transformer
The transformer design addresses high capacitance and inductance variability by aligning turns and using a magnetic core to reduce noise and improve circuit tolerance, achieving efficient leakage inductance and capacitance control.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- COILCRAFT INC
- Filing Date
- 2024-06-28
- Publication Date
- 2026-07-21
AI Technical Summary
Existing transformers used in gate drive circuits and open-loop LLC converters face issues with high winding-to-winding capacitance and leakage inductance variability, leading to noise and inaccurate circuit behavior.
A transformer design with a specific winding configuration and core structure that includes a primary and secondary winding with aligned turns and a 1:1 turn ratio, along with a magnetic core, to reduce winding-to-winding capacitance and control leakage inductance, using materials like copper and polyester insulation.
The design achieves reduced noise and improved tolerance in circuit behavior by minimizing winding-to-winding capacitance to 0.1-1.5 pF and increasing leakage inductance to 10-12 μH, simplifying circuits and reducing costs by eliminating external matching inductors.
Smart Images
Figure 2026524188000001_ABST
Abstract
Description
[Technical Field]
[0001] Mutual citation for related applications
[0001] This application claims the rights of U.S. Patent Application No. 18 / 216,976, filed on 30 June 2023. By this reference, the entire contents of this patent application are included in this application. [Background technology]
[0002]
[0002] Generally, this application relates to transformers or coupled inductors, such as those used in conjunction with gate drive circuits. Such transformers may be suitable for use in open-loop LLC converters. Some non-limiting examples in which such transformers or coupled inductors may be used include circuits for high-voltage isolated communications transformers, common-mode chokes, SEPIC converters, half-bridge converters, full-bridge converters, and DC / DC converters. [Overview of the project] [Means for solving the problem]
[0003]
[0003] According to the embodiment, the transformer includes a core portion which includes a first longitudinal region extending between a first far end and a first longitudinal endpoint of the core, and a second longitudinal region adjacent to the first longitudinal region which extends between a second far end and a second longitudinal endpoint of the core; a primary winding disposed around the first longitudinal region of the core portion, wherein the primary winding comprises a plurality of layers, each layer comprising a plurality of turns, and adjacent turns in each layer are arranged at a certain distance from each other; and a secondary winding disposed around the second longitudinal region of the core portion. The secondary winding comprises a plurality of layers, each layer comprising a plurality of turns, and adjacent turns in each layer are arranged at a certain distance from each other. Multiple turns of the primary winding are wound around a first longitudinal region, starting near the first far end, extending toward the first longitudinal endpoint in the first layer, then reversing direction and extending in the opposite direction toward the first far end, thereby forming two turn layers in the second layer, which are arranged around the first layer. Multiple turns of the second winding are wound around a second longitudinal region, starting near the second far end, extending toward the second longitudinal endpoint in the first layer, then reversing direction and extending in the opposite direction toward the second far end in the second layer, which are arranged around the first layer. A first portion of the capacitor is formed in the primary winding by one turn from each layer directly facing the first longitudinal endpoint, and a second portion of the capacitor is formed in the secondary winding by one turn from each layer directly facing the second longitudinal endpoint. The primary winding may have only two turn layers. The centerlines of the wires in the first layer of the primary winding may be substantially aligned with the centerlines of the wires in the second layer of the primary winding, and the centerlines of the wires in the first layer of the secondary winding may be substantially aligned with the centerlines of the wires in the second layer of the secondary winding. The transformer may further include a first primary terminal, a second primary terminal, a first secondary terminal, a second secondary terminal, a first primary lead wire connected to the first primary terminal, a second primary lead wire connected to the second primary terminal, a first secondary lead wire connected to the first secondary terminal, and a second secondary lead wire connected to the second secondary terminal.The first turn in the innermost layer of the primary winding is connected to the first primary lead wire, the last turn in the outermost layer of the primary winding is connected to the second primary lead wire, the first turn in the innermost layer of the secondary winding is connected to the first secondary lead wire, and the last turn in the outermost layer of the secondary winding is connected to the second secondary lead wire. The capacitance of the capacitor can be between approximately 0.1 and 1.5 pF (e.g., 0.7 pF). The leakage inductance of the transformer can be between approximately 10 and 12 μH.
