, and mod() represents the modulo operation;

[0029] Step 4: Divide the winding into subgroup A and subgroup B, with turn ratios of n and n p1 :n s1 and n p1 +1:n s1 +1, the number of the two groups is n1 and n2 respectively. In each subgroup, the primary and secondary windings are completely interleaved;

[0030] Step 5, let Treat the original transformer as a new transformer with a turns ratio of n1:n2, a primary winding of subgroup A, and a secondary winding of subgroup B. Return to step 1 and iterate again until the conditions in step 2 or step 3 are met to exit the iteration.

[0031] The present invention is further described below through a specific embodiment.

[0032] To facilitate comparison with the prior art, this embodiment takes a planar transformer with 16 turns of the primary winding, 12 turns of the secondary winding, and only one winding per layer as an example, and specifically includes the following steps:

[0033] Step a, N p =16,N s =12, the number of turns of the primary winding is greater than that of the secondary winding, and there is no need to swap the primary and secondary windings;

[0034] Step b, since N s ≠0, so the condition of step 2 is not met and the iteration cannot be exited.

[0035] Step c, let n = N p -N s =4, the condition in step 3 is not met, the iteration cannot be exited, and the grouping parameters are calculated. The grouping parameters are divided into:

[0036] In step d, the windings are divided into subgroups A and B according to the grouping parameters. The turns ratio of subgroup A is 4:3, the turns ratio of subgroup B is 5:4, the number of subgroups A is 4, and the number of subgroups B is 0. Within each subgroup, the primary and secondary windings are completely interleaved, so the arrangement of subgroup A is "PSPSPSP", and the arrangement of subgroup B is "PSPSPSPSP".

[0037] Step e, let The primary winding of the new transformer is subgroup A, the secondary winding is subgroup B, and the turns ratio is 4:0. Continue the iteration;

[0038] Step f, the number of turns of the primary winding of the new transformer is greater than the number of turns of the secondary winding, and there is no need to interchange the primary and secondary windings;

[0039] In step g, the number of turns of the secondary winding of the new transformer is 0, which meets the conditions of step 2 and the iteration can be exited. The final winding arrangement is arranged as 4 subgroups A from top to bottom, that is, "(PSPSPSP)-(PSPSPSP)-(PSPSPSP)-(PSPSPSP)".

[0040] For a planar transformer with a turns ratio of 16:12, the magnetomotive force distribution in the winding arranged according to the method of this embodiment is as follows: Figure 3 As shown, the leakage inductance L can be obtained leakage for:

[0041]

[0042] Compared with the leakage inductance of the fully interleaved structure transformer calculated in the background art, the leakage inductance of the transformer wound using the method of this embodiment is significantly smaller. Since the leakage inductance is proportional to the integral of the square of the magnetic field strength in the transformer, it can be calculated by H 2 The -x curve compares the leakage inductance of the two structures more intuitively. Figure 4 As shown, the curve of the transformer wound by the method of this embodiment is significantly lower than the curve of the transformer with a fully interleaved structure in the background art, and thus has a smaller leakage inductance.

[0043] Using Ansys finite element simulation software, a planar transformer with an EQ40 / 20 core, a 0.2mm thick PCB layer, and a 2oz copper thickness was simulated. The simulation results for leakage inductance were as follows: the leakage inductance value at 100kHz was 454nH under the fully interleaved winding method; the leakage inductance value at 100kHz was 117nH under the grouped interleaved winding method proposed in this embodiment. Experiments verified the two schemes, and the leakage inductance values ​​measured at 100kHz were 307.12nH and 155.05nH, respectively. Both simulation and experimental results confirm the superiority of the scheme proposed in this embodiment in terms of transformer leakage inductance, namely, the leakage inductance value of the grouped interleaved winding scheme proposed in this embodiment is much lower than that of the traditional fully interleaved winding scheme.

[0044] It is not difficult to find that the present invention creates a low-leakage inductance transformer that is interleaved and wound in groups according to the number of turns of the primary and secondary windings. By rationally arranging the positions of the primary and secondary windings, the energy within the transformer is minimized, and the leakage inductance of a planar transformer with any turns ratio can be minimized. Compared to traditional winding methods, transformers wound using the present invention have lower leakage inductance, reducing transformer losses and improving system efficiency. It also reduces the negative impact of voltage spikes caused by energy stored in the leakage inductance when the switch switches between states.

Claims

1. A method for winding a planar transformer with low leakage inductance, wherein: The difference between the number of turns of the primary winding and the number of turns of the secondary winding is greater than 1, and the method is characterized in that it includes the following steps: (1) Compare the number of turns of the primary winding and the number of turns of the secondary winding. If the number of turns of the primary winding is less than that of the secondary winding, swap the number of turns of the primary winding with the number of turns of the secondary winding to ensure that the number of turns of the primary winding is not less than that of the secondary winding; if the number of turns of the primary winding is greater than that of the secondary winding, proceed to the next step; (2) Determine whether the number of turns of the secondary winding is 0. If so, arrange the primary windings in order from top to bottom. If not, proceed to the next step. (3) Pass Calculate the grouping parameters, where floor() represents the rounding down operation. ()mod() represents the modulo operation, N p is the number of turns of the primary winding, N s is the number of turns of the secondary winding, n=N p -N s , n p1 ,n s1 ,n1,n2 are grouping parameters; (4) The windings are divided into a first subgroup and a second subgroup according to the grouping parameters, and the primary and secondary windings in each subgroup are completely interlaced, wherein the turns ratio of the first subgroup is n p1 :n s1 , the turns ratio of the second subgroup is n p1 +1:n s1 +1, the number of the first subgroup is n1, and the number of the second subgroup is n2; (5) The original transformer is regarded as a new transformer with a turns ratio of the number of the first subgroup: the number of the second subgroup, the primary winding is the first subgroup, and the secondary winding is the second subgroup; return to step (1) until the condition in step (2) is met.

2. A planar transformer comprising a primary winding and a secondary winding, characterized in that: The primary winding and the secondary winding are wound using the low leakage inductance planar transformer winding method as claimed in claim 1.

Images