A planar transformer and power conversion circuit

Abstract

This invention provides a planar transformer and a power conversion circuit, comprising a first composite winding layer, a second composite winding layer, a third composite winding layer, a fourth composite winding layer, and a primary winding, arranged sequentially from top to bottom. The first composite winding layer includes a first winding and a second winding; the second composite winding layer includes a third winding; the third composite winding layer includes a fourth winding; and the fourth composite winding layer includes a fifth winding and a sixth winding. The advantages of this invention are: it provides a planar transformer with a reasonable structure that can effectively suppress common-mode noise. This planar transformer does not have a shielding winding between the primary and secondary windings; by adjusting the structure of the secondary winding, it achieves the purpose of reducing common-mode noise, reducing the number of PCB layers, lowering production costs, and reducing debugging time, thus possessing good practical and application value.

Description

Technical Field

[0001] This invention relates to the field of switching power supply PCB transformer technology, and in particular to a planar transformer and power conversion circuit. Background Technology

[0002] Planar transformers, unlike wire-wound transformers, have the windings printed on a PCB, laminated together, and finally fitted with a magnetic core. This reduces the transformer's size while achieving the same function as a conventional wire-wound transformer. In flyback power supplies, planar transformers also suffer from common-mode noise due to interlayer capacitance and winding structure. Existing PCB planar transformers, similar to conventional wire-wound transformers, primarily address common-mode noise by adding a shielding layer between the primary and secondary windings. This causes the common-mode noise from the primary winding to the shielding layer and from the secondary winding to the shielding layer to cancel out to near zero, thus reducing common-mode noise. However, this method increases the number of PCB layers, increasing cost.

[0003] Improvements to existing technologies are needed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a planar transformer and power conversion circuit with reasonable structure, low cost, and effective reduction of common-mode noise, in order to address the shortcomings of the prior art.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a planar transformer, comprising a first composite winding layer, a second composite winding layer, a third composite winding layer, a fourth composite winding layer and a primary winding, wherein the first composite winding layer, the second composite winding layer, the secondary winding, the third composite winding layer and the fourth composite winding layer are arranged sequentially from top to bottom.

[0006] The first composite winding layer includes a first winding and a second winding, wherein the first winding is a primary winding and the second winding is at least a portion of a secondary shielding winding;

[0007] The second composite winding layer includes a third winding and a first feedback winding, wherein the third winding is at least a portion of the primary winding;

[0008] The third composite winding layer includes a fourth winding and a second feedback winding, wherein the fourth winding is at least a portion of the primary winding;

[0009] The fourth composite winding layer includes a fifth winding and a sixth winding, wherein the fifth winding is a secondary winding and the sixth winding is at least a portion of the secondary shielding winding.

[0010] Furthermore, the first-stage winding is at least a portion of the secondary winding; the second-stage winding is at least a portion of the secondary winding.

[0011] Furthermore, the primary winding includes a first winding layer, a second winding layer, a third winding layer, and a fourth winding layer, which are arranged sequentially from top to bottom, and the first end of the primary winding is located on the second winding layer or the third winding layer.

[0012] Furthermore, the second end of the primary winding is disposed in the second composite winding layer or the third composite winding layer.

[0013] Furthermore, the first end of the primary winding is connected to the moving potential point of the primary circuit, and the second end of the primary winding is connected to the stationary potential point of the primary circuit.

[0014] Furthermore, the first end of the first feedback winding is connected to the dynamic potential point of the secondary circuit, the second end of the first feedback winding is connected to the first end of the second feedback winding, and the second end of the second feedback winding is connected to the static potential point of the secondary circuit.

[0015] Furthermore, the winding direction of the first feedback winding is opposite to that of the second feedback winding.

[0016] Furthermore, the first end of the secondary shielding winding is connected to the static potential point of the secondary circuit, while the second end of the secondary shielding winding is left unconnected.

