Flyback transformer for pfc with an air gap in which permanent magnet is inserted

Abstract

The present invention provides a flyback transformer for PFC that can increase the effective magnetic flux within the air gap of the transformer and optimally manage the fringing flux, thereby reducing transformer losses and increasing efficiency, and enabling miniaturization, weight reduction, and increased current capacity. A flyback transformer for PFC according to the first invention of the present invention is a flyback transformer for a Power Factor Correction (PFC) function, comprising an air gap into which a permanent magnet is inserted having a magnetic pole direction positioned identically to the direction of the magnetic flux generated in the ferrite coil winding of the flyback transformer, wherein the air gap is formed inside the ferrite core of the flyback transformer, and the permanent magnet maintains a uniform magnetic potential distribution on both ends of the air gap and optimally manages the fringing flux to reduce transformer losses, increase efficiency, and achieve miniaturization.

Description

Technology Field

[0001] The present invention relates to a flyback transformer for PFC, and more specifically, to a flyback transformer for PFC that performs a Power Factor Correction (PFC) function, wherein a permanent magnet is inserted into the air gap of an inductor to optimize magnetic characteristics, thereby achieving miniaturization, weight reduction, high efficiency, and increased current capacity of the inductor. Background Technology

[0003] Recently, as the power consumption of various electronic devices such as TVs, laptops, and computers has increased, the power required for power supply units to power these devices is also rising. At the same time, along with the performance of electronic devices, miniaturization, high efficiency, low electromagnetic interference (EMI), and low cost are emerging as important requirements.

[0004] An inductor functions to supply high voltage to a load by applying a flyback pulse to the primary side through switching operation when a DC voltage is applied, and subsequently rectifying the boosted high voltage on the secondary side. Since the switching frequency of such inductors is high, it is common to use ferrite cores, which have low hysteresis and eddy current losses. However, ferrite cores have the disadvantage of easily becoming magnetically saturated due to the magnetic flux generated by the DC current. To compensate for this, methods such as inserting an air gap between the ferrite cores or increasing the core cross-sectional area are used. Inserting an air gap reduces the slope of the hysteresis curve, allowing more current to flow; however, losses within the air gap increase as the gap size increases, placing a limit on the size of the air gap. Furthermore, increasing the core cross-sectional area leads to an increase in the size of the inductor.

[0005] The magnetic flux generated by the coil windings in an inductor can be subdivided into effective magnetic flux, leakage flux, and fringing flux caused by the influence of the air gap. Among these, fringing flux is a phenomenon in which magnetic flux bulges outward when set within the air gap, increasing the effective area of ​​the air gap and decreasing the magnetic flux density. Since fringing flux is directly proportional to the length of the air gap, it is necessary to design the transformer by optimizing the fringing flux to improve performance. Prior art literature

[0007] Public Notice No. 10-1993-0007987 Flyback Transformer for Power Enhancement Registration No. 10-0160569 Flyback Transformer Registration No. 10-1934446 Magnetic Integrated Circuit and Method for Reducing Magnetic Flux Density by Phase Shift The problem to be solved

[0008] The present invention aims to provide a flyback transformer for PFC that can reduce losses and increase efficiency of the flyback transformer by increasing the effective magnetic flux within the air gap of the flyback transformer and optimally managing the fringing flux, thereby enabling miniaturization, weight reduction, and increased current capacity.

[0009] In addition, the present invention has another objective of providing a flyback transformer for PFC that can reduce manufacturing costs and reduce EMI by optimizing the magnetic characteristics of the flyback transformer.

[0010] The problems solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0012] A flyback transformer for PFC according to the first invention of the present invention is a flyback transformer for a Power Factor Correction (PFC) function, comprising an air gap into which a permanent magnet is inserted having a magnetic pole direction positioned identically to the direction of the magnetic flux generated in the ferrite coil winding of the flyback transformer, wherein the air gap is formed inside the ferrite core of the flyback transformer, and the permanent magnet maintains a uniform magnetic potential distribution on both ends of the air gap and optimally manages the fringing flux to reduce transformer losses, increase efficiency, and achieve miniaturization.

