CN217468172U - Transformer, power conversion circuit and adapter - Google Patents

Abstract

The embodiment of the application discloses a transformer, a power conversion circuit and an adapter, wherein the transformer comprises a first primary winding, a second primary winding, a secondary winding, a first shielding coil, a first shielding foil and a second shielding coil; the second primary winding is arranged around the periphery of the first primary winding; the secondary winding is arranged between the first primary winding and the second primary winding; the first shielding coil is arranged between the first primary winding and the secondary winding; the first shielding foil is arranged between the first shielding coil and the secondary winding; the second shielding coil is arranged between the secondary winding and the second primary winding. The transformer of the embodiment of the application has a good interference suppression effect, so that the transformer without the Y capacitor can be provided, the influence of leakage current on the touch sensitivity of a touch screen of electronic equipment is avoided, and meanwhile, the production cost can be reduced due to the fact that the Y capacitor is not provided.

Description

Transformer, power conversion circuit and adapter

Technical Field

The application relates to the field of switching power supplies, in particular to a transformer, a power conversion circuit and an adapter.

Background

In the related art, most of the electronic devices for home use have a power supply, which is usually a switching power supply. In order to solve the problem of electromagnetic interference, a Y capacitor is usually added between the primary and secondary of the transformer. However, due to the existence of the Y capacitor, a leakage current is generated between the primary coil and the secondary coil, and thus the touch screen of the electronic device is prone to touch inflexibility, crash and the like in a charging state.

SUMMERY OF THE UTILITY MODEL

The embodiment of the application provides a transformer, a power conversion circuit and an adapter, which can solve the technical problems in the related art.

In a first aspect, an embodiment of the present application provides a transformer, including a first primary winding, a second primary winding, a secondary winding, a first shielding coil, a first shielding foil, and a second shielding coil; the second primary winding is arranged around the periphery of the first primary winding; a secondary winding disposed between the first primary winding and the second primary winding; the first shielding coil is arranged between the first primary winding and the secondary winding and used for inhibiting conducted interference between the first primary winding and the secondary winding; the first shielding foil is arranged between the first shielding coil and the secondary winding and used for inhibiting the radiation interference of the first primary winding and the first shielding coil to the secondary winding; the second shielding coil is arranged between the secondary winding and the second primary winding and used for inhibiting conducted interference between the second primary winding and the secondary winding.

In some exemplary embodiments, the apparatus further comprises a second shielding foil disposed between the secondary winding and the second shielding coil for suppressing radiation interference of the second primary winding and the second shielding coil.

In some exemplary embodiments, the number of turns of the first primary winding is greater than the number of turns of the second primary winding.

In some exemplary embodiments, the number of turns of the first shield foil is 0.8-1.0 turn, and the first shield foil is disposed end-to-end insulated.

In some exemplary embodiments, the first primary winding is wound in 2-3 layers.

In some exemplary embodiments, the first primary winding, the first shield coil, and the secondary winding satisfy the following relational expressions: p1+ W1 ═ 2N; wherein P1 is the number of turns of the first primary winding, W1 is the number of turns of the first shield coil, and N is the number of turns of the secondary winding.

In some exemplary embodiments, one end of the first shielding coil is connected to a potential dead point of the first primary winding, and the other end of the first shielding coil is arranged in a floating manner; one end of the second shielding coil is connected with the potential quiescent point of the second primary winding, and the other end of the second shielding coil is suspended in the air; and said first shielding foil is arranged grounded.

In some exemplary embodiments, the coil further comprises a bobbin and a magnetic core, the bobbin has a winding slot and a magnetic core slot, and the first primary winding is wound in the winding slot; the magnetic core is at least partially accommodated in the magnetic core groove.

In a second aspect, an embodiment of the present application provides a power conversion circuit, including a transformer, a primary circuit, and a secondary circuit as described in any one of the above embodiments; the first primary winding is provided with a first end and a second end, the second primary winding is provided with a third end and a fourth end, and the second end is electrically connected with the third end; a primary circuit electrically connected to the first and fourth terminals; and the secondary circuit is electrically connected with two ends of the secondary winding.

In a third aspect, an embodiment of the present application provides an adapter including the power conversion circuit as described above.

