Quasi-planar transformer structure

Abstract

The invention relates to a quasi-planar transformer, which may include: a first winding including one or more turns of a wire; a second winding comprising one or more turns of conductive traces disposed on the printed circuit board; and a magnetic core positioned relative to the first winding and the second winding so as to provide a magnetic flux path coupling the first winding and the second winding. The first winding may be a primary winding having a first half wound in a clockwise direction on a first side of the printed circuit board and a second half wound in a counter-clockwise direction on a second side of the printed circuit board, where the first half and the second half are formed from a single continuous wire. The single continuous wire may pass through an opening in the printed circuit board. The first half and the second half of the primary winding may be secured to the printed circuit board.

Description

Background Art

[0001] The flyback converter is a frequently used power converter topology. The flyback converter includes a flyback transformer, which in a true technical sense is actually a coupled inductor. The flyback transformer operates differently from a conventional forward mode power transformer. For example, the primary and secondary windings of the flyback transformer conduct alternately rather than simultaneously. In addition, an air gap may be introduced in the magnetic flux path to allow storage of energy. Summary of the invention

[0002] For various reasons, including the differences described above, conventionally constructed transformers may be suboptimal when used in flyback converter applications. Alternative transformer configurations and construction techniques are disclosed herein that may produce improved transformers for flyback operation. Additionally, some aspects of these transformers and construction techniques may also be applied to transformers used in non-flyback applications.

[0003] A quasi-planar transformer may include: a first winding including one or more turns of a conductor; a second winding including one or more turns of a conductive trace disposed on a printed circuit board; and a magnetic core positioned relative to the first winding and the second winding so as to provide a magnetic flux path coupling the first winding and the second winding. The first winding may be a primary winding having a first half wound in a clockwise direction on a first side of the printed circuit board and a second half wound in a counterclockwise direction on a second side of the printed circuit board, wherein the first half and the second half are formed by a single continuous conductor. The single continuous conductor may pass through an opening in the printed circuit board. The first half and the second half of the primary winding may be fixed to the printed circuit board.

[0004] The second winding may be a secondary winding formed on a first plurality of layers of the printed circuit board, and the first plurality of layers may be interconnected by vias passing through at least the first plurality of layers of the printed circuit board. The quasi-planar transformer may also include a tertiary winding formed on a second plurality of layers of the printed circuit board, and the second plurality of layers may be interconnected by vias passing through at least the second plurality of layers of the printed circuit board.

[0005] The magnetic core may include an E core and an I core fixed to the E core, the first winding and the second winding being arranged in a winding window defined by the E core and the I core. The magnetic core may include an air gap between a central leg of the E core and the I core.

[0006] The winding window defined by the E-core and the I-core can be higher than the height of the assembly including the first winding and the second winding, and the assembly including the first winding and the second winding can be arranged in the winding window away from the air gap. The quasi-planar transformer can also include a notch located in the central leg of the E-core, and the printed circuit board can include a tab mounted in the notch. One or more through holes connecting one or more layers of the printed circuit board can be arranged in the tab. The printed circuit board can also include a notch located near the tab, and the size of the notch can be determined to define an opening for a continuous wire used to form the first winding to pass through the printed circuit board. One or more internal corners of the E-core that define the winding window can be formed to include a curved channel.

[0007] A quasi-planar transformer may include one or more turns of a continuous wire segment wound in a first direction on a first side of a printed circuit board and one or more turns of the continuous wire segment wound in a second direction opposite to the first direction on a second side of the printed circuit board, wherein the continuous wire segment passes through the printed circuit board. The transformer may also include at least one printed winding, the printed winding including one or more turns of a conductive trace located on the printed circuit board. The wound primary winding and the printed circuit board may be disposed within a magnetic core that provides a magnetic flux path coupling the wound primary winding and the at least one printed winding.

[0008] The magnetic core may include an E-core having a center column that passes through the printed circuit board, the at least one printed winding, and the wound primary winding. The height of the center column of the E-core may define an air gap in the magnetic flux path, and the printed circuit board may be disposed as far away from the air gap as possible within a core window defined by the E-core. The E-core may define a slot, and the printed circuit board may define a tab disposed within the slot. The continuous wire segment may pass through the printed circuit board at least partially within the slot. The continuous wire segment may pass through the printed circuit board near the slot.

[0009] The at least one printed winding may include a secondary winding formed on a first plurality of layers of the printed circuit board. The first plurality of layers may be interconnected by through holes passing through at least the first plurality of layers of the printed circuit board. The through holes passing through at least the first plurality of layers may be located in the tab. The at least one printed winding may also include a tertiary winding formed on a second plurality of layers of the printed circuit board. The second plurality of layers may be interconnected by through holes passing through at least the second plurality of layers of the printed circuit board. The through holes passing through at least the second plurality of layers may be located in the tab. One or more inner corners of the E-core may be formed to include a curved channel.

[0010] A method of assembling a quasi-planar transformer may include passing a continuous wire through an opening in a printed circuit board having one or more printed circuit traces defining one or more printed circuit windings of the quasi-planar transformer; winding the continuous wire in a first direction to form a first half of a wire wound winding on a first side of the printed circuit board; and winding the continuous wire in a second direction opposite the first direction to form a second half of the wire wound winding on a second side of the printed circuit board. The method may also include securing the first half and the second half of the winding to the printed circuit board. The continuous magnetic wire may be a self-bonding wire, and securing the first half and the second half of the winding may include applying heat to the assembly.