[0013] Preferably, the permanent magnet is coupled to the lower end of the upper core protrusion facing the lower core protrusion where the coil winding is wound, thereby forming an air gap.

[0014] Preferably, the permanent magnet is coupled to the upper part of the lower core protrusion on the side where the coil winding is wound to form an air gap.

[0015] Preferably, the permanent magnet is characterized by being positioned to maintain a uniform magnetic potential distribution on both ends of the air gap.

[0016] In addition, the flyback transformer for PFC according to the second invention of the present invention comprises: an upper core located at the top of the core; a lower core located at the bottom of the core and coupled with the upper core to form a closed magnetic circuit; an upper core protrusion protruding downward inward from the center of the upper core; a lower core protrusion protruding upward inward from the center of the lower core and facing the upper core protrusion to form a magnetic circuit; a ferrite coil winding wound around the lower core protrusion; a permanent magnet coupled to the lower end of the upper core protrusion; and an air gap formed between the permanent magnet and the lower core protrusion, wherein the magnetic pole direction of the permanent magnet is positioned in the same direction as the magnetic flux generated in the ferrite coil winding.

[0017] Preferably, the length of the air gap is characterized by being 0.05 to 2% of the length from the starting point of the upper core protrusion to the starting point of the lower core protrusion.

[0018] In addition, the flyback transformer for PFC according to the third invention of the present invention comprises: an upper core located at the top of the core; a lower core located at the bottom of the core and coupled with the upper core to form a closed magnetic circuit; an upper core protrusion protruding downward inward from the center of the upper core; a lower core protrusion protruding upward inward from the center of the lower core and facing the upper core protrusion to form a magnetic circuit; a ferrite coil winding and a secondary winding wound around the lower core protrusion; a permanent magnet coupled to the upper end of the lower core protrusion; and an air gap formed between the permanent magnet and the upper core protrusion, wherein the magnetic pole direction of the permanent magnet is positioned in the same as the direction of the magnetic flux generated in the ferrite coil winding. Effects of the invention

[0020] According to the present invention, by effectively placing a permanent magnet within the air gap of a flyback transformer, the following remarkable effects can be obtained.

[0021] First, according to the present invention, the effective magnetic flux of the flyback transformer is increased so that the size of the flyback transformer can be reduced by about 30% compared to the conventional one while maintaining the same performance, and thus, weight reduction can also be achieved.

[0022] Second, according to the present invention, the manufacturing cost can be significantly reduced by saving material costs through miniaturization.

[0023] Third, according to the present invention, losses in a flyback transformer can be reduced and efficiency increased by maintaining a uniform magnetic potential distribution within the air gap and optimally managing the fringing flux.

[0024] Fourth, according to the present invention, the current receiving capacity of a flyback transformer can be increased through optimized magnetic flux management.

[0025] Fifth, according to the present invention, improved magnetic flux management can prevent unnecessary current from being converted into heat and contribute to reducing the generation of electromagnetic waves.

[0026] Sixth, according to the present invention, the cross-sectional area of ​​the core can be reduced by half for the same power capacity, and a low-cost core material with a low maximum magnetic flux density (Bmax) can be selected, thereby increasing the design freedom of the flyback transformer.

