Resonant circuit output current stability control method, device and chip

Abstract

The application provides a resonant circuit output current stability control method, device and chip, relates to the technical field of power electronics, and the method comprises the following steps: acquiring a voltage change value of a resonant capacitor voltage in a specified half switching period; in the specified half switching period, an integral quantity of excitation current is zero; determining a sampling value and a reference value of constant current control according to the resonant capacitor voltage change value, a numerical relationship between an output current and the resonant capacitor voltage change value and a rated output current; the numerical relationship is that the output current is equal to the ratio of the product of the number of turns of a primary winding, the resonant capacitor and the resonant capacitor voltage change value to the product of the number of turns of a secondary winding and a switching period; and generating a driving control signal based on the difference between the sampling value and the reference value, so that the real-time output current is equal to the rated output current. The application constructs the numerical relationship between the output current and the resonant capacitor voltage change value, and realizes high-precision output current constant current control by using the resonant capacitor voltage sampled at a specific moment.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a method, device and chip for stabilizing the output current of a resonant circuit. Background Technology

[0002] Resonant circuits are widely used in communication power supplies, new energy, electric vehicle charging, industrial power supplies, and lighting technologies. In recent years, with the deepening of application scenarios, higher requirements have been placed on the output performance of these circuits. The inherent nonlinear gain characteristics of resonant circuits often lead to unstable output current, necessitating constant current control.

[0003] The mainstream approach to constant current control in resonant circuits has traditionally involved sampling the secondary-side output current and establishing a closed-loop feedback system to adjust the switching frequency or duty cycle. While this approach is direct and effective, it requires adding a high-precision current sampling circuit and an isolated feedback channel to the secondary side, resulting in a complex system and high current stabilization costs.

[0004] To overcome the shortcomings of secondary-side sampling, the industry has also proposed a scheme to achieve constant current control of the output through the primary-side resonant cavity current. However, this scheme requires sampling multiple parameters such as input voltage, output voltage, resonant current, and excitation current, and performing very complex calculations on the sampled values ​​of these parameters in a short period of time, which still requires high hardware and software costs. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a method, device and chip for stabilizing the output current of a resonant circuit, which establishes a numerical relationship between the output current and the change in the resonant capacitor voltage. By using the resonant capacitor voltage sampled at a specific time, high-precision constant current control of the output current can be achieved without complex real-time calculations and high hardware costs.

[0006] In a first aspect, embodiments of this application provide a method for stabilizing the output current of a resonant circuit, the method comprising:

[0007] Obtain the voltage change of the resonant capacitor voltage within a specified half-switching cycle; wherein, within the specified half-switching cycle, the integral of the excitation current is zero; Based on the resonant capacitor voltage change, the numerical relationship between the output current and the resonant capacitor voltage change, and the rated output current, the sampling value and reference value for constant current control are determined; wherein, the numerical relationship between the output current and the resonant capacitor voltage change is: the output current is equal to twice the product of the number of turns in the primary winding, the resonant capacitor, and the resonant capacitor voltage change, and the product of the number of turns in the secondary winding and the switching cycle. Based on the difference between the sampled value and the reference value, a drive control signal for the switching transistor is generated to make the real-time output current consistent with the rated output current.

[0008] In one possible implementation, when the switching frequency is greater than or equal to the resonant frequency, the resonant circuit is in an over-resonance state, and the start and end times of the specified half-switching cycle are respectively: the moment when the resonant current and the excitation current are equal in the negative current cycle and the moment when the resonant current and the excitation current are equal in the positive current cycle; when the switching frequency is less than the resonant frequency, the resonant circuit is in an under-resonance state, and the start and end times of the specified half-switching cycle are respectively: the midpoint moment when the resonant current and the excitation current are continuously equal in the negative current cycle and the midpoint moment when the resonant current and the excitation current are continuously equal in the positive current cycle, or the start moment when the resonant current and the excitation current are continuously equal in the negative current cycle and the end moment when the resonant current and the excitation current are continuously equal in the positive current cycle.

[0009] In one possible implementation, determining the sampled value and reference value for constant current control based on the resonant capacitor voltage change, the numerical relationship between the output current and the resonant capacitor voltage change, and the rated output current includes: Based on the numerical relationship between the output current and the change in resonant capacitor voltage, the change in resonant capacitor voltage is converted into a real-time output current, the real-time output current is determined as a sampled value, and the rated output current is determined as a reference value; or, based on the numerical relationship between the output current and the change in resonant capacitor voltage, the rated output current is converted into a standard resonant capacitor voltage change value, the standard resonant capacitor voltage change value is determined as a reference value, and the resonant capacitor voltage change value is determined as a sampled value.

[0010] In one possible implementation, when bilateral sampling is used to acquire the resonant capacitor voltage, acquiring the voltage change value of the resonant capacitor voltage within a specified half-switching cycle includes: Obtain the times when the voltage surge inflection point and the voltage drop inflection point occur in the auxiliary winding of the transformer in the resonant circuit; If the resonant circuit is in an over-resonance state, the voltage surge inflection point and the voltage drop inflection point within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time; if the resonant circuit is in an under-resonance state, the midpoint of two consecutive voltage surge inflection points and the midpoint of two consecutive voltage drop inflection points within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time, or the first voltage surge inflection point and the second voltage drop inflection point within two consecutive voltage surge inflection points within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time. The resonant capacitor voltage is sampled at the start time and the end time of the voltage sampling, and the difference between the sampled resonant capacitor voltages is determined as the change value of the resonant capacitor voltage.

[0011] In one possible implementation, when using single-sided sampling to acquire the resonant capacitor voltage, acquiring the voltage change value of the resonant capacitor voltage within a specified half-switching cycle includes: Obtain the moment when the voltage drop inflection point of the transformer auxiliary winding of the resonant circuit occurs; If the resonant circuit is in an over-resonance state, the voltage drop inflection point is taken as the voltage sampling time; if the resonant circuit is in an under-resonance state, the midpoint of two consecutive voltage drop inflection points within the same switching cycle is taken as the voltage sampling time, or the second voltage drop inflection point among two consecutive voltage drop inflection points within the same switching cycle is taken as the voltage sampling time. The resonant capacitor voltage is sampled at the voltage sampling time, and the value of twice the resonant capacitor voltage, or the difference between twice the resonant capacitor voltage and the bias voltage, is determined as the resonant capacitor voltage change value.

