Resonant converter and control method thereof

Abstract

A resonant converter and control method thereof. The resonant converter includes a transformer, a resonant network, a control circuit, and primary and secondary circuits. At least one of the primary switches is turned on during a period from a first switching moment to a second switching moment. The resonant network is coupled between the primary circuit and a primary winding. Current in the resonant network changes direction at a first moment, the first moment being between the first switching moment and the second switching moment. The secondary circuit is coupled to the secondary winding. At least one of the secondary switches is turned on during first and second preset time periods to clamp the secondary winding with a preset voltage, causing the current in the resonant network to increase in a first direction and the output current of the resonant converter to increase in a second direction or to be equal to zero. In this way, the gain of the resonant converter is increased.

Description

Technical Field

[0001] The present disclosure relates to a converter, and more particularly to a resonant converter and a control method thereof. Background Art

[0002] Traditional resonant converters use variable frequency control. When the operating frequency of the resonant converter is lower than the resonant frequency, the primary switches can achieve zero voltage switching (ZVS), and the secondary switches can achieve zero current switching (ZCS). Resonant converters are widely used in high-efficiency, high-frequency, and high-power systems, such as high-end servers, network switches, storage devices, telecommunications base stations, data centers, and more. Among them, inductor-inductor-capacitor (LLC) resonant converters are widely used in power conversion systems.

[0003] Network power supplies generally need to meet holdup time and power line disturbance (PLD) requirements. Holdup time refers to the time, for example, 10 to 20 milliseconds, that the LLC resonant converter's input voltage must be maintained after a power failure, to provide system backup. PLD represents the period, for example, 10 milliseconds, after input power is lost and restored. During this time, the LLC resonant converter's output voltage must remain within a specific voltage range without interrupting system operation.

[0004] A network power supply includes a power factor correction (PFC) circuit and an LLC resonant converter. The LLC resonant converter's input is connected to the PFC's output. When the input power fails, the PFC's bulk voltage decreases, and the LLC resonant converter's output voltage cannot remain within a specified voltage range when the PFC's bulk voltage drops below a certain threshold.

[0005] There is a growing body of research focused on increasing the hold-up time of power supplies. One approach is to increase the capacitance of the capacitor at the PFC output. This approach can extend the hold-up time, but also increases cost and space within the power supply. Another technical solution is to add a boost circuit between the PFC and LLC resonant converters. This approach can also increase the hold-up time, but also increases cost and the design complexity of the power supply.

[0006] The above-mentioned technical solutions have disadvantages such as high cost and low power density. Summary of the Invention

[0007] An embodiment of the present invention includes a resonant converter. The resonant converter includes a primary circuit, a transformer, a resonant network, a secondary circuit, and a control circuit. The primary circuit is configured to receive an input voltage and includes a plurality of primary switches. The primary switches are configured to operate at a switching frequency, wherein at least one of the primary switches is configured to be turned on during a period from a first switching moment to a second switching moment. The transformer has a primary winding and a secondary winding. The resonant network is coupled between the primary circuit and the primary winding, wherein a current in the resonant network changes direction at a first moment, the first moment being between the first switching moment and the second switching moment. The secondary circuit is coupled to the secondary winding and is configured to provide an output voltage to a load, and includes a plurality of secondary switches. At least one first of the secondary switches is configured to be turned on during a first predetermined period from the first moment to the second moment to clamp the secondary winding with a predetermined voltage, such that the current in the resonant network increases in a first direction and the output current of the resonant converter increases in a second direction or is equal to zero. At least one second of the secondary switches is configured to conduct during a second predetermined time period from a third moment to a second switching moment to clamp the secondary winding via a predetermined voltage, causing the current in the resonant network to increase in a first direction and the output current of the resonant converter to increase in a second direction or to be equal to zero, wherein the third moment is between the second moment and the second switching moment. A control circuit is coupled to the primary switch and the secondary switch. The control circuit is configured to control at least one of the primary switches to conduct during a period from the first switching moment to the second switching moment, and to control at least one of the first secondary switches to conduct during the first predetermined time period and at least one of the second secondary switches to conduct during the second predetermined time period.

[0008] In some embodiments, the control circuit is further configured to adjust the first preset time period and / or the second preset time period according to the output voltage, or to adjust the first preset time period and / or the second preset time period according to the output voltage and the input voltage.

[0009] In some embodiments, the control circuit is further configured to control the secondary switch to be disconnected during a third predetermined time period from a fourth moment to the third moment, so that the output current of the resonant converter is equal to zero, wherein the fourth moment is between the second moment and the third moment.

[0010] In some embodiments, the control circuit is further configured to adjust the third preset time period according to the output voltage, or to adjust the third preset time period according to the output voltage and the input voltage.

[0011] In some embodiments, the secondary winding further includes: a first end, a second end, and a center tap end. The secondary switch includes a first switch and a second switch. The first end of the first switch is coupled to the first end of the secondary winding. The first end of the second switch is coupled to the second end of the secondary winding, and the second end of the second switch is coupled to the second end of the first switch. In some embodiments, the second end of the first switch is coupled to the first output end of the resonant converter and the center tap end is coupled to the second output end of the resonant converter, and the control circuit is further configured to control the second switch to conduct during a first preset time period to clamp the secondary winding through a preset voltage, so that the current of the resonant network increases in a direction and the output current of the resonant converter increases in a second direction, and to control the second switch to conduct during a second preset time interval to clamp the secondary winding through a preset voltage in a direction, so that the current of the resonant network increases in the first direction and the output current of the resonant converter increases in the second direction. In some embodiments, the second end of the first switch is coupled to the second output end of the resonant converter and the center tap end is coupled to the first output end of the resonant converter, and the control circuit is also used to control the first switch to be turned on within a first preset time period to clamp the secondary winding through a preset voltage, so that the current of the resonant network increases in a first direction and the output current of the resonant converter increases in a second direction, and to control the first switch to be turned on within a second preset time period to clamp the secondary winding through a preset voltage, so that the current of the resonant network increases in a first direction and the output current of the resonant converter increases in a second direction.

[0012] In some embodiments, the control circuit is further configured to control the first switch and the second switch to be disconnected during a third preset time period from a fourth moment to a third moment, so that the output current of the resonant converter is equal to zero, wherein the fourth moment is between the second moment and the third moment.

[0013] In some embodiments, the secondary switch includes a first switch, a second switch, a third switch, and a fourth switch. A first end of the first switch is coupled to a first end of the secondary winding, and a second end of the first switch is coupled to a first output end of the resonant converter. A first end of the second switch is coupled to a first end of the secondary winding, and a second end of the second switch is coupled to a second output end of the resonant converter. A first end of the third switch is coupled to a second end of the first switch, and a second end of the third switch is coupled to a second end of the secondary winding. A first end of the fourth switch is coupled to a second end of the secondary winding, and a second end of the fourth switch is coupled to a second end of the second switch.

[0014] In some embodiments, the first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. The control circuit is further configured to control the second switch group to be conductive within a first preset time period or a second preset time period, thereby clamping the secondary winding via a preset voltage, thereby increasing the current in the resonant network in a first direction and the output current of the resonant converter in a second direction.

[0015] In some embodiments, the first switch and the third switch form a third switch group, and the second switch and the fourth switch form a fourth switch group. The control circuit is further configured to control one of the third switch group and the fourth switch group to be conductive within a first predetermined time period or a second predetermined time period, thereby clamping the secondary winding via a predetermined voltage, causing the current in the resonant network to increase in a first direction, and for the predetermined voltage to be zero and the output current of the resonant converter to be zero.

[0016] In some embodiments, the control circuit is further configured to control at least three of the first switch, the second switch, the third switch, and the fourth switch to be disconnected during a third preset time period from a fourth moment to a third moment so that the output current of the resonant converter is equal to zero, wherein the fourth moment is between the second moment and the third moment.

[0017] In some embodiments, the control circuit further includes: a voltage-controlled oscillator, a primary-side driver, an output sampling processor, a comparator, a control loop, an advance time control circuit, a lag time control circuit, and a secondary-side driver. The voltage-controlled oscillator is configured to provide a switching frequency. The primary-side driver is configured to drive the primary-side switch according to the switching frequency. The output sampling processor is configured to receive an output voltage and provide a proportional output voltage. The comparator is configured to compare the proportional output voltage with a reference voltage and generate an error signal corresponding to the difference between the proportional output voltage and the reference voltage. The control loop is configured to receive the error signal and provide a control signal. The advance time control circuit is configured to receive the control signal and provide a first phase-shifted signal. The lag time control circuit is configured to receive the control signal and provide a second phase-shifted signal. The secondary-side driver is configured to drive at least a first of the secondary-side switches to conduct during a first predetermined time interval and to drive at least a second of the secondary-side switches to conduct during a second predetermined time interval according to the switching frequency, the first phase shift signal, and the second phase shift signal.

[0018] In some embodiments, the switching frequency is substantially equal to the predetermined frequency.

[0019] In some embodiments, the control circuit is further configured to adjust the first preset time period and / or the second preset time period according to the output voltage and the switching frequency.

[0020] In some embodiments, the control circuit further includes an output sampling processor, a comparator, a control loop, a voltage-controlled oscillator, a primary driver, a first phase shift angle generator, a second phase shift angle generator, an advance time control circuit, a lag time control circuit, and a secondary driver. The output sampling processor receives an output voltage and provides a proportional output voltage. The comparator receives the proportional output voltage and a reference voltage and provides an error signal. The control loop receives the error signal and provides a control signal. The voltage-controlled oscillator receives the control signal and provides a switching frequency. The primary driver drives the primary switch according to the switching frequency. The first phase shift angle generator provides a first phase shift angle. The second phase shift angle generator provides a second phase shift angle. The advance time control circuit receives the first phase shift angle and provides a first phase shift signal. The lag time control circuit receives the second phase shift angle and provides a second phase shift signal. The secondary driver is configured to drive at least a first secondary switch to conduct during a first preset period of time according to the switching frequency, the first phase-shifted signal, and the second phase-shifted signal, and to drive at least a second secondary switch to conduct during a second preset period of time.

[0021] In some embodiments, the first phase shift angle is a first fixed value, and the second phase shift angle is a second fixed value.

[0022] In some embodiments, the control circuit is further configured to adjust the first preset time period and / or the second preset time period according to the output voltage, the first phase shift angle, and the second phase shift angle.

[0023] In some embodiments, the control circuit further includes an input sampling processor, an output sampling processor, a comparator, a control loop, a voltage-controlled oscillator, a primary driver, a first phase-shift angle generator, a second phase-shift angle generator, an advance time control circuit, a lag time control circuit, and a secondary driver. The input sampling processor receives an input voltage and provides a proportional input voltage. The output sampling processor receives an output voltage and provides a proportional output voltage. The comparator receives the proportional output voltage and a reference voltage and provides an error signal. The control loop receives the error signal and provides a control signal. The voltage-controlled oscillator receives the control signal and provides a switching frequency. The primary driver drives the primary switch according to the switching frequency. The first phase-shift angle generator receives the proportional input voltage, the proportional output voltage, and the switching frequency to provide a first phase-shift angle. The second phase-shift angle generator receives the proportional input voltage, the proportional output voltage, and the switching frequency to provide a second phase-shift angle. The advance time control circuit receives the first phase-shift angle and provides a first phase-shift signal. The hysteresis time control circuit is configured to receive a second phase shift angle and provide a second phase shift signal. The secondary driver is configured to drive at least a first of the secondary switches to conduct during a first predetermined time period, and to drive at least a second of the secondary switches to conduct during a second predetermined time period, based on a switching frequency, the first phase shift signal, and the second phase shift signal.