[0027] The effects of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. Brief explanation of the drawing

[0029] FIG. 1 is a schematic diagram of a flyback transformer for a PFC having an air gap into which a permanent magnet is inserted according to a first embodiment of the present invention. FIG. 2 is a schematic diagram of a flyback transformer for a PFC having an air gap into which a permanent magnet is inserted according to a second embodiment of the present invention. FIG. 3 is a schematic diagram of a flyback transformer for a PFC having an air gap into which a permanent magnet is inserted according to a third embodiment of the present invention. FIG. 4 is a schematic diagram of a flyback transformer for a PFC having an air gap into which a permanent magnet is inserted according to the fourth embodiment of the present invention. Figure 5 is a table showing characteristic test data by permanent magnet placement position and direction according to the present invention. Figure 6 is a graph of characteristic test data by permanent magnet placement position and direction according to the present invention. FIG. 7 is an example of a hysteresis curve according to a first embodiment of the present invention. Specific details for implementing the invention

[0030] Further objects, features, and advantages of the present invention can be more clearly understood from the following detailed description and the accompanying drawings.

[0031] Before providing a detailed description of the present invention, it should be understood that the present invention is capable of various modifications and may have various embodiments, and that the examples described below and illustrated in the drawings are not intended to limit the present invention to specific embodiments, but rather include all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention.

[0032] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0033] The terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0034] Furthermore, in the description referring to the attached drawings, identical components are assigned the same reference numeral regardless of drawing symbols, and redundant descriptions thereof are omitted. In describing the present invention, if it is determined that a detailed description of related prior art could unnecessarily obscure the essence of the present invention, such detailed description is omitted.

[0035] The definitions of the key terms used in this invention are as follows.

[0036] PFC (Power Factor Correction): A technology that reduces power loss occurring during the power conversion process.

[0037] Flyback transformer: A combined flyback transformer with a gap core, in which an input voltage is applied to the primary winding during each cycle to store energy in the core gap, and then transfers the energy to the secondary winding to supply power to the load.

[0038] Air Gap: A non-magnetic space intentionally created inside the core of a flyback transformer, which serves to prevent magnetic saturation, control magnetic flux, and regulate voltage and current.

[0039] Fringing Flux: A phenomenon in which magnetic flux lines bulge outward from the air gap when magnetic flux is applied to the air gap, which increases the effective area of ​​the air gap and reduces the magnetic flux density.

[0041] According to one aspect of the present invention, a flyback transformer for PFC is provided, characterized by placing a permanent magnet within an air gap of a ferrite core.

[0042] Here, the direction of the magnetic poles of the permanent magnet is characterized by being located in the same direction as the magnetic flux generated in the coil winding.

[0043] In addition, the permanent magnet may be positioned on the opposite side of the side where the ferrite coil winding is wound, or on the side where the ferrite coil winding is wound.

[0044] In order to increase the effective magnetic flux of a transformer, improve efficiency, and increase current capacity, the present invention performed an air gap structure optimization simulation and conducted tests by placing permanent magnets at various locations to verify this. As a result of the tests, placing permanent magnets with poles identical to the magnetic flux direction on the cross-section of the air gap of the core in the same direction as the magnetic flux direction of the core exhibited the best characteristics. It was verified that by placing permanent magnets within the air gap in this manner, the magnetic potential distribution on both ends of the air gap is maintained uniformly, thereby optimally managing fringing flux, which reduces losses in the flyback transformer, increases efficiency, and enables miniaturization.

[0045] The present invention performed simulations using Maxwell software to find optimal conditions for cores of flyback transformers of various structures, and based on the simulation results, fabricated and evaluated prototypes in various cases. As a result of the evaluation, it was demonstrated that the amount of current that can be supplied to the flyback transformer changes significantly depending on the position of the permanent magnet within the air gap.

[0046] The present invention is based on improving the magnetic characteristics of a flyback transformer for PFC by inserting a permanent magnet into the air gap of a ferrite core.

[0047] Specifically, the present invention can be applied to a unidirectional flyback transformer and is characterized by arranging permanent magnets with poles in the same direction as the magnetic flux direction in the air gap section of the core in the same direction as the magnetic flux direction of the core of the flyback transformer.

[0048] FIG. 1 is a schematic diagram of a flyback transformer for a PFC having an air gap into which a permanent magnet is inserted according to a first embodiment of the present invention.