[0012] In one possible implementation, if the resonant circuit is in an over-resonance state, any moment within the dead time when the lower transistor is turned off and the upper transistor is turned on is determined as the voltage sampling start time, or the moment when the upper transistor is turned on is determined as the voltage sampling start time.

[0013] In one possible implementation, the operating state of the resonant circuit is determined using any of the following methods: If the current switching frequency is greater than or equal to the resonant frequency, the resonant circuit operates in an over-resonance state; if the current switching frequency is less than the resonant frequency, the resonant circuit operates in an under-resonance state. If the voltage inflection point of the auxiliary winding voltage occurs within any dead time period driven by the primary-side switch, then the operating state of the resonant circuit is over-resonance; otherwise, the operating state of the resonant circuit is under-resonance. If an auxiliary winding voltage inflection point occurs within half a switching cycle, the resonant circuit operates in an over-resonance state; if two auxiliary winding voltage inflection points occur within half a switching cycle, the resonant circuit operates in an under-resonance state.

[0014] In one possible implementation, the rated output current is a variable.

[0015] Secondly, embodiments of this application provide a resonant circuit output current stabilization device, the device comprising: The resonant capacitor voltage change value acquisition module is used to acquire the voltage change value of the resonant capacitor within a specified half-switching cycle; The sampling value or reference value calculation module is used to calculate the sampling value or reference value of constant current control based on the change value of resonant capacitor voltage or rated output current, and the numerical relationship between output current and change value of resonant capacitor voltage. The constant current loop control module is used to generate a drive control signal for the switching transistor based on the difference between the sampled value and the reference value.

[0016] In one possible implementation, the sampling value or reference value calculation module is used to convert the change value of the resonant capacitor voltage into a real-time output current based on the numerical relationship between the output current and the change value of the resonant capacitor voltage, and send the real-time output current to the constant current loop control module. The constant current loop control module is also used to take the received real-time output current as a sample value and the input rated output current as a reference value.

[0017] In one possible implementation, the device further includes an inflection point detection module and a sampling time determination module; The inflection point detection module is used to detect the voltage inflection point of the transformer auxiliary winding of the resonant circuit. The sampling time determination module is used to determine the voltage sampling time of the resonant capacitor voltage based on the occurrence time of the voltage inflection point of the auxiliary winding. The module for obtaining the voltage change value of the resonant capacitor is also used to sample the voltage of the resonant capacitor at the voltage sampling time and calculate the voltage change value of the resonant capacitor.

[0018] In one possible implementation, the device further includes a rated output current determination module for generating a rated output current based on a light intensity signal or an external temperature.

[0019] Thirdly, embodiments of this application provide a chip including the resonant circuit output current stabilization device described in any of the second aspects.

[0020] This application provides a method, device, and chip for stabilizing the output current of a resonant circuit. By combining the voltage inflection point information of the transformer auxiliary winding, the method samples the natural current integral signal of the resonant capacitor voltage at a specific sampling time. After performing simple calculations with the sampled resonant capacitor voltage signal and fixed parameters such as the current switching cycle, the number of turns on the primary and secondary sides of the transformer, and the resonant capacitor, the method accurately estimates the real-time output current. Based on the difference between the real-time output current and the rated output current, the method controls the drive of the switching transistor to achieve high-precision constant current control of the output current.

[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 A flowchart of the output current stabilization method for resonant circuits provided in an embodiment of this application is shown; Figure 2 The topology of the half-bridge LLC resonant circuit provided in the embodiment of this application is shown; Figure 3 The diagram shows the operating waveform of the half-bridge LLC resonant circuit in the over-resonance state provided in the embodiment of this application. Figure 4 This paper shows one of the operating waveforms of the half-bridge LLC resonant circuit in the underresonance state provided in an embodiment of this application. Figure 5 This shows the second waveform diagram of the under-resonance state of the half-bridge LLC resonant circuit provided in the embodiment of this application; Figure 6 The following diagrams illustrate the operating waveforms of the resonant capacitor voltage under different sampling methods provided in the embodiments of this application. Figure 7 A schematic diagram of the voltage drop inflection point detection circuit provided in an embodiment of this application is shown; Figure 8 This paper shows one of the structural schematic diagrams of the resonant circuit output current stabilization device provided in an embodiment of this application; Figure 9This is a second schematic diagram of the structure of the resonant circuit output current stabilization device provided in an embodiment of this application; Figure 10 The third schematic diagram shows the structure of the resonant circuit output current stabilization device provided in the embodiments of this application. 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. The described embodiments are only some embodiments of this application, and not all embodiments. 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] In practice, resonant circuits inherently possess nonlinear gain characteristics, which often leads to unstable output current, necessitating constant current control. The mainstream approach for achieving constant current control in resonant circuits has traditionally been to sample the secondary-side output current and construct a closed-loop feedback system to adjust the switching frequency or duty cycle. While this approach is direct and effective, it requires adding a high-precision current sampling circuit and an isolated feedback channel on the secondary side, resulting in a complex system and high current stabilization costs.

[0026] To overcome the shortcomings of secondary-side sampling, the industry has also proposed a scheme to achieve constant current control of the output through the primary-side resonant cavity current. However, this scheme requires sampling multiple parameters such as input voltage, output voltage, resonant current, and excitation current, and performing very complex calculations on the sampled values ​​of these parameters in a short period of time, which still requires high hardware and software costs.

[0027] To address the aforementioned issues, this application provides a method, device, and chip for stabilizing the output current of a resonant circuit. By combining the voltage inflection point information of the transformer auxiliary winding, the inherent current integral signal of the resonant capacitor voltage is sampled at a specific sampling time. After performing simple calculations with the sampled resonant capacitor voltage signal, the current switching cycle, and fixed parameters such as the number of turns on the primary and secondary sides of the transformer and the resonant capacitor, the real-time output current is accurately estimated. Based on the difference between the real-time output current and the rated output current, the switching transistor is driven and controlled to achieve high-precision constant current control of the output current.

