CN117526714A

CN117526714A - DC-DC converter and DC-DC converter

Info

Publication number: CN117526714A
Application number: CN202210929492.7A
Authority: CN
Inventors: 夏琦; 冷阳; 张晋颖; 刘静丽; 刘雁开
Original assignee: Great Wall Power Technology Co ltd
Current assignee: Great Wall Power Technology Co ltd
Priority date: 2022-08-03
Filing date: 2022-08-03
Publication date: 2024-02-06

Abstract

The invention provides a DC-DC converter and a DC-DC conversion device, which relate to the field of power sources and comprise a first switch branch formed by a second switch tube, a fourth switch tube and a sixth switch tube which are sequentially connected in series, a second switch branch formed by a third switch tube, a fifth switch tube and a seventh switch tube which are sequentially connected in series, a first flying capacitor connected with a common node of the second switch tube and the fourth switch tube and a common node of the fifth switch tube and the seventh switch tube at a second end, a second flying capacitor connected with a common node of the third switch tube and the fifth switch tube and a common node of the fourth switch tube and the sixth switch tube at a second end, and a primary winding and a secondary winding which are serially connected between the common node of the fourth switch tube and the sixth switch tube and the common node of the fifth switch tube and the seventh switch tube; the output inductor connected between the common node of the primary and secondary windings and the output capacitor can greatly improve the efficiency of the power converter and reduce the volume and cost of the power converter.

Description

DC-DC converter and DC-DC converter

Technical Field

The invention relates to the field of power supplies, in particular to a DC-DC converter and a DC-DC conversion device.

Background

Services supported by data centers are now necessary for society and there are more and more services supported by them. Therefore, with the development of technology, the energy consumption of the data center will increase.

In order to meet the high-efficiency requirement of the system, the on-board power supply mode of the server starts to change from a 12V bus to a 40V-60V bus, namely, the voltage of the 40V-60V bus is changed to 12V on the server board. There are two schemes for the current 40V-60V to 12V conversion.

The first solution is to use an isolated converter, such as a full bridge converter. It uses a transformer to step down and provide physical isolation to meet safety requirements. In this topology, because of the physical isolation of the primary and secondary sides of the transformer, both the primary and secondary sides have respective references to ground. In order to realize the conversion from the high voltage at the primary side to the low voltage at the secondary side, the number of windings at the primary side is relatively large, and the primary side current does not flow through the secondary side, so that the secondary side alternating current is large, which increases the coil loss of the whole transformer. This approach affects continued improvement in efficiency and increases the cost of the product (e.g., circuit board).

The second approach is to use a non-isolated converter, such as a Buck converter. In order to reduce losses and increase the efficiency of the system, primary and secondary side isolation is eliminated. However, under the condition that the input voltage is 40V-60V and the output voltage is 12V, the duty ratio of the switching tube is very small in the traditional Buck circuit, which can lead to the fact that the effective value of the switching tube current is large, the Buck circuit cannot work at the optimal efficiency point, and the efficiency cannot be continuously improved.

Therefore, there is a strong need in the industry for a new solution to boost the efficiency of 40V-60V bus voltage to 12V conversion.

Disclosure of Invention

The present invention proposes a DC-DC conversion device comprising: a DC-DC converter comprising: the first switching branch comprises a second switching tube, a fourth switching tube and a sixth switching tube which are sequentially connected in series, the first end of the first switching branch is connected with the positive end of the input voltage through a first switching unit, and the second end of the first switching branch is connected with the negative end of the input voltage; the second switching branch comprises a third switching tube, a fifth switching tube and a seventh switching tube which are sequentially connected in series, the first end of the second switching branch is connected with the positive end of the input voltage through the first switching unit, and the second end of the second switching branch is connected with the negative end of the input voltage; the first flying capacitor is characterized in that a first end of the first flying capacitor is connected with a common node of a second switching tube and a fourth switching tube, and a second end of the first flying capacitor is connected with a common node of a fifth switching tube and a seventh switching tube; the first end of the second flying capacitor is connected with the common node of the third switching tube and the fifth switching tube, and the second end of the second flying capacitor is connected with the common node of the fourth switching tube and the sixth switching tube; the first end of the primary winding of the transformer is connected with a common node of the fourth switching tube and the sixth switching tube, and the second end of the primary winding of the transformer is connected with the first end of the secondary winding of the transformer; the second end of the secondary winding of the transformer is connected with a common node of the fifth switching tube and the seventh switching tube; the first end of the output inductor is connected with the second end of the primary winding of the transformer, and the second end of the output inductor is used for being connected with the first end of the output capacitor; and the controller is configured to receive the sampling signal from the DC-DC converter so as to output a switching control signal to control the switching tube of the DC-DC converter to be turned on or off.

The present application also provides a DC-DC converter comprising: the first switching branch comprises a second switching tube, a fourth switching tube and a sixth switching tube which are sequentially connected in series, the first end of the first switching branch is connected with the positive end of the input voltage through a first switching unit, and the second end of the first switching branch is connected with the negative end of the input voltage; the second switching branch comprises a third switching tube, a fifth switching tube and a seventh switching tube which are sequentially connected in series, the first end of the second switching branch is connected with the positive end of the input voltage through the first switching unit, and the second end of the second switching branch is connected with the negative end of the input voltage; the first flying capacitor is characterized in that a first end of the first flying capacitor is connected with a common node of a second switching tube and a fourth switching tube, and a second end of the first flying capacitor is connected with a common node of a fifth switching tube and a seventh switching tube; the first end of the second flying capacitor is connected with the common node of the third switching tube and the fifth switching tube, and the second end of the second flying capacitor is connected with the common node of the fourth switching tube and the sixth switching tube; the first end of the primary winding of the transformer is connected with a common node of the fourth switching tube and the sixth switching tube, and the second end of the primary winding of the transformer is connected with the first end of the secondary winding of the transformer; the second end of the secondary winding of the transformer is connected with a common node of the fifth switching tube and the seventh switching tube; and the first end of the output inductor is connected with the second end of the primary winding of the transformer, and the second end of the output inductor is used for being connected with the first end of the output capacitor.

Drawings

Fig. 1 is a schematic diagram of a DC-DC converter according to an embodiment of the invention.

Fig. 2 is a schematic diagram of a DC-DC converter according to another embodiment of the present invention.

Fig. 3 is a schematic diagram of a driving waveform of the switching tube when the DC-DC converter in fig. 1 is operated with D less than 0.5.

