Synchronous rectification circuit and switching power supply

Abstract

The invention discloses a synchronous rectification circuit and a switching power supply, the switching power supply adopts a resonant converter topology and comprises first to Nth transformers, and the synchronous rectification circuit comprises first to Nth current transformers, first to Nth groups of switching devices, first to Nth groups of diodes, N resistors, first to Nth groups of comparison modules and a controller, each group of comparison modules comprises two comparison modules, each comparison module is used for sampling the voltage at the two ends of the connected diode, and the controller is used for processing the sampling result of each comparison module and the primary side control signal of the switching power supply and controlling the on and off of the corresponding switching device according to the processing result. According to the invention, accurate control of the synchronous rectifier tube can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply, and in particular to a synchronous rectification circuit and a switching power supply. Background Art

[0002] With the rapid development of power electronics technology, switching power supplies are moving towards high miniaturization and high power density. Multiphase resonant converter topology is widely used in high power supply applications due to its advantages of soft switching and low current ripple. Figure 1 The schematic diagram is a typical three-phase resonant topology circuit schematic. The primary inverter circuit includes a first bridge arm composed of a switch tube Q1a and a switch tube Q1b, a second bridge arm composed of a switch tube Q2a and a switch tube Q2b, and a third bridge arm composed of a switch tube Q3a and a switch tube Q3b. The resonant branch connected to the switch tube Q1a and the switch tube Q1b includes a resonant inductor L1 and a resonant capacitor C2, the resonant branch connected to the switch tube Q2a and the switch tube Q2b includes a resonant inductor L3 and a resonant capacitor C3, and the resonant branch connected to the switch tube Q3a and the switch tube Q3b includes a resonant inductor L5 and a resonant capacitor C4.

[0003] In the process of switching power supply pursuing high efficiency, synchronous rectification technology stands out in low voltage and high current situations, especially in resonant topology, where synchronous rectification technology can greatly improve the efficiency of the system. The existing synchronous rectification technologies are mainly as follows:

[0004] 1. Detect the voltage drop of the parasitic body diode of the rectifier. When the rectifier body diode is detected to be turned on, it means that there is current flowing through the rectifier. At this time, the rectifier can be turned on to realize synchronous rectification. When the current flowing through the rectifier decreases, the voltage drop of the rectifier also decreases. When it is less than a certain threshold, the rectifier is turned off to realize synchronous rectification. This method of detecting the opening of the body diode and the closing of the conduction voltage drop is relatively simple to implement, but in high current situations, the rectifier has lead inductance and PCB routing inductance, which will affect the precise opening and closing of the synchronous rectifier. Especially in high frequency, the influence of parasitic inductance is greater. At this time, it is difficult to achieve precise opening and closing of the synchronous rectifier. In addition, in the case of low voltage and high current, the conduction voltage drop of the rectifier itself is very small, so it is difficult to achieve accurate shutdown.

[0005] 2. Active synchronous rectification technology. In some specific topologies, the primary switch tube and the secondary rectifier tube have a specific switching sequence in CCM. At this time, the secondary rectifier tube is actively controlled according to the switching status of the primary side to achieve synchronous rectification. This synchronous rectification method is simple, but can only be used in specific topologies and specific working modes. In resonant topologies, when the system works in DCM mode, active synchronous rectification technology cannot work stably and reliably.

[0006] 3. Current detection type synchronous rectification technology. Directly detecting the current flowing through the rectifier tube can also realize the detection of synchronous rectification. The Chinese patent application with publication number CN105099230A uses a current transformer to detect the transformer winding current, and detects the conduction status of the corresponding diode after triangle connection rectification to realize synchronous rectification. This method can realize the synchronous rectification function more accurately, but this method is only suitable for triangle connection and resonant topology working in normal resonant mode, and cannot work in Y-type connection or phase shift state.

[0007] It should be noted that the above information disclosed in the background technology section is only intended to deepen the understanding of the overall background technology of this application, and should not be regarded as admitting or suggesting in any form that the information constitutes prior art already known to those skilled in the art. Summary of the invention

[0008] In view of this, the technical problem to be solved by the present invention is to provide a synchronous rectification circuit and a switching power supply, which can at least solve one of the technical problems existing in the prior art to a certain extent.

