Buck converter

Abstract

Disclosed in the present invention is a buck converter. The buck converter comprises a power supply module, a switch module, a magnetically integrated transformer, a rectifier module and a load, wherein the magnetically integrated transformer comprises a first winding, a second winding, a third winding, a fourth winding, a first side leg of a magnetic core, a second side leg of the magnetic core, and a center leg of the magnetic core; and the switch module is used for controlling a power supply Vin outputted by the power supply module to flow into the magnetically integrated transformer, and in cooperation with the rectification function of the rectifier module, clamping the voltage of the third winding at Vo and / or clamping the voltage of the fourth winding at -Vo, Vo being the voltage across the load, and Vin>Vo. In the present invention, no isolation device is provided, the number of turns of a transformer is reduced, and an independent output inductor is not required, thereby reducing the structural complexity of the buck converter, shortening the development cycle of the buck converter, and reducing the development cost of the buck converter.

Description

Voltage reducing converter TECHNICAL FIELD

[0001] The present application relates to the field of switching power supply, in particular to a voltage reducing converter. BACKGROUND

[0002] In recent years, with the increase of computing capacity, the power demand of server single board card is getting larger and larger, especially with the widespread use of rack-mounted servers, the current of DC power supply bus is getting larger and larger, and the power supply architecture using 48V bus to supply power to server board card gradually replaces the traditional architecture of 12V bus; this 48V architecture usually converts the AC grid power into 48V DC bus through an AC power supply, and then converts 48V into 12V, and 12V into various voltages as low as 0.6V required by chipsets for power supply to chipsets. There are also some solutions that directly convert 48V into about 1V CPU core voltage for CPU power supply. In addition to the low voltage power supply as low as 0.6V required by each chipset in the server system, there are also many 12V loads such as fans and memories, and the method of converting 48V to 12V and then converting 12V to voltage for power supply to chipsets has gradually become the mainstream.

[0003] On the one hand, the server market is huge in size and has high cost pressure; on the other hand, the global energy saving and consumption reduction requirements are getting higher and higher, which makes the low-cost and high-efficiency 48V to 12V become a very important research direction in the field of power electronics, many research resources enter this field, and many research results are presented in succession. The most common solution in the current market is to continuously optimize the 48V to 12V module power supply widely used in the traditional communication field; most of the power head enterprises in this application adopt isolated half-bridge or full-bridge hard switching scheme; in order to achieve higher efficiency and power density, this development direction continuously increases the number of layers and copper thickness of PCB, continuously optimizes the design of isolation transformer, selects power MOS tube with better performance, which leads to more complex structure of the converter, further leading to longer development cycle and increasing development cost of the converter.

[0004] SUMMARY

[0005] The present application aims at overcoming the deficiencies in the prior art, and provides a voltage reducing converter.

[0006] In order to achieve the above-mentioned application purpose, the present application provides the following technical scheme:

[0007] A voltage reducing converter, comprising a power module, a switching module, a magnetic integrated transformer, a rectifier module and a load,

[0008] The magnetic integrated transformer is connected with the load and the rectifier module respectively, and comprises a first winding, a second winding, a third winding, a fourth winding, a first side column of a magnetic core, a second side column of the magnetic core, and a middle column of the magnetic core.

[0009] The switch module is connected with the power module, the rectifier module, and the magnetic integrated transformer respectively, the power module is connected with the load and the rectifier module respectively, the switch module is used for controlling the power Vin output by the power module to flow into the magnetic integrated transformer, and cooperates with the rectification of the rectifier module to clamp the voltage of the third winding at Vo and / or clamp the voltage of the fourth winding at -Vo, wherein Vo is the voltage across the load, and Vin>Vo.

[0010] Further, the switch module comprises a first switch tube, a second switch tube, a third switch tube, and a fourth switch tube, and the rectifier module comprises a first rectifier tube and a second rectifier tube.