[0028] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0029] See Figure 1 As shown, Figure 1 A flowchart of a method for stabilizing the output current of a resonant circuit provided in this application embodiment is shown. The method includes the following steps: S1: Obtain the voltage change value of the resonant capacitor voltage within a specified half-switching cycle; wherein, within the specified half-switching cycle, the integral of the excitation current is zero; S2: Based on the resonant capacitor voltage change value, the numerical relationship between the output current and the resonant capacitor voltage change value, and the rated output current, determine the sampling value and reference value for constant current control; wherein, the numerical relationship between the output current and the resonant capacitor voltage change value is: the output current is equal to twice the product of the number of turns in the primary winding, the resonant capacitor, and the resonant capacitor voltage change value, and the product of the number of turns in the secondary winding and the switching cycle. S3: Based on the difference between the sampled value and the reference value, generate a drive control signal for the switching transistor so that the real-time output current matches the rated output current.

[0030] This application's embodiments calculate the real-time output current based on the real-time sampled resonant capacitor voltage. By comparing the deviation between the real-time output current and the rated output current, the drive control signal of the switching transistor is adjusted. Alternatively, the rated output current is converted into a standard resonant capacitor voltage change value, and the drive control signal of the switching transistor is adjusted by comparing the deviation between the resonant capacitor voltage change value and the standard resonant capacitor voltage change value, thereby achieving constant current output from the circuit. Taking a half-bridge LLC resonant circuit as an example, the numerical relationship between the output current and the resonant capacitor voltage change value is illustrated.

[0031] See Figure 2 As shown, Figure 2 The topology of the half-bridge LLC resonant circuit provided in the embodiments of this application is as follows: Figure 2 In the diagram, 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, and Vo is the output voltage.

[0032] In resonant circuits, there is a natural integral relationship between the resonant capacitor voltage and the resonant current:

[0033] Where t1 and t2 are arbitrary times and t2>t1, This represents the resonant current at any given time. This represents the change in the resonant capacitor voltage VCR within the time range of [t1, t2].

[0034] The difference between the resonant current and the excitation current is the current transmitted to the secondary side:

[0035] in, Let Np and Ns represent the excitation current at any given time, and Np and Ns be the number of turns in the primary and secondary windings of the transformer, respectively. This represents the secondary current at any given time.

[0036] The output current Iout is the secondary current. Integrals:

[0037] The operating states of resonant circuits include over-resonance and under-resonance states, when the switching frequency f sw Greater than or equal to the resonant frequency f r At this time, resonant circuits are in an over-resonance state, when the switching frequency f sw Less than the resonant frequency f r At this time, resonant circuits are in an underresonant state. The resonant frequency is... .

[0038] When a resonant circuit is in an over-resonance state, see [link / reference]. Figure 3 As shown, Figure 3 The waveform diagram of the over-resonance state of the half-bridge LLC resonant circuit provided in the embodiments of this application is shown in the following figure. Figure 3 From top to bottom, the figures are: the waveform of the resonant capacitor voltage VCR changing with time t, and the resonant current. and excitation current The waveforms of the transformer auxiliary winding voltage VAUX changing with time t, the waveforms of the driving voltage HG of the upper tube Q1 changing with time t, and the waveforms of the driving voltage LG of the lower tube Q2 changing with time t.

[0039] exist Figure 3 In the context of a specified half-switching cycle (taking the time interval [t_aux1, t_aux2] as an example), the resonant current... and excitation current The area enclosed (S2+S3) can reflect the output current Iout and the resonant current. The integral area over the time interval [t_aux1, t_aux2] is (-S1+S3+S4), due to the excitation current. There exists a symmetry within the time interval [t_aux1, t_aux2], which is due to... The resulting area satisfies S4 = S1 + S2. Substituting "S4 = S1 + S2" into "-S1 + S3 + S4" allows us to determine the resonant current. The integral area (-S1+S3+S4) over the time interval [t_aux1,t_aux2] is represented as (S2+S3), and Tsw represents the switching period. Therefore, the following numerical relationship exists:

[0040] Accordingly, 1 / Cr is a constant, and Transformed into:

[0041] A numerical relationship between the output current and the change in resonant capacitor voltage can be derived:

[0042] In the time interval [t_aux1, t_aux2], t_aux1 represents the moment when the resonant current equals the excitation current during the negative current cycle, and t_aux2 represents the moment when the resonant current equals the excitation current during the positive current cycle. When the resonant circuit is in an over-resonance state, the voltage change of the resonant capacitor voltage within a specified half-switching cycle is expressed as follows: .

[0043] It should be noted that "negative current period" refers to the time range during which the resonant current is negative, while "positive current period" refers to the time range during which the resonant current is positive.

[0044] When a resonant circuit is in an underresonant state, see [link to relevant documentation]. Figure 4 As shown, Figure 4 This is one of the waveform diagrams showing the underresonance state of the half-bridge LLC resonant circuit provided in an embodiment of this application. Figure 4 In the context of a specified half-switching cycle (taking the time interval [t_aux1', t_aux2'] as an example), the resonant current... and excitation current The area enclosed (S4+S5) can reflect the output current Iout and the resonant current. The integral area over the time interval [t_aux1', t_aux2'] is (-S2-S3+S5+S6+S1'). Let S1=S1'≈S2=S2', then the excitation current... There exists an approximate symmetry within the time interval [t_aux1', t_aux2'], due to... The resulting area satisfies S2+S3+S4=S6+S1'. Substituting "S1'=S2+S3+S4-S6" into "-S2-S3+S5+S6+S1'", the resonant current can be reduced. The integral area (-S2-S3+S5+S6+S1') over the time interval [t_aux1',t_aux2'] is represented as (S4+S5). Therefore, the following numerical relationship exists:

[0045] Accordingly, Transformed into:

[0046] A numerical relationship between the output current and the change in resonant capacitor voltage can be derived:

[0047] In the time interval [t_aux1', t_aux2'], t_aux1' represents the midpoint of the period during which the resonant current and the excitation current are continuously equal, and t_aux2' represents the midpoint of the period during which the resonant current and the excitation current are continuously equal. When the resonant circuit is in an under-resonant state, the voltage change of the resonant capacitor voltage within a specified half-switching cycle is expressed as follows: .

[0048] and All of these were obtained using a symmetrical sampling method. The above derivation is performed under the underresonant state. and The numerical relationship involves approximate calculations, resulting in a very small error in the derivation. To make the numerical relationship between the output current and the resonant capacitor voltage change more accurate and to eliminate this very small error, an asymmetric sampling method is used to sample the resonant capacitor voltage. (See also...) Figure 5 As shown, Figure 5 The second waveform diagram of the under-resonance state of the half-bridge LLC resonant circuit provided in the embodiments of this application.