[0017] Furthermore, the second winding is disposed outside the first winding, and the sixth winding is disposed outside the fifth winding.

[0018] Furthermore, the first feedback winding is disposed outside the third winding, and the second feedback winding is disposed outside the fourth winding.

[0019] The beneficial effects of this invention are as follows: It provides a planar transformer with a reasonable structure that can effectively suppress common-mode noise. This planar transformer does not have a shielding winding between the primary and secondary windings. By adjusting the structure of the secondary winding, it achieves the purpose of reducing common-mode noise, reducing the number of PCB layers, reducing production costs, and reducing debugging time. It has good practical and application value. Attached Figure Description

[0020] The specific structure of the present invention will be described in detail below with reference to the accompanying drawings:

[0021] Figure 1 This is a schematic diagram of the circuit structure of the present invention;

[0022] Figure 2 This is a schematic diagram of the circuit structure of one embodiment of the power conversion circuit of the present invention;

[0023] Figure 3 This is a schematic diagram of the circuit structure of another embodiment of the power conversion circuit of the present invention;

[0024] Figure 4 This is a schematic cross-sectional view of the planar transformer of the present invention;

[0025] Figure 5 This is an EMI test diagram of the L1 line of the planar transformer of the present invention;

[0026] Figure 6 This is an N-line EMI test diagram of the planar transformer of the present invention;

[0027] 1-Primary circuit; 2-Secondary circuit; 3-Secondary shielding winding; 4-First feedback circuit; 5-Secondary feedback circuit;

[0028] 100-E tablets; 101-I tablets;

[0029] 211-First winding; 212-Second winding; 221-Third winding; 222-First feedback winding; 230-Primary winding; 241-Fourth winding; 242-Second feedback winding; 251-Fifth winding; 252-Sixth winding. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0033] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0035] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0036] To facilitate understanding of the embodiments of this application, some terms involved in the embodiments of this application will be introduced first below.

[0037] Static potential point: In a circuit network, the voltage potential amplitude at a network node remains relatively constant during circuit operation, without high-frequency jumps or oscillations. For example, the filter capacitors after rectification in the primary side circuit and the filter capacitors after rectification in the secondary side circuit; the positive or negative terminals of these capacitors and the network nodes directly connected to them are the static potential points.

[0038] Moving point in primary circuit: can refer to a circuit node or network on the primary side of the circuit topology that experiences voltage jumps as the primary switch is turned on and off, such as the node where the primary winding connects to the switch.

[0039] Moving point in secondary circuit: can refer to a circuit node or network on the secondary side of the circuit topology that has voltage jumps as the secondary rectifier switch (including diode) is turned on and off, such as the node where the secondary winding is connected to the rectifier diode.

[0040] Please see Figure 1 The power conversion circuit in the embodiments of this application typically includes a primary circuit, a secondary circuit, and a planar transformer. The planar transformer is disposed between the primary circuit and the secondary circuit. The primary circuit typically includes a rectifier unit and a primary filter capacitor, and the secondary circuit typically includes a filter capacitor and a filter rectifier unit.

[0041] When the voltage Vp on the primary side is higher than that on the secondary side, a negative charge Cps will be generated on the secondary side; when the voltage Vs on the secondary side is higher than that on the shielding layer, a positive charge Csp will be generated on the secondary side. Since Vp*cps and Vs*Csp are in opposite directions, they can cancel each other out when their voltages are equal.

[0042] This application includes two typical circuits, as shown below. Figure 2 The circuit structure shown and as Figure 3 The circuit structure shown is shown.

