A soft start method and apparatus for resonant type circuits

Abstract

The application provides a soft starting method and device for a resonant circuit, wherein the soft starting method comprises simultaneously performing time constraint and charge quantity constraint control driving off; the time constraint is that if a driving on time after a resonant current zero-crossing is greater than a zero-crossing time reference threshold, corresponding driving is controlled to be off; wherein the zero-crossing time reference threshold increases with a preset time speed along with the increase of a soft starting time; the charge quantity constraint is that if a resonant capacitor voltage amplitude is greater than a capacitor voltage reference threshold, corresponding driving is controlled to be off; wherein the capacitor voltage reference threshold increases with a preset voltage speed along with the change of the soft starting time. The application uses the time constraint to stabilize the resonant current, uses the charge quantity constraint to realize fast starting, and effectively suppresses the resonant current sharp peak while taking into account the soft starting speed.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a soft-start method and apparatus for resonant circuits. Background Technology

[0002] Resonant circuits are circuits that use inductors and capacitors to induce resonance at a specific frequency. They include various types such as series resonance, parallel resonance, LLC resonance, and CLLC resonance. By setting the number of switching transistors, they can be divided into full-bridge resonance and half-bridge resonance. Based on the direction of power transmission, they can be divided into unidirectional resonance and bidirectional resonance. They are flexible and practical electronic devices that are widely used in communication power supplies, new energy, electric vehicles, and industrial power supplies.

[0003] However, resonant circuit topologies face a common and critical technical challenge during power-on startup: because the output filter capacitor voltage is zero at startup, it is equivalent to a short circuit on the transformer secondary side, resulting in extremely low resonant network impedance. This leads to massive resonant current surges and voltage stresses under the excitation of the DC bus voltage. These excessive current and voltage spikes not only threaten the safety of power switching devices (such as MOSFETs), resonant capacitors, and magnetic components, shortening their lifespan, but may even directly damage the devices, severely limiting the reliability and application range of resonant circuits.

[0004] Therefore, there is an urgent need for a soft-start strategy for resonant circuits that can effectively suppress starting shocks. Summary of the Invention

[0005] In view of this, the purpose of the embodiments of this application is to provide a soft-start method and apparatus for resonant circuits, which uses time constraints to stabilize the resonant current and uses charge constraints to achieve rapid start-up, effectively suppressing resonant current spikes while taking into account the soft-start speed.

[0006] In a first aspect, embodiments of this application provide a soft-start method for resonant circuits, the soft-start method comprising:

[0007] Simultaneously execute time constraint and charge constraint control to drive shutdown; The time constraint is as follows: if the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off; wherein, the zero-crossing time reference threshold increases with the soft start time according to a preset time growth rate. The charge constraint is as follows: if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the corresponding drive is controlled to shut down; wherein, the capacitor voltage reference threshold changes with the soft start time according to a preset voltage increase.

[0008] In one possible implementation, the soft-start process is divided into two stages according to time sequence: Time-constrained dominant phase: If the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off; Charge constraint-driven stage: If the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the corresponding drive is controlled to shut down, and the preset time acceleration of the zero-crossing time reference threshold is increased, or the zero-crossing time reference threshold is updated to the maximum value of the zero-crossing time; after the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold for the first time, the capacitor voltage reference threshold is controlled to increase with the soft start time according to the preset voltage acceleration. When the capacitor voltage reference threshold increases to be equal to the closed-loop charge reference threshold, the soft start ends.

[0009] In one possible implementation, the resonant circuit includes an upper transistor and a lower transistor as its switching transistors. The resonant circuit employs single-sided capacitor voltage control. The step of controlling the corresponding drive to shut down if the amplitude of the resonant capacitor voltage exceeds a capacitor voltage reference threshold includes: If the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the drive of the upper transistor is turned off. After inserting the dead time, the drive of the lower transistor is turned on, and the conduction time of the lower transistor is controlled to be consistent with that of the upper transistor.

[0010] In one possible implementation, the resonant circuit includes an upper transistor and a lower transistor as its switching transistors. The resonant circuit employs bilateral capacitor voltage control. The capacitor voltage reference threshold includes an upper transistor voltage reference threshold and a lower transistor voltage reference threshold. The step of controlling the corresponding drive to shut down if the resonant capacitor voltage amplitude is greater than the capacitor voltage reference threshold includes: If the resonant capacitor voltage is greater than the upper transistor voltage reference threshold, the drive of the upper transistor is turned off; if the resonant capacitor voltage is less than the lower transistor voltage reference threshold, the drive of the lower transistor is turned off.

[0011] In one possible implementation, the soft-start method further includes: If the resonant current is greater than the overcurrent limit reference threshold, then the preset time increase rate of the zero-crossing time reference threshold and the preset voltage increase rate of the capacitor voltage reference threshold are reduced, or the zero-crossing time reference threshold and the capacitor voltage reference threshold are kept constant until the resonant current is less than the overcurrent limit reference threshold for a first number of consecutive switching cycles, then the restriction on the growth / maintenance of the zero-crossing time reference threshold and the capacitor voltage reference threshold is lifted; wherein, the overcurrent limit reference threshold increases with the soft-start time according to the preset current increase rate until it increases to the maximum value of the overcurrent limit and remains constant.

[0012] In one possible implementation, a transition phase also exists between the time-constrained dominant phase and the charge-constrained dominant phase: If the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, and the drive conduction time after the resonant current crosses zero is less than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off until the capacitor voltage amplitude is greater than the capacitor voltage reference threshold for a second consecutive number of switching cycles, then the charge constraint-dominated stage is entered.

[0013] Secondly, embodiments of this application provide a soft-start device for resonant circuits, the soft-start device comprising: The timer starts when the resonant current crosses zero and is reset at the falling edge of the drive. It is used to measure the drive conduction time after the resonant current crosses zero. The zero-crossing time reference threshold generation module is used to generate a zero-crossing time reference threshold in real time according to a preset time increase rate and the soft start time. The current timer comparator has a positive terminal input for the drive conduction time after the resonant current crosses zero, a reference terminal input for the zero-crossing time reference threshold, and an output level used to control the switch drive. The capacitor voltage reference threshold generation module is used to generate a capacitor voltage reference threshold in real time according to a preset voltage increase rate and soft start time. The charge-controlled comparator takes the resonant capacitor voltage as input at its positive terminal and the capacitor voltage reference threshold as input at its reference terminal. Its output level is used to control the switch drive.

