Switching power supply and its transformer

Abstract

The present invention provides a transformer, comprising a primary winding and a secondary winding. Wherein, the primary winding includes a first winding and a power supply winding, the first winding and the power supply winding are connected in series, and the first end of the switching tube is connected to the node between the first winding and the power supply winding; the secondary winding includes a second winding and a third winding, wherein, the third winding and the second winding are connected in series via a diode. The present invention also provides a switching power supply, in which the first winding and the power supply winding of the transformer cancel each other out the common-mode noise current from the primary to the secondary, and the second winding and the third winding cancel each other out the common-mode noise current from the secondary to the primary, reducing electromagnetic interference.

Description

Technical Field

[0001] The present invention relates to the technical field of power supplies, and particularly to a switching power supply and a transformer thereof. Background Art

[0002] With the rapid development of power electronics technology, people have put forward higher and higher requirements for the charging speed and volume of chargers, that is, the charging speed is required to be faster and the volume is required to be smaller. Among them, increasing the operating frequency of the switching power supply is an effective means to solve the charging speed and volume, but it will exacerbate the electromagnetic interference (EMI) of the switching power supply.

[0003] The transformer is an indispensable basic component in the switching power supply. The windings of the planar transformer are formed by stacking multiple printed circuit boards, which have the advantages of good consistency and low cost. The planar transformer also has advantages in height and volume. The thin structure of its conductors can reduce the influence brought by the high-frequency effect and thus reduce power consumption; and the tight coupling between the primary winding and the secondary winding can reduce the leakage inductance and thus reduce the loss, but it will bring a larger interlayer capacitance and thus exacerbate the electromagnetic interference.

[0004] In the prior art, generally, a shielding layer is provided between the primary winding layer and the secondary winding layer or a shielding layer is provided on the primary winding layer or the secondary winding layer to reduce the influence of electromagnetic interference. However, adjusting the number of turns of the shielding winding on the shielding layer cannot well balance the effects of conducted emission and radiated emission, and an ideal effect of suppressing electromagnetic interference cannot be obtained, which instead prolongs the development cycle of the switching power supply and reduces the development efficiency. When a shielding layer is provided on the primary winding layer or the secondary winding layer, a PCB board with more than 6 layers is required, and the cost is high. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is how to reduce electromagnetic interference only by using the primary winding and the secondary winding.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] According to one aspect of the present invention, a transformer is provided, including a primary winding and a secondary winding. Among them, the primary winding includes a first winding and a power supply winding, the first winding and the power supply winding are connected in series, and the first end of the switching tube is connected to the node between the first winding and the power supply winding; the secondary winding includes a second winding and a third winding, wherein the third winding and the second winding are connected in series via a diode.

[0008] Preferably, the second end of the first winding serves as the second end of the primary winding, and the first end of the power supply winding serves as the first end of the primary winding.

[0009] Preferably, the second end of the first winding is connected to the primary ground via a first capacitor, and the first end is connected to the first end of the switching transistor.

[0010] Preferably, the power supply winding includes a fourth winding and a fifth winding, and the fifth winding and the fourth winding are connected in series.

[0011] Preferably, the first end of the fourth winding is connected to the primary ground, the second end of the fourth winding is connected to the first end of the fifth winding, and the first end of the fifth winding is connected to the second end of the fifth winding via a first diode and a second capacitor, and the second end of the fifth winding is connected to the chip ground.

[0012] Preferably, the first end of the second winding serves as the first end of the secondary winding, the second end of the third winding serves as the second end of the secondary winding, and the second end of the third winding is connected to the secondary ground.

[0013] Preferably, the first end of the third winding is connected to the second end of the second winding via a second switching transistor, the positive electrode of the second switching transistor is connected to the first end of the third winding, and the negative electrode of the second switching transistor is connected to the second end of the second winding.