[0024] In some embodiments, the control circuit is further configured to adjust the first preset time period and / or the second preset time period according to the output voltage and the input voltage.

[0025] An embodiment of the present invention includes a method for controlling a resonant converter, wherein the resonant converter includes a primary circuit, a resonant network coupled to the primary circuit, a transformer having a primary winding and a secondary winding coupled to the resonant network, a secondary circuit coupled to the secondary winding, and a control circuit coupled to the primary circuit and the secondary circuit, wherein the primary circuit includes a plurality of primary switches, and the secondary circuit includes a plurality of secondary switches, the method comprising: controlling the primary switches of the primary circuit according to a switching frequency, the primary circuit being used to receive an input voltage; wherein controlling the primary switches comprises: turning on at least one of the primary switches in a time period from a first switching moment to a second switching moment; converting the input voltage through the transformer and the resonant network; and controlling the secondary switches of the secondary circuit to provide an output voltage to a load, wherein controlling the secondary switches The present invention comprises: turning on at least one first of the secondary switches in a first preset time period from a first moment to a second moment to clamp the secondary winding through a preset voltage, so that the current of the resonant network increases in a first direction, and the output current of the resonant converter increases in a second direction or is equal to zero, wherein the first moment and the second moment are between the first switching moment and the second switching moment, and the current of the resonant network changes a flow direction at the first moment; turning on at least one second of the secondary switches in a second preset time period from a third moment to the second switching moment to clamp the secondary winding through a preset voltage, so that the current of the resonant network increases in the first direction, and the output current of the resonant converter increases in the second direction or is equal to zero, wherein the third moment is between the second moment and the second switching moment.

[0026] In some embodiments, the method further includes: adjusting the first preset time period and / or the second preset time period according to the output voltage; or adjusting the first preset time period and / or the second preset time period according to the output voltage and the input voltage.

[0027] In some embodiments, the method further includes: controlling the secondary switch to be disconnected during a third preset time period from a fourth moment to a third moment, so that the output current of the resonant converter is equal to zero, wherein the fourth moment is between the second moment and the third moment.

[0028] In some embodiments, the method further includes: adjusting the third preset time period according to the output voltage; or adjusting the third preset time period according to the output voltage and the input voltage.

[0029] In some embodiments, controlling the secondary switch further includes: turning on the second switch within a first preset time period; turning off the first switch and the second switch within a third preset time period from the fourth moment to the third moment; and turning on the second switch within a second preset time period; wherein the first end of the first switch is coupled to the first end of the secondary winding, and the second end of the first switch is coupled to a second end of the second switch, the second end of the second switch is coupled to the first output end of the resonant converter, and the first end of the second switch is coupled to the second end of the secondary winding, and the second output end of the resonant converter is coupled to the center tap end, wherein the two coils of the secondary winding are coupled in series with each other at the center tap end.

[0030] In some embodiments, controlling the secondary switch further includes: turning on a second switch group within a first preset time period or a second preset time period, the second switch group being formed by a second switch and a third switch; and turning off at least three of the first switch, the second switch, the third switch, and the fourth switch within a third preset time period from a fourth moment to a third moment, wherein the fourth moment is between the second moment and the third moment, wherein the first end of the first switch is coupled to the first end of the second switch, and the second end of the first switch is coupled to the first end of the third switch, the first end of the second switch is coupled to the first end of the secondary winding, and the second end of the second switch is coupled to the second output end of the resonant converter, the first end of the third switch is coupled to the first output end of the resonant converter, and the second end of the third switch is coupled to the second end of the secondary winding, and the first end of the fourth switch is coupled to the second end of the secondary winding, and the second end of the fourth switch is coupled to the second end of the second switch.

[0031] In some embodiments, controlling the secondary switch further includes: turning on one of the third switch group and the fourth switch group within a first preset time period or a second preset time period, the third switch group being formed by the second switch and the fourth switch, and the fourth switch group being formed by the first switch and the third switch; and turning off at least three of the first switch, the second switch, the third switch, and the fourth switch within a third preset time period from a fourth moment to a third moment, wherein the fourth moment is between the second moment and the third moment, wherein the first end of the first switch is coupled to the first end of the second switch, and the second end of the first switch is coupled to the first end of the third switch, the first end of the second switch is coupled to the first end of the secondary winding, and the second end of the second switch is coupled to the second output end of the resonant converter, the first end of the third switch is coupled to the first output end of the resonant converter, and the second end of the third switch is coupled to the second end of the secondary winding, and the first end of the fourth switch is coupled to the second end of the secondary winding, and the second end of the fourth switch is coupled to the second end of the second switch.

[0032] In some embodiments, controlling the primary switch further comprises: providing a switching frequency; and driving the primary switch according to the switching frequency. Controlling the secondary switch further comprises: receiving an output voltage and providing a proportional output voltage; comparing the proportional output voltage with a reference voltage; generating an error signal based on a difference between the proportional output voltage and the reference voltage; receiving the error signal and providing a control signal; providing a first phase-shifted signal according to the control signal; providing a second phase-shifted signal according to the control signal; and driving at least a first of the secondary switches to conduct during a first predetermined time period, and driving at least a second of the secondary switches to conduct during a second predetermined time period, according to the switching frequency, the first phase-shifted signal, and the second phase-shifted signal.

[0033] In some embodiments, controlling the primary switch further comprises: receiving an output voltage and providing a proportional output voltage; comparing the proportional output voltage with a reference voltage; generating an error signal based on a difference between the proportional output voltage and the reference voltage; providing a control signal based on the error signal; generating a switching frequency based on the control signal; and driving the primary switch based on the switching frequency. Controlling the secondary switch further comprises: providing a first phase-shifted signal based on a first phase-shifted angle; providing a second phase-shifted signal based on a second phase-shifted angle; and driving at least a first of the secondary switches to conduct during a first predetermined time period, and driving at least a second of the secondary switches to conduct during a second predetermined time period, based on the switching frequency, the first phase-shifted signal, and the second phase-shifted signal.

[0034] In some embodiments, controlling the primary switch further comprises: receiving an output voltage and providing a proportional output voltage; comparing the proportional output voltage with a reference voltage; generating an error signal based on a difference between the proportional output voltage and the reference voltage; providing a control signal based on the error signal; generating a switching frequency based on the control signal; and driving the primary switch based on the switching frequency. Controlling the secondary switch further comprises: providing a proportional input voltage based on the input voltage; providing a first phase shift angle based on the switching frequency, the proportional input voltage, and the proportional output voltage; providing a first phase shift signal based on the first phase shift angle; providing a second phase shift angle based on the switching frequency, the proportional input voltage, and the proportional output voltage; providing a second phase shift signal based on the second phase shift angle; and driving at least a first of the secondary switches to conduct during a first preset time period, and driving at least a second of the secondary switches to conduct during a second preset time period, based on the switching frequency, the first phase shift signal, and the second phase shift signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present disclosure can be fully understood by reading the following detailed description of the embodiments and referring to the accompanying drawings.

[0036] Figure 1 is a circuit diagram of a resonant converter according to some embodiments of the present invention;

[0037] Figure 2 is a control timing diagram of a resonant converter according to some embodiments of the present invention;

[0038] Figure 3 is a circuit diagram of a resonant converter according to some embodiments of the present invention;

[0039] Figure 4 is a control timing diagram of a resonant converter according to some embodiments of the present invention;

[0040] Figure 5A is a circuit diagram of a resonant converter with a control circuit according to some embodiments of the present invention;

[0041] Figure 5B is a circuit diagram of a resonant converter with a control circuit according to some embodiments of the present invention;

[0042] Figure 5C FIG. 4 is a circuit diagram of a resonant converter with a control circuit according to some embodiments of the present invention. DETAILED DESCRIPTION

[0043] As used herein, when an element is referred to as being "connected" or "coupled," it may refer to being "electrically connected" or "electrically coupled." "Connected" or "coupled" may also refer to the coordinated operation or interaction between two or more elements. Furthermore, while terms such as "first," "second," and so on are used herein to describe different elements, these terms are intended solely to distinguish between elements or operations described using the same technical terms. Unless the context clearly indicates otherwise, these terms are not intended to specify or imply an order or sequence, nor are they intended to limit the present invention.

[0044] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the present invention, and will not be interpreted as idealized or overly formal unless explicitly defined as such herein.

[0045] The terms used herein are for the purpose of describing specific embodiments only and are not restrictive. As used herein, unless the content clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms, including "at least one". "Or" means "and / or". As used herein, the term "and / or" includes any and all combinations of one or more of the relevant listed items. It should also be understood that when used in this specification, the terms "include" and / or "comprising" specify the presence and / or parts of the features, regions, entireties, steps, operations, elements, components and / or parts, but do not exclude the presence or addition of one or more other features, regions, entireties, steps, operations, elements, components and / or their combinations.

[0046] The following drawings illustrate various embodiments of the present invention. For clarity, many practical details are included in the following description. However, it should be understood that these practical details are not intended to limit the present invention. In other words, these practical details are not essential to some embodiments of the present disclosure. Furthermore, to simplify the drawings, some commonly used structures and components are depicted in simplified schematic form.

[0047] Figure 1 FIG. 1 is a circuit diagram of a resonant converter 100 according to some embodiments of the present invention. Figure 1 As shown, resonant converter 100 is configured to receive an input voltage VI1 from an input power source 101 and provide an output voltage VO1 to a load 109. Input voltage VI1 can be replaced by input current or input power, and output voltage VO1 can be replaced by output current or output power. Resonant converter 100 includes a primary circuit 110, a resonant network 120, a transformer 130, a secondary circuit 140, and a control circuit 150.

[0048] In some embodiments, the primary circuit 110 is coupled to the input power source 101 to receive an input voltage VI1. The transformer 130 has a primary winding and a secondary winding. A resonant network 120 is coupled between the primary circuit 110 and the primary winding. The resonant network 120 can be implemented as an inductor-inductor-capacitor (LLC) resonant network, an LC resonant network, or an LCC resonant network. The secondary circuit 140 is coupled between the secondary winding and the load 109. In some embodiments, the primary circuit 110 is configured to receive electrical energy from the input power source 101 and transfer the electrical energy to the resonant network. In some embodiments, the input power source 101 is the output capacitor of a previous circuit, or the DC output of an independent DC power supply or other circuit. The resonant network 120 is configured to store electrical energy and transfer it to the transformer 130. The transformer 130 is configured to transfer electrical energy to the secondary circuit 140, and the secondary circuit 140 is configured to receive electrical energy and provide it to the load 109. The transformer 130 can be used to transfer power from the secondary circuit 140 to the resonant network 120 and / or the input power source 101 . The control circuit 150 is used to control the primary circuit 110 and the secondary circuit 140 .