Fig. 4 is a schematic diagram of an operating waveform of the DC-DC converter of fig. 1 when D is less than 0.5.

Fig. 5 is a schematic diagram of the DC-DC converter operating in a first mode of operation.

Fig. 6 is a schematic diagram of the DC-DC converter operating in a second mode of operation.

Fig. 7 is a schematic diagram of the DC-DC converter operating in a third mode of operation.

Fig. 8 is a schematic diagram of a driving waveform of the switching tube when the DC-DC converter of fig. 1 is operated with D greater than 0.5.

Fig. 9 is a schematic diagram of an operating waveform of the DC-DC converter of fig. 1 when D is greater than 0.5.

Fig. 10 is a schematic diagram of the DC-DC converter operating in a fourth mode of operation.

Fig. 11 is a schematic diagram of the DC-DC converter operating in a fifth mode of operation.

Fig. 12 is a schematic diagram of the DC-DC converter operating in a sixth mode of operation.

Fig. 13 is a schematic diagram of a typical full-bridge inverter circuit.

Fig. 14 is a schematic diagram of a DC-DC converter according to another embodiment of the present invention.

Fig. 15 is a schematic diagram of a controller according to an embodiment of the invention.

Fig. 16 is a schematic diagram of the controller local circuit operation waveforms shown in fig. 15.

Detailed Description

The following description of the embodiments of the present invention will be made more apparent and fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In one embodiment of the present invention, a DC-DC converter is provided. Specifically, referring to fig. 1, a schematic diagram of a DC-DC converter according to an embodiment of the present invention includes:

the DC-DC converter 100 includes:

the first switching branch comprises a second switching tube Q2, a fourth switching tube Q4 and a sixth switching tube Q6 which are sequentially connected in series, wherein the first end of the first switching branch is connected with an input voltage positive end vin+ through a first switching unit 110, and the second end of the first switching branch is connected with an input voltage negative end Vin-;

the second switching branch comprises a third switching tube Q3, a fifth switching tube Q5 and a seventh switching tube Q7 which are sequentially connected in series, wherein the first end of the second switching branch is connected with an input voltage positive end vin+ through a first switching unit 110, and the second end of the second switching branch is connected with an input voltage negative end Vin-;

The first flying capacitor Cb1 has a first end connected with the common node of the second switching tube Q2 and the fourth switching tube Q4 and a second end connected with the common node of the fifth switching tube Q5 and the seventh switching tube Q7;

the first end of the second flying capacitor Cb2 is connected with the common node of the third switching tube Q3 and the fifth switching tube Q5, and the second end of the second flying capacitor Cb2 is connected with the common node of the fourth switching tube Q4 and the sixth switching tube Q6;

the primary winding Np of the transformer is connected with a common node of the fourth switching tube Q4 and the sixth switching tube Q6 at a first end, and is connected with the first end of the secondary winding Ns of the transformer at a second end;

the second end of the transformer secondary winding Ns is connected with a common node of a fifth switching tube Q5 and a seventh switching tube Q7;

the first end of the output inductor Lo is connected with the second end of the primary winding Np of the transformer, and the second end of the output inductor Lo is used for being connected with the first end of the output capacitor Co;

the controller 200 is configured to receive a sampling signal from the DC-DC converter 100 to output a switching control signal to control the switching transistor of the DC-DC converter 100 to be turned on or off.

In one embodiment, the turn ratio of the primary winding Np of the transformer to the secondary winding Ns of the transformer is 1:1. that is, the number of turns of the primary winding Np of the transformer is the same as that of the secondary winding Ns of the transformer. In one embodiment, the primary winding Np of the transformer and the secondary winding Ns of the transformer are each one turn.

In one embodiment, a first end of the primary winding Np of the transformer is coupled with a first end of the secondary winding Ns of the transformer, as shown in fig. 1. In another embodiment, the second end of the primary winding Np of the transformer is coupled with the second end of the secondary winding Ns of the transformer. The primary winding Np of the transformer is coupled to the load (not shown) connected to the output capacitor Co, and the secondary winding Ns of the transformer is coupled to the load connected to the output capacitor Co.

In an embodiment, as shown in fig. 1, the first switching unit 110 includes a first switching tube Q1, and the first end of the first switching branch and the first end of the second switching branch are connected to the positive input voltage terminal vin+ through the first switching tube Q1. Referring to fig. 2, a DC-DC converter according to another embodiment of the invention is shown, the first switching unit 110 includes a first sub-switching tube Q11 and a second sub-switching tube Q12, a first end of the first switching branch is connected to the positive input voltage terminal vin+ through the first sub-switching tube Q11, and a first end of the second switching branch is connected to the positive input voltage terminal vin+ through the second sub-switching tube Q12. The first switching unit 110 includes a first switching tube Q1, that is, the DC-DC converter 100 shown in fig. 1, in order to explain the operation principle thereof.

