Transformer for flyback switching power supply and flyback switching power supply

Abstract

The application relates to a transformer for a flyback switching power supply and the flyback switching power supply, two of the first primary winding, the second primary winding and the third primary winding of the transformer are connected in parallel and connected with the other in series to form a primary winding unit, the primary winding unit is connected between the static point pin and the dynamic point pin of the transformer, and a Y-shaped winding method or an inverted Y-shaped winding method with the dynamic point pin as a reference point can be formed; when the inverted Y-shaped winding method is adopted, the magnetic field generated by the primary winding is distributed in an axial symmetry in the winding window, the leakage inductance can be obviously reduced, and the power supply efficiency can be improved; the Y-shaped winding method or the inverted Y-shaped winding method can distribute more turns in the primary winding which is not connected in parallel, the number of the windings connected in parallel is reduced, and the parasitic capacitance of the secondary winding can be reduced.

Description

Technical Field

[0001] This application belongs to the field of power electronics technology, and in particular relates to a transformer for a flyback switching power supply and a flyback switching power supply. Background Technology

[0002] Currently, flyback topology transformers with high energy efficiency requirements often employ the five-layer winding method, such as... Figure 1 As shown, this winding method involves five layers of alternating windings, i.e., from the inside to the outside of the magnetic core, the windings are: primary-secondary-primary-secondary-primary, with the shielding winding typically located between the first secondary winding and the second primary winding. However, the five-layer sandwich winding method has the following problems: the leakage inductance accounts for about 1% of the total inductance, and the leakage inductance spike is still relatively high in flyback applications; the parasitic capacitance of the five-layer sandwich winding method is relatively large, and the five-layer sandwich winding method requires one more transformer pin compared to the four-layer sandwich winding method. Utility Model Content

[0003] The purpose of this application is to provide a transformer and a flyback switching power supply for flyback switching power supplies, aiming to solve the problems of large number of pins, large leakage inductance, and large parasitic capacitance of traditional flyback topology transformers, which affect the overall energy efficiency.

[0004] In a first aspect, embodiments of this application provide a transformer for a flyback switching power supply, including a magnetic core, a frame disposed on the magnetic core, and a winding wound on the frame, the winding including a primary winding and a secondary winding.

[0005] The primary winding includes a first primary winding, a second primary winding, and a third primary winding. Two of the first primary winding, the second primary winding, and the third primary winding are connected in parallel, and the third primary winding is connected in series to form a primary winding unit. The primary winding unit is connected between the stationary pin and the moving pin of the transformer. The stationary pin is used to connect to the input terminal of the flyback switching power supply, and the moving pin is used to connect to the switching transistor of the flyback switching power supply.

[0006] In some embodiments, the secondary winding includes a primary winding and a secondary winding, wherein the primary winding and the secondary winding are connected in parallel between the positive and negative output terminals of the transformer.

[0007] In some embodiments, the first primary winding, the first secondary winding, the second primary winding, the second secondary winding, and the third primary winding are sequentially stacked and wound outward from the magnetic core.

[0008] In some embodiments, a shielding winding is further included, the shielding winding being wound between the first primary winding and the second primary winding.

[0009] In some embodiments, an auxiliary winding is further included, which is wound outside the third primary winding.

[0010] In some embodiments, the sum of the number of windings in the two parallel windings in the primary winding unit is equal to the number of windings in the other winding.

[0011] In some embodiments, the two parallel windings in the primary winding unit have the same number of windings.

[0012] In some embodiments, the first end of the second primary winding and the third primary winding connected in parallel is connected to the stationary pin, the second end of the second primary winding and the third primary winding connected in parallel is connected to the first end of the first primary winding, and the second end of the first primary winding is connected to the moving pin.

[0013] In some embodiments, the first end of the second primary winding is connected to the stationary pin, the second end of the second primary winding is connected to the first end of the first primary winding and the third primary winding connected in parallel, and the second end of the first primary winding and the third primary winding connected in parallel is connected to the moving pin.

[0014] Secondly, embodiments of this application provide a flyback switching power supply, including an input circuit, an output circuit, and a transformer for the flyback switching power supply as described above. The input circuit includes an input terminal and a switching transistor. The stationary pin of the transformer is connected to the input terminal, and the moving pin of the transformer is grounded through the switching transistor. The positive and negative output terminals of the transformer are connected to the output circuit.