[0043] Please see Figure 2 A power conversion circuit includes a primary circuit, a secondary circuit, a planar transformer, and a feedback output circuit. The planar transformer is positioned between the primary and secondary circuits. The planar transformer includes a primary winding Np, a secondary winding Ns, and a feedback winding Na. The planar transformer is connected to the primary circuit via the primary winding Np, to the secondary circuit via the secondary winding Ns, and to the feedback output circuit via the feedback winding Ns. The secondary circuit includes a rectifier unit for the secondary winding Ns, and the feedback circuit includes a rectifier unit for the feedback winding Na. The rectifier unit for the secondary winding Ns is connected to the negative terminal of the secondary output, and the rectifier unit for the feedback winding Na is connected to the negative terminal of the feedback output. Because it is a flyback circuit, the winding direction of the primary winding of the planar transformer is opposite to that of the secondary winding.

[0044] Specifically, the primary circuit includes primary switching transistors QHS and QLS, resonant capacitor Cr, and primary current sensing resistor Rshunt; the secondary circuit includes synchronous rectification SR MOS and output filter capacitor Cout.

[0045] When the primary switch QHS is turned on, the primary switch QLS is turned off, and energy is stored in the primary winding and resonant capacitor Cr. The secondary winding is turned off. When the primary switch QHS is turned off, the primary switch QLS is turned on, the secondary winding is turned on, and energy is output to the load through the synchronous rectifier SR MOS and the output filter capacitor Cout.

[0046] Please see Figure 3 A power conversion circuit includes a primary circuit 1, a planar transformer, a secondary circuit 2, a secondary shielding winding 3, a first feedback circuit 4, and a second feedback circuit 5. The planar transformer is disposed between the primary circuit 1 and the secondary circuit 2. The planar transformer includes a primary winding Np, a secondary winding Ns, a first feedback winding T1D, and a second feedback winding T1E. The planar transformer is connected to the primary circuit 1 through the primary winding Np, to the secondary circuit 2 through the secondary winding Ns, to the first feedback circuit 4 through the first feedback winding T1D, and to the second feedback circuit 5 through the second feedback winding T1E. The secondary shielding winding 3 is connected to the stationary point of the secondary circuit 2. The secondary circuit 2 includes a secondary winding Ns rectifier unit, and the feedback circuit includes a feedback winding Na rectifier unit. The secondary winding Ns rectifier unit is connected to the secondary output positive terminal, and the feedback winding Na rectifier unit is connected to the feedback output positive terminal. Because it is a flyback circuit, the winding direction of the primary winding of the planar transformer is opposite to the winding direction of the secondary winding.

[0047] Please see Figure 4 A planar transformer 200 includes a first composite winding layer, a second composite winding layer, a third composite winding layer, a fourth composite winding layer, and a primary winding. The first composite winding layer, the second composite winding layer, the secondary winding, the third composite winding layer, and the fourth composite winding layer are arranged sequentially from top to bottom. The planar transformer also includes a magnetic core. In this embodiment, an EI type magnetic core is used, wherein the I-plate 101 is disposed at the bottom, the E-plate 100 is disposed at the top, and the air gap is more than 1.5mm away from the circuit board. The winding post of the E-plate 100 of the magnetic core may be provided with the first composite winding layer, the second composite winding layer, the third composite winding layer, the fourth composite winding layer, and the primary winding composed of multiple circuit boards.

[0048] Depending on the width of the circuit board, the number of turns and the line width of the primary winding can be adjusted so that the planar transformer can be used on 6-layer, 8-layer, or 10-layer boards.

[0049] In addition, the power can be expanded by adjusting the line width of the circuit board or adding a magnetic core, making the planar transformer suitable for flyback or hybrid flyback topology circuits of 45-200W.

[0050] Specifically, the first composite winding layer includes a first winding 211 and a second winding 212. The first winding 211 is a primary winding, and the second winding 212 is at least a portion of a secondary shielding winding. The second winding is disposed outside the first winding.

[0051] The second composite winding layer includes a third winding 221, which is at least a portion of the primary winding;

[0052] The third composite winding layer includes a fourth winding 241, which is at least a portion of the primary winding.

