CN220873382U - Y-capacitor-free transformer and switching power supply circuit - Google Patents

Abstract

A Y-capacitance-free transformer and a switching power supply circuit, wherein the Y-capacitance-free transformer comprises: the magnetic core is sequentially wound with a primary winding, a shielding winding and a secondary winding; the primary winding is used for being connected with the primary side circuit, the secondary winding is used for being connected with the secondary side circuit, and the shielding winding is used for being connected with the ground terminal; the winding direction of the primary winding is opposite to the winding direction of the secondary winding, and the winding direction of the primary winding is the same as the winding direction of the shielding winding. The winding directions of the primary winding and the secondary winding are controlled, so that the same-name ends of the primary winding and the secondary winding are distributed uniformly, the induced voltage directions of the primary winding and the secondary winding shielding winding in the transformer are the same, the moving points and the static points are respectively uniform by placing the secondary diode at the negative end of the secondary winding, the induced voltage difference between the primary winding and the secondary winding is small, the inter-turn element displacement current is small, and the aim of inhibiting common-mode interference is fulfilled.

Description

Y-capacitor-free transformer and switching power supply circuit

Technical Field

The application belongs to the technical field of power supplies, and particularly relates to a Y-capacitor-free transformer and a switching power supply circuit.

Background

When the transformer of the switching power supply works, displacement current flowing from the primary winding to the secondary winding, displacement current flowing from the primary winding to the ground terminal, displacement current flowing from the secondary winding to the primary winding and displacement current flowing from the secondary winding to the ground terminal are generated respectively through turn-to-turn parasitic capacitance between the windings. These displacement currents can propagate through the coupling of the distribution parameters of the transformers and power devices and the stray parameters of the leads, PCB traces, etc., causing severe electromagnetic interference to the utility grid.

In order to effectively reduce the conduction common mode electromagnetic interference, a Y capacitor is often adopted in a switching power supply circuit to bridge the primary and the secondary, a return path is provided for displacement current generated in the switching process, and the ground is prevented from being reflowed. But the Y capacitance in the switching power supply may cause some leakage current. Such leakage currents can cause not only safety problems for the user, but also noise to the system. For example, in voice communication type IT devices, leakage currents can cause strong power frequency interference, which can couple to audible hum in the telephone line.

Disclosure of utility model

The application aims to provide a Y-capacitor-free transformer and a switching power supply circuit, and aims to solve the problem of electromagnetic interference of a transformer of a traditional switching power supply.

A first aspect of an embodiment of the present application provides a Y-capacitance-free transformer, including: a magnetic core, a primary winding, a shielding winding and a secondary winding which are sequentially wound on the magnetic core; the primary winding is used for being connected with a primary side circuit, the secondary winding is used for being connected with a secondary side circuit, the shielding winding is used for being connected with a ground end, the primary winding, the shielding winding and the secondary winding are mutually magnetically coupled, the winding direction of the primary winding is opposite to the winding direction of the secondary winding, and the winding direction of the primary winding is the same as the winding direction of the shielding winding.

In one embodiment, the number of winding layers of the primary winding is at least 3; the primary winding is wound from a single enameled wire.

In one embodiment, the number of winding layers of the secondary winding is at least 1; the secondary winding is wound by a single three-layer insulated wire.

In one embodiment, the number of winding layers of the shielding winding is at least 1; the shielding winding is wound by three enamelled wires.

In one embodiment, the semiconductor device further comprises a first insulating layer, a second insulating layer and a third insulating layer; the first insulating layer is arranged between the primary winding and the shielding winding, the second insulating layer is arranged between the shielding winding and the secondary winding, and the third insulating layer is arranged on the outer side of the secondary winding.

In one embodiment, the first insulating layer, the second insulating layer and the third insulating layer each comprise a multi-layer insulating tape.

In one embodiment, the device further comprises an auxiliary winding wound between the primary winding and the magnetic core, the auxiliary winding and the primary winding are mutually magnetically coupled, and the auxiliary winding outputs an auxiliary voltage.

In one embodiment, the number of winding layers of the auxiliary winding is at least 1; the auxiliary winding is wound by two enamelled wires.