[0049] A flyback transformer for PFC having an air gap into which a permanent magnet is inserted according to a first embodiment of the present invention comprises: a top core (110) located at the top of the core that contributes to forming a magnetic circuit; a bottom core (120) located at the bottom of the core that combines with the top core (110) to form a closed magnetic circuit; a top core protrusion (130) protruding downward inward from the center of the top core (110); a bottom core protrusion (140) protruding upward inward from the center of the bottom core (120) and facing the top core protrusion (130) to form a magnetic circuit; ferrite coil windings (150-1, 150-2) wound around the bottom core protrusion (140); a permanent magnet (160) coupled to the center of the top core protrusion (130) to apply a bias magnetic field within the core; and the top core protrusion (130) of the top core (110) and the bottom core of the bottom core (120). It includes an air gap (170), which is a non-magnetic space formed between the protrusions (140).

[0050] According to the present invention, it is preferable that the length (B) of the air gap (170) be maintained at 0.05 to 2% of the length (A) from the starting point of the upper core protrusion (130) to the starting point of the lower core protrusion (140). According to the first embodiment, the length from the starting point of the upper core protrusion (130) to the starting point of the lower core protrusion (140) is 15 mm, and the length of the air gap (170) is 0.6 mm. FIGS. 1 to 4 show the length (B) of the air gap in an exaggerated manner to aid understanding.

[0051] If the air gap is too small, the margin for the core to store energy is reduced, causing the core to saturate easily at high currents and resulting in abnormal operation. Just before saturation, the magnetic flux changes rapidly, increasing hysteresis losses and eddy current losses, and the reduced energy storage prevents the supply of sufficient energy during the switching cycle. On the other hand, if the air gap is too large, magnetic flux leaks out of the core, reducing magnetic circuit efficiency. The magnetic circuit impedance decreases, reducing the primary winding inductance. This causes excessive current spikes during switching operations, and the prolonged energy storage time makes circuit control difficult during high-frequency operation. Additionally, increased leakage flux leads to severe external interference, and the difficulty in concentrating magnetic flux reduces energy transfer efficiency and causes heat generation.

[0052] Here, reference numeral 150-1 indicates the direction in which current penetrates the ground of the drawing at a specific location within the ferrite coil winding (150) in the direction of the first winding of the ferrite coil winding, and reference numeral 150-2 indicates the direction in which current penetrates the ground of the drawing at a specific location within the ferrite coil winding (150) in the direction of the second winding of the ferrite coil winding. This signifies a current flow direction opposite to that of 150-1. Reference numeral 121 is a through hole formed in the lower core, reference numerals 180-1 and 180-2 are pins connected to the winding, and the arrow drawn in the air gap (170) part signifies the direction of magnetic flux formed according to the current flowing through the winding.

[0053] Meanwhile, a permanent magnet (160) is coupled to the center of the upper core protrusion (130) to apply a bias magnetic field within the core. This can improve the saturation characteristics of the core and contribute to optimizing the inductance and efficiency of the flyback transformer. The N pole and S pole are indicated in the drawing.

[0054] According to the present invention, the connection between the upper core protrusion (130) of the ferrite core and the permanent magnet (160) must be precise to ensure stable performance and durability of the flyback transformer. The connection method may be selected considering the size and shape of the permanent magnet, the required mechanical strength, and the manufacturing process, and the following methods may be exemplified.

[0055] According to one embodiment of the present invention, a recess or pocket corresponding to the shape of a permanent magnet (160) is machined in the center of the upper core protrusion (130), and the permanent magnet (160) can be inserted into this recess or pocket to be physically fixed.

[0056] This groove can be precisely machined to match the outer contour of the permanent magnet and designed to allow the permanent magnet to be fully inserted into the core or partially exposed. Using this method, the positional stability of the permanent magnet is high, resistance to external forces is excellent, and the path of the magnetic circuit is predictable.