[0049] exist Figure 5 In the middle, the resonant current The integral area over the time interval [t_aux3, t_aux6] is (-S1-S2-S3+S5+S6+S1'+S2'), and the excitation current is... There exists a symmetry within the time interval [t_aux3, t_aux6], which is due to... The resulting area satisfies S1+S2+S3+S4=S6+S1'+S2'. Substituting "S1'+S2'=S1+S2+S3+S4-S6" into "-S1-S2-S3+S5+S6+S1'+S2'", the resonant current can be reduced. The integral area (-S1-S2-S3+S5+S6+S1'+S2') over the time interval [t_aux3,t_aux6] is represented as (S4+S5). Therefore, the following numerical relationship exists:

[0050] Accordingly, Transformed into:

[0051] A numerical relationship between the output current and the change in resonant capacitor voltage can be derived:

[0052] In the time interval [t_aux3, t_aux6], t_aux3 represents the start time when the resonant current and the excitation current are continuously equal during the negative current cycle, and t_aux6 represents the end time when the resonant current and the excitation current are continuously equal during the positive current cycle. When the resonant circuit is in an under-resonant state, the voltage change of the resonant capacitor voltage during the time interval [t_aux3, t_aux6] is expressed as follows: Although the time interval [t_aux3, t_aux6] is not half a switching cycle, but actually longer than half a switching cycle, and The numerical relationship is and The correction of the approximate numerical relationship has certain practical value. In order to unify the terminology, in the embodiments of this application, [t_aux3,t_aux6] is also referred to as the specified half-switching cycle.

[0053] In this embodiment, when the circuit is in an over-resonance state, "specified half-switching cycle" refers to the time from "the moment when the resonant current and the excitation current are equal in the negative current cycle" to "the moment when the resonant current and the excitation current are equal in the positive current cycle". When the circuit is in an under-resonance state, since the resonant current and the excitation current will be equal for a period of time, "specified half-switching cycle" refers to the time from "the midpoint of the continuous equality of the resonant current and the excitation current in the negative current cycle" to "the midpoint of the continuous equality of the resonant current and the excitation current in the positive current cycle", or "the beginning of the continuous equality of the resonant current and the excitation current in the negative current cycle" to "the end of the continuous equality of the resonant current and the excitation current in the positive current cycle".

[0054] In summary and Numerical relationships and Numerical relationships and From the numerical relationship, we can deduce that there is a numerical relationship between the output current and the change in resonant capacitor voltage in any operating state of a resonant circuit:

[0055] in, This represents the voltage change of the resonant capacitor voltage within a specified half-switching cycle under any operating state of a resonant circuit.

[0056] Since the number of turns Np and Ns of the transformer primary and secondary windings, as well as the resonant capacitance Cr, are fixed parameters, in order to reduce the computational complexity, we will... Abstracted into a fixed coefficient k, we get .

[0057] The above derivation process of the "numerical relationship between the output current and the change in the resonant capacitor voltage" in step S2, taking a half-bridge LLC resonant circuit as an example, is also applicable to any resonant circuit in which the integral area of ​​the excitation current within a "specified half-switching cycle" is zero or approximately zero, such as an LC series resonant circuit.

[0058] The specific implementation methods of steps S1 to S3 are described below.

[0059] S1: Obtain the voltage change value of the resonant capacitor voltage within a specified half-switching cycle; wherein, within the specified half-switching cycle, the integral of the excitation current is zero.

[0060] When the circuit is in an over-resonance state, obtain the resonant capacitor voltage change value from "the moment when the resonant current and the excitation current are equal during the negative current cycle" to "the moment when the resonant current and the excitation current are equal during the positive current cycle".

[0061] When the circuit is in an underresonant state, obtain the change value of the resonant capacitor voltage from the "midpoint of the time when the resonant current and the excitation current are continuously equal during the negative current cycle" to the "midpoint of the time when the resonant current and the excitation current are continuously equal during the positive current cycle", or obtain the change value of the resonant capacitor voltage from the "start of the time when the resonant current and the excitation current are continuously equal during the negative current cycle" to the "end of the time when the resonant current and the excitation current are continuously equal during the positive current cycle".

[0062] It should be noted that there is a numerical ratio between the actual sampled resonant capacitor voltage and the true resonant capacitor voltage. It is necessary to preset the sampling ratio coefficient of the resonant capacitor voltage, and the product of the sampled resonant capacitor voltage and this ratio coefficient is taken as the true resonant capacitor voltage.

[0063] S2: Determine the sampling value and reference value of constant current control based on the resonant capacitor voltage change value, the numerical relationship between the output current and the resonant capacitor voltage change value, and the rated output current; wherein, the numerical relationship between the output current and the resonant capacitor voltage change value is: the output current is equal to twice the product of the number of turns of the primary winding, the resonant capacitor, and the resonant capacitor voltage change value, and the product of the number of turns of the secondary winding and the switching cycle.

[0064] Based on the numerical relationship between the output current and the change in resonant capacitor voltage, the change in resonant capacitor voltage obtained in step S1 can be converted into real-time output current, and the real-time output current can be used as the sampled value, while the rated output current can be used as the reference value; alternatively, the rated output current can be converted into the change in standard resonant capacitor voltage, and the change in standard resonant capacitor voltage can be used as the reference value, while the change in resonant capacitor voltage obtained in S1 can be used as the sampled value.

[0065] The aforementioned rated output current refers to the current that a resonant circuit needs to output stably. It can be a constant or a variable. Embodiments of this application can be applied to scenarios such as LED dimming and battery charging. For example, the LED luminous intensity can be controlled by adjusting the rated output current. Therefore, when it is necessary to change the LED luminous intensity, the rated output current is dynamically adjusted to a current magnitude that matches the LED luminous intensity. The rated output current can also be dynamically adjusted according to the external temperature; for example, the higher the external temperature, the lower the rated output current, thereby achieving derating operation due to overheating.

[0066] S3: Based on the difference between the sampled value and the reference value, generate a drive control signal for the switching transistor so that the real-time output current matches the rated output current.