A second aspect of the embodiment of the present application provides a switching power supply circuit, including a primary side circuit, a secondary side circuit, and a Y-capacitor-free transformer as described above; a first end of a primary winding of the Y-free capacitance transformer is connected with a first output end of the primary side circuit so as to be connected with a power supply through the primary side circuit; a second end of a primary winding of the Y-free capacitance transformer is connected with a second output end of the primary side circuit so as to be connected with primary ground through the primary side circuit; a first end of a secondary winding of the Y-free capacitance transformer is connected with a first input end of the secondary side circuit so as to be connected with secondary ground through the secondary side circuit; a second end of a secondary winding of the Y-free capacitance transformer is connected with a second input end of the secondary side circuit so as to be connected with a load through the secondary side circuit; the first end of the shielding winding of the Y-free capacitance transformer is suspended, and the second end of the shielding winding is connected with the primary ground; the secondary side circuit comprises a secondary diode, wherein the anode of the secondary diode is connected with the secondary ground, and the cathode of the secondary diode is the first input end.

In one embodiment, the primary side circuit includes a rectifying and filtering module and a flyback switch module, an input end of the rectifying and filtering module is used for being connected with the power supply, an output end of the rectifying and filtering module is connected with the flyback switch module, and the flyback switch module is provided with a first output end and a second output end.

Compared with the prior art, the embodiment of the application has the beneficial effects that: the Y-free capacitor transformer can enable the same-name ends of the primary winding and the secondary winding to be distributed uniformly by controlling the winding directions of the primary winding and the secondary winding, the induced voltage directions of the primary winding and the secondary winding shielding winding in the transformer are the same, the induced voltage difference between the primary winding and the secondary winding is smaller, the inter-turn element displacement current is smaller, and therefore common mode interference is restrained.

The switching power supply circuit can make the dynamic and static points respectively consistent by placing the secondary diode at the negative end of the secondary winding, so as to further inhibit common mode interference.

Drawings

FIG. 1 is a spectrum diagram of the electromagnetic compatibility test result of a conventional flyback switching power supply;

Fig. 2 is a schematic structural diagram of a transformer without Y capacitor according to an embodiment of the present application;

FIG. 3 is a schematic diagram of another embodiment of a transformer without Y-capacitor according to the present application;

fig. 4 is a schematic circuit diagram of a switching power supply circuit according to an embodiment of the application;

FIG. 5 is a graph showing the results of an electromagnetic compatibility test according to an embodiment of the present application;

Fig. 6 is another schematic circuit diagram of a switching power supply circuit according to an embodiment of the application.

The above figures illustrate: 10. a Y-free capacitor transformer; 20. a primary side circuit; 21. a rectifying and filtering module; 22. a flyback switch module; 30. a secondary side circuit; 40. a switching power supply circuit; 50. a power supply; 60. a load; 100. a magnetic core; 200. a primary winding; 300. shielding the winding; 400. a secondary winding; 510. a first insulating layer; 520. a second insulating layer; 530. a third insulating layer; 600. an auxiliary winding.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.

It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or be indirectly connected to the other element.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

When the transformer of the flyback switching power supply works, the displacement current flowing from the primary winding to the secondary winding, the displacement current flowing from the primary winding to the ground terminal, the displacement current flowing from the secondary winding to the primary winding and the displacement current flowing from the secondary winding to the ground terminal are generated respectively through the turn-to-turn parasitic capacitance between the windings.

Because the same-name end and the dynamic and static point distribution in the transformer are influenced, the displacement current of the primary winding flowing to the ground end and the displacement current of the secondary winding flowing to the ground end cannot be restrained, the adjustment shielding winding can only restrain the displacement current of the primary winding flowing to the secondary winding and the displacement current of the secondary winding flowing to the primary winding, and the common-mode interference of the transformer cannot be restrained completely.

The spectrum diagram of the electromagnetic compatibility test result of the traditional flyback switching power supply is shown in fig. 1, and in each frequency band, the electromagnetic interference generated by the traditional flyback switching power supply is large.

Fig. 2 is a schematic structural diagram of a Y-capacitor-less transformer according to an embodiment of the present application, and for convenience of explanation, only the parts related to the embodiment are shown, which are described in detail below:

A Y-free capacitive transformer 10, comprising: a magnetic core 100, and a primary winding 200, a shield winding 300, and a secondary winding 400 sequentially wound on the magnetic core 100. The Y-capacitor-free transformer 10 can be applied to a switching power supply circuit to convert voltage.