[0057] According to another embodiment of the present invention, the permanent magnet (160) can be fixed using an adhesive, such that it can be directly attached to the surface of the upper core protrusion (130) using an epoxy resin, a silicone-based adhesive, or other industrial high-strength adhesive. After cleaning the adhesive surface, the adhesive is applied and cured while fixed. Using this method, the application is easy with a simple process and can be cost-effective as no additional processing is required. The adhesive layer may also provide a small vibration absorption effect.

[0058] According to another embodiment of the present invention, a permanent magnet (160) can be pressed or fixed to an upper core protrusion (130) using a mechanical device such as a separate fixing clip, bracket, or casing. This can be assembled together primarily during the core assembly stage. Using this method, disassembly and reassembly are possible, and the magnet can be fixed immediately without adhesive curing time.

[0060] FIG. 2 is a schematic diagram of a flyback transformer for PFC having an air gap with a permanent magnet inserted according to a second embodiment of the present invention, FIG. 3 is a schematic diagram of a flyback transformer for PFC having an air gap with a permanent magnet inserted according to a third embodiment of the present invention, and FIG. 4 is a schematic diagram of a flyback transformer for PFC having an air gap with a permanent magnet inserted according to a fourth embodiment of the present invention.

[0061] The second embodiment of the present invention is mostly identical to the structure of the first embodiment, except that the permanent magnet (260) is coupled to the upper part of the lower core protrusion (240).

[0062] The third embodiment of the present invention differs in that the winding direction of the ferrite coil windings (350-1, 350-2) is opposite to that of the first embodiment, and the polarity of the permanent magnet (360) coupled to the lower end of the upper core protrusion (330) is opposite.

[0063] The fourth embodiment of the present invention is mostly identical to the structure of the third embodiment, except that the permanent magnet (460) is coupled to the upper part of the lower core protrusion (440).

[0065] Figure 5 is a table showing characteristic test data by permanent magnet placement position and direction according to the present invention.

[0066] If there are no permanent magnets in the core of the flyback transformer (Q'ty = 0), the magnetic flux density value decreases rapidly with increasing current. For example, at 0A the value is 145.1 Gauss, at 20A it is 89.1 Gauss, and at 25A there is no value, indicating that saturation starts quickly and sustains performance is low.

[0067] When three magnets are arranged (Q'ty = 3), a higher value is maintained even with an increase in current, and the operating range of the core can be extended by maintaining 124.5 Gauss even at 25A.

[0069] FIG. 6 is a graph of characteristic test data by permanent magnet placement position and direction according to the present invention, and is a graph of data tested on the characteristics of eight samples with different permanent magnet placement positions and directions.

[0070] The curves that remain flat at the top indicate that the magnetic flux value remains nearly constant even as the current increases, showing that the permanent magnet is positioned very effectively to suppress magnetic flux saturation and maintain performance.

[0071] Meanwhile, the curves that drop sharply from the intermediate current (8~15A) indicate that the permanent magnet is positioned to have general performance, and as the DC bias increases, saturation gradually occurs, causing the inductance to decrease and the core to approach saturation.

[0072] And the curves that drop rapidly from 10A or less indicate that the permanent magnets are positioned with low magnetic flux retention performance, and that the position / pole direction of the permanent magnets does not contribute to saturation suppression.

[0074] FIG. 7 is an example of a hysteresis curve according to a first embodiment of the present invention.

[0075] The curve width (B_r) and area represent the residual magnetic flux density (B_r) and core loss, respectively; a smaller area indicates lower core loss and higher efficiency. By arranging permanent magnets with poles aligned with the magnetic flux direction of the transformer core, the curve can be kept closer to vertical due to the effect of maintaining a constant magnetic flux density and delaying saturation.

[0076] In addition, the saturation magnetic field (B_s) saturates at approximately ±1.0 T, and due to the ferrite characteristics, a distinct nonlinear transition region is observed, and it can be seen that the inductance decreases sharply in the high current region due to saturation.