[0053] The fourth composite winding layer includes a fifth winding 251 and a sixth winding 252. The fifth winding 251 is a secondary winding, and the sixth winding 252 is at least a portion of the secondary shielding winding. The sixth winding is located outside the fifth winding.

[0054] The voltage of the secondary winding can be determined based on the number of turns of the first winding 211 and the fifth winding 251.

[0055] In addition, the first winding 211 and the fifth winding 251 can be configured as a series connection or a parallel connection as needed.

[0056] When the first winding 211 and the fifth winding 251 are connected in series, the first primary winding is at least a part of the secondary winding; the second primary winding is at least a part of the secondary winding.

[0057] The primary winding includes a first winding layer, a second winding layer, a third winding layer, and a fourth winding layer, arranged sequentially from top to bottom. The first end of the primary winding is located on either the second or third winding layer. The second end of the primary winding is located on either the second or third composite winding layer. The first end of the primary winding is connected to the dynamic potential point of the primary circuit, and the second end of the primary winding is connected to the static potential point of the primary circuit.

[0058] In this embodiment, the first end of the primary winding is disposed on the second winding layer, and is connected sequentially through the third winding layer, the first winding layer, the fourth winding layer, the second composite winding layer, and the second end of the primary winding disposed on the third composite winding layer.

[0059] Since the first end of the primary winding is connected to the potential dynamic point of the primary circuit, setting the first end of the primary winding in the second winding layer of the primary winding can keep the layer with large voltage changes away from the circuit layer where the secondary winding is located, effectively reducing the interference between the primary and secondary windings.

[0060] Since both the second and third composite winding layers are voltage rest points, placing the last two turns of the primary winding in the second and third composite winding layers can serve as a shield. Moreover, due to the relatively low voltage and small induced electric field in the secondary winding, common-mode interference can be significantly reduced.

[0061] The second composite winding layer also includes a first feedback winding 222, which is located outside the third winding 221; the third composite winding layer also includes a second feedback winding 242, which is located outside the fourth winding 241. It should be noted that "outer side" in the above description refers to the side of the winding post furthest from the magnetic core.

[0062] The first end of the first feedback winding 222 is connected to the dynamic potential point of the secondary circuit, the second end of the first feedback winding 222 is connected to the first end of the second feedback winding 242, and the second end of the second feedback winding 242 is connected to the static potential point of the secondary circuit.

[0063] Additional voltage can be supplied through the feedback winding, for example, to power small power devices such as the main control chip. The number of turns in the feedback winding is determined according to the power supply voltage required by the main control chip. The number of turns in the feedback winding = (power supply voltage * number of turns in the secondary winding) / output voltage.

[0064] To counteract the common-mode current, the winding direction of the first feedback winding 222 is opposite to that of the second feedback winding 242.

[0065] The first end of the secondary shielding winding is connected to the static potential point of the secondary circuit, and the second end of the secondary shielding winding is left unconnected.

[0066] The secondary shielding winding can adjust the junction capacitance between the primary and secondary windings, allowing them to cancel each other out.

[0067] In this embodiment, the primary winding, the first feedback winding 222 and the second feedback winding 242 are wound according to the phase, and can be wound in a clockwise direction or in a counterclockwise direction.

[0068] The number of turns and length of the secondary shielding winding can be adjusted according to the common-mode current of the primary and secondary windings, thereby achieving better common-mode noise suppression.

[0069] As can be seen from the above description, the beneficial effects of the present invention are as follows: It provides a planar transformer with a reasonable structure that can effectively suppress common-mode noise. The planar transformer does not have a shielding winding between the primary and secondary windings. By adjusting the structure of the secondary winding, the common-mode noise is reduced, the number of PCB layers is reduced, the production cost is reduced, and the debugging time is reduced. It has good practical and application value.

[0070] Experimental Example

[0071] The relationship between the length of the secondary shielding winding and the common-mode value is shown in Table 1.