The primary winding 200 is used for being connected with a primary side circuit 20 of the switching power supply circuit, the secondary winding 400 is used for being connected with a secondary side circuit 30 of the switching power supply circuit, the shielding winding 300 is used for being connected with a ground terminal, and the primary winding 200, the shielding winding 300 and the secondary winding 400 are mutually magnetically coupled. The transfer of electrical energy can be achieved by the magnetic coupling between the primary winding 200 and the secondary winding 400, the electrical energy being transferred from the primary side circuit 20 to the secondary side circuit 30, and the output voltage of the secondary winding 400 being regulated during the transfer of electrical energy based on the input voltage of the primary winding 200 by setting the number of turns of the primary winding 200 and the secondary winding 400 and the duty cycle of the switching power supply of the primary side circuit 20.

The winding direction of the primary winding 200 is opposite to the winding direction of the secondary winding 400, and the winding direction of the primary winding 200 is the same as the winding direction of the shield winding 300.

By providing the number of turns, the wire diameter, the density, and the like of the shield winding 300, the sum of the displacement current flowing from the primary winding 200 to the secondary winding 400 and the displacement current flowing from the secondary winding 400 to the primary winding 200 can be as close to 0 as possible. Let the displacement current be I ₀, the parasitic capacitance be C ₀, the induced voltage of two windings be V ₁ and V ₀ respectively, according to the formula: It is known that the larger the difference between the induced voltages between the two windings, the larger the corresponding displacement current. Meanwhile, the positions of the homonymous ends of the two windings can be controlled and controlled by controlling the winding direction of the windings. Therefore, when the winding direction of the primary winding 200 is opposite to the winding direction of the secondary winding 400, and the winding direction of the primary winding 200 is the same as the winding direction of the shield winding 300, the same name ends of the primary winding 200, the shield winding 300 and the secondary winding 400 are all located on the same side, the induced voltage of the primary winding 200, the induced voltage of the shield winding 300 and the induced voltage in the secondary winding 400 are all the same, and by placing the secondary diode of the secondary side circuit 30 at the negative end of the secondary winding 400, the dynamic and static points can be respectively consistent, finally, the difference of the induced voltages between the windings is reduced, and the inter-turn displacement current is suppressed, so that the displacement current flowing to the secondary winding 400 from the primary winding 200, the displacement current flowing to the ground end from the primary winding 200, and the displacement current flowing to the ground end from the secondary winding 400 are reduced at the source, and the purpose of suppressing common mode interference generated by the displacement current is achieved.

In one embodiment, the number of winding layers of the primary winding 200 is at least 3. The primary winding 200 is wound from a single enameled wire. Parameters such as the number of winding layers, winding density, wire diameter, specific number of turns and the like of the primary winding 200 can be set according to actual requirements, the primary winding 200 can be wound in a Z-shaped winding mode, and winding directions of all layers of the primary winding 200 are the same.

Illustratively, as shown in fig. 2, the number of winding layers of the primary winding 200 is 3, and the primary winding 200 is wound clockwise from the primary side to the secondary side of the transformer bobbin. Both the winding start and end of the primary winding 200 are used for connection to the primary side circuit 20.

In one embodiment, the number of windings of the secondary winding 400 is at least 1; the secondary winding 400 is wound from a single three-layer insulated wire. Parameters such as the number of winding layers, winding density, wire diameter, and specific number of turns of the secondary winding 400 may be set according to actual requirements.

Illustratively, as shown in fig. 2, the number of winding layers of the secondary winding 400 is 1, and the secondary winding 400 is wound in a counterclockwise direction, as viewed from the primary side toward the secondary side, opposite to the winding direction of the primary winding 200. Both the winding start and end of the secondary winding 400 are used for connection to the secondary side circuit 30.

In one embodiment, the number of windings of the shield winding 300 is at least 1; the shield winding 300 is wound from three enameled wires. The number of winding layers, winding density, wire diameter, specific number of turns, and other parameters of the shield winding 300 can be set according to actual requirements. The sum of the displacement current flowing from the primary winding 200 to the secondary winding 400 and the displacement current flowing from the secondary winding 400 to the primary winding 200 can be made 0 by configuring the number of winding layers, the winding density, the wire diameter, and the specific number of turns of the shield winding 300 appropriately to suppress common mode interference.