[0049] like Figure 1 As shown, the primary circuit 110 is implemented as a half-bridge circuit including switches SP11 and SP12. Switches SP11 and SP12 are coupled in series. Switch SP11 is coupled to the input power source 101 at a node N10. Switch SP12 is coupled to the input power source 101 at a node N12. In some embodiments, switches SP11 and SP12 are configured to operate according to a switching frequency determined by the control circuit 150. In some other embodiments, the primary circuit 110 is implemented as a full-bridge circuit, such as Figure 3 The primary circuit 310 is shown.

[0050] like Figure 1As shown, resonant network 120 is implemented as an LLC resonant network including inductor LR1, magnetizing inductor LM1, and capacitor CR1. Magnetizing inductor LM1 is coupled in parallel to primary winding LP1. Magnetizing inductor LM1 is an inductance independent of primary winding LP1, or it is a stray inductance of primary winding LP1. During operation of resonant converter 100, magnetizing current ILM1 flows through magnetizing inductor LM1. A first end of inductor LR1 is coupled to switches SP11 and SP12 at node N11, while a second end of inductor LR1 is coupled to primary winding LP1 at node N13. A first end of capacitor CR1 is coupled to primary winding LP1 at node N14, while a second end of capacitor CR1 is coupled to switch SP12 at node N12. During operation of resonant converter 100, current ILR1 flows through inductor LR1. In some embodiments, resonant network 120 is implemented as an LLC resonant network comprising an inductor, a magnetizing inductor, and two capacitors connected in series. A first end of the inductor is coupled to nodes SP11 and SP12 at a node N11, and a second end of the inductor is coupled to primary winding LP1 at a node N13. The series connection point of the two capacitors is coupled to primary winding LP1 at a node N14, and the two series capacitors are connected to nodes N10 and N12, respectively.

[0051] like Figure 1 As shown, transformer 130 is a center-tapped transformer comprising a primary winding LP1 and a secondary winding. The secondary winding comprises two coils LN11 and LN12. The secondary winding of the center-tapped transformer includes a first terminal N17, a center-tap terminal N16, and a second terminal N18. Coils LN11 and LN12 are connected in series at the center-tap terminal N16 and coupled to the secondary circuit 140. The output voltage is the input voltage multiplied by the turns ratio of the secondary winding to the primary winding.

[0052] like Figure 1 As shown, the secondary circuit 140 is implemented as a half-bridge circuit including switches SS11 and SS12. The first end of the switch SS11 is coupled to the first end N17 of the secondary winding, and the second end of the switch SS11 is coupled to the first output end N15 of the resonant converter 100. The first end of the switch SS12 is coupled to the second end N18 of the secondary winding, and the second end of the switch SS12 is coupled to the second end of the switch SS11. The center tap end N16 is coupled to the second output end of the resonant converter 100. The load 109 is coupled to the first output end and the second output end of the resonant converter 100. In some other embodiments, the secondary circuit 140 is implemented as a full-bridge circuit, such as Figure 3 The secondary circuit 340 is shown.

[0053] In some embodiments, the control circuit 150 is coupled to the primary circuit 110 and the secondary circuit 140, and is used to control the switches SP11 and SP12 of the primary circuit 110 to operate at a switching frequency (eg, as described below and Figures 5A to 5C The switching frequency FS) shown in the figure operates.

[0054] In some embodiments, at least one of the switches SP11 and SP12 is used to switch from a first switching moment (eg Figure 2 and Figure 4 The time T20 and T40 shown) until the second switching time (eg Figure 2 and Figure 4 It is turned on at the times T25 and T45 shown.

[0055] In some embodiments, the control circuit 150 is used to control the switches SS11 and SS12 of the secondary circuit 140 so that at least one of the secondary switches SS11 and SS12 is switched on during a time period (eg Figure 2 and Figure 4 The circuit is turned on in the time periods [T21-T22], [T24-T25], [T41-T42] and [T44-T45]) to clamp the secondary winding (e.g. Figure 1 and Figure 3 (as shown), increasing the resonant network current ILR1 and the resonant converter's output current. The clamping voltage is a preset voltage, which can be a reverse voltage or zero. This allows energy from the input power source 101 and the secondary circuit 140 to be stored in the resonant network 120, increasing the current ILR1 and extending the hold-up time of the resonant converter 100. When the preset voltage is a reverse voltage, the polarity of the reverse voltage is opposite to the polarity of the induced voltage in the secondary winding. When the secondary winding is short-circuited, the preset voltage is zero. During the hold-up time, the output voltage of the resonant converter 100 is maintained within a specified voltage range.

[0056] In some embodiments, the control circuit 150 is used to adjust the first preset time period (e.g., time periods [T21-T22] and [T41-T42]) and / or adjust the second preset time period (e.g., time periods [T24-T25] and [T44-T45]) according to the output voltage VO1, or to adjust the first preset time period and / or adjust the second preset time period according to the output voltage VO1 and the input voltage VI1.

[0057] In some embodiments, when either the first preset time period or the second preset time period increases, the gain of the resonant converter 100 increases, such that the output voltage of the resonant converter 100 is maintained within a specific voltage range.

[0058] In some embodiments, the control circuit 150 is used to control the secondary side switches SS11 and SS12 to be disconnected in a third time period (e.g., time periods [T23-T24] and [T43-T44]), where the third preset time period is after the first preset time period and before the second preset time period, to adjust the gain of the resonant converter 100 and achieve zero current switching (ZCS) of the switches SS11 and SS12.

[0059] In some embodiments, the control circuit 150 is configured to adjust the third time period according to the output voltage VO1 , or to adjust the third time period according to the output voltage VO1 and the input voltage VI1 .

[0060] In some embodiments, switches SS11 and SS12 operate at a switching frequency determined by the control circuit 150. Therefore, switches SS11 and SS12 of the secondary circuit 140 and switches SP11 and SP12 of the primary circuit 110 operate at the same switching frequency. In other embodiments, switches SS11 and SS12 operate at a different switching frequency than switches SP11 and SP12. For example, the switching frequency of switches SS11 and SS12 is a positive integer multiple of the switching frequency of switches SP11 and SP12.

[0061] In some embodiments, coils LN11 and LN12 are secondary windings of transformer 130. Node N16 is referred to as the center tap of the secondary winding of transformer 130. Nodes N17 and N18 are referred to as the two ends of the secondary winding of transformer 130.

[0062] like Figure 1 As shown, the control circuit 150 is used to control the switches SP11 and SP12 of the primary circuit 110 and the switches SS11 and SS12 of the secondary circuit 140. In some embodiments, the control circuit 150 is used to determine the switching frequency, on-time, and off-time of the switches SP11 and SP12 and the switches SS11 and SS12 according to the output voltage VO1 and the input voltage VI1.

[0063] For example, when the output voltage is lower than the target voltage, the control circuit 150 reduces the switching frequency to increase the gain of the resonant converter 100. Therefore, the control circuit 150 is configured to adjust the switching frequency until the output voltage is substantially equal to the target voltage.

[0064] Figure 2 FIG. 1 is a control timing diagram of the resonant converter 100 according to some embodiments of the present invention. Figure 2 As shown, the timing diagram 200 illustrates the operation of the resonant converter 100 at times T20 to T27.

[0065] like Figure 2 and Figure 1As shown, the timing diagram 200 illustrates the driving signals of the switches SS11, SS12 and the switches SP11, SP12 at different times. In addition, the timing diagram 200 also illustrates the current waveforms of the currents IL1, ILR1 and ILM1.

[0066] Because the switches in resonant converter 100 operate at the switching frequency, the following description focuses on the operation of the switches during the time period [T20-T25], which is half a switching cycle. The operation of the switches in resonant converter 100 during periods other than the time period [T20-T25] is similar to the operation during the time period [T20-T25]. For example, during the time period [T26-T27], the operation of switches SS11 and SS12 and switches SP11 and SP12 is the same as during the time period [T20-T25]. The operation of switches SS11 and SS12 and switches SP11 and SP12 during the time period [T25-T26] complements their operation during the time period [T20-T25], where the number of switches turned on and off during the time period [T20-T25] complements the number of switches turned on and off during the time period [T25-T26].

[0067] like Figure 2 As shown, in the period [T20-T25], the switch SP11 is turned on and the switch SP12 is turned off.

[0068] like Figure 2 As shown, in the time period [T20-T21], the switch SS11 is turned off and the switch SS12 is turned on, so that the current IL1 flows from the node N16 through the coil LN12 to the switch SS12.

[0069] During the time period [T20-T21], the current ILR1 flows from the node N13 through the inductor LR1 to the node N11. The electrical energy is transferred from the inductor LR1 to the capacitor CR1, the input power source 101 and the secondary circuit 140.

[0070] In some other embodiments, during the time period [T20-T21], the switch SS12 is turned off and the switch SS11 is turned on, so that the current IL1 flows from the node N17 through the coil LN11 to the node N16.

[0071] During the time period [T20-T21], the current ILR1 flows from the node N13 through the inductor LR1 to the node N11. Power is transferred from the inductor LR1 and the secondary circuit 140 to the capacitor CR1 and the input power source 101.

[0072] As described above, the current ILR1 and the current IL1 quickly approach zero at time T21.

[0073] like Figure 2As shown, after time T21, current ILR1 changes its direction, such that during the time period [T21-T22], current ILR1 flows from node N11 through inductor LR1 to node N13, for example, in the first direction. Power is transferred from input power source 101 and capacitor CR1 to secondary circuit 140 and inductor LR1.

[0074] In some embodiments, during the time period [T20-T21], the secondary winding is clamped to a predetermined voltage, where the predetermined voltage is a reverse voltage. The polarity of the reverse voltage is opposite to the polarity of the induced voltage in the secondary winding, and current ILR1 rapidly increases from a negative value to zero, while current IL1 rapidly decreases from a positive value to zero. Power is transferred from input power source 101 and secondary circuit 140 to resonant network 120.

[0075] like Figure 2 As shown, during the time period [T21-T22], switch SS12 is turned on and switch SS11 is turned off, causing current IL1 to flow from switch SS12 through coil LN12 to node N16. Coil LN12 is clamped by a reverse voltage, where the polarity of the reverse voltage is opposite to the polarity of the induced voltage in coil LN12. Current ILR1 increases in a first direction, and current IL1 increases in a second direction due to the reverse voltage. Power is transferred from input power source 101 and secondary circuit 140 to resonant network 120. In one embodiment, the reverse voltage is equal to the output voltage of resonant converter 100.

[0076] As described above, as power is transferred from the input power source 101 and the secondary circuit 140 to the resonant network 120, the current ILR1 rapidly increases during the time period [T21-T22] due to the conduction of the switch SS12. Through the switching action during the time period [T21-T22], the current ILR1 rapidly approaches the desired current.