Specifically, referring to fig. 3, the driving waveform diagram of the switching tube when the DC-DC converter shown in fig. 1 is operated with D less than 0.5, where D is the duty ratio of the second switching tube Q2 to the fifth switching tube Q5. Please refer to fig. 4, which illustrates an operation waveform diagram of the DC-DC converter in fig. 1 when D is less than 0.5. As shown in fig. 3, the driving signal of the first switching tube Q1 is always high, i.e., the first switching tube Q1 is always on. During the period from t0 to t1, i.e., during the period from 0 to DTs (Ts is the time of one switching cycle. Specifically, the duty cycle D is the ratio of the on time of the switching tube to the switching cycle), the DC-DC converter 100 operates in the first operation mode, and please refer to the schematic diagram of the DC-DC converter shown in fig. 5 when operating in the first operation mode. The controller 200 turns on the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 according to the high level of the switching control signals of the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 outputted by the sampling signals, and turns off the third switching tube Q3, the fourth switching tube Q4 and the seventh switching tube Q7 according to the low level of the switching control signals of the third switching tube S3, the fourth switching tube Q4 and the seventh switching tube Q7 outputted by the sampling signals. The first flying capacitor Cb1 and the second flying capacitor Cb2 are connected between the positive input voltage end vin+ and the negative input voltage end Vin-through the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 which are conducted, and then the voltages on the first flying capacitor Cb1 and the second flying capacitor Cb2 are 1/2Vin. During this period, the first flying capacitor Cb1 is charged, and the charging current thereof flows from the positive input voltage terminal vin+ through the turned-on first switching tube Q1, second switching tube Q2, first flying capacitor Cb1, transformer secondary winding Ns, output inductor Lo, and load connected to the output capacitor Co in order, and returns to the negative input voltage terminal Vin-. Meanwhile, the second flying capacitor Cb2 discharges, and the discharge current sequentially flows through the turned-on fifth switching tube Q5, the secondary winding Ns of the transformer, the output inductor Lo, and the load connected to the output capacitor Co, and then flows through the turned-on sixth switching tube Q6 back to the second flying capacitor Cb2, that Is, the charge current of the first flying capacitor Cb1 and the discharge current of the second flying capacitor Cb2 form the secondary current Is, and the secondary current Is gradually increases, as shown in fig. 4. According to the basic principle of the transformer, the secondary current Is flowing through the secondary winding Ns of the transformer induces a primary current Ip on the primary winding Np of the transformer. As can be seen from the coupling relationship between the primary winding and the secondary winding of the transformer shown in fig. 1, the primary current Ip sequentially flows through the primary winding Np of the transformer, the output inductor Lo1, the load connected to the output capacitor Co, the turned-on sixth switching tube Q6, and then returns to the primary winding Np of the transformer, and the primary current Ip also gradually increases. According to the above analysis, in the first operation mode, the currents of the primary winding Np of the transformer and the secondary winding Ns of the transformer flow through the output inductance Lo to the load. That Is, the inductor current ILo flowing through the output inductor Lo Is the sum of the primary current Ip and the secondary current Is, and the inductor current ILo also gradually increases, as shown in fig. 4.

As shown in fig. 5, when the voltage at the second end of the secondary winding Ns of the transformer is equal to the voltage on the second flying capacitor Cb2, that is, 1/2Vin, and the voltage at the first end of the primary winding Np of the transformer is zero, the voltage drop at the common node M of the primary winding Np of the transformer (that is, the second end of the primary winding Np of the transformer and the first end of the secondary winding Ns of the transformer) is 1/4Vin.

Next, during the period from t1 to t2, i.e., during the period from DTs to Ts/2, the DC-DC converter 100 operates in the second operation mode, please refer to the schematic diagram of fig. 6 when the DC-DC converter operates in the second operation mode, and please refer to fig. 3 and 4. The controller 200 outputs the switching control signals of the second switching tube Q2 to the fifth switching tube Q5 according to the sampling signals to be at low level, and the second switching tube Q2 to the fifth switching tube Q5 are turned off, so that the voltage on the first flying capacitor Cb1 and the voltage on the second flying capacitor Cb2 remain unchanged. The controller 200 outputs the switching control signals of the sixth switching tube Q6 and the seventh switching tube Q7 to be high level according to the sampling signals, and the sixth switching tube Q6 and the seventh switching tube Q7 are turned on. The inductor current ILo flowing through the output inductor Lo freewheels through the load connected to the output capacitor Co, the turned-on seventh switching tube Q7 and the secondary winding Ns, and simultaneously freewheels through the load connected to the output capacitor Co, the turned-on sixth switching tube Q6 and the primary winding Np, and the primary current Ip and the secondary current Is are gradually reduced as shown in fig. 4. Here, the inductor current ILo flowing through the output inductor Lo Is the sum of the primary current Ip and the secondary current Is, and the inductor current Ilo Is also gradually reduced.

Referring to fig. 6, since the sixth switching tube Q6 and the seventh switching tube Q7 are turned on, the voltages at the second end of the secondary winding Ns and the first end of the primary winding Np are both zero, and the voltage at the common node M of the primary winding Np is also zero.

Next, during the period from t2 to t3, i.e., the period from Ts/2 to (1/2+D) Ts, the DC-DC converter 100 operates in the third operation mode, please refer to fig. 7, which is a schematic diagram of the DC-DC converter operating in the third operation mode, and please refer to fig. 3 and 4. The controller 200 turns on the third switching tube S3, the fourth switching tube Q4 and the seventh switching tube Q7 according to the high level of the switching control signals of the third switching tube S3, the fourth switching tube Q4 and the seventh switching tube Q7 outputted by the sampling signal, and turns off the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 according to the low level of the switching control signals of the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 outputted by the sampling signal. Referring to fig. 7, the first flying capacitor Cb1 and the second flying capacitor Cb2 are connected between the positive input voltage terminal vin+ and the negative input voltage terminal Vin-through the third switching tube Q3, the fourth switching tube Q4 and the seventh switching tube Q7 that are turned on, so that the voltages on the first flying capacitor Cb1 and the second flying capacitor Cb2 are both 1/2Vin. During this period, the second flying capacitor Cb2 is charged, and the charging current thereof flows from the positive terminal vin+ of the input voltage through the turned-on first switching tube Q1, third switching tube Q3, second flying capacitor Cb2, primary winding Np of the transformer and output inductor Lo in order, then flows to the load connected to the output capacitor Co, and then returns to the negative terminal Vin-of the input voltage. Meanwhile, the first flying capacitor Cb1 discharges, and the discharge current thereof sequentially flows through the fourth switching tube Q4, the primary winding Np of the transformer, and the output inductor Lo, then flows to the load connected to the output capacitor Co, and then flows back to the first flying capacitor Cb1 through the seventh switching tube Q7, that Is, the charge current of the second flying capacitor Cb2 and the discharge current of the first flying capacitor Cb1 form the secondary current Is, and the secondary current Is gradually increases, as shown in fig. 4. According to the basic principle of the transformer, the primary current Ip flowing through the primary winding Np of the transformer induces a secondary current Is on the secondary winding Ns of the transformer, and according to the coupling relationship of the primary and secondary windings of the transformer shown in fig. 1, the secondary current Is sequentially flows through the output inductor Lo1 and the load connected to the output capacitor Co, and then returns to the secondary winding Ns of the transformer through the conducting seventh switching tube Q7, and the secondary current Is also gradually increases. According to the above analysis, in the third operation mode, the currents of the primary winding Np of the transformer and the secondary winding Ns of the transformer flow through the output inductance Lo to the load. The inductor current ILo flowing through the output inductor Lo Is the sum of the primary current Ip and the secondary current Is, and the inductor current ILo Is also gradually increased as shown in fig. 4. Compared with the first working mode, the first flying capacitor Cb1 is changed from charge to discharge, the second flying capacitor Cb2 is changed from discharge to charge, and the voltages on the first flying capacitor Cb1 and the second flying capacitor Cb2 are kept at 1/2Vin in a plurality of cycle, however, in practical application, certain errors may exist.

