A transformer suitable for small and medium power, wide voltage input range

Abstract

The application discloses a transformer suitable for small and medium power and wide voltage input range, which comprises a primary winding, a VCC winding and a secondary winding. The primary winding is a three-section staggered winding structure, comprising a first primary winding of an initial section winding, a third primary winding of a middle section winding and a second primary winding of a terminal section winding. The first primary winding, the second primary winding and the third primary winding are wound in order from inside to outside. The VCC winding is wound between the first primary winding and the second primary winding. The secondary winding is wound between the VCC winding and the second primary winding. The primary winding is split into the first primary winding, the second primary winding and the third primary winding, and the third primary winding of the middle section winding and the second primary winding of the terminal section winding are staggered, so that the common mode voltage and the common mode current can be greatly reduced in a low leakage current scene.

Description

Technical Field

[0001] This application relates to the technical field of transformers, and in particular to a transformer suitable for small and medium power applications with a wide voltage input range. Background Technology

[0002] Switching power supply transformers are core magnetic components in power products such as chargers and adapters. Their winding structure directly determines electromagnetic interference (EMI) performance and electrical safety levels. Traditional transformer winding methods are mainly divided into two categories: sequential winding and sandwich winding.

[0003] Sequential winding involves winding the primary winding first and then the secondary winding. This method results in lower winding coupling but higher leakage inductance, making it suitable for low-power applications or those with less stringent EMI requirements. Sandwich winding employs a symmetrical structure of "1 / 2Np primary ~ secondary ~ 1 / 2Np primary" or an asymmetrical structure of "1 / Np1 primary ~ secondary ~ 1 / Np2 primary" (where Np = Np1 + Np2; a symmetrical structure occurs when Np1 and Np2 are close, and an asymmetrical structure occurs when they differ significantly). Named for the secondary winding sandwiched between the two primary windings, it offers higher winding coupling and lower leakage inductance, and is widely used in small and medium-power transformers.

[0004] However, the traditional sandwich winding method can only meet basic usage requirements when leakage current requirements are not high, i.e., when a large-capacity Y capacitor is allowed between the primary and secondary sides to suppress common-mode interference. But with the continuous upgrading of requirements for low leakage current and high electrical safety in consumer electronics and industrial power supplies, the market has seen a stringent demand for "Y capacitor-free design," which means that only a very small Y capacitor is allowed between the primary and secondary sides, or even no Y capacitor is allowed at all. Therefore, with the current market's explosive demand for low leakage current in power products such as chargers and adapters, the EMI control defects of the traditional sandwich winding method have become a common technical pain point in the industry, and an innovative design solution that can optimize the electromagnetic coupling characteristics of the winding from the root is urgently needed. Summary of the Invention

[0005] The purpose of this application is to provide a transformer suitable for small and medium power and wide voltage input range. By splitting the primary winding into three sections—a first primary winding, a second primary winding, and a third primary winding—and alternating the third primary winding of the middle section with the second primary winding of the end section, the common-mode voltage and common-mode current are significantly reduced in low leakage current scenarios.

[0006] This application provides a transformer suitable for small to medium power applications with a wide voltage input range, the transformer comprising: The primary winding is a three-segment staggered winding structure, including the first primary winding of the initial segment, the third primary winding of the middle segment, and the second primary winding of the final segment. The first primary winding, the second primary winding, and the third primary winding are wound in order from the inside to the outside. The VCC winding is wound between the first primary winding and the second primary winding; The secondary winding is wound between the VCC winding and the second primary winding.

[0007] Furthermore, the transformer also includes a cancelling winding, which is wound between the secondary winding and the second primary winding to cancel the post-common-mode noise of the secondary winding.

[0008] Furthermore, the transformer also includes a balancing winding, which is wound between the first primary winding and the VCC winding to balance the pre-common-mode noise of the secondary winding. Among them, the stationary positions of the secondary winding, the VCC winding, the canceling winding, and the second primary winding are physically aligned.

[0009] Furthermore, the VCC winding and the decoupling winding are wound in parallel, and the m strands of the VCC winding and the n strands of the decoupling winding are wound together in a single layer, where m and n are natural numbers between 1 and 3. Among them, the static point of the canceling winding, the balancing winding and the decoupling winding is connected to the primary ground or the high voltage terminal; the potential direction of the secondary winding is opposite to that of the balancing winding and the canceling winding; the potential direction of the secondary winding is the same as that of the VCC winding, the first primary winding of the initial section winding, the third primary winding of the middle section winding and the second primary winding of the final section winding, so that the positive and negative charges induced in the secondary winding by other windings cancel each other out.