[0009] As a first aspect of the present invention, the embodiment and technical solution of the synchronous rectification circuit provided are as follows:

[0010] A synchronous rectification circuit is applied to a switching power supply, wherein the switching power supply adopts a resonant converter topology, the switching power supply comprises a first transformer to an Nth transformer, wherein N is greater than or equal to 3, and the secondary windings of each transformer adopt an N-delta connection or a star connection, wherein the synchronous rectification circuit comprises:

[0011] A first current transformer to an Nth current transformer;

[0012] The first group of switch devices to the Nth group of switch devices are connected in parallel, and each group of the first group of switch devices to the Nth group of switch devices includes two switch devices connected in series, which are connected in series to form a first midpoint to an Nth midpoint, each midpoint is connected to one end of the primary inductance of the corresponding current transformer, and the other end of the primary inductance of each current transformer is used to connect one end of the secondary inductance of the corresponding transformer;

[0013] The first group of diodes to the Nth group of diodes, and N resistors, each group of the first group of diodes to the Nth group of diodes includes four full-bridge connected diodes, the midpoint of one bridge arm in each group of diodes is connected to one end of the secondary inductor of the corresponding current transformer, and the midpoint of another bridge arm is connected to the other end of the secondary inductor of the corresponding current transformer, the positive output end of each group of diodes is connected to one end of the corresponding resistor, and the negative output end and the other end of the corresponding resistor are connected together to be connected to the secondary ground of the switching power supply;

[0014] The first group of comparison modules to the Nth group of comparison modules and the controller, each group of comparison modules includes two comparison modules, which are respectively connected between the anode and the cathode of a low-end diode in the corresponding group of diodes, and each comparison module in each group of comparison modules is used to sample the voltage across the connected diode. The controller is connected to each comparison module in each group of comparison modules, and is used to process the sampling results of each comparison module with the primary control signal of the switching power supply, and control the conduction and shutdown of the corresponding switching devices in each group of switching devices according to the processing results.

[0015] Furthermore, when the switching power supply operates in a normal resonant mode, the sampling results of each comparison module are logically processed with the primary side control signal; when the switching power supply operates in a secondary side phase shift state, the sampling results of each comparison module are logically processed with the primary side control signal after the phase shift.

[0016] Furthermore, the control logic for controlling the on and off of corresponding switch devices in each group of switch devices is:

[0017] When the switching power supply operates in the normal resonant mode, if the diode is turned on and the primary control signal is at a high level, the switch device corresponding to the turned-on diode is controlled to be turned on; if the diode is turned off or the primary control signal is at a low level, the switch device corresponding to the turned-off diode is controlled to be turned off;

[0018] When the switching power supply operates in the secondary side phase shift state, if the diode is turned on and the primary side control signal after the phase shift is at a high level, the switching device corresponding to the turned-on diode is controlled to be turned on; if the diode is turned off or the primary side control signal after the phase shift is at a low level, the switching device corresponding to the turned-off diode is controlled to be turned off.

[0019] Further, the other end of the primary inductance of each current transformer, one end of the corresponding secondary inductance of the current transformer and one end of the corresponding secondary inductance of the transformer are configured as the same-named ends.

[0020] Preferably, N is 3.

[0021] Preferably, each switch device in the first group of switch devices to the Nth group of switch devices is a MOS tube.

[0022] As a second aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0023] A switching power supply, the switching power supply adopts a resonant converter topology, the switching power supply includes a first transformer to an Nth transformer, N is greater than or equal to 3, and the secondary windings of each transformer adopt an N-delta connection or a star connection, wherein: the switching power supply includes the synchronous rectification circuit described in any one of the first aspects above.