As shown in fig. 7, at this time, the voltage at the first end of the primary winding Np of the transformer is equal to the voltage on the first flying capacitor Cb1, i.e. 1/2Vin, and the voltage at the second end of the secondary winding Ns of the transformer is zero, so that the voltage drop at the common node M of the primary winding Np of the transformer is 1/4Vin.

Next, during t3 to t4, i.e., (1/2+D) Ts to Ts time period, the DC-DC converter 100 operates again in the second operation mode. Referring specifically to fig. 6, 3 and 4 and the above description, the details are not repeated here.

Referring to fig. 8, a schematic diagram of a driving waveform of the switching tube when the DC-DC converter in fig. 1 is operated with D greater than 0.5 is shown. Please refer to fig. 9, which illustrates an operation waveform diagram of the DC-DC converter in fig. 1 when D is greater than 0.5. During t0 to t1, the DC-DC converter 100 operates in the fourth operation mode, the controller 200 turns on the first, second and third switching transistors Q1, Q2 and Q3 according to the high level of the switching control signals of the first, second and third switching transistors Q1, Q2 and Q3 output by the sampling signal, and the controller 200 turns off the fourth to seventh switching transistors Q4 to Q7 according to the low level of the switching control signals of the fourth to seventh switching transistors Q4 to Q7 output by the sampling signal. Referring to fig. 10, when the DC-DC converter shown in fig. 10 Is operated in the fourth operation mode, the first flying capacitor Cb1 Is charged through the turned-on first switching tube Q1 and the turned-on second switching tube Q2, and the second flying capacitor Cb2 Is charged through the turned-on first switching tube Q1 and the turned-on third switching tube Q3, the charging current of the first flying capacitor Cb1 forms the secondary side current Is, the charging current of the second flying capacitor Cb2 forms the primary side current Ip, and the primary side current Ip and the secondary side current Is gradually increase, and the primary side current Ip and the secondary side current Is flow to the output inductor Lo, so that the inductance ILo flowing through the output inductor Lo gradually increases, as shown in fig. 9.

As shown in fig. 10, when the voltage at the second end of the secondary winding Ns of the transformer is equal to 1/2Vin and the voltage at the first end of the primary winding Np of the transformer is also equal to 1/2Vin, the voltage at the common node M of the primary and secondary windings of the transformer is also equal to 1/2Vin.

Next, during t1 to t2, the DC-DC converter 100 operates in the fifth operation mode, and please refer to fig. 11, which is a schematic diagram illustrating the DC-DC converter operating in the fifth operation mode, and fig. 8 and 9. The controller 200 outputs the switching control signals of the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 according to the sampling signals, and the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 are turned on. The controller 200 switches off the first, third, fourth and seventh switching transistors Q1, Q3, Q4 and Q7 according to the low level of the switching control signals of the first, third, fourth and seventh switching transistors Q1, Q3, Q4 and Q7 output by the sampling signal. The voltage on the first flying capacitor Cb1 remains unchanged, the second flying capacitor Cb2 discharges through the turned-on fifth switching tube Q5, the secondary winding Ns, the output inductor Lo, the load connected to the output capacitor Co, and the turned-on sixth switching tube Q6, forming the secondary current Is, and the secondary current Is gradually decreases, as shown in fig. 9. According to the basic principle of the transformer, the secondary current Is flowing through the secondary winding Ns of the transformer induces a primary current Ip on the primary winding Np of the transformer, and according to the coupling relationship of the primary winding and the secondary winding of the transformer shown in fig. 1, the primary current Ip sequentially flows through the output inductor Lo1, the load connected to the output capacitor Co, and then returns to the primary winding Np of the transformer through the conducting sixth switching tube Q6, and the primary current Ip also gradually decreases. When the primary current Ip and the secondary current Is flow through the output inductor Lo, the inductance ILo flowing through the output inductor Lo Is also gradually reduced, as shown in fig. 9.

As shown in fig. 11, at this time, the voltage at the second end of the secondary winding Ns of the transformer is equal to the voltage on the second flying capacitor Cb2, i.e. 1/2Vin, and the voltage at the first end of the primary winding Np of the transformer is zero, so that the voltage drop at the common node M of the primary winding Np of the transformer is 1/4Vin.

In this fifth mode of operation, the second flying capacitor Cb2 discharges, the voltage of the first flying capacitor Cb1 is maintained, and the sum of the voltage of the first flying capacitor Cb1 and the voltage of the second flying capacitor Cb2 is equal to the voltage of the input capacitor Cin connected between the positive input voltage terminal vin+ and the negative input voltage terminal Vin-, as shown in fig. 8 at time t 2. Since in the fourth mode of operation, both the first flying capacitor Cb1 and the second flying capacitor Cb2 are charged, the sum of the voltages thereon may be greater than the input voltage Vin. In order to avoid the following operation modes, the voltage of the first flying capacitor Cb1 and the voltage of the second flying capacitor Cb2 are opposite to the voltage on the input capacitor Cin to generate an impulse current, and avoid the first flying capacitor Cb1 and the second flying capacitor Cb2 from discharging to generate a loss, so that the second flying capacitor Cb2 is discharged in the fifth operation mode. Specifically, the turn-off time of the first switch Q1 is required to discharge the second flying capacitor Cb2 until the sum of the voltage of the first flying capacitor Cb1 and the voltage of the second flying capacitor Cb2 is equal to the voltage on the input capacitor Cin.

Next, at time t2, the first switching tube Q1 is switched from off to on, and the states of the other switching tubes are unchanged until time t3, that is, during the period from t2 to t3, the DC-DC converter operates in the first operation mode as shown in fig. 5. During this period, the second flying capacitor Cb2 Is discharged, the first flying capacitor Cb1 Is charged, and the secondary side current Is, the primary side current Ip and the inductance current ILo are gradually reduced because D Is greater than 0.5, and the voltage drop at the common node M of the primary and secondary side windings of the transformer Is 1/4Vin.

Next, during t3 to t4, the DC-DC converter 100 operates again in the fourth operation mode. Referring to fig. 10, fig. 8 and fig. 9 and the above description, details are not repeated here.