[0011] The method may also include arranging the assembly including the printed circuit board and the first winding half and the second winding half in a magnetic core, the magnetic core providing a magnetic flux path between the wire-wound winding and the one or more printed circuit windings. The magnetic core may define an air gap, and arranging the assembly including the printed circuit board and the first winding half and the second winding half in the magnetic core includes positioning and fixing the assembly as far away from the air gap as possible within a window defined by the magnetic core. The method may also include arranging the assembly including the printed circuit board and the first winding half and the second winding half in a magnetic core, the magnetic core providing a magnetic flux path between the wire-wound winding and the one or more printed circuit windings. The magnetic core may define an air gap, and arranging the assembly including the printed circuit board and the first winding half and the second winding half in the magnetic core may also include positioning and fixing the assembly as far away from the air gap as possible within a window defined by the magnetic core.

[0012] The quasi-planar transformer may be assembled according to any of the above methods. The one or more printed circuit windings may include secondary windings formed on a first plurality of layers of the printed circuit board, and the first plurality of layers may be interconnected by vias passing through at least the first plurality of layers of the printed circuit board. The one or more printed circuit windings may include tertiary windings formed on a second plurality of layers of the printed circuit board, and the second plurality of layers may be interconnected by vias passing through at least the second plurality of layers of the printed circuit board.

[0013] The quasi-planar transformer assembled by the above method may include a magnetic core, the magnetic core including an E core and an I core fixed to the E core, and the first winding and the second winding are arranged in a winding window defined by the E core and the I core. The magnetic core may define an air gap between the central leg of the E core and the I core. The winding window defined by the E core and the I core may be higher than the height of the assembly including the first winding and the second winding. The assembly including the first winding and the second winding may be arranged in the winding window away from the air gap. The E core may define a recess in the central leg of the E core, and the printed circuit board may include a tab mounted in the recess. One or more through holes connecting one or more layers of the printed circuit board may be arranged in the tab. The printed circuit board may also include a recess located near the tab. The size of the recess may be determined to define an opening through which a continuous wire for forming the first winding passes through the printed circuit board. One or more internal corners of the E core defining the winding window may be formed to include a curved channel.

[0014] A magnetic core for use with a printed circuit board transformer may include one or more internal corners of the magnetic core formed to include a curved channel that serves as a strain relief and helps position a printed circuit board within a core window defined by the core. The magnetic core may be an E-core. The center column of the E-core may define a recess that is configured to receive a complementary tab of a printed circuit board of the printed circuit board transformer. The center column of the E-core may be shorter than the outer legs of the E-core so that when assembled with an I-core, the resulting core has an air gap. The core may be made of a ferrite material. A printed circuit board transformer may include a printed circuit board having one or more turns of conductive traces disposed thereon and a magnetic core as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of an exemplary flyback converter is shown.

[0016] Figure 2 The PCB layers of a planar transformer are shown.

[0017] Figure 3 A magnetic core for a planar transformer is shown.

[0018] Figure 4 The assembly of a planar transformer is shown.

[0019] Figure 5 A schematic diagram of a quasi-planar transformer is shown.

[0020] FIG. 6A to FIG. 6B A plan view and a cross-sectional view of a quasi-planar transformer PCB assembly are shown.

[0021] 7A to 7CVarious arrangements for passing the magnet wire of a wound primary winding through the PCB assembly of a quasi-planar transformer are shown.

[0022] FIG. 8A to FIG. 8D The construction of a wound primary winding for a quasi-planar transformer is shown.

[0023] Fig. 9 The construction of a quasi-planar transformer is shown.

[0024] FIG. 10A to FIG. 10B The magnetic flux associated with a quasi-planar flyback transformer is shown.

[0025] Fig.11 A core configuration is shown for a planar transformer including but not limited to a quasi-planar transformer.

[0026] Fig.12 A PCB assembly configuration is shown for a planar transformer including but not limited to a quasi-planar transformer. DETAILED DESCRIPTION

[0027] In the following description, for the purpose of explanation, many specific details are set forth in order to provide a thorough understanding of the disclosed concepts. As part of this description, some of the drawings in the drawings of the present disclosure represent structures and devices in block diagram form for simplicity. For the sake of clarity, not all features of actual implementations are described in the present disclosure. In addition, the language used in the present disclosure is selected for readability and instructional purposes and has not been selected to describe or limit the disclosed subject matter. Instead, the attached claims are intended for this purpose.

[0028] Various embodiments of the disclosed concepts are illustrated by way of example, and are not limited to individual drawings, in which similar reference numerals indicate similar elements. For simplicity and clear illustration, reference numerals are repeated in different drawings to indicate corresponding or similar elements, where appropriate. In addition, many specific details are shown in order to provide a full understanding of the specific implementation described herein. In other cases, methods, procedures, and components are not described in detail to avoid blurring the related functions described. Mentioning "one", "a kind of" or "another" embodiment in the present disclosure is not necessarily the same or different embodiments, and this means at least one. A given drawing may be used to illustrate more than one embodiment or more than one type of features of the present disclosure, and all elements in the drawings may not be required for a given embodiment or type. When provided in a given drawing, the reference numeral refers to the same element throughout several drawings, but it may not be repeated in each drawing. Unless otherwise specified, the drawings are not drawn to scale, and the proportions of certain components may be enlarged to better illustrate the details and features of the present disclosure.