[0010] Furthermore, the secondary winding, VCC winding, decoupling winding, and balancing winding are evenly distributed in terms of potential along the winding axis, so that the negative charge induced in adjacent layers at each physical location of the secondary winding is equal to the positive charge, thereby eliminating the leakage of common-mode current on the secondary winding. In this process, the induced charge on the secondary winding is finely adjusted by finely adjusting the number of turns in the balancing winding and the potential distribution between the VCC winding and the decoupling winding.

[0011] Furthermore, the second primary winding consists of N strands wound in parallel and tightly wound into a single layer, where N is a natural number between 1 and 3.

[0012] Furthermore, the stationary position of the second primary winding is physically aligned with the stationary position of the secondary winding, and the winding directions of the two are consistent. The number of turns of the second primary winding is similar to or equal to the number of turns of the secondary winding, so that the second primary winding can act as a common-mode voltage cancellation winding to cancel the common-mode voltage between the second primary winding and the secondary winding.

[0013] Furthermore, the stationary positions of the secondary winding, the second primary winding, and the canceling winding are physically aligned, the stationary position of the canceling winding is electrically connected to the primary ground or the high-voltage terminal, and the potential direction of the canceling winding is opposite to that of the secondary winding and the second primary winding.

[0014] Furthermore, when transformers are used in low-leakage-current power supply products such as chargers and adapters, a very small Y capacitor may be connected between the primary winding and the secondary winding, or no Y capacitor may be connected at all.

[0015] Furthermore, the winding sequence of the transformer from the inside out is as follows: first primary winding, balance winding, VCC winding and decoupling winding wound in parallel, secondary winding, offset winding, second primary winding, and third primary winding.

[0016] Unlike existing technologies, this application divides the primary winding into three sections: a first primary winding, a second primary winding, and a third primary winding. The third primary winding in the middle section is alternately arranged with the second primary winding in the end section. This constructs the second primary winding as a canceling winding to cancel the common-mode voltage of the secondary winding, thereby significantly reducing the common-mode voltage and common-mode current.

[0017] Meanwhile, this application can be directly applied to low leakage current power supply products such as chargers and adapters. A very small Y capacitor or no Y capacitor is allowed to be connected between the primary and secondary sides, which completely avoids the risk of batch non-conformity caused by inconsistent EMI performance during mass production. It has a significant cost-performance advantage in low leakage current (low Y or no Y capacitor) scenarios.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this application. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the topology of the transformer in the first embodiment of this application; Figure 2 This is a schematic diagram of the specific structure of the transformer in the first embodiment of this application; Figure 3 This is a schematic diagram of the topology of the second embodiment of the transformer in this application; Figure 4 This is a schematic diagram of the specific structure of the second embodiment of the transformer in this application; Figure 5 yes Figure 3 Potential distribution diagram of the intermediate secondary front winding; Figure 6 yes Figure 3 Cross-sectional view of the secondary rear winding; Figure 7 This is the EMI simulation result of the second embodiment of the transformer in this application; Figure 8 This is a diagram showing the CE test results of a conventionally wound transformer; Figure 9 This is a CE test result diagram of the second embodiment of the transformer in this application; Icon labels: N P1 - First primary winding; N P2 -Second primary winding; N P3 -Third primary winding; N VCC -VCC winding; N S - Secondary winding; S1 - Balance winding; S2 - Cancellation winding; S3 - Decoupling winding. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of this application, the transformer suitable for small and medium power and a wide voltage input range provided in this application will be described in further detail below with reference to the accompanying drawings and specific embodiments. It is understood that the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0022] The terms "first," "second," etc., used in this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0023] Since the EMI control deficiencies of traditional sandwich winding have become a common technical pain point in the industry, this application provides a transformer that addresses the challenges of existing sandwich transformers in low leakage current scenarios (i.e., low Y or no Y capacitance). It employs a unique three-segment interleaved winding structure for the primary winding. Specifically, the primary winding is divided into three segments: a first primary winding, a second primary winding, and a third primary winding. The third primary winding in the middle segment is interleaved with the second primary winding in the final segment. This significantly reduces common-mode voltage and common-mode current in low leakage current scenarios, reduces or simplifies the EMI filter, and improves the EMI consistency of the transformer. This application solves the industry pain point of repeated EMI rectification at the design level, and is expected to shorten the development cycle of switching power supplies by more than 30%, while completely avoiding the risk of batch defects caused by inconsistent EMI performance during mass production.

