Starting control circuit and resonant converter

Abstract

The invention is suitable for the technical field of resonant converters, and provides a starting control circuit and a resonant converter. The starting control circuit comprises a feedback module, a comparison selection module and a logical operation module, the comparison selection module is electrically connected with the feedback module and the logical operation module, the feedback module is used for being electrically connected with the output end of a resonant conversion circuit in the resonant converter, and the logical operation module is used for being electrically connected with a driving circuit in the resonant converter. According to the starting control circuit provided by the embodiment of the invention, the resonant capacitor voltage constraint threshold value which is gradually enlarged along with the starting process can be constructed, smooth establishment of resonant capacitor direct current bias is realized, the fluctuation amplitude of the resonant capacitor voltage is limited, the problem that the total bus voltage is applied to the resonant inductor in a traditional scheme is avoided, and the starting control circuit is suitable for a high-voltage power supply. Finally, the resonance current peak value in the starting stage is effectively suppressed, and the impact of current stress on core devices such as a switching tube and a resonance inductor is reduced.

Description

Technical Field

[0001] This application belongs to the field of resonant converter technology, and particularly relates to a start-up control circuit and a resonant converter. Background Technology

[0002] Resonant converters, with their high efficiency, high power density, and soft-switching characteristics, have been widely used in various power electronic devices such as industrial power supplies, server power supplies, and new energy converters. In practical applications, converters often face load-bearing startup conditions. In traditional resonant converters, during the load-bearing startup phase, the initial voltages of both the output capacitor and the resonant capacitor are zero, resulting in an approximately zero voltage across the transformer's magnetizing inductor. When the high-side switch in the topology turns on, the entire input bus voltage is applied across the resonant inductor, causing the resonant current flowing into the resonant cavity to rise rapidly, forming an extremely high current peak and generating severe current stress. Summary of the Invention

[0003] This application provides a start-up control circuit and a resonant converter, which can solve the problem of extremely high peak current flowing into the resonant cavity during the load start-up phase of traditional resonant converters.

[0004] In a first aspect, embodiments of this application provide a start-up control circuit applied to a resonant converter. The start-up control circuit includes a feedback module, a comparison and selection module, and a logic operation module. The comparison and selection module is electrically connected to the feedback module and the logic operation module, respectively. The feedback module is used to be electrically connected to the output terminal of the resonant converter circuit in the resonant converter, and the logic operation module is used to be electrically connected to the drive circuit in the resonant converter. The feedback module is used to acquire the output voltage of the resonant converter circuit and output a feedback voltage based on the output voltage. The comparison and selection module is used to compare the feedback voltage with the soft-start ramp voltage, and select the lower voltage between the feedback voltage and the soft-start ramp voltage as the threshold voltage to be output to the logic operation module. The soft-start ramp voltage rises from zero to a first preset value at a first fixed slope when the resonant converter is started. The logic operation module is used to calculate the sum of the common-mode voltage and the threshold voltage and output a first logic signal; at the same time, it calculates the difference between the common-mode voltage and the threshold voltage and outputs a second logic signal; wherein, when the resonant converter is started, the common-mode voltage rises from zero to a second preset value at a second fixed slope; the first logic signal is used to instruct the driving circuit to output a first driving command to drive the upper transistor in the resonant converter circuit; and the second logic signal is used to instruct the driving circuit to output a second driving command to drive the lower transistor in the resonant converter circuit.

[0005] In one possible implementation of the first aspect, the output voltage includes a first voltage and a second voltage, the feedback module includes a feedback unit and a voltage divider unit, the feedback unit is electrically connected to the voltage divider unit and the comparison selection module respectively, and both the feedback unit and the voltage divider unit are used to be electrically connected to the output terminal of the resonant converter circuit; The voltage divider unit is used to divide the first voltage to obtain a divided voltage; the feedback unit is used to output the feedback voltage based on the divided voltage and the second voltage.

[0006] In one possible implementation of the first aspect, the feedback unit includes a first resistor, a second resistor, a third resistor, an optocoupler, and a precision controllable voltage regulator. A first terminal of the first resistor is electrically connected to a first power supply. A second terminal of the first resistor is electrically connected to a first conducting terminal of the optocoupler and the comparison selection module. A first terminal of the second resistor is electrically connected to a first terminal of the third resistor and a first control terminal of the optocoupler. A second terminal of the second resistor is used to receive the second voltage. A second terminal of the third resistor is electrically connected to a second control terminal of the optocoupler and a first conducting terminal of the precision controllable voltage regulator. The control terminal of the precision controllable voltage regulator is electrically connected to the voltage divider unit. Both the second conducting terminal of the precision controllable voltage regulator and the second conducting terminal of the optocoupler are grounded.