[0029] Figure 1An exemplary flyback converter 100 is shown, which has its coupled inductor TX1, also known as a "flyback transformer", including a primary winding P1 and a secondary winding S1. An air gap can be introduced in the magnetic circuit of the flyback transformer core to achieve the desired inductance for energy storage. In operation, when the switch Q1 is closed, the flyback transformer current ramps up in the primary winding P1. When Q1 is turned off, energy is transferred to the output load via the V_ output bus through the secondary winding S1 and the rectifier diode D2. The filter capacitor C2 can be used to smooth the output DC bus. A clamp circuit including capacitor C1, diode D1 and resistor R1 can be used to dissipate energy stored in the leakage inductance to limit the voltage spike caused by the switching operation. In some designs, an active clamp circuit can be used to recover some of the energy that would otherwise be lost due to the above operation. The flyback converter shown is exemplary, and variations of the configuration shown are possible. However, these variations and detailed operation of the flyback converter are beyond the scope of this document.

[0030] The flyback transformer TX1 is an important element of the flyback converter. In some applications, in addition to the primary winding P1 and the secondary winding S2 described above, several auxiliary windings may also be wound on the same core. These auxiliary windings may be used, for example, to provide various internal DC bias voltages for the control circuit system. The flyback transformer may also include one or more "dummy" shield windings to reduce circulating common mode currents, which may be used, for example, to meet electromagnetic interference ("EMI") compliance requirements. For the purposes of this disclosure, such auxiliary windings and "dummy" shield windings are described as "tertiary windings". In addition, enhanced insulation may be provided between the primary side winding and the secondary side winding to meet various institutional safety requirements, such as the requirements of organizations such as Underwriters Laboratories (UL). In some applications, this may be achieved by using triple insulated wire or barrier tape winding and multiple layers of insulation tape at the isolation boundary. Additionally or alternatively, there are several well-known safety agency-approved insulation systems in the field of transformer design.

[0031] Due to these and other design complexities, the cost of wirewound transformers continues to rise significantly. Most of the cost is associated with the winding process rather than the materials. As labor costs continue to rise, in many cases, the transformer can be the most expensive part of the flyback converter. In addition to these cost issues, wirewound transformers can also have large variations in parameters such as leakage inductance and parasitic capacitance. This variation can cause corresponding variations in the efficiency and EMI performance of the flyback converter.

[0032] Unlike wire-wound transformers, planar transformers use a multi-layer printed circuit board ("PCB") to form the windings. A PCB core material or a thick resin layer (commonly known as prepreg) can be used to provide reinforced insulation between the primary and secondary windings. The primary and secondary winding turns can be formed by copper traces of a specific width along the magnetic path. Figure 2 An example of a 12-layer PCB that can be used in a flyback transformer is shown. The transformer shown uses multi-level interleaving. The winding structure in the above example is as follows:

[0033] - Layers L3, L4, L9 and L10 feature secondary winding (S1) traces. Each layer includes one turn, and the traces in these four layers are connected in series through plated through-holes to form a 4-turn secondary winding.

[0034] - Layers L2, L5, L8 and L11 feature tertiary winding traces. Each layer includes one turn, and the traces in these four layers are connected in series through vias to form a 4-turn tertiary winding.

[0035] - Layers L1, L6, L7 and L12 feature a primary winding (P1) trace. Each layer comprises 4 turns, and they are connected in series to form a 16-turn primary winding.

[0036] Referenced above Figure 2 The described PCB can be placed in a suitable ferrite core to form a flyback transformer. Figure 3 An exemplary ferrite core 300 is shown, which includes an E-core 302 (so named due to its E-shaped cross-section) and an I-core or plate 301 (also named by reference to its shape). The core can be configured so that there is an air gap between the center column of the E-core 302 and the surface of the I-core 301 to provide the desired magnetic properties (i.e., inductance) for energy storage in a flyback transformer application. Alternatively, for other applications, a planar transformer can be constructed without this gap.

[0037] Figure 4 The assembly of an exemplary planar transformer is shown. Winding 404 can be formed on a printed circuit board 403. The printed circuit board 403 can include slots to allow the E core 402 and the I core 401 to be arranged around the winding. The cores can be secured with glue, spring clips 405 as shown, or other suitable means. Copper pins or pins from another conductive material ( Figure 4 Not shown, but in Figures 7 to 8 below. Fig. 9 ) can be inserted into the termination hole for interconnection, and the structure can be wrapped with polyester tape for integrity. Moreover, various core geometries can be used in such planar transformer designs, including, for example, EQ, EE, EP, etc.

[0038] Planar transformers (such as those described above) can provide a compact and low-profile flyback transformer that is simple and, therefore, relatively inexpensive to build. However, such planar transformer designs may suffer from high eddy current losses. More specifically, because in a flyback converter, the primary and secondary windings are alternately conducting, there is always a non-conducting winding near the conducting winding. Because in planar transformer designs, the windings typically use relatively wide PCB traces, the non-conducting winding may suffer from high eddy current losses. Additionally, in flyback transformer applications, the magnetic field in the air gap can cause current flow in confined areas of all windings, further increasing losses. Therefore, although such planar transformer designs provide a simple and cost-effective construction, they may be inefficient due to these (and potentially other) losses.