[0078] The flyback transformer according to the present invention means that by placing a permanent magnet within the air gap, the magnetic potential distribution on both ends of the air gap is maintained uniformly, and the fringing flux is optimally managed, thereby reducing losses, increasing efficiency, and achieving miniaturization of the flyback transformer.

[0079] The present invention effectively improves upon the fundamental limitations of conventional flyback transformers, namely magnetic saturation of the core and the resulting performance degradation. In particular, it is distinguished by maximizing the performance of the flyback transformer by actively controlling magnetic flux through the integration of permanent magnets within the air gap, rather than simply inserting an air gap or increasing the size of the core. This presents an original solution distinct from the core assembly methods, magnetic integration, and switching phase control discussed in existing patent literature.

[0080] In particular, the present invention has been confirmed to be effective for flyback transformers in the 200 to 500 W range.

[0081] The embodiments described in this specification and the accompanying drawings are merely illustrative of a part of the technical concept included in the present invention. Accordingly, since the embodiments disclosed in this specification are intended to explain, not limit, the technical concept of the present invention, it is obvious that the scope of the technical concept of the present invention is not limited by these embodiments. All variations and specific embodiments that can be easily deduced by a person skilled in the art within the scope of the technical concept included in the specification and drawings of the present invention should be interpreted as being included within the scope of the rights of the present invention. Explanation of the symbols

[0083] 110: Upper core 120: Lower core 130: Upper core protrusion 140: Lower core protrusion 150-1, 150-2: Ferrite coil windings 160: Permanent magnet 170: Air gap

Claims

Claim 1 A unidirectional flyback transformer performing a PFC function comprises: an upper core located at the top of the core; a lower core coupled with the upper core to form a closed magnetic circuit; an upper core protrusion protruding downward from the central part of the upper core; a lower core protrusion protruding upward from the central part of the lower core and facing the upper core protrusion; a ferrite coil winding and a secondary winding wound around the circumference of the lower core protrusion; and a permanent magnet directly coupled to one end of either the upper core protrusion or the lower core protrusion. A flyback transformer for a PFC comprising: an exposed magnetic pole surface of the permanent magnet and an air gap formed between the other end of the upper core protrusion and the lower core protrusion; wherein the ferrite coil winding is configured to generate a main magnetic flux in a central magnetic path including the upper core protrusion, the permanent magnet, the air gap, and the lower core protrusion upon the application of an input voltage so as to store magnetic energy in the air gap; wherein the secondary winding is configured to transfer the magnetic energy stored in the air gap to the load side; and wherein the permanent magnet is magnetized such that, based on the direction of travel of the main magnetic flux passing through the central magnetic path in the energy storage section where an input voltage is applied to the ferrite coil winding, the magnetic pole surface into which the main magnetic flux flows into the permanent magnet becomes the S pole and the magnetic pole surface out which the main magnetic flux flows out of the permanent magnet becomes the N pole, so that the direction of magnetic flux inside the permanent magnet coincides with the direction of travel of the main magnetic flux. Claim 2 A flyback transformer for a PFC according to claim 1, characterized in that the permanent magnet is directly coupled to the lower end of the upper core protrusion, and the air gap is formed between the lower pole surface of the permanent magnet and the upper end of the lower core protrusion. Claim 3 A flyback transformer for a PFC according to claim 1, characterized in that the permanent magnet is directly coupled to the upper end of the lower core protrusion, and the air gap is formed between the upper pole surface of the permanent magnet and the lower end of the upper core protrusion. Claim 4 A flyback transformer for a PFC according to claim 2, wherein a groove or pocket corresponding to the external shape of the permanent magnet is formed in the center of the lower part of the upper core protrusion, the permanent magnet is inserted into the groove or pocket and physically fixed, and at least a portion of the permanent magnet is exposed toward the air gap. Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete

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