Illustratively, as shown in fig. 2, the number of winding layers of the shield winding 300 is 1, and the shield winding 300 is wound in a clockwise direction from the primary side to the secondary side, which is the same as the winding direction of the primary winding 200. The winding start end of the shielding winding 300 is used for ground connection, and the winding tail end of the shielding winding 300 is suspended. The ground may be the ground of the primary side circuit 20.

In one embodiment, Y-free capacitive transformer 10 further includes a first insulating layer 510, a second insulating layer 520, and a third insulating layer 530. The first insulation layer 510 is disposed between the primary winding 200 and the shield winding 300, the second insulation layer 520 is disposed between the shield winding 300 and the secondary winding 400, and the third insulation layer 530 is disposed outside the secondary winding 400.

The first, second and third insulating layers 510, 520 and 530 serve to isolate the respective windings from each other. It is to be understood that the materials of the first insulating layer 510, the second insulating layer 520 and the third insulating layer 530 may be insulating materials with different dielectric constants, and the embodiment is not limited herein specifically, and the replacement of insulating materials with different dielectric constants may also play a role in adjusting the interlayer parasitic capacitance, so that the means for adjusting the common mode noise is more various.

In one embodiment, the first, second and third insulating layers 510, 520 and 530 each comprise a multi-layered insulating tape. The number of layers of the insulating adhesive tape can be set according to actual requirements. In some embodiments, the first insulating layer 510, the second insulating layer 520, and the third insulating layer 530 may be made of other insulating materials, for example, cable paper or the like.

Illustratively, as shown in fig. 2, the first insulating layer 510 and the third insulating layer 530 each include two layers of insulating tape, and the second insulating layer 520 includes three layers of insulating tape.

In one embodiment, as shown in fig. 3, the Y-free capacitance transformer 10 further includes an auxiliary winding 600 and a fourth insulation layer 540, wherein the fourth insulation layer 540 includes a plurality of layers of insulating tape. The auxiliary winding 600 is wound between the primary winding 200 and the magnetic core 100, and a fourth insulation layer 540 is disposed between the auxiliary winding 600 and the primary winding 200, the auxiliary winding 600 being for outputting an auxiliary voltage. The auxiliary voltage drives electronic components that require a specific voltage drive, for example, can drive the operation of the individual chips in the primary side circuit 20.

In one embodiment, the number of winding layers of the auxiliary winding 600 is at least 1; the auxiliary winding 600 is wound from two enameled wires. Parameters such as the number of winding layers, winding density, wire diameter, and specific number of turns of the auxiliary winding 600 may be set according to actual requirements.

Illustratively, as shown in fig. 3, the number of winding layers of the auxiliary winding 600 is 1, and the auxiliary winding 600 is wound in a clockwise direction from the primary side to the secondary side, which is the same as the winding direction of the primary winding 200. The fourth insulating layer 540 includes two layers of insulating tape.

Fig. 4 is a schematic circuit diagram of a switching power supply circuit according to an embodiment of the present application, and for convenience of explanation, only the portions related to the embodiment are shown, and the details are as follows:

A switching power supply circuit 40 comprising a primary side circuit 20, a secondary side circuit 30 and a Y-capacitor-less transformer 10 according to any of the embodiments described above. A first terminal of the primary winding 200 of the Y-capacitance-free transformer 10 is connected to a first output terminal of the primary side circuit 20 to be connected to the power supply 50 through the primary side circuit 20. A second terminal of the primary winding 200 of the Y-capacitance-free transformer 10 is connected to a second output terminal of the primary side circuit 20 to be connected to the primary ground GND1 through the primary side circuit 20. A first end of the secondary winding 400 of the Y-capacitance-free transformer 10 is connected to a first input terminal of the secondary side circuit 30 to be connected to the secondary ground GND2 through the secondary side circuit 30. A second terminal of the secondary winding 400 of the Y-capacitance-free transformer 10 is connected to a second input terminal of the secondary side circuit 30 to be connected to the load 60 through the secondary side circuit 30. The first end of the shield winding 300 of the Y-capacitance-free transformer 10 is suspended, and the second end of the shield winding 300 is connected to the primary ground GND 1. The secondary side circuit 30 includes a secondary diode D1, the positive electrode of the secondary diode D1 is connected to the secondary ground GND2, and the negative electrode of the secondary diode D1 is the first input terminal of the secondary side circuit 30.