[0039] In order to potentially overcome these deficiencies of prior art planar transformers while still achieving the cost and simplicity benefits associated with planar designs, a quasi-planar transformer design as described in more detail below can be employed. A quasi-planar flyback transformer can use a multi-layer PCB similar to the multi-layer PCB used in a conventional planar transformer for a secondary winding and a tertiary winding combined with a primary winding wound with magnetic wire. The magnetic wire can be a Litz type wire to reduce high frequency losses in the primary winding. The PCB can incorporate enhanced insulation by using a glued joint for the secondary winding. In at least some embodiments, a continuous primary winding without any joints can form an interlaced or sandwiched winding (as described in more detail below). In other words, a PCB containing a secondary (and tertiary) winding can be sandwiched between the two halves of the primary winding without any physical connection or joint between the two halves of the primary winding.

[0040] The following description explains the construction of an exemplary quasi-planar transformer. Figure 5 An exemplary schematic diagram of a quasi-planar transformer 500 is shown. The primary winding can have 16 turns, divided into two equal parts in P1 and P2, each having 8 turns. (Other turns can be used depending on the requirements of a particular application.) The center point between P1 and P2 is shown as A. As described above, the primary winding can be continuous so that A is not a connection, but simply the midpoint of the winding. The tertiary winding (e.g., the bias power supply winding) can have 4 turns, divided into two equal parts P3 and P4, each consisting of 2 turns. (Other turns can be used depending on the requirements of a particular application.) The center point of the connection between P3 and P4 is shown as B. The secondary winding can have 4 turns, divided into two equal parts S1 and S2, each consisting of 2 turns. (Other turns can be used depending on the requirements of a particular application.) The center point of the connection between S1 and S2 is shown as C. Connections B and C can be formed through vias in a printed circuit board, as described in more detail below.

[0041] Fig. 6A A plan view 600a of an exemplary PCB 603 is shown, and Figure 6B A cross-sectional view through PCB 603 is shown. In the example shown, a four-layer PCB can be used to accommodate the secondary winding and the tertiary winding. In other embodiments, more or fewer layers may be appropriate, depending on the specific winding design, which may include more layers, more turns per layer, etc. In any case, in this example, the second and third PCB layers may include windings S1 and S2, while the first and fourth PCB layers may include tertiary windings P3 and P4. Nodes B and C may be formed using plated through-holes 606. The through-hole 606b for connecting C is made to pass only through the second and third layers, otherwise buried in PCB 603. In other words, through-hole C is not seen in the outer layers of PCB 603, thereby meeting the enhanced insulation requirements of various safety agencies. In addition, the traces of primary windings S1 and S2 can be kept away from the edge of the PCB and away from the through-hole 606a for connecting B at a certain minimum distance, which can be specified by various safety agencies. Via 606a for connection B may pass through all four PCB layers, but a minimum separation distance d may be provided between the via and the traces of S1 and S2 and via 606b for connection C. The above construction is exemplary only, as there are many alternative ways to construct such a PCB while meeting appropriate safety requirements.

[0042] Now go to Figure 6B , showing a cross-sectional view 600b. Starting from the top, layer 607a can be an additional insulating layer, such as an insulating tape, in addition to the PCB itself. This insulating layer can provide insulation for the winding layer P3 (the above-mentioned "first" layer) from components outside the PCB. It can be seen that the through hole 606a connects this first layer (tertiary winding P3) to the fourth / bottom layer with the tertiary winding P4. Below the PCB layer with the tertiary winding P3 is an insulating layer 608, below which is the above-mentioned "second" PCB layer, which includes the secondary winding S1 and the insulator 610. Below this layer is another insulating layer 609, followed by the above-mentioned "third" PCB layer, which includes the secondary winding S2 and the insulator 610. As shown, the through hole 606b for the connection C between the secondary winding halves S1 and S2 only passes through the necessary inner layers. Further down is the additional insulating layer 608, below which is the above-mentioned "fourth" PCB layer including the tertiary winding P4. It can be seen that via 606a connects the "first" and "fourth" PCB layers through all intermediate layers.

[0043] The material thickness of the reinforced insulation layers 608 and 609 may be dictated by various safety agencies. For example, for UL reinforced insulation requirements, a thickness >0.4mm is required if a single layer of prepreg is used. Alternatively, if each layer is approved as a basic insulator, three separate thinner prepreg layers may be stacked to meet the requirement. The width of the void-free seal along the edge of the PCB may need to have a required width specified by the relevant safety agency. The glued joint may also need to be certified by such safety agencies. In any case, well-known processes have been established in the industry to manufacture such multi-layer PCBs that meet applicable reinforced insulation requirements.

[0044] As described above, a quasi-planar transformer may include a continuous primary winding divided into two equal parts sandwiching a PCB assembly. To achieve this, the magnet wire may be passed through an opening created for the center leg of the core through the PCB assembly. This may be achieved, for example, by incorporating a slot along the perimeter of the inner contour of the PCB. There are a variety of possible configurations, and in Fig. 7A , Figure 7B and Figure 7C Several examples are shown in .