[0007] In one possible implementation of the first aspect, the voltage divider unit includes a first voltage divider resistor and a second voltage divider resistor, a first terminal of the first voltage divider resistor is used to receive the first voltage, a second terminal of the first voltage divider resistor is electrically connected to the first terminal of the second voltage divider resistor and the feedback unit, and a second terminal of the second voltage divider resistor is grounded.

[0008] In one possible implementation of the first aspect, the comparison selection module includes a first comparator and a two-way selector. The first input terminal of the first comparator is electrically connected to the feedback module for receiving the feedback voltage. The second input terminal of the first comparator is used to receive the soft-start ramp voltage. The non-output terminal of the first comparator is electrically connected to the control terminal of the two-way selector. The first terminal of the two-way selector is used to receive the feedback voltage. The second terminal of the two-way selector is used to receive the soft-start ramp voltage. The output terminal of the two-way selector is electrically connected to the logic operation module.

[0009] In one possible implementation of the first aspect, the logic operation module includes an adder and a subtractor. The first input terminal of the adder is used to receive the common-mode voltage, the second input terminal of the adder is used to receive the threshold voltage, and the output terminal of the adder is used to be electrically connected to the driving circuit. The first input terminal of the subtractor is used to receive the common-mode voltage, the second input terminal of the subtractor is used to receive the threshold voltage, and the output terminal of the subtractor is used to be electrically connected to the driving circuit.

[0010] Secondly, embodiments of this application provide a resonant converter, including a resonant converter circuit, a driving circuit, and a start-up control circuit as described in the first aspect, wherein the driving circuit is electrically connected to the logic operation modules in the resonant converter circuit and the start-up control circuit, respectively. The driving circuit is used to output a first driving instruction and a second driving instruction according to the first logic signal and the second logic signal output by the logic operation module; the resonant conversion circuit is used to adjust the output voltage according to the first driving instruction and the second driving instruction.

[0011] In one possible implementation of the second aspect, the driving circuit includes a first arithmetic unit, a trigger unit, and a signal output unit. The first arithmetic unit is electrically connected to the logic arithmetic module and the trigger unit, respectively, and the signal output unit is electrically connected to the trigger unit and the resonant conversion circuit, respectively. The first arithmetic unit is configured to output a first arithmetic voltage and a second arithmetic voltage based on the resonant capacitor voltage, the first logic signal, and the second logic signal; the triggering unit is configured to output a first level signal and a second level signal based on the first arithmetic voltage and the second arithmetic voltage; the signal output unit is configured to output a second driving instruction based on the first level signal, and also to output the first driving instruction based on the second level signal.

[0012] In one possible implementation of the second aspect, the resonant converter further includes a compensation circuit, which is electrically connected to the resonant capacitors in the driving circuit and the resonant converter circuit, respectively. The compensation circuit is used to divide the voltage of the resonant capacitor and inject compensation current into the midpoint of the voltage-dividing capacitor.

[0013] In one possible implementation of the second aspect, the compensation circuit includes a first voltage-dividing capacitor, a second voltage-dividing capacitor, a first driving current source, and a second driving current source. The first terminal of the first voltage-dividing capacitor is electrically connected to the resonant capacitor in the resonant conversion circuit. The second terminal of the first voltage-dividing capacitor is electrically connected to the first terminal of the second voltage-dividing capacitor, the control terminal of the first driving current source, and the control terminal of the second driving current source, respectively. The second terminal of the second voltage-dividing capacitor is grounded. The input terminal of the first driving current source is used to receive the first driving command, and the input terminal of the second driving current source is used to receive the second driving command.

[0014] The beneficial effects of the embodiments in this application compared with the prior art are: This application provides a startup control circuit, including a feedback module, a comparison and selection module, and a logic operation module. The control circuit compares the feedback voltage with the soft-start ramp voltage through the comparison and selection module, selecting the lower of the two voltages as the threshold voltage. The soft-start ramp voltage rises from zero at a first fixed slope during startup, ensuring that the initial threshold voltage is dominated by the gradually increasing soft-start ramp voltage, increasing synchronously rather than reaching its maximum value initially. Subsequently, the logic operation module adds and subtracts the common-mode voltage, which rises from zero at a second fixed slope during startup, from the threshold voltage, generating dynamically changing first and second logic signals. The gradual increase in the common-mode voltage simulates the establishment process of the resonant capacitor's steady-state DC bias, providing a smooth bias reference for the resonant capacitor voltage. This allows the DC bias of the resonant capacitor voltage to gradually rise synchronously, avoiding a large instantaneous voltage difference with the bus voltage. This gradually limits the maximum value of the voltage across the resonant inductor, slows the rise rate of the resonant current, and suppresses current peaks.