[0014] In one possible implementation, the zero-crossing time reference threshold generation module is further configured to increase the preset time acceleration of the zero-crossing time reference threshold or update the zero-crossing time reference threshold to the maximum value of the zero-crossing time when the charge control comparator continuously outputs a second number of high levels. The capacitor voltage reference threshold generation module is also used to generate an initial capacitor voltage reference threshold, and when the charge control comparator continuously outputs a second number of high levels, the initial capacitor voltage reference threshold is increased according to a preset voltage growth rate with the soft start time, until the capacitor voltage reference threshold increases to the closed-loop charge reference threshold and remains unchanged.

[0015] In one possible implementation, the soft starter further includes an overcurrent limiting reference threshold generation module and a current limiting comparator. The overcurrent limit reference threshold generation module is used to generate an overcurrent limit reference threshold in real time according to the preset current growth rate and the soft start time, until the overcurrent limit reference threshold increases to the maximum value of the overcurrent limit and remains unchanged. The current limiting comparator has a positive input of resonant current, a reference input of overcurrent limiting reference threshold, and an output connected to a zero-crossing time reference threshold generation module and a capacitor voltage reference threshold generation module. The zero-crossing time reference threshold generation module is further configured to reduce the preset time acceleration of the zero-crossing time reference threshold or control the zero-crossing time reference threshold to remain unchanged when receiving a high-level signal output by the current limiting comparator, and restore the zero-crossing time reference threshold to its original state when receiving a first number of consecutive low-level signals output by the current limiting comparator. The capacitor voltage reference threshold generation module is further configured to reduce the preset voltage increase rate of the capacitor voltage reference threshold or control the capacitor voltage reference threshold to remain unchanged when receiving a high-level signal output by the current limiting comparator, and restore the capacitor voltage reference threshold to its original state when receiving a first number of consecutive low-level signals output by the current limiting comparator.

[0016] Thirdly, embodiments of this application provide a circuit controller, including: The first unit is used to control the corresponding drive to turn off if the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold; wherein the zero-crossing time reference threshold increases with the soft start time according to a preset time growth rate. The second unit is used to control the corresponding drive to shut down if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold; wherein the capacitor voltage reference threshold changes with the soft start time according to a preset voltage increase.

[0017] In one possible implementation, the second unit is further configured to control the corresponding drive to shut down if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, and simultaneously increase the preset time acceleration of the zero-crossing time reference threshold, or update the zero-crossing time reference threshold to the maximum value of the zero-crossing time; after the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold for the first time, control the capacitor voltage reference threshold to increase with the soft start time according to the preset voltage acceleration.

[0018] In one possible implementation, the circuit controller further includes: The third unit is configured to, if the resonant current is greater than the overcurrent limit reference threshold, reduce the preset time increase rate of the zero-crossing time reference threshold and reduce the preset voltage increase rate of the capacitor voltage reference threshold, or control the zero-crossing time reference threshold and the capacitor voltage reference threshold to remain unchanged until the resonant current is less than the overcurrent limit reference threshold for a consecutive first number of switching cycles, then release the restriction on the growth / maintenance of the zero-crossing time reference threshold and the capacitor voltage reference threshold; wherein, the overcurrent limit reference threshold increases with the soft-start time according to the preset current increase rate until it increases to the maximum value of the overcurrent limit and remains unchanged.

[0019] Fourthly, embodiments of this application provide a chip including the circuit controller described in any of the third aspects.

[0020] This application provides a soft-start method and apparatus for resonant circuits, which simultaneously executes time-constraint and charge-constraint control to drive shutdown. Time constraints stabilize the resonant current, while charge constraints enable rapid startup, effectively suppressing resonant current spikes while maintaining a fast soft-start speed. In this two-stage soft-start approach, time constraints are used initially upon power-up, switching to charge constraints when the resonant capacitor voltage amplitude exceeds a reference threshold. This allows for a natural transition and smooth connection between the two stages, effectively suppressing resonant cavity current spikes during startup and enabling rapid and stable circuit system establishment. Furthermore, by incorporating overcurrent limiting throughout the soft-start process, the soft-start speed can be maximized while ensuring safe and reliable startup.

[0021] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The topology of the half-bridge LLC resonant circuit provided in the embodiment of this application is shown; Figure 2 This paper shows one of the working waveform diagrams of the soft-start process of the half-bridge LLC resonant circuit provided in the embodiment of this application; Figure 3 This shows the second working waveform diagram of the soft-start process of the half-bridge LLC resonant circuit provided in the embodiment of this application; Figure 4 A timing diagram of the soft-start stage provided in an embodiment of this application is shown; Figure 5 A schematic diagram of the structure of a soft starter for resonant circuits provided in an embodiment of this application is shown; Figure 6 This diagram illustrates the working principle of the time constraint module provided in an embodiment of this application. Figure 7 This paper shows a schematic diagram illustrating the working principle of the charge constraint module provided in an embodiment of this application. Figure 8 One of the working principle diagrams of the resonant current limiting module provided in this application embodiment is shown; Figure 9 This is a second schematic diagram illustrating the working principle of the resonant current limiting module provided in an embodiment of this application; Figure 10 A schematic diagram of an electronic device provided in an embodiment of this application is shown. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0025] A common and critical technical challenge in resonant circuit topologies during power-on startup is the extremely low impedance of the resonant network. Since the output filter capacitor voltage is zero at startup, it is equivalent to a short circuit on the transformer secondary side. This results in massive resonant current surges and voltage stresses generated under the excitation of the DC bus voltage. These excessive current and voltage spikes not only threaten the safety of power switching devices (such as MOSFETs), resonant capacitors, and magnetic components, shortening their lifespan, but may even directly damage the devices, severely limiting the reliability and application range of resonant circuits.

[0026] To suppress starting shock, several soft-start strategies have been proposed at present: Traditional single-variable control methods include frequency reduction starting (PFM), duty cycle adjustment starting (PWM), and hybrid starting methods combining both. PFM starts at a switching frequency much higher than the resonant frequency and then gradually decreases to the operating point. While simple to control, it may operate in open-loop saturation during the initial startup phase, resulting in relatively high current stress. PWM starting, on the other hand, starts with a small duty cycle and increases linearly. While it can control the energy injection rate, it is limited in applications requiring a fixed duty cycle (e.g., 0.5) and has limited ability to suppress current peaks. Both PFM and PWM starting are essentially linear adjustments in a single control dimension, making it difficult to match the nonlinear dynamic characteristics of an LLC resonant cavity during startup, and thus difficult to balance rapid startup with device safety.