[0067] In practice, a constant current loop controller is used to generate the drive control signal. This constant current loop controller is also called a constant current circuit. Loop control refers to PID (Proportional-Integral-Derivative) control in engineering, or a simplified PI (Proportional-Integral) control, or a further simplified I (Integral) control. The constant current loop calculates the difference between the reference value and the sampled value, and the error is used to generate the drive control signal through the PID (or PI or I) circuit. The magnitude of the drive control signal maps to the control quantity of the drive. For example, if it controls the conduction time, a larger drive control signal value results in a longer conduction time. If it is charge-type control, a larger drive control signal value results in a higher reference voltage for the VCR. In short, the magnitude of the drive control signal is positively correlated with the output power.

[0068] It should be noted that the closed-loop control of the current loop does not restrict whether it works in conjunction with other loops (such as the output voltage loop) after the output drive control signal. Furthermore, the current loop can be applied to different drive conduction control schemes, including but not limited to bilateral charge control, single-sided charge control, direct frequency control, conduction time control, duty cycle control, time shift control, phase shift control, etc.

[0069] Furthermore, when executing step S1 to obtain the voltage change value of the resonant capacitor voltage within a specified half-switching cycle, the key is how to accurately locate the start and end times of the "specified half-switching cycle". In this embodiment, an auxiliary winding is added to the secondary side of the transformer in the resonant circuit. The "specified half-switching cycle" is located based on the occurrence time of the voltage inflection point of the auxiliary winding, and the sampling of the resonant capacitor voltage is completed at the located time.

[0070] The sampling methods for resonant capacitor voltage include bilateral sampling and single-sided sampling. Single-sided sampling is a simplification of bilateral sampling, where the resonant capacitor voltage is de-DC-diverted before single-sided sampling. A bias voltage can also be superimposed on the single-sided sampling. For bilateral sampling, the start and end times of the "specified half-switching cycle" need to be clearly defined. The difference between the resonant capacitor voltage sampled at the end time and the resonant capacitor voltage sampled at the start time is taken as the resonant capacitor voltage change value. For single-sided sampling, only the end time of the "specified half-switching cycle" needs to be clearly defined. Either twice the resonant capacitor voltage sampled at the end time is taken as the resonant capacitor voltage change value, or the difference between twice the resonant capacitor voltage sampled at the end time and the bias voltage is taken as the resonant capacitor voltage change value.

[0071] See Figure 6 As shown, Figure 6 The diagram shows the operating waveforms of the resonant capacitor voltage under different sampling methods provided in the embodiments of this application. Figure 6 In the image, from top to bottom, are the working waveforms of the resonant capacitor voltage with bilateral sampling, the working waveform of the resonant capacitor voltage with single-sided sampling, and the working waveform of the resonant capacitor voltage with single-sided sampling and superimposed bias voltage. Figure 6 In this context, t_aux1 represents the start time of the "specified half-switching cycle", t_aux2 represents the end time of the "specified half-switching cycle", VCR_aux1 represents the resonant capacitor voltage sampled at the start time of the "specified half-switching cycle", and VCR_aux2 represents the resonant capacitor voltage sampled at the end time of the "specified half-switching cycle". This represents the change in resonant capacitor voltage within a specified half-switching cycle. When using bilateral sampling, =VCR_aux2-VCR_aux1, when using single-sided sampling =2·VCR_aux2, when using single-sided sampling and superimposing the bias voltage Voffset =2·VCR_aux2-Voffset.

[0072] When bilateral sampling is used, step S1, in acquiring the voltage change value of the resonant capacitor voltage within a specified half-switching cycle, includes steps S111-S113: S111: Obtain the time of voltage surge inflection point and voltage drop inflection point of the transformer auxiliary winding of the resonant circuit.

[0073] Resonant circuits include a transformer, with an auxiliary winding added to the secondary side of the transformer. The voltage waveform of the auxiliary winding exhibits multiple inflection points, including the inflection point where the voltage value changes from "rising" to "remaining constant," the inflection point where the voltage value changes from "remaining constant" to "falling," the inflection point where the voltage value changes from "falling" to "remaining constant," and the inflection point where the voltage value changes from "remaining constant" to "falling" is called the "voltage decrease inflection point," and the inflection point where the voltage value changes from "remaining constant" to "rising" is called the "voltage increase inflection point." Correspondingly, the moment when the voltage value changes from "remaining constant" to "falling" is called the "voltage decrease inflection point occurrence time," and the moment when the voltage value changes from "remaining constant" to "rising" is called the "voltage increase inflection point occurrence time."

[0074] Figure 2 In this circuit, an auxiliary winding is added to the secondary side of the transformer. VAUX is the voltage of the auxiliary winding. The LLC controller collects the resonant capacitor voltage VCR and the auxiliary winding voltage VAUX from the circuit, and controls the circuit to output constant current based on these two parameters. Specifically, it adjusts the driving voltage HG of the upper tube Q1 and the driving voltage LG of the lower tube Q2, so that the real-time output current is consistent with the rated output current.

[0075] As one possible implementation method, see Figure 7 As shown, Figure 7 This is a schematic diagram of the voltage drop inflection point detection circuit provided in the embodiments of this application. Figure 7 In this diagram, "Cmp+" represents the voltage after VAUX has been filtered by the filter circuit, and "Cmp-" represents the voltage after VAUX has been superimposed with a fixed bias (V_bias). "Cmp+" is connected to the positive terminal of the comparator, and "Cmp-" is connected to the negative terminal. "Cmp+" will have a delay after filtering, while "Cmp-" will follow the slope change in real time. When "Cmp+" is higher than "Cmp-", the comparator output flips to a high level, identifying the "voltage drop inflection point". Figure 7 The "VAUX_knee" parameter defines the moment when the output flips to a high level as the "voltage drop inflection point occurrence time". Figure 7By swapping the positive and negative terminals of the comparator, a voltage surge inflection point detection circuit is obtained, which can identify the "voltage surge inflection point" and obtain the "time when the voltage surge inflection point occurs".

[0076] When the circuit is in an overresonant state, there is one voltage surge inflection point and one voltage drop inflection point within one switching cycle; when the circuit is in an underresonant state, there are two consecutive voltage surge inflection points and two consecutive voltage drop inflection points within one switching cycle. Taking the inflection points within any switching cycle as an example, in... Figure 3 In the diagram, point a represents the "voltage surge inflection point," and point b represents the "voltage decrease inflection point." Figure 4 In the diagram, points c and d represent "voltage surge inflection points", and points e and f represent "voltage decrease inflection points".