[0015] In summary, the start-up control circuit provided in this application can construct a resonant capacitor voltage constraint threshold that gradually expands during the start-up process. This achieves both the smooth establishment of the DC bias of the resonant capacitor and limits the fluctuation range of the resonant capacitor voltage, avoiding the problem of applying the full bus voltage to the resonant inductor in traditional solutions. Furthermore, because the threshold voltage always maintains a gradually increasing dynamic characteristic without signal abrupt changes, the fluctuation range of the resonant capacitor voltage gradually expands in tandem with the bias reference, avoiding secondary current surges caused by threshold abrupt changes. Ultimately, this effectively suppresses the resonant current peak during the start-up phase and reduces the impact of current stress on core components such as the switching transistor and resonant inductor.

[0016] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a circuit diagram of a resonant converter; Figure 2 This is a schematic diagram illustrating the principle of controlling the resonant converter by controlling the voltage increment of the resonant capacitor; Figure 3 This is a waveform diagram illustrating the control of the resonant converter by controlling the voltage increment of the resonant capacitor. Figure 4 This is a schematic block diagram of a start-up control circuit provided in one embodiment of this application; Figure 5 This is a circuit diagram of a feedback module provided in an embodiment of this application; Figure 6 This is a circuit diagram of a comparison selection module provided in an embodiment of this application; Figure 7 This is a schematic diagram of the comparison and selection module provided in one embodiment of this application; Figure 8 This is a schematic diagram of the operating waveform of the comparison and selection module provided in an embodiment of this application; Figure 9 This is a circuit diagram of a logic operation module and a driving circuit provided in an embodiment of this application; Figure 10 This is a circuit diagram of the compensation circuit and the resonant conversion circuit provided in an embodiment of this application; Figure 11 This is a schematic diagram of the working waveform provided in an embodiment of this application.

[0019] In the diagram: 10. Start-up control circuit; 101. Feedback module; 1011. Feedback unit; 1012. Voltage divider unit; 102. Comparison and selection module; 103. Logic operation module; 20. Resonance conversion circuit; 30. Drive circuit; 301. First operation unit; 302. Trigger unit; 303. Signal output unit; 40. Compensation circuit. Detailed Implementation

[0020] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0021] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0022] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0023] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [the described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [the described condition or event] is detected," or "in response to detection of [the described condition or event]."

[0024] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0025] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0026] Figure 1The circuit structure of a resonant converter (taking a half-bridge resonant converter as an example) is shown. During the start-up phase under load, the initial voltages of both the output capacitor and the resonant capacitor are zero, resulting in an approximately zero voltage across the transformer's magnetizing inductor. When the high-side switch in the topology turns on, the entire input bus voltage is applied across the resonant inductor, causing the resonant current flowing into the resonant cavity to rise rapidly, forming an extremely high current peak and generating severe current stress. Furthermore, after the high-side switch turns off, the insufficient turn-on time of the low-side switch prevents the resonant current from decreasing from the positive phase to the negative phase, thus causing the high-side switch to lose the ZVS condition in the next operation, thereby affecting the reliability of the resonant converter.

[0027] In existing control methods for current-mode resonant half-bridge converters, regardless of the specific implementation, the core idea is to precisely control the magnitude of charge or current flowing from the input DC power supply into the resonant cavity. In practice, the voltage amplitude of the resonant capacitor in the resonant cavity is typically used as the controlled object; therefore, the voltage amplitude of the resonant capacitor precisely represents the integral of the charge flowing into the resonant cavity. According to the formula for stored power in a capacitor, the voltage increment ΔVCr of the capacitor is positively correlated with the power. Therefore, the relationship between the input power Pin of the resonant converter and the voltage increment ΔVCr, the resonant capacitor voltage Cr, the switching frequency fsw, and the bus input voltage Vin can be derived: Pin = ΔVCr * Cr * fsw * Vin.

[0028] Therefore, the resonant converter can be controlled by controlling ΔVCr, and the existing method is bang-bang control. Figure 2 and Figure 3 As shown, by setting two limit lines, Vcr(H) and Vcr(L), and comparing them with the sampled value Vcr of the actual capacitor voltage, the voltage of the resonant capacitor and ΔVCr can be controlled. Here, Vcr(H) represents the upper limit threshold (high threshold) of the resonant capacitor voltage, Vcr(L) represents the lower limit threshold (low threshold) of the resonant capacitor voltage, GATEHS is the gate drive signal of S1, GATELS is the gate drive signal of S2, and Vboost is the input voltage.

[0029] To illustrate the technical solution described in this application, specific embodiments are provided below.

[0030] Figure 4 A schematic block diagram of a start-up control circuit 10 according to an embodiment of this application is shown. See also Figure 4As shown, the start-up control circuit 10 is applied to the resonant converter. The start-up control circuit 10 includes a feedback module 101, a comparison and selection module 102, and a logic operation module 103. The comparison and selection module 102 is electrically connected to the feedback module 101 and the logic operation module 103, respectively. The feedback module 101 is used to be electrically connected to the output terminal of the resonant converter circuit 20 in the resonant converter. The logic operation module 103 is used to be electrically connected to the drive circuit 30 in the resonant converter. The drive circuit 30 is electrically connected to the upper and lower transistors in the resonant converter circuit 20.