The second end of the primary winding 200 is a winding start end of the primary winding 200, the first end of the primary winding 200 is a winding end of the primary winding 200, the first end of the secondary winding 400 is a winding start end of the secondary winding 400, the second end of the secondary winding 400 is a winding end of the secondary winding 400, the second end of the shielding winding 300 is a winding start end of the shielding winding 300, and the first end of the shielding winding 300 is a winding end of the shielding winding 300.

At this time, the second end of the primary winding 200, the second end of the secondary winding 400 and the second end of the shield winding 300 are the same name ends. The induced voltages of the primary winding 200, the induced voltages of the shield winding 300 and the induced voltages of the secondary winding 400 are the same in the directions in the windings, the dynamic and static points of the windings are the same, the difference of the induced voltages between the windings is small, and the displacement current is restrained, so that the purpose of restraining common mode interference generated by the displacement current is achieved. The spectrum diagram of the electromagnetic compatibility test result in this embodiment is shown in fig. 5, and in each frequency band, the electromagnetic interference generated in this embodiment is small, and especially in the frequency band of 500 kHz-10 MHz is greatly improved.

In an embodiment, the primary side circuit 20 includes a rectifying and filtering module 21 and a flyback switch module 22, an input end of the rectifying and filtering module 21 is connected to the power supply 50, an output end of the rectifying and filtering module 21 is connected to the flyback switch module 22, and the flyback switch module 22 is provided with a first output end and a second output end.

Illustratively, the rectifying and filtering module 21 includes a first diode D2, a second diode D3, a third diode D4, a fourth diode D5, a first capacitor C1, a second capacitor C2, and a filtering inductance L1.

The positive electrode of the first diode D2 is connected to the live wire L of the power supply 50, and the negative electrode of the first diode D2 is connected to the first end of the first capacitor C1. The positive electrode of the second diode D3 is connected to the zero line N of the power supply 50, and the negative electrode of the second diode D3 is connected to the first end of the first capacitor C1. The positive electrode of the third diode D4 is connected to the second end of the first capacitor C1, and the negative electrode of the third diode D4 is connected to the live wire L of the power supply 50. The anode of the fourth diode D5 is connected to the second end of the first capacitor C1, and the cathode of the fourth diode D5 is connected to the zero line N of the power supply 50. The second end of the first capacitor C1 is further connected to the first end of the filter inductor L1, the first end of the second capacitor C2 is connected to the first end of the first capacitor C1 and the first end of the primary winding 200, and the second end of the second capacitor C2 is connected to the second end of the filter inductor L1 and the primary ground GND 1. The first end of the first capacitor C1 is the first output end of the primary-side circuit 20. The power supply 50 may be an ac power supply, and is configured to provide ac power to the rectifying and filtering module 21, and the rectifying and filtering module 21 may rectify and filter the ac power provided by the power supply 50.

Illustratively, the flyback switching module 22 includes a switching tube Q1, a first conducting terminal of the switching tube Q1 is connected to the second terminal of the primary winding 200, and a second conducting terminal of the switching tube Q1 is connected to the primary ground GND 1. By controlling the on and off of the switching transistor Q1, the storage and release of electric energy in the Y-capacitor-less transformer 10 can be controlled. The switching tube Q1 may be an N-type metal-oxide semiconductor (MOS) tube, the first conducting end of the switching tube Q1 corresponds to the drain electrode of the N-type MOS tube, the second conducting end of the switching tube Q1 corresponds to the source electrode of the N-type MOS tube, and the controlled end of the switching tube Q1 corresponds to the gate electrode of the N-type MOS tube. The first conducting end of the switching tube Q1 is the second output end of the primary side circuit 20.

The secondary side circuit 30 further includes a third capacitor C3, wherein a first end of the third capacitor C3 is connected to the first end of the secondary winding 400 and the secondary ground GND2, respectively, a second end of the third capacitor C3 is connected to the second end of the secondary winding 400, and a second end of the third capacitor C3 is used for being connected to the load 60 to output electric energy to the load 60. The first end of the third capacitor C3 is the second input end of the secondary side circuit 30.