Next, during t4 to t5, the DC-DC converter 100 operates in the sixth operation mode, please refer to fig. 12, which is a schematic diagram illustrating the DC-DC converter operating in the sixth operation mode, and please refer to fig. 8 and 9. The controller 200 outputs the switching control signals of the third switching tube Q3, the fourth switching tube Q4 and the seventh switching tube Q7 according to the sampling signals, and the third switching tube Q3, the fourth switching tube Q4 and the seventh switching tube Q7 are turned on. The controller 200 switches off the first switching tube Q1, the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 according to the low level of the switching control signals of the first switching tube Q1, the second switching tube Q2, the fifth switching tube Q5 and the sixth switching tube Q6 output by the sampling signals. The voltage on the second flying capacitor Cb2 remains unchanged, the first flying capacitor Cb1 discharges through the fourth switching tube Q4, the primary winding Np, the output inductor Lo, the load connected to the output capacitor Co, and the seventh switching tube Q7, forming a primary current Ip, and the primary current Ip gradually decreases, as shown in fig. 9. According to the basic principle of the transformer, the primary current Ip flowing through the primary winding Np of the transformer induces a secondary current Is on the secondary winding Ns of the transformer, and according to the coupling relationship of the primary and secondary windings of the transformer shown in fig. 1, the secondary current Is sequentially flows through the output inductor Lo1 and the load connected to the output capacitor Co, and then returns to the secondary winding Ns of the transformer through the conducted seventh switching tube Q7, and the secondary current Is gradually decreases. When the primary current Ip and the secondary current Is flow through the output inductor Lo, the inductance ILo flowing through the output inductor Lo Is also gradually reduced, as shown in fig. 9.

As shown in fig. 12, at this time, the voltage at the first end of the primary winding Np of the transformer is equal to the voltage on the first flying capacitor Cb1, i.e. 1/2Vin, and the voltage at the second end of the secondary winding Ns of the transformer is zero, so that the voltage drop at the common node M of the primary winding and the secondary winding of the transformer is 1/4Vin.

Similar to the fifth mode of operation, the voltage of the second flying capacitor Cb2 is maintained, the first flying capacitor Cb1 is discharged, and the sum of the voltage of the first flying capacitor Cb1 and the voltage of the second flying capacitor Cb2 is equal to the voltage of the input capacitor Cin connected between the positive terminal vin+ of the input voltage and the negative terminal Vin-of the input voltage, as shown in FIG. 8 at time t 5. In order to avoid the following working modes, the voltage of the first flying capacitor Cb1 and the voltage of the second flying capacitor Cb2 are opposite to the voltage on the input capacitor Cin to generate impulse current, and avoid the first flying capacitor Cb1 and the second flying capacitor Cb2 from discharging to generate loss.

Next, at time t5, the first switching tube Q1 is switched from off to on, and the states of the other switching tubes are unchanged until time t6, that is, time Ts, the DC-DC converter operates in the third operation mode as shown in fig. 7. During this period, the first flying capacitor Cb1 Is discharged, the second flying capacitor Cb2 Is charged, and the secondary side current Is, the primary side current Ip and the inductance current ILo are gradually reduced because D Is greater than 0.5, and the voltage drop at the common node M of the primary and secondary side windings of the transformer Is 1/4Vin.

Thus, when D is smaller than 0.5, the DC-DC converter 100 sequentially operates in the first, second, third, and second operation modes in one switching period Ts, and when D is larger than 0.5, the DC-DC converter 100 sequentially operates in the fourth, fifth, first, fourth, sixth, and third operation modes in one switching period Ts, so as to convert the input voltage Vin into the output voltage Vo. As described above, the first flying capacitor Cb1 and the second flying capacitor Cb2 are connected in series to input voltage Vin and the voltage-reducing function of the transformer, so that the output-input voltage relationship of the DC-DC converter 100 is vo=1/2 vin×d.

For the first solution mentioned in the prior art, an isolated converter, such as a full bridge converter, is used. Referring to fig. 13, a schematic circuit diagram of a typical full-bridge converter includes a primary side switch unit, a transformer T and a rectifying unit, wherein the transformer T physically isolates primary and secondary sides, so that both the primary and secondary sides have their own ground references, such as GND1 and GND2. In order to realize the conversion from high voltage at the primary side to low voltage at the secondary side, the number of turns of the primary side is relatively large, three turns of the primary side winding Np are required to be selected for the conversion from 40V to 60V input to 12V output, and two turns of the secondary side winding Ns, namely the ratio of the primary side to the secondary side turns is 3:2, the voltage drop across the secondary winding Ns of the transformer is 2/3Vin. In the DC-DC converter 100 of the present invention, the voltage drop at the first end of the output inductor Lo is 1/2Vin through one turn of the primary winding Np of the transformer, one turn of the secondary winding Ns of the transformer, and the first flying capacitor Cb1 and the second flying capacitor Cb 2. That is, the DC-DC converter 100 of the present application can reduce the number of turns of the primary winding Np and the secondary winding Ns and the step-down ratio is larger than that of the conventional full-bridge converter. Transformers are the largest size devices in power converters, which have been an obstacle to the miniaturization of the converters. The DC-DC converter 100 of the present application can achieve a reduction in winding coil turns, thereby significantly reducing the transformer volume, thereby reducing the overall converter volume, while meeting the market demand for miniaturization. And the fewer winding turns can also reduce the loss and cost of the winding.

For the second solution mentioned in the prior art, a non-isolated converter is used, such as a Buck converter, where the output voltage and the input voltage have the following relationship: vo=vin×d (D is the duty cycle of the switching tube), for a 40V-60V input to 12V output conversion, the duty cycle of the switching tube will be small, and the Buck circuit cannot operate at the optimal efficiency point. As can be seen from the above analysis, the DC-DC converter 100 of the present application has the following relationship between the output voltage and the input voltage: vo=1/2 vin×d, and the duty cycle of the switching tube can be increased, so that the Buck circuit can work at a better efficiency point.

According to the above analysis, see also fig. 4 and 9, the voltage at the intermediate point of the transformer jumps at twice the switching frequency of the DC-DC converter, so that the current ripple through the transformer is small, mainly DC current. For the traditional transformer topology, the current of the transformer is mainly high-frequency current with the switching frequency, and the alternating current impedance of the transformer winding is far greater than the direct current impedance of the transformer winding due to the proximity effect and the skin effect of the high-frequency current, so that the efficiency of the transformer winding is low. In this application, the transformer mainly flows DC current, and the loss is mainly caused by direct current impedance, so that the efficiency of the transformer can be improved. Similarly, the ripple frequency of the output inductor Lo is twice the switching frequency of the DC-DC converter, so that the volume of the output inductor Lo can be greatly reduced, and the power density of the DC-DC converter can be improved.