[0015] The beneficial effects of this application embodiment compared with related technologies are as follows: Two of the first primary winding, second primary winding, and third primary winding of the transformer are connected in parallel and then connected in series with the third primary winding to form a primary winding unit. The primary winding unit is connected between the stationary pin and the moving pin of the transformer, which can form a Y-type winding or an inverted Y-type winding with the moving pin as the reference point, thus reducing one transformer pin. In addition, the inverted Y-type winding makes the magnetic field generated by the primary winding axially symmetrically distributed in the winding window, which can significantly reduce leakage inductance and improve overall energy efficiency. The Y-type winding or inverted Y-type winding can distribute more turns in the non-parallel primary windings, thereby reducing the number of parallel windings and helping to reduce the parasitic capacitance of the secondary winding. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a transformer using the conventional five-layer winding method;

[0017] Figure 2 This refers to the method of generating transformer leakage inductance;

[0018] Figure 3 This is a schematic diagram of the magnetic flux density generated by a single-turn planar energized coil of a transformer, where the spherical infinite element represents the region with an infinitely far boundary.

[0019] Figure 4 This is a schematic diagram of the structure of a transformer using the conventional five-layer winding method;

[0020] Figure 5 A circuit diagram of a flyback switching power supply provided in an embodiment of this application;

[0021] Figure 6 A circuit diagram of a transformer (Y-wound) for a flyback switching power supply provided in an embodiment of this application;

[0022] Figure 7 for Figure 6 A schematic diagram of the structure of a transformer used in a flyback switching power supply is shown.

[0023] Figure 8 A circuit diagram of a transformer (inverted Y-type winding) for a flyback switching power supply provided in an embodiment of this application;

[0024] Figure 9 for Figure 8 A schematic diagram of the structure of a transformer used in a flyback switching power supply is shown.

[0025] Figure 10 A circuit diagram of a transformer (Y-wound) for a flyback switching power supply provided in an embodiment of this application;

[0026] Figure 11 for Figure 10 A schematic diagram of the structure of a transformer used in a flyback switching power supply is shown.

[0027] Figure 12 This is a schematic diagram of the structure of a transformer using the conventional four-sided winding method. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0029] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0030] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0032] Flyback switching power supplies are widely used in small and medium power electronic devices due to their simple structure, low cost, and ease of implementing multiple outputs. Their working principle is as follows: when the switching device, such as a MOSFET, is turned on, the primary winding of the transformer stores energy, and no current flows through the secondary winding. When the switching device is turned off, the energy from the primary winding is coupled to the secondary winding, and after rectification and filtering, DC power is output. During this process, the magnetic field lines generated by the transformer coil cannot completely pass through the secondary coil, so there will inevitably be some magnetic flux that cannot be coupled to the secondary (i.e., leakage inductance). The larger the leakage inductance, the lower the efficiency of energy transfer by the transformer, leading to increased power losses, especially when operating at high switching frequencies, which limits the development of switching power supplies towards high power density. Furthermore, at the instant the MOSFET is turned off, the current in the leakage inductance cannot change abruptly, causing oscillations between the drain and source pins of the MOSFET, resulting in a very high voltage spike between the drain and source. This spike not only increases the turn-off losses of the MOSFET but can also lead to MOSFET breakdown and damage.

[0033] Leakage inductance can be reduced by improving transformer design and manufacturing processes. Current transformer winding methods often employ sandwich (three layers of windings interleaved), four-layer (four layers of windings interleaved), or even five-layer (five layers of windings interleaved) windings. These methods increase coupling between the primary and secondary windings, reducing leakage inductance. The five-layer winding method is generally considered the most complex type in small-to-medium power flyback transformers, and winding schemes with more than five layers of interleaved windings offer very low marginal benefits for improving energy efficiency.

[0034] Leakage inductance in conventional transformers can be categorized into two types. The first type occurs because the permeability of the magnetic core is not infinite relative to other materials in the transformer, causing magnetic flux leakage as the magnetic lines of force entering the core may still escape and leak out. Figure 2 As shown in the left figure; the second type of leakage originates from a certain distance between the currents in the primary and secondary windings, causing the generated magnetic field lines to cross the region between the primary and secondary currents (see...). Figure 2 In the right figure, red and orange represent the primary coil plane, and blue represents the region between them (hereinafter referred to as the leakage region). Because the magnetic field distribution of a finite-length energized solenoid is concentrated near the coil (see...),... Figure 3 Therefore, the magnetic flux in the leakage region is quite considerable. Assuming the core is a perfect magnetic conductor, and as... Figure 1 The magnetic field lines generated by the N1 winding shown are all absorbed by the magnetic core. In this case, the key to reducing leakage inductance is to reduce the proportion of magnetic flux passing through the leakage region to the total magnetic flux. This can be achieved by matching the inner and outer windings with an appropriate number of turns and wire diameter to match the minimum leakage inductance. In addition to leakage inductance, some studies have also pointed out that the location of the transformer's distributed capacitance also affects the transformer's losses, which are more pronounced for small-power transformers.