[0027] Control methods based on resonant cavity parameter detection: Some current-type LLC schemes achieve closed-loop control by sampling the resonant cavity capacitor voltage. The soft-start strategy of this scheme typically involves gradually increasing the reference voltage value of the resonant capacitor. However, this scheme also has some drawbacks. For example, during the initial startup phase, the electrical performance parameters of the resonant cavity have not yet reached a stable state. Simply controlling the resonant capacitor voltage value cannot suppress the reactive current during startup, leading to excessive resonant cavity current stress. Other schemes implement a soft-start strategy by controlling the resonant capacitor voltage reference and superimposing overcurrent protection limits. Although resonant current overcurrent protection can effectively reduce current stress, once cycle-by-cycle overcurrent protection is triggered, for a single-sided resonant capacitor voltage control method, since the conduction time of the lower transistor and the upper transistor is consistent, once cycle-by-cycle overcurrent protection occurs on one side, the resonant capacitor voltage will continuously deviate from the center value, and the resonant current will become asymmetrical, making subsequent operating cycles more prone to triggering overcurrent protection. Furthermore, such schemes may cause the resonant current to remain close to the overcurrent protection point during the initial soft-start phase, and the large current may introduce stress and noise problems.

[0028] Advanced nonlinear control methods: In recent years, nonlinear control techniques such as trajectory control and dead-time control have emerged. Although these methods can achieve good results in current suppression and start-up time, their control algorithms are usually very complex, requiring extremely high processing power from the controller and high accuracy from the sensors, which increases the difficulty and cost of system implementation.

[0029] In summary, existing soft-start technology for resonant converters struggles to achieve an ideal balance between control performance, implementation complexity, cost, and versatility.

[0030] To address the aforementioned issues, this application provides a soft-start method and apparatus for resonant circuits. It simultaneously implements time-constraint and charge-constraint control for drive shutdown. Time constraints stabilize the resonant current, while charge constraints enable rapid startup, effectively suppressing resonant current spikes while maintaining soft-start speed. Furthermore, segmented soft-start is achieved under the constraints of three control parameters: resonant capacitor voltage, drive conduction time, and resonant current. Upon power-on, the drive conduction time after the resonant current crosses zero is used to control the drive, making the resonant current more stable. Then, a smooth switch to resonant capacitor voltage control is implemented to achieve rapid startup under controlled power conditions, effectively reducing the resonant current spike during soft-start while ensuring startup speed. In addition, a reference threshold for drive shutdown is limited when the resonant current is in an overcurrent state, further limiting the startup current and maximizing soft-start speed.

[0031] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. The soft-start control strategy of this application is applicable to various types of resonant circuits, including series resonance, parallel resonance, LLC resonance, CLLC resonance, full-bridge resonance, half-bridge resonance, unidirectional resonance, and bidirectional resonance. To facilitate understanding of the embodiments of this application, a soft-start method for resonant circuits disclosed in the embodiments of this application will be described in detail using a half-bridge LLC resonant circuit as an example.

[0032] See Figure 1 As shown, Figure 1 The topology of the half-bridge LLC resonant circuit provided in the embodiments of this application is as follows: Figure 1 In this circuit, VIN is the DC bus voltage, Q1, Q2, Q3, and Q4 are switching transistors, Q1 is the upper transistor on the primary side, Q2 is the lower transistor on the primary side, Lr is the resonant inductor, Cr is the resonant capacitor, Lm is the magnetizing inductor, Co is the filter capacitor, Vo is the output voltage, and the LLC controller is used to control the half-bridge LLC resonant circuit to complete the soft start. The LLC controller collects the resonant current ISEN and the resonant capacitor voltage VCR from the circuit. The external loop collects VFB and sends VFB to the LLC controller, where VFB represents the loop feedback output. During the soft start phase, the upper transistor Q1 and the lower transistor Q2 on the primary side remain complementary and conduct.

[0033] The soft-start method for resonant circuits provided in this application specifically includes: Simultaneously execute time constraint and charge constraint control to drive shutdown; The time constraint is as follows: if the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off; wherein, the zero-crossing time reference threshold increases with the soft start time according to a preset time growth rate. The charge constraint is as follows: if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the corresponding drive is controlled to shut down; wherein, the capacitor voltage reference threshold changes with the soft start time according to a preset voltage increase.

[0034] During the entire soft-start process, the two control parameters, namely the drive conduction time after the resonant current crosses zero and the resonant capacitor voltage, act simultaneously. If either control parameter reaches the reference threshold, the corresponding switching transistor drive is turned off.

[0035] The above soft-start method will be explained in detail below with the working waveform of the half-bridge LLC resonant circuit during the soft-start process.

[0036] See Figure 2 As shown, Figure 2 This is one of the waveform diagrams showing the soft-start process of the half-bridge LLC resonant circuit provided in this application embodiment. t represents the soft-start time, ISEN is the resonant current, VCR is the resonant capacitor voltage, HG is the drive voltage of the upper transistor Q1, LG is the drive voltage of the lower transistor Q2, Tc is the drive conduction time after the resonant current crosses zero, measured by the timer counter, Tref is the zero-crossing time reference threshold, and VCR_ref is the capacitor voltage reference threshold. After the resonant current ISEN crosses zero at point a, the timer counter starts measuring the drive conduction time of the upper transistor until the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold Tref. At the falling edge of HG, the drive of the upper transistor is turned off, and the timer counter resets. After the resonant current ISEN crosses zero at point b, the timer counter starts measuring the drive conduction time of the lower transistor until the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold Tref. At the falling edge of LG, the drive of the lower transistor is turned off, and the timer counter resets. At the same time, the amplitude of the resonant capacitor voltage VCR is greater than the capacitor voltage reference threshold VCR_ref at point c, and the upper transistor drive is turned off at the falling edge of HG.

[0037] After the soft start begins, the time reference threshold Tref increases with the soft start time according to a preset time growth rate. This preset growth rate can be a fixed rate or a dynamically changing rate that varies with the soft start time. That is, different time reference threshold growth rates are set at different stages of the soft start, or the time reference threshold is increased in some stages and kept constant in others. Specifically, the decision to increase the time reference threshold or its growth rate is determined based on the actual operating conditions of the resonant circuit. For example, if the initial value of Tref is 0, and Tref increases by 1 ns for every 10 µs increase in the soft start time t, then Tref = 10 µs. -4 t (unit: µs) can be used to set the initial value and rising slope of Tref according to the actual usage of resonant circuits.

[0038] Correspondingly, the preset voltage growth rate of the capacitor voltage reference threshold is similar to the preset time growth rate of the time reference threshold. The preset voltage growth rate can be a fixed value or a dynamic value. The growth rate can be zero (i.e., the capacitor voltage reference threshold remains unchanged) or it can continuously change in different growth trends such as a linear function or a quadratic function. Specifically, the capacitor voltage reference threshold is set or dynamically adjusted according to the actual working conditions of the resonant circuit.