[0077] S112: If the resonant circuit is in an over-resonance state, the voltage surge inflection point and the voltage drop inflection point within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time; if the resonant circuit is in an under-resonance state, the midpoint of two consecutive voltage surge inflection points and the midpoint of two consecutive voltage drop inflection points within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time, or the first voltage surge inflection point and the second voltage drop inflection point within two consecutive voltage surge inflection points within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time.

[0078] exist Figure 3 In the diagram, point a corresponds to time point t_aux1, which represents the "time when the voltage surge inflection point occurs", and point b corresponds to time point t_aux2, which represents the "time when the voltage decrease inflection point occurs". Figure 3 The circuit is in an over-resonance state. t_aux1 is taken as the start time of voltage sampling, and t_aux2 is taken as the end time of voltage sampling.

[0079] exist Figure 4 In the diagram, the time points corresponding to points c and d are t_aux3 and t_aux4, which represent two consecutive "voltage surge inflection points". The time points corresponding to points e and f are t_aux5 and t_aux6, which represent two consecutive "voltage decrease inflection points". Figure 4The circuit is in an underresonant state. t_aux1' is the midpoint of t_aux3 and t_aux4, t_aux1'=(t_aux3+t_aux4) / 2. t_aux2' is the midpoint of t_aux5 and t_aux6, t_aux2'=(t_aux5+t_aux6) / 2. t_aux1' is taken as the start time of voltage sampling, and t_aux2' is taken as the end time of voltage sampling. Figure 5 The circuit is also in an under-resonance state. t_aux3 is taken as the start time of voltage sampling and t_aux6 is taken as the end time of voltage sampling.

[0080] In practical engineering, when a circuit is in an underresonant state, the midpoint time between two consecutive voltage surge inflection points (or voltage decrease inflection points) can be obtained using the "first inflection point + delay" method. For example, the time difference between two consecutive inflection points can be recorded, and this time difference divided by 2 can be used as the delay time after the first inflection point. Since the time difference between two consecutive inflection points is very short, any time between two consecutive voltage surge inflection points (or voltage decrease inflection points) can also be approximated as the midpoint time and used as the voltage sampling time.

[0081] Optionally, when the resonant circuit is in an over-resonance state, the voltage sampling start time can be approximated using the switching transistor information: any moment within the dead time when the lower transistor Q2 is turned off and the upper transistor Q1 is turned on can be used as the voltage sampling start time. This "any moment" can be randomly selected or preset; for example, the midpoint, 1 / 3 point, or 1 / 4 point of the dead time can be set as the voltage sampling start time. Using "any moment" will introduce some error, but it simplifies the design in practical engineering, and the error is acceptable. Alternatively, the moment when the upper transistor Q1 is turned on can be used as the voltage sampling start time.

[0082] S113: Sample the resonant capacitor voltage at the start time of voltage sampling and at the end time of voltage sampling respectively, and determine the difference between the sampled resonant capacitor voltage as the change value of the resonant capacitor voltage.

[0083] The resonant capacitor voltage sampled at the start of voltage sampling is denoted as VCR_aux1, and the resonant capacitor voltage sampled at the end of voltage sampling is denoted as VCR_aux2. The difference between VCR_aux2 and VCR_aux1 is determined as the change in resonant capacitor voltage. .

[0084] When using single-sided sampling, step S1, in acquiring the voltage change value of the resonant capacitor voltage within a specified half-switching cycle, includes steps S121-S123: S121: Obtain the moment when the voltage drop inflection point of the auxiliary winding of the transformer in the resonant circuit occurs.

[0085] S122: If the resonant circuit is in an over-resonance state, the voltage drop inflection point is taken as the voltage sampling time; if the resonant circuit is in an under-resonance state, the midpoint of two consecutive voltage drop inflection points within the same switching cycle is taken as the voltage sampling time, or the second voltage drop inflection point among two consecutive voltage drop inflection points within the same switching cycle is taken as the voltage sampling time.

[0086] Figure 3 The circuit is in an over-resonance state, and t_aux2 is taken as the voltage sampling time.

[0087] Figure 4 The circuit is in an underresonant state, t_aux2'=(t_aux5+t_aux6) / 2, and t_aux2' is taken as the voltage sampling time. Figure 5 The circuit is also in an under-resonant state, and t_aux6 is taken as the voltage sampling time.

[0088] S123: Sample the resonant capacitor voltage at the voltage sampling time, and determine the resonant capacitor voltage change value as twice the resonant capacitor voltage or the difference between twice the resonant capacitor voltage and the bias voltage.

[0089] The resonant capacitor voltage sampled at the voltage sampling time is VCR_aux2. When using single-sided sampling, the change value of the resonant capacitor voltage is... =2·VCR_aux2, when using single-sided sampling and superimposing the bias voltage Voffset =2·VCR_aux2-Voffset.

[0090] When obtaining the resonant capacitor voltage change value using steps S111-S113 or steps S121-S123, it is necessary to distinguish the operating state of the resonant circuit.

[0091] The operating state of a resonant circuit can be determined using any of the following methods: (1) Based on the current switching frequency f sw With resonant frequency f r Determine the size relationship: if f sw ≥f r Then the circuit is in an over-resonance state; if f sw <f r If so, the circuit is in an underresonant state.

[0092] (2) If the voltage inflection point of the auxiliary winding voltage occurs (the voltage drop inflection point or the voltage increase inflection point) within any dead time of the primary-side switch, the circuit is in an over-resonance state; otherwise, the circuit is in an under-resonance state.

[0093] (3) If an auxiliary winding voltage inflection point (voltage drop inflection point or voltage increase inflection point) occurs within half a switching cycle, the circuit is in an over-resonance state; if two auxiliary winding voltage inflection points occur within half a switching cycle, the circuit is in an under-resonance state.

[0094] The resonant circuit output current stabilization method provided in this application has the following characteristics compared to the schemes of "sampling the secondary output current and forming a closed-loop feedback system to adjust the switching frequency or duty cycle" and "achieving constant output current control through the primary resonant cavity current": 1. No need to sample the secondary-side output current, reducing the hardware cost of isolation devices.

[0095] 2. By combining the voltage inflection point information of the transformer auxiliary winding, the voltage of the resonant capacitor is sampled at a specific sampling time to obtain a signal that can reflect the output current information.