[0035] The conventional five-inch winding structure is shown below. Figure 1 (Ignoring auxiliary windings), the winding includes the first, second, and third primary windings P1, P2, and P3; the first and second secondary windings S1 and S2; the shielding winding P4; and the auxiliary winding P5. The parameters are: EQ3019 magnetic core, inductance 525uH. A typical winding scheme is shown below. Figure 4 The first, second, and third primary windings P1, P2, and P3 are all 0.1mm*40 strands, 11 turns of stranded enameled wire wound in one layer. The first, second, and third primary windings P1, P2, and P3 are connected in series end to end. The first and second primary windings S1 and S2 are both 0.45mm triple-insulated wire wound in 14 turns. The first and second primary windings S1 and S2 are double-wire wound in two layers and connected in parallel. The second and third primary windings P2 and P3 are single-wire wound in one layer. It can be seen that the number of wires and layers of adjacent windings are different, which makes the leakage area of ​​this winding method two places, one between the first primary winding S1 and the second primary winding P2, and the other between the second primary winding S2 and the third primary winding P3.

[0036] To address the aforementioned issues, this application proposes a new transformer winding scheme. Please refer to [link / reference needed]. Figure 5This application provides a transformer 10 for a flyback switching power supply. The flyback switching power supply includes an input circuit 11, an output circuit 12, and the transformer 10. The input circuit 11 includes an input terminal VIN and a switching transistor Q1. The stationary pin PIN3 of the transformer 10 is connected to the input terminal VIN, and the moving pin PIN1 of the transformer 10 is grounded through the switching transistor Q1. The positive output pin PIN11 and the negative output pin PIN12 of the transformer 10 are connected to the output circuit 12. The input terminal VIN is the high-voltage bus input terminal.

[0037] In some embodiments, the input circuit 11 includes an input terminal VIN, a startup circuit R1, a switching transistor Q1, and a PWM control chip U1. The input terminal VIN is connected to the drain of the main switching transistor Q1 through the primary winding 310 of the transformer 10. The source of the switching transistor Q1 is connected to the CS (current sampling) pin of the PWM control chip U1 and grounded through the sampling resistor R2. The GATE pin of the PWM control chip U1 is connected to the gate of the main switching transistor Q1. The auxiliary winding P5 and the startup circuit R1 are connected to the VDD (power supply) pin of the PWM control chip U1. The startup circuit R1 is connected to the input terminal VIN and generally includes a current-limiting resistor. In addition, the flyback switching power supply generally also includes a voltage detection circuit 13, which detects the output voltage of the output section and inputs it to the FB (feedback) pin of the PWM control chip U1 through an optocoupler U2. The circuit structure of the voltage detection circuit 13 can be found in [reference needed]. Figure 5 Example. It is understood that the input terminal VIN may include a rectifier bridge and a filter capacitor for connecting AC voltage; the input terminal VIN may also be a DC input terminal for connecting DC power. The output circuit 12 includes rectifier diodes D1 / D2 and a filter capacitor C1. The rectifier diodes D1 / D2 are connected between the positive output terminal PIN11 of the transformer 10 and the positive output terminal V+ of the output circuit 12, and the filter capacitor C1 is connected between the positive and negative output terminals V+ / V- of the output circuit 12. It is understood that the above is merely a brief description of the input circuit 11 and output circuit 12 of a flyback switching power supply in one specific embodiment, which is exemplary and used to illustrate the technical solution of this application, and not to limit it. Those skilled in the art should understand that the input circuit 11 and output circuit 12 of the flyback switching power supply can also have other equivalent embodiments.

[0038] Please see Figures 5 to 11 The transformer 10 includes a magnetic core 100, a frame 200 disposed on the magnetic core 100, and a winding 300 wound on the frame 200. The winding 300 includes a primary winding 310 and a secondary winding 320.