[0004]
[0004] The transformer may further include a first side core portion coupled to a first far end of the core portion, a second side core portion coupled to a second far end of the core portion, and an upper core portion coupled to the first and second side core portions. The first side core portion may be directly coupled (e.g., joined) to the first far end of the core portion, and the second side core portion may be directly coupled (e.g., joined) to the second far end of the core portion. The upper core portion may be bonded to the first and second side core portions. The transformer may also constitute a gate-driven transformer. The first layer of the primary winding and the first layer of the secondary winding may be wound directly on the core portion. The primary winding may have between about 10 and 40 turns (e.g., 24 turns), and the secondary winding may have between about 10 and 40 turns (e.g., 24 turns).
[0005]
[0005] According to an embodiment, a method for assembling a transformer including a core portion having a first longitudinal region defined by a first far end and a first longitudinal endpoint, a second longitudinal region defined by a second far end and a second longitudinal endpoint, and a core portion, includes the steps of arranging a primary winding around the core portion, starting the primary winding near the first far end of the core portion, continuously adding turns in the first layer extending toward the first longitudinal endpoint, then reversing the direction, continuously adding turns in the second layer extending in the opposite direction toward the first far end, with adjacent turns spaced a certain distance apart; and arranging a secondary winding around the core portion, starting the secondary winding near the second far end of the core portion, continuously adding turns in the first layer extending toward the second longitudinal endpoint, then reversing the direction, continuously adding turns in the second layer extending in the opposite direction toward the second far end, with adjacent turns spaced a certain distance apart. The transformer may further include a first side core portion coupled to a first far end of the core portion and a second side core portion coupled to a second far end of the core portion, and the method described above may further include the step of attaching the upper core portion to the first side core portion and the second side core portion. The step of attaching the upper core portion may be performed after the steps of arranging the primary winding and arranging the secondary winding. The step of attaching the upper core portion may include the steps of forming a gap between the upper core portion and the first side core portion and forming a gap between the upper core portion and the second side core portion. The method may further include the steps of forming third and fourth layers on the primary winding in the same way as forming the first and second layers of the primary winding, and forming third and fourth layers on the secondary winding in the same way as forming the first and second layers of the secondary winding. [Brief explanation of the drawing]
[0006] [Figure 1] This is a perspective view of a transformer according to an embodiment. [Figure 2] This is an elevation view of a transformer according to an embodiment. [Figure 3] This is a cross-sectional view of a transformer according to an embodiment. [Figure 4] This is a bottom view of a transformer according to an embodiment. [Figure 5] This is a circuit diagram modeling a transformer according to an embodiment. [Figure 6] This is a flowchart showing how to assemble a transformer according to the embodiment. [Modes for carrying out the invention]
[0007] The above summary and the following detailed description of the specific techniques of this application will be better understood when read in conjunction with the accompanying drawings. The drawings illustrate specific techniques for illustrative purposes only. However, it should be understood that the claims are not limited to the configurations and means shown in the accompanying drawings. Furthermore, the appearances shown in the drawings are just one of many ornamental appearances that can be employed to achieve the function of the described system.
[0008]
[0013] Figures 1 to 4 show perspective views, elevation views, cross-sectional views, and bottom views of the transformer 100 according to an embodiment, respectively. The transformer 100 includes a core portion 110, a first side core portion 120, a second side core portion 130, an upper core portion 140, a primary winding 150, and a secondary winding 160. The transformer 100 can also form part of a circuit, such as a gate drive circuit that drives the gate of a transistor, such as a MOSFET transistor. The transformer 100 can also be used as a component in an open-loop LLC conversion circuit.
[0009]
[0014] The core portion 110 may have a rectangular three-dimensional shape as shown in the figure. The core portion 110 may have other shapes, such as a cylindrical shape. The primary winding 150 and the secondary winding 160 can be wound around the core portion 110. The core portion has an outer diameter along the depth dimension, which may be less than the depth of the first side core portion 120 and the second side core portion 130. The core portion 110 has an outer diameter along the height dimension, which may be less than the height of the first side core portion 120 and the second side core portion 130.
[0010]
[0015] The core portion 110 includes a first longitudinal region 111, a first far end 112, a first longitudinal endpoint 113, a second longitudinal region 114, a second far end 115, and a second longitudinal endpoint 116. The first far end 112 is defined by the end of the core portion 110 adjacent to the first side core portion 120, or by the intersection line between the core portion 110 and the first side core portion 120. The second far end 115 is defined by the end of the core portion 110 adjacent to the second side core portion 130, or by the intersection line between the core portion 110 and the second side core portion 130. The first longitudinal region 111 is defined as the region between the first far end 112 and the first longitudinal endpoint 113. The first longitudinal endpoint 113 may be any suitable position on the core portion 110 between the locations where the primary winding 150 and the secondary winding 160 are located. The second longitudinal region 114 is defined as the region between the second far end 115 and the second longitudinal endpoint 116. The second longitudinal endpoint 116 may be any suitable position on the core portion 110 between the locations where the primary winding 150 and the secondary winding 160 are located.