[0011] The positive terminal of the power module is electrically connected with the positive terminal of the first switch tube, the negative terminal of the first switch tube is electrically connected with the positive terminal of the second switch tube, the negative terminal of the second switch tube is electrically connected with the negative terminal of the first rectifier tube, the positive terminal of the first rectifier tube is grounded and electrically connected with the negative terminal of the power module, the positive terminal of the power module is also electrically connected with the positive terminal of the third switch tube, the negative terminal of the third switch tube is electrically connected with the positive terminal of the fourth switch tube, the negative terminal of the fourth switch tube is electrically connected with the negative terminal of the second rectifier tube, and the positive terminal of the second rectifier tube is electrically connected with the positive terminal of the first rectifier tube.

[0012] The same terminal of the first winding is electrically connected between the negative terminal of the first switch tube and the positive terminal of the second switch tube, the non-same terminal of the first winding is electrically connected with the same terminal of the second winding, the non-same terminal of the second winding is electrically connected between the negative terminal of the third switch tube and the positive terminal of the fourth switch tube, the same terminal of the fourth winding is electrically connected between the negative terminal of the fourth switch tube and the negative terminal of the second rectifier tube, the non-same terminal of the fourth winding is electrically connected with the same terminal of the third winding, the non-same terminal of the third winding is electrically connected between the negative terminal of the second switch tube and the negative terminal of the first rectifier tube, the positive terminal of the load is electrically connected between the same terminal of the third winding and the non-same terminal of the fourth winding, and the negative terminal of the load is electrically connected between the positive terminal of the first rectifier tube and the positive terminal of the second rectifier tube.

[0013] Further, the number of turns of the first winding is equal to the number of turns of the second winding, and the number of turns of the third winding is equal to the number of turns of the fourth winding.

[0014] Further, the first switch tube and the fourth switch tube are turned on, the second switch tube and the third switch tube are turned off, the first rectifier tube is turned on, and the voltage of the third winding is clamped at Vo; the first switch tube and the second switch tube are turned off, the second switch tube and the third switch tube are turned on, the second rectifier tube D2 is turned on, and the voltage of the fourth winding is clamped at -Vo; the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are turned off, the first rectifier tube and the second rectifier tube are turned on, the voltage of the third winding is clamped at Vo, and the voltage of the fourth winding is clamped at -Vo.

[0015] Further, the relationship between the power Vin output by the power supply module and the voltage Vo across the load is expressed as: Vo = Vin * Dn2 / (n1 + n2), wherein D is the duty cycle of the switch module.

[0016] Further, the magnetic core is EE type or EI type.

[0017] Further, the middle section of the column of the magnetic core is provided with an air gap

[0018] Further, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are all field effect tubes.

[0019] The positive electrode of the power supply module is electrically connected with the source electrode of the first switch tube, the drain electrode of the first switch tube is electrically connected with the source electrode of the second switch tube, the drain electrode of the second switch tube is electrically connected with the negative end of the first rectifier tube, the positive end of the first rectifier tube is grounded and electrically connected with the negative electrode of the power supply module, the positive electrode of the power supply module is also electrically connected with the source electrode of the third switch tube, the drain electrode of the third switch tube is electrically connected with the source electrode of the fourth switch tube, the drain electrode of the fourth switch tube is electrically connected with the negative end of the second rectifier tube, and the positive end of the second rectifier tube is electrically connected with the positive end of the first rectifier tube.

[0020] The same name end of the first winding is electrically connected between the drain of the first switch tube and the source of the second switch tube, the non-same name end of the first winding is electrically connected with the same name end of the second winding, the non-same name end of the second winding is electrically connected between the drain of the third switch tube and the source of the fourth switch tube, the same name end of the fourth winding is electrically connected between the drain of the fourth switch tube and the negative end of the second rectifier tube, the non-same name end of the fourth winding is electrically connected with the same name end of the third winding, the non-same name end of the third winding is electrically connected between the drain of the second switch tube and the negative end of the first rectifier tube, the positive end of the load is electrically connected between the same name end of the third winding and the non-same name end of the fourth winding, and the negative end of the load is electrically connected between the positive end of the first rectifier tube and the positive end of the second rectifier tube.

[0021] Further, the first rectifier tube and the second rectifier tube are diodes or synchronous rectifier tubes.

[0022] Further, a first capacitor is further included, a first end of the first capacitor is electrically connected between the drain of the first switch tube and the source of the second switch tube, and a second end of the first capacitor is electrically connected with the same name end of the first winding.