As can be seen from the above analysis of the operation mode of the DC-DC converter 100, the primary current Ip and the secondary current Is are equalized to the output inductor Lo. Referring to fig. 13 again, the primary current Ip of the conventional full-bridge converter does not flow to the load, and the output current Io flowing to the load needs to flow through the secondary winding Ns, so that the secondary current Is equal to Io. The primary current Ip and the secondary current Is of the DC-DC converter 100 of the present application flow to the load, and the turn ratio of the primary winding Np of the transformer to the secondary winding Ns of the transformer Is 1: under the condition of 1, the secondary side current Is equal to the primary side current Ip, and then the secondary side current Is equal to 1/2Io (Io=ilo), so that the winding loss of the transformer Is greatly reduced, the heat dissipation pressure Is further reduced, the volume of the transformer Is further reduced, the power density of the power converter Is raised, and great convenience Is brought to the design of the power converter. The turn ratio of the primary winding Np of the transformer to the secondary winding Ns of the transformer is 1:1, the winding is also greatly convenient.

That is, the DC-DC converter 100 of the present application can reduce the number of primary and secondary winding turns, reduce the effective value of secondary winding current, and increase the duty cycle of the switching tube, thereby greatly increasing the power converter efficiency and reducing the power converter volume and cost.

In one embodiment, the second terminal of the output capacitor Co Is connected to the negative input voltage terminal Vin-, so that the primary current Ip or the secondary current Is can flow from the positive input voltage terminal vin+ to the load and back to the negative input voltage terminal Vin-. More specifically, the second terminal of the output capacitor Co is directly connected to the negative input voltage terminal Vin-.

The output inductor Lo in the above may be an independent inductor. In one embodiment of the present application, the primary winding Np of the transformer, the secondary winding Ns of the transformer and the output inductor Lo are integrated into one magnetic element, thereby further increasing the power density of the DC-DC converter. The leakage inductance of the transformer can also be used as the output inductance Lo to increase the power density of the DC-DC converter.

In an embodiment of the present application, when switching between adjacent operation modes, a dead time may be further included between driving signals of the switching tube, so as to improve reliability of the DC-DC converter.

As can be seen from the above analysis, with the DC-DC converter 100 shown in fig. 1, when D is greater than 0.5, the switching frequency of the first switching tube Q1 is twice that of the second and third switching tubes Q2 and Q3, and is turned off when the second and third switching tubes Q2 and Q3 are turned off, as shown in fig. 2. As shown in fig. 2, the DC-DC converter according to another embodiment of the present invention splits the first switching tube Q1 of the DC-DC converter shown in fig. 1 into two switching tubes, namely a first sub-switching tube Q11 and a second sub-switching tube Q12, so that the first sub-switching tube Q11 can be turned off when the second switching tube Q2 is turned off, and the second sub-switching tube Q12 can be turned off when the third switching tube Q3 is turned off, so that the switching frequency of the first sub-switching tube Q11 and the second sub-switching tube Q12 can be reduced, and the efficiency of the DC-DC converter can be further improved. When D is less than 0.5, the first sub-switching tube Q11 and the second sub-switching tube Q12 are normally on. The other working principles are the same as those described above, and will not be described here again.

In fig. 8, taking the example that the first switching tube Q1 is turned off when the second switching tube Q2 and the third switching tube Q3 are turned off, in practical application, the first switching tube Q1 may be turned off earlier than the turning-off time of the second switching tube Q2 and the third switching tube Q3.

Referring to fig. 14, a schematic diagram of a DC-DC converter according to another embodiment of the present invention further includes a first capacitor C1 in addition to the DC-DC converter shown in fig. 2, wherein the first capacitor C1 is connected between a first end of the first switching leg and a first end of the second switching leg. Under normal conditions, the voltage of one end of the second switching tube Q2 connected with the first end of the first switching branch is the same as the voltage of one end of the third switching tube Q3 connected with the first end of the second switching branch, so that the voltage stress born by the first sub-switching tube Q11 and the second sub-switching tube Q12 during operation is the same. However, in actual operation, the circuit has some parasitic parameters, which may cause some stress when the switching tube is switched, and the first capacitor C1 may be added to absorb the voltage stress. The working principle is the same as that of the DC-DC converter shown in fig. 2, and will not be described here again.

In an embodiment of the present application, the sampling signal may be one or more of an input voltage, an output voltage, an input current, an output current, a duty cycle, and the like of the DC-DC converter 100. As long as it is a signal reflecting the state of the DC-DC converter 100. In an embodiment of the present application, the controller 200 may determine whether D is greater than 0.5 or less than 0.5 according to the duty ratios of the second switching tube Q2 and the third switching tube Q3, and correspondingly output a switching control signal when D is greater than 0.5 and a switching control signal when D is less than 0.5.

The controller 200 of the present application may be a digital controller, such as a DSP; or may be an analog controller; or the digital control and the analog controller are matched for use.

According to the above analysis, the control logic of the first switching tube Q1 is different between D greater than 0.5 and D less than 0.5, please refer to the partial schematic diagram of the controller in fig. 15, the controller 200 includes:

the and operation unit 210 is configured to receive the switch control signals of the second switch tube Q2 and the third switch tube Q3, when the switch control signals of the second switch tube Q2 and the third switch tube Q3 are both high, the output signal S1 of the and operation unit 210 is high, and when D is greater than 0.5, during the period from t0 to t1, the switch control signals of the second switch tube Q2 and the third switch tube Q3 are both high, and the output signal S1 of the and operation unit 210 is high, please refer to the schematic diagram of the controller local circuit operation waveform shown in fig. 16;

the integrating unit 220 receives the output signal S1 of the and operation unit 210, and is configured to integrate the output signal S1 of the and operation unit 210 to obtain an output signal S2 of the integrating unit 220, where when D is greater than 0.5, the output signal S2 of the integrating unit 220 gradually increases during a period from t0 to t1, and gradually decreases to zero after time t1, for example, decreases to zero until time t2, please refer to the schematic diagram of the controller local circuit operation waveform shown in fig. 16;