[0024] Compared with the prior art, the embodiments of the present invention have at least the following beneficial effects:

[0025] 1. The synchronous rectification circuit includes the first current transformer to the Nth current transformer, the first group of diodes to the Nth group of diodes, N resistors and the first group of comparison modules to the Nth group of comparison modules. Each comparison module in each group of comparison modules is used to sample the voltage across the connected diode. The controller processes the sampling results of each comparison module and the primary control signal of the switching power supply, and controls the conduction and shutdown of the corresponding switching devices in each group of switching devices according to the processing results. Since the controller directly detects the rectifier current to turn on and off the rectifier tube, compared with the solution of detecting the voltage drop of the parasitic diode of the rectifier tube, it will not be affected by the lead inductance, PCB routing inductance and parasitic inductance, and the control is more accurate and reliable.

[0026] 2. Since the controller directly detects the rectifier current to turn on and off the rectifier tube, it is not affected by the connection, rectification and working mode of the resonant converter. Compared with the same type of current detection method, it can work in both delta connection and Y-shaped topology connection mode;

[0027] 3. Similarly, since the controller directly detects the current flowing through the rectifier tube, the resonant topology can also operate in resonant mode and phase-shift mode, broadening the application range of synchronous rectification. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a typical three-phase resonant topology circuit schematic diagram in the background technology;

[0029] Figure 2 A schematic diagram of a first synchronous rectification circuit according to a first embodiment of the present invention applied to a switching power supply;

[0030] Figure 3 A schematic diagram of a second synchronous rectification circuit according to the first embodiment of the present invention applied to a switching power supply;

[0031] Figure 4 This is a schematic diagram of a third synchronous rectification circuit according to the first embodiment of the present invention applied to a switching power supply. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0034] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0035] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0036] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0037] First embodiment

[0038] This embodiment provides a synchronous rectification circuit, which is applied to a switching power supply. Figure 2 This is a schematic diagram of the first synchronous rectification circuit of the first embodiment of the present invention applied to a switching power supply, see Figure 2 The switching power supply adopts a resonant converter topology, the switching power supply includes a first transformer TX1 to an Nth transformer TXn, N is greater than or equal to 3, and the secondary windings of each transformer are connected in an N-shaped manner, wherein the synchronous rectification circuit includes:

[0039] The first current transformer to the Nth current transformer; specifically, the first current transformer includes a primary inductor CT1P and a secondary inductor CT1S, the second current transformer includes a primary inductor CT2P and a secondary inductor CT2S, the third current transformer includes a primary inductor CT3P and a secondary inductor CT3S, and the Nth current transformer includes a primary inductor CTnP and a secondary inductor CTnS;

[0040] The first group of switch devices to the Nth group of switch devices are connected in parallel, each group of the first group of switch devices to the Nth group of switch devices includes two switch devices connected in series, which are connected in series to form a first midpoint to an Nth midpoint, each midpoint is connected to one end of the primary inductance of the corresponding current transformer, and the other end of the primary inductance of each current transformer is used to connect to one end of the secondary inductance of the corresponding transformer; specifically, the first group of switch devices includes switch devices Q1a and Q1b connected in series, the second group of switch devices includes switch devices Q2a and Q2b connected in series, the third group of switch devices includes switch devices Q3a and Q3b connected in series, and the Nth group of switch devices includes switch devices Qna and Qnb connected in series;

[0041] The first group of diodes to the Nth group of diodes, and N resistors R1 to Rn, each group of the first group of diodes to the Nth group of diodes includes four full-bridge connected diodes, the midpoint of one bridge arm in each group of diodes is connected to one end of the secondary inductor of the corresponding current transformer, and the midpoint of another bridge arm is connected to the other end of the secondary inductor of the corresponding current transformer, the positive output end of each group of diodes is connected to one end of the corresponding resistor, and the negative output end and the other end of the corresponding resistor are connected together to connect to the secondary ground GNDS of the switching power supply; specifically, the first group of diodes includes full-bridge connected diodes D1a1, D1a2, D1b1 and D1b2, the second group of diodes includes full-bridge connected diodes D2a1, D2a2, D2b1 and D2b2, the third group of diodes includes full-bridge connected diodes D3a1, D3a2, D3b1 and D3b2, the Nth group of diodes includes full-bridge connected diodes Dna1, Dna2, Dnb1 and Dnb2, wherein the function of each resistor R is to provide a current loop.

