Synchronous rectification soft switching circuit, power conversion circuit and power supply circuit
By using switch tubes that replace transistors and diodes in the Buck circuit and using soft switch circuit control to achieve zero voltage shutdown and conduction, the problems of switching losses and volume increase in the prior art are solved, and high-efficiency high-frequency soft switch operation is achieved.
Patent Information
- Application Number
- CN202510576891.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-06
- Publication Date
- 2025-08-05
AI Technical Summary
In the prior art, the soft switching method of the Buck circuit has the problem of additional frequency modulation circuits leading to an increase in volume and excessive loss of auxiliary circuits, especially when the switching frequency increases.
The first switching tube is used to replace the transistor of the standard BUCK circuit, the second switching tube is used to replace the diode, and the zero voltage shutdown and zero voltage turn-on are achieved through the soft switching circuit control, combining the transformer unit and the current cut-off unit to reduce switching losses.
Without affecting the switching speed and frequency, it significantly reduces switching losses, improves circuit efficiency, and achieves efficient high-frequency soft switch operation.
Smart Images
Figure CN120433607A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of switch circuits, and in particular to a synchronous rectification soft switch circuit, a power conversion circuit and a power supply circuit. Background Art
[0002] The introduction of synchronous rectification technology has improved the efficiency of Buck circuits, especially in low-voltage, high-current output. With the maturity and application of third-generation semiconductor devices such as SiC and GaN, the switching frequency of circuits has continued to increase. However, the increase in switching frequency will introduce more switching losses and EMI problems, so soft switching technology has been further introduced.
[0003] In the current existing technology, methods such as quasi-resonance, zero-switching PWM, and zero-conversion PWM have been proposed to address the soft switching problem in Buck circuit applications. However, these methods have disadvantages such as the need for additional frequency modulation circuits, which leads to increased volume and excessive auxiliary circuit losses. Summary of the Invention
[0004] Embodiments of the present invention provide a synchronous rectification soft switching circuit, a power conversion circuit, and a power supply circuit to fully reduce the switching characteristics of a switching tube, reduce its switching loss without affecting its switching speed and switching frequency, and achieve efficient and high-frequency soft switching operation.
[0005] In a first aspect, an embodiment of the present invention provides a synchronous rectification soft switching circuit, comprising: a synchronous rectification circuit and a soft switching circuit.
[0006] The synchronous rectification circuit includes: a first buck circuit; wherein, in the first buck circuit, a first switching tube is used to replace the transistor of the standard buck circuit, and a second switching tube is used to replace the diode of the standard buck circuit; the drain of the first switching tube is connected to the positive electrode of the power supply in the standard buck circuit, the drain of the second switching tube is connected to the source of the first switching tube, and the source of the second switching tube is connected to the negative electrode of the power supply in the standard buck circuit.
[0007] The first interface of the soft switching circuit is connected to the drain of the first switching tube, the second interface of the soft switching circuit is connected to the source of the first switching tube, and the third interface of the soft switching circuit is connected to the output end of the first BUCK circuit.
[0008] The soft switching circuit is used to control the first switch tube to achieve zero voltage shutdown and control the second switch tube to achieve zero voltage conduction.
[0009] In a possible implementation, the first BUCK circuit includes: a first power supply, a first switching tube, a second switching tube, a first inductor, and a filter circuit.
[0010] The positive electrode of the first power supply is connected to the drain of the first switching tube, the negative electrode of the first power supply is grounded, the source of the first switching tube is connected to the drain of the second switching tube, the source of the second switching tube is connected to the negative electrode of the first power supply, the first end of the first inductor is connected to the source of the first switching tube, the second end of the first inductor is connected to the first input end of the filter circuit, and the second input end of the filter circuit is grounded; the output end of the filter circuit is the output end of the first buck circuit.
[0011] In a possible implementation, the filtering circuit includes: a first capacitor and a first resistor.
[0012] The first end of the first capacitor is the first input end of the filter circuit, and the second end of the first capacitor is the second input end of the filter circuit.
