A soft-switching BUCK converter and control method thereof

Abstract

The present invention provides a soft-switching BUCK converter and a control method thereof, wherein the BUCK converter comprises: a first power switch tube, a second power switch tube, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode and a third diode, wherein the first power switch tube and the second power switch tube are connected to a power supply, the first power switch tube is connected in series with the second inductor, the first capacitor is connected in parallel with the first power switch tube, the second power switch tube is connected in series with the first inductor, the first inductor is connected in series with the second inductor, the first diode is connected to the primary side of the transformer, the primary side of the transformer is connected to the first power switch tube and the first inductor, the secondary side of the transformer is connected to the third diode and grounded, the third diode is connected to a load, and the second inductor is connected in series with the load. The method controls the BUCK converter. The soft-switching BUCK converter and the control method thereof provided in the embodiment of the present invention improve the reliability of the circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a soft-switching BUCK converter and a control method thereof. Background Art

[0002] The BUCK converter has many advantages such as simple structure, light weight and high efficiency. It is a widely used circuit. Due to its excellent voltage transformation function, it can be directly used in places where direct voltage reduction is required.

[0003] The BUCK converter can achieve voltage reduction, but the high-frequency switch used in the converter is often in a hard switching working state, that is, a working state in which the voltage and current are not zero. According to P=UI, the switch will produce power loss in the hard switching working state, and in the high-frequency state, the power loss will be greater and will produce harsh noise. There are many problems such as high switching loss and large voltage and current stress. Summary of the invention

[0004] In view of the problems in the prior art, the embodiments of the present invention provide a soft-switching BUCK converter and a control method thereof, which can at least partially solve the problems in the prior art.

[0005] In one aspect, the present invention provides a soft-switching BUCK converter, comprising a first power switch tube, a second power switch tube, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode and a third diode, wherein:

[0006] The drains of the first power switch tube and the second power switch tube are respectively connected to the positive electrode of the power supply, the source of the first power switch tube is connected to the first end of the second inductor, the first capacitor is respectively connected to the two ends of the first power switch tube, the source of the second power switch tube is connected to the first end of the first inductor, and the second end of the first inductor is connected to the first end of the second inductor;

[0007] The cathode of the first diode is connected to the source of the second power switch tube and the first end of the first inductor respectively, the anode of the first diode is connected to the first end of the primary side of the transformer, the second end of the primary side of the transformer is connected to the source of the first power switch tube and the second end of the first inductor respectively, the first end of the secondary side of the transformer is grounded, the second end of the secondary side of the transformer is connected to the anode of the third diode, and the cathode of the third diode is connected to the first end of the load;

[0008] The second end of the second inductor is connected to the first end of the load, the second end of the load is grounded, the cathode of the second diode is connected to the first end of the second inductor, and the anode of the second diode is grounded.

[0009] The first inductance is smaller than the second inductance.

[0010] The driving pulse widths of the first power switch tube and the second power switch tube are the same.

[0011] The second power switch tube is closed before the first power switch tube is closed.

[0012] The second power switch tube is disconnected before the first power switch tube is disconnected.

[0013] The clamping voltage of the secondary side of the transformer is equal to the voltage across the load.

[0014] Wherein, a second capacitor is also included, a first end of the second capacitor is respectively connected to the second end of the second inductor and the first end of the load, and a second end of the second capacitor is grounded.

[0015] Wherein, the first power switch tube and the second power switch tube are metal-oxide semiconductor field effect transistors or insulated gate bipolar transistors.

[0016] On the other hand, the present invention provides a control method of a BUCK converter using the soft switching method described in any of the above embodiments, comprising:

[0017] The second power switch tube is closed and the first power switch tube is kept open, so that the current of the power supply passes through the second power switch tube, the first inductor and the second inductor to supply power to the load;

[0018] After a first preset time, the first power switch tube is closed, so that the current of the power supply passes through the first branch and the second branch, and then flows through the second inductor to supply power to the load; wherein the first branch includes the second power switch tube and the first inductor connected in series, and the second branch includes the first power switch;

[0019] The second power switch tube is disconnected so that the energy stored in the first inductor is output to the load through the secondary side of the transformer and the third diode, and the first power switch tube is disconnected after a second preset time so that the power supply stops supplying power to the load.