The comparator unit 230 receives the output signal S2 of the integrating unit 220 and the zero voltage input signal, and is configured to output a high level when the output signal S2 of the integrating unit 220 is greater than zero, and then the output signal S3 of the comparator unit 230 is at a high level during the period from t0 to t2, please refer to the controller local circuit operation waveform diagram shown in fig. 16;

an exclusive or operation unit 240 for receiving the output signal S3 of the comparator unit 230 and the output signal S1 of the and operation unit 210, wherein when the output signal S3 of the comparator unit 230 is different from the output signal S1 of the and operation unit 210, the output signal S4 of the exclusive or operation unit 240 is at a high level, and when the output signal S3 of the comparator unit 230 is identical to the output signal S1 of the and operation unit 210, the output signal S4 of the exclusive or operation unit 240 is at a low level, and during the period t0 to t1, the output signal S4 of the exclusive or operation unit 240 is at a low level, and during the period t1 to t2, the output signal S4 of the exclusive or operation unit 240 is at a high level, please refer to the controller local circuit operation waveform diagram shown in fig. 16;

the non-operation unit 250 receives the output signal S4 of the exclusive-or operation unit 240, and is configured to invert the output signal S4 of the exclusive-or operation unit 240 as the switching control signal of the first switching tube Q1, and the switching control signal of the first switching tube Q1 is at a high level during the period from t0 to t1, and the switching control signal of the first switching tube Q1 is at a low level during the period from t1 to t2, please refer to the schematic diagram of the controller local circuit operation waveform shown in fig. 16.

The integrating unit 220 includes a resistor and a capacitor, and by adjusting the values of the resistor and the capacitor, the time for the output signal S2 of the integrating unit to decrease from the maximum value to zero, that is, the time length from t1 to t2, that is, the off time of the first switching tube Q1, is adjusted. As described in the foregoing analysis, the sum of the voltage of the first flying capacitor Cb1 and the voltage of the second flying capacitor Cb2 discharged to the first flying capacitor Cb1 and the voltage of the second flying capacitor Cb2 is equal to the voltage of the input capacitor Cin during the off time of the first switching tube Q1. The turn-off time of the first switching tube Q1 can be adjusted by adjusting the values of the resistor and the capacitor.

As described above, the period from t0 to t2 is taken as an example to explain that the controller local circuit obtains the switch control signal of the first switch tube Q1, and the principle of obtaining the switch control signal of the first switch tube Q1 in other time periods is the same, which is not described herein again.

When D is smaller than 0.5, since the switching control signal of the second switching tube Q2 and the switching control signal of the third switching tube Q3 are out of phase by 180 °, and the switching control signal of the second switching tube Q2 and the third switching tube Q3 have no common on time, the output signal S1 of the sum operation unit 210, the output signal S2 of the integration unit 220, the output signal S3 of the comparator unit 230, and the output signal S4 of the exclusive-or operation unit 240 are always at low level, and the switching control signal of the first switching tube Q1 is always at high level, and the first switching tube Q1 is always on.

In an embodiment of the present application, a DC-DC converter is also provided. Specifically, please refer to the DC-DC converter 100 in fig. 1, the DC-DC converter shown in fig. 2 and 14, which are the same as the corresponding DC-DC converter described above in terms of structure, operation principle and advantages, and are not described herein.

In an embodiment of the present invention, the switching tubes (the first switching tube Q1 to the seventh switching tube Q7) are all implemented by including a single switching tube, and in practical application, each switching tube may include a plurality of switching tubes connected in series and/or in parallel.

In an embodiment of the present invention, the switching transistors (the first switching transistor Q1 to the seventh switching transistor Q7) may be metal oxide semiconductor field effect transistors, bipolar junction transistors, superjunction transistors, insulated gate bipolar transistors, gallium nitride based power devices, and/or the like. The device which can receive a switch control signal to turn on or off can be used in the industry.

In an embodiment of the present invention, the switching transistors are MOSFETs (metal oxide semiconductor field effect transistors) and each include a source, a drain and a gate. For the DC-DC converter 100 shown in fig. 1, the source of the first switching tube Q1 is connected to the positive input voltage terminal vin+ and the drain is connected to the first terminal of the first switching branch and the first terminal of the second switching branch. The drain electrode of the second switching tube Q2 is connected with the first end of the first switching branch, the source electrode of the second switching tube Q2 is connected with the drain electrode of the fourth switching tube Q4, the source electrode of the fourth switching tube Q4 is connected with the drain electrode of the sixth switching tube Q6, and the source electrode of the sixth switching tube Q6 is connected with the negative input voltage terminal Vin-. The drain electrode of the third switching tube Q3 is connected with the first end of the second switching branch, the source electrode of the third switching tube Q3 is connected with the drain electrode of the fifth switching tube Q5, the source electrode of the fifth switching tube Q5 is connected with the drain electrode of the seventh switching tube Q7, and the source electrode of the seventh switching tube Q7 is connected with the negative input voltage terminal Vin-. For the DC-DC converter shown in fig. 2, the sources of the first sub-switching tube Q11 and the second sub-switching tube Q12 are connected to the positive input voltage terminal vin+, the drain of the first sub-switching tube Q11 is connected to the first terminal of the first switching branch, the drain of the second sub-switching tube Q12 is connected to the first terminal of the second switching branch, and other connection relationships are the same as those of the DC-DC converter 100 in fig. 1, and will not be repeated here.

In an embodiment of the present application, the input voltage Vin received between the positive input voltage terminal vin+ and the negative input voltage terminal Vin-of the DC-DC converter 100 is between 40V and 60V, and the output voltage Vo formed at two ends of the output capacitor Co is 12V, which may have a certain error.