[0039] The primary winding 310 includes a first primary winding P1, a second primary winding P2, and a third primary winding P3. Two of the first primary winding P1, the second primary winding P2, and the third primary winding P3 are connected in parallel and then connected in series with the third primary winding to form a primary winding unit. The primary winding unit is connected between the stationary pin PIN3 and the moving pin PIN1 of the transformer 10. The stationary pin PIN3 is used to connect to the input terminal of the flyback switching power supply, and the moving pin PIN1 is used to connect to the switching transistor of the flyback switching power supply.

[0040] The primary winding unit is connected between the stationary pin PIN3 and the moving pin PIN1 of the transformer 10. The primary winding unit can be configured as a Y-type winding or an inverted Y-type winding with the moving pin PIN1 as the reference point, which can reduce one pin of the transformer 10. In addition, the inverted Y-type winding makes the magnetic field generated by the primary winding 310 axially symmetrically distributed in the winding window, which can significantly reduce leakage inductance and improve overall energy efficiency. The Y-type winding or inverted Y-type winding can distribute more turns in the non-parallel primary winding, reducing the number of parallel windings and helping to reduce the parasitic capacitance of the secondary winding 320.

[0041] Please see Figure 6 and Figure 7 In some embodiments, the first end of the parallel connection of the second primary winding P2 and the third primary winding P3 is connected to the stationary pin PIN3, and the second end of the parallel connection of the second primary winding P2 and the third primary winding P3 is connected to the first end of the first primary winding P1, i.e., both are connected to the center tap PIN2. The second end of the first primary winding P1 is connected to the moving pin PIN1. This allows the primary winding unit to form a Y-shaped winding with the moving pin PIN1 as the reference point.

[0042] The number of wires used in the first primary winding P1 is twice that of the second primary winding P2 or the third primary winding P3. The number of turns and wires in the second primary winding P2 and the third primary winding P3 are the same.

[0043] Please see Figure 8 and Figure 9 In some embodiments, the first end of the second primary winding P2 is connected to the stationary pin PIN3, the second end of the second primary winding P2 is connected to the first end of the parallel connection of the first primary winding P1 and the third primary winding P3, i.e., they are all connected to the center tap PIN2, and the second end of the parallel connection of the first primary winding P1 and the third primary winding P3 is connected to the moving pin PIN1. This allows the primary winding unit to form an inverted Y-shaped winding with the moving pin PIN1 as the reference point.

[0044] The number of wires used in the second primary winding P2 is twice that of the first primary winding P1 or the third primary winding P3. The number of turns and wires in the first primary winding P1 and the third primary winding P3 are the same.

[0045] It is understandable that the sum of the wire counts of two windings in a parallel configuration equals the wire count of the other winding, and the winding order of the three can be adjusted according to the requirements of energy efficiency and electromagnetic interference (EMI) testing. For example, Figure 7 and Figure 9 The winding direction is from the inside out of the magnetic core 100, and when viewed from the bottom of the magnetic core 100 (the bottom of the magnetic core 100 refers to the side where the pins are set) to the top, the winding is counterclockwise.

[0046] Please see Figures 5 to 9 In some embodiments, the secondary winding 320 includes a primary winding S1 and a secondary winding S2, which are connected in parallel between the positive and negative output terminals of the transformer 10.

[0047] Please see Figure 7 , Figure 9 and Figure 11 In some embodiments, the first primary winding P1, the first primary winding S1, the second primary winding P2, the second primary winding S2, and the third primary winding P3 are sequentially stacked and wound outward from the magnetic core 100. It is understood that in other embodiments, the winding order of the first primary winding P1, the second primary winding P2, and the third primary winding P3 can be changed. For example, from the magnetic core 100 outward, the order could be: first primary winding P1, third primary winding P3, second primary winding P2; or: second primary winding P2, first primary winding P1, third primary winding P3; or: second primary winding P2, third primary winding P3, first primary winding P1; or: third primary winding P3, second primary winding P2, first primary winding P1; or: third primary winding P3, first primary winding P1, second primary winding P2.

[0048] Please see Figure 7 , Figure 9 and Figure 11 In some embodiments, the primary winding 310 further includes a shielding winding P4, which is wound between the first primary winding S1 and the second primary winding P2.