[0020] The first preset time and the second preset time are both greater than time t d ,in:

[0021] t d =t+t'

[0022] t=L1I D2 / V in

[0023]

[0024] Where, L1 is the inductance of the first inductor, V in is the voltage of the power supply, I D2 is the current of the second diode when the second power switch tube is turned on, and C1 is the capacitance of the first capacitor.

[0025] The buck converter of soft switching mode and the control method thereof provided by the embodiment of the present invention include a first power switch tube, a second power switch tube, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode and a third diode, wherein the drains of the first power switch tube and the second power switch tube are respectively connected to the positive electrode of the power supply, the source of the first power switch tube is connected to the first end of the second inductor, the first capacitor is respectively connected to the two ends of the first power switch tube, the source of the second power switch tube is connected to the first end of the first inductor, the second end of the first inductor is connected to the first end of the second inductor, the cathode of the first diode is respectively connected to the source of the second power switch tube and the first end of the first inductor, The positive electrode of the first diode is connected to the first end of the primary side of the transformer, the second end of the primary side of the transformer is respectively connected to the source of the first power switch tube and the second end of the first inductor, the first end of the secondary side of the transformer is grounded, the second end of the secondary side of the transformer is connected to the positive electrode of the third diode, the negative electrode of the third diode is connected to the first end of the load, the second end of the second inductor is connected to the first end of the load, the second end of the load is grounded, the negative electrode of the second diode is connected to the first end of the second inductor, and the positive electrode of the second diode is grounded, thereby realizing zero voltage conduction and shutdown of the first power switch tube, and zero current conduction and zero voltage shutdown of the second power switch tube, reducing the switching loss of the power switch tube and improving the reliability of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0027] Figure 1 It is a structural schematic diagram of a soft-switching BUCK converter provided in one embodiment of the present invention.

[0028] Figure 2 It is a schematic diagram of simulation waveforms of a driving signal, voltage and current of a second power switch tube provided in an embodiment of the present invention.

[0029] Figure 3It is a schematic diagram of simulation waveforms of a driving signal, voltage and current of a first power switch tube provided in an embodiment of the present invention.

[0030] Figure 4 It is a flowchart of a control method of a soft-switching BUCK converter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention. It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other arbitrarily.

[0032] In order to facilitate the understanding of the technical solution provided by the present application, the research background of the technical solution of the present application is briefly described below. According to the presence or absence of auxiliary switch tubes, soft switching technology can be divided into active soft switching technology and passive soft switching technology; if divided according to the development history of technology, there are several types such as quasi-resonant circuit, zero switching PWM circuit, zero conversion PWM circuit, etc. Among them, the resonant voltage peak of the traditional quasi-resonant circuit is large, and the requirements for the device are increased, while the latter two circuits often introduce auxiliary switches, which are active soft switching circuits, and can better realize the soft switching of the main circuit. However, only when the auxiliary switch is also in soft switching operation can full soft switching operation be achieved, and the control becomes relatively complicated. In comparison, the resonant circuit of the zero conversion PWM circuit is not on the main circuit and is less affected by the main circuit. The soft switching mode BUCK converter provided in the embodiment of the present invention adopts active switching circuits of auxiliary switches and main switches, and both the main and auxiliary switch tubes realize soft switching, which reduces the voltage and current stress of the auxiliary switch and the main switch.