[0013] The first end of the first resistor is connected to the first end of the first capacitor, and the second end of the first resistor is connected to the second end of the first capacitor.
[0014] The first end of the first resistor is the output end of the filter circuit.
[0015] In a possible implementation, the soft switching circuit includes: a third switching tube, a voltage transformation unit, a second inductor, and a current cutoff unit.
[0016] The drain of the third switching tube is connected to the first interface of the soft switching circuit, the source of the third switching tube is connected to the first input end of the transformer unit, the second input end of the transformer unit is connected to the first end of the second inductor, the second end of the second inductor is connected to the second interface of the soft switching circuit, the first end of the current cutoff unit is connected to the third interface of the soft switching circuit, the second end of the current cutoff unit is connected to the first output end of the transformer unit, and the second output end of the transformer unit is grounded.
[0017] The current in the current cutoff unit flows from the first output end of the voltage transformation unit to the third interface of the soft switching circuit.
[0018] In a possible implementation, the transformation unit includes at least a first transformer.
[0019] The secondary side like-name terminal of the first transformer is the first input terminal of the voltage transformation unit, and the secondary side unlike-name terminal of the first transformer is the second input terminal of the voltage transformation unit.
[0020] The primary like-name end of the first transformer is the first output end of the transformer unit, and the primary unlike-name end of the first transformer is the second output end of the transformer unit.
[0021] In a possible implementation, the current cutoff unit includes at least a first diode.
[0022] The cathode of the first diode is the first end of the current cutoff unit, and the anode of the first diode is the second end of the current cutoff unit.
[0023] In a possible implementation, the maximum operating current of the third switch tube is greater than 24A.
[0024] In a possible implementation, the primary-to-secondary winding ratio of the first transformer is greater than or equal to 0.6.
[0025] In a second aspect, an embodiment of the present invention provides a power conversion circuit, comprising: any one of a DC-DC power conversion circuit, a DC-AC power conversion circuit, an AC-DC power conversion circuit and an AC-AC power conversion circuit, and the synchronous rectification soft switching circuit described in any one of the first aspects.
[0026] In a third aspect, an embodiment of the present invention provides a power supply circuit, comprising: a load and the synchronous rectification soft switching circuit described in any one of the first aspects.
[0027] In the embodiment of the present invention, the thyristors and diodes in the original buck circuit (i.e., the standard buck circuit) are replaced by first and second switching tubes. Based on the first and second switching tubes, zero-voltage turn-off and zero-voltage turn-on are achieved through soft switching circuit control. This can fully reduce the switching characteristics of the switching tubes, reduce their switching losses without affecting their switching speed and switching frequency, and improve the operating efficiency of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 1 is a structural diagram of a synchronous rectification soft switching circuit provided by an embodiment of the present invention;
[0029] Figure 2 The waveform timing diagram of each switch tube and each inductor within one cycle provided by the embodiment of the present invention is shown. DETAILED DESCRIPTION
[0030] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0031] See also Figure 1 , which shows a schematic structural diagram of a synchronous rectification soft switching circuit provided by an embodiment of the present invention, and is described in detail as follows:
[0032] A synchronous rectification soft switching circuit includes: a synchronous rectification circuit 101 and a soft switching circuit 102.
[0033] The synchronous rectification circuit 101 includes: a first buck circuit; wherein, in the first buck circuit, a first switch tube S1 is used to replace the transistor of the standard buck circuit, and a second switch tube S2 is used to replace the diode of the standard buck circuit; the drain of the first switch tube S1 is connected to the positive electrode of the power supply U1 in the standard buck circuit, the drain of the second switch tube S2 is connected to the source of the first switch tube S1, and the source of the second switch tube S2 is connected to the negative electrode of the power supply in the standard buck circuit.
[0034] The first interface M1 of the soft switching circuit 102 is connected to the drain of the first switch S1 , the second interface M2 of the soft switching circuit 102 is connected to the source of the first switch S1 , and the third interface M3 of the soft switching circuit 102 is connected to the output end of the first BUCK circuit.