[0014] According to another aspect of the present invention, there is provided a switching power supply, including: a main circuit for converting an input voltage into an output voltage, the main circuit including the transformer, the switching transistor, the second switching transistor, and the third capacitor described above; a control circuit including a driving end, a current sampling end, and a power supply end; the switching transistor is connected in series between the first end of the first winding and the current sampling end of the control circuit; the control end of the switching transistor is connected to the driving end of the control circuit, and the power supply winding is connected to the power supply end of the control circuit via a first diode to supply power to the control circuit.

[0015] Preferably, at least one of the fourth winding and the fifth winding serves as a power supply winding to supply power to the control circuit.

[0016] The beneficial effects of the present invention are as follows:

[0017] For the switching power supply and the transformer provided by the embodiments of the present invention, the primary winding of the transformer includes a first winding and a power supply winding connected in series via a switching transistor, the secondary winding includes a second winding and a third winding connected in series via a diode, the first winding and the power supply winding cancel each other out the common-mode noise current from the primary to the secondary, and the second winding and the third winding cancel each other out the common-mode noise current from the secondary to the primary, reducing electromagnetic interference.

[0018] Furthermore, the transformer only has a primary winding and a secondary winding, which is not only simple in structure but also can realize the power supply to the control circuit.

[0019] Furthermore, the transformer does not need to be separately provided with a shielding winding and a power supply winding, and a PCB circuit board with 4 layers or less can be adopted, reducing the production cost.

[0020] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following takes the preferred embodiments of the present invention and combines with the drawings to describe in detail as follows. Description of the Drawings

[0021] Figure 1 Showing a schematic structural diagram of a transformer in the prior art;

[0022] Figure 2 Showing a schematic circuit diagram of a switching power supply to which a transformer in the prior art is applied;

[0023] Figure 3 Showing a schematic structural diagram of a transformer provided by an embodiment of the present invention;

[0024] Figure 4 Showing a schematic circuit diagram of a switching power supply to which the transformer of the embodiment of the present invention is applied. Detailed Embodiments

[0025] The following combines the drawings and embodiments to further describe in detail the specific embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0026] Figure 1 Showing a schematic structural diagram of a transformer in the prior art; Figure 2 Showing a schematic circuit diagram of a switching power supply to which a transformer in the prior art is applied. As Figure 1 and Figure 2 shown, the switching power supply in the prior art includes a main circuit 110 and a control circuit 120. Among them, the main circuit 110 includes a transformer T1, a switching transistor Q, a first capacitor C1, a second capacitor C2, a third capacitor C3, and a first diode D1 and a second switching transistor. The transformer T1 includes a primary winding, an auxiliary winding N2, a secondary winding N3, and a shielding winding N4. Among them, the primary winding includes a first winding N1 and a fifth winding N5.

[0027] The first end of the first winding N1 is connected to the second end of the fifth winding N5, and the second end of the first winding N1 is used as the second end of the primary winding; the first end of the fifth winding is used as the first end of the primary winding. The first end is the same-name end, and the second end is the different-name end, but it is not limited thereto.

[0028] Among them, the first end of the primary winding of transformer T1 is connected to the current sampling terminal CS of the control circuit via the switching transistor Q, and the second end of the primary winding is connected to the primary ground GND via the first capacitor C1. The control terminal of the switching transistor Q is connected to the driving terminal Gate of the control circuit. The first end of the auxiliary winding N2 is connected to the primary ground GND via the first diode D1 and the second capacitor C2, and the second end is connected to the primary ground GND. The node between the first diode D1 and the second capacitor C2 is connected to the power supply terminal VDD of the control circuit to provide the supply voltage VDD to the control circuit. The first end of the shielding winding N4 is connected to the primary ground GND, and the second end is suspended to reduce electromagnetic interference. The first end of the secondary winding N3 of transformer T1 is connected to the secondary ground SGND via the second switching transistor and the third capacitor C3, and the second end of the secondary winding N3 is connected to the secondary ground SGND.