[0042] The first group of comparison modules to the Nth group of comparison modules and the controller, each group of comparison modules includes two comparison modules, which are respectively connected between the anode and the cathode of a low-end diode in the corresponding group of diodes, and each comparison module in each group of comparison modules is used to sample the voltage across the connected diode. The controller is connected to each comparison module in each group of comparison modules, and is used to process the sampling results of each comparison module with the primary side control signal of the switching power supply, and control the conduction and shutdown of the corresponding switching devices in each group of switching devices according to the processing results; specifically, the first group of comparison modules includes the B1a comparison module and the B1b comparison module, the second group of comparison modules includes the B2a comparison module and the B2b comparison module, and the third group of comparison modules includes the B3a comparison module and the B3b comparison module, the Nth group of comparison modules includes the Bna comparison module and the Bnb comparison module, the controller outputs the control signal GS1a to control the conduction and shutoff of the switching device Q1a, the output control signal GS1b to control the conduction and shutoff of the switching device Q1b, the output control signal GS2a to control the conduction and shutoff of the switching device Q2a, the output control signal GS2b to control the conduction and shutoff of the switching device Q2b, the output control signal GS3a to control the conduction and shutoff of the switching device Q3a, the output control signal GS3b to control the conduction and shutoff of the switching device Q3b, the output control signal GSna to control the conduction and shutoff of the switching device Qna, and the output control signal GSnb to control the conduction and shutoff of the switching device Qnb.

[0043] Transformers TX1 to TXn are connected in an N-shaped manner, that is, the other end of transformer TX1 is connected to one end of transformer TX2, the other end of transformer TX2 is connected to one end of transformer TX3, and so on. The other end of transformer TXn is connected to one end of transformer TX1. This n-phase connection method can broaden the power range of the switching power supply. The synchronous rectification circuit of this embodiment indirectly detects the current flowing through the rectifier tube through a current transformer. Since this detection method directly detects the current, it is not affected by the connection, rectification method and working method of the resonant converter, so it can work when the secondary windings of each transformer are connected in an N-shaped manner.

[0044] The synchronous rectification circuit of this embodiment can also work when the secondary windings of each transformer are connected in star shape. The secondary windings of each transformer are connected in star shape, which means that the other ends of the secondary windings of each transformer are connected together.

[0045] It can be understood that there is a corresponding relationship between each transformer, each current transformer, each group of switch devices and each switch device therein, each group of diodes and each diode therein, each resistor, each group of comparison modules and each comparison module therein in the present invention. Figure 2 , the corresponding relationship is as follows:

[0046] A first transformer TX1, a first inductor current transformer including a primary inductor CT1P and a secondary inductor CT1S, a first group of switch devices including switch devices Q1a and Q1b, a first group of diodes including diodes D1a1, D1a2, D1b1 and D1b2, a resistor R1, a first group of comparison modules including a B1a comparison module and a B1b comparison module, a low-end diode in the first group of diodes refers to diodes D1a2 and D1b2 whose anodes are connected to a secondary ground GNDS of the switching power supply, the diode D1a2 corresponds to the switch device Q1a, and the diode D1b2 corresponds to the switch device Q1b;

[0047] A second transformer TX2, including a second inductor current transformer having a primary inductor CT2P and a secondary inductor CT2S, a second group of switch devices including switch devices Q2a and Q2b, a second group of diodes including diodes D2a1, D2a2, D2b1 and D2b2, a resistor R2, a second group of comparison modules including a B2a comparison module and a B2b comparison module, the low-end diodes in the second group of diodes refer to diodes D2a2 and D2b2 whose anodes are connected to a secondary ground GNDS of the switching power supply, the diode D2a2 corresponds to the switch device Q2a, and the diode D2b2 corresponds to the switch device Q2b;

[0048] A third transformer TX3, including a third inductor current transformer including a primary inductor CT3P and a secondary inductor CT3S, a third group of switch devices including switch devices Q3a and Q3b, a third group of diodes including diodes D3a1, D3a2, D3b1 and D3b2, a resistor R3, a third group of comparison modules including a B3a comparison module and a B3b comparison module, the low-end diodes in the third group of diodes refer to diodes D3a2 and D3b2 whose anodes are connected to the secondary ground GNDS of the switching power supply, the diode D3a2 corresponds to the switch device Q3a, and the diode D3b2 corresponds to the switch device Q3b;