[0039] For charge constraint control strategies, there are various charge-based control methods: Single-sided capacitor voltage control: The LLC controller only controls the on-time of the upper transistor, and the on-time of the lower transistor follows that of the upper transistor. If the sampled value of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the drive of the upper transistor is turned off. After inserting the dead time, the drive of the lower transistor is turned on, and the on-time of the lower transistor is controlled to be consistent with that of the upper transistor to avoid current imbalance. Here, "single-sided capacitor voltage control" is usually referred to in this field as "single-sided VCR control," and "VCR control" is also known as "charge-type control."

[0040] Bilateral capacitor voltage control: The reference threshold for the upper transistor's capacitor voltage is called the upper transistor voltage reference threshold, and the reference threshold for the lower transistor's capacitor voltage is called the lower transistor voltage reference threshold. If the resonant capacitor voltage is greater than the upper transistor voltage reference threshold, the drive of the upper transistor is turned off; if the resonant capacitor voltage is less than the lower transistor voltage reference threshold, the drive of the lower transistor is turned off. The calculation formulas for the upper transistor voltage reference threshold VTH and the lower transistor voltage reference threshold VTL are: VTH = VOFFSET + VCR_ref, VTL = VOFFSET - VCR_ref, where VOFFSET represents the center value of VCR during steady-state operation, i.e., 1 / 2 VIN. Here, "bilateral capacitor voltage control" is usually referred to as "bilateral VCR control" in this field, "upper transistor voltage reference threshold" is usually referred to as "VTH" in this field, and "lower transistor voltage reference threshold" is usually referred to as "VTL" in this field.

[0041] The resonant capacitor voltage used in single-sided capacitor voltage control and double-sided capacitor voltage control can be obtained by the LLC controller from the half-bridge LLC resonant circuit in real time; or it can be obtained by integrating the resonant current ISEN and fitting the VCR signal. In this method, the LLC controller only needs to collect the resonant current ISEN from the circuit and does not need to collect the resonant capacitor voltage VCR.

[0042] Furthermore, the soft-start process is divided into two stages according to the time sequence: Time-constrained dominant phase: If the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off; Charge constraint-driven stage: If the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the corresponding drive is controlled to shut down, and the preset time acceleration of the zero-crossing time reference threshold is increased, or the zero-crossing time reference threshold is updated to the maximum value of the zero-crossing time; after the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold for the first time, the capacitor voltage reference threshold is controlled to increase with the soft start time according to the preset voltage acceleration. When the capacitor voltage reference threshold increases to be equal to the closed-loop charge reference threshold, the soft start ends.

[0043] During the time-constraint-dominated phase, since the output voltage has not yet been established and the resonant capacitor voltage has not reached the capacitor voltage reference threshold, soft start is performed by gradually increasing the zero-crossing time reference threshold. During the charge-constraint-dominated phase, the resonant capacitor voltage reaches the capacitor voltage reference threshold, and the control of the resonant capacitor voltage will take over the soft start process. The preset time acceleration of the zero-crossing time reference threshold is increased (the growth method of the preset time acceleration is not limited here; any method that increases the change in the zero-crossing time reference threshold per unit time is applicable), or the zero-crossing time reference threshold is completely released, up to the maximum zero-crossing time value (here, the maximum zero-crossing time value can be a preset fixed value, or it can be dynamically generated based on the zero-crossing time reference threshold at the moment the threshold is completely released, for example, using twice the value of the zero-crossing time reference threshold at the moment the threshold is completely released as the maximum zero-crossing time value). Both of these methods of adjusting the zero-crossing time reference threshold are to make the time constraint exit, so that the charge constraint takes over the time constraint as the dominant factor in the soft start drive control of the resonant circuit, and at the same time, the capacitor voltage reference threshold begins to gradually increase, and the switching transistor drive is controlled by the resonant capacitor voltage.

[0044] In this embodiment of the application, after the soft start begins, the capacitor voltage reference threshold remains unchanged until the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold for the first time. The capacitor voltage reference threshold increases with the soft start time according to a preset voltage growth rate. The initial value and rising slope of the capacitor voltage reference threshold VCR_ref can be set according to the actual usage of the resonant circuit.

[0045] See Figure 3 As shown, Figure 3 This is the second waveform diagram of the soft-start process of the half-bridge LLC resonant circuit provided in the embodiments of this application. Figure 3 In this context, VCR_ref_A is the closed-loop charge reference threshold, and VCR_ref' is the reference threshold for mapping charge constraints to time constraints.

[0046] The first stage of soft starting is the time-constrained stage, dominated by the time parameter (the drive conduction time after the resonant current crosses zero). During this stage, the resonant capacitor voltage VCR is always less than the capacitor voltage reference threshold VCR_ref, and VCR_ref remains unchanged.

[0047] The second stage of soft-start is the charge constraint-driven stage, dominated by the VCR voltage parameter (resonant capacitor voltage). The amplitude of the resonant capacitor voltage VCR is greater than the capacitor voltage reference threshold VCR_ref at point c. At the falling edge of HG, the upper transistor drive is turned off, and the time reference threshold Tref is updated to the maximum zero-crossing time Tref_A to avoid accidental triggering of the time constraint condition in subsequent operations. During this stage, the drive conduction time after the resonant current crosses zero is always less than Tref_A, and the capacitor voltage reference threshold increases with the soft-start time according to a preset voltage increase rate. The closed-loop charge reference threshold VCR_ref_A is obtained through feedback mapping from the external loop of the system. This value decreases with the soft-start time t during the soft-start stage. The soft-start ends when VCR_ref intersects with the closed-loop charge reference threshold VCR_ref_A.

[0048] It should be noted that during the time-constrained phase, if the VCR does not reach VCR_ref, the drive is turned off due to the influence of the time control parameter (the drive conduction time after the resonant current crosses zero). Here, a virtual time value VCR_ref' is created. It is assumed that the circuit is constrained by charge rather than time at this time. When the VCR rises to the assumed capacitor voltage reference threshold, the drive is turned off. At this time, the Tref corresponding to the assumed capacitor voltage reference threshold is VCR_ref'.

[0049] To ensure a smooth and stable switch between control modes, a transition phase is added between the time-constrained dominant phase and the charge-constrained dominant phase. The specific control method is as follows: If the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, and the drive conduction time after the resonant current crosses zero is less than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off until the capacitor voltage amplitude is greater than the capacitor voltage reference threshold for the second consecutive number of switching cycles, then the charge constraint-dominated stage is entered.

[0050] Here, the second number of switching cycles is a constant period, which can be set according to the actual circuit conditions, such as 10 switching cycles or 20 switching cycles.