[0035] The soft switching circuit 102 is used to control the first switch tube S1 to achieve zero voltage turn-off, and to control the second switch tube S2 to achieve zero voltage turn-on.
[0036] In a possible implementation, the first BUCK circuit includes: a first power supply U1 , a first switch tube S1 , a second switch tube S2 , a first inductor L, and a filter circuit.
[0037] The positive electrode of the first power supply U1 is connected to the drain of the first switching tube S1, the negative electrode of the first power supply U1 is grounded, the source of the first switching tube S1 is connected to the drain of the second switching tube S2, the source of the second switching tube S2 is connected to the negative electrode of the first power supply U1, the first end of the first inductor L is connected to the source of the first switching tube S1, the second end of the first inductor L is connected to the first input end of the filter circuit, and the second input end of the filter circuit is grounded; the output end of the filter circuit is the output end of the first buck circuit.
[0038] In a possible implementation, the filtering circuit includes: a first capacitor C0 and a first resistor R.
[0039] The first end of the first capacitor C0 is the first input end of the filter circuit, and the second end of the first capacitor C0 is the second input end of the filter circuit.
[0040] A first end of the first resistor R is connected to a first end of the first capacitor C0 , and a second end of the first resistor R is connected to a second end of the first capacitor C0 .
[0041] The first end of the first resistor R is the output end of the filter circuit.
[0042] In a possible implementation, the soft switching circuit 102 includes: a third switch tube S3, a voltage transformation unit T, a second inductor Lr, and a current cutoff unit.
[0043] The drain of the third switch tube S3 is connected to the first interface M1 of the soft switching circuit 102, the source of the third switch tube S3 is connected to the first input end of the transformer unit T, the second input end of the transformer unit T is connected to the first end of the second inductor Lr, the second end of the second inductor Lr is connected to the second interface M2 of the soft switching circuit 102, the first end of the current cutoff unit is connected to the third interface M3 of the soft switching circuit 102, the second end of the current cutoff unit is connected to the first output end of the transformer unit T, and the second output end of the transformer unit T is grounded.
[0044] The current in the current cutoff unit flows from the first output terminal of the transformer unit T to the third interface M3 of the soft switching circuit 102 .
[0045] For example, the first, second, and third switching transistors S1, S2, and S3 have similar structures, all consisting of MOS transistors, diodes, and capacitors. The first switching transistor S1 consists of a MOS transistor Q1, a diode D1, and a capacitor C1; the second switching transistor S2 consists of a MOS transistor Q2, a diode D2, and a capacitor C2; and the third switching transistor S3 consists of a MOS transistor Q3, a diode D3, and a capacitor C3.
[0046] Exemplarily, the first inductor L is a resonant inductor, and its energy can only flow to the load end due to the presence of the current cutoff unit, thereby preventing the current from flowing into the soft switching circuit and reducing energy loss.
[0047] In addition, the soft switching circuit 102 is independent of the synchronous rectification circuit 101, and can achieve a plug-and-play effect without affecting the normal operation of the synchronous rectification circuit 101 itself (that is, when the soft switching circuit 102 is not connected, the synchronous rectification circuit 101 can also realize the basic functions of the BUCK circuit).
[0048] In a possible implementation, the transformation unit includes at least a first transformer.
[0049] The secondary side like-name terminal of the first transformer is the first input terminal of the transformation unit T, and the secondary side unlike-name terminal of the first transformer is the second input terminal of the transformation unit T.
[0050] The primary like-name end of the first transformer is the first output end of the transformer unit T, and the primary unlike-name end of the first transformer is the second output end of the transformer unit T.
[0051] In a possible implementation, the current cutoff unit includes at least a first diode D4.
[0052] The cathode of the first diode D4 is the first end of the current cutoff unit, and the anode of the first diode D4 is the second end of the current cutoff unit.
[0053] In a possible implementation, the maximum operating current of the third switch tube is greater than 24A.