[0049] The Nth transformer TXn, the Nth inductor current transformer including the primary inductor CTnP and the secondary inductor CTnS, the Nth group of switching devices including the switching devices Qna and Qnb, the Nth group of diodes including diodes Dna1, Dna2, Dnb1 and Dnb2, the resistor Rn, the Nth group of comparison modules including the Bna comparison module and the Bnb comparison module, the low-end diodes in the Nth group of diodes refer to the diodes Dna2 and Dnb2 whose anodes are connected to the secondary ground GNDS of the switching power supply, the diode Dna2 corresponds to the switching device Qna, and the diode Dnb2 corresponds to the switching device Qnb.

[0050] The synchronous rectification circuit of this embodiment indirectly detects the current flowing through the rectifier tube through a current transformer, and the controller directly detects the rectification current to control the opening and closing of the rectifier tube (i.e., each switch tube in the first group of switch devices to the Nth group of switch devices). Compared with the scheme of detecting the voltage drop of the parasitic body diode of the rectifier tube, it will not be affected by the lead inductance, PCB wiring inductance and parasitic inductance, and the control is more accurate and reliable. At the same time, since the controller directly detects the rectification current to control the opening and closing of the rectifier tube, it is not affected by the connection, rectification mode and working mode of the resonant converter. Compared with the same type of current detection mode, it can work in both the triangle connection and the Y-shaped topology connection mode. In addition, since the current flowing through the rectifier tube is directly sampled, the resonant topology can also work in the resonant mode and the phase shift mode, which broadens the application range of the synchronous rectification.

[0051] Furthermore, when the switching power supply operates in the normal resonant mode, the sampling results of each comparison module are logically processed with the primary control signal, and this processing is to avoid the erroneous opening of the secondary synchronous rectifier tube caused by false detection; when the switching power supply operates in the secondary phase shift state, the sampling results of each comparison module are logically processed with the primary control signal after the phase shift, and this processing is also to avoid the erroneous opening of the secondary synchronous rectifier tube caused by false detection.

[0052] Furthermore, the control logic for controlling the on and off of the corresponding switch devices in each group of switch devices is:

[0053] When the switching power supply operates in the normal resonant mode, if the diode is turned on and the primary control signal is at a high level, the switch device corresponding to the turned-on diode is controlled to be turned on; if the diode is turned off or the primary control signal is at a low level, the switch device corresponding to the turned-off diode is controlled to be turned off;

[0054] When the switching power supply operates in the secondary side phase shift state, if the diode is turned on and the primary side control signal after the phase shift is at a high level, the switching device corresponding to the turned-on diode is controlled to be turned on; if the diode is turned off or the primary side control signal after the phase shift is at a low level, the switching device corresponding to the turned-off diode is controlled to be turned off.

[0055] Furthermore, the other end of the primary inductance of each current transformer, one end of the secondary inductance of the corresponding current transformer and one end of the secondary inductance of the corresponding transformer are configured as the same-named ends, ensuring that the current flow direction of the detection circuit is consistent with the current flow direction of the rectifier tube.

[0056] Preferably, N is 3, which is beneficial to reduce the current ripple of the switching power supply and save the cost of the switching power supply, and reduce the volume of the system. Figure 3 and Figure 4 The clock N is 3, among which Figure 3The secondary windings of each transformer are connected in a triangle. Figure 4 The secondary windings of each transformer are connected in star shape.

[0057] Preferably, each switch device in the first group of switch devices to the Nth group of switch devices is a MOS tube.

[0058] Second embodiment

[0059] The present embodiment provides a switching power supply, which adopts a resonant converter topology. The switching power supply includes a first transformer to an Nth transformer, N is greater than or equal to 3, and the secondary windings of each transformer are connected in an N-delta connection or a star connection, wherein: the switching power supply includes any one of the synchronous rectification circuits in the first embodiment.