[0051] Furthermore, the resonant current of the resonant cavity can be introduced as a third control parameter. The drive conduction time after the resonant current crosses zero, the resonant capacitor voltage, and the resonant current all act simultaneously to achieve soft-start. If either the drive conduction time after the resonant current crosses zero or the resonant capacitor voltage reaches a reference threshold, the corresponding switching transistor drive is turned off. The specific implementation is consistent with the above. The function of the resonant current is as follows: If the resonant current is greater than the overcurrent limit reference threshold, then the preset time increase rate of the zero-crossing time reference threshold and the preset voltage increase rate of the capacitor voltage reference threshold are reduced, or the zero-crossing time reference threshold and the capacitor voltage reference threshold are kept constant until the resonant current is less than the overcurrent limit reference threshold for a first number of consecutive switching cycles, then the restriction on the growth / maintenance of the zero-crossing time reference threshold and the capacitor voltage reference threshold is lifted; wherein, the overcurrent limit reference threshold increases with the soft-start time according to the preset current increase rate until it increases to the maximum value of the overcurrent limit and remains constant.

[0052] If the resonant current is greater than the overcurrent limit reference threshold, the resonant cavity is in an overcurrent state. The zero-crossing time reference threshold and the capacitor voltage reference threshold are controlled to slow down the rate of increase (the method of reducing the preset time rate of increase or the preset voltage rate of increase is not limited; any method that reduces the change in the zero-crossing time reference threshold or the capacitor voltage reference threshold per unit time is applicable) or remain unchanged until the resonant current is less than the overcurrent limit reference threshold for a first number of consecutive switching cycles (e.g., 10, 20, or other constant number of switching cycles, specifically set according to the actual working conditions of the circuit). At this time, the overcurrent state is released, and the zero-crossing time reference threshold and the capacitor voltage reference threshold are restored to their original state. If the original state is a fixed value, it remains unchanged; if the original state continues to increase, the rate of increase is restored.

[0053] The overcurrent limiting reference threshold increases with the preset current growth rate and soft start time. The initial value and rising slope of the overcurrent limiting reference threshold can be set according to the actual use of the resonant circuit. The reference threshold can increase with a smooth curve trend or increase step by step.

[0054] For example, suppose the overcurrent limiting reference threshold OCP_ref in steady state is OCP_TH (i.e., the maximum overcurrent limit), and the initial value of the overcurrent limiting reference threshold OCP_ref at the start of soft start is 0.5. OCP_TH, within 10ms, changes OCP_ref from 0.5 OCP_TH rises to OCP_TH, meaning OCP_ref increases by 0.00005 within 1µs. The formula for calculating OCP_TH can be summarized as: OCP_ref = 0.5 OCP_TH + 0.00005 OCP_TH t (in microseconds) is used to ensure the overcurrent limiting reference threshold increases in a smooth, curve-like manner. Alternatively, OCP_ref increases by 0.1 every 2 milliseconds. OCP_TH is equivalent to having 0.5. OCP_TH, 0.6 OCP_TH, 0.7 OCP_TH, 0.8 OCP_TH, 0.9 OCP_TH, 1.0 For these six levels of OCP_TH, one level is switched every 2 ms.

[0055] See Figure 4 as shown Figure 4 is the timing diagram of the soft start-up phase provided by the embodiment of the present application. When only the time constraint is executed, the conduction time of the drive is Ton_treg. When only the charge quantity constraint is executed, the conduction time of the drive is Ton_vcr. When both the time constraint and the charge quantity constraint are executed, the conduction time of the drive is min{Ton_treg, Ton_vcr}. According to the magnitude of the conduction time of the drive under the time constraint and the charge quantity constraint, the soft start-up process is divided into two stages: The first stage: The time constraint dominates the control (Ton_treg < Ton_vcr). In this stage, the reference threshold VCR_ref of the charge quantity control remains unchanged, VCR_ref’ remains unchanged, and is higher than the gradually increasing Tref. At this time, the drive is mainly restricted by the time constraint, and the charge quantity constraint is in a "standby" state.

[0056] The second stage: The charge quantity constraint dominates the control (Ton_treg ≥ Ton_vcr). In this stage, the reference threshold of the time constraint remains at the maximum value Tref_A unchanged. Tref_A is much higher than the VCR_ref’ mapped by the reference threshold of the charge quantity constraint in the time dimension. Therefore, in this stage, the charge quantity constraint dominates the drive logic control. When the capacitance voltage reference threshold of the charge quantity constraint gradually increases and intersects with the closed-loop reference quantity VCR_ref_A mapped by the system loop feedback VFB, the second stage ends, that is, the soft start-up ends. After that, the drive is only controlled by the charge quantity reference obtained from the closed-loop feedback of VFB in a steady state.

[0057] Switching between the first stage and the second stage: During the entire soft start-up process, the time constraint and the charge quantity constraint exist simultaneously. The drive logic is ultimately controlled by the "more stringent" constraint. When the reference quantity of the time constraint exceeds the reference of the charge quantity constraint (i.e., Tref > VCR_ref’), the system automatically switches to the second stage of the soft start-up.

[0058] In these two soft start-up stages, the resonant cavity overcurrent limit exists simultaneously, and the limit threshold OC_ref of the resonant current ILr gradually increases and no longer changes after the soft start-up ends.

[0059] Based on the same inventive concept, this application also provides a soft-start device for resonant circuits, corresponding to the soft-start method for resonant circuits, to implement the aforementioned soft-start method for resonant circuits.

[0060] Soft starters for resonant circuits include: The timer starts when the resonant current crosses zero and is reset at the falling edge of the drive. It is used to measure the drive conduction time after the resonant current crosses zero. The zero-crossing time reference threshold generation module is used to generate a zero-crossing time reference threshold in real time according to a preset time increase rate and the soft start time. The current timer comparator has a positive terminal input for the drive conduction time after the resonant current crosses zero, a reference terminal input for the zero-crossing time reference threshold, and an output level used to control the switch drive. The capacitor voltage reference threshold generation module is used to generate a capacitor voltage reference threshold in real time according to a preset voltage increase rate and soft start time. The charge-controlled comparator takes the resonant capacitor voltage as input at its positive terminal and the capacitor voltage reference threshold as input at its reference terminal. Its output level is used to control the switch drive.

[0061] In one possible implementation, the zero-crossing time reference threshold generation module is further configured to increase the preset time acceleration of the zero-crossing time reference threshold or update the zero-crossing time reference threshold to the maximum value of the zero-crossing time when the charge control comparator continuously outputs a second number of high levels. The capacitor voltage reference threshold generation module is also used to generate an initial capacitor voltage reference threshold, and when the charge control comparator continuously outputs a second number of high levels, the initial capacitor voltage reference threshold is increased according to a preset voltage growth rate with the soft start time, until the capacitor voltage reference threshold increases to the closed-loop charge reference threshold and remains unchanged.