[0029] The transformers in the prior art adopt a sandwich structure and require a separate shielding winding and auxiliary winding, with a complex structure and high cost.

[0030] Figure 3 The structural schematic diagram of the transformer provided by the embodiment of the present invention is shown; Figure 4 The circuit schematic diagram of the switching power supply to which the transformer of the embodiment of the present invention is applied is shown. As Figure 3 and Figure 4 shown, the switching power supply includes a main circuit 210 and a control circuit 220.

[0031] Among them, the main circuit 210 includes a transformer T2, a switching transistor Q, a first capacitor C1, a second capacitor C2, a third capacitor C3, and a first diode D1 and a second switching transistor. The transformer T2 includes a primary winding Pri and a secondary winding Sec.

[0032] In this embodiment, the primary winding Pri includes a first winding N1 and a power supply winding, and the first winding N1 and the power supply winding are connected in series; the secondary winding Sec includes a second winding N2 and a third winding N3, wherein the third winding N3 and the second winding N2 are connected in series via a diode D.

[0033] Specifically, the center tap of the primary winding Pri outputs the first winding N1 and the power supply winding connected in series, and the center tap of the secondary winding Sec outputs the second winding N2 and the third winding N3 connected in series. The first winding N1 and the power supply winding have the same number of turns and the same wire diameter; the second winding N2 and the third winding N3 have the same number of turns and the same wire diameter.

[0034] In this embodiment, the second end of the first winding N1 serves as the second end of the primary winding Pri, and the first end of the power supply winding serves as the first end of the primary winding Pri. The first end of the winding is the same-name end, and the second end is the different-name end, but it is not limited thereto.

[0035] The second end of the first winding N1 is connected to the primary ground GND via the first capacitor C1, and the first end is connected to the first end of the switching transistor Q. The second end of the switching transistor Q is connected to the current sampling terminal CS of the control circuit 220.

[0036] In this embodiment, the power supply winding includes a fourth winding N4 and a fifth winding N5, and the fifth winding N5 and the fourth winding N4 are connected in series. Specifically, the first end of the fourth winding N4 is connected to the primary ground GND, the second end of the fourth winding N4 is connected to the first end of the fifth winding N5, and the first end of the fifth winding N5 is connected to the second end of the fifth winding N5 via the first diode D1 and the second capacitor C2, and the second end of the fifth winding N5 is connected to the chip ground.

[0037] The first end of the second winding N2 serves as the first end of the secondary winding Sec, the second end of the third winding N3 serves as the second end of the secondary winding Sec, and the second end of the third winding N3 is connected to the secondary ground SGND. The first end of the third winding N3 is connected to the second end of the second winding N2 via a second switching transistor, the positive electrode of the second switching transistor is connected to the first end of the third winding N3, and the negative electrode of the second switching transistor is connected to the second end of the second winding N2. In this embodiment, the second switching transistor is, for example, the second diode D2.

[0038] The control circuit 220 includes a driving terminal Gate, a current sampling terminal CS, a power supply terminal VDD, and a grounding terminal GND.

[0039] In this embodiment, the switching transistor Q is connected in series between the first end of the first winding N1 and the current sampling terminal CS of the control circuit 220; the control end of the switching transistor Q is connected to the driving terminal Gate of the control circuit 220, and the power supply winding is connected to the power supply terminal VDD of the control circuit via the first diode D1 to supply power to the control circuit 220.