[0060] The above embodiments of the present invention are not intended to limit the protection scope of the present invention, and the implementation modes of the present invention are not limited thereto. All other modifications, replacements or changes made to the above structures of the present invention based on the above contents of the present invention, in accordance with common technical knowledge and customary means in the art, without departing from the above basic technical ideas of the present invention, should fall within the protection scope of the present invention.

Claims

1. A synchronous rectification circuit, applied to a switching power supply, wherein the switching power supply adopts a resonant converter topology, the switching power supply comprises a first transformer to an Nth transformer, wherein N is greater than or equal to 3, and the secondary windings of each transformer adopt an N-delta connection or a star connection, wherein: The synchronous rectification circuit comprises: A first current transformer to an Nth current transformer; The first group of switch devices to the Nth group of switch devices are connected in parallel, and each group of the first group of switch devices to the Nth group of switch devices includes two switch devices connected in series, which are connected in series to form a first midpoint to an Nth midpoint, each midpoint is connected to one end of the primary inductance of the corresponding current transformer, and the other end of the primary inductance of each current transformer is used to connect one end of the secondary inductance of the corresponding transformer; The first group of diodes to the Nth group of diodes, and N resistors, each group of the first group of diodes to the Nth group of diodes includes four full-bridge connected diodes, the midpoint of one bridge arm in each group of diodes is connected to one end of the secondary inductor of the corresponding current transformer, and the midpoint of another bridge arm is connected to the other end of the secondary inductor of the corresponding current transformer, the positive output end of each group of diodes is connected to one end of the corresponding resistor, and the negative output end and the other end of the corresponding resistor are connected together to be connected to the secondary ground of the switching power supply; The first group of comparison modules to the Nth group of comparison modules and the controller, each group of comparison modules includes two comparison modules, which are respectively connected between the anode and the cathode of a low-end diode in the corresponding group of diodes, and each comparison module in each group of comparison modules is used to sample the voltage across the connected diode. The controller is connected to each comparison module in each group of comparison modules, and is used to process the sampling results of each comparison module with the primary control signal of the switching power supply, and control the conduction and shutdown of the corresponding switching devices in each group of switching devices according to the processing results.

2. The synchronous rectification circuit according to claim 1, characterized in that: When the switching power supply operates in the normal resonant mode, the sampling results of each comparison module are logically processed with the primary side control signal; when the switching power supply operates in the secondary side phase shift state, the sampling results of each comparison module are logically processed with the primary side control signal after the phase shift.

3. The synchronous rectification circuit according to claim 2, characterized in that: The control logic for controlling the on and off of the corresponding switch devices in each group of switch devices is: When the switching power supply operates in the normal resonant mode, if the diode is turned on and the primary control signal is at a high level, the switch device corresponding to the turned-on diode is controlled to be turned on; if the diode is turned off or the primary control signal is at a low level, the switch device corresponding to the turned-off diode is controlled to be turned off; When the switching power supply operates in the secondary side phase shift state, if the diode is turned on and the primary side control signal after the phase shift is at a high level, the switching device corresponding to the turned-on diode is controlled to be turned on; if the diode is turned off or the primary side control signal after the phase shift is at a low level, the switching device corresponding to the turned-off diode is controlled to be turned off.

4. The synchronous rectification circuit according to any one of claims 1 to 3, characterized in that: The other end of the primary inductance of each current transformer, one end of the secondary inductance of the corresponding current transformer and one end of the secondary inductance of the corresponding transformer are configured as the same-named ends.

5. The synchronous rectification circuit according to any one of claims 1 to 3, characterized in that: The N is 3.

6. The synchronous rectification circuit according to any one of claims 1 to 3, characterized in that: Each of the switch devices in the first group of switch devices to the Nth group of switch devices is a MOS tube.

7. A switching power supply, the switching power supply adopting a resonant converter topology, the switching power supply comprising a first transformer to an Nth transformer, wherein N is greater than or equal to 3, and the secondary windings of each transformer adopt an N-delta connection or a star connection, characterized in that: The switching power supply comprises the synchronous rectification circuit according to any one of claims 1 to 6.

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