[0077] In some embodiments, the control circuit 150 is used to control the switches SS11 and SS12 to adjust the current ILR1. Figure 2 In this embodiment, time T22 is defined as the time at which switch SS12 is turned off during the time period [T21-T23]. In other words, control circuit 150 is configured to determine time T22 by turning off switch SS12 during the time period [T21-T23]. For example, before turning off switch SS12, control circuit 150 maintains switch SS12 on for a longer period, thereby increasing the time period [T21-T22]. Consequently, current ILR1 increases in the first direction during the longer time period [T21-T22], and the duration of the increase increases.

[0078] As described above, the control circuit 150 is configured to adjust the current ILR1 . Therefore, by controlling the switches SS11 and SS12 to adjust the time period [T21-T22], the control circuit 150 is configured to adjust the current ILR1 so that the output voltage increases until the output voltage is substantially equal to the desired target voltage.

[0079] like Figure 2 As shown, during the time period [T22-T23], the current ILR1 flows from the node N11 through the inductor LR1 to the node N13. During the time period [T22-T23], the power is transferred from the resonant network 120 and the input power source 101 to the secondary circuit 140 through the transformer 130.

[0080] During the time period [T22-T23], switch SS12 is turned off and switch SS11 is turned on, causing current IL1 to flow from node N16 through coil LN11 to switch SS11. Power is transferred from resonant network 120 and input power source 101 to secondary circuit 140 via transformer 130.

[0081] like Figure 2 As shown, during the time period [T23-T24], current ILR1 flows from node N11 through inductor LR1 to node N13. During the time period [T23-T24], power is transferred from input power source 101 to capacitor CR1. Inductor LR1 and capacitor CR1 of resonant network 120 are in a resonant state.

[0082] During the time period [T23-T24], switches SS11 and SS12 are both turned off, making current IL1 substantially zero. During the time period [T23-T24] from time T23 to time T24, control circuit 150 is configured to adjust the gain of resonant converter 100 and control switches SS11 and SS12 to be turned off to achieve ZCS of switches SS11 and SS12.

[0083] In some embodiments, the control circuit 150 is configured to adjust the time period [T23-T24] according to the output voltage VO1 , or the control circuit 150 is configured to adjust the time period [T23-T24] according to the output voltage VO1 and the input voltage VI1 .

[0084] like Figure 2 As shown, in the time period [T24-T25], the current ILR1 flows from the node N11 through the inductor LR1 to the node N13.

[0085] In the period [T24-T25], the switch SS12 is turned on and the switch SS11 is turned off, so that the current IL1 flows from the switch SS12 through the coil LN12 to the node N16.

[0086] In some embodiments, coil LN12 is clamped by the reverse voltage, and current ILR1 increases in a first direction and current IL1 increases in a second direction due to the reverse voltage. Power is transferred from secondary circuit 140 and input power source 101 to resonant network 120 .

[0087] As described above, since power is transferred from the input power source 101 and the secondary circuit 140 to the resonant network 120 , the current ILR1 increases rapidly during the time period [T24-T25].

[0088] In some embodiments, the control circuit 150 is used to control the switches SS11 and SS12 to adjust the time period [T24-T25] so that the current ILR1 increases to increase the holding time. Figure 2 In this embodiment, time T24 is defined as the time at which switch SS12 is turned on during the time period [T23-T25]. In other words, control circuit 150 is configured to determine time T24 by turning on switch SS12 during the time period [T23-T25]. For example, control circuit 150 is configured to turn on switch SS12 earlier during the time period [T23-T25], causing time T24 to shift later and correspondingly increasing the time period [T24-T25]. Consequently, current ILR1 increases during the longer time period [T24-T25].

[0089] In some embodiments, when the time T24 moves forward, the time period [T23-T24] decreases accordingly. In other words, the control circuit 150 is configured to control the time period [T23-T24] by adjusting the time T24.

[0090] Similarly, in some embodiments, time T22 is defined as the time during the time period [T21-T23] when switch SS12 is off and switch SS11 is on. Control circuit 150 is configured to determine time T22 by turning on switch SS11 during the time period [T21-T23]. For example, control circuit 150 is configured to turn on switch SS11 later in the time period [T21-T23], shifting time T22 earlier and correspondingly increasing the time period [T21-T22]. Consequently, current ILR1 increases over a longer time period [T21-T22], thereby increasing the holding time.

[0091] As described above, the control circuit 150 is used to adjust the current ILR1 . Therefore, by controlling the switches SS11 and SS12 to adjust the time period [T24-T25], the control circuit 150 is used to adjust the output voltage until the output voltage is substantially equal to the desired preset voltage.

[0092] In some other embodiments, the switching operation during the time period [T20-T25] is implemented by the resonant converter 300 described below. When the resonant converter 300 operates according to the control sequence described above, the switches SP31-SP34 and SS31-SS34 of the resonant converter 300 operate as follows: switches SP31 and SP34 operate similarly to switch SP11, switches SP32 and SP33 operate similarly to switch SP12, switches SS32 and SS33 operate similarly to switch SS12, and switches SS31 and SS34 operate similarly to switch SS11. Further details are described below.

[0093] Figure 3 FIG. 1 is a circuit diagram of a resonant converter 300 according to some embodiments of the present invention. Figure 3 As shown, the resonant converter 300 is used to receive an input voltage VI3 and provide an output voltage VO3 to a load 309. The resonant converter 300 includes a primary circuit 310, a resonant network 320, a transformer 330, a secondary circuit 340, and a control circuit 350. The configuration and operation of the components of the resonant converter 300 are similar to those of FIG. Figure 1 The configuration and operation of the components of the resonant converter 100 are shown in FIG. Figure 3 In the related embodiments, some descriptions are not repeated.

[0094] like Figure 3 As shown, the primary circuit 310 is implemented as a full-bridge circuit including switches SP31 to SP34. Switches SP31 and SP32 are coupled in series. Switches SP31 and SP32 are coupled to the input power supply 301 at nodes N31 and N32, respectively. Switches SP33 and SP34 are coupled in series. Switches SP33 and SP34 are also coupled to the input power supply 301 at nodes N31 and N32, respectively. In some embodiments, switches SP31 to SP34 are used to operate according to the switching frequency determined by the control circuit 350. In some other embodiments, the primary circuit 310 is implemented as a half-bridge circuit, such as Figure 1 The primary circuit 110 is shown.

[0095] like Figure 3 As shown, resonant network 320 includes inductor LR3, magnetizing inductor LM3, and capacitor CR3. Magnetizing inductor LM3 can be implemented as an inductor independent of primary winding LP3 or as a stray inductance of primary winding LP3. A first end of inductor LR3 is coupled to switches SP31 and SP32 at a node N33, and a second end of inductor LR3 is coupled to primary winding LP3 of transformer 330 at a node N35. A first end of capacitor CR3 is coupled to switches SP33 and SP34 at a node N34, and a second end of capacitor CR3 is coupled to primary winding LP3 at a node N36. During operation of resonant converter 300, current ILR3 flows through inductor LR3.

[0096] like Figure 3 As shown, transformer 330 includes a primary winding LP3 and a secondary winding LN3. A first end of primary winding LP3 is coupled to inductor LR3 at node N35, and a second end of primary winding LP3 is coupled to capacitor CR3 at node N36. Secondary winding LN3 is coupled to secondary circuit 340. During operation of resonant converter 300, current ILM3 flows through magnetizing inductor LM3. In some embodiments, the voltage of secondary winding LN3 is obtained by sensing the voltage of primary winding LP3.

[0097] like Figure 3 As shown, the secondary circuit 340 is implemented as a full-bridge circuit including switches SS31-SS34. Switches SS31-SS34 are coupled in series. Switches SS31 and SS32 are coupled to the secondary winding LN3 at a node N37. Switches SS33 and SS34 are coupled to the secondary winding LN3 at a node N38. Switches SS31 and SS33 are coupled to the first output terminal of the resonant converter 300 at a node N39. Switches SS32 and SS34 are coupled to the second output terminal of the resonant converter 300 at a node N310. Nodes N39 and N310 are coupled to the load 309. In some other embodiments, the secondary circuit 340 is implemented as a half-bridge circuit, such as Figure 1 The secondary circuit 140 is shown.

[0098] In some embodiments, switches SS31-SS34 operate at a switching frequency determined by control circuit 150. Therefore, switches SS31-SS34 and switches SP31-SP34 of primary circuit 310 can operate at the same switching frequency. In other embodiments, switches SS31-SS34 and switches SP31-SP34 operate at different switching frequencies. For example, the switching frequency of switches SS31-SS34 is a positive integer multiple of the switching frequency of switches SP31-SP34.

[0099] like Figure 3 As shown, the control circuit 350 is used to control the switches SP31-SP34 of the primary circuit 310 and the switches SS31-SS34 of the secondary circuit 340. In some embodiments, the control circuit 350 is used to control the switching frequency, on-time, and off-time of the switches SP31-SP34 and the switches SS31-SS34 based on the output voltage VO3. In some embodiments, the control circuit 350 is used to control the switching frequency, on-time, and off-time of the switches SP31-SP34 and the switches SS31-SS34 based on the output voltage VO3 and the input voltage VI3.

[0100] For example, the control circuit 350 reduces the switching frequency to increase the gain of the resonant converter 300. Therefore, the control circuit 350 is configured to adjust the switching frequency to adjust the gain of the resonant converter 300.

[0101] In some embodiments, the operation of the resonant converter 300 is illustrated by the timing diagram 200 .

[0102] like Figure 3 and Figure 2 As shown, in the period [T20-T25], the switches SP31 and SP34 are turned on and the switches SP32 and SP33 are turned off.

[0103] like Figure 2 As shown, during the time period [T20-T21], switches SS32 and SS33 are turned on, and switches SS31 and SS34 are turned off, causing current IL3 to flow from node N37 through secondary winding LN3 to node N38. Energy is transferred from inductor LR3 to capacitor CR3, input power source 301, and secondary circuit 340.

[0104] During the period [T20-T21], the current ILR3 flows from the node N35 through the inductor LR3 to the node N33.

[0105] In some other embodiments, during the time period [T20-T21], switches SS32 and SS33 are turned off, and switches SS31 and SS34 are turned on, causing current IL3 to flow from node N37 through secondary winding LN3 to node N38. Energy is transferred from secondary circuit 340 and inductor LR3 to capacitor CR3 and input power source 301.

[0106] During the period [T20-T21], the current ILR3 flows from the node N35 through the inductor LR3 to the node N33.

[0107] As described above, since the electric energy is transferred from the inductor LR3 and the secondary circuit 340 to the capacitor CR3 and the input power source 301 , the current ILR3 and the current IL1 quickly approach zero in the time period [T20-T21].

[0108] like Figure 2 As shown, in the time period [T20-T21], the current ILR3 increases from a negative value to zero. After time T21, the current ILR3 changes its flow direction, so that in the time period [T21-T22], the current ILR3 flows from the node N33 through the inductor LR3 to the node N35.

[0109] In some embodiments, during the time period [T21-T22], the secondary winding LN3 is clamped by the reverse voltage, and the current ILR3 increases in a first direction and the output current IL1 increases in a second direction due to the reverse voltage. Power is transferred from the input power source 301 and the secondary circuit 340 to the resonant network 320.