[0023] Further, the first end of the first capacitor is electrically connected to the non-same name end of the first winding, and the second end of the first capacitor is electrically connected to the same name end of the second winding.

[0024] Further, the load includes a resistance and a second capacitor connected in parallel.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] The step-down converter structure of the present application includes a power supply module, a switch module, a magnetic integrated transformer, a rectifier module and a load, and does not be provided with an isolating device, reduces the number of turns of the transformer, reduces the structural complexity of the step-down converter, greatly reduces the number of layers of PCB in the field of adopting multi-layer PCB and flat transformer technology, reduces the development cost of the step-down converter, shortens the development cycle of the step-down converter, and utilizes the magnetic integration technology, does not need an independent output filter inductor, helps to reduce the volume and weight of the step-down converter, improves the electric energy conversion efficiency and power density, and further, the switch module controls the power Vin output by the power supply module to flow into the magnetic integrated transformer, and cooperates with the rectification effect of the rectifier module to clamp the voltage of the third winding at Vo and / or clamp the voltage of the fourth winding at -Vo, so that the voltage of the load can be stabilized at Vo. BRIEF DESCRIPTION OF DRAWINGS

[0027] Fig. 1 is a schematic diagram of the system structure of a step-down converter;

[0028] Fig. 2 is a schematic diagram of the circuit structure of the step-down converter;

[0029] Fig. 3 is a schematic diagram of the circuit structure of the rectifier tube being a synchronous rectifier tube;

[0030] Fig. 4 is a schematic diagram of the circuit structure of the series gap capacitor between the magnetic core and the switching module;

[0031] Fig. 5 is a schematic diagram of the circuit structure of the series gap capacitor between the magnetic cores. DETAILED DESCRIPTION

[0032] The present application will be further described in conjunction with test examples and specific embodiments. However, it should not be understood that the scope of the above-mentioned subject matter of the present application is limited to the following examples, and any technology realized based on the content of the present application falls within the scope of the present application.

[0033] In order to reduce the complexity of the structure of the step-down converter in the prior art, as shown in Figs. 1 and 2, the present disclosure provides a step-down converter, which comprises a power supply module 1, a switching module 2, a magnetic integrated transformer 3, a rectifier module 4 and a load 5,

[0034] The magnetic integrated transformer 3 is connected with the load 5 and the rectifier module 4 respectively, and comprises a first winding N1, a second winding N2, a third winding N3, a fourth winding N4, a first side column of a magnetic core, a second side column of the magnetic core, a middle column of the magnetic core, the first winding N1 and the third winding N3 are wound on the first side column of the magnetic core, and the second winding N2 and the fourth winding N4 are wound on the second side column of the magnetic core. By using the magnetic integration technology, an independent output filter inductor is not needed, the number of magnetic devices is reduced, which helps to reduce the volume and weight of the step-down converter, higher power output can be achieved in a smaller space, and the power conversion efficiency and power density are improved.

[0035] In some embodiments, the type of the magnetic core is EE or EI, and as a preferred embodiment of the present embodiment, the middle section of the middle column of the magnetic core is provided with an air gap, so that the magnetic integrated transformer 3 is more easily produced in industry, and the production cost of the step-down converter is also reduced, and the air gap also helps to prevent the magnetic core from being saturated under high voltage or high current conditions.

[0036] The switching module 2 is connected with the power supply module 1, the rectifier module 4 and the magnetic integrated transformer 3 respectively, the power supply module 1 is connected with the load 5 and the rectifier module 4 respectively, and the switching module 2 is used to control the power Vin output by the power supply module 1 to flow into the magnetic integrated transformer 3, and cooperates with the rectification of the rectifier module 4 to clamp the voltage of the third winding N3 at Vo and / or clamp the voltage of the fourth winding N4 at -Vo, Vo is the voltage across the load 5, and Vin>Vo.