[0024] This application can be directly applied to the development and mass production of low leakage current power supply products such as chargers and adapters. A very small Y capacitor may be connected between the primary winding and the secondary winding, or no Y capacitor may be connected.

[0025] This application provides a transformer suitable for small to medium power applications with a wide voltage input range. Please refer to [link / reference] for details. Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the topology of the transformer according to the first embodiment of this application. Figure 2 This is a schematic diagram of the specific structure of the first embodiment of the transformer in this application.

[0026] like Figure 1 and Figure 2 As shown, the transformer in this embodiment includes at least a primary winding and a VCC winding N. VCC Secondary winding N S And decoupling winding S3. In this embodiment, the primary winding is a three-segment interleaved winding structure, including the first primary winding N of the initial segment winding. P1 The third primary winding N of the middle section winding P3 and the second primary winding N of the last section winding P2 The first primary winding N P1 Second primary winding N P2 and the third primary winding N P3 The windings are arranged from the inside out. Specifically, the second primary winding N... P2 The outermost layer of the transformer, the third primary winding N P3 This is the outermost layer of the transformer.

[0027] In this embodiment, the VCC winding N VCC Winded on the first primary winding N P1 With the second primary winding N P2 Between. Among them, VCC winding N VCCThe VCC winding N is wound in parallel with the decoupling winding S3. VCC The m strands of the decoupling winding S3 are wound together with the n strands of the decoupling winding S3 in a single layer, where m and n are natural numbers between 1 and 3.

[0028] The secondary winding N in this embodiment S Winded on VCC winding N VCC With the second primary winding N P2 Between. Second primary winding N P2 N strands are wrapped tightly together in one layer, where N is a natural number between 1 and 3.

[0029] Specifically, such as Figure 1 As shown, the primary side (i.e., the primary winding side) includes the first primary winding N. P1 Second primary winding N P2 Third primary winding N P3 VCC winding N VCC And decoupling winding S3, secondary side (i.e., secondary side) is provided with secondary winding N S .

[0030] Among them, such as Figure 2 As shown, the windings wound sequentially from the bottom of the frame upwards are the first primary winding N. P1 The VCC winding N is wound in parallel. VCC With decoupling winding S3 and secondary winding N S Second primary winding N P2 and the third primary winding N P3 .

[0031] This application also provides another transformer suitable for low-power sequential winding; please refer to [link to relevant documentation]. Figures 3-4 , Figure 3 This is a schematic diagram of the topology of the second embodiment of the transformer in this application. Figure 4 This is a schematic diagram of the specific structure of the second embodiment of the transformer in this application.

[0032] Based on the above embodiments, the transformer in this embodiment further includes a balancing winding S1 and a canceling winding S2. The balancing winding S1 is wound around the first primary winding N. P1 With VCC winding N VCC Between, used to balance the secondary winding N S Pre-common-mode noise cancellation; canceling winding S2 is wound on secondary winding N S With the second primary winding N P2 Between, used to offset secondary winding N S Post-common-mode noise.

[0033] Optionally, the balancing winding S1, the canceling winding S2, and the decoupling winding S3 in this embodiment are all common-mode voltage canceling or balancing windings. Their functions are not changed by the difference in winding name or letter code, and can be replaced by other names in other applications.

[0034] Specifically, such as Figure 3 As shown, the primary side (i.e., the primary winding side) includes the first primary winding N. P1 Second primary winding N P2 Third primary winding N P3 Balance winding S1, offset winding S2, VCC winding N VCC And decoupling winding S3, secondary side (i.e., secondary side) is provided with secondary winding N S .

[0035] Among them, such as Figure 4 As shown, the windings wound sequentially from the bottom of the frame upwards are the first primary winding N. P1 Balance winding S1, and parallel VCC winding N VCC With decoupling winding S3 and secondary winding N S , offset winding S2, second primary winding N P2 and the third primary winding N P3 .