[0054] In a possible implementation, the primary-to-secondary winding ratio of the first transformer is greater than or equal to 0.6.
[0055] Specifically, the primary-to-secondary coil ratio in this application specifically refers to the number of coil turns N at the first output terminal and the second output terminal. n The number of coil turns N at the first input terminal and the second input terminal p ratio.
[0056] In order to more specifically describe the zero-voltage turn-off of the first switch tube and the zero-voltage turn-on of the second switch tube, the following explanation is given:
[0057] like Figure 2 As shown, Figure 2 The waveforms of the source voltage, drain voltage, current of the first inductor and current of the second inductor of the three switching tubes over time in a whole cycle are shown. S1_GS Represents the gate-source voltage of the first switch tube S1, V S2_GS Represents the gate-source voltage of the second switch tube S2, V S3_GS Represents the gate-source voltage of the third switch tube S3, V S1_DS Represents the drain-source voltage of the first switch tube S1, V S2_DS represents the drain-source voltage of the second switch tube S2, i Lr represents the current of the second inductor Lr, i L represents the current in the first inductor Lr. Before time t0, the first and third switches S1 and S3 are on, while the second switch S2 is off. At time t0, the current in the second inductor Lr drops to zero, the third switch S3 turns off, and S1 remains on. At time t1, the first switch S1 turns off, achieving zero-voltage turn-off of the first switch S1. At this time, the body diode of the second switch S2 conducts in reverse, clamping its drain-source voltage to 0V. From t2 to t3, the body diode of the second switch S2 remains in reverse conduction until time t3, when the second switch S2 turns on, achieving zero-voltage turn-on of the second switch S2.
[0058] From time t3 to time t4, the second switch S2 remains on, and the energy in the first inductor L continues to be transferred to the first capacitor C0 and the first resistor R. At time t4, the third switch S3 turns on, and the first diode D4 turns on. The output voltage is clamped across the primary winding of the first transformer, and the current in the second inductor Lr increases linearly. At time t5, the current in the second inductor Lr equals the current in the first inductor L, and the second switch S2 turns off, achieving zero-voltage turn-off. After time t5, the current in the second inductor Lr becomes greater than the current in the first inductor L, causing the drain-source voltage of the first switch S1 to rise and the drain-source voltage of the second switch S2 to decrease. At time t6, the drain-source voltage of the second switch S2 equals the voltage of the first power supply U1, the drain-source voltage of the first switch S1 reaches zero, and the body diode of the first switch S1 turns on. At time t7, the first switch S1 turns on, achieving zero-voltage turn-on. At time t8, the current in the second inductor Lr drops to 0, the third switch S3 is turned off, the first diode D4 is cut off, and the next cycle of operation begins.
[0059] In some specific embodiments, the first transformer, the second inductor Lr, the MOS transistor Q3 of the third switch transistor S3 and the capacitor C3 of the third switch transistor S3 all have certain requirements, and the soft switching effect of the present application cannot be achieved by arbitrary settings.
[0060] (1) Transformer design
[0061] If the secondary coupling inductor L of the first transformer p , the primary coupling inductor of the first transformer L n The turns ratio is N, and the coupling coefficient k is close to 1. Then the relationship between inductance and number of turns is approximately:
[0062]
[0063] At time t6, during the resonance process, the terminal voltage V C2_max for
[0064]
[0065] V C2_max The maximum value must be higher than the input voltage. V0 is the output voltage of the synchronous rectification soft switching circuit, and V1 is the voltage of the power supply U1. Therefore, the turns ratio of the first transformer must meet the following conditions:
[0066]
[0067] Among them, D on It represents the positive duty cycle of the main circuit, that is, the driving duty cycle of the first switch tube S1.
[0068] Based on the input and output voltage parameters, N must be no less than 0.6. The relationship between the turns ratio of the first transformer and the parameters of the first switch S1 is not directly given. Ideally, the turns ratio of the first transformer must satisfy the above equation to resonate the drain-source voltage of the MOS transistor Q1 of the first switch S1 to zero at time t6, allowing Q1 to achieve zero-voltage turn-on. However, a too large turns ratio will result in excessive current in Lr, increasing losses in the auxiliary branch. In this circuit, the turns ratio N is set to 1.