[0037] In some embodiments, the switch module 2 includes a first switch S1, a second switch S2, a third switch S3 and a fourth switch S4, the rectifier module 4 includes a first rectifier D1 and a second rectifier D2, the positive pole of the power supply module 1 is electrically connected to the positive terminal of the first switch S1, the negative terminal of the first switch S1 is electrically connected to the positive terminal of the second switch S2, the negative terminal of the second switch S2 is electrically connected to the negative terminal of the first rectifier D1, the positive terminal of the first rectifier D1 is grounded and electrically connected to the negative pole of the power supply module 1, the positive pole of the power supply module 1 is also electrically connected to the positive terminal of the third switch S3, the negative terminal of the third switch S3 is electrically connected to the positive terminal of the fourth switch S4, the negative terminal of the fourth switch S4 is electrically connected to the negative terminal of the second rectifier D2, the positive terminal of the second rectifier D2 is electrically connected to the positive terminal of the first rectifier D1, the same terminal of the first winding N1 is electrically connected between the negative terminal of the first switch S1 and the positive terminal of the second switch S2, the non-same terminal of the first winding N1 is electrically connected to the same terminal of the second winding N2, the non-same terminal of the second winding N2 is electrically connected between the negative terminal of the third switch S3 and the positive terminal of the fourth switch S4, the same terminal of the fourth winding N4 is electrically connected between the negative terminal of the fourth switch S4 and the negative terminal of the second rectifier D2, the non-same terminal of the fourth winding N4 is electrically connected to the same terminal of the third winding N3, the non-same terminal of the third winding N3 is electrically connected between the negative terminal of the second switch S2 and the negative terminal of the first rectifier D1, the positive terminal of the load 5 is electrically connected between the same terminal of the third winding N3 and the non-same terminal of the fourth winding N4, and the negative terminal of the load 5 is electrically connected between the positive terminal of the first rectifier D1 and the positive terminal of the second rectifier D2.

[0038] In some embodiments, the load 5 includes a resistance R0 and a second capacitor Co connected in parallel, and the second capacitor Co is used for filtering to ensure that the voltage received by the resistance R0 is stable and has small fluctuations.

[0039] In some embodiments, the number of turns of the first winding N1 is equal to the number of turns of the second winding N2, which is n1, and the number of turns of the third winding N3 is equal to the number of turns of the fourth winding N4, which is n2. The first winding N1 and the second winding N2 are primary windings, and the third winding N3 and the fourth winding N4 are secondary windings. The transformer can achieve a fixed voltage ratio, i.e. the secondary voltage will be lower than the primary voltage, ensuring that the load can work at a safe and effective voltage level. When the number of turns of the two windings is equal and they are wound on the same side of the magnetic core, they can better balance the magnetic flux, reduce the leakage magnetic flux and improve the efficiency of the transformer; when the primary and secondary windings are wound on the corresponding side columns of two magnetic cores respectively, this structure helps to uniformly utilize the permeability of the magnetic core and reduces the risk of core saturation.

[0040] In some embodiments, the first switch S1 and the fourth switch S4 are turned on, the second switch S2 and the third switch S3 are turned off, the first rectifier D1 is turned on, and the voltage V_N3 of the third winding N3 is clamped at Vo; the first switch S1 and the second switch S2 are turned off, the second switch S2 and the third switch S3 are turned on, the second rectifier D2 is turned on, and the voltage V_N4 of the fourth winding N4 is clamped at -Vo; the first switch S1, the second switch S2, the third switch S3 and the fourth switch S4 are turned off, the first rectifier D1 and the second rectifier D2 are turned on, the voltage V_N3 of the third winding N3 is clamped at Vo, and the voltage V_N4 of the fourth winding N4 is clamped at -Vo.

[0041] In some embodiments, the relationship between the power Vin output by the power supply module 1 and the voltage Vo across the load 5 module is expressed as: Vo = Vin*Dn2 / (n1+n2), where D is the duty cycle of the switching module 2, and adjusting the size of the duty cycle D can adjust the size of the output voltage; when D = 0.5, the output voltage reaches a maximum value, Vo = 0.5Vin*n2 / (n1+n2).