[0036] Specifically, in this embodiment, the secondary winding N S The static position of the VCC winding N VCC The static position, the offset winding S2, and the second primary winding N P2 Physical alignment of the static point positions.

[0037] Among them, the static point of the cancelling winding S2, the balancing winding S1, and the decoupling winding S3 is electrically connected to the primary ground or the high-voltage terminal, and the secondary winding N... S The secondary winding N has a potential direction opposite to that of the balancing winding S1 and the canceling winding S2. S and VCC winding N VCC The first primary winding N of the initial winding P1 The third primary winding N of the middle section winding P3 and the second primary winding N of the last section winding P2 The potential directions are the same, so that the other windings are in the same direction as the secondary winding N. S The induced positive and negative charges cancel each other out.

[0038] Secondary winding N S VCC winding N VCC The decoupling winding S3 and the balancing winding S1 have a uniform potential distribution along the winding axis, so that the secondary winding N... S At each physical location, the negative and positive charges induced in adjacent layers are equal to eliminate the secondary winding N.S Common-mode current leakage.

[0039] In this application, the number of turns of the balance winding S1 is finely adjusted to finely adjust the VCC winding N. VCC By adjusting the potential distribution of the decoupling winding S3, the secondary winding N can be finely adjusted. S The induced charge on the VCC winding. Specifically, this depends on the N winding of the VCC winding. VCC With decoupling winding S3 in secondary winding N S Induced charge Q on - cmn Q + cmn To determine the balance, the number of turns in the balance winding S1 is finely adjusted, and the number of turns in the VCC winding N is also finely adjusted. VCC This fine-tunes the potential distribution on the decoupling winding S3, thereby adjusting the secondary winding N. S The induced charge on it, to achieve Q - cmn =Q + cmn .

[0040] In this embodiment, the VCC winding N VCC Decoupling winding S3, balancing winding S1, and first primary winding N P1 All are secondary windings N S The front windings are precisely aligned with the static point positions of each front winding, making the winding polarity unique and clear, eliminating the need for repeated trial windings and EMI testing.

[0041] Parallel VCC winding N VCC With decoupling winding S3 in secondary winding N S Induced charge Q on - Q + They can be balanced and canceled out, therefore, to ensure that the secondary front winding is in the secondary winding N S The positive and negative charges induced in the upper winding cancel each other out, requiring the design of the secondary winding N. S VCC winding N VCC The decoupling winding S3 and the balancing winding S1 have regular and uniform potential distribution along the winding axis. When the potential of the adjacent layer is higher than that of the secondary winding N... S At that time, the secondary winding N S A negative charge Q is induced at position n. - cmn Similarly, when the potential of the adjacent layer is lower than that of the secondary winding N S At that time, the secondary winding N S A positive charge Q is induced at position n. + cmn .

[0042] Please see Figure 5 , Figure 5 yes Figure 3 Potential distribution diagram of the intermediate secondary front winding. (See diagram below.) Figure 5 As shown, secondary winding N S Q at each physical position along the winding axis - cm1 =Q + cm1 Q - cm2 =Q + cm2 Q - cmn =Q + cmn Then the secondary winding N S There is no common-mode current leakage, and no common-mode voltage noise is generated on the power transformer, thus solving the EMI problem.

[0043] Specifically, VCC winding N VCC Decoupling winding S3 and secondary winding N S The number of turns is determined based on the transformer's operating conditions, VCC winding N VCC Decoupling winding S3 and secondary winding N S The number of turns represents the potential distribution along the winding axis. Where, Q cmn =C cmn ×ΔV cmn C cmn The equivalent capacitance between adjacent layer positions n is determined by the potential difference +ΔV between adjacent layers. cmn -ΔV cmn Q was obtained respectively - cmn Q + cmn .

[0044] Therefore, this application is based on VCC winding N VCC Decoupling winding S3 and secondary winding N S Induced charge Q on - cmn Q + cmn To determine the balance, the number of turns in the balance winding S1 is finely adjusted, and the number of turns in the VCC winding N is also finely adjusted. VCC The potential distribution on the decoupling winding S3 is used to fine-tune the secondary winding N. S Induced charge Q on - cmn Q + cmn In order to achieve Q - cmn =Q + cmn .