[0069] (2) The second inductor Lr and the capacitor C3 of the third switch tube S3
[0070] The total resonance time of Lr and C3 and the maximum current flowing through Lr can be obtained from the modal analysis above. The values of Lr and C3 are positively correlated with the duration of each stage of the resonance process. If Lr is too large, the total transition time will be too long; if Lr is too small, the peak value of the resonant inductor current in the auxiliary branch will be too large, and the loss will increase. A larger value of C3 will make the drain-source voltage change more slowly during the on-off process of the switch tube Q1, and the loss of Q1 will be smaller; if C3 is too large, the time between t5 and t6 will increase, and the peak current of the resonant inductor will be larger, resulting in increased losses. Therefore, the design size of the resonant capacitor and the capacitor should be moderate.
[0071] The current i of the second inductor Lr at time t6 is Lr The value of (t6) is not less than the first inductor L current i L , for the time period t between t7 and t8 78 There is t 78 ≥0.2Lr. Since the switching frequency is 1MHz, the switching period t is 1μs. In general, it is hoped that the total transition time is as short as possible, generally not exceeding one tenth of the switching tube period. Under the condition that the turns ratio N is 1, t 78 If it is greater than 0.2Lr, then Lr≤0.5μH.
[0072] In the time period t between time t1 and time t2 12 During the dead time, the following conditions must be met:
[0073] t 12 =V1·2C3 / i L ≤t dead
[0074] The time period t between time t5 and time t6 56 During the dead time, the following conditions must be met:
[0075]
[0076] Controller dead time t deadThe time duration is 100ns. Based on the above constraints and the cost of the inductor, the second inductor Lr is selected to be 0.5μH and the capacitor C3 is selected to be 1nF.
[0077] (3) MOS tube Q3 of the third switch tube S3
[0078] When the third switch tube S3 is turned on, the current flowing through the second inductor Lr is i Lr From the perspective of energy transfer, during the resonance process, the relationship between the second inductor Lr and the capacitor C3 approximately satisfies:
[0079]
[0080] Consider the extreme case, that is, when V1 takes the maximum value, i Lr The maximum is about 19 A. Considering the safety margin, the maximum operating current of the third switch S3 should be greater than 24 A. The maximum operating current of the third switch S3 is related to the parameters of the second inductor Lr and is not directly given.
[0081] The above-mentioned synchronous rectification soft-switching circuit replaces the thyristor and diode in the original buck circuit (i.e., the standard buck circuit) with the first and second switching tubes. Based on the first and second switching tubes, zero-voltage shutdown and zero-voltage conduction are achieved through soft-switching circuit control, which can fully reduce the switching characteristics of the switching tubes, reduce their switching losses without affecting their switching speed and switching frequency, and improve the circuit's operating efficiency.
[0082] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.
[0083] An embodiment of the present application also shows a power conversion circuit, including: any one of a DC-DC power conversion circuit, a DC-AC power conversion circuit, an AC-DC power conversion circuit and an AC-AC power conversion circuit, and a synchronous rectification soft switching circuit described in any of the above items.
[0084] An embodiment of the present application further shows a power supply circuit, comprising: a load and any one of the synchronous rectification soft switching circuits described above.
[0085] In the above embodiments, the descriptions of each embodiment have their own focus. For parts not described or recorded in detail in one embodiment, please refer to the relevant descriptions of other embodiments. Unless otherwise specified or there is a logical conflict, the terms and / or descriptions between different embodiments are consistent and can be referenced to each other. The technical features of different embodiments can be combined to form new embodiments based on their inherent logical relationships.
[0086] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.