[0110] like Figure 2 As shown, during the time period [T21-T22], switches SS32 and SS33 are turned on and switches SS31 and SS34 are turned off, causing current IL3 to flow from node N38 through secondary winding LN3 to node N37. Power is transferred from input power source 301 and secondary circuit 340 to resonant network 320.

[0111] As described above, as power is transferred from input power source 301 and secondary circuit 340 to resonant network 320, current ILR3 rapidly increases in the first direction and current IL3 increases in the second direction during time period [T21-T22] due to the conduction of switches SS32 and SS33. The action of the switches during time period [T21-T22] allows current ILR3 to quickly approach the desired current.

[0112] During the time period [T22-T23], switches SS32 and SS33 are off and switches SS31 and SS34 are on, causing current IL3 to flow from node N38 through secondary winding LN3 to node N37. Power is transferred from input power source 301 and resonant network 320 to secondary circuit 340.

[0113] like Figure 2 As shown, during the time period [T23-T24], current ILR3 flows from node N33 through inductor LR3 to node N35. During the time period [T23-T24], power is transferred from input power supply 301 to resonant network 320. Inductor LR3 and capacitor CR3 of resonant network 320 are in a resonant state.

[0114] During the time period [T23-T24], the switches SS31-SS34 are turned off, so that the current IL3 is substantially equal to zero.

[0115] like Figure 2 As shown, in the time period [T24-T25], the current ILR3 flows from the node N33 through the inductor LR3 to the node N35.

[0116] During the time period [T24-T25], the switches SS32 and SS33 are turned on and the switches SS31 and SS34 are turned off, so that the current IL3 flows from the node N38 through the secondary winding LN3 to the node N37.

[0117] In some embodiments, current IL3 flows through secondary winding LN3, and the induced voltage between nodes N37 and N38 of secondary winding LN3 is clamped by the reverse voltage. During time period [T24-T25], secondary winding LN3 is clamped by the reverse voltage, where the reverse voltage is equal to the output voltage of resonant converter 300. Current ILR3 increases in a first direction, and current IL3 increases in a second direction due to the reverse voltage. Power is transferred from secondary circuit 340 and input power source 301 to resonant network 320.

[0118] As described above, since power is transferred from the input power source 301 and the secondary circuit 340 to the resonant network 320 , the current ILR3 increases rapidly during the time period [T24-T25] to increase the gain of the resonant converter 300 .

[0119] In some embodiments, the control circuit 350 is used to control the switches SS31-SS34 to adjust the output voltage by adjusting the current ILR3. The control circuit 350 is similar to the control circuit 150 described above. Therefore, for the sake of brevity, some descriptions are not repeated.

[0120] Figure 4 FIG. 1 is a control timing diagram of the resonant converter 300 according to some embodiments of the present invention. Figure 2 As shown, the timing diagram 400 illustrates the operation of the resonant converter 300 at times T40 to T47.

[0121] like Figure 4 and Figure 3 As shown, the timing diagram 400 illustrates the driving signals of the switches SP31 - SP34 and the switches SS31 and SS34 . In addition, the timing diagram 400 also illustrates the current waveforms of the currents IL3 , ILR3 and ILM3 .

[0122] Because the switches in resonant converter 300 operate at the switching frequency, the following description focuses on the switch operation during the time period [T40-T45]. The time period [T40-T45] between time T40 and time T45 represents half a switching cycle. The operation of the switches in resonant converter 300 in time periods other than [T40-T45] is similar to the operation during the time period [T40-T45]. For example, the operation of switches SS31-SS34 and switches SP31-SP34 in the time period [T46-T47] is similar to the operation during the time period [T40-T45]. The operation of switches SS31-SS34 and switches SP31-SP34 in the time period [T45-T46] is complementary to the operation during the time period [T40-T45], where the number of switches turned on and off during the time period [T40-T45] is complementary to the number of switches turned on and off during the time period [T45-T46].

[0123] like Figure 4 As shown, during the time period [T40-T41], the current ILR3 flows from the node N35 through the inductor LR3 to the node N33. When the secondary winding LN3 is short-circuited, the electric energy is transferred from the inductor LR3 to the capacitor CR3 and the input power supply 301.

[0124] As described above, due to the short circuit of the secondary winding LN3, electric energy is transferred from the inductor LR3 to the capacitor CR3 and the input power supply 301. In the time period [T40-T41], the current ILR3 increases rapidly from a negative value to zero and the current IL3 decreases from a positive value to zero.

[0125] In some other embodiments, switches SS31 and SS34 form a first switch group, switches SS32 and SS33 form a second switch group, switches SS31 and SS33 form a third switch group, and switches SS32 and SS34 form a fourth switch group. In some embodiments, during the time period [T40-T41], one of the third and fourth switch groups is turned on, short-circuiting the secondary winding LN3. In some embodiments, the fourth switch group (switches SS32 and SS34) is turned on and the third switch group (switches SS31 and SS33) is turned off, shorting the secondary winding LN3. Electrical energy is transferred from inductor LR3 to capacitor CR3 and input power supply 301. In some other embodiments, the fourth switch group (switches SS32 and SS34) is turned off and the third switch group (switches SS31 and SS33) is turned on, shorting the secondary winding LN3. Electrical energy is transferred from inductor LR3 to capacitor CR3 and input power supply 301.

[0126] In some other embodiments, during the time period [T40-T41], the first switch group is on and the second switch group is off, causing the secondary winding LN3 to be reverse-voltage clamped. In some embodiments, the second switch group (switches SS32 and SS33) is off and the first switch group (switches SS31 and SS34) is on, causing current IL3 to flow from node N37 through secondary winding LN3 to node N38. Energy is transferred from inductor LR3 and secondary circuit 340 to capacitor CR3 and input power source 301.

[0127] In some other embodiments, during the time period [T40-T41], the first switch group is off and the second switch group is on. For example, the second switch group (switches SS32 and SS33) is on and the first switch group (switches SS31 and SS34) is off, causing current IL3 to flow from node N37 through secondary winding LN3 to node N38. Energy is transferred from inductor LR3 to capacitor CR3, input power source 301, and secondary circuit 340.

[0128] like Figure 4As shown, at time T41, current ILR3 approaches zero. After time T41, current ILR3 changes its flow direction, so that in a time period [T41-T42], current ILR3 flows from node N33 through inductor LR3 to node N35.

[0129] like Figure 4 As shown, in the time period [T41-T42], the secondary winding LN3 is short-circuited or clamped by the reverse voltage. When the secondary winding LN3 is short-circuited, the current IL3 flowing through the load 309 is substantially equal to zero.

[0130] During the time period [T41-T42], the secondary winding LN3 is short-circuited, and power is transferred from the input power source 301 and capacitor CR3 to the inductor LR3. When the secondary winding LN3 is reverse-clamped, power is transferred from the secondary circuit 340, capacitor CR3, and input power source 301 to the inductor LR3.

[0131] As described above, since the electric energy is transferred to the inductor LR3 , during the period [T41 - T42], the current ILR3 increases rapidly in the first direction, and the current IL3 increases in the second direction.

[0132] In some other embodiments, switches SS31 and SS34 form a first switch group, switches SS32 and SS33 form a second switch group, switches SS31 and SS33 form a third switch group, and switches SS32 and SS34 form a fourth switch group. In some embodiments, during the time period [T41-T42], one of the third and fourth switch groups is turned on, short-circuiting the secondary winding LN3. In some embodiments, the fourth switch group (switches SS32 and SS34) is turned on and the third switch group (switches SS31 and SS33) is turned off, shorting the secondary winding LN3. Power is transferred from the input power supply 301 and capacitor CR3 to the inductor LR3. In some other embodiments, the fourth switch group (switches SS32 and SS34) is turned off and the third switch group (switches SS31 and SS33) is turned on, shorting the secondary winding LN3. The preset voltage is zero, and the current IL3 is zero. Power is transferred from the input power supply 301 and capacitor CR3 to the inductor LR3.

[0133] In some other embodiments, during the time period [T41-T42], the second switch group is turned on, causing the secondary winding LN3 to be reverse-voltage clamped. In some embodiments, the second switch group (switches SS32 and SS33) is turned on, and the first switch group (switches SS31 and SS34) is turned off. Current IL3 flows from node N38 through secondary winding LN3 to node N37. Power is transferred from input power source 301, capacitor CR3, and secondary circuit 340 to inductor LR3.

[0134] In some embodiments, the control circuit 350 is used to control the switches SS31-SS34 to adjust the current ILR3. Figure 4 In this embodiment, time T42 is defined as the time at which switch SS32 is turned off during the time period [T41-T43]. In other words, control circuit 350 determines time T42 by turning off switch SS32 during the time period [T41-T43]. For example, before turning off switch SS32, control circuit 350 maintains switches SS32 and SS34 on and switches SS31 and SS33 off for a longer period, thereby increasing the time period [T41-T42]. Consequently, current ILR3 increases rapidly in the first direction during the longer time period [T41-T42].

[0135] As described above, the control circuit 350 is configured to adjust the current ILR3 . Therefore, by controlling the switches SS31 ˜ SS34 during the time period [T40 - T42 ], the control circuit 350 is configured to adjust the output voltage until the output voltage is substantially equal to the desired target voltage.

[0136] During a time period [T42-T43], the switches SS32 and SS33 are turned off and the switches SS31 and SS34 are turned on, so that the current IL3 flows from the node N38 through the coil LN3 to the node N37.

[0137] During the time period [T42-T43], the current ILR3 flows from the node N33 through the inductor LR3 to the node N35. During the time period [T42-T43], power is transferred from the input power source 301 and the resonant network 320 to the secondary circuit 340.

[0138] like Figure 4 As shown, in the time period [T43-T44], at least three switches (eg, switches SS32-SS34) are turned off, so that the current IL3 is substantially equal to zero.

[0139] During the time period [T43-T44], current ILR3 flows from node N33 through inductor LR3 to node N35. During the time period [T43-T44], power is transferred from input power source 301 to resonant network 320. Inductor LR3 and capacitor CR3 of resonant network 320 are in a resonant state. The gain of resonant converter 300 is adjusted, and switches SS31-SS34 can achieve zero-current switching (ZCS).

[0140] In the above embodiment, corresponding to Figure 4 The time T43 is defined by the time when the switch SS33 is turned on and the switch SS34 is turned off. The time T43 can be adjusted.

[0141] like Figure 4As shown, in the time period [T44-T45], the secondary winding LN3 is short-circuited or clamped by the reverse voltage. When the secondary winding LN3 is short-circuited, the current IL3 flowing through the load 309 is substantially equal to zero.

[0142] In some embodiments, during a time period [T44-T45], one of the third and fourth switch groups is turned on to short-circuit the secondary winding LN3. In some embodiments, the fourth switch group (switches SS32 and SS34) is turned off, and the third switch group (switches SS31 and SS33) is turned on to short-circuit the secondary winding LN3, making the current IL3 substantially zero.

[0143] During the time period [T44-T45], the current ILR3 flows from the node N33 through the inductor LR3 to the node N35 .