[0033] Figure 1 FIG. 1 is a schematic diagram of a soft-switching BUCK converter according to an embodiment of the present invention. Figure 1 As shown, the structure of the soft-switching BUCK converter provided in the embodiment of the present invention includes a first power switch tube 1, a second power switch tube 2, a first capacitor 3, a first inductor 4, a second inductor 5, a transformer 6, a first diode 7, a second diode 8 and a third diode 9, wherein:

[0034] The drains of the first power switch tube 1 and the second power switch tube 2 are respectively connected to the positive electrode of the power supply, the source of the first power switch tube 1 is connected to the first end of the second inductor 5, the first capacitor 3 is respectively connected to the two ends of the first power switch tube 1, the source of the second power switch tube 2 is connected to the first end of the first inductor 4, and the second end of the first inductor 4 is connected to the first end of the second inductor 5;

[0035] The cathode of the first diode 7 is connected to the source of the second power switch tube 2 and the first end of the first inductor 4 respectively, the anode of the first diode 7 is connected to the primary first end a of the transformer 6, the primary second end b of the transformer 6 is connected to the source of the first power switch tube 1 and the second end of the first inductor 4 respectively, the secondary first end d of the transformer 6 is grounded, the secondary second end c of the transformer 6 is connected to the anode of the third diode 9, and the cathode of the third diode 9 is connected to the first end of the load 10;

[0036] The second end of the second inductor 5 is connected to the first end of the load 10 , the second end of the load 10 is grounded, the cathode of the second diode 8 is connected to the first end of the second inductor 5 , and the anode of the second diode 8 is grounded.

[0037] The working principle of the soft switching BUCK converter provided by the embodiment of the present invention is described below.

[0038] When the circuit is working in a stable state, the current in the first inductor 4 is zero. After the power supply Vin is turned on, the second power switch tube 2 is closed, and the first power switch tube 1 is in an open state. At this time, the current in the power supply Vin flows through the second power switch tube 2, the first inductor 4, and the second inductor 5 to supply power to the load 10. After the first preset time, Figure 1 When the voltage at A is close to the voltage of the power supply Vin, the first power switch tube 1 is closed. At this time, the first power switch tube 1 and the second power switch tube 2 are both closed, and the current of the power supply Vin is divided into two branches. The first branch passes through the second power switch tube 2 and the first inductor 4, and the second branch passes through the first power switch tube 1. The current of the two branches is Figure 1 After merging at A, the current flows through the second inductor 5 and then supplies power to the load 10. In the process of the power switch being closed, when the second power switch tube 2 is closed, since the current of the first inductor 4 is zero, the conduction current during the closing process of the second power switch tube 2 is approximately zero, and the second power switch tube 2 can be regarded as zero current conduction; when the first power switch tube 1 is closed, due to Figure 1 The voltage at A is approximately equal to the voltage of the power supply Vin, so when the first power switch tube 1 is closed, the voltage between its source and drain is approximately zero, and the first power switch tube 1 can be regarded as zero voltage conduction. Among them, the first preset time is set according to actual needs, and the embodiment of the present invention does not limit it.

[0039] When the power supply Vin needs to stop supplying power to the load 10, the second power switch tube 2 is first disconnected, and the current of the second power switch tube 2 is transferred to the first power switch tube 1. The current of the first inductor 4 passes through the primary side (coil a / b) of the transformer 6 and the first diode 7, and then returns to the first inductor 4. The energy stored in the first inductor 4 passes through the secondary side (coil c / d) of the transformer 6 and the third diode 9, and is output to the load 10. When the secondary side (coil c / d) of the transformer 6 flows with current, the clamping voltage at both ends is equal to the output voltage, that is, the voltage at both ends of the load 10. By designing the transformation ratio of the transformer 6, the voltage at both ends of the primary side of the transformer 6 when the current flows is a very small constant value compared to the voltage of the power supply Vin, for example, 3V. Assuming that the first diode 7 is an ideal device, when the second power switch tube 2 is disconnected, the first diode 7 is immediately turned on, and the drain voltage of the second power switch tube 2 is approximately clamped at the voltage of the power supply Vin. The second power switch tube 2 can be regarded as zero voltage shutdown. After the second preset time, the first power switch tube 1 is disconnected. Due to the presence of the first capacitor 3, the voltage between the drain and the source of the first power switch tube 1 is approximately zero during the disconnection process, and the first power switch tube 1 can be regarded as zero voltage disconnection. After the first power switch tube 1 is disconnected, the power supply Vin charges the first capacitor 3, and the current is supplied to the load 10 through the first capacitor 3 and the second inductor 5. When the charging of the first capacitor 3 is completed, the second diode 8 is turned on, and the current charges the load 10 through the second diode 8 and the second inductor 5, wherein the second preset time is set according to actual needs, and the embodiment of the present invention does not limit it.