[0031] Specifically, the start-up control circuit 10 compares the feedback voltage Vopto with the soft-start ramp voltage V3 through the comparison and selection module 102, and selects the lower of the two voltages as the threshold voltage VTH. The soft-start ramp voltage V3 rises from zero at a first fixed slope during start-up, ensuring that the initial threshold voltage VTH is dominated by the gradually increasing soft-start ramp voltage V3, increasing synchronously rather than reaching its maximum value initially. Then, the logic operation module 103 adds and subtracts the common-mode voltage VCM, which rises from zero at a second fixed slope during start-up, from the threshold voltage VTH, generating dynamically changing first logic signal VHH and second logic signal VHL. The gradual rise of the common-mode voltage VCM simulates the establishment process of the resonant capacitor's steady-state DC bias, providing a smooth bias reference for the resonant capacitor voltage VCR. This allows the DC bias of the resonant capacitor voltage VCR to rise synchronously and gradually, avoiding a large instantaneous voltage difference with the bus voltage. This gradually limits the maximum value of the voltage across the resonant inductor, slows the rise rate of the resonant current, and suppresses current peaks.

[0032] In summary, the start-up control circuit 10 provided in this application can construct a resonant capacitor voltage VCR constraint threshold that gradually expands during the start-up process. This achieves both the smooth establishment of the DC bias of the resonant capacitor and limits the fluctuation range of the resonant capacitor voltage VCR, avoiding the problem of applying the full bus voltage to the resonant inductor in traditional solutions. Furthermore, because the threshold voltage VTH always maintains a gradually increasing dynamic characteristic without signal abrupt changes, the fluctuation range of the resonant capacitor voltage VCR gradually expands in tandem with the bias reference, avoiding secondary current surges caused by threshold abrupt changes. Ultimately, this effectively suppresses the resonant current peak during the start-up phase and reduces the impact of current stress on core components such as the switching transistor and resonant inductor.

[0033] It should be noted that the selection logic of the comparison selection module 102 in this application, during the initial startup phase, is dominated by the gradually increasing soft-start ramp voltage V3 due to the high feedback voltage Vopto, ensuring that the threshold voltage VTH increases synchronously with the soft-start process. After the closed loop stabilizes, the feedback voltage Vopto drops below the soft-start ramp voltage V3, and the threshold voltage VTH automatically switches to be dominated by the feedback voltage Vopto, achieving a smooth transition between soft start and closed-loop control. Therefore, this application simultaneously achieves a smooth transition between the soft-start stage and the closed-loop control stage, avoiding current surges caused by mode switching and improving the stability and reliability of the resonant converter circuit 20 during startup.

[0034] For example, after power-on, the system enters a soft-start process. At this time, the output voltage or output current regulated by the secondary closed-loop controller has not yet reached the closed-loop control set value. The closed-loop control circuit will set the feedback voltage Vopto to the highest voltage level, and the soft-start ramp voltage V3 can increase from 0 to a maximum value of 2.5V with a fixed slope. The common-mode voltage VCM can also increase from 0 to 2.5V with a fixed slope to simulate the gradual increase of the DC bias voltage of the resonant capacitor in the actual system.

[0035] In some embodiments, such as Figure 5 As shown, the output voltage includes a first voltage Vout and a second voltage Vout_ac, wherein the first voltage Vout is a DC output voltage and the second voltage Vout_ac is an AC output voltage. The feedback module 101 includes a feedback unit 1011 and a voltage divider unit 1012. The feedback unit 1011 is electrically connected to the voltage divider unit 1012 and the comparison and selection module 102, respectively. Both the feedback unit 1011 and the voltage divider unit 1012 are used to be electrically connected to the output terminal of the resonant converter circuit 20.

[0036] Specifically, the voltage divider unit 1012 divides the DC output voltage of the resonant converter circuit 20 to obtain a divided voltage VFB, reducing the voltage, which is usually higher than the reference voltage of the feedback unit 1011, to a voltage range that the feedback unit 1011 can recognize. The feedback unit 1011 receives this divided voltage VFB and performs dynamic compensation in conjunction with the AC output voltage. By comparing the built-in reference voltage with the divided voltage VFB in real time, it identifies the deviation of the DC output voltage and then converts the deviation into a feedback voltage Vopto that can be used for subsequent control. This ensures that the feedback voltage Vopto can accurately reflect the steady-state value of the DC output voltage and cope with the dynamic fluctuations of AC ripple. It provides a reliable signal source for the comparison selection module 102 to select the lower value between the feedback voltage Vopto and the soft-start ramp voltage V3 as the threshold voltage VTH, ultimately ensuring the effectiveness of soft-start control and peak current suppression.