[0144] In some other embodiments, during the time period [T44-T45], the fourth switch group (switches SS32 and SS34) is turned on and the third switch group (switches SS31 and SS33) is turned off to short-circuit the secondary winding LN3. Power is transferred from the input power source 301 to the resonant network 320.

[0145] In some other embodiments, during time period [T44-T45], the second switch group (switches SS32 and SS33) is turned on and the first switch group (switches SS31 and SS34) is turned off, causing current IL3 to flow from node N38 through secondary winding LN3 to node N37. Secondary winding LN3 is reverse-voltage clamped. Power is transferred from input power source 301 to secondary circuit 340 and resonant network 320.

[0146] As described above, since power is transferred from the input power source 301 and the secondary circuit 340 to the resonant network 320 , during the time period [T44-T45], the current ILR3 increases in the first direction, thereby increasing the holding time of the resonant converter.

[0147] In some embodiments, the control circuit 350 is used to control the switches SS31-SS34 to adjust the current ILR3 to increase the holding time of the resonant converter 300. Figure 4In this embodiment, time T44 is defined as the time at which switch SS33 is turned on during the time period [T43-T45]. In other words, control circuit 350 is configured to determine time T44 by turning on switch SS33 during the time period [T43-T45]. For example, control circuit 350 is configured to turn on switch SS33 earlier during the time period [T43-T45], shifting time T44 later and correspondingly increasing the time period [T44-T45]. Consequently, current ILR3 increases during the longer time period [T44-T45]. In some other embodiments, control circuit 350 is configured to turn on switch SS33 before time T43 to further increase current ILR3.

[0148] In some embodiments, when the time T44 moves forward, the time period [T44-T45] decreases accordingly. In other words, the control circuit 350 is configured to control the time period [T44-T45] by adjusting the time T44.

[0149] Similarly, in some embodiments, time T42 is defined as the time during the time period [T41-T43] when switch SS32 is off and switch SS31 is on. Control circuit 350 is configured to determine time T42 by turning on switch SS31 during the time period [T41-T43]. For example, control circuit 350 is configured to turn on switch SS31 and turn off switch SS32 later during the time period [T41-T43], thereby shifting time T42 earlier and correspondingly increasing the time period [T41-T42]. Consequently, current ILR3 increases during the longer time period [T41-T42], thereby increasing the holding time.

[0150] As described above, the control circuit 350 is used to adjust the current ILR3 . Therefore, by controlling the switches SS31 ˜ SS34 during the time period [T44 - T45 ], the control circuit 350 is used to adjust the output voltage until the output voltage is substantially equal to the desired preset voltage.

[0151] Figure 5A FIG. 5 is a circuit diagram of a resonant converter 500A with a control circuit according to some embodiments of the present invention. Figure 5A As shown, the resonant converter 500A is coupled to an input power source 501 to receive an input voltage VI5. The resonant converter 500A is configured to receive the input voltage VI5 and provide an output voltage VO5 to a load 509. The resonant converter 500A includes a primary circuit 510, a resonant network 520, a transformer 530, a secondary circuit 540, and a control circuit 550A. The configuration and operation of the components of the resonant converter 500A are similar to those of FIG. Figure 1 The resonant converter 100 and Figure 3 The resonant converter 300 is shown. Therefore, for the sake of brevity, some of the descriptions are not repeated.

[0152] like Figure 5A As shown, the primary circuit 510 is implemented as a full-bridge circuit including switches SP51-SP54. The configuration and operation of the primary circuit 510 are similar to those of FIG. Figure 3 The configuration and operation of the primary circuit 310 are shown in FIG. Therefore, for the sake of brevity, some descriptions are not repeated. In some embodiments, the switches SP51 to SP54 are used to operate according to the switching frequency FS determined by the control circuit 550A. In some other embodiments, the primary circuit 510 is implemented as a half-bridge circuit. Figure 1 The primary circuit 110 is shown.

[0153] like Figure 5A As shown, the resonant network 520 is implemented to include an inductor LR5. When the resonant converter 500A is operating, a current ILR5 flows through the inductor LR5.

[0154] like Figure 5A and Figure 1 As shown, the configuration and operation of transformer 530 are similar to Figure 1 The configuration and operation of the transformer 130 are shown. Therefore, for the sake of brevity, some descriptions are not repeated.

[0155] like Figure 5A As shown, the secondary circuit 540 is implemented as a half-bridge circuit including switches SS51 and SS52. The first terminal of switch SS51 is coupled to the first terminal of the secondary winding, the second terminal of switch SS51 is coupled to the second terminal of switch SS52, the first terminal of switch SS52 is coupled to the second terminal of the secondary winding, and the second terminal of switch SS51 is coupled to the second output terminal of the resonant converter 500A. The center tap terminal of the secondary winding is coupled to the first output terminal of the resonant converter 500A. The configuration and operation of the secondary circuit 540 are similar to those of FIG. Figure 1 The configuration and operation of the secondary circuit 140 are shown. Figure 1 and Figure 5AThe differences are as follows. In the time period [T21-T22], the switch SS52 is turned off and the switch SS51 is turned on, so that the current IL5 flows in the direction from the load through the secondary winding to the switch SS51. The secondary winding is clamped by the reverse voltage, and the current ILR5 increases in the first direction and the current IL5 increases in the second direction due to the reverse voltage. Electrical energy is transferred from the input power supply 501 and the secondary circuit 540 to the resonant network 520. In the time period [T24-T25], the switch SS52 is turned off and the switch SS51 is turned on, so that the current IL5 flows in the direction from the load through the secondary winding to the switch SS51. The secondary winding is clamped by the reverse voltage, and the current ILR5 increases in the first direction and the current IL5 increases in the second direction due to the reverse voltage. Therefore, for the sake of brevity, some of the descriptions will not be repeated. In some embodiments, the switch SS51 is used to operate at a switching frequency FS determined by the control circuit 550A. In some other embodiments, the secondary circuit 540 is implemented as a full-bridge circuit, such as Figure 3 The secondary circuit 340 is shown.

[0156] like Figure 5A As shown, the control circuit 550A includes a voltage-controlled oscillator 553A, a primary driver 554, an output sampling processor 551, a comparator 507, a control loop 552A, a voltage-controlled oscillator 553A, a primary driver 554, an advance time control circuit 557A, a lag time control circuit 558A and a secondary driver 559.

[0157] In some embodiments, the control circuit 550A is configured to adjust the first preset time period and / or the second preset time period according to the output voltage VO5 and the switching frequency FS.

[0158] In some embodiments, the output sampling processor 551 is configured to receive the output voltage VO5 and provide a proportional output voltage VOS based on the output voltage VO5. The output sampling processor 551 calculates and generates the proportional output voltage VOS based on the output voltage VO5, wherein the proportional output voltage VOS and the output voltage VO5 have a specific proportional relationship.

[0159] In some embodiments, comparator 507 is configured to compare the scaled output voltage VOS with a reference voltage VRF and generate an error signal VE. Error signal VE corresponds to the difference between the scaled output voltage VOS and the reference voltage VRF. In some embodiments, reference voltage VRF can be replaced by a reference current or a reference power. Control circuit 550A is configured to adjust the output voltage so that the scaled output voltage is substantially equal to the reference voltage.

[0160] In some embodiments, the control loop 552A is configured to receive the error signal VE and provide a control signal VEA.

[0161] In some embodiments, the advance timing control circuit 557A is configured to receive the control signal VEA and provide a phase-shift signal PSS1. In various embodiments, the phase-shift signal PSS1 corresponds to a time period [T24-T25] or a time period [T44-T45].

[0162] In some embodiments, the dead time control circuit 558A is configured to receive the control signal VEA and provide a phase-shift signal PSS2. In various embodiments, the phase-shift signal PSS2 corresponds to a time period [T21-T22] or a time period [T41-T42].

[0163] In some embodiments, the voltage controlled oscillator 553A is used to provide a switching frequency FS.

[0164] In some embodiments, the switching frequency FS is substantially equal to a predetermined frequency. In some other embodiments, the voltage controlled oscillator 553A is configured to adjust the output voltage VO5 by adjusting the first phase-shifted signal PSS1 and the second phase-shifted signal PSS2.

[0165] In some embodiments, the primary driver 554 is configured to receive a switching frequency FS and drive the switches SP51 - SP54 according to the switching frequency FS. The primary driver 554 provides a primary driving signal to drive the switches SP51 - SP54 to operate at the switching frequency FS.

[0166] In some embodiments, the secondary driver 559 is configured to receive the switching frequency FS and the phase-shift signals PSS1 and PSS2 and drive switches SS51 and SS52 such that the first switch SS51 is turned on during a first predetermined time period (e.g., time period [T21-T22] and time period [T41-T42]) and the first switch SS51 is turned on during a second predetermined time period (e.g., time period [T24-T25] and time period [T44-T45]). The secondary driver 559 provides a secondary drive signal to drive the switches SS51 and SS52 based on the switching frequency FS and the phase-shift signals PSS1 and PSS2.

[0167] In some embodiments, when the input power source is lost and the proportional output voltage is lower than the reference voltage VRF, the lead time control circuit 557A is configured to adjust the phase shift signal PSS1 and the lag time control circuit 558A is configured to adjust the phase shift signal PSS2. The secondary driver 559 drives the first switch SS51 on and the second switch SS52 off during a first predetermined time period (e.g., time period [T21-T22] and time period [T41-T42]) and a second predetermined time period (e.g., time period [T24-T25] and time period [T44-T45]). In some embodiments, the predetermined frequency FM is determined based on the characteristics of the resonant converter 500A, such that the resonant converter 500A operates at a switching frequency FS that is equal to the predetermined frequency FM. In some embodiments, the predetermined frequency is a minimum switching frequency.

[0168] In various embodiments, different control methods are provided for adjusting the first predetermined time period (e.g., time period [T21-T22] and time period [T41-T42]) and the second predetermined time period (e.g., time period [T24-T25] and time period [T44-T45]) to increase the output voltage. The following describes three methods with detailed examples.

[0169] The first control method is as follows. First, the lead time control circuit 557A increases the second preset time period by moving the endpoints of the second preset time period (e.g., time T24 and time T44) backward until the endpoints of the second preset time period reach the zero current switching point. The zero current switching point is defined as the time when the current through the load is substantially equal to zero. For example, Figure 2 and Figure 4 As shown, the currents IL1 and IL3 passing through the load are substantially equal to zero at times T23 and T43, respectively. Therefore, times T23 and T43 correspond to zero current switching points.

[0170] Then, after the endpoints of the second preset time period reach the zero current switching point, the second preset time period is fixed and the hysteresis time control circuit 558A increases the first preset time period by shifting the endpoints of the first preset time period (e.g., time T22 and time T42) forward until the current ILR5 reaches the preset current. After the current ILR5 reaches the preset current, the first preset time period is fixed.

[0171] The second control method is as follows. First, the lag time control circuit 558A increases the first preset time period by shifting the endpoint of the first preset time period forward until the current ILR5 reaches the preset current. After the current ILR5 reaches the preset current, the first preset time period is fixed and the second preset time period begins to increase until the endpoint of the second preset time period reaches the zero current switching point.