[0040] The function of the transformer 6 is to transfer the energy in the first inductor 4 to the output power supply end when the second power switch tube 2 is turned off, and the voltage at the output power supply end is stable, so that the primary side (coil a / b) of the transformer 6 can be guaranteed to have a designable voltage. The transformation ratio of the transformer 6 is determined by the voltage clamped by the primary side of the transformer 6 during the energy transfer process and the secondary side voltage. If the primary side clamping voltage of the transformer 6 is high, the energy transfer process in the first inductor 4 is faster, the phase shift between the driving of the first power switch tube 1 and the second power switch tube 2 is smaller, but the voltage of the second power switch tube 2 during the shutdown process is higher, and the shutdown loss is higher; if the primary side clamping voltage of the transformer 6 is low, the energy transfer process in the first inductor 4 is slower, the phase shift between the driving of the first power switch tube 1 and the second power switch tube 2 is longer, and the voltage of the second power switch tube 2 during the shutdown process is lower, and the shutdown loss is also lower. Due to the function of the transformer 6, the inductance value of the first inductor 4 can have a wider range of selection.

[0041] It can be seen from the working principle of the soft-switching BUCK converter provided by the embodiment of the present invention that the working process of the second inductor 5 during the opening and closing process of the power supply Vin is exactly the same as the working process of the inductor in the existing BUCK converter, outputting the same power and the current not increasing. The first inductor 4 outputs the energy stored in itself to the load 10 through the transformer 6 only when the second power switch tube 2 is turned off, but because the inductance of the first inductor 4 is small, the increased stress brought to the switch tube second power switch tube 2 by the energy output to the load 10 can be ignored. After the first capacitor 3 is charged, the energy in the discharge process is stored in the first inductor 4, and supplied to the load 10 through the first inductor 4 to the second inductor 5, so there is no loss of energy on the first capacitor 3. In summary, in the soft-switching BUCK converter provided by the embodiment of the present invention, the first power switch tube 1 and the second power switch tube 2 realize zero current and zero voltage switching, thereby reducing switching losses. The soft-switching BUCK converter provided by the embodiment of the present invention does not increase the current and voltage stress of the power switch tube, realizes soft switching, reduces the switching loss of the power switch tube, and improves the reliability of the circuit.

[0042] The soft-switching BUCK converter provided by the embodiment of the present invention includes a first power switch tube, a second power switch tube, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode and a third diode. The drains of the first power switch tube and the second power switch tube are respectively connected to the positive electrode of the power supply, the source of the first power switch tube is connected to the first end of the second inductor, the first capacitor is respectively connected to the two ends of the first power switch tube, the source of the second power switch tube is connected to the first end of the first inductor, the second end of the first inductor is connected to the first end of the second inductor, the cathode of the first diode is respectively connected to the source of the second power switch tube and the first end of the first inductor, and the first and second The positive electrode of the diode is connected to the first end of the primary side of the transformer, the second end of the primary side of the transformer is respectively connected to the source of the first power switch tube and the second end of the first inductor, the first end of the secondary side of the transformer is grounded, the second end of the secondary side of the transformer is connected to the positive electrode of the third diode, the negative electrode of the third diode is connected to the first end of the load, the second end of the second inductor is connected to the first end of the load, the second end of the load is grounded, the negative electrode of the second diode is connected to the first end of the second inductor, and the positive electrode of the second diode is grounded, so that zero voltage conduction and shutdown of the first power switch tube, and zero current conduction and zero voltage shutdown of the second power switch tube are realized, the switching loss of the power switch tube is reduced, and the reliability of the circuit is improved.