[0045] Fig. 7A A first configuration 700a is shown, wherein a PCB assembly 703a is disposed in an E core 702a. Fig. 7A It also shows the above Figure 4 The interconnect pins 711 are provided in the terminal holes in the PCB assembly 703a. ) An additional insulating layer 712 (see Figure 6B 607a / 607b). As best seen in the enlarged area, core 702a may have slots 714a formed therein for reasons discussed below with reference to Fig.12 A rectangular slot 713a may also be provided in the PCB assembly 703a having a width and depth at least as large as the maximum diameter of the primary magnet wire, thereby allowing the magnet wire to pass through a hole in the interior of the PCB assembly 703a, as described below with respect to FIG. 8A to FIG. 8D Shown in more detail.

[0046] Figure 7B A second configuration 700b is shown, wherein a PCB assembly 703b is disposed in an E core 702b. Figure 7B It also shows the above Figure 4 The interconnect pins 711 are provided in the termination holes in the PCB assembly 703b. ) An additional insulating layer 712 (see Figure 6B 607a / 607b). As best seen in the enlarged area, core 702b may have slots 714b formed therein for reasons discussed below with reference to Fig.12A cutout 713b in the PCB assembly 703a and a portion of the core slot 714b may also be provided which may have a combined width at least as large as the maximum diameter of the primary magnet wire, thereby allowing the magnet wire to pass through the hole in the center of the PCB assembly 703b, as described below with reference to FIG. 8A to FIG. 8D Shown in more detail.

[0047] Figure 7C A third configuration 700c is shown, wherein a PCB assembly 703c is disposed in an E core 702c. Figure 7C It also shows the above Figure 4 The interconnect pins 711 are provided in the termination holes in the PCB assembly 703c. ) An additional insulating layer 712 (see Figure 6B 607a / 607b). As best seen in the enlarged area, core 702c may have slots 714c formed therein for reasons discussed below with reference to Fig.12 The rectangular slot 714c in the center post of the core 702c can have a depth greater than the maximum diameter of the primary magnet wire, thereby allowing the magnet wire to pass through the hole in the center of the PCB assembly 703c, as described below with respect to FIG. 8A to FIG. 8D Shown in more detail.

[0048] The above arrangement is merely exemplary, and there are many alternative configurations that can accomplish the same purpose of passing magnet wire through a PCB.

[0049] FIG. 8A to FIG. 8D The construction of a wound primary winding for a quasi-planar transformer is shown. Fig. 8A Initially, the magnet wire 815 for the primary winding may be passed through the PCB assembly 803, for example using the method described above with respect to 7A to 7C Sufficient wire length may be left at both ends (i.e., on either side of the PCB assembly 803) to allow for winding of the respective halves P1 and P2 of the primary winding. Figure 8B As shown in , the primary coil P1 can be wound on a first side of the PCB assembly 803 so that the inner diameter of the coil is not less than the inner diameter of the PCB opening (for the center column of the core) and the outer diameter of the coil does not extend beyond the outer edge of the PCB. In the example shown, the cross-sections of the coil, PCB assembly, and opening through the PCB are circular, but other shapes may be used as appropriate, in which case the above inner diameter may be understood to describe the size of the area defined by the coil and / or the opening through the PCB. In any case, a specific winding direction or phase (e.g., clockwise or counterclockwise) should be maintained for the P1 coil winding.

[0050] like Figure 8BAs shown in , by pulling the free wire end 815b, the formed coil P1 coil can be pressed against the surface of the PCB assembly 803 surface. Figure 8C As shown in FIG. 8 , another primary coil P2 can be wound on the other side of the PCB 803. Coil P2 can be wound in an opposite direction or phase relative to the first coil P1. Thus, if P1 is wound clockwise, P2 can be wound counterclockwise, and vice versa. The length of the free wire can be selected so that after completing the necessary number of turns of winding P2, coil P2 sits flush on the PCB 803, as shown in FIG. Figure 8C As a result, a continuous primary winding is formed in which the two windings P1 and P2 are naturally connected in series without any joints because they are formed by the same continuous length of wire. Various techniques can be used to glue the two primary windings P1 and P2 to the PCB 803 to hold them in a fixed position. One such exemplary technique can be the use of self-bonding wire, which causes the wire to stick to adjacent turns and the PCB 803 after applying heat. Heat can be applied during the winding process or as a post-process. Several winding techniques can achieve the desired winding stack through an automated process.

[0051] Using insulated magnet wire can simplify the assembly process and eliminate the need for multiple discrete insulators to prevent insulation breakdown between the primary winding and the core. One such type of wire is PFA wire, which uses a basic insulation layer with excellent tensile strength. Alternatively, magnet wire can be used with a discrete insulation mechanism. In any case, the finished coil / PCB assembly 816 is Fig.8D , including connections between the windings and appropriate interconnect pins 711 as required.

[0052] Fig. 9 An assembly / construction process 900 for a quasi-planar transformer as described above is shown. First, a PCB assembly (920) with terminal pins may have magnet wires (922) passing therethrough, as described above with respect to Fig. 8A As described. One side of the primary coil (P1) can then be wound (924) followed by the other side primary coil (P2) being wound (926) in the opposite direction. This produces (928) a PCB assembly 816 which can then be placed within the core (930) where the core halves are secured by appropriate means to produce the final transformer 940. If the primary wire is not insulated, an external insulator 607a / 607b / 712 can be used between the primary coil and the ferrite core. If the primary wire is insulated, this external insulator can optionally be omitted.