[0096] 3. It does not require complex integrator circuits internally, but is controlled by the natural "current integration signal" of the resonant capacitor voltage.

[0097] 4. Based on the principle of geometric symmetry, the output current is estimated more accurately by calculating the sampled resonant capacitor voltage with the current switching period and coefficient k, which can achieve high-precision constant current control of the output.

[0098] 5. It can be applied to LED dimming scenarios, and achieve LED dimming control by dynamically adjusting the rated output current.

[0099] Based on the same inventive concept, this application also provides a resonant circuit output current stabilization device corresponding to the resonant circuit output current stabilization method. Since the principle of the device in this application is similar to the above-mentioned resonant circuit output current stabilization method in this application, the implementation of the device can refer to the implementation of the method, and the repeated parts will not be described again.

[0100] A resonant circuit output current stabilization device, the device comprising the following modules: The resonant capacitor voltage change value acquisition module is used to acquire the voltage change value of the resonant capacitor within a specified half-switching cycle; The sampling value or reference value calculation module is used to calculate the sampling value or reference value of constant current control based on the change value of resonant capacitor voltage or rated output current, and the numerical relationship between output current and change value of resonant capacitor voltage. The constant current loop control module is used to generate a drive control signal for the switching transistor based on the difference between the sampled value and the reference value.

[0101] In one possible implementation, the sampling value or reference value calculation module is used to convert the change value of the resonant capacitor voltage into a real-time output current based on the numerical relationship between the output current and the change value of the resonant capacitor voltage, and send the real-time output current to the constant current loop control module. The constant current loop control module is also used to take the received real-time output current as a sample value and the input rated output current as a reference value.

[0102] In one possible implementation, the sampling value or reference value calculation module is further configured to convert the rated output current into a standard resonant capacitor voltage change value based on the numerical relationship between the output current and the resonant capacitor voltage change value, and send the standard resonant capacitor voltage change value to the constant current loop control module. The constant current loop control module is further configured to use the received standard resonant capacitor voltage change value as a reference value and the resonant capacitor voltage change value sent by the resonant capacitor voltage change value acquisition module as a sample value.

[0103] In one possible implementation, the device further includes an inflection point detection module and a sampling time determination module; The inflection point detection module is used to detect the voltage inflection point of the transformer auxiliary winding of the resonant circuit. The sampling time determination module is used to determine the voltage sampling time of the resonant capacitor voltage based on the occurrence time of the voltage inflection point of the auxiliary winding. The module for obtaining the voltage change value of the resonant capacitor is also used to sample the voltage of the resonant capacitor at the voltage sampling time and calculate the voltage change value of the resonant capacitor.

[0104] In one possible implementation, the device further includes a rated output current determination module for generating a rated output current based on the light intensity signal or external temperature. The light intensity signal includes a DIM signal and an ADIM signal. The DIM signal is typically a periodic logic level, while the ADIM signal is typically an analog level.

[0105] See Figure 8 As shown, Figure 8 This is one of the structural schematic diagrams of the resonant circuit output current stabilization device provided in the embodiments of this application. Figure 8 In this module, the inflection point detection module detects the inflection point of the auxiliary winding voltage VAUX; the sampling time determination module determines the sampling time of the resonant capacitor voltage based on the occurrence time of the auxiliary winding voltage inflection point; the resonant capacitor voltage change value acquisition module samples the resonant capacitor voltage VCR at the sampling time and calculates the resonant capacitor voltage change value; and the output current conversion module (i.e., the sampling value or reference value calculation module mentioned above) converts the resonant capacitor voltage change value... Substitution The constant current loop control module calculates the real-time output current, uses the real-time output current as a sample value and the rated output current as a reference value to generate a drive control signal. The drive conduction control module is controlled by the drive control signal to adjust the upper MOSFET drive voltage HG and the lower MOSFET drive voltage LG so that the real-time output current is consistent with the rated output current.

[0106] See Figure 9 As shown, Figure 9 This is the second schematic diagram of the structure of the resonant circuit output current stabilization device provided in the embodiments of this application. Figure 9 The working principles of the inflection point detection module, sampling time determination module, resonant capacitor voltage change value acquisition module, and drive conduction control module are as follows: Figure 8 The working principle of the corresponding module is consistent with that of the standard resonant capacitor voltage change conversion module (i.e., the sampling value or reference value calculation module mentioned above), which substitutes the rated output current into the input. The constant current loop control module calculates the standard resonant capacitor voltage change value, uses the standard resonant capacitor voltage change value as a reference value, and uses the resonant capacitor voltage change value input by the resonant capacitor voltage change value acquisition module as a sample value to generate a drive control signal.

[0107] See Figure 10 As shown, Figure 10 This is the third schematic diagram of the resonant circuit output current stabilization device provided in the embodiments of this application. Figure 10 This device is suitable for LED dimming applications, controlling the output current to regulate the luminous intensity of the LED. Compared to... Figure 8 The device, Figure 10 A rated output current determination module has been added to dynamically generate the rated output current based on the DIM signal or ADIM signal. The DIM signal is usually a periodic logic level, and different duty cycles correspond to different rated output currents, which serve as a current reference to control different light intensities. The ADIM signal is usually an analog level, and different voltage values ​​correspond to different rated output currents, thereby controlling different light intensities.

[0108] This application also provides a chip including the above-described resonant circuit output current stabilization device.