[0042] In some embodiments, as shown in FIGS. 2-5, the types of the first switch S1, the second switch S2, the third switch S3 and the fourth switch S4 are all field effect tubes. The positive electrode of the power supply module 1 is electrically connected to the source electrode of the first switch S1, the drain electrode of the first switch S1 is electrically connected to the source electrode of the second switch S2, the drain electrode of the second switch S2 is electrically connected to the negative terminal of the first rectifier D1, the positive terminal of the first rectifier D1 is grounded and electrically connected to the negative electrode of the power supply module, the positive electrode of the power supply module is also electrically connected to the source electrode of the third switch S3, the drain electrode of the third switch S3 is electrically connected to the source electrode of the fourth switch S4, the drain electrode of the fourth switch S4 is electrically connected to the negative terminal of the second rectifier D2, and the positive terminal of the second rectifier D2 is electrically connected to the positive terminal of the first rectifier D1.

[0043] The same name end of the first winding N1 is electrically connected between the drain of the first switch tube S1 and the source of the second switch tube S2, the non-same name end of the first winding N1 is electrically connected with the same name end of the second winding N2, the non-same name end of the second winding N2 is electrically connected between the drain of the third switch tube S3 and the source of the fourth switch tube S4, the same name end of the fourth winding N4 is electrically connected between the drain of the fourth switch tube S4 and the negative end of the second rectifier D2, the non-same name end of the fourth winding N4 is electrically connected with the same name end of the third winding N3, the non-same name end of the third winding N3 is electrically connected between the drain of the second switch tube S2 and the negative end of the first rectifier D1, the positive end of the resistor R0 is electrically connected between the same name end of the third winding N3 and the non-same name end of the fourth winding N4, and the negative end of the resistor R0 is electrically connected between the positive end of the first rectifier D1 and the positive end of the second rectifier D2. The advantage of the field effect tube as a switch tube lies in low power consumption, high speed, high input impedance, good high frequency performance, and high efficiency and flexibility in power conversion and control circuit.

[0044] In some embodiments, as shown in FIG. 2, the types of the first rectifier D1 and the second rectifier D2 are diodes, the positive pole of the power module 1 is electrically connected with the source of the first switch tube S1, the drain of the first switch tube S1 is electrically connected with the source of the second switch tube S2, the drain of the second switch tube S2 is electrically connected with the cathode of the first rectifier D1, the anode of the first rectifier D1 is grounded and electrically connected with the negative pole of the power module, the positive pole of the power module is also electrically connected with the source of the third switch tube S3, the drain of the third switch tube S3 is electrically connected with the source of the fourth switch tube S4, the drain of the fourth switch tube S4 is electrically connected with the cathode of the second rectifier D2, the anode of the second rectifier D2 is electrically connected with the anode of the first rectifier D1,

[0045] The same name end of the first winding N1 is electrically connected between the drain of the first switch tube S1 and the source of the second switch tube S2, the non-same name end of the first winding N1 is electrically connected with the same name end of the second winding N2, the non-same name end of the second winding N2 is electrically connected between the drain of the third switch tube S3 and the source of the fourth switch tube S4, the same name end of the fourth winding N4 is electrically connected between the drain of the fourth switch tube S4 and the cathode of the second rectifier D2, the non-same name end of the fourth winding N4 is electrically connected with the same name end of the third winding N3, the non-same name end of the third winding N3 is electrically connected between the drain of the second switch tube S2 and the cathode of the first rectifier D1, the positive end of the resistor R0 is electrically connected between the same name end of the third winding N3 and the non-same name end of the fourth winding N4, and the negative end of the resistor R0 is electrically connected between the anode of the first rectifier D1 and the anode of the second rectifier D2. Diodes are used for rectification without high frequency operation or extremely high conversion frequency, which has high stability and low cost.

[0046] In some embodiments, as shown in FIG. 3, the first rectifier D1 and the second rectifier D2 are of the type of synchronous rectifier, preferably field effect transistor, and the first switch S1, the second switch S2, the third switch S3 and the fourth switch S4 are also of the type of field effect transistor. The positive pole of the power module 1 is electrically connected to the source of the first switch S1, the drain of the first switch S1 is electrically connected to the source of the second switch S2, the drain of the second switch S2 is electrically connected to the source of the first rectifier D1, the drain of the first rectifier D1 is grounded and electrically connected to the negative pole of the power module 1, the positive pole of the power module 1 is also electrically connected to the source of the third switch S3, the drain of the third switch S3 is electrically connected to the source of the fourth switch S4, the drain of the fourth switch S4 is electrically connected to the source of the second rectifier D2, and the drain of the second rectifier D2 is electrically connected to the drain of the first rectifier D1.