[0011]
[0016] The first side core portion 120 may include one or more legs and corresponding feet (two legs and feet, as shown in the figure). The feet of the first side core portion 120 may be configured to rest on a substrate such as a circuit board. The feet may include recesses or other structures to accommodate all or part of the terminals 158, as will be discussed below. Alternatively, the feet may be substantially flat and may have no such structures at all.
[0012]
[0017] The second side core portion 130 may include one or more legs and corresponding feet (two legs and feet, as shown in the figure). The feet of the second side core portion 130 may be configured to rest on a substrate such as a circuit board. The feet may include recesses or other structures to accommodate all or part of the terminals 168, as will be discussed below. Alternatively, the feet may be substantially flat and may have no such structures at all.
[0013]
[0018] The upper core portion 140 may be a separate piece from the core portion 110, the first side core portion 120, and / or the second side core portion 130. The upper core portion 140 may contact the first side core portion 120 (e.g., on the upper surface of the first side core portion 120), or as shown in FIG. 2, a gap may be maintained therebetween. For example, an epoxy or other filler, or a cushioning material, or another type of spacer may be disposed between the upper core portion 140 and the first side core portion 120 to maintain the gap. The gap may be between 0.02 and 0.10 mm. An adhesive or epoxy material can maintain a fixed positional relationship between the upper core portion 140 and the first side core portion 120. The upper core portion 140 may contact the second side core portion 130 (e.g., on the upper surface of the second side core portion 130), or as shown in FIG. 2, a gap may be maintained therebetween. The gap may be between 0.02 and 0.10 mm. For example, an epoxy or other filler, or a cushioning material, or another type of spacer may be disposed between the upper core portion 140 and the second side core portion 130 to maintain the gap. An adhesive or epoxy material can maintain a fixed positional relationship between the upper core portion 140 and the second side core portion 130. As further discussed in the context of FIG. 6, after winding the primary winding 150 and the secondary winding 160, the upper core portion 140 may be added to the transformer 100.
[0014]
[0019] The core portion 110, the first side core portion 120, the second side core portion 130, and the upper core portion 140 together form a magnetic core and promote the transfer of energy between the primary winding 150 and the secondary winding 160.
[0015]
[0020] The primary winding 150 includes a conductor and can be made of a material such as copper or copper-clad aluminum. The conductor may be insulated by a material such as polyester. The primary winding 150 may be wound directly on the core portion 110 (with the layer 152 in contact with the core portion 110), or there may be an intermediary structure or material between the primary winding 150 and the core portion 110. The primary winding 150 can extend between two terminals 158. The primary winding 150 only needs to be wound a certain number of turns 151 around a first longitudinal region 111 of the core portion 110. The primary winding 150 may be wound starting from a first primary lead wire connected to the terminals 158. Turns 151 are formed within the first layer 152 by winding a conductor around the first longitudinal region 111, starting from the first primary lead wire. An additional turn 151 is added, extending from the first far end 112 toward the first longitudinal end 113. The turns 151 in the first layer 152 are spaced a fixed distance apart from each other. In other words, the distance between the first and second turns is the same as the distance between the second and third turns in the first layer 152.
[0016]
[0021] At a certain point, the winding direction of the primary winding 150 is reversed so that one turn 155 in the first layer 152 directly faces the first longitudinal end point 113. Then, a turn 151 is added in the second layer 153 so that one turn 156 in the second layer 153 directly faces the first longitudinal end point 113. The turn 151 is added in the second layer 153 and extends from the turn 156 toward the first distal end 112. The turns 151 in the second layer 153 are spaced apart from each other by a certain distance. The turns 151 in the second layer 153 may be directly placed on top of the turns in the first layer 152 (as shown in the figure, so that the center lines of the conductors are aligned vertically), or the turns 151 may be offset between the first layer 152 and the second layer 153 (completely or partially offset, etc.). The certain distance between the turns in the first layer 152 and the turns in the second layer 153 may be the same. After finishing the second layer 153, additional layers (for example, the third and fourth layers, the fifth and sixth layers, etc.) may be added in the same manner. Regardless of whether additional layers are added or not, after the last turn 151 is wound around the core portion 110, the conductor reaches the second primary lead wire, and then the second primary lead wire is connected to the terminal 158. The terminal 158 may include a solder pad, a part of a ball-grid array, a through pin, etc. The number of turns 151 in each layer may be between 10 and 40, such as 24 turns 151 in the first layer 152 and 24 turns 151 in the second layer 153.