[0037] In some embodiments, such as Figure 5As shown, the feedback unit 1011 includes a first resistor R1, a second resistor R2, a third resistor R11, an optocoupler U13, and a precision controllable voltage regulator U14. The first end of the first resistor R1 is electrically connected to the first power supply V6. The second end of the first resistor R1 is electrically connected to the first conducting end of the optocoupler U13 and the comparison selection module 102, respectively. The first end of the second resistor R2 is electrically connected to the first end of the third resistor R11 and the first control end of the optocoupler U13, respectively. The second end of the second resistor R2 is used to receive the second voltage Vout_ac. The second end of the third resistor R11 is electrically connected to the second control end of the optocoupler U13 and the first conducting end of the precision controllable voltage regulator U14, respectively. The control end of the precision controllable voltage regulator U14 is electrically connected to the voltage divider unit 1012. The second conducting ends of the precision controllable voltage regulator U14 and the second conducting ends of the optocoupler U13 are both grounded.

[0038] Specifically, the first resistor R1 acts as a current-limiting resistor, limiting the current flowing from the first power supply V6 into the first conducting terminal (collector of the phototransistor) of the optocoupler U13 to prevent damage to the optocoupler U13 due to overcurrent. It also provides a stable feedback voltage (Vopto) output path for the comparison selection module 102. The second resistor R2 transmits the AC output voltage, introducing it to the control side of the optocoupler U13 (anode of the light-emitting diode) to compensate for the ripple of the feedback signal. The third resistor R11 works in conjunction with the precision controllable voltage regulator U14, acting as a current limiter and voltage divider to ensure the stability of the voltage transmitted to the precision controllable voltage regulator U14. The optocoupler U13 acts as an isolation device, achieving electrical isolation between the secondary output side and the primary control side of the resonant converter circuit 20. It also converts the current signal output from the precision controllable voltage regulator U14 into a voltage signal, which is then transmitted to the comparison selection module 102. The precision controllable voltage regulator U14 (such as TL431) serves as the core of the reference comparison. It receives the divided voltage VFB output by the voltage divider unit 1012, compares it with the internal reference voltage, and controls the light intensity of the optocoupler U13 by adjusting its own conduction current, thereby adjusting the amplitude of the feedback voltage Vopto to achieve accurate feedback of the DC output voltage.

[0039] For example, the resistance of the first resistor R1 can be selected as 20kΩ, the resistance of the second resistor R2 can be selected as 3kΩ, and the resistance of the third resistor R11 can be selected as 1kΩ.

[0040] In some embodiments, such as Figure 5 As shown, the voltage divider unit 1012 includes a first voltage divider resistor R8 and a second voltage divider resistor R7. The first end of the first voltage divider resistor R8 is used to receive the first voltage Vout. The second end of the first voltage divider resistor R8 is electrically connected to the first end of the second voltage divider resistor R7 and the feedback unit 1011, respectively. The second end of the second voltage divider resistor R7 is grounded.

[0041] Specifically, the first voltage divider resistor R8 and the second voltage divider resistor R7 form a series voltage divider network. The first terminal of the first voltage divider resistor R8 receives the DC output voltage. Through a reasonable resistance ratio, the two divide the voltage, which is higher than the reference voltage of the precision controllable voltage regulator U14, to its recognizable voltage range. At the same time, the connection node of the first voltage divider resistor R8 and the second voltage divider resistor R7 outputs a stable divided voltage VFB, which is transmitted to the control terminal of the precision controllable voltage regulator U14 in the feedback unit 1011, providing a precise DC voltage input for subsequent voltage reference comparison.

[0042] For example, the resistance of the first voltage divider resistor R8 can be selected as 20kΩ, and the resistance of the second voltage divider resistor R7 can be selected as 2.3kΩ.

[0043] It should be noted that the feedback unit 1011 also includes capacitors C4 (470pF), C6 (1nF), C7 (22nF), and resistor R12 (1kΩ). The connection relationships can be found in [reference needed]. Figure 5 As shown, the capacitor serves both filtering and coupling matching functions. The specific functions and parameter selection criteria of the capacitors and resistors will not be elaborated upon here.

[0044] In some embodiments, such as Figure 6 As shown, the comparison selection module 102 includes a first comparator U15 and a two-way selector U114. The first input terminal of the first comparator U15 is electrically connected to the feedback module 101 and is used to receive the feedback voltage Vopto. The second input terminal of the first comparator U15 is used to receive the soft-start ramp voltage V3. The non-output terminal of the first comparator U15 is electrically connected to the control terminal of the two-way selector U114. The first terminal of the two-way selector U114 is used to receive the feedback voltage Vopto, and the second terminal of the two-way selector U114 is used to receive the soft-start ramp voltage V3. The output terminal of the two-way selector U114 is electrically connected to the logic operation module 103.