[0047] The same end of the first winding N1 is electrically connected between the drain of the first switch S1 and the source of the second switch S2, the non-same end of the first winding N1 is electrically connected to the same end of the second winding N2, the non-same end of the second winding N2 is electrically connected between the drain of the third switch S3 and the source of the fourth switch S4, the same end of the fourth winding N4 is electrically connected between the drain of the fourth switch S4 and the source of the second rectifier D2, the non-same end of the fourth winding N4 is electrically connected to the same end of the third winding N3, the non-same end of the third winding N3 is electrically connected between the drain of the second switch S2 and the source of the first rectifier D1, the positive end of the resistor R0 is electrically connected between the same end of the third winding N3 and the non-same end of the fourth winding N4, and the negative end of the resistor R0 is electrically connected between the drain of the first rectifier D1 and the drain of the second rectifier D2. In the high-efficiency and light-weight power supply system, the synchronous rectifier has obvious advantages in improving conversion efficiency, reducing heat generation, improving response speed and control ability.

[0048] In some embodiments, the step-down converter further comprises a first capacitor Cs, as shown in FIG. 4, the first end of the first capacitor Cs is electrically connected between the drain of the first switch S1 and the source of the second switch S2, and the second end of the first capacitor Cs is electrically connected to the same end of the first winding N1. By filtering out the direct current component in the magnetic integrated transformer voltage, it helps to prevent the influence of the direct current component on other parts of the circuit.

[0049] As shown in FIG. 5, the first end of the first capacitor Cs is electrically connected to the non-same end of the first winding N1, and the second end of the first capacitor Cs is electrically connected to the same end of the second winding N2. The first capacitor Cs prevents the passage of direct current components, thereby suppressing the direct current components in the current of the first winding N1 and the second winding N2, which helps to prevent the influence of the direct current component on other parts of the circuit.

[0050] The above merely preferred embodiments of the present application are not used to limit the present application, any modification, equivalent replacement and improvement etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A step-down converter, characterized by, The power module, the switch module, the magnetic integrated transformer, the rectifier module and the load, The magnetic integrated transformer is connected with the load and the rectifier module respectively, and comprises a first winding, a second winding, a third winding, a fourth winding, a first edge column of a magnetic core, a second edge column of the magnetic core, a middle column of the magnetic core, the first winding and the third winding are wound on the first edge column of the magnetic core, and the second winding and the fourth winding are wound on the second edge column of the magnetic core. The switch module is connected with the power module, the rectifier module and the magnetic integrated transformer respectively, the power module is connected with the load and the rectifier module respectively, the switch module is used for controlling the power Vin output by the power module to flow into the magnetic integrated transformer, and the third winding voltage is clamped at Vo and / or the fourth winding voltage is clamped at -Vo in cooperation with the rectification of the rectifier module, Vo is the voltage across the load, and Vin>Vo.

2. The step-down converter of claim 1, wherein, The switch module comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, and the rectifier module comprises a first rectifier tube and a second rectifier tube, The positive terminal of the power module is electrically connected with the positive terminal of the first switch tube, the negative terminal of the first switch tube is electrically connected with the positive terminal of the second switch tube, the negative terminal of the second switch tube is electrically connected with the negative terminal of the first rectifier tube, the positive terminal of the first rectifier tube is grounded and electrically connected with the negative pole of the power module, the positive pole of the power module is also electrically connected with the positive terminal of the third switch tube, the negative terminal of the third switch tube is electrically connected with the positive terminal of the fourth switch tube, the negative terminal of the fourth switch tube is electrically connected with the negative terminal of the second rectifier tube, and the positive terminal of the second rectifier tube is electrically connected with the positive terminal of the first rectifier tube, The same terminal of the first winding is electrically connected between the negative terminal of the first switch tube and the positive terminal of the second switch tube, the non-same terminal of the first winding is electrically connected with the same terminal of the second winding, the non-same terminal of the second winding is electrically connected between the negative terminal of the third switch tube and the positive terminal of the fourth switch tube, the same terminal of the fourth winding is electrically connected between the negative terminal of the fourth switch tube and the negative terminal of the second rectifier tube, the non-same terminal of the fourth winding is electrically connected with the same terminal of the third winding, the non-same terminal of the third winding is electrically connected between the negative terminal of the second switch tube and the negative terminal of the first rectifier tube, the positive terminal of the load is electrically connected between the same terminal of the third winding and the non-same terminal of the fourth winding, and the negative terminal of the load is electrically connected between the positive terminal of the first rectifier tube and the positive terminal of the second rectifier tube. The number of turns of the first winding is equal to the number of turns of the second winding, and the number of turns of the third winding is equal to the number of turns of the fourth winding.