[0062] In one possible implementation, the soft starter further includes an overcurrent limiting reference threshold generation module and a current limiting comparator. The overcurrent limit reference threshold generation module is used to generate an overcurrent limit reference threshold in real time according to the preset current growth rate and the soft start time, until the overcurrent limit reference threshold increases to the maximum value of the overcurrent limit and remains unchanged. The current limiting comparator has a positive input of resonant current, a reference input of overcurrent limiting reference threshold, and an output connected to a zero-crossing time reference threshold generation module and a capacitor voltage reference threshold generation module. The zero-crossing time reference threshold generation module is further configured to reduce the preset time acceleration of the zero-crossing time reference threshold or control the zero-crossing time reference threshold to remain unchanged when receiving a high-level signal output by the current limiting comparator, and restore the zero-crossing time reference threshold to its original state when receiving a first number of consecutive low-level signals output by the current limiting comparator. The capacitor voltage reference threshold generation module is further configured to reduce the preset voltage increase rate of the capacitor voltage reference threshold or control the capacitor voltage reference threshold to remain unchanged when receiving a high-level signal output by the current limiting comparator, and restore the capacitor voltage reference threshold to its original state when receiving a first number of consecutive low-level signals output by the current limiting comparator.

[0063] In one possible implementation, the soft starter further includes: The RS flip-flop has a set element for the dead-time timing end, a reset element for the result of an OR gate between the output level of the current timer comparator and the output level of the charge control comparator, and an output element for controlling the drive level.

[0064] The operating principle of a device or module for a soft starter used in resonant circuits is explained in one possible implementation.

[0065] See Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 As shown, Figure 5 This is a schematic diagram of the structure of a soft starter device for resonant circuits provided in an embodiment of this application. Figure 5 The soft starter in the device achieves soft start by simultaneously controlling three parameters: the drive conduction time after the current crosses zero, the resonant capacitor voltage, and the resonant current. The drive level is controlled by an RS trigger. Figure 6 This is a schematic diagram illustrating the working principle of the time constraint module provided in an embodiment of this application. Figure 6 In this module, a timer, a zero-crossing time reference threshold generation module, and a current timing comparator are used to implement time constraints for the switching transistors. Figure 7 This is a schematic diagram illustrating the working principle of the charge constraint module provided in an embodiment of this application. Figure 7 In this module, the capacitor voltage reference threshold generation module and the charge control comparator implement the charge constraint of the switching transistor. Figure 8 This is one of the working principle diagrams of the resonant current limiting module provided in the embodiments of this application. Figure 9 This is the second schematic diagram of the working principle of the resonant current limiting module provided in the embodiments of this application. Figure 8 and Figure 9In the middle, the overcurrent limiting reference threshold generation module and the current limiting comparator realize the limitation of the resonant current on the capacitor voltage reference threshold and the zero-crossing time reference threshold.

[0066] In practical use of soft starters, the outputs of the current timing comparator and the charge control comparator simultaneously affect the drive's shutdown signal. The output of the current limiting comparator does not directly participate in the drive's switching, but it does influence the increase of the overcurrent limit reference threshold and the capacitor voltage reference threshold. (Combined...) Figures 5-9 The working principle of one possible implementation of a soft starter for resonant circuits is explained: Time constraint module: The timer counter starts timing when the resonant current ISEN crosses zero and is reset at the falling edge of HG / LG. Therefore, the timer counter can obtain the drive conduction time Tc after the resonant current crosses zero. When this timing is greater than the zero-crossing time reference threshold Tref, the current timing comparator outputs a low level, causing the HG / LG level to decrease and triggering the drive to turn off. Figure 6 In the diagram, "HG / LG rst" indicates the turn-off time of HG / LG controlled by the output level of the current timer comparator. The zero-crossing time reference threshold Tref gradually increases with the soft-start time t. When the current limit comparator output goes high, generating a trigger signal cmp_oc, the circuit is in an overcurrent state. The current limit comparator sends the trigger signal cmp_oc to the zero-crossing time reference threshold generation module. At this time, the zero-crossing time reference threshold Tref will remain unchanged until the overcurrent state disappears, at which point Tref will return to its original state, remaining unchanged or continuing to increase. When Tref increases to a certain level, the drive will be triggered to shut down by the charge constraint module. At this point, the drive conduction time after the resonant current crosses zero is no longer greater than Tref. After this state persists for a period of time (for example, the resonant capacitor voltage is greater than the capacitor voltage reference threshold for 10 consecutive switching cycles), the system will determine that the charge constraint has taken over drive control, and Tref will increase to its maximum value Tref_A, causing the soft-start time constraint mechanism to exit.

[0067] Charge Constraint Module: In the initial stage of soft start, the capacitor voltage reference threshold remains unchanged. At this time, the resonant capacitor voltage has not yet reached the capacitor voltage reference threshold, and the drive is controlled by the time constraint module. Compared to using only the charge constraint module, the drive will shut down earlier. During this stage, the charge constraint module is in a "standby" state, and the capacitor voltage reference threshold remains unchanged. As the zero-crossing time reference threshold gradually increases with the soft start time, it gradually opens up, and the charge control comparator starts to go high and gradually takes over the drive control. This process occurs naturally with the soft start process, so there is no control switching issue. After the charge constraint takes over the drive control, its reference threshold VCR_ref will gradually increase. If the resonant cavity current is in an overcurrent state during this process, the current limiting comparator output goes high, generating a trigger signal cmp_oc. The current limiting comparator sends the trigger signal cmp_oc to the capacitor voltage reference threshold generation module. At this time, VCR_ref will remain unchanged until the current limiting state is released, at which point VCR_ref returns to its original state, remaining unchanged or continuing to increase. VCR_ref gradually increases with the soft-start time, while the closed-loop charge reference threshold VCR_ref_A mapped by the loop feedback VFB gradually decreases with the soft-start time. When VCR_ref and VCR_ref_A intersect, the system reaches closed loop, and the soft start ends. Figure 7 In this context, "HG / LGrst" indicates the time when the output level of the charge control comparator controls the turn-off of HG / LG.