[0049] Please see Figure 7 , Figure 9 and Figure 11 In some embodiments, the primary winding 310 further includes an auxiliary winding P5, which is wound outside the third primary winding P3. It is understood that the auxiliary winding P5 can also serve a shielding function, and depending on the adjustment, it can be wound in many positions, not limited to outside the primary winding unit, but can be wound within the primary winding unit.

[0050] For example, the winding 300 of transformer 10 is uniformly wound in seven layers N1-N7 along the skeleton axis. The first primary winding P1, the second primary winding P2, and the third primary winding P3 are located in the first layer N1, the fourth layer N4, and the sixth layer N6, respectively. The first primary winding S1 and the second primary winding S2 are located in the second layer N2 and the fifth layer N5, respectively. The shielding winding P4 is located in the third layer N3, and the auxiliary winding is located in the seventh layer N7. The winding direction of winding 300 is from the bottom of the transformer (i.e., the side where the pins are set) to the top, and the direction of the wires winding around the skeleton is counterclockwise.

[0051] In some embodiments, the sum of the number of windings in the two parallel windings of the primary winding unit is equal to the number of windings in the other winding. In some embodiments, the number of windings in the two parallel windings of the primary winding unit is the same.

[0052] For example, please refer to Figure 7 In the Y-type winding method, the number of windings in the first primary winding P1 is the sum of the winding parameters of the second primary winding P2 and the number of windings in the third primary winding P3. The number of windings in the second primary winding P2 and the third primary winding P3 is the same. Please refer to [link / reference]. Figure 9 In the inverted Y-shaped winding method, the number of windings in the second primary winding P2 is the sum of the number of windings in the first primary winding P1 and the third primary winding P3, and the number of windings in the first primary winding P1 and the third primary winding P3 is the same. For example, the single-wire parameters of all the above windings are similar.

[0053] Understandable Figure 7 , Figure 9 and Figure 11 The winding diagrams shown for each winding layer N1 to N7 are merely a visual representation of the winding structure and do not represent the actual number of winding layers, winding direction, number of turns, wire diameter, number of wires, or winding tightness.

[0054] The transformer 10 provided in this application embodiment includes two forms: Y-type winding and inverted Y-type winding. Without increasing the cost of the transformer winding, the magnetic field and capacitance distribution of the transformer 10 are adjusted by combining the series and parallel connection of the moving point pin PIN1 to the stationary point pin PIN3 of the primary winding 310, thereby improving the energy efficiency and other performance of the transformer 10 and meeting the needs of large-scale production of small and medium power flyback switching power supplies.

[0055] Please see Figures 5 to 9 The transformer 10 provided in this application embodiment has three primary windings P1 / P2 / P3, and the series connection node of the three primary windings P1 / P2 / P3 represents the center tap pin PIN2 of the transformer 10.

[0056] In some embodiments, the structure of winding 300 can be flexibly adjusted. The three primary windings P1 / P2 / P3 and the shielding winding P4 can be freely adjusted to design the transformer 10 according to the actual situation, thereby obtaining lower leakage inductance and better performance. For example, for magnetic cores with a large Ae value and good outer wrapping effect (such as PQ4532), the leakage area of ​​the outer winding is small. In this case, using an inverted Y-shaped winding method makes the magnetic field generated by the primary winding 310 axially symmetrically distributed in the winding window, forming an optimal match with the leakage area, which can significantly reduce leakage inductance. For another example, using a Y-shaped winding method can distribute more turns in the winding of the first layer N1, so that the shielding winding P4 located in the fourth layer N4 has a better shielding effect on the first primary winding P1 and the first secondary winding S1, and the second primary winding P2 and the third secondary winding P3 have fewer wires, resulting in smaller parasitic capacitance to the secondary winding 320.

[0057] The placement of the moving contact pin PIN1 now offers more options; it can be placed on the middle layer. (See [reference]). Figure 10 The Y-shaped winding is shielded by the two secondary windings S1 and S2 and the auxiliary winding P5; alternatively, it can be placed in the first layer N1, see [reference needed]. Figure 7 It is shielded by magnetic core 100 and primary winding S1.

[0058] Please see Figure 7 Due to the effect of the shielding winding P4 and the parallel connection between the second primary winding P2 and the third primary winding P3, the distributed capacitance of the primary winding 310 of the transformer 10 is concentrated in the first layer N1, which helps to reduce the loss of the transformer 10 under certain circumstances.