[0043] On the basis of the above embodiments, further, the first inductor 4 is smaller than the second inductor 5, and the first inductor 4 can be set to the order of uH, such as 10uH, and the second inductor 5 can be set to tens of uH to hundreds of uH, such as 66uH.

[0044] On the basis of the above embodiments, further, the driving pulse widths of the first power switch tube 1 and the second power switch tube 2 are the same.

[0045] On the basis of the above embodiments, further, the second power switch tube 2 is closed before the first power switch tube 1 is closed, that is, the second power switch tube 2 is closed first, and after the first preset time, the first power switch tube 1 is closed, so that the second power switch tube 2 is turned on with zero current and the first power switch tube 1 is turned on with zero voltage.

[0046] On the basis of the above embodiments, further, the second power switch tube 2 is turned off before the first power switch tube 1 is turned off, that is, the second power switch tube 2 is turned off first, and after the second preset time, the first power switch tube 1 is turned off, so that the second power switch tube 2 is turned off with zero voltage, and the first power switch tube 1 is turned off with zero voltage.

[0047] On the basis of the above embodiments, further, the clamping voltage of the secondary side of the transformer 6 is equal to the output voltage, that is, equal to the voltage across the load 10 .

[0048] On the basis of the above embodiments, further, the soft switching BUCK converter provided in the embodiment of the present invention also includes a second capacitor 10, a first end of the second capacitor 10 is respectively connected to the second end of the second inductor 5 and the first end of the load 10, and a second end of the second capacitor 10 is grounded.

[0049] On the basis of the above embodiments, further, the first power switch tube 1 is a metal-oxide-semiconductor field-effect transistor (Metal-Oxide-Semiconductor Field-Effect Transistor, referred to as MOSFET) or an insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, referred to as IGBT), and the second power switch tube 2 is a MOSFET or an IGBT.

[0050] The soft-switching BUCK converter provided by the embodiment of the present invention can be divided into 7 modes in one switching cycle. Figure 1 Each electronic device in the embodiment is an ideal device, and the working process of the soft switching BUCK converter is analyzed as follows.

[0051] Mode 1 (t0-t1): Before time t0, the first power switch tube 1 and the second power switch tube 2 are disconnected, and the current of the first power switch tube 1 and the second power switch tube 2 is 0. The BUCK converter operates in the current continuous mode, the second inductor 5 is continuous through the second diode 8, and the voltage at point A in the circuit is 0. The current of the first inductor 4 drops to 0, the current of the primary and secondary sides of the transformer 6 is 0, and the voltage across the first capacitor 3 is equal to the voltage of the power supply Vin. At time t0, the second power switch tube 2 is closed. Due to the presence of the inductance of the first inductor 4, the conduction current of the second power switch tube 2 cannot change suddenly, and the second power switch tube 2 is turned on with zero current. After the second power switch tube 2 is turned on, the current of the first inductor 4 increases linearly under the action of the power supply Vin, and the current of the second diode 8 decreases linearly. The second diode 8 is turned off with zero current, and the current of the second diode 8 becomes 0 at time t1. Assume that the current of the second diode 8 at time t0 is I D2 , then the time from the second power switch tube 2 to the second diode 8 when the current is zero is t, t = L1I D2 / V in , where L1 is the inductance of the first inductor 4, V in is the voltage of the power supply Vin.

[0052] Mode 2 (t1-t2): At t1, the current of the second diode 8 becomes zero, and the second diode 8 is turned off with zero current. The first inductor 4 and the first capacitor 3 start to work in resonance, the current in the first inductor 4 increases, the voltage across the first capacitor 3 decreases, and the voltage at point A in the circuit gradually increases. At t2, the voltage across the first capacitor 3 drops to zero, and the voltage at point A in the circuit rises to the voltage of the power supply Vin. The time it takes for the voltage across the first capacitor 3 to drop to 0 is t c , Wherein, L1 is the inductance of the first inductor 4 , and C1 is the capacitance of the first capacitor 3 .