[0068] The current limiting module compares the sampled value of the resonant current ISEN with the overcurrent limiting reference threshold OC_ref. When ISEN is greater than OC_ref, the current limiting comparator is triggered, the circuit is in an overcurrent state, the comparator output goes high, generating a trigger signal cmp_oc. The overcurrent state is latched and sent to the zero-crossing time reference threshold generation module and the capacitor voltage reference threshold generation module. This controls Tref and VCR_ref to remain at their current values ​​until the overcurrent state is lifted, at which point they will continue to increase. To better limit the start-up current, the overcurrent limiting reference threshold gradually increases with the soft-start time t until it reaches the normal overcurrent threshold (i.e., the maximum overcurrent limit), after which it remains unchanged. The overcurrent limiting reference threshold increases in various ways, including but not limited to continuous curves such as linear, quadratic, inverse proportional, and logarithmic increases, as well as step-by-step increases. This curve / step can typically be calculated by the digital core and output via a DAC, or it can be implemented analogically. Figure 8 In the middle, the overcurrent limit reference threshold increases with a linear function curve trend. Figure 9 In this process, the overcurrent limit reference threshold increases in a step-by-step manner.

[0069] Figure 5In this circuit, the set element (S) of the RS flip-flop indicates the end of the dead-time timing, the reset element (R) is the OR logic result of the output of the current timing comparator and the output of the charge control comparator, and the output element (Q) is compared with the primary-side MOSFET of the resonant circuit (e.g., Figure 1 The gate terminals of Q1 and Q2 in the circuit are connected to generate the driving PWM signal.

[0070] The outputs of the current timer comparator and the charge control comparator are ORed and then reset by an RS flip-flop. Therefore, if either the current timer comparator or the charge control comparator goes high, the drive will be turned off.

[0071] The embodiments of this application have the following characteristics: 1. The limitation of multiple control parameters can effectively suppress the current spikes in the resonant cavity during the startup phase, enabling the system to establish up quickly and stably.

[0072] 2. The phased soft start can adapt to different systems and applications. In the initial power-on stage, the resonant current is stabilized by time constraints. After switching to charge constraints, it can start up as quickly as possible while the power is controlled.

[0073] 3. The two stages can achieve a natural transition and smooth connection.

[0074] 4. By adding overcurrent limiting throughout the process, the soft start speed can be increased as much as possible while ensuring safe and reliable starting.

[0075] 5. The system variables required for steady-state control are used as control parameters, eliminating the need for additional sampling or hardware circuits.

[0076] This application also provides a circuit controller, including: The first unit is used to control the corresponding drive to turn off if the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold; wherein the zero-crossing time reference threshold increases with the soft start time according to a preset time growth rate. The second unit is used to control the corresponding drive to shut down if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold; wherein the capacitor voltage reference threshold changes with the soft start time according to a preset voltage increase.

[0077] In this embodiment of the application, the second unit is further configured to control the corresponding drive to shut down if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, and at the same time increase the preset time acceleration of the zero-crossing time reference threshold, or update the zero-crossing time reference threshold to the maximum value of the zero-crossing time; after the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold for the first time, control the capacitor voltage reference threshold to increase with the soft start time according to the preset voltage acceleration.

[0078] In this embodiment of the application, when the second unit executes the action of controlling the corresponding drive to shut down if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, it includes: If the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the drive of the upper transistor is turned off. After inserting the dead time, the drive of the lower transistor is turned on, and the conduction time of the lower transistor is controlled to be consistent with that of the upper transistor.

[0079] In this embodiment of the application, when the second unit executes the action of controlling the corresponding drive to shut down if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, it further includes: If the resonant capacitor voltage is greater than the upper transistor voltage reference threshold, the drive of the upper transistor is turned off; if the resonant capacitor voltage is less than the lower transistor voltage reference threshold, the drive of the lower transistor is turned off.

[0080] In this embodiment of the application, the circuit controller further includes: The third unit is configured to, if the resonant current is greater than the overcurrent limit reference threshold, reduce the preset time increase rate of the zero-crossing time reference threshold and reduce the preset voltage increase rate of the capacitor voltage reference threshold, or control the zero-crossing time reference threshold and the capacitor voltage reference threshold to remain unchanged until the resonant current is less than the overcurrent limit reference threshold for a consecutive first number of switching cycles, then release the restriction on the growth / maintenance of the zero-crossing time reference threshold and the capacitor voltage reference threshold; wherein, the overcurrent limit reference threshold increases with the soft-start time according to the preset current increase rate until it increases to the maximum value of the overcurrent limit and remains unchanged.

[0081] In this embodiment of the application, the circuit controller further includes: The fourth unit is used to control the corresponding drive to turn off if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold and the drive conduction time after the resonant current crosses zero is less than the zero-crossing time reference threshold, until the capacitor voltage amplitude is greater than the capacitor voltage reference threshold for a second consecutive number of switching cycles, then the control strategy of the second unit is executed.

[0082] This application also provides a chip including the circuit controller described above.

[0083] See Figure 10 As shown, Figure 10This is a schematic diagram of an electronic device provided in an embodiment of this application. The electronic device 1000 includes a processor 1001, a memory 1002, and a bus 1003. The memory 1002 stores machine-readable instructions executable by the processor 1001. When the electronic device is running, the processor 1001 communicates with the memory 1002 via the bus 1003. The processor 1001 executes the machine-readable instructions to perform the steps of the soft-start method for resonant circuits described above.

[0084] Specifically, the memory 1002 and processor 1001 described above can be general-purpose memory and processor, without any specific limitations. When the processor 1001 runs the computer program stored in the memory 1002, it can execute the soft-start method for resonant circuits described above.

[0085] Corresponding to the soft-start method for resonant circuits described above, this application also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps of the soft-start method for resonant circuits described above.

[0086] Finally, it should be noted that the above-described embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The scope of protection of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this application. Such modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A soft-start method for resonant circuits, characterized in that, The soft-start method includes: Simultaneously execute time constraint and charge constraint control to drive shutdown; The time constraint is as follows: if the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off; wherein, the zero-crossing time reference threshold increases with the soft start time according to a preset time growth rate. The charge constraint is as follows: if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the corresponding drive is controlled to shut down; wherein, the capacitor voltage reference threshold varies with the soft start time according to a preset voltage increase rate. The soft-start method further includes: If the resonant current is greater than the overcurrent limit reference threshold, then the preset time increase rate of the zero-crossing time reference threshold and the preset voltage increase rate of the capacitor voltage reference threshold are reduced, or the zero-crossing time reference threshold and the capacitor voltage reference threshold are kept constant until the resonant current is less than the overcurrent limit reference threshold for a first number of consecutive switching cycles, then the restriction on the growth / maintenance of the zero-crossing time reference threshold and the capacitor voltage reference threshold is lifted; wherein, the overcurrent limit reference threshold increases with the soft-start time according to the preset current increase rate until it increases to the maximum value of the overcurrent limit and remains constant.