[0045] Specifically, the first comparator U15, as the core of the voltage comparison, receives the feedback voltage Vopto at its first input terminal and the soft-start ramp voltage V3 at its second input terminal. It compares the amplitudes of the two voltages in real time and outputs the logic level corresponding to the comparison result via the inverting output terminal (non-output terminal), providing a precise selection control signal for the two-way selector U114. Based on the control signal output by the first comparator U15, the two-way selector U114 selectively conducts between the feedback voltage Vopto and the soft-start ramp voltage V3, always selecting the voltage with the lower amplitude as the threshold voltage VTH to be output to the logic operation module 103. This achieves a smooth switch between the soft-start stage and the closed-loop control stage, ensuring the dynamic gradual change characteristics of the threshold voltage VTH during startup.

[0046] like Figure 7As shown, the comparison selection module 102, composed of the first comparator U15 and the two-way selector U114, operates as follows: During the soft-start phase, the soft-start ramp voltage V3 is lower than the feedback voltage Vopto. At this time, the soft-start ramp voltage V3 is used as the dominant signal to achieve smooth control of the resonant converter's start-up power. After the soft-start is completed and the closed-loop operation phase begins, the feedback voltage Vopto is lower than the soft-start ramp voltage V3. At this time, the feedback voltage Vopto is used as the dominant signal to achieve control of the resonant converter's steady-state power. Combined with... Figure 8 As shown in the operating waveforms, the final output threshold voltage VTH waveform exhibits a segmented following characteristic: during the soft-start phase, the waveform of the threshold voltage VTH is consistent with the waveform of the soft-start ramp voltage V3; after the soft-start is completed, the waveform of the threshold voltage VTH is consistent with the waveform of the feedback voltage Vopto.

[0047] In some embodiments, such as Figure 9 As shown, the logic operation module 103 includes an adder U2 and a subtractor E5. The first input terminal of the adder U2 is used to receive the common-mode voltage VCM, the second input terminal of the adder U2 is used to receive the threshold voltage VTH, and the output terminal of the adder U2 is used to be electrically connected to the driving circuit 30. The first input terminal of the subtractor E5 is used to receive the common-mode voltage VCM, the second input terminal of the subtractor E5 is used to receive the threshold voltage VTH, and the output terminal of the subtractor E5 is used to be electrically connected to the driving circuit 30.

[0048] Specifically, adder U2, acting as the upper threshold generation device, adds the common-mode voltage VCM to the threshold voltage VTH, outputting a first logic signal VHH representing the upper threshold of the resonant capacitor voltage VCR, i.e., VHH = VCM + VTH. Subtractor E5, acting as the lower threshold generation device, subtracts the common-mode voltage VCM from the threshold voltage VTH, outputting a second logic signal VHL representing the lower threshold of the resonant capacitor voltage VCR, i.e., VHL = VCM - VTH. Together, they construct a dynamically changing constraint range for the resonant capacitor voltage VCR during startup, providing the core logic basis for the drive circuit 30 to output drive commands and precisely control the on / off timing of the upper and lower transistors in the half-bridge resonant converter circuit 20.

[0049] This application embodiment also provides a resonant converter, including a resonant converter circuit 20, a drive circuit 30 and the aforementioned start-up control circuit 10, wherein the drive circuit 30 is electrically connected to the logic operation module 103 in the resonant converter circuit 20 and the start-up control circuit 10, respectively.

[0050] Specifically, the drive circuit 30 receives the first logic signal VHH and the second logic signal VHL output by the logic operation module 103, and converts them into a first drive command D_H and a second drive command D_L with sufficient driving capability, controlling the turn-on and turn-off timing of the switching transistors (upper and lower transistors) in the resonant converter circuit 20. As the core power conversion unit of the converter, the resonant converter circuit 20 adjusts the energy transfer process of its internal resonant cavity according to the drive commands output by the drive circuit 30, thereby achieving stable regulation of the output voltage.

[0051] The resonant converter adopts the above-mentioned start-up control circuit 10, which can realize soft-start control in the start-up stage by constraining the threshold of the resonant capacitor voltage VCR through dynamic construction. This effectively suppresses the peak start-up current, reduces the impact of current stress on core components such as switching transistors and resonant inductors, and achieves a smooth transition between the soft-start stage and the closed-loop control stage. It avoids secondary current impact caused by mode switching and greatly improves the stability and reliability of the resonant converter's start-up operation.

[0052] In some embodiments, such as Figure 9 As shown, the driving circuit 30 includes a first arithmetic unit 301, a trigger unit 302, and a signal output unit 303. The first arithmetic unit 301 is electrically connected to the logic arithmetic module 103 and the trigger unit 302, respectively. The signal output unit 303 is electrically connected to the trigger unit 302 and the resonant conversion circuit 20, respectively.