[0109] 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 method for stabilizing the output current of a resonant circuit, characterized in that, The method includes: Obtain the voltage change of the resonant capacitor voltage within a specified half-switching cycle; wherein, within the specified half-switching cycle, the integral of the excitation current is zero; Based on the resonant capacitor voltage change, the numerical relationship between the output current and the resonant capacitor voltage change, and the rated output current, the sampling value and reference value for constant current control are determined; wherein, the numerical relationship between the output current and the resonant capacitor voltage change is: the output current is equal to twice the product of the number of turns in the primary winding, the resonant capacitor, and the resonant capacitor voltage change, and the product of the number of turns in the secondary winding and the switching cycle. Based on the difference between the sampled value and the reference value, a drive control signal for the switching transistor is generated so that the real-time output current is consistent with the rated output current. The process of determining the sampling value and reference value for constant current control based on the resonant capacitor voltage change, the numerical relationship between the output current and the resonant capacitor voltage change, and the rated output current includes: Based on the numerical relationship between the output current and the change in resonant capacitor voltage, the change in resonant capacitor voltage is converted into a real-time output current, the real-time output current is determined as a sampled value, and the rated output current is determined as a reference value; or, based on the numerical relationship between the output current and the change in resonant capacitor voltage, the rated output current is converted into a standard resonant capacitor voltage change value, the standard resonant capacitor voltage change value is determined as a reference value, and the resonant capacitor voltage change value is determined as a sampled value. When using bilateral sampling to obtain the resonant capacitor voltage, obtaining the voltage change value of the resonant capacitor voltage within a specified half-switching cycle includes: Obtain the times when the voltage surge inflection point and the voltage drop inflection point occur in the auxiliary winding of the transformer in the resonant circuit; If the resonant circuit is in an over-resonance state, the voltage surge inflection point and the voltage drop inflection point within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time; if the resonant circuit is in an under-resonance state, the midpoint of two consecutive voltage surge inflection points and the midpoint of two consecutive voltage drop inflection points within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time, or the first voltage surge inflection point and the second voltage drop inflection point within two consecutive voltage surge inflection points within the same switching cycle are respectively taken as the voltage sampling start time and voltage sampling end time. The resonant capacitor voltage is sampled at the start time and the end time of the voltage sampling, and the difference between the sampled resonant capacitor voltages is determined as the change value of the resonant capacitor voltage.

2. The method for stabilizing the output current of a resonant circuit according to claim 1, characterized in that, When the switching frequency is greater than or equal to the resonant frequency, the resonant circuit is in an over-resonance state. The start and end times of the specified half-switching cycle are respectively: the moment when the resonant current and the excitation current are equal in the negative current cycle and the moment when the resonant current and the excitation current are equal in the positive current cycle. When the switching frequency is less than the resonant frequency, the resonant circuit is in an under-resonance state. The start and end times of the specified half-switching cycle are respectively: the midpoint moment when the resonant current and the excitation current are continuously equal in the negative current cycle and the midpoint moment when the resonant current and the excitation current are continuously equal in the positive current cycle, or the start moment when the resonant current and the excitation current are continuously equal in the negative current cycle and the end moment when the resonant current and the excitation current are continuously equal in the positive current cycle.

3. The method for stabilizing the output current of a resonant circuit according to claim 1, characterized in that, When using single-sided sampling to obtain the resonant capacitor voltage, obtaining the voltage change value of the resonant capacitor voltage within a specified half-switching cycle includes: Obtain the moment when the voltage drop inflection point of the transformer auxiliary winding of the resonant circuit occurs; If the resonant circuit is in an over-resonance state, the voltage drop inflection point is taken as the voltage sampling time; if the resonant circuit is in an under-resonance state, the midpoint of two consecutive voltage drop inflection points within the same switching cycle is taken as the voltage sampling time, or the second voltage drop inflection point among two consecutive voltage drop inflection points within the same switching cycle is taken as the voltage sampling time. The resonant capacitor voltage is sampled at the voltage sampling time, and the value of twice the resonant capacitor voltage, or the difference between twice the resonant capacitor voltage and the bias voltage, is determined as the resonant capacitor voltage change value.

4. The method for stabilizing the output current of a resonant circuit according to claim 1, characterized in that, If the resonant circuit is in an over-resonance state, any moment within the dead time when the lower transistor is turned off and the upper transistor is turned on is determined as the voltage sampling start time, or the moment when the upper transistor is turned on is determined as the voltage sampling start time.

5. The method for stabilizing the output current of a resonant circuit according to claim 1, characterized in that, The operating state of the resonant circuit can be determined using any of the following methods: If the current switching frequency is greater than or equal to the resonant frequency, the resonant circuit operates in an over-resonance state; if the current switching frequency is less than the resonant frequency, the resonant circuit operates in an under-resonance state. If the voltage inflection point of the auxiliary winding voltage occurs within any dead time period driven by the primary-side switch, then the operating state of the resonant circuit is over-resonance; otherwise, the operating state of the resonant circuit is under-resonance. If an auxiliary winding voltage inflection point occurs within half a switching cycle, the operating state of the resonant circuit is an over-resonance state. If two auxiliary winding voltage inflection points occur within half a switching cycle, the operating state of the resonant circuit is under-resonance.

6. The method for stabilizing the output current of a resonant circuit according to claim 1, characterized in that, The rated output current is a variable.

7. A resonant circuit output current stabilization device, characterized in that, The device includes: The resonant capacitor voltage change value acquisition module is used to acquire the voltage change value of the resonant capacitor within a specified half-switching cycle; The sampling value or reference value calculation module is used to calculate the sampling value or reference value of constant current control based on the change value of resonant capacitor voltage or rated output current, and the numerical relationship between output current and change value of resonant capacitor voltage. The constant current loop control module is used to generate drive control signals for the switching transistors based on the difference between the sampled value and the reference value. The sampling value or reference value calculation module is used to convert the change value of the resonant capacitor voltage into a real-time output current based on the numerical relationship between the output current and the change value of the resonant capacitor voltage, and send the real-time output current to the constant current loop control module. The constant current loop control module is also used to take the received real-time output current as a sample value and the input rated output current as a reference value. The sampling value or reference value calculation module is also used to convert the rated output current into a standard resonant capacitor voltage change value based on the numerical relationship between the output current and the resonant capacitor voltage change value, and send the standard resonant capacitor voltage change value to the constant current loop control module. The constant current loop control module is also used to determine the change value of the resonant capacitor voltage as a sample value, and to use the received change value of the standard resonant capacitor voltage as a reference value; The device also includes an inflection point detection module and a sampling time determination module; The inflection point detection module is used to detect the voltage inflection point of the transformer auxiliary winding of the resonant circuit. The sampling time determination module is used to determine the voltage sampling time of the resonant capacitor voltage based on the occurrence time of the voltage inflection point of the auxiliary winding. The module for obtaining the voltage change value of the resonant capacitor is also used to sample the voltage of the resonant capacitor at the voltage sampling time and calculate the voltage change value of the resonant capacitor.

8. The resonant circuit output current stabilization device according to claim 7, characterized in that, The device also includes a rated output current determination module, used to generate a rated output current based on the light intensity signal or the external temperature.

9. A chip, characterized in that, Including the resonant circuit output current stabilization device as described in any one of claims 7-8.

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