[0045] In the third primary winding N P3 With the second primary winding N P2 After the interleaved winding setup, the second primary winding N P2 Number of turns and secondary winding N S The number of turns of the second primary winding N is similar or equal. P2 The static position and the secondary winding N S The static points are physically aligned, and the winding directions of both are consistent, forming the same potential distribution along the winding axis between the primary and secondary windings, so that the second primary winding N... P2 As a common-mode voltage cancellation winding, it cancels the second primary winding N P2 With secondary winding N S The common-mode voltage between them. Optionally, the second primary winding N P2 Number of turns and secondary winding N S The error value of the number of turns can be less than or equal to 10%.

[0046] On the other hand, secondary winding N S The static position of the second primary winding N P2 The static point position of the neutral winding S2 is physically aligned with that of the secondary winding N. The static point of the neutral winding S2 is electrically connected to the primary ground or the high-voltage terminal. The winding direction of the neutral winding S2 is aligned with that of the secondary winding N. S and the second primary winding N P2 The winding direction is opposite.

[0047] In this embodiment, the offset winding S2 and the second primary winding N P2 and the third primary winding N P3 All are secondary windings N S The rear windings are precisely aligned at their static points, ensuring the winding polarity is determined and eliminating the need for repeated trial windings and tests.

[0048] Please see Figure 6 , Figure 6 yes Figure 3 Cross-sectional view of the secondary winding after winding, and the second primary winding N with the same or similar number of turns. P2 With secondary winding N S A common-mode current of equal magnitude and opposite direction is generated on the canceling winding S2, which cancels each other out. cm11 =I cm12 I cm21 =I cm22 ... I cmn1 =I cmn2 To eliminate the second primary winding N P2 With secondary winding N S The common-mode voltage between the two sides ensures that the power supply does not generate common-mode noise, thus solving the EMI problem.

[0049] In this embodiment, the secondary winding N is adjusted by regulating the balancing winding S1, the canceling winding S2, and the decoupling winding S3. S Induced charge Q on - cmn =Q + cmn I cmn1 =I cmn2 This ensures that the common-mode current flowing through the LISN during EMI CE testing is less than the limit requirement, thus effectively solving the EMI problem of switching power supplies.

[0050] This application adopts an original primary winding staggered three-segment winding structure, which is achieved by splitting the primary winding into three segments and adding a balancing winding S1 and a parallel VCC winding N between the inner primary winding and the secondary winding. VCC Compared to the decoupling winding S3, the spacing between the primary and secondary windings is significantly increased. Taking typical parameters as an example, in the traditional structure, the outer radius of the primary winding r1 = 5.0 mm, the inner radius of the secondary winding r2 = 5.165 mm, and the spacing is only about 0.165 mm, with a distributed capacitance between the primary and secondary windings of about 72 pF. However, in this application, the spacing between the inner primary and secondary windings is increased to about 0.575 mm (including the thickness of the adhesive tape, balancing winding, and VCC winding), and the inner radius r2 of the secondary winding is increased to 5.575 mm. The capacitance between the inner primary and secondary windings is reduced from 72 pF to about 21 pF, a reduction of more than 70%. Since the displacement current is proportional to the capacitance value, the common-mode current from the primary to the secondary winding is also reduced by more than 70%.

[0051] Further reading Figures 7-9 , Figure 7 This is the EMI simulation result of the second embodiment of the transformer in this application; Figure 8 This is a graph showing the CE test results of a conventionally wound transformer. Figure 9 This is a CE test result diagram of the second embodiment of the transformer in this application. This application performs EMI characteristic simulation tests and CE conduction tests on the transformer of this application, and obtains the following results: Figure 7 and Figure 9 The test results shown are as follows: This application conducted EMI characteristic simulation tests and CE conduction tests on transformers using the traditional sequential winding method, and obtained the following results respectively. Figure 7 and Figure 8 The test results are shown.

[0052] like Figure 7 As shown in the figure, curve S4 represents the spectrum obtained from the simulation of a conventionally wound transformer, and curve S5 represents the spectrum obtained from the simulation of the transformer of this application. Comparing curves S4 and S5, it can be seen that the amplitude of curve S4 is higher than that of curve S5, that is, the amplitude of the spectrum obtained from the transformer simulation of this application is lower than that obtained from the simulation of a conventionally wound transformer.