[0053] Specifically, the first arithmetic unit 301 receives the resonant capacitor voltage VCR and the first logic signal VHH and the second logic signal VHL output by the logic operation module 103. Through arithmetic processing, it generates a first operational voltage SSS and a second operational voltage RRR that match the switching control requirements of the resonant converter circuit 20. The trigger unit 302, based on the two operational voltages output by the first arithmetic unit 301, generates a first level signal and a second level signal with timing control function to control the timing of the drive command triggering. The signal output unit 303 converts the level signal output by the trigger unit 302 into a first drive command D_H and a second drive command D_L with sufficient driving capability and transmits them to the resonant converter circuit 20. This controls the on / off state of the switching transistors in the resonant converter circuit 20. The three units work together to complete the conversion and transmission from control logic signals to power drive commands.

[0054] It should be noted that the first arithmetic unit 301 consists of four comparators (U5, U21, U6, U8) with comparison functions and two AND gates (U3, U7) with logic operation functions. The specific connection relationships and working principles will not be elaborated upon further. Specifically, U5, U21, and U3 work together to operate on the resonant capacitor voltage VCR and the first logic signal VHH to obtain the first operational voltage SSS. U6, U8, and U7 work together to operate on the resonant capacitor voltage VCR and the second logic signal VHL to obtain the second operational voltage RRR.

[0055] The triggering unit 302 includes an RS flip-flop U4. The S terminal of the RS flip-flop U4 receives a first operational voltage SSS, and the R terminal of the RS flip-flop U4 receives a second operational voltage RRR. The output terminal of the RS flip-flop U4 is connected to the signal output unit 303. Since the RS flip-flop U4 is a commonly used flip-flop, its specific working principle will not be described in detail here.

[0056] The signal output unit 303 consists of two inverters (U1 and U9) with inverting functions and three AND gates (U11, U12, and U10) with logic operation functions. The specific connection relationships and working principles are not detailed here. U1 and U11 work together to process the first level signal to obtain the second drive instruction D_L, which drives the upper transistor. U12, U9, and U10 work together to process the second level signal to obtain the first drive instruction D_H.

[0057] In some embodiments, such as Figure 10 As shown, the resonant converter also includes a compensation circuit 40, which is electrically connected to the resonant capacitors in the drive circuit 30 and the resonant converter circuit 20, respectively.

[0058] Specifically, the compensation circuit 40 performs voltage division sampling on the resonant capacitor and injects compensation current into the midpoint of the voltage divider capacitor to balance the conduction time consistency between the high-side drive signal and the low-side drive signal output by the drive circuit 30, corrects the deviation in the resonant capacitor voltage VCR sampling process, and ensures that the threshold signal generated by the logic operation module 103 matches the actual voltage of the resonant capacitor. This improves the control accuracy of the resonant converter during startup and steady-state operation, and avoids current fluctuations and increased losses caused by asymmetric timing of the drive signals.

[0059] In some embodiments, such as Figure 10As shown, the compensation circuit 40 includes a first voltage divider capacitor C5, a second voltage divider capacitor C8, a first driving current source G6, and a second driving current source G5. The first end of the first voltage divider capacitor C5 is electrically connected to the resonant capacitor in the resonant converter circuit 20. The second end of the first voltage divider capacitor C5 is electrically connected to the first end of the second voltage divider capacitor C8, the control terminal of the first driving current source G6, and the control terminal of the second driving current source G5, respectively. The second end of the second voltage divider capacitor C8 is grounded. The input terminal of the first driving current source G6 is used to receive the first driving command D_H, and the input terminal of the second driving current source G5 is used to receive the second driving command D_L.

[0060] Specifically, the first voltage-dividing capacitor C5 and the second voltage-dividing capacitor C8 form a series voltage-dividing network to sample the resonant capacitor voltage VCR in the resonant converter circuit 20, forming the midpoint voltage of the voltage divider, providing a precise sampling node for the injection of compensation current. The first drive current source G6 receives the first drive command D_H and injects a compensation current of corresponding amplitude into the midpoint of the voltage-dividing capacitor according to the timing state of the first drive command D_H; the second drive current source G5 receives the second drive command D_L and synchronously responds to the timing state of the second drive command D_L to inject a matching compensation current into the midpoint of the voltage-dividing capacitor. The two work together to balance the conduction time consistency of the high-side and low-side drive signals (HG and LG), correct the sampling deviation of the resonant capacitor voltage VCR, and ensure the accuracy of subsequent control logic.

[0061] It should be noted that the resonant converter circuit 20 includes the upper transistor, lower transistor, resonant inductor, resonant capacitor, and output devices on the secondary side of the transformer, all of which are typical components of the resonant converter circuit 20 and will not be elaborated upon here. This application mainly proposes a soft-start method based on bang-bang control. The simplest implementation principle is that when VCR is greater than Vcr(H), HG (high-side drive signal) is turned off, and then LG (low-side drive signal) is turned on after a dead time. When VCR is less than Vcr(L), LG (low-side drive signal) is turned off.