[0059] Compared to Figure 4 The conventional transformer shown can save one transformer pin, simplifying the process, offering greater flexibility in bobbin selection, and improving energy efficiency.

[0060] See Figure 4 , 7 9 and Figure 12 As shown in Tables 1 and 2, compared to the five-layer winding using the same materials, the Y-type winding, taking EQ3019 and EQ39.6 cores as examples, has a leakage inductance as low as approximately 0.41-0.56% of the total inductance, a 57.7% reduction in primary AC impedance, a 0.19% increase in efficiency percentage, a 11V decrease in Vds of the switching transistor Q1, and a reduction in the primary-secondary capacitance from 208pF to 193.5pF. The winding scheme parameters and test results are shown in Tables 1 and 2. It is evident that the Y-type winding is superior to the conventional five-layer winding in terms of both efficiency and switching transistor stress, and represents a significant improvement over the four-layer winding using the same materials.

[0061] Taking the PQ4532 core using an inverted Y-type winding as an example, the improvement is significant. Leakage inductance can be reduced to 0.4%–0.7% of the total inductance (compared to 0.7%–1% for conventional five-sided winding), efficiency percentage is improved by 0.15%–0.3%, and the Vds of the switching transistor Q1 decreases by 30V. In high-power flyback switching power supplies, the transformer advantages of this application's technical solution are even more pronounced. While the leakage inductance of the Y-type winding is not reduced compared to the five-sided winding, its lower AC impedance results in higher overall efficiency than the conventional five-sided winding; furthermore, saving one pin is also a significant advantage.

[0062] Table 1, Y-shaped winding method of this application embodiment (see Table 1) Figure 7 ) and inverted Y-shaped winding method (see Figure 9 ), compared to a regular four-sided sandwich (see Figure 12 ), Five-point wrapping method (see Figure 4 Example:

[0063]

[0064] Table 2. Test results of EQ3019 magnetic core using different winding methods:

[0065]

[0066] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A transformer for a flyback switching power supply, characterized in that, It includes a magnetic core, a frame disposed on the magnetic core, and a winding wound on the frame, wherein the winding includes a primary winding and a secondary winding; The primary winding includes a first primary winding, a second primary winding, and a third primary winding. Two of the first primary winding, the second primary winding, and the third primary winding are connected in parallel and then connected in series with the third primary winding to form a primary winding unit. The primary winding unit is connected between the stationary pin and the moving pin of the transformer. The stationary pin is used to connect to the input terminal of the flyback switching power supply, and the moving pin is used to connect to the switching transistor of the flyback switching power supply.

2. The transformer as described in claim 1, characterized in that, The secondary winding includes a primary winding and a secondary winding, which are connected in parallel between the positive and negative output terminals of the transformer.

3. The transformer as described in claim 2, characterized in that, The first primary winding, the first secondary winding, the second primary winding, the second secondary winding, and the third primary winding are sequentially stacked and wound outward from the magnetic core.

4. The transformer as described in claim 3, characterized in that, It also includes a shielding winding, which is wound between the first primary winding and the second primary winding.

5. The transformer as described in claim 3 or 4, characterized in that, It also includes an auxiliary winding, which is wound outside the third primary winding.

6. The transformer as described in claim 1, characterized in that, The sum of the number of windings in the two parallel windings in the primary winding unit is equal to the number of windings in the other winding.

7. The transformer as described in claim 1 or 6, characterized in that, The two parallel windings in the primary winding unit have the same number of windings.

8. The transformer as described in claim 1 or 2, characterized in that, The first end of the second primary winding and the third primary winding connected in parallel is connected to the stationary pin, the second end of the second primary winding and the third primary winding connected in parallel is connected to the first end of the first primary winding, and the second end of the first primary winding is connected to the moving pin.

9. The transformer as described in claim 1 or 2, characterized in that, The first end of the second primary winding is connected to the stationary pin, the second end of the second primary winding is connected to the first end of the first primary winding and the third primary winding connected in parallel, and the second end of the first primary winding and the third primary winding connected in parallel is connected to the moving pin.

10. A flyback switching power supply, characterized in that, The power supply includes an input circuit, an output circuit, and a transformer for a flyback switching power supply as described in any one of claims 1 to 9. The input circuit includes an input terminal and a switching transistor. The stationary pin of the transformer is connected to the input terminal, and the moving pin of the transformer is grounded through the switching transistor. The positive and negative output terminals of the transformer are connected to the output circuit.

Images