[0053] This application is compared Figure 8 and Figure 9 This clearly demonstrates that the transformer in this application exhibits significantly improved EMI performance. (Comparison) Figure 8 and Figure 9 The conducted or radiated interference amplitude of the transformer in this application is 10-20 dB lower than that of conventional wound transformers, thereby reducing or simplifying EMI filters.

[0054] The transformer in this application not only reduces the CE QP noise amplitude, but also significantly reduces the CE AV noise amplitude, including a 10dB reduction in AV low-frequency noise of ≤550KHz, which is difficult for traditional general-purpose EMI filters to filter out.

[0055] The transformer using this application can easily pass conducted and radiated EMI tests without relying on large-capacity Y capacitors or complex common-mode filters. It can reduce the number of components in the EMI filter by 30%-50%, reduce the core size of the common-mode inductor by 40%, and reduce the overall BOM cost of the power supply product by 5%-10%.

[0056] The above are merely embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A transformer suitable for small to medium power applications and a wide voltage input range, characterized in that, include: The primary winding is a three-segment staggered winding structure, including a first primary winding in the initial segment, a third primary winding in the middle segment, and a second primary winding in the final segment. The first primary winding, the second primary winding, and the third primary winding are wound in order from the inside to the outside. VCC winding, wherein the VCC winding is wound between the first primary winding and the second primary winding; The secondary winding is wound between the VCC winding and the second primary winding.

2. The transformer according to claim 1, characterized in that, The transformer also includes a cancelling winding, which is wound between the secondary winding and the second primary winding to cancel the post-common-mode noise of the secondary winding.

3. The transformer according to claim 2, characterized in that, The transformer also includes a balancing winding, which is wound between the first primary winding and the VCC winding to balance the pre-common-mode noise of the secondary winding. The stationary positions of the secondary winding, the VCC winding, the canceling winding, and the second primary winding are physically aligned.

4. The transformer according to claim 3, characterized in that, The VCC winding and the decoupling winding are wound in parallel, and the m strands of the VCC winding and the n strands of the decoupling winding are wound together in a whole layer, where m and n are natural numbers between 1 and 3. The neutral point of the canceling winding, the balancing winding, and the decoupling winding is electrically connected to the primary ground or the high-voltage terminal; the potential direction of the secondary winding is opposite to that of the balancing winding and the canceling winding; the potential direction of the secondary winding is the same as that of the VCC winding, the first primary winding of the initial section winding, the third primary winding of the middle section winding, and the second primary winding of the final section winding, so that the positive and negative charges induced by the other windings on the secondary winding cancel each other out.

5. The transformer according to claim 4, characterized in that, The secondary winding, the VCC winding, the decoupling winding, and the balancing winding are evenly distributed in terms of potential along the winding axis, so that the negative charge induced in adjacent layers at each physical location of the secondary winding is equal to the positive charge, thereby eliminating the common-mode current leakage on the secondary winding. Specifically, by fine-tuning the number of turns of the balancing winding, the potential distribution between the VCC winding and the decoupling winding is fine-tuned, thereby fine-tuning the induced charge on the secondary winding.

6. The transformer according to claim 1, characterized in that, The second primary winding consists of N strands wound in parallel and tightly wound into a single layer, where N is a natural number between 1 and 3.

7. The transformer according to claim 6, characterized in that, The stationary position of the second primary winding is physically aligned with the stationary position of the secondary winding, and their winding directions are the same. The number of turns of the second primary winding is similar to or equal to the number of turns of the secondary winding, so that the second primary winding can act as a common-mode voltage cancellation winding to cancel the common-mode voltage between the second primary winding and the secondary winding.

8. The transformer according to claim 2, characterized in that, The stationary position of the secondary winding, the stationary position of the second primary winding, and the stationary position of the canceling winding are physically aligned. The stationary position of the canceling winding is electrically connected to the primary ground or the high-voltage terminal. The potential direction of the canceling winding is opposite to the potential direction of the secondary winding and the second primary winding.

9. The transformer according to claim 1, characterized in that, The transformer is used in low leakage current power supply products such as chargers and adapters. A very small Y capacitor may be connected between the primary and secondary sides of the transformer, or no Y capacitor may be connected.

10. The transformer according to claim 1, characterized in that, The winding sequence of the transformer from the inside out is as follows: the first primary winding, the balancing winding, the VCC winding and the decoupling winding wound in parallel, the secondary winding, the offset winding, the second primary winding, and the third primary winding.

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