[0172] For the first and second control methods described above, after the second preset time period reaches the zero current switching point, the second preset time period may be further increased to further increase the gain of the resonant converter 500A.

[0173] The third control method is as follows. First, the lead time control circuit 557A increases the second preset time period by shifting the endpoint of the second preset time period backward. Next, the lag time control circuit 558A increases the first preset time period by shifting the endpoint of the first preset time period forward. After the endpoint of the second preset time period reaches the zero current switching point and the current ILR5 reaches the preset current, the first preset time period is fixed and the second preset time period is fixed to increase the gain of the resonant converter 500A.

[0174] In some embodiments, the switching frequency FS is fixed such that the switching frequency FS is substantially equal to the predetermined frequency FM.

[0175] Figure 5B FIG. 5 is a circuit diagram of a resonant converter 500B with a control circuit according to some embodiments of the present invention. Figure 5B and Figure 5A As shown, the configuration and operation of resonant converter 500B are similar to those of resonant converter 500A. Therefore, for the sake of brevity, some descriptions are not repeated.

[0176] like Figure 5B and Figure 5A As shown, the differences between resonant converter 500B and 500A are concentrated in control circuit 550B. The differences between resonant converter 500B and 500A include that control circuit 550B includes a control loop 552B, a voltage-controlled oscillator 553B, phase-shift angle generators 555B and 556B, an advance time control circuit 557B, and a lag time control circuit 558B.

[0177] In some embodiments, the control circuit 550B is configured to adjust the first predetermined time period and / or the second predetermined time period according to the output voltage VO5 and the phase shift angles PSA1 and PSA2. The details of the phase shift angles PSA1 and PSA2 are described below.

[0178] In some embodiments, the control loop 552B is configured to receive the error signal VE and provide a control signal VEA to the voltage controlled oscillator 553B.

[0179] In some embodiments, the voltage controlled oscillator 553B is configured to receive the control signal VEA and provide a switching frequency FS. In some embodiments, the voltage controlled oscillator 553B is configured to adjust the switching frequency FS based on the control signal VEA. For example, the voltage controlled oscillator 553B adjusts the switching frequency FS.

[0180] In some embodiments, the phase-shift angle generator 555B is configured to provide the phase-shift angle PSA1 to the advance time control circuit 557B. In some embodiments, the phase-shift angle PSA1 is a first fixed value.

[0181] In some embodiments, the advance timing control circuit 557B is configured to receive the phase shift angle PSA1 and provide a phase shift signal PSS1 to the secondary driver 559. In various embodiments, the phase shift signal PSS1 corresponds to a time period [T24-T25] or a time period [T44-T45]. In some embodiments, the advance timing control circuit 557B is configured to generate the phase shift signal PSS1 based on the phase shift angle PSA1.

[0182] In some embodiments, the phase-shift angle generator 556B is configured to provide the phase-shift angle PSA2 to the lag time control circuit 558B. In some embodiments, the phase-shift angle PSA2 is a second fixed value. In some embodiments, the first fixed value and the second fixed value are the same. In other embodiments, the first fixed value and the second fixed value are different.

[0183] In some embodiments, the lag time control circuit 558B is configured to receive the phase shift angle PSA2 and provide a phase shift signal PSS2 to the secondary driver 559. In various embodiments, the phase shift signal PSS2 corresponds to the time period [T21-T22] or the time period [T41-T42]. In some embodiments, the lead time control circuit 558B is configured to generate the phase shift signal PSS2 based on the phase shift angle PSA2.

[0184] In some embodiments, the secondary driver 559 is configured to receive the switching frequency FS and the phase-shift signals PSS1 and PSS2 and drive the switches SS51 and SS52 such that the switch SS51 is turned on during a first predetermined period and the switch SS52 is turned on during a second predetermined period.

[0185] In some embodiments, when the phase shift angles PSA1 and PSA2 are fixed, the voltage controlled oscillator 553B is used to reduce the switching frequency to increase the output voltage. In some embodiments, the increase in input voltage is referred to as an increase in the gain of the resonant converter 500B.

[0186] Figure 5C FIG. 5 is a circuit diagram of a resonant converter 500C with a control circuit according to some embodiments of the present invention. Figure 5C and Figure 5B As shown, the configuration and operation of resonant converter 500C are similar to those of resonant converter 500B. Therefore, for the sake of brevity, some descriptions are not repeated.

[0187] like Figure 5C and Figure 5BAs shown, the differences between resonant converters 500C and 500B are concentrated in control circuit 550C. The differences between resonant converters 500C and 500B include that control circuit 550C includes a control loop 552C, a voltage-controlled oscillator 553C, phase-shift angle generators 555C and 556C, an advance time control circuit 557C, a lag time control circuit 558C, and an input sampling processor 505. The operations of control loop 552C, voltage-controlled oscillator 553C, advance time control circuit 557C, and lag time control circuit 558C are similar to those of control loop 552B, voltage-controlled oscillator 553B, advance time control circuit 557B, and lag time control circuit 558B. Therefore, for the sake of brevity, some descriptions are omitted.

[0188] In some embodiments, the control circuit 550C is configured to adjust the first preset time period and / or the second preset time period according to the output voltage VO5 and the input voltage VI5.

[0189] In some embodiments, the input sampling processor 505 is configured to receive the input voltage VI5 and provide a proportional input voltage VIS. In some embodiments, the proportional input voltage VIS corresponds to the input voltage.

[0190] In some embodiments, the phase-shift angle generator 555C is configured to receive the proportional input voltage VIS, the proportional output voltage VOS, and the switching frequency FS to provide the phase-shift angle PSA1.

[0191] In some embodiments, the phase-shift angle generator 556C is configured to receive the proportional input voltage VIS, the proportional output voltage VOS, and the switching frequency FS to provide the phase-shift angle PSA2.

[0192] In some implementations, when the input voltage decreases, for example, when the input terminal of the resonant converter is powered off, the output voltage of the resonant converter decreases.

[0193] Compared to the above approach, some embodiments of the present disclosure provide a different approach by adjusting the phase shift angles PSA1 and PSA2 and the switching frequency FS to maintain the output voltage VO5. In addition, the first and second predetermined time periods are adjusted to increase the hold time of the resonant converter 500C.

[0194] Although the present invention has been disclosed above with reference to the embodiments, they are not intended to limit the present invention. Anyone with ordinary knowledge in the technical field may make slight changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope defined in the appended claims.

Claims

1. A resonant converter, characterized in that: include: The primary circuit is used to receive the input voltage and includes: a plurality of primary switches configured to operate at a switching frequency, wherein at least one of the primary switches is configured to be turned on during a period from a first switching moment to a second switching moment; A transformer having a primary winding and a secondary winding; a resonant network coupled between the primary circuit and the primary winding, wherein a current in the resonant network changes direction at a first moment, the first moment being between the first switching moment and the second switching moment; The secondary circuit is coupled to the secondary winding and is used to provide an output voltage to a load, and includes: a plurality of secondary switches, wherein at least a first one of the secondary switches is configured to be turned on during a first predetermined time period from the first moment to a second moment to clamp the secondary winding via a predetermined voltage, so that the current of the resonant network increases in a first direction and the output current of the resonant converter increases in a second direction or is equal to zero; and At least a second one of the secondary switches is configured to be turned on during a second predetermined time period from a third moment to the second switching moment to clamp the secondary winding via the predetermined voltage, so that the current in the resonant network increases in the first direction and the output current of the resonant converter increases in the second direction or is equal to zero, wherein the third moment is between the second moment and the second switching moment; and A control circuit is coupled to the primary switches and the secondary switches. The control circuit is configured to control at least one of the primary switches to be turned on during a period from the first switching moment to the second switching moment, and to control the at least one first of the secondary switches to be turned on during the first preset time period and the at least one second of the secondary switches to be turned on during the second preset time period.

2. The resonant converter according to claim 1, wherein: The control circuit is further configured to adjust the first preset time period and / or the second preset time period according to the output voltage, or to adjust the first preset time period and / or the second preset time period according to the output voltage and the input voltage.

3. The resonant converter according to claim 1, wherein: The control circuit is further configured to control the secondary side switches to be disconnected during a third preset time period from a fourth moment to the third moment, so that the output current of the resonant converter is equal to zero, wherein the fourth moment is between the second moment and the third moment.

4. The resonant converter according to claim 3, wherein: The control circuit is further configured to adjust the third preset time period according to the output voltage, or to adjust the third preset time period according to the output voltage and the input voltage.

5. The resonant converter according to claim 1, wherein: The secondary winding further includes: a first end, a second end and a center tap end; The secondary side switches include: a first switch, a first terminal of the first switch coupled to the first terminal of the secondary winding; and a second switch, wherein a first end of the second switch is coupled to the second end of the secondary winding, and a second end of the second switch is coupled to the second end of the first switch; wherein the second end of the first switch is coupled to the first output end of the resonant converter and the center tap end is coupled to the second output end of the resonant converter, and the control circuit is further configured to control the second switch to be turned on during the first preset time period to clamp the secondary winding through the preset voltage so that the current of the resonant network increases in the first direction and the output current of the resonant converter increases in the second direction, and to control the second switch to be turned on during the second preset time period to clamp the secondary winding through the preset voltage so that the current of the resonant network increases in the first direction and the output current of the resonant converter increases in the second direction; or The second end of the first switch is coupled to the second output end of the resonant converter and the center tap end is coupled to the first output end of the resonant converter, and the control circuit is also used to control the first switch to be turned on within the first preset time period to clamp the secondary winding through the preset voltage, so that the current of the resonant network increases in the first direction and the output current of the resonant converter increases in the second direction, and to control the first switch to be turned on within the second preset time period to clamp the secondary winding through the preset voltage, so that the current of the resonant network increases in the first direction and the output current of the resonant converter increases in the second direction.

6. The resonant converter according to claim 5, wherein: The control circuit is further configured to control the first switch and the second switch to be disconnected during a third preset time period from a fourth moment to the third moment, so that the output current of the resonant converter is equal to zero, wherein the fourth moment is between the second moment and the third moment.

7. The resonant converter according to claim 1, wherein: The secondary side switches include: a first switch, wherein a first terminal of the first switch is coupled to the first terminal of the secondary winding, and a second terminal of the first switch is coupled to the first output terminal of the resonant converter; a second switch, wherein a first end of the second switch is coupled to the first end of the secondary winding, and a second end of the second switch is coupled to the second output end of the resonant converter; a third switch, wherein a first end of the third switch is coupled to the second end of the first switch, and a second end of the third switch is coupled to the second end of the secondary winding; A fourth switch has a first terminal coupled to the second terminal of the secondary winding, and a second terminal coupled to the second terminal of the second switch.

8. The resonant converter according to claim 7, wherein: The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group; as well as The control circuit is also used to control the second switch group to be turned on within the first preset time period or the second preset time period, and clamp the secondary winding through the preset voltage, so that the current in the resonant network increases in the first direction and the output current of the resonant converter increases in the second direction.