In an embodiment of the present application, the capacitance values of the first flying capacitor Cb1 and the second flying capacitor Cb2 are the same, so that the voltages thereon are 1/2Vin. Of course, it may also have some error.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention 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 or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. A DC-DC conversion device, comprising:

a DC-DC converter comprising:

the first switching branch comprises a second switching tube, a fourth switching tube and a sixth switching tube which are sequentially connected in series, the first end of the first switching branch is connected with the positive end of the input voltage through a first switching unit, and the second end of the first switching branch is connected with the negative end of the input voltage;

The second switching branch comprises a third switching tube, a fifth switching tube and a seventh switching tube which are sequentially connected in series, the first end of the second switching branch is connected with the positive end of the input voltage through the first switching unit, and the second end of the second switching branch is connected with the negative end of the input voltage;

the first flying capacitor is characterized in that a first end of the first flying capacitor is connected with a common node of a second switching tube and a fourth switching tube, and a second end of the first flying capacitor is connected with a common node of a fifth switching tube and a seventh switching tube;

the first end of the second flying capacitor is connected with the common node of the third switching tube and the fifth switching tube, and the second end of the second flying capacitor is connected with the common node of the fourth switching tube and the sixth switching tube;

the first end of the primary winding of the transformer is connected with a common node of the fourth switching tube and the sixth switching tube, and the second end of the primary winding of the transformer is connected with the first end of the secondary winding of the transformer;

the second end of the secondary winding of the transformer is connected with a common node of the fifth switching tube and the seventh switching tube;

the first end of the output inductor is connected with the second end of the primary winding of the transformer, and the second end of the output inductor is used for being connected with the first end of the output capacitor;

and the controller is configured to receive the sampling signal from the DC-DC converter so as to output a switching control signal to control the switching tube of the DC-DC converter to be turned on or off.

2. A DC-DC converter according to claim 1, characterized in that a first end of the primary winding of the transformer is coupled to a first end of the secondary winding of the transformer, or a second end of the primary winding of the transformer is coupled to a second end of the secondary winding of the transformer.

3. A DC-DC converter according to claim 1 or 2, characterized in that the turn ratio of the primary winding of the transformer to the secondary winding of the transformer is 1:1.

4. A DC-DC converter as claimed in claim 1, characterized in that the second terminal of the output capacitor is connected to the negative terminal of the input voltage.

5. A DC-DC conversion device according to claim 1 or 3, characterized in that the first switching unit comprises a first switching tube, and that the first end of the first switching branch and the first end of the second switching branch are connected to the input voltage positive terminal via the first switching tube.

6. The DC-DC converter of claim 5, wherein when the duty ratio D of the second to fifth switching transistors is less than 0.5, the controller is configured to output a switching control signal to cause the DC-DC converter to sequentially operate in the first operation mode, the second operation mode, the third operation mode, and the second operation mode in one switching cycle, wherein:

In a first working mode, the first switching tube, the second switching tube, the fifth switching tube and the sixth switching tube are conducted, and the third switching tube, the fourth switching tube and the seventh switching tube are turned off;

in a second working mode, the first switching tube, the sixth switching tube and the seventh switching tube are conducted, and the second switching tube to the fifth switching tube are turned off;

in a third working mode, the first switching tube, the third switching tube, the fourth switching tube and the seventh switching tube are conducted, and the second switching tube, the fifth switching tube and the sixth switching tube are turned off.

7. A DC-DC conversion device according to claim 5 or 6, wherein when the duty ratio D of the second to fifth switching transistors is greater than 0.5, the controller is configured to output a switching control signal to cause the DC-DC converter to sequentially operate in a fourth operation mode, a fifth operation mode, a first operation mode, a fourth operation mode, a sixth operation mode and a third operation mode in one switching cycle, wherein:

in a fourth working mode, the first switching tube, the second switching tube and the third switching tube are conducted, and the fourth switching tube to the seventh switching tube are turned off;

in a fifth working mode, the second switching tube, the fifth switching tube and the sixth switching tube are conducted, and the first switching tube, the third switching tube, the fourth switching tube and the seventh switching tube are turned off;

in a sixth working mode, the third switching tube, the fourth switching tube and the seventh switching tube are conducted, and the first switching tube, the second switching tube, the fifth switching tube and the sixth switching tube are turned off;

8. The DC-DC conversion apparatus according to claim 1, wherein the first switching unit includes a first sub-switching tube and a second sub-switching tube, a first end of the first switching branch is connected to the input voltage positive terminal through the first sub-switching tube, and a first end of the second switching branch is connected to the input voltage positive terminal through the second sub-switching tube.

9. The DC-DC conversion apparatus according to claim 8, wherein when the duty ratio D of the second to fifth switching transistors is greater than 0.5, the controller is configured to output a switching control signal such that the first sub-switching transistor is turned off when the second switching transistor is turned off, and the second sub-switching transistor is turned off when the third switching transistor is turned off;

When the duty ratio D of the second to fifth switching transistors is less than 0.5, the controller is configured to output a switching control signal such that the first and second sub switching transistors are normally on.

10. The DC-DC conversion apparatus according to claim 1, wherein the controller includes:

the AND operation unit is used for receiving the switch control signals of the second switch tube and the third switch tube and outputting output signals of the AND operation unit;

an integrating unit for receiving the output signal of the AND operation unit and integrating the output signal of the AND operation unit to output the output signal of the integrating unit;

a comparator unit receiving the output signal of the integration unit and the zero voltage input signal for outputting a high level when the output signal of the integration unit is greater than zero to output the output signal of the comparator unit 2;

and an exclusive-or operation unit for receiving the output signal of the comparator unit and the output signal of the AND operation unit and outputting the output signal of the exclusive-or operation unit.

And the non-operation unit receives the output signal of the exclusive OR operation unit and outputs a switch control signal of the first switch tube.

11. A DC-DC converter, comprising:

and the first end of the output inductor is connected with the second end of the primary winding of the transformer, and the second end of the output inductor is used for being connected with the first end of the output capacitor.

12. A DC-DC converter according to claim 11, characterized in that a first end of the primary winding of the transformer is coupled to a first end homonymous end of the secondary winding of the transformer, or a second end of the primary winding of the transformer is coupled to a second end homonymous end of the secondary winding of the transformer.

13. A DC-DC converter according to claim 11, characterized in that the turn ratio of the primary winding of the transformer to the secondary winding of the transformer is 1:1.

14. A DC-DC converter according to claim 11, wherein the first switching unit comprises a first switching tube, and the first end of the first switching leg and the first end of the second switching leg are connected to the input voltage positive terminal through the first switching tube.

15. The DC-DC converter of claim 11, wherein the first switching unit includes a first sub-switching tube and a second sub-switching tube, the first end of the first switching leg is connected to the input voltage positive terminal through the first sub-switching tube, and the first end of the second switching leg is connected to the input voltage positive terminal through the second sub-switching tube.

16. A DC-DC converter as in claim 15, further comprising a first capacitor connected between the first end of the first switching leg and the first end of the second switching leg.