[0053] Mode 3 (t2-t3): At t2, the voltage drop across the first capacitor 3 is 0, and the power supply Vin outputs energy through the second power switch tube 2, the first inductor 4 and the second inductor 5. Thereafter, when the first power switch tube 1 is turned on at any time, it is turned on at zero voltage.

[0054] Mode 4 (t3-t4): At t3, the first power switch tube 1 is closed and turned on at zero voltage. At this time, both the first power switch tube 1 and the second power switch tube 2 are turned on, and the power supply Vin outputs energy backward through the first power switch tube 1 and the second power switch tube 2. The current of the first power switch tube 1 gradually increases, and the current of the second power switch tube 2 gradually decreases.

[0055] Mode 5 (t4-t5): At t4, the second power switch tube 2 is disconnected and the first diode 9 is turned on. Assuming that the primary-to-secondary turns ratio of the transformer 6 is 10, the secondary clamp is located at the output load end, and the voltage across the load 10 is 48V, the primary voltage of the transformer 6 is 4.8V, and the energy of the first inductor 4 is output to the load 10 through the transformer 6. Theoretically, there is no energy loss in the first inductor 4. Since the primary voltage of the transformer 6 is very small relative to the output voltage, it can be considered that the shutdown process of the second power switch tube 2 is zero voltage shutdown. The current of the second power switch tube 2 is transferred to the first power switch tube 1. At t5, the current of the first inductor 4 is zero. Assuming that the current of the first inductor 4 is I at the moment when the second power switch tube 2 is disconnected L1 , the primary voltage of transformer 6 is V 原 The time from when the second power switch 2 is turned off to when the current of the first inductor 4 is zero is t L , Wherein, L1 is the inductance of the first inductor 4 .

[0056] Mode 6 (t5-t6): After time t5, the first power switch tube 1 is disconnected. Since the voltage across the first capacitor 3 cannot change suddenly, the first power switch tube 1 is turned off with zero voltage, and the voltage across the first capacitor 3 gradually increases.

[0057] Mode 7 (t6-t7): At t6, the voltage across the first capacitor 3 is equal to the voltage of the power supply Vin, and the second diode 8 is turned on for freewheeling. At t7, the second power switch tube 2 is turned on, and the next switching cycle begins.

[0058] Figure 2 is a schematic diagram of simulated waveforms of a driving signal, voltage and current of a second power switch tube provided in an embodiment of the present invention, Figure 3 FIG. 1 is a schematic diagram of simulated waveforms of a driving signal, voltage and current of a first power switch tube provided in an embodiment of the present invention. Figure 2 and Figure 3 As shown, the first power switch tube 1 realizes zero voltage switching, and the second power switch tube 2 realizes zero current conduction and zero voltage shutdown. Figure 2 and Figure 3 The simulation waveform in is obtained by simulation under the conditions that the voltage of the power supply Vin is 96V, the inductance L1 of the first inductor 4 is 2uH, the inductance L2 of the second inductor 5 is 66uH, the turns ratio of the transformer 6 is 10, the capacitance C2 of the second capacitor 11 is 100uF, the resistance of the load 10 is 5 ohms, the switching frequency is 25KHz, the driving phase difference between the first power switch tube 1 and the second power switch tube 2 is 4us, and the duty cycle is 60%.

[0059] The soft-switching BUCK converter provided in the embodiment of the present invention has a simple circuit structure, is easy to drive, uses a small number of components, and has small voltage stress and current stress of the first power switch tube and the second power switch tube, which is beneficial to cost saving. The soft switching of the power switch tube can be achieved under a large load range and a large duty cycle, thereby improving the working efficiency of the system.

[0060] Figure 4 FIG. 1 is a flow chart of a control method of a soft-switching BUCK converter according to an embodiment of the present invention. Figure 4 As shown, the control method of the BUCK converter using the soft switching method described in any of the above embodiments provided in an embodiment of the present invention includes:

[0061] S401, close the second power switch tube and keep the first power switch tube open, so that the current of the power supply passes through the second power switch tube, the first inductor and the second inductor to supply power to the load;

[0062] Specifically, after the power supply is turned on, the second power switch tube is closed and the first power switch tube is kept open. At this time, the current in the power supply flows through the second power switch tube, the first inductor and the second inductor to supply power to the load. When the second power switch tube is closed, since the current in the first inductor is zero, the conduction current during the closing process of the second power switch tube is approximately zero, and the second power switch tube can be regarded as zero current conduction.