3. The step-down converter of claim 2, wherein, ​ 4. The step-down converter of claim 3, wherein, Turning on the first switch tube and the fourth switch tube, turning off the second switch tube and the third switch tube, the first rectifier tube is turned on, and the voltage of the third winding is clamped at Vo; turning off the first switch tube and the second switch tube, turning on the second switch tube and the third switch tube, the second rectifier tube D2 is turned on, and the voltage of the fourth winding is clamped at -Vo; turning off the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, the first rectifier tube and the second rectifier tube are turned on, the voltage of the third winding is clamped at Vo, and the voltage of the fourth winding is clamped at -Vo.

5. The step-down converter of claim 4, wherein, The relationship expression between the power Vin output by the power supply module and the voltage Vo across the load is: Vo=Vin*D n2 / (n1+n2), wherein D is the duty cycle of the switching module.

6. The step-down converter of claim 1, wherein, The magnetic core is EE type or EI type.

7. The step-down converter of claim 6, wherein, The middle section of the column in the magnetic core is provided with an air gap.

8. The step-down converter of claim 2, wherein, The types of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are all field effect tubes, The positive electrode of the power supply module is electrically connected with the source electrode of the first switch tube, the drain electrode of the first switch tube is electrically connected with the source electrode of the second switch tube, the drain electrode of the second switch tube is electrically connected with the negative end of the first rectifier tube, the positive end of the first rectifier tube is grounded and electrically connected with the negative electrode of the power supply module, the positive electrode of the power supply module is also electrically connected with the source electrode of the third switch tube, the drain electrode of the third switch tube is electrically connected with the source electrode of the fourth switch tube, the drain electrode of the fourth switch tube is electrically connected with the negative end of the second rectifier tube, and the positive end of the second rectifier tube is electrically connected with the positive end of the first rectifier tube, The same end of the first winding is electrically connected between the drain electrode of the first switch tube and the source electrode of the second switch tube, the non-same end of the first winding is electrically connected with the same end of the second winding, the non-same end of the second winding is electrically connected between the drain electrode of the third switch tube and the source electrode of the fourth switch tube, the same end of the fourth winding is electrically connected between the drain electrode of the fourth switch tube and the negative end of the second rectifier tube, the non-same end of the fourth winding is electrically connected with the same end of the third winding, the non-same end of the third winding is electrically connected between the drain electrode of the second switch tube and the negative end of the first rectifier tube, the positive end of the load is electrically connected between the same end of the third winding and the non-same end of the fourth winding, and the negative end of the load is electrically connected between the positive end of the first rectifier tube and the positive end of the second rectifier tube.

9. The step-down converter of claim 2, wherein, The types of the first rectifier tube and the second rectifier tube are diodes or synchronous rectifier tubes.

10. The step-down converter of claim 9, wherein, A first capacitor is further included, a first end of the first capacitor is electrically connected between the drain electrode of the first switch tube and the source electrode of the second switch tube, and a second end of the first capacitor is electrically connected with the same end of the first winding.

11. The step-down converter of claim 10, wherein, The first end of the first capacitor is electrically connected with the non-same end of the first winding, and the second end of the first capacitor is electrically connected with the same end of the second winding.

12. The step-down converter of claim 9, wherein, The load includes a resistance and a second capacitor connected in parallel.

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