[0053] Reference Fig. 9942, high eddy current losses may result if the coil assembly 816 is placed very close to the air gap 944 in the center leg of the magnetic core. Therefore, the window height of the E-core can be selected to be longer than the thickness of the coil assembly. (The window height is effectively defined by the inner length of the top and bottom legs of the E-core 902 that mate with the I-core 901. The center leg of the E-core 902 can be shorter than these outer legs to define the air gap 944, which is described below. Fig. 10A and Fig. 10B ) By selecting a window height for the E core that is greater than the height of the coil assembly 816, the coil assembly can be pushed down to the "bottom" surface of the core window, thereby maximizing the distance from the air gap 944 and preventing it from moving closer to the air gap. In some embodiments, a compressible foam pad can be used for this purpose, or the coil assembly 816 can be glued to the bottom surface of the E core. In other cases, the coil assembly 816 and the E core 902 can have dimensions that allow for a friction / interference fit to secure the coil assembly 816 to the "bottom" of the core window. (As described above, "bottom" refers to the "bottom" of the core window.) Fig. 9 , and may be in any orientation in an actual physical implementation. The point is that the PCB assembly 816 should be placed in the core as far away from the air gap 944 as possible.)

[0054] After placement of the I core 901, the combined core assembly may be secured by tape or glue or by retaining clips as described above with respect to Figure 4 As discussed. It should also be noted that the shape of the PCB and primary winding can be circular, oval, square or rectangular (or any other suitable shape), depending on the choice of core geometry. In addition, the examples shown (and other embodiments herein) show a PCB dedicated to a quasi-planar transformer, but the PCB assembly can also include other components. In such a configuration, connecting pins 711 may not be required, and PCB traces, through-holes or other interconnect technologies can be used to make connections from the coil to other components.

[0055] Fig. 10A and Fig. 10B A cross-sectional view of half of a quasi-planar transformer as described above is shown. The E core 1002 and the I core 1001 are joined to form an air gap 944. Disposed within the core window 1003 are the primary windings P1 and P2, the tertiary windings P3 and P4, and the secondary windings S1 and S2, all of which may be configured as described above. Fig. 10A The intensity of the edge flux originating from the air gap 944 in the center leg of the E-core 1002 is shown, with the strongest flux being in the air gap 944, decreasing rapidly where the air gap 944 meets the core window 1003, and continuing to decrease gradually across the core window 1003 as one moves away from the air gap 944. Fig. 10BThe direction vector 1050 of this edge flux is shown. This flux effect can cause the current in the winding to be pulled toward the top surface and thus increase the effective AC resistance of the winding, which in turn increases power losses. (In this context, "top" again refers to FIG. 10A to FIG. 10B ) To avoid or minimize this effect, the coil assembly can be kept as far away from the air gap 944 as possible. However, this spacing can be optimized to provide the best performance of the flyback transformer for a given design / application.

[0056] More specifically, the optimal spacing depends on various design factors, including, for example, the size of the wire used, the operating flux density, and the ratio of copper losses to core losses in a given design. To increase this space, a taller core can be used. The coil can then be pushed to the "bottom" side of the core window, and as the height of the core increases, the space between the coil and the air gap 944 also increases. This can help reduce the effects of edge flux on the coil. However, increasing the height of the core increases the volume of the core, which can result in higher core losses. A given quasi-planar transformer design can be optimized so that copper losses are reduced to an optimal level without an excessive increase in core losses. At this particular spacing, the best compromise between reduced copper losses and increased core losses is achieved. For any given design, the appropriate spacing can be determined by magnetic simulation or by experimentation in the context of an actual power converter design.

[0057] Fig.11 The E-core 1102 is shown in isometric view 1100a, plan view 1100b, and cross-sectional view 1100c. (Cross-sectional view 1100c includes PCB assembly 816 disposed within the core window and also shows the I-core 1101 in position, although air gap 944 has been omitted.) More specifically, Fig.11 A core construction technique is shown that can be used to maximize the core window width while not compromising the mechanical robustness of the ferrite core. Practical manufacturing techniques for such cores do not allow for sharp 90 degree angles, particularly internal angles, such as those defining the core window. As a result, the chamfer or curved radius (blend) between the "vertical" and "horizontal" sides of the core window can prevent the coil assembly 816 from resting on the "bottom" of the core window. (As above, the terms "vertical", "horizontal", and "bottom" refer to the vertical and horizontal sides of the core window.) Fig.11orientation, not necessarily the orientation in the physical implementation. To accommodate this, the window can be made wider than necessary so that on the bottom surface, there is enough space between the chamfers / curves to allow the PCB assembly to be located on the bottom of the core window. As an alternative, a curved channel 1160 can be formed at the inner edge of the core. This can allow the gap between the PCB assembly width and the internal ferrite core window width to be reduced, while also avoiding stress concentrations associated with the sharp edges of the ferrite core. The additional effective width of the core window, which will still allow the PCB assembly to rest securely on the bottom of the core window, can allow for a wider PCB width, and in turn, wider traces on the PCB, thereby reducing trace resistance and helping to achieve higher efficiency. In addition, the core construction technology does not have to be limited to the core construction techniques described above with respect to Figure 5 to Figure 1 0, but can also be combined with the above Figures 2 to 4 The conventional planar transformer is used.