[0063] S402: After a first preset time, close the first power switch tube, so that the current of the power supply passes through the first branch and the second branch, and then flows through the second inductor to supply power to the load; wherein the first branch includes the second power switch tube and the first inductor connected in series, and the second branch includes the first power switch;

[0064] Specifically, after the second power switch tube is closed for a first preset time, the voltage at the input end of the second inductor is approximately equal to the voltage of the power supply, and the first power switch tube is closed. At this time, the first power switch tube and the second power switch tube are both closed, and the current of the power supply is divided into two branches, the first branch includes the second power switch tube and the first inductor connected in series, and the second branch includes the first power switch. After the current of the power supply flows through the first branch and the second branch respectively, it converges at the input end of the second inductor, and then supplies power to the load through the second inductor. When the first power switch tube is closed, since the voltage at the input end of the second inductor is approximately equal to the voltage of the power supply, the voltage between the source and the drain of the first power switch tube is approximately zero when the first power switch tube is closed, and the first power switch tube can be regarded as zero voltage conduction. Among them, the first preset time is set according to actual needs, and the embodiment of the present invention is not limited.

[0065] S403, disconnecting the second power switch tube, so that the energy stored in the first inductor is output to the load through the secondary side of the transformer and the third diode, and disconnecting the first power switch tube after a second preset time, so that the power supply stops supplying power to the load.

[0066] Specifically, when the power supply stops supplying power to the load, the second power switch tube is first disconnected, and the current of the second power switch tube is transferred to the first power switch tube. The current of the first inductor passes through the primary side of the transformer and the first diode, and then returns to the first inductor. The energy stored in the first inductor passes through the secondary side of the transformer and the third diode, and is output to the load. After the second power switch tube is disconnected for a second preset time, the first power switch tube is disconnected, so that the power supply stops supplying power to the load. When the second power switch tube is disconnected, the first diode is immediately turned on, and the drain voltage of the second power switch tube is approximately clamped to the voltage of the power supply. The second power switch tube can be regarded as zero voltage shutdown. When the first power switch tube is disconnected, due to the presence of the first capacitor, the voltage between the drain and the source of the first power switch tube is approximately zero during the disconnection process. The first power switch tube can be regarded as zero voltage disconnection.

[0067] The control method of the soft-switching BUCK converter provided in the embodiment of the present invention can close the second power switch tube and keep the first power switch tube disconnected, so that the current of the power supply passes through the second power switch tube, the first inductor and the second inductor to supply power to the load. After a first preset time, the first power switch tube is closed, so that the current of the power supply passes through the first branch and the second branch and then flows through the second inductor to supply power to the load, and then the second power switch tube is disconnected, so that the energy stored in the first inductor is output to the load through the secondary side of the transformer and the third diode, and the first power switch tube is disconnected after the second preset time, so that the power supply stops supplying power to the load, thereby realizing zero voltage conduction and shutdown of the first power switch tube, and zero current conduction and zero voltage shutdown of the second power switch tube, reducing the switching loss of the power switch tube and improving the reliability of the circuit.

[0068] On the basis of the above embodiments, further, the first preset time and the second preset time are both greater than the time t d ,in:

[0069] t d =t+t'

[0070] t=L1I D2 / V in

[0071]

[0072] Where, L1 is the inductance of the first inductor, V in is the voltage of the power supply, I D2 is the current of the second diode when the second power switch tube is turned on, and C1 is the capacitance of the first capacitor.