[0062] This application enables soft-start by using the common-mode voltage VCM of Vcr(H) and Vcr(L) and the VCR control voltage together, to approximate the actual voltage waveform of the resonant capacitor. The operating waveform is as follows: Figure 11 As shown, IL is the resonant inductor current. VCM rises from 0 to 2.5V within 0~150us, and Vcr(H) and Vcr(L) also rise synchronously based on the bias of VCM. During the 150us soft-start time, the DC bias voltage of the resonant voltage also gradually rises from 0 to Vin / 2, thus starting stable resonant operation.

[0063] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0064] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications 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 included within the protection scope of this application.

Claims

1. A start-up control circuit, characterized in that, The start-up control circuit, applied to a resonant converter, includes a feedback module, a comparison and selection module, and a logic operation module. The comparison and selection module is electrically connected to the feedback module and the logic operation module, respectively. The feedback module is electrically connected to the output terminal of the resonant converter circuit in the resonant converter, and the logic operation module is electrically connected to the drive circuit in the resonant converter. The feedback module is used to acquire the output voltage of the resonant converter circuit and output a feedback voltage based on the output voltage. The comparison and selection module is used to compare the feedback voltage with the soft-start ramp voltage, and select the lower voltage between the feedback voltage and the soft-start ramp voltage as the threshold voltage to be output to the logic operation module. The soft-start ramp voltage rises from zero to a first preset value at a first fixed slope when the resonant converter is started. The logic operation module is used to calculate the sum of the common-mode voltage and the threshold voltage and output a first logic signal; at the same time, it calculates the difference between the common-mode voltage and the threshold voltage and outputs a second logic signal; wherein, when the resonant converter is started, the common-mode voltage rises from zero to a second preset value at a second fixed slope; the first logic signal is used to instruct the driving circuit to output a first driving command to drive the upper transistor in the resonant converter circuit; and the second logic signal is used to instruct the driving circuit to output a second driving command to drive the lower transistor in the resonant converter circuit.

2. The start-up control circuit according to claim 1, characterized in that, The output voltage includes a first voltage and a second voltage. The feedback module includes a feedback unit and a voltage divider unit. The feedback unit is electrically connected to the voltage divider unit and the comparison selection module, respectively. Both the feedback unit and the voltage divider unit are used to be electrically connected to the output terminal of the resonant converter circuit. The voltage divider unit is used to divide the first voltage to obtain a divided voltage; the feedback unit is used to output the feedback voltage based on the divided voltage and the second voltage.

3. The start-up control circuit according to claim 2, characterized in that, The feedback unit includes a first resistor, a second resistor, a third resistor, an optocoupler, and a precision controllable voltage regulator. The first end of the first resistor is electrically connected to a first power supply. The second end of the first resistor is electrically connected to the first conducting terminal of the optocoupler and the comparison selection module. The first end of the second resistor is electrically connected to the first end of the third resistor and the first control terminal of the optocoupler. The second end of the second resistor is used to receive the second voltage. The second end of the third resistor is electrically connected to the second control terminal of the optocoupler and the first conducting terminal of the precision controllable voltage regulator. The control terminal of the precision controllable voltage regulator is electrically connected to the voltage divider unit. The second conducting terminal of the precision controllable voltage regulator and the second conducting terminal of the optocoupler are both grounded.

4. The start-up control circuit according to claim 2, characterized in that, The voltage divider unit includes a first voltage divider resistor and a second voltage divider resistor. The first end of the first voltage divider resistor is used to receive the first voltage. The second end of the first voltage divider resistor is electrically connected to the first end of the second voltage divider resistor and the feedback unit, respectively. The second end of the second voltage divider resistor is grounded.

5. The start-up control circuit according to claim 1, characterized in that, The comparison selection module includes a first comparator and a two-way selector. The first input terminal of the first comparator is electrically connected to the feedback module to receive the feedback voltage. The second input terminal of the first comparator is used to receive the soft-start ramp voltage. The NOT output terminal of the first comparator is electrically connected to the control terminal of the two-way selector. The first terminal of the two-way selector is used to receive the feedback voltage, and the second terminal of the two-way selector is used to receive the soft-start ramp voltage. The output terminal of the two-way selector is electrically connected to the logic operation module.

6. The start-up control circuit according to claim 1, characterized in that, The logic operation module includes an adder and a subtractor. The first input terminal of the adder is used to receive the common-mode voltage, the second input terminal of the adder is used to receive the threshold voltage, and the output terminal of the adder is used to be electrically connected to the driving circuit. The first input terminal of the subtractor is used to receive the common-mode voltage, the second input terminal of the subtractor is used to receive the threshold voltage, and the output terminal of the subtractor is used to be electrically connected to the driving circuit.

7. A resonant converter, characterized in that, The device includes a resonant converter circuit, a driving circuit, and a start-