[0058] Fig.12 A PCB assembly configuration for a planar transformer including, but not limited to, a quasi-planar transformer is shown. In order to reduce the size of the PCB 1203, the through holes connecting the different layers of the PCB 1203 may be shifted into the center column 1270 of the ferrite core 1202. More specifically, a recess 1271a may be formed in the center column that may accommodate a corresponding small tab 1271b on the PCB 1203 that extends into the recess 1271a. The interconnecting through holes may be disposed within the recess 1271a. As a result of this configuration, the overall size of the PCB 1203 may be reduced, and the length of the individual windings may also be reduced, thereby reducing the overall resistance and also helping to achieve higher efficiency. In addition, the construction technique need not be limited to the above-described construction techniques. Figure 5 to Figure 1 0, but can also be combined with the above Figures 2 to 4 The conventional planar transformer is used.

[0059] Exemplary embodiments of modified configurations of quasi-planar transformers and planar transformers have been described above. Such configurations can be used in a variety of applications, but may be particularly advantageous when used in conjunction with a flyback transformer, although both quasi-planar transformers and planar transformers as described herein can be advantageously applied to other converter topologies, including forward converters, resonant converters, and the like. Although many specific features and various embodiments have been described, it should be understood that the various features and embodiments may be combined into various arrangements in a particular implementation unless otherwise indicated as mutually exclusive. Therefore, the various embodiments described above are provided by way of example only and should not be construed as limiting the scope of the present disclosure. Various modifications and changes may be made to the principles and embodiments herein without departing from the scope of the present disclosure and without departing from the scope of the claims.

Claims

1. A quasi-planar transformer, comprising: a first winding, the first winding comprising one or more turns of a wire; a second winding comprising one or more turns of a conductive trace disposed on a printed circuit board; and A magnetic core is positioned relative to the first winding and the second winding to provide a magnetic flux path coupling the first winding and the second winding.

2. The quasi-planar transformer of claim 1 , wherein the first winding is a primary winding having a first half wound in a clockwise direction on a first side of the printed circuit board and a second half wound in a counterclockwise direction on a second side of the printed circuit board, wherein the first half and the second half are formed by a single continuous wire.

3. The quasi-planar transformer of claim 2, wherein the single continuous wire passes through an opening in the printed circuit board. 4 . The quasi-planar transformer of claim 3 , wherein the first half and the second half of the primary winding are fixed to the printed circuit board.

5. The quasi-planar transformer of claim 1, wherein the second winding is a secondary winding formed on a first plurality of layers of the printed circuit board, and the first plurality of layers are interconnected by vias passing through at least the first plurality of layers of the printed circuit board.

6. The quasi-planar transformer of claim 5, further comprising tertiary windings formed on a second plurality of layers of the printed circuit board, and the second plurality of layers are interconnected by vias passing through at least the second plurality of layers of the printed circuit board. 7 . The quasi-planar transformer according to claim 1 , wherein the magnetic core comprises an E core and an I core fixed to the E core, and the first winding and the second winding are arranged in a winding window defined by the E core and the I core.

8. The quasi-planar transformer according to claim 7, wherein: The magnetic core includes an air gap between a central leg of the E-core and the I-core; The winding window defined by the E core and the I core is higher than the height of an assembly including the first winding and the second winding; and The assembly including the first winding and the second winding is disposed within the winding window away from the air gap.

9. The quasi-planar transformer of claim 7, further comprising a recess in the center leg of the E-core, wherein the printed circuit board comprises a tab mounted within the recess, and wherein one or more through holes connecting one or more layers of the printed circuit board are disposed within the tab.

10. The quasi-planar transformer of claim 9, wherein the printed circuit board further comprises a notch located adjacent the tab, the notch being sized to define an opening through which a continuous conductor forming the first winding passes through the printed circuit board.

11. The quasi-planar transformer of claim 7, wherein one or more interior corners of the E-core defining the winding window are formed to include a curved channel.

12. A quasi-planar transformer, comprising: a wound primary winding comprising one or more turns of a continuous conductor segment wound in a first direction on a first side of a printed circuit board and one or more turns of the continuous conductor segment wound in a second direction opposite to the first direction on a second side of the printed circuit board, wherein the continuous conductor segment passes through the printed circuit board; and at least one printed winding comprising one or more turns of a conductive trace on the printed circuit board; The wound primary winding and the printed circuit board are disposed within a magnetic core, the magnetic core providing a magnetic flux path coupling the wound primary winding and the at least one printed winding.

13. The quasi-planar transformer of claim 12, wherein the magnetic core comprises an E-core having a center leg passing through the printed circuit board, the at least one printed winding, and the wound primary winding.

14. The quasi-planar transformer of claim 13, wherein the height of the center column of the E-core defines an air gap in the magnetic flux path, and the printed circuit board is disposed within a core window defined by the E-core as far as possible from the air gap.

15. The quasi-planar transformer of claim 13, wherein the E-core defines a slot and the printed circuit board defines a tab disposed within the slot.

16. The quasi-planar transformer of claim 15, wherein the continuous conductor segment passes through the printed circuit board at least partially within the slot.

17. The quasi-planar transformer of claim 15, wherein the continuous conductor segment passes through the printed circuit board adjacent the slot.