Has the advantages that: the transformer comprises a first primary winding, a second primary winding, a first shielding foil and a second shielding foil, wherein the first shielding coil has a good suppression effect on conduction interference between the first primary winding and the second primary winding, the second shielding coil has a good suppression effect on conduction interference between the second primary winding and the second secondary winding, and the first shielding foil has a good suppression effect on radiation interference of the first primary winding. Secondly, because the transformer has a good interference suppression effect, the transformer in the embodiment of the application can cancel the Y capacitor bridged on the primary circuit and the secondary circuit, so that the transformer without the Y capacitor can be provided, the influence of leakage current on the touch sensitivity of the touch screen of the electronic equipment is avoided, and meanwhile, the production cost can be reduced due to the fact that no Y capacitor is provided.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required to be used in the embodiments will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic partial cross-sectional view of a transformer in one embodiment of the present application;

FIG. 2 is a schematic partial cross-sectional view of a transformer in another embodiment of the present application;

fig. 3 is a schematic diagram of a power conversion circuit according to an embodiment of the present application.

Description of reference numerals: 100. a transformer; 110. a first primary winding; 120. a second primary winding; 130. a secondary winding; 140. a first shield coil; 150. a first shielding foil; 160. a second shield coil; 170. a second shielding foil; 180. a coil bobbin; 180a, a winding slot; 190. an auxiliary winding; 190a, an insulating tape; 200. a power conversion circuit; 210. a primary circuit; 220. a secondary circuit.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In the related art, a primary winding of a transformer transfers energy to a secondary winding through a magnetic field. In order to increase the coupling of the transformer, reduce the leakage inductance, and improve the energy conversion efficiency, the transformer usually uses a sandwich winding method, i.e. the coil form of the transformer is primary coil-secondary coil-primary coil, and the secondary coil is sandwiched between the two primary coils. However, the voltage difference between different coils due to different voltages of the coils causes the generation of interlayer capacitance, and thus the electromagnetic interference of the transformer is serious.

To facilitate understanding of the embodiments of the present application, some terms related to the embodiments of the present application will be described first.

Electromagnetic Interference (EMI) refers to an Interference phenomenon generated after Electromagnetic waves and electronic components act, and includes two types, namely conduction Interference and radiation Interference.

Conducted interference refers to coupling (interfering) a signal on one electrical network to another electrical network through a conductive medium. Such as wires, conductive components of the device, power supplies, common impedances, ground planes, resistors, inductors, capacitors, and mutual inductors, are all possible transmission circuits that conduct interference.

Radiated interference refers to the coupling (interference) of an interfering source medium's signal to another electrical network in the form of an electromagnetic wave. For example, high frequency signal lines, pins of integrated circuits, various connectors, etc. may be radiation interference sources with antenna characteristics, which can emit electromagnetic waves and affect the normal operation of other systems or other subsystems in the system.

Potential quiescent point: the voltage potential amplitude of the network node in the circuit network keeps relatively constant in the working process of the circuit without high-frequency jump or oscillation.

As shown in fig. 1 and 2, a transformer 100 according to a first aspect of the present embodiment includes a primary winding, a secondary winding 130, a first shielding coil 140, a first shielding foil 150, and a second shielding coil 160. In order to reduce magnetic leakage, the primary winding includes a first primary winding 110 and a second primary winding 120, the first primary winding 110 is disposed at the innermost circumference, and the second primary winding 120 is disposed at the outermost circumference. Each winding of the transformer 100 includes, in order from the inner ring to the outer ring, a first primary winding 110, a first shielding coil 140, a first shielding foil 150, a secondary winding 130, a second shielding coil 160, and a second primary winding 120.

The first shielding coil 140 is disposed between the first primary winding 110 and the secondary winding 130, and the first shielding coil 140 is used for suppressing conducted interference between the first primary winding 110 and the secondary winding 130. Specifically, a first interlayer capacitor exists between the first primary winding 110 and the secondary winding 130 due to a voltage difference, the first interlayer capacitor generates a first current, the magnitude of the first current is related to the relative position and the turn ratio of the first primary winding 110 and the secondary winding 130, and the flow direction of the first current is related to the winding direction between the first primary winding 110 and the secondary winding 130. Accordingly, the winding direction and the number of turns of the first shield coil 140 can be set according to the magnitude and the flow direction of the first current, so that the current generated by the first shield coil 140 and the first current cancel each other out. The first shield coil 140 has a relatively good suppression effect on conducted interference, but has a relatively poor suppression effect on radiated interference.

The first shielding foil 150 is disposed between the first shielding coil 140 and the secondary winding 130, and the first shielding foil 150 is used for suppressing the radiation interference of the first primary winding 110 and the first shielding coil 140 to the secondary winding 130. The above-mentioned suppression of the radiation interference (interference electromagnetic wave) may include a case where the first shielding foil 150 may absorb the above-mentioned interference electromagnetic wave by the eddy current loss; second, the first shielding foil 150 may reflect a portion of the interference electromagnetic waves; third, the first shielding foil 150 generates a reverse electromagnetic field due to electromagnetic induction, which can cancel part of the interfering electromagnetic waves. The first shielding foil 150 has a relatively poor suppression effect on the conducted interference and a relatively good suppression effect on the radiated interference.

The second shielding coil 160 is disposed between the secondary winding 130 and the second primary winding 120, and the second shielding coil 160 is used for suppressing conducted interference between the second primary winding 120 and the secondary winding 130, specifically, a second interlayer capacitance exists between the second primary winding 120 and the secondary winding 130 due to a voltage difference, the second interlayer capacitance generates a second current, a magnitude of the second current is related to a relative position and a turn ratio of the second primary winding 120 and the secondary winding 130, and a flowing direction of the second current is related to a winding direction between the second primary winding 120 and the secondary winding 130. Accordingly, the winding direction and the number of turns of the second shield coil 160 can be set according to the magnitude and the flow direction of the second current, so that the current generated by the second shield coil 160 and the second current cancel each other out. The second shield coil 160 has a relatively good suppression effect on conducted interference, but has a relatively poor suppression effect on radiated interference.

It should be noted that the first primary winding 110, the first shielding coil 140, the first shielding foil 150, the secondary winding 130, the second shielding coil 160, and the second primary winding 120 may be arranged in close contact as possible, so as to reduce leakage inductance and reduce interlayer capacitance interference.

In summary, the first shielding coil 140 has a better effect of suppressing conducted interference between the first primary winding 110 and the secondary winding 130, the second shielding coil 160 has a better effect of suppressing conducted interference between the second primary winding 120 and the secondary winding 130, and the first shielding foil 150 has a better effect of suppressing radiated interference between the first primary winding 110 and the first shielding coil 140, and due to the cooperation of the first shielding coil 140, the second shielding coil 160, and the first shielding foil 150, the transformer 100 in the embodiment of the present application can have both a better effect of suppressing conducted interference and a better effect of suppressing radiated interference. Secondly, since the transformer 100 has a better EMI suppression effect, the transformer 100 in the embodiment of the present application can cancel the Y capacitor bridged over the primary circuit 210 and the secondary circuit 220, so that the transformer 100 without the Y capacitor can be provided, the touch sensitivity of the touch screen of the electronic device is prevented from being affected by the leakage current, and meanwhile, the production cost can be reduced without the Y capacitor.

As shown in fig. 2, in some embodiments, the transformer 100 further includes a second shielding foil 170, the second shielding foil 170 is disposed between the secondary winding 130 and the second shielding coil 160, and the second shielding foil 170 is used for suppressing the radiation interference of the second primary winding 120 and the second shielding coil 160. Generally, current flows from the first primary winding 110 to the second primary winding 120, and the voltage of the first primary winding 110 is higher than that of the second primary winding 120, so that the radiation interference intensity of the first primary winding 110 is stronger than that of the second primary winding 120, i.e. the first primary winding 110 is the main radiation interference source. Therefore, even if the second shield foils 170 are provided, the second shield foils 170 exert a radiation interference suppressing effect that is weaker than the radiation suppressing effect exerted by the first shield foils 150. Therefore, whether to arrange the second shielding foil 170 may be selected according to actual detection conditions, and when the radiation interference of the second primary winding 120 to the secondary winding 130 meets the safety requirements, the second shielding foil 170 may be selected not to be arranged. When the radiated interference of the secondary winding 130 by the second primary winding 120 does not meet the safety requirements, the second shielding foil 170 may be optionally disposed.

As shown in fig. 1 and 2, in some embodiments, the number of turns of the first primary winding 110 is greater than the number of turns of the second primary winding 120. The first primary winding 110 is relatively close to the inner turn and the second primary winding 120 is relatively close to the outer turn, the average radius of the first primary winding 110 is smaller than the average radius of the second primary winding 120, and the first primary winding 110 consumes less material per single turn of the coil than the second primary winding 120. In the case where the total number of turns of the first primary winding 110 and the second primary winding 120 is constant, the number of turns of the first primary winding 110 is set relatively more, and the number of turns of the second primary winding 120 can be set relatively less, so that material can be saved. Meanwhile, since the number of turns of the first primary winding 110 is greater than that of the second primary winding 120, the voltage drop value of the first primary winding 110 is also greater, so that the radiation interference of the transformer 100 can be mainly concentrated on the first primary winding 110. Accordingly, the second primary winding 120 may be provided without the second shielding foil 170, thereby reducing the volume of the transformer 100 and saving materials.

In some embodiments, the number of turns of the first shield foil 150 is 0.8-1.0 turn, and the first shield foil 150 is disposed end-to-end insulated. If the number of turns of the first shielding foil 150 is too small (for example, 0.7 turns), the coverage is limited, and the radiation suppression effect is poor; if the number of turns of the first shielding foil 150 is too large (more than 1.1 turns), the material is wasted, and the first two ends need to be pasted with insulating tapes, which increases the difficulty of production and manufacture. In some embodiments, it is preferable that the number of turns of the first shielding foil 150 is 0.9.

With continued reference to fig. 1 and 2, in some embodiments, the first primary winding 110 may be wound with 2-3 layers, and the second primary winding may be wound with 1 layer. Generally speaking, voltages in a power grid are different corresponding to different power systems, in order to enable the transformer 100 to keep an output voltage constant under different input voltages, a plurality of taps are generally arranged on a primary winding of the transformer 100, the plurality of taps are connected to a tap changer, and a turn ratio of the primary winding and a secondary winding 130 of the transformer 100 is changed by connecting the tap changer with different taps, so that the output voltage of the transformer 100 is ensured to be constant. However, the taps may cause the primary windings to deform, for example, when the first primary winding 110 is circular, the taps may cause the first primary winding 110 to be out of round, thereby affecting the winding of subsequent windings. Having 2 or 3 layers of the first primary winding 110 may slow this deformation compared to having 1 layer of the first primary winding 110, making the outer turn of the first primary winding 110 more rounded. In addition, the more the number of layers of the winding is, the more obvious the effect of generating interlayer capacitance between the windings is, and the number of layers wound by the first primary winding 110 is set to be 2 or 3, so that the interlayer capacitance of the first primary winding 110 can be controlled within a reasonable range. It should be noted that the first shielding foil 150 has a smooth surface, and when the first shielding foil 150 is disposed in close contact with the first shielding coil 140, the first shielding foil can also perform a shaping function, so as to facilitate the winding of the secondary winding 130.

In some embodiments, the first primary winding 110, the first shield coil 140, and the secondary winding 130 substantially satisfy the following relationship: p1+ W1 is 2N, where P1 is the number of turns of the first primary winding 110, W1 is the number of turns of the first shield coil 140, and N is the number of turns of the secondary winding 130. Through a plurality of experimental tests, it is known that when P1+ W1 is 2N, the first shielding coil 140 has a better effect of suppressing the conducted interference of the transformer 100. When P1+ W1 > 2N or P1+ W1 < 2N, the suppression effect of the first shield coil 140 on the conducted interference of the transformer 100 tends to be deteriorated.

With continued reference to fig. 1 and 2, a, b, c, d, E, f, g represent the different connections of the transformer 100, E represents ground, and NC represents floating. In a specific connection mode of the windings of the transformer 100, the first shielding coil 140 may have one end connected to the potential quiescent point of the first primary winding 110 and the other end floating. On one hand, since one end of the first shielding coil 140 is connected to the potential dead point of the first primary winding 110, the common mode current generated by the first shielding coil 140 and the first current can be cancelled by setting the winding direction and the number of turns of the first shielding coil 140, so as to prevent the first current from flowing to the ground as much as possible and generating conduction interference. On the other hand, the first shield coil 140 can also suppress conducted interference generated by the jump voltage of the first primary winding 110. The floating may mean that there is no electrical connection between the other end of the first shielding coil 140 and any conductor, and no electrical connection between the other end of the first shielding coil and any element, so as to avoid conduction interference caused by the flow of charges to the ground as much as possible. Similarly, the second shielding coil 160 may have one end connected to the potential quiescent point of the second primary winding 120 and the other end floating, so that the common mode current generated by the second shielding coil 160 and the second current cancel each other. The first shield foil 150 may be grounded through a wire so that the potential of the first shield foil 150 maintains a zero potential, ensuring the shielding effect of the first shield foil 150.

Referring again to fig. 1 and 2, in some embodiments, the transformer 100 further includes a bobbin 180 and a magnetic core (not shown). The bobbin 180 is used to fix the first primary winding 110, the first shielding coil 140, the first shielding foil 150, the secondary winding 130, the second shielding coil 160, the second primary winding 120, and the magnetic core. Specifically, the bobbin 180 has a winding slot 180a and a magnetic core slot (not shown), and the first primary winding 110 is wound around the winding slot 180 a. The magnetic core is used for electromagnetic mutual inductance, and at least part of the magnetic core is accommodated in the magnetic core groove. When ac current is applied to the primary winding, an ac magnetic flux is generated within the core, thereby inducing a current in the secondary winding 130. Preferably, the magnetic cores are all located in the magnetic core slots to reduce leakage inductance and improve the efficiency of the transformer 100. Coil skeleton 180 and magnetic core can set up different shapes as required.

In some embodiments, the transformer 100 further includes an auxiliary winding 190, the auxiliary winding 190 being disposed between the second shield coil 160 and the second primary winding 120. The auxiliary winding 190 can be used for supplying power to a circuit board or a chip and the like, meanwhile, the auxiliary winding 190 can also play a certain shielding role, common mode interference current and differential mode capacitance current are reduced, electromagnetic interference is optimized and improved, leakage inductance of the sandwich winding transformer 100 and output voltage fluctuation caused by insufficient coupling are reduced, and the adjustment rate is improved.

In some embodiments, the first primary winding 110, the first shielding coil 140, the second shielding coil 160, and the second primary winding 120 may be wound by an enameled wire, and the enameled wire has a thinner insulating layer, which may reduce the volume of the transformer 100, and meanwhile, the enameled wire has a better heat conducting capability, which may enable the transformer 100 to have a better heat dissipation capability. The first shielding foil 150 may be a copper foil having good shielding performance and thermal conductivity. Secondary winding 130 may be wound from an insulated wire, which may be comprised of an insulating sheath and a wire. The insulating sheath and the lead can be formed integrally, for example, the lead is sleeved with the insulating sheath. The insulation sheath and the wires may also be separately disposed, for example, the insulation sheath covers the outer layer of the first shielding foil 150, and the insulation sheath is provided with a plurality of grooves, and the wires are wound in the grooves.

In some embodiments, the first shielding coil 140 is a close-wound coil, and the first shielding coil 140 is wound to fill the winding slots 180a of the bobbin 180, so as to enhance the interference suppression effect. Since the number of turns of the second shielding coil 160 is smaller than that of the first shielding coil 140, the second shielding coil 160 may be a loosely wound or tightly wound coil.

As shown in fig. 1 and fig. 2, in some embodiments, the transformer 100 further includes an insulating tape 190a, and the insulating tape 190a can reduce the risk of breakdown, reduce the generation of distributed capacitance, reduce the electromagnetic interference between layers, and ensure the shielding effect. The insulating tape 190a is provided at least in one of the following positions: between the first primary winding 110 and the first shield coil 140; between the first shield coil 140 and the first shield foil 150; between the first shielding foil 150 and the secondary winding 130; between secondary winding 130 and second shield coil 160; between the second shield coil 160 and the auxiliary winding 190, between the auxiliary winding 190 and the second primary winding 120, and the outer layer of the second primary winding 120.

Preferably, as shown in fig. 1, an insulation tape 190a is disposed between the windings of the transformer 100, that is, an insulation tape 190a is disposed between the first primary winding 110 and the first shielding coil 140, an insulation tape 190a is disposed between the first shielding coil 140 and the first shielding foil 150, an insulation tape 190a is disposed between the first shielding foil 150 and the secondary winding 130, an insulation tape 190a is disposed between the secondary winding 130 and the second shielding coil 160, an insulation tape 190a is disposed between the second shielding coil 160 and the auxiliary winding 190, an insulation tape 190a is disposed between the auxiliary winding 190 and the second primary winding 120, and an insulation tape 190a is disposed on an outer layer of the second primary winding 120.

Alternatively, as shown in fig. 2, the insulating tapes 190a are disposed between the windings of the transformer 100, that is, the insulating tapes 190a are disposed between the first primary winding 110 and the first shielding coil 140, the insulating tapes 190a are disposed between the first shielding coil 140 and the first shielding foil 150, the insulating tapes 190a are disposed between the first shielding foil 150 and the secondary winding 130, the insulating tapes 190a are disposed between the secondary winding 130 and the second shielding foil 170, the insulating tapes 190a are disposed between the second shielding foil 170 and the second shielding coil 160, the insulating tapes 190a are disposed between the second shielding coil 160 and the auxiliary winding 190, the insulating tapes 190a are disposed between the auxiliary winding 190 and the second primary winding 120, and the insulating tapes 190a are disposed on the outer layer of the second primary winding 120.

As shown in fig. 3, a second aspect of the embodiment of the present application provides a power conversion circuit 200, where the power conversion circuit 200 includes the transformer 100, the primary circuit 210, and the secondary circuit 220 as described above, and the transformer 100 is disposed between the primary circuit 210 and the secondary circuit 220. Specifically, the first primary winding 110 has a first end and a second end, the second primary winding 120 has a third end and a fourth end, the second end is electrically connected to the third end (referring to fig. 1 and 2, the first primary winding 110 is connected to the second primary winding 120 through the d-connection end), the first end and the fourth end are electrically connected to two ends of the primary circuit 210, and two ends of the secondary winding 130 are electrically connected to two ends of the secondary circuit 220.

The third aspect of the embodiment of the present application provides an adapter, which includes the power conversion circuit 200 as described above. The adapter improves the balance between electromagnetic radiation and leakage, so that the adapter can pass the electromagnetic radiation test without a Y capacitor. The method is suitable for products such as mobile phone chargers and fixed station power supplies which are sensitive to leakage current.

The same or similar reference numerals in the drawings of the present embodiment correspond to the same or similar components; in the description of the present application, it is to be understood that if there is an orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", etc. based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not intended to indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and are not to be construed as limitations of the present patent, and specific meanings of the above terms may be understood by those skilled in the art according to specific situations.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims (10)

1. A transformer, comprising:

a first primary winding;

the second primary winding is arranged around the periphery of the first primary winding;

a secondary winding disposed between the first primary winding and the second primary winding;

a first shielding coil disposed between the first primary winding and the secondary winding for suppressing conducted interference between the first primary winding and the secondary winding;

the first shielding foil is arranged between the first shielding coil and the secondary winding and used for inhibiting the radiation interference of the first primary winding and the first shielding coil to the secondary winding;

and the second shielding coil is arranged between the secondary winding and the second primary winding and used for inhibiting conducted interference between the second primary winding and the secondary winding.

2. The transformer of claim 1, further comprising:

and the second shielding foil is arranged between the secondary winding and the second shielding coil and used for inhibiting the radiation interference of the second primary winding and the second shielding coil.

3. The transformer of claim 1, wherein the first primary winding has a greater number of turns than the second primary winding.

4. The transformer of claim 1, wherein the first shielding foil has 0.8-1.0 turns and is insulated end-to-end.

5. The transformer of claim 1, wherein the first primary winding is wound in 2-3 layers.

6. The transformer of claim 1, wherein the first primary winding, the first shield coil, and the secondary winding satisfy the following relationship:

P1+W1＝2N；

wherein P1 is the number of turns of the first primary winding, W1 is the number of turns of the first shield coil, and N is the number of turns of the secondary winding.

7. The transformer according to any one of claims 1 to 6, wherein one end of the first shielding coil is connected to a potential dead point of the first primary winding, and the other end of the first shielding coil is suspended; one end of the second shielding coil is connected with the potential quiescent point of the second primary winding, and the other end of the second shielding coil is suspended in the air; and

the first shielding foil is arranged grounded.

8. The transformer according to any one of claims 1 to 6, further comprising:

the coil framework is provided with a winding slot and a magnetic core slot, and the first primary winding is wound in the winding slot;

and the magnetic core is at least partially accommodated in the magnetic core groove.

9. A power conversion circuit, comprising:

the transformer of any one of claims 1-8, the first primary winding having a first end and a second end, the second primary winding having a third end and a fourth end, the second end electrically connected to the third end;

a primary circuit electrically connected to the first and fourth terminals; and

and the secondary circuit is electrically connected with two ends of the secondary winding.

10. An adapter comprising the power conversion circuit of claim 9.

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