[0072]

[0073] Table 1

[0074] Therefore, when the number of turns in the secondary shielding winding is 1.5, the common-mode rejection is optimal, and the optimal conduction test result is greater than 6dB.

[0075] Please see Figure 5 and Figure 6 , Figure 5 The waveform of the EMI test on the L1 line of the planar transformer is shown when the output voltage is 230V and the load is 20V 6A@120W full load.

[0076] Figure 6 The waveform of the EMI test on the N-line of the planar transformer is shown when the output voltage is 230V and the load is 20V 6A@120W at full load.

[0077] The EMI test results for L1 and N lines are shown in Table 2:

[0078]

[0079] Table 2

[0080] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A planar transformer, characterized by: It includes a first composite winding layer, a second composite winding layer, a third composite winding layer, a fourth composite winding layer, and a primary winding, which are arranged sequentially from top to bottom. The first composite winding layer includes a first winding and a second winding, wherein the first winding is a primary winding and the second winding is at least a portion of a secondary shielding winding; The second composite winding layer includes a third winding and a first feedback winding, wherein the third winding is at least a portion of the primary winding; The third composite winding layer includes a fourth winding and a second feedback winding, wherein the fourth winding is at least a portion of the primary winding; The fourth composite winding layer includes a fifth winding and a sixth winding, wherein the fifth winding is a secondary winding and the sixth winding is at least a portion of the secondary shielding winding; The first end of the secondary shielding winding is connected to the potential static point of the secondary circuit. The potential static point is a circuit node where the voltage amplitude remains relatively constant and there are no high-frequency jumps or oscillations. The second end of the secondary shielding winding is left floating. The second winding is disposed outside the first winding, and the sixth winding is disposed outside the fifth winding.

2. The planar transformer as described in claim 1, characterized in that: The first-stage winding is at least a portion of the secondary winding; the second-stage winding is at least a portion of the secondary winding.

3. The planar transformer as described in claim 2, characterized in that: The primary winding includes a first winding layer, a second winding layer, a third winding layer, and a fourth winding layer, which are arranged sequentially from top to bottom. The first end of the primary winding is located on the second winding layer or the third winding layer.

4. The planar transformer as described in claim 3, characterized in that: The second end of the primary winding is disposed in the second composite winding layer or the third composite winding layer.

5. The planar transformer as described in claim 4, characterized in that: The first end of the primary winding is connected to the dynamic potential point of the primary circuit, which is a circuit node whose voltage jumps as the secondary rectifier switch is turned on and off. The second end of the primary winding is connected to the static potential point of the primary circuit.

6. The planar transformer as described in claim 5, characterized in that: The first end of the first feedback winding is connected to the moving point of the secondary circuit, the second end of the first feedback winding is connected to the first end of the second feedback winding, and the second end of the second feedback winding is connected to the stationary point of the secondary circuit.

7. The planar transformer as described in claim 6, characterized in that: The winding direction of the first feedback winding is opposite to that of the second feedback winding.

8. The planar transformer as described in claim 7, characterized in that: The first feedback winding is disposed outside the third winding, and the second feedback winding is disposed outside the fourth winding.

9. A power conversion circuit, characterized in that: The planar transformer according to any one of claims 1-8 further includes a primary circuit, a secondary circuit, and a feedback circuit. The secondary circuit includes a secondary winding rectifier unit connected to the secondary output positive terminal. The feedback circuit includes a feedback winding rectifier unit connected to the feedback output positive terminal. The winding direction of the primary winding of the planar transformer is opposite to the winding direction of the secondary winding.

10. A power conversion circuit, characterized in that: The planar transformer according to any one of claims 1-8 further includes a primary circuit, a secondary circuit, and a feedback circuit. The secondary circuit includes a secondary winding rectifier unit connected to the secondary output negative terminal. The feedback circuit includes a feedback winding rectifier unit connected to the feedback output negative terminal. The winding direction of the primary winding of the planar transformer is opposite to the winding direction of the secondary winding.

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