18. The quasi-planar transformer according to claim 15, wherein: the at least one printed winding comprising a secondary winding formed on a first plurality of layers of the printed circuit board; the first plurality of layers are interconnected by vias passing through at least the first plurality of layers of the printed circuit board; and The through-holes through at least the first plurality of layers are located in the tabs.

19. The quasi-planar transformer of claim 18, wherein: The at least one printed winding further comprises a tertiary winding formed on a second plurality of layers of the printed circuit board; the second plurality of layers are interconnected by vias passing through at least the second plurality of layers of the printed circuit board; and The through-holes through at least the second plurality of layers are located in the tabs.

20. The quasi-planar transformer of claim 13, wherein one or more interior corners of the E-core are formed to include a curved channel.

21. A method of assembling a quasi-planar transformer, the method comprising: passing a continuous conductor through an opening in a printed circuit board having one or more printed circuit traces defining one or more printed circuit windings of the quasi-planar transformer; winding the continuous wire in a first direction to form a first half of a wirewound winding on a first side of the printed circuit board; as well as The continuous conductor is wound in a second direction opposite the first direction to form a second half of the wirewound winding on a second side of the printed circuit board.

22. The method of claim 21, further comprising securing the first and second halves of the winding to the printed circuit board.

23. The method of claim 22, wherein the continuous magnet wire is a self-bonding wire and securing the first and second halves of the winding includes applying heat to the assembly.

24. The method of claim 22, further comprising disposing an assembly including the printed circuit board and the first and second winding halves within a magnetic core that provides a magnetic flux path between the wire-wound winding and the one or more printed circuit windings.

25. The method of claim 24, wherein the magnetic core defines an air gap, and wherein positioning the assembly including the printed circuit board and the first winding half and the second winding half within the magnetic core includes positioning and securing the assembly within a window defined by the magnetic core as far away from the air gap as possible.

26. The method of claim 21, further comprising disposing an assembly including the printed circuit board and the first and second winding halves within a magnetic core that provides a magnetic flux path between the wire-wound winding and the one or more printed circuit windings.

27. The method of claim 26, wherein the magnetic core defines an air gap, and wherein positioning the assembly including the printed circuit board and the first winding half and the second winding half within the magnetic core includes positioning and securing the assembly within a window defined by the magnetic core as far away from the air gap as possible.

28. A quasi-planar transformer assembled according to the method of claim 21.

29. The quasi-planar transformer of claim 28, wherein the one or more printed circuit windings include secondary windings formed on a first plurality of layers of the printed circuit board, and the first plurality of layers are interconnected by vias passing through at least the first plurality of layers of the printed circuit board.

30. The quasi-planar transformer of claim 29, wherein the one or more printed circuit windings include tertiary windings formed on a second plurality of layers of the printed circuit board, and the second plurality of layers are interconnected by vias passing through at least the second plurality of layers of the printed circuit board.

31. A quasi-planar transformer assembled according to the method of claim 24, wherein the magnetic core comprises an E core and an I core fixed to the E core, and the first winding and the second winding are arranged in a winding window defined by the E core and the I core.

32. The quasi-planar transformer of claim 31 , wherein: The magnetic core includes an air gap between a central leg of the E-core and the I-core; The winding window defined by the E core and the I core is higher than the height of an assembly including the first winding and the second winding; and The assembly including the first winding and the second winding is disposed within the winding window away from the air gap.

33. The quasi-planar transformer of claim 31, wherein: The E-core defines a recess in a central leg of the E-core; The printed circuit board includes a tab that fits within the recess; and One or more through holes connecting one or more layers of the printed circuit board are disposed in the tab.

34. The quasi-planar transformer of claim 33, wherein the printed circuit board further comprises a notch located adjacent the tab and sized to define an opening through which a continuous conductor forming the first winding passes through the printed circuit board.

35. The quasi-planar transformer of claim 31, wherein one or more interior corners of the E-core defining the winding window are formed to include a curved channel.

36. A magnetic core for use with a printed circuit board transformer wherein one or more interior corners of the magnetic core are formed to include a curved channel that acts as a strain relief and helps position a printed circuit board within a core window defined by the magnetic core.

37. The magnetic core of claim 36, wherein the magnetic core is an E-core.

38. The magnetic core of claim 37, wherein a center leg of the E-core defines a notch configured to receive a complementary tab of a printed circuit board of the printed circuit board transformer.

39. The magnetic core of claim 37, wherein the center leg of the E-core is shorter than the outside legs of the E-core such that when assembled with an I-core, the resulting core has an air gap.

40. The magnetic core of claim 36, wherein the core is made of a ferrite material.

41. A printed circuit board transformer, the printed circuit board transformer comprising: A printed circuit board, wherein one or more turns of conductive traces are provided on the printed circuit board; and A magnetic core wherein one or more interior corners of the magnetic core are formed to include a curved channel that acts as a strain relief and aids in positioning a printed circuit board within a core window defined by the ferrite core.

42. The printed circuit board transformer of claim 41, wherein the magnetic core is an E-core.

43. The printed circuit board transformer of claim 42, wherein a center post of the E-core defines a recess configured to receive a complementary tab of a printed circuit board of the printed circuit board transformer.

44. The printed circuit board transformer of claim 42, wherein the center leg of the E-core is shorter than the outside legs of the E-core such that when assembled with an I-core, the resulting core has an air gap.

45. The printed circuit board transformer of claim 41 wherein said core is made of a ferrite material.

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