[0017]
[0022] The secondary winding 160 may be the same as or identical to the primary winding 150. The secondary winding 160 includes a conductor and can be made of a material such as copper or copper-clad aluminum. The conductor is preferably insulated by a material such as polyester. The secondary winding 160 may be wound directly on the core portion 110 (with the layer 162 in contact with the core portion 110), or there may be an intermediary structure or material between the secondary winding 160 and the core portion 110. The secondary winding 160 may extend between two terminals 168. The secondary winding 160 only needs to be wound a certain number of turns 161 around the second longitudinal region 114 of the core portion 110. The secondary winding 160 may be wound starting from a first secondary lead wire connected to the terminals 168. Starting from the first secondary lead wire, turns 161 are formed within the first layer 162 by winding the conductor around the second longitudinal region 114. An additional turn 161 is added, extending from the second far end 115 toward the second longitudinal end 116. The turns 161 in the first layer 162 are spaced a fixed distance apart from each other. In other words, the distance between the first and second turns is the same as the distance between the second and third turns in the first layer 162.
[0018]
[0023] At a certain point, the winding direction in the secondary winding 160 is reversed so that one turn 165 in the first layer 162 directly faces the second longitudinal endpoint 116. Then, a turn 161 is added in the second layer 163 so that one turn 166 in the second layer 163 directly faces the second longitudinal endpoint 116. The turn 161 is added in the second layer 163 and extends from turn 166 toward the second far end 115. The turns 161 in the second layer 163 are spaced a certain distance apart from each other. The turns 161 in the second layer 163 may rest directly on the turns in the first layer 162 (as shown in the figure, so that the centerlines of the conductors are aligned vertically), or the turns 161 may be offset between the first layer 162 and the second layer 163 (completely or partially offset, etc.). The certain distance between the turns in the first layer 162 and the turns in the second layer 163 may be the same. After completing the second layer 163, additional layers (e.g., third and fourth layers, fifth and sixth layers, etc.) may be added in the same manner. Regardless of whether additional layers are added or not, after winding the final turn 161 around the core portion 110, the conductor reaches the second secondary lead wire, which is then connected to terminal 168. Terminal 168 may include a solder pad, a ball-grid array portion, a through pin, etc. The number of turns 161 in each layer may be between 10 and 40, such as 24 turns 161 in the first layer 152 and 24 turns 161 in the second layer 153.
[0019]
[0024] The primary winding 150 and the secondary winding 160 are preferably configured such that the transformer has a 1:1 ratio, but other ratios are also possible. For example, the number of turns in turn 151 may be equal to the number of turns in turn 161, thereby resulting in a 1:1 ratio. The number of turns in turn 151 does not have to be equal to the number of turns in turn 161. For example, turn 151 may be twice the number of turns in turn 161. In addition, one or more additional windings may be in parallel with the secondary winding 160 to form a transformer with multiple outputs.
[0020]
[0025] The primary winding 150 and secondary winding 160 are configured such that turns 155 and 156 face turns 165 and 166 to form a winding-to-winding capacitor. If additional layers exist (beyond layers 152, 153, 162, and 163), the additional facing turns also form part of the winding-to-winding capacitor. This configuration of the primary winding 150 and secondary winding 160 allows for a relatively small capacitance of the winding-to-winding capacitor formed by 155, 156, 165, and 166. For example, the winding-to-winding capacitance can be between approximately 0.1 and 1.5 pF (e.g., 0.7 pF). The reduction in winding-to-winding capacitance can reduce noise in the open-loop LLC converter. In "core and bobbin" designs, an increase in winding-to-winding capacitance may be observed between the primary and secondary windings, and the embodiments herein can result in a reduction in winding-to-winding capacitance.
[0021]
[0026] Furthermore, the leakage inductance generated by the configuration of the primary winding 150 and the secondary winding 160 can be controlled, increasing the tolerance between transformers 100 (e.g., less than 10%). Core and bobbin type transformers have an even higher tolerance for leakage inductance (e.g., 30%), which can lead to more inaccurate circuit behavior between units. Moreover, the leakage inductance in transformer 100 can be relatively large, between 10 and 12 μH. This is much larger than what is seen in core and bobbin type transformers (e.g., 2 to 4 μH). By increasing the leakage inductance, external matching inductors can be eliminated, thereby simplifying the circuit and reducing costs.