9. The resonant converter according to claim 7, wherein: The first switch and the third switch form a third switch group, and the second switch and the fourth switch form a fourth switch group; and The control circuit is further configured to control one of the third switch group and the fourth switch group to be turned on within the first preset time period or the second preset time period, and to clamp the secondary winding via the preset voltage so that the current of the resonant network increases in the first direction, and the preset voltage is equal to zero and the output current of the resonant converter is equal to zero.

10. The resonant converter according to claim 7, wherein: The control circuit is further configured to control at least three of the first switch, the second switch, the third switch, and the fourth switch to be disconnected within a third preset time from a fourth moment to the third moment, so that the output current of the resonant converter is equal to zero, wherein the fourth moment is between the second moment and the third moment.

11. The resonant converter according to claim 1, wherein: The control circuit further includes: A voltage controlled oscillator for providing the switching frequency; A primary-side driver, configured to drive the primary-side switches according to the switching frequency; an output sampling processor for receiving the output voltage and providing a proportional output voltage; a comparator for comparing the proportional output voltage with a reference voltage and for generating an error signal corresponding to a difference between the proportional output voltage and the reference voltage; a control loop for receiving the error signal and providing a control signal; an advance time control circuit, configured to receive the control signal and provide a first phase-shifted signal; a lag time control circuit, configured to receive the control signal and provide a second phase-shifted signal; and The secondary driver is configured to drive at least a first one of the secondary switches to conduct during the first preset time period and drive at least a second one of the secondary switches to conduct during the second preset time period according to the switching frequency, the first phase-shifted signal, and the second phase-shifted signal.

12. The resonant converter according to claim 11, wherein: The switching frequency is substantially equal to the preset frequency.

13. The resonant converter according to claim 11, wherein: The control circuit is further configured to adjust the first preset time period and / or the second preset time period according to the output voltage and the switching frequency.

14. The resonant converter according to claim 1, wherein: The control circuit further includes: an output sampling processor for receiving the output voltage and providing a proportional output voltage; a comparator for receiving the proportional output voltage and a reference voltage and providing an error signal; a control loop for receiving the error signal and providing a control signal; a voltage controlled oscillator, configured to receive the control signal and provide the switching frequency; A primary-side driver, configured to drive the primary-side switches according to the switching frequency; A first phase shift angle generator, for providing a first phase shift angle; A second phase shift angle generator, for providing a second phase shift angle; an advance time control circuit, configured to receive the first phase shift angle and provide a first phase shift signal; a lag time control circuit, configured to receive the second phase shift angle and provide a second phase shift signal; and The secondary driver is configured to drive at least a first one of the secondary switches to conduct during the first preset time period and drive at least a second one of the secondary switches to conduct during the second preset time period according to the switching frequency, the first phase-shifted signal, and the second phase-shifted signal.

15. The resonant converter according to claim 14, wherein: The first phase shift angle is a first fixed value, and the second phase shift angle is a second fixed value.

16. The resonant converter according to claim 14, wherein: The control circuit is further configured to adjust the first preset time period and / or the second preset time period according to the output voltage, the first phase shift angle, and the second phase shift angle.

17. The resonant converter according to claim 1, wherein: The control circuit further includes: an input sampling processor for receiving the input voltage and providing a proportional input voltage; an output sampling processor for receiving the output voltage and providing a proportional output voltage; a comparator for receiving the proportional output voltage and a reference voltage and providing an error signal; a control loop for receiving the error signal and providing a control signal; a voltage controlled oscillator, configured to receive the control signal and provide the switching frequency; A primary-side driver, configured to drive the primary-side switches according to the switching frequency; A first phase shift angle generator is configured to receive the proportional input voltage, the proportional output voltage and the switching frequency to provide a first phase shift angle; A second phase shift angle generator, configured to receive the proportional input voltage, the proportional output voltage and the switching frequency to provide a second phase shift angle; an advance time control circuit, configured to receive the first phase shift angle and provide a first phase shift signal; a lag time control circuit, configured to receive the second phase shift angle and provide a second phase shift signal; and The secondary driver is configured to drive at least a first one of the secondary switches to conduct during the first preset time period and drive at least a second one of the secondary switches to conduct during the second preset time period according to the switching frequency, the first phase-shifted signal, and the second phase-shifted signal.

18. The resonant converter according to claim 17, wherein: The control circuit is further configured to adjust the first preset time period and / or the second preset time period according to the output voltage and the input voltage.

19. A method for controlling a resonant converter, characterized in that: The resonant converter includes a primary circuit, a resonant network coupled to the primary circuit, a transformer having a primary winding coupled to the resonant network and a secondary winding, a secondary circuit coupled to the secondary winding, and a control circuit coupled to the primary circuit and the secondary circuit, wherein the primary circuit includes a plurality of primary switches, and the secondary circuit includes a plurality of secondary switches. The method includes: controlling the primary switches of the primary circuit according to a switching frequency, wherein the primary circuit is used to receive an input voltage; Controlling the primary side switches includes: Turning on at least one of the primary switches during a period from a first switching moment to a second switching moment; Converting the input voltage through the transformer and the resonant network; and controlling the secondary side switches of the secondary side circuit to provide an output voltage to a load, Controlling the secondary side switches includes: At least one first one of the secondary switches is turned on during a first predetermined time period from a first moment to a second moment to clamp the secondary winding with a predetermined voltage, so that the current of the resonant network increases in a first direction and the output current of the resonant converter increases in a second direction or is equal to zero, wherein the first moment and the second moment are between the first switching moment and the second switching moment, and the current of the resonant network changes its flow direction at the first moment; and At least a second one of the secondary switches is turned on in a second preset time period from a third moment to the second switching moment to clamp the secondary winding through the preset voltage, so that the current of the resonant network increases in the first direction, and the output current of the resonant converter increases in the second direction or is equal to zero, wherein the third moment is between the second moment and the second switching moment.

20. The method according to claim 19, characterized in that Also includes: adjusting the first preset time period and / or the second preset time period according to the output voltage; or The first preset time period and / or the second preset time period are adjusted according to the output voltage and the input voltage.

21. The method according to claim 19, wherein Also includes: The secondary switches are controlled to be disconnected during a third preset time period from a fourth moment to the third moment, so that the output current of the resonant converter is equal to zero, wherein the fourth moment is between the second moment and the third moment.

22. The method according to claim 21, characterized in that Also includes: adjusting the third preset time period according to the output voltage; or The third preset time period is adjusted according to the output voltage and the input voltage.

23. The method according to claim 19, wherein Controlling the secondary side switches also includes: turning on the second switch within the first preset time period; turning off the first switch and the second switch within a third preset time period from a fourth moment to the third moment; and turning on the second switch within the second preset time period; in The first end of the first switch is coupled to the first end of the secondary winding, and the second end of the first switch is coupled to the second end of the second switch. The second end of the second switch is coupled to the first output end of the resonant converter, and the first end of the second switch is coupled to the second end of the secondary winding, and The second output terminal of the resonant converter is coupled to a center tap terminal, wherein the two coils of the secondary winding are coupled to the center tap terminal in series.

24. The method according to claim 19, wherein Controlling the secondary side switches also includes: Turning on a second switch group within the first preset time period or the second preset time period, the second switch group being formed by a second switch and a third switch; at least three of the first switch, the second switch, the third switch, and the fourth switch are turned off within a third preset time period from a fourth moment to the third moment, wherein the fourth moment is between the second moment and the third moment; in The first end of the first switch is coupled to the first end of the second switch, and the second end of the first switch is coupled to the first end of the third switch. The first end of the second switch is coupled to the first end of the secondary winding, and the second end of the second switch is coupled to the second output end of the resonant converter. The first end of the third switch is coupled to the first output end of the resonant converter, and the second end of the third switch is coupled to the second end of the secondary winding, and A first terminal of the fourth switch is coupled to the second terminal of the secondary winding, and a second terminal of the fourth switch is coupled to the second terminal of the second switch.

25. The method according to claim 19, wherein Controlling the secondary side switches also includes: turning on one of a third switch group and a fourth switch group during the first preset time period or the second preset time period, wherein the third switch group is formed by the second switch and the fourth switch, and the fourth switch group is formed by the first switch and the third switch; at least three of the first switch, the second switch, the third switch, and the fourth switch are turned off within a third preset time period from a fourth moment to the third moment, wherein the fourth moment is between the second moment and the third moment; in The first end of the first switch is coupled to the first end of the second switch, and the second end of the first switch is coupled to the first end of the third switch. The first end of the second switch is coupled to the first end of the secondary winding, and the second end of the second switch is coupled to the second output end of the resonant converter. The first end of the third switch is coupled to the first output end of the resonant converter, and the second end of the third switch is coupled to the second end of the secondary winding, and A first terminal of the fourth switch is coupled to the second terminal of the secondary winding, and a second terminal of the fourth switch is coupled to the second terminal of the second switch.

26. The method according to claim 19, wherein Controlling these primary side switches also includes: providing the switching frequency; and driving the primary switches according to the switching frequency; and Controlling the secondary side switches also includes: receiving the output voltage and providing a proportional output voltage; comparing the proportional output voltage with a reference voltage; generating an error signal based on a difference between the scaled output voltage and the reference voltage; receiving the error signal and providing a control signal; providing a first phase-shifted signal according to the control signal; providing a second phase-shifted signal according to the control signal; and At least a first one of the secondary switches is driven to be turned on in the first preset time period according to the switching frequency, the first phase-shifted signal, and the second phase-shifted signal, and at least a second one of the secondary switches is driven to be turned on in the second preset time period.

27. The method according to claim 19, wherein Controlling these primary side switches also includes: receiving the output voltage and providing a proportional output voltage; comparing the proportional output voltage with a reference voltage; generating an error signal based on a difference between the scaled output voltage and the reference voltage; providing a control signal based on the error signal; generating the switching frequency according to the control signal; and driving the primary switches according to the switching frequency; and Controlling the secondary side switches also includes: providing a first phase-shifted signal according to a first phase-shifted angle; providing a second phase-shifted signal according to a second phase-shift angle; and At least a first one of the secondary switches is driven to be turned on in the first preset time period according to the switching frequency, the first phase-shifted signal, and the second phase-shifted signal, and at least a second one of the secondary switches is driven to be turned on in the second preset time period.

28. The method according to claim 19, wherein Controlling these primary side switches also includes: receiving the output voltage and providing a proportional output voltage; comparing the proportional output voltage with a reference voltage; generating an error signal based on a difference between the scaled output voltage and the reference voltage; providing a control signal based on the error signal; generating the switching frequency according to the control signal; and driving the primary switches according to the switching frequency; and Controlling the secondary side switches also includes: providing a proportional input voltage according to the input voltage; providing a first phase shift angle according to the switching frequency, the proportional input voltage, and the proportional output voltage; Providing a first phase-shifted signal according to the first phase-shifted angle; providing a second phase shift angle according to the switching frequency, the proportional input voltage, and the proportional output voltage; providing a second phase-shifted signal according to the second phase-shifted angle; and At least a first one of the secondary switches is driven to be turned on in the first preset time period according to the switching frequency, the first phase-shifted signal, and the second phase-shifted signal, and at least a second one of the secondary switches is driven to be turned on in the second preset time period.

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