[0073] Specifically, in order to obtain the best possible soft switching effect of the power switch tube, the first preset time is greater than the time t d , the second preset time is also greater than time t d That is to say, the time that the driving pulse of the first power switch tube lags behind the driving pulse of the second power switch tube is greater than the time t d Among them, t d =t+t'. t is the time from the second power switch tube being turned on to the current of the second diode being zero, t=L1I D2 / V in , where L1 is the inductance of the first inductor, V in is the voltage of the power supply, I D2 is the current of the second diode when the second power switch is turned on. After the current in the second diode becomes zero, the first inductor and the first capacitor start to resonate, the current in the first inductor increases, and the voltage across the first capacitor decreases. Figure 1 The time taken for the voltage at point A to gradually rise to the power supply voltage is t'. Wherein, L1 is the inductance of the first inductor, and C1 is the capacitance of the first capacitor. Wherein, the inductance of the first inductor can be set at the order of 10uH, and the capacitance of the first capacitor can be set at the order of 10nF. d It may occupy one tenth to one fifth of the driving pulse period of the first power switch tube or the second power switch tube.

[0074] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0075] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0076] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0077] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0078] In the description of this specification, the description with reference to the terms "one embodiment", "a specific embodiment", "some embodiments", "for example", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0079] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A soft-switching BUCK converter, characterized in that: It includes a first power switch tube, a second power switch tube, a first capacitor, a first inductor, a second inductor, a transformer, a first diode, a second diode and a third diode, wherein: The drains of the first power switch tube and the second power switch tube are respectively connected to the positive electrode of the power supply, the source of the first power switch tube is connected to the first end of the second inductor, the first capacitor is respectively connected to the two ends of the first power switch tube, the source of the second power switch tube is connected to the first end of the first inductor, and the second end of the first inductor is connected to the first end of the second inductor; The cathode of the first diode is connected to the source of the second power switch tube and the first end of the first inductor respectively, the anode of the first diode is connected to the first end of the primary side of the transformer, the second end of the primary side of the transformer is connected to the source of the first power switch tube and the second end of the first inductor respectively, the first end of the secondary side of the transformer is grounded, the second end of the secondary side of the transformer is connected to the anode of the third diode, and the cathode of the third diode is connected to the first end of the load; The second end of the second inductor is connected to the first end of the load, the second end of the load is grounded, the cathode of the second diode is connected to the first end of the second inductor, and the anode of the second diode is grounded; Wherein, the second power switch tube is closed before the first power switch tube is closed; the second power switch tube is opened before the first power switch tube is opened; wherein the first inductance is smaller than the second inductance; The BUCK converter further includes a second capacitor, a first end of the second capacitor is respectively connected to the second end of the second inductor and the first end of the load, and a second end of the second capacitor is grounded.

2. The BUCK converter according to claim 1, characterized in that: The driving pulse widths of the first power switch tube and the second power switch tube are the same.

3. The BUCK converter according to claim 1, characterized in that: The clamping voltage of the secondary side of the transformer is equal to the voltage across the load.

4. The BUCK converter according to any one of claims 1 to 3, characterized in that: The first power switch tube and the second power switch tube are metal-oxide semiconductor field effect transistors or insulated gate bipolar transistors.

5. A control method for a soft-switching BUCK converter according to any one of claims 1 to 4, characterized in that: include: The second power switch tube is closed and the first power switch tube is kept open, so that the current of the power supply passes through the second power switch tube, the first inductor and the second inductor to supply power to the load; After a first preset time, the first power switch tube is closed, so that the current of the power supply passes through the first branch and the second branch, and then flows through the second inductor to supply power to the load; wherein the first branch includes the second power switch tube and the first inductor connected in series, and the second branch includes the first power switch; The second power switch tube is disconnected so that the energy stored in the first inductor is output to the load through the secondary side of the transformer and the third diode, and the first power switch tube is disconnected after a second preset time so that the power supply stops supplying power to the load.

6. The method according to claim 5, characterized in that The first preset time and the second preset time are both greater than time t d ,in: t d =t+t' t=L1I D2 / V in Where, L1 is the inductance of the first inductor, V in is the voltage of the power supply, I D2 is the current of the second diode when the second power switch tube is turned on, and C1 is the capacitance of the first capacitor.

Images