[0022]
[0027] Figure 5 is a circuit diagram modeling the transformer 100 according to the embodiment. The modeling of the transformer 100 is C p (Capacity of primary winding 150), R p (DC resistance of primary winding 150), L lk (Leakage inductance), R c (Core-loss resistor), L m(Magnetization inductance), C m (Inter-winding capacitance), R s (DC resistance of the secondary winding 160), and C s (Capacitance of the secondary winding 160) can be performed by taking into account. As discussed above, L lk can be made relatively large (for example, between 10 and 12 μH, such as 11 μH). Furthermore, as discussed above, C m (Inter-winding capacitance) can be made relatively small (for example, between 0.1 and 15.0 pF, such as 0.7 pF). To give an example of other values for the transformer 100, C p = 3.5 pF, R p = 0.4 Ω, R c = 2.5 kΩ, L m = 100 μH, R s = 0.4 Ω, C s = 3.5 pF.
[0023]
[0028] FIG. 6 is a flowchart 600 of a method of assembling a transformer according to an embodiment. For illustrative purposes, embodiments of the method will be described with respect to the transformer 100. The steps may be executed in a different order or repetitively. For example, step 620 may be executed before step 610, or the execution of these steps may overlap in time.
[0024]
[0029] In step 610, the primary winding 150 is disposed around the core portion 110, i.e., wound. The primary winding 150 can be wound starting from the first turn 151 closest to the first distal end 112, continuing to add turns 151 in the first layer 152, and extending toward the first longitudinal end point 113. Thereafter, the winding direction is reversed, turns 151 are added in the second layer 153, and extended in the opposite direction toward the first distal end 112. Adjacent turns 151 can be spaced apart by a certain distance. Additional layers may be added (for example, the third and fourth layers, the fifth and sixth layers, etc.).
[0025]
[0030] In step 620, the secondary winding 160 is positioned, i.e., wound, around the core portion 110. The secondary winding 160 can be wound by starting with the first turn 161 closest to the second far end 115, continuing to add turns 161 in the first layer 162, and extending toward the second longitudinal end 116. Then, the winding direction is reversed, and turns 161 are added in the second layer 163, extending toward the second far end 115 in the opposite direction. Adjacent turns 161 can be spaced a certain distance apart. Additional layers may be added (e.g., third and fourth layers, fifth and sixth layers, etc.).
[0026]
[0031] In step 630, the upper core portion 140 can be attached to the first side core portion 120 and / or the second side core portion 130. For example, adhesive may be used to maintain the gaps between the upper core portion 140 and the first side core portion 120, and between the upper core portion 140 and the second side core portion 130. Optionally, step 630 may be performed after steps 610 and 620. Manufacturing can be simplified by adding the upper core portion 140 after the primary winding 150 and secondary winding 160 have been placed on the core portion 110.
[0027]
[0032] Furthermore, it will be understood by those skilled in the art that various modifications can be made and equivalents can be substituted without departing from the scope of the novel technology disclosed herein. In addition, many modifications can be made to the teachings of the novel technology herein without departing from that scope to adapt them to specific situations or materials. Therefore, the novel technology herein is not intended to be limited to the specific technology disclosed, but to include all technologies that fall within the scope of the attached claims.
Claims
1. It is a transformer, A core portion comprising a first longitudinal region extending between a first far end and a first longitudinal endpoint of the core, and a second longitudinal region adjacent to the first longitudinal region and extending between a second far end and a second longitudinal endpoint of the core, A primary winding arranged around a first longitudinal region of the core portion, wherein the primary winding comprises a plurality of layers, each layer comprises a plurality of turns, and adjacent turns in each layer are arranged at a certain distance from each other; A secondary winding arranged around a second longitudinal region of the core portion, wherein the secondary winding comprises a plurality of layers, each layer comprising a plurality of turns, and adjacent turns in each layer are arranged at a certain distance from each other; Equipped with, Multiple turns of the primary winding begin near the first far end and are wound around the first longitudinal region, extending toward the first longitudinal endpoint in the first layer, then reversing direction and extending in the opposite direction toward the first far end, thereby forming two turn layers in the second layer, the second layer being arranged around the first layer. Multiple turns of the second winding begin near the second far end and are wound around the second longitudinal region, extending toward the second longitudinal endpoint in the first layer, then reversing direction and extending in the opposite direction toward the second far end in the second layer, so that the second layer is positioned around the first layer. A first portion of the capacitor is formed within the primary winding by one turn from each layer directly facing the first longitudinal endpoint. A transformer in which, in one turn from each layer directly facing the second longitudinal endpoint, the second portion of the capacitor is formed within the secondary winding.