2. The soft-start method for resonant circuits according to claim 1, characterized in that, The soft-start process is divided into two stages according to the sequence of time: Time-constrained dominant phase: If the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off; Charge constraint-dominated stage: If the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the corresponding drive is controlled to turn off, and the preset time acceleration of the zero-crossing time reference threshold is increased, or the zero-crossing time reference threshold is updated to the maximum value of the zero-crossing time. After the amplitude of the resonant capacitor voltage first exceeds the capacitor voltage reference threshold, the capacitor voltage reference threshold is controlled to increase with the soft start time according to a preset voltage growth rate. When the capacitor voltage reference threshold increases to be equal to the closed-loop charge reference threshold, the soft start ends.

3. The soft-start method for resonant circuits according to claim 1, characterized in that, The resonant circuit includes an upper transistor and a lower transistor as its switching transistors. The resonant circuit uses single-sided capacitor voltage control. If the amplitude of the resonant capacitor voltage exceeds a capacitor voltage reference threshold, the corresponding drive is controlled to shut down. This includes: If the resonant capacitor voltage is greater than the capacitor voltage reference threshold, the drive of the upper transistor is turned off. After inserting the dead time, the drive of the lower transistor is turned on, and the conduction time of the lower transistor is controlled to be consistent with that of the upper transistor.

4. The soft-start method for resonant circuits according to claim 1, characterized in that, The resonant circuit's switching transistors include an upper transistor and a lower transistor. The resonant circuit employs bilateral capacitor voltage control. The capacitor voltage reference threshold includes an upper transistor voltage reference threshold and a lower transistor voltage reference threshold. If the amplitude of the resonant capacitor voltage exceeds the capacitor voltage reference threshold, the corresponding drive is controlled to shut down, including: If the resonant capacitor voltage is greater than the upper transistor voltage reference threshold, the drive of the upper transistor is turned off; if the resonant capacitor voltage is less than the lower transistor voltage reference threshold, the drive of the lower transistor is turned off.

5. The soft-start method for resonant circuits according to claim 2, characterized in that, There is also a transition phase between the time-constrained dominant phase and the charge-constrained dominant phase: If the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, and the drive conduction time after the resonant current crosses zero is less than the zero-crossing time reference threshold, then the corresponding drive is controlled to turn off until the capacitor voltage amplitude is greater than the capacitor voltage reference threshold for a second consecutive number of switching cycles, then the charge constraint-dominated stage is entered.

6. A soft starter for resonant circuits, characterized in that, The soft starter includes: The timer starts when the resonant current crosses zero and is reset at the falling edge of the drive. It is used to measure the drive conduction time after the resonant current crosses zero. The zero-crossing time reference threshold generation module is used to generate a zero-crossing time reference threshold in real time according to a preset time increase rate and the soft start time. The current timer comparator has a positive terminal input for the drive conduction time after the resonant current crosses zero, a reference terminal input for the zero-crossing time reference threshold, and an output level used to control the switch drive. The capacitor voltage reference threshold generation module is used to generate a capacitor voltage reference threshold in real time according to a preset voltage increase rate and soft start time. A charge-controlled comparator whose positive terminal is input to the resonant capacitor voltage, whose reference terminal is input to the capacitor voltage reference threshold, and whose output level is used to control the switch drive. The zero-crossing time reference threshold generation module is also used to increase the preset time acceleration of the zero-crossing time reference threshold or update the zero-crossing time reference threshold to the maximum value of the zero-crossing time when the charge control comparator continuously outputs a second number of high levels. The capacitor voltage reference threshold generation module is also used to generate an initial capacitor voltage reference threshold, and when the charge control comparator continuously outputs a second number of high levels, the initial capacitor voltage reference threshold is increased according to a preset voltage growth rate with the soft start time, until the capacitor voltage reference threshold increases to the closed-loop charge reference threshold and remains unchanged.

7. The soft starter for resonant circuits according to claim 6, characterized in that, The soft starter also includes an overcurrent limiting reference threshold generation module and a current limiting comparator. The overcurrent limit reference threshold generation module is used to generate an overcurrent limit reference threshold in real time according to the preset current growth rate and the soft start time, until the overcurrent limit reference threshold increases to the maximum value of the overcurrent limit and remains unchanged. The current limiting comparator has a positive input of resonant current, a reference input of overcurrent limiting reference threshold, and an output connected to a zero-crossing time reference threshold generation module and a capacitor voltage reference threshold generation module. The zero-crossing time reference threshold generation module is further configured to reduce the preset time acceleration of the zero-crossing time reference threshold or control the zero-crossing time reference threshold to remain unchanged when receiving a high-level signal output by the current limiting comparator, and restore the zero-crossing time reference threshold to its original state when receiving a first number of consecutive low-level signals output by the current limiting comparator. The capacitor voltage reference threshold generation module is further configured to reduce the preset voltage increase rate of the capacitor voltage reference threshold or control the capacitor voltage reference threshold to remain unchanged when receiving a high-level signal output by the current limiting comparator, and restore the capacitor voltage reference threshold to its original state when receiving a first number of consecutive low-level signals output by the current limiting comparator.

8. A circuit controller, characterized in that, include: The first unit is used to control the corresponding drive to turn off if the drive conduction time after the resonant current crosses zero is greater than the zero-crossing time reference threshold; wherein the zero-crossing time reference threshold increases with the soft start time according to a preset time growth rate. The second unit is used to control the corresponding drive to shut down if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold; wherein the capacitor voltage reference threshold changes with the soft start time according to a preset voltage increase rate. The second unit is also used to control the corresponding drive to shut down if the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold, and at the same time increase the preset time acceleration of the zero-crossing time reference threshold, or update the zero-crossing time reference threshold to the maximum value of the zero-crossing time; after the amplitude of the resonant capacitor voltage is greater than the capacitor voltage reference threshold for the first time, control the capacitor voltage reference threshold to increase with the soft start time according to the preset voltage acceleration.

9. A circuit controller according to claim 8, characterized in that, The circuit controller further includes: The third unit is configured to, if the resonant current is greater than the overcurrent limit reference threshold, reduce the preset time increase rate of the zero-crossing time reference threshold and reduce the preset voltage increase rate of the capacitor voltage reference threshold, or control the zero-crossing time reference threshold and the capacitor voltage reference threshold to remain unchanged until the resonant current is less than the overcurrent limit reference threshold for a consecutive first number of switching cycles, then release the restriction on the growth / maintenance of the zero-crossing time reference threshold and the capacitor voltage reference threshold; wherein, the overcurrent limit reference threshold increases with the soft-start time according to the preset current increase rate until it increases to the maximum value of the overcurrent limit and remains unchanged.

10. A chip, characterized in that, Including the circuit controller as described in any one of claims 8-9.

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