Claims
1. A synchronous rectification soft switching circuit, characterized in that: include: Synchronous rectification circuit and soft switching circuit; The synchronous rectification circuit includes: a first buck circuit; wherein the first buck circuit uses a first switch tube to replace the transistor of the standard buck circuit, and uses a second switch tube to replace the diode of the standard buck circuit; the drain of the first switch tube is connected to the positive electrode of the power supply in the standard buck circuit, the drain of the second switch tube is connected to the source of the first switch tube, and the source of the second switch tube is connected to the negative electrode of the power supply in the standard buck circuit; The first interface of the soft switching circuit is connected to the drain of the first switching transistor, the second interface of the soft switching circuit is connected to the source of the first switching transistor, and the third interface of the soft switching circuit is connected to the output end of the first buck circuit; The soft switching circuit is used to control the first switch tube to achieve zero voltage shutdown and control the second switch tube to achieve zero voltage conduction.
2. The synchronous rectification soft switching circuit according to claim 1, characterized in that: The first BUCK circuit includes: a first power supply, a first switch tube, a second switch tube, a first inductor and a filter circuit; The positive electrode of the first power supply is connected to the drain of the first switching tube, the negative electrode of the first power supply is grounded, the source of the first switching tube is connected to the drain of the second switching tube, the source of the second switching tube is connected to the negative electrode of the first power supply, the first end of the first inductor is connected to the source of the first switching tube, the second end of the first inductor is connected to the first input end of the filter circuit, and the second input end of the filter circuit is grounded; the output end of the filter circuit is the output end of the first buck circuit.
3. The synchronous rectification soft switching circuit according to claim 2, characterized in that: The filtering circuit includes: a first capacitor and a first resistor; The first end of the first capacitor is the first input end of the filter circuit, and the second end of the first capacitor is the second input end of the filter circuit; A first end of the first resistor is connected to a first end of the first capacitor, and a second end of the first resistor is connected to a second end of the first capacitor; The first end of the first resistor is the output end of the filter circuit.
4. The synchronous rectification soft switching circuit according to claim 1, characterized in that: The soft switching circuit includes: a third switching tube, a voltage transformation unit, a second inductor and a current cut-off unit; The drain of the third switching transistor is connected to the first interface of the soft switching circuit, the source of the third switching transistor is connected to the first input end of the voltage transformation unit, the second input end of the voltage transformation unit is connected to the first end of the second inductor, the second end of the second inductor is connected to the second interface of the soft switching circuit, the first end of the current cutoff unit is connected to the third interface of the soft switching circuit, the second end of the current cutoff unit is connected to the first output end of the voltage transformation unit, and the second output end of the voltage transformation unit is grounded; The current in the current cutoff unit flows from the first output end of the voltage transformation unit to the third interface of the soft switching circuit.
5. The synchronous rectification soft switching circuit according to claim 4, characterized in that: The transformer unit includes at least a first transformer; The secondary side like-named terminal of the first transformer is the first input terminal of the transformer unit, and the secondary side unlike-named terminal of the first transformer is the second input terminal of the transformer unit; The primary like-named end of the first transformer is the first output end of the transformation unit, and the primary unlike-named end of the first transformer is the second output end of the transformation unit.
6. The synchronous rectification soft switching circuit according to claim 4, characterized in that: The current cutoff unit includes at least a first diode; The cathode of the first diode is the first end of the current cutoff unit, and the anode of the first diode is the second end of the current cutoff unit.
7. The synchronous rectification soft switching circuit according to claim 4, characterized in that: The maximum operating current of the third switch tube is greater than 24A.
8. The synchronous rectification soft switching circuit according to claim 5, characterized in that: The primary-to-secondary winding ratio of the first transformer is greater than or equal to 0.
6.
9. A power conversion circuit, characterized in that: include: Any one of a DC-DC power conversion circuit, a DC-AC power conversion circuit, an AC-DC power conversion circuit, and an AC-AC power conversion circuit, and a synchronous rectification soft switching circuit as claimed in any one of claims 1 to 8.
10. A power supply circuit, characterized in that: include: A load and a synchronous rectification soft switching circuit according to any one of claims 1 to 8.