2. A transformer according to claim 1, wherein the primary winding has two layers and the secondary winding has two layers.
3. A transformer according to claim 1, wherein the centerlines of the wires in the first layer of the primary winding are substantially aligned with the centerlines of the wires in the second layer of the primary winding, and the centerlines of the wires in the first layer of the secondary winding are substantially aligned with the centerlines of the wires in the second layer of the secondary winding.
4. A transformer according to claim 1, further comprising: a first primary terminal, a second primary terminal, a first secondary terminal, a second secondary terminal, a first primary lead wire connected to the first primary terminal, a second primary lead wire connected to the second primary terminal, a first secondary lead wire connected to the first secondary terminal, and a second secondary lead wire connected to the second secondary terminal, The first turn in the innermost layer of the primary winding is connected to the first primary lead wire. The last turn in the outermost layer of the primary winding is connected to the second primary lead wire. The first turn in the innermost layer of the secondary winding is connected to the first secondary lead wire. A transformer in which the last turn in the outermost layer of the secondary winding is connected to the second secondary lead wire.
5. A transformer according to claim 1, wherein the capacitance of the capacitor is in the range of about 0.1 to 1.5 pF.
6. A transformer according to claim 5, wherein the capacity is approximately 0.7 pF.
7. A transformer according to claim 1, wherein the leakage inductance includes a range of 10 to 12 μH.
8. The transformer according to claim 1, further, A first side core portion connected to the first far end of the core portion, A second side core portion connected to the second far end of the core portion, The upper core portion is connected to the first side core portion and the second side core portion, A transformer equipped with a transformer.
9. A transformer according to claim 8, wherein the first side core portion is directly coupled to the first far end of the core portion, and the second side core portion is directly coupled to the second far end of the core portion.
10. A transformer according to claim 9, wherein the first side core portion and the core portion are combined, and the second side core portion and the core portion are combined.
11. A transformer according to claim 8, wherein the upper core portion is bonded to the first side core portion and the second side core portion.
12. A transformer according to claim 1, wherein the transformer constitutes a gate-driven transformer.
13. A transformer according to claim 1, wherein the first layer of the primary winding and the first layer of the secondary winding are wound directly on the core portion.
14. A transformer according to claim 1, wherein the primary winding includes about 10 to 40 turns, and the secondary winding includes about 10 to 40 turns.
15. A transformer according to claim 14, wherein the primary winding includes 24 turns and the secondary winding includes 24 turns.
16. A method for assembling a transformer including a core portion having a first longitudinal region defined by a first far end and a first longitudinal endpoint, a second longitudinal region defined by a second far end and a second longitudinal endpoint, and a core portion, A step of arranging a primary winding around the core portion, wherein the primary winding is started near the first far end of the core portion, turns are continuously added in the first layer extending toward the first longitudinal endpoint, the direction is reversed, turns are continuously added in the second layer extending in the opposite direction toward the first far end, and adjacent turns are spaced a certain distance apart. A step of arranging a secondary winding around the core portion, wherein the secondary winding is started near the second far end of the core portion, turns are continuously added in the first layer extending toward the second longitudinal endpoint, the direction is then reversed, turns are continuously added in the second layer extending toward the second far end in the opposite direction, and adjacent turns are spaced a certain distance apart. Methods that include...
17. A method according to claim 16, wherein the transformer further includes a first side core portion coupled to a first far end of the core portion and a second side core portion coupled to a second far end of the core portion, and the method further includes the step of attaching an upper core portion to the first side core portion and the second side core portion.
18. A method according to claim 17, wherein the step of attaching the upper core portion is performed after the step of arranging the primary winding and the step of arranging the secondary winding.
19. A method according to claim 17, wherein the step of attaching the upper core portion includes the step of forming a gap between the upper core portion and the first side core portion, and the step of forming a gap between the upper core portion and the second side core portion.
20. The method according to claim 16, further, The steps include forming a third and fourth layer within the primary winding, similar to forming the first and second layers of the primary winding, The steps include forming a third and fourth layer within the secondary winding, similar to forming the first and second layers of the secondary winding, Methods that include...