In an embodiment, as shown in fig. 6, the flyback switch module 22 may use a flyback switch chip U1 and its peripheral circuit to connect with the primary winding 200, instead of the switching tube Q1 to realize the power transformation of the switching power supply circuit 40. The auxiliary winding 600 is also connected to the flyback switch chip U1 and its peripheral circuit, and is used for driving the flyback switch chip U1 to operate.

It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-described division of the functional units and modules is illustrated, and in practical application, the above-described functional distribution may be performed by different functional units and modules according to needs, i.e. the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-described functions. The functional units and modules in the embodiments may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. In addition, the specific names of the functional units and modules are only for distinguishing from each other, and are not used for limiting the protection scope of the present application. The specific working process of the units and modules in the above system may refer to the corresponding process in the foregoing method embodiment, which is not described herein again.

In the foregoing embodiments, the descriptions of the embodiments are emphasized, and in part, not described or illustrated in any particular embodiment, reference is made to the related descriptions of other embodiments.

The above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application, and are intended to be included in the scope of the present application.

Claims (10)

1. A Y-free capacitive transformer comprising: a magnetic core, a primary winding, a shielding winding and a secondary winding which are sequentially wound on the magnetic core; the primary winding is used for being connected with a primary side circuit, the secondary winding is used for being connected with a secondary side circuit, the shielding winding is used for being connected with a ground end, and the primary winding, the shielding winding and the secondary winding are mutually magnetically coupled, and the device is characterized in that:

The winding direction of the primary winding is opposite to the winding direction of the secondary winding, and the winding direction of the primary winding is the same as the winding direction of the shielding winding.

2. The Y-free capacitive transformer of claim 1, wherein the number of winding layers of the primary winding is at least 3; the primary winding is wound from a single enameled wire.

3. The Y-free capacitive transformer of claim 1, wherein the number of windings of the secondary winding is at least 1; the secondary winding is wound by a single three-layer insulated wire.

4. The Y-free capacitive transformer of claim 1, wherein the number of windings of the shield winding is at least 1; the shielding winding is wound by three enamelled wires.

5. The Y-free capacitive transformer of any one of claims 1-4, further comprising a first insulating layer, a second insulating layer, and a third insulating layer;

The first insulating layer is arranged between the primary winding and the shielding winding, the second insulating layer is arranged between the shielding winding and the secondary winding, and the third insulating layer is arranged on the outer side of the secondary winding.

6. The Y-free capacitive transformer of claim 5, wherein the first insulating layer, the second insulating layer, and the third insulating layer each comprise a multi-layer insulating tape.

7. The Y-free capacitive transformer of any one of claims 1-4, further comprising an auxiliary winding wound between the primary winding and the magnetic core, the auxiliary winding magnetically coupled to the primary winding, the auxiliary winding outputting an auxiliary voltage.

8. The Y-free capacitive transformer of claim 7, wherein the number of windings of the auxiliary winding is at least 1; the auxiliary winding is wound by two enamelled wires.

9. A switching power supply circuit comprising a primary side circuit, a secondary side circuit and a Y-capacitor-less transformer as claimed in any one of claims 1 to 8;

A first end of a primary winding of the Y-free capacitance transformer is connected with a first output end of the primary side circuit so as to be connected with a power supply through the primary side circuit; a second end of a primary winding of the Y-free capacitance transformer is connected with a second output end of the primary side circuit so as to be connected with primary ground through the primary side circuit;

A first end of a secondary winding of the Y-free capacitance transformer is connected with a first input end of the secondary side circuit so as to be connected with secondary ground through the secondary side circuit; a second end of a secondary winding of the Y-free capacitance transformer is connected with a second input end of the secondary side circuit so as to be connected with a load through the secondary side circuit;

The first end of the shielding winding of the Y-free capacitance transformer is suspended, and the second end of the shielding winding is connected with the primary ground;

The secondary side circuit comprises a secondary diode, wherein the anode of the secondary diode is connected with the secondary ground, and the cathode of the secondary diode is the first input end.

10. The switching power supply circuit according to claim 9, wherein the primary side circuit includes a rectifying and filtering module and a flyback switching module, an input terminal of the rectifying and filtering module is configured to be connected to the power supply, an output terminal of the rectifying and filtering module is connected to the flyback switching module, and the flyback switching module is provided with the first output terminal and the second output terminal.