[0040] At least one of the fourth winding N4 and the fifth winding N5 serves as a power supply winding to supply power to the control circuit 220. The number of turns of the fourth winding N4 and the fifth winding N5 can be different, and different turn ratios are set according to the magnitude of the supplied power supply voltage. The embodiment of the present invention adopts a two-winding structure. The primary winding forms the first winding and the power supply winding through a center tap, and the secondary winding forms the second winding and the third winding through a tap. The first winding N1 and the power supply winding have the same number of turns and the same wire diameter, and can cancel each other out the common-mode noise current from the primary to the secondary; the second winding N2 and the third winding N3 have the same number of turns and the same wire diameter, and can cancel each other out the common-mode noise current from the secondary to the primary, thereby reducing electromagnetic interference. See Figure 4, the common-mode noise current from the primary to the secondary flows out of the first common-mode parasitic capacitance Cps1 and then flows into the second common-mode parasitic capacitance Cps2, forming a common-mode current loop inside the transformer, so that the common-mode noise current does not enter the power grid, thereby reducing electromagnetic interference.

[0041] The switching power supply and its transformer provided by the embodiments of the present invention. The primary winding of the transformer includes a first winding and a power supply winding connected in series via a switching tube. The secondary winding includes a second winding and a third winding connected in series via a diode. The first winding and the power supply winding cancel out the common-mode noise current from the primary to the secondary, and the second winding and the third winding cancel out the common-mode noise current from the secondary to the primary, reducing electromagnetic interference.

[0042] Furthermore, the transformer only has a primary winding and a secondary winding, which is not only simple in structure but also can supply power to the control circuit.

[0043] Furthermore, the transformer does not need to be provided with a separate shielding winding and a power supply winding, and a PCB circuit board with 4 layers or less can be used, reducing production costs.

[0044] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0045] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A transformer, characterized in that, it includes a primary winding and a secondary winding, wherein, the primary winding includes a first winding and a power supply winding, the first winding and the power supply winding are connected in series, and the first end of the switching tube is connected to the node between the first winding and the power supply winding, and the second end of the switching tube is connected to the current sampling end of the control circuit; the number of turns of the first winding and the power supply winding is the same, and the wire diameter is consistent; the power supply winding includes a fourth winding and a fifth winding, the fourth winding and the fifth winding are connected in series; the first end of the fourth winding is connected to the primary ground, and the second end is connected to the first end of the fifth winding; the first end of the fifth winding is also connected to the positive electrode of the first diode, and the second end is connected to the chip ground end; the negative electrode of the first diode is connected to the second end of the fifth winding through the second capacitor, and the negative electrode of the first diode is also connected to the power supply end of the control circuit; the secondary winding includes a second winding and a third winding, wherein, the third winding and the second winding are connected in series via a diode; the number of turns of the second winding and the third winding is the same, and the wire diameter is consistent.

2. The transformer according to claim 1, characterized in that, the second end of the first winding serves as the second end of the primary winding, and the first end of the power supply winding serves as the first end of the primary winding.

3. The transformer according to claim 1, characterized in that, the second end of the first winding is connected to the primary ground via the first capacitor, and the first end is connected to the first end of the switching tube.

4. The transformer according to claim 1, characterized in that, the first end of the second winding serves as the first end of the secondary winding, the second end of the third winding serves as the second end of the secondary winding, and the second end of the third winding is connected to the secondary ground.

5. The transformer according to claim 4, characterized in that, the first end of the third winding is connected to the second end of the second winding via the second switching tube, the positive electrode of the second switching tube is connected to the first end of the third winding, and the negative electrode of the second switching tube is connected to the second end of the second winding.

6. A switching power supply, characterized in that, it includes: a main circuit for converting an input voltage into an output voltage, the main circuit includes a transformer, a switching tube, a second switching tube and a third capacitor as described in any one of claims 1-5; a control circuit, the control circuit includes a driving end, a current sampling end and a power supply end; the switching tube is connected in series between the first end of the first winding and the current sampling end of the control circuit; the control end of the switching tube is connected to the driving end of the control circuit, and the power supply winding is connected to the power supply end of the control circuit via the first diode to supply power to the control circuit.

7. The switching power supply according to claim 6, characterized in that, at least one of the fourth winding and the fifth winding serves as a power supply winding to supply power to the control circuit.

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