CN215912039U

CN215912039U - Switching power supply circuit and power adapter

Info

Publication number: CN215912039U
Application number: CN202122229484.5U
Authority: CN
Inventors: 支继东; 尹昱; 孙家文; 陶运
Original assignee: Gree Electric Appliances Inc of Zhuhai
Current assignee: Gree Electric Appliances Inc of Zhuhai
Priority date: 2021-09-14
Filing date: 2021-09-14
Publication date: 2022-02-25
Anticipated expiration: 2031-09-14

Abstract

The utility model discloses a switching power supply circuit and a power adapter. Wherein, this circuit includes: the transformer-based power supply comprises a switching power supply, a rectifying circuit, a transformer and a load circuit, wherein the switching power supply comprises a main switching device and a control circuit, one end of the control circuit is connected with the output end of a primary winding of the transformer, the other end of the control circuit is connected with the output end of the rectifying circuit, a grid electrode of the main switching device is connected with the control circuit, a drain electrode of the main switching device is connected with the output end of the rectifying circuit, and a source electrode of the main switching device is grounded; the input end of the rectifying circuit is connected with a power supply, and the output end of the rectifying circuit is connected with the input end of the primary winding of the transformer; the transformer includes a primary winding connected to the output of the rectifier circuit and a secondary winding connected to the load circuit. The utility model solves the technical problems of large volume and high cost caused by the fact that the transformer in the switching power supply circuit is provided with the auxiliary winding in the related technology.

Description

Switching power supply circuit and power adapter

Technical Field

The utility model relates to the field of switching power supplies, in particular to a switching power supply circuit and a power adapter.

Background

The switching power supply is a power supply which utilizes the modern power electronic technology to control the duty ratio of a switch and maintain the output stable voltage. The intelligent terminal has the advantages of small volume, light weight, high efficiency and the like, and is widely applied to electronic products such as intelligent terminals, automatic products, instruments and meters and the like. In recent years, the market share of switching power supplies, particularly small-power flyback switching power supplies, has increased year by year.

In the related art, a general switching power supply circuit is formed by connecting a primary winding of a high-frequency transformer and a main switching device in series, and a secondary winding of the high-frequency transformer is connected with a load. The ac low impedance bypass circuit is used to provide a bypass path for common mode interference, and is generally composed of one or more series capacitors. When the switching power supply is used, the transformer with the auxiliary winding has relatively large volume, high leakage inductance, complex circuit, more loop components and high cost, and the load connected with the secondary winding can bring EMI (electromagnetic interference) electromagnetic interference.

In view of the above problems, no effective solution has been proposed.

SUMMERY OF THE UTILITY MODEL

The embodiment of the utility model provides a switching power supply circuit and a power adapter, which at least solve the technical problems of large volume and high cost caused by the fact that a transformer in the switching power supply circuit is provided with an auxiliary winding in the related technology.

According to an aspect of the embodiments of the present invention, there is provided a switching power supply 10, a rectifier circuit 20, a transformer 30 and a load circuit 40, wherein the switching power supply 10 includes a main switching device and a control circuit, one end of the control circuit is connected to an output end of a primary winding of the transformer 30, the other end of the control circuit is connected to an output end of the rectifier circuit 20, a gate of the main switching device is connected to the control circuit, a drain of the main switching device is connected to an output end of the rectifier circuit 20, and a source of the main switching device is grounded; the input end of the rectifying circuit 20 is connected with a power supply, and the output end of the rectifying circuit 20 is connected with the input end of the primary winding of the transformer 30; the transformer 30 includes a primary winding connected to the output terminal of the rectifier circuit 20 and a secondary winding connected to the load circuit 40.

Optionally, the transformer 30 includes: a magnetic core, the primary winding, the secondary winding, and a shield winding; the magnetic core comprises a plurality of magnetic core skeletons for arranging the primary winding or the secondary winding; the primary winding with secondary winding sets up respectively on the magnetic core skeleton of difference, shielding winding sets up primary winding with on the magnetic core skeleton between the secondary winding, wherein, primary winding, secondary winding with shielding winding all adopts insulating material parcel.

Optionally, the primary winding includes: the power supply comprises a first part and a second part, wherein the first part and the second part are respectively arranged on different magnetic core frameworks, one end of the first part is connected with the switching power supply 10, the other end of the first part is connected with one end of the second part, and the other end of the second part is connected with an output end of the rectifying circuit 20.

Optionally, one end of the first portion is connected to a control circuit of the switching power supply 10.

Optionally, the magnetic core is connected to a dead point of the secondary winding.

Optionally, the drain of the main switching device is connected to the output end of the rectifying circuit 20 through an absorption circuit.

Optionally, the load circuit 40 includes: the follow current circuit is connected with the input end of the secondary winding, and the input end of the filter circuit is connected with the output end of the follow current circuit; and the output end of the filter circuit is connected with a load.

Optionally, an input end of the rectifying circuit 20 is connected to an alternating current power supply, and an output end of the rectifying circuit 20 is a direct current bus output end; the direct current bus output end comprises a direct current bus positive end and a direct current bus negative end, and the direct current bus negative end is grounded.

Optionally, the other end of the control circuit is connected to the positive end of the dc bus; the drain electrode of the main switching device is connected with the positive end of the direct current bus; the primary winding is connected with the positive end of the direct current bus.

According to another aspect of the embodiments of the present invention, there is also provided a power adapter, which is characterized by including the switching power supply circuit described in any one of the above.

In the embodiment of the present invention, the switching power supply 10 includes a main switching device and a control circuit, one end of the control circuit is connected to the output end of the primary winding of the transformer 30, the other end of the control circuit is connected to the output end of the rectifying circuit 20, the gate of the main switching device is connected to the control circuit, the drain of the main switching device is connected to the output end of the rectifying circuit 20, and the source of the main switching device is grounded; the input end of the rectifying circuit 20 is connected with a power supply, and the output end of the rectifying circuit 20 is connected with the input end of the primary winding of the transformer 30; the transformer 30 comprises a primary winding and a secondary winding, the primary winding is connected with the output end of the rectifying circuit 20, the secondary winding is connected with the load circuit 40, the control circuit of the switching power supply directly gets power from the drain electrode of the rectifying circuit or the main switching device, the auxiliary winding of the transformer is cancelled, the transformer only comprises the primary winding and the secondary winding, and therefore the technical effects of reducing the size of the transformer, reducing leakage inductance, simplifying the circuit and reducing cost are achieved, and the technical problems that the size is large and the cost is high due to the fact that the transformer in the switching power supply circuit in the related art is provided with the auxiliary winding are solved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the utility model and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the utility model and together with the description serve to explain the utility model without limiting the utility model. In the drawings:

fig. 1 is a schematic diagram of a switching power supply circuit according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a related art switching power supply circuit according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a transformer winding according to an embodiment of the utility model;

FIG. 4-1 is a schematic diagram of an EMI test curve of a switching power supply circuit according to an embodiment of the present invention;

fig. 4-2 is a schematic diagram of an EMI test result of a switching power supply circuit according to an embodiment of the present invention.

The reference numbers in the above figures are as follows:

10-switching power supply, 20-rectifying circuit, 30-transformer, 40-load circuit.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the utility model described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a circuit, system, article, or apparatus that comprises a list of structures is not necessarily limited to those specific structures, but may include other structures not expressly listed or inherent to such circuit, system, article, or apparatus.

Fig. 1 is a schematic diagram of a switching power supply circuit according to an embodiment of the present invention, and as shown in fig. 1, according to an aspect of an embodiment of the present invention, there are provided a switching power supply 10, a rectifier circuit 20, a transformer 30 and a load circuit 40,

the switching power supply 10 comprises a main switching device and a control circuit, wherein one end of the control circuit is connected with the output end of a primary winding of the transformer 30, the other end of the control circuit is connected with the output end of the rectifying circuit 20, a grid electrode of the main switching device is connected with the control circuit, a drain electrode of the main switching device is connected with the output end of the rectifying circuit 20, and a source electrode of the main switching device is grounded; the input end of the rectifying circuit 20 is connected with a power supply, and the output end of the rectifying circuit 20 is connected with the input end of the primary winding of the transformer 30; the transformer 30 includes a primary winding connected to the output of the rectifier circuit 20 and a secondary winding connected to the load circuit 40.

Through the circuit, the switching power supply 10 comprises a main switching device and a control circuit, one end of the control circuit is connected with the output end of the primary winding of the transformer 30, the other end of the control circuit is connected with the output end of the rectifying circuit 20, the grid electrode of the main switching device is connected with the control circuit, the drain electrode of the main switching device is connected with the output end of the rectifying circuit 20, and the source electrode of the main switching device is grounded; the input end of the rectifying circuit 20 is connected with a power supply, and the output end of the rectifying circuit 20 is connected with the input end of the primary winding of the transformer 30; the transformer 30 comprises a primary winding and a secondary winding, the primary winding is connected with the output end of the rectifying circuit 20, the secondary winding is connected with the load circuit 40, the control circuit of the switching power supply directly gets power from the drain electrode of the rectifying circuit or the main switching device, the auxiliary winding of the transformer is cancelled, the transformer only comprises the primary winding and the secondary winding, and therefore the technical effects of reducing the size of the transformer, reducing leakage inductance, simplifying the circuit and reducing cost are achieved, and the technical problems that the size is large and the cost is high due to the fact that the transformer in the switching power supply circuit in the related art is provided with the auxiliary winding are solved.

The switching power supply 10 includes a main switching device and a control circuit, the main switching device may be a transistor or a thyristor, and includes a drain, a source and a gate, the control circuit is connected to the gate of the main switching device, the drain of the main switching device is connected to the output end of the rectifying circuit 20, and the control circuit can get power through the drain of the main switching device.

One end of the control circuit is connected with the output end of the primary winding of the transformer 30, the primary winding is connected with the output end of the rectifying circuit 20, and the other end of the control circuit is connected with the output end of the rectifying circuit 20, so that the control circuit and the output circuit of the rectifying circuit 20 form a loop, and the control circuit can directly take electricity from the output end of the rectifying circuit 20.

The control circuit of the switching power supply 10 gets power from the output end of the rectifying circuit 20 or the drain electrode of the main switching device, so that the control circuit is prevented from getting power from the auxiliary winding of the transformer 30, the transformer 30 is large in size and high in cost, the circuit is complex, the size of the transformer 30 is effectively reduced, the circuit is simplified, and the cost is reduced.

The gate of the main switch device is connected to the control circuit, the drain of the main switch device is connected to the output terminal of the rectifier circuit 20, when the gate is connected to the drain, the control circuit can form a loop with the output circuit of the rectifier circuit 20 through the main switch device, and the drain of the main switch device is used to take power from the output circuit of the rectifier circuit 20. The source electrode of the main switching device is grounded, so that the subsequent control of the main switching device is facilitated.

The input end of the above-mentioned rectifier circuit 20 is connected with the power supply, the power supply can be an alternating current power supply, the alternating current power supply is input into the rectifier circuit 20 through the positive input end and the negative input end, optionally, the input end of the rectifier circuit 20 is connected with the alternating current power supply, the output end of the rectifier circuit 20 is the output end of the direct current bus; the output terminal of the dc bus includes a positive terminal of the dc bus and a negative terminal of the dc bus, the negative terminal of the dc bus is grounded, and the positive terminal of the dc bus is used as the output terminal of the positive circuit 20 and is connected to the control circuit, the primary winding of the transformer 30, and the gate of the main switching device. The output terminal of the rectifying circuit 20 is connected to the input terminal of the primary winding of the transformer 30, and the positive terminal of the dc bus of the rectifying circuit 20 may be connected to the input terminal of the primary winding of the transformer 30.

The transformer 30 includes a primary winding and a secondary winding, and an auxiliary winding for connection with a control circuit is eliminated, so that the size of the transformer can be reduced, the circuit can be simplified, and the cost can be reduced. The primary winding is connected to the output end of the rectifying circuit 20, that is, the input end of the primary winding is connected to the positive end of the dc bus of the rectifying circuit 20, and the secondary winding is connected to the load circuit 40, and is used for supplying power to the load after transforming the dc current at the positive end of the dc bus.

Optionally, the transformer 30 includes: a magnetic core, a primary winding, a secondary winding, and a shield winding; the magnetic core comprises a plurality of magnetic core skeletons for arranging the primary winding or the secondary winding; the primary winding and the secondary winding are respectively arranged on different magnetic core frameworks, the shielding winding is arranged on the magnetic core framework between the primary winding and the secondary winding, and the primary winding, the secondary winding and the shielding winding are all wrapped by insulating materials.

As shown in fig. 3, the magnetic core includes a rectangular frame of a half-enclosed structure, i.e., a white frame structure in fig. 3, and a plurality of transverse black line segments disposed therebetween, i.e., the magnetic core skeleton for disposing the primary winding or the secondary winding. The primary winding and the secondary winding are respectively arranged on different magnetic core frameworks, and the shielding winding is arranged on the magnetic core framework between the primary winding and the secondary winding, wherein the primary winding, the secondary winding and the shielding winding are wrapped by insulating materials to ensure that the primary winding, the secondary winding and the shielding winding are not conducted due to overlarge distance or voltage, so that the normal operation of current on each winding is ensured, the normal operation of the transformer is also ensured, and the working stability and reliability of the transformer are improved.

Optionally, the primary winding comprises: the switching power supply comprises a first part and a second part, wherein the first part and the second part are respectively arranged on different magnetic core skeletons, one end of the first part is connected with the switching power supply 10, the other end of the first part is connected with one end of the second part, and the other end of the second part is connected with an output end of the rectifying circuit 20.

The primary winding includes a first portion and a second portion, as shown in fig. 3, the first portion and the second portion are respectively disposed on different magnetic core frames, a solid circle 4 of the first portion is a starting position of the winding of the first portion, the starting position is connected to the control circuit of the switching power supply 10, an open circle 2 of the first portion is a middle point of the transformer, and is actually communicated with the solid circle 2 of the second portion, so as to transmit the current passing through the winding of the first portion to the second portion to increase the number of turns of the coil of the primary winding, and an output terminal 1 of the second portion is connected to a positive terminal of the dc bus of the rectifier circuit 20.

The primary winding is divided into the first part and the second part, so that the influence of the primary winding on the secondary winding can be effectively dispersed, because the coils of the primary winding are connected in series, the voltage can be accumulated, and under the condition that the number of the coils of the primary winding is large, the voltage is large, and the risk of insulation breakdown is increased.

Optionally, one end of the first part is connected to a control circuit of the switching power supply 10.

As shown in fig. 3, the first end of the first part where the winding starts is connected to the control circuit of the switching power supply 10, and the first part and the second part are connected in series, so that the first part is connected to the positive terminal of the dc bus of the rectifier circuit 20, and the other end of the control circuit is connected to the positive terminal of the dc bus of the rectifier circuit 20, so that the control circuit is connected to the positive terminal of the dc bus to take power from the positive terminal of the dc bus. The situation that the control circuit gets power from the auxiliary winding of the transformer 30, the transformer 30 is large in size and high in cost, and the circuit is complex is avoided.

The magnetic core of the transformer is connected with the dead point of the secondary winding, and the transformer is not provided with an auxiliary winding, so that the circuit of the primary winding is highly isolated from the circuit of the secondary winding, and the EMI interference from a load end is effectively inhibited.

Optionally, the drain of the main switching device is connected to the output terminal of the rectifying circuit 20 through an absorption circuit.

The drain of the main switching device is connected to the output terminal of the rectifier circuit 20 through an absorption circuit, that is, the drain of the main switching device is connected to the positive terminal of the dc bus of the rectifier circuit 20 through an absorption circuit, and the absorption circuit is also a buffer circuit for performing circuit protection on the main switching device. Generally consisting of resistors, capacitors and diodes.

Optionally, the load circuit 40 includes: the current follow circuit and the filter circuit are connected, wherein the current follow circuit is connected with the input end of the secondary winding, and the input end of the filter circuit is connected with the output end of the current follow circuit; the output end of the filter circuit is connected with a load.

The load circuit 40 includes a freewheeling circuit and a filter circuit, the freewheeling circuit may be provided with a corresponding absorption circuit to protect the freewheeling circuit, the freewheeling circuit is connected to the secondary winding, and may include a freewheeling diode for freewheeling the output circuit of the secondary winding, so that the output current of the secondary winding is more stable. Thereby effectively and safely supplying power to the load. The input end of the filter circuit is connected with the output end of the follow current circuit, the output end of the filter circuit is connected with the load, current after the follow current circuit is filtered, ripple waves of the current are eliminated, and the ripple waves are prevented from influencing the work of the load.

Optionally, the other end of the control circuit is connected with the positive end of the direct current bus; the drain electrode of the main switching device is connected with the positive end of the direct current bus; the primary winding is connected with the positive end of the direct current bus.

Because one end of the control circuit is connected with the primary winding of the transformer 30, the primary winding is connected with the positive end of the direct current bus of the rectification circuit 20, and the other end of the control circuit is connected with the positive end of the direct current bus, the control circuit can be connected into the positive end of the direct current bus, the control circuit can directly take electricity from the positive end of the direct current bus, and the problem of transformer volume increase caused by taking electricity from the auxiliary winding of the transformer is avoided.

The drain electrode of the main switching device is connected with the positive end of the direct current bus, the grid electrode of the main switching device is connected with the control circuit, the control circuit is connected with the positive end of the direct current bus, and the control circuit can also get electricity from the positive end of the direct current bus through the drain electrode of the main switching device. The problem of the transformer volume increase that the electricity got and leads to from the auxiliary winding of transformer is avoided.

It should be noted that the present application also provides an alternative implementation, and the details of the implementation are described below.

In the electromagnetic interference isolation switch power supply circuit and the power adapter, the transformer and the circuit structure are optimized, and the switch power supply circuit without the auxiliary winding and through primary side power taking and feedback is designed. The transformer with the auxiliary winding has relatively large volume and high leakage inductance; the circuit is complex, the number of loop components is large, and the cost is high; and the problem of isolating EMI interference from secondary loads. The control circuit of the main power device is used for getting power from the direct current bus or the drain electrode, the transformer has no auxiliary winding, the volume of the transformer is relatively reduced, the leakage inductance is reduced, and the circuit structure is simplified. Through the special design of the transformer winding, the Y capacitor is omitted, so that the primary and secondary circuits are highly isolated, and the EMI interference from a load end is effectively inhibited.

Fig. 2 is a schematic diagram of a related art switching power supply circuit according to an embodiment of the present invention, and as shown in fig. 2, a related art general switching power supply circuit includes a rectifying and filtering circuit, an absorption circuit, a power conversion circuit, a high-frequency transformer and low-impedance bypass circuit, an auxiliary winding power supply circuit, a main switching device and a control circuit thereof. The input of the alternating current power supply is connected to the rectification filter circuit, the rectification filter circuit is connected with a circuit formed by connecting a primary winding of the high-frequency transformer and the main switching device in series, two secondary windings of the high-frequency transformer are connected with the output filter circuit in series after passing through the follow current and the absorption circuit thereof, and the output filter circuit is connected with the load. The ac low impedance bypass circuit is used to provide a bypass path for common mode interference, and is generally composed of one or more series capacitors. In particular, 2nF ceramic capacitors are used in series in this embodiment.

As shown in fig. 1, the emi isolator power supply circuit according to this embodiment eliminates an auxiliary winding power supply circuit and an ac low impedance bypass circuit, and changes the feedback mode from secondary feedback to primary feedback for taking power from the bus, thereby greatly reducing the primary and secondary connected loops and the interference coupling path.

Fig. 3 is a schematic diagram of a winding of a transformer, a winding structure of the transformer, as shown in fig. 3, a solid circle in fig. 3 represents a winding start position of the winding and may also represent an electrical phase, specifically, a solid circle 4 represents a winding start position of a first portion of a primary winding, a solid circle 1 represents a winding start position of a shield winding, a solid circle 2 represents a winding start position of a second portion of the primary winding, and

solid circles

6 and 8 represent winding start positions of a secondary winding. The transformer comprises a primary winding, a secondary winding, a shielding winding and a primary winding, wherein the primary winding comprises a second part, a secondary winding, the shielding winding and a first part from outside to inside in sequence, the windings are wound on a transformer framework, the windings are insulated by adopting an insulating tape, and the number of turns of the tape is usually 1-3. The second part of the primary winding is only wound on 1 layer and is paved on the whole layer in a close winding or sparse winding mode, one end of the second part of the primary winding is connected with the positive electrode of the direct current bus, and the other end of the second part of the primary winding is connected with the middle node of the transformer. And the secondary winding determines the number, the wire diameter and the number of turns of the winding according to the number of output circuits, current and voltage. The shielding winding is wound by adopting metal foil, metal strip or metal wire, is fully wound by 1 layer and can adopt a multi-strand parallel winding mode; the shielding winding is connected with the positive end of the direct current bus, and the head end and the tail end of the shielding winding cannot be short-circuited. The first part and the second part of the primary winding adopt the same wire materials, and are usually wound by an integer number of layers, and the number of layers and the number of turns of the first part are not required to be close to or equal to those of the second part; one end of the first part of the primary winding is connected with the middle node of the transformer, and the other end of the first part of the primary winding is connected with the main power device. In particular, the core is connected to the dead point GND of the secondary by a lead wire, guides the interference back to the secondary and isolates the interference between the primary and secondary by a shield winding, blocking the propagation path of the interference.

The main power device and the control circuit thereof can be integrated in a chip, and can also adopt discrete devices. As shown in fig. 1, the control circuit may be powered by a dc bus or drain voltage. The voltage is output to use primary side feedback.

The whole circuit of the embodiment is simple, the later-stage PCB layout is convenient, the device model selection is favorable for automatic assembly, and the excellent EMC performance can be ensured while the control circuit is low in cost. Fig. 4-1 is a schematic diagram of an EMI test curve of a switching power supply circuit according to an embodiment of the present invention, and fig. 4-2 is a schematic diagram of an EMI test result of a switching power supply circuit according to an embodiment of the present invention, as shown in fig. 4-1 and fig. 4-2, for an actual measurement result of conducted EMI of a switching power supply circuit according to the embodiment, a margin in a frequency band of 150kHz to 30MHz is higher than 6.46dB, and completely meets the national standard requirement.

The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.

In the above embodiments of the present invention, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

In the embodiments provided in the present application, it should be understood that the disclosed technology can be implemented in other ways. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the circuit may be a logical division, and in actual implementation, there may be another division, for example, multiple units or components may be combined or integrated into another system or circuit, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, units or modules, and may be in an electrical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A switching power supply circuit, comprising: a switching power supply (10), a rectifying circuit (20), a transformer (30) and a load circuit (40),

the switching power supply (10) comprises a main switching device and a control circuit, wherein one end of the control circuit is connected with the output end of a primary winding of the transformer (30), the other end of the control circuit is connected with the output end of the rectifying circuit (20), the grid electrode of the main switching device is connected with the control circuit, the drain electrode of the main switching device is connected with the output end of the rectifying circuit (20), and the source electrode of the main switching device is grounded;

the input end of the rectifying circuit (20) is connected with a power supply, and the output end of the rectifying circuit (20) is connected with the input end of the primary winding of the transformer (30);

the transformer (30) comprises a primary winding and a secondary winding, the primary winding is connected with the output end of the rectifying circuit (20), and the secondary winding is connected with the load circuit (40).

2. A switching power supply circuit according to claim 1, characterized in that the transformer (30) comprises: a magnetic core, the primary winding, the secondary winding, and a shield winding;

the magnetic core comprises a plurality of magnetic core skeletons for arranging the primary winding or the secondary winding;

the primary winding with secondary winding sets up respectively on the magnetic core skeleton of difference, shielding winding sets up primary winding with on the magnetic core skeleton between the secondary winding, wherein, primary winding, secondary winding with shielding winding all adopts insulating material parcel.

3. The switching power supply circuit according to claim 2, wherein the primary winding includes: a first portion and a second portion, wherein,

the first part and the second part are respectively arranged on different magnetic core frameworks, one end of the first part is connected with the switching power supply (10), the other end of the first part is connected with one end of the second part, and the other end of the second part is connected with the output end of the rectifying circuit (20).

4. A switching power supply circuit according to claim 3, characterized in that one end of the first part is connected to a control circuit of the switching power supply (10).

5. A switching power supply circuit according to claim 3, wherein said magnetic core is connected to a dead point of said secondary winding.

6. A switching power supply circuit according to claim 1, wherein the drain of said main switching device is connected to the output of said rectifying circuit (20) through an absorption circuit.

7. The switching power supply circuit according to claim 1, wherein the load circuit (40) comprises: the current-continuing circuit, the filter circuit,

the follow current circuit is connected with the input end of the secondary winding, and the input end of the filter circuit is connected with the output end of the follow current circuit;

and the output end of the filter circuit is connected with a load.

8. The switching power supply circuit according to claim 1, wherein an input terminal of the rectifying circuit (20) is connected to an alternating current power supply, and an output terminal of the rectifying circuit (20) is a direct current bus output terminal; the direct current bus output end comprises a direct current bus positive end and a direct current bus negative end, and the direct current bus negative end is grounded.

9. The switching power supply circuit according to claim 8, wherein the other end of the control circuit is connected to the positive terminal of the dc bus;

the drain electrode of the main switching device is connected with the positive end of the direct current bus;

the primary winding is connected with the positive end of the direct current bus.

10. A power adapter, characterized in that it comprises a switching power supply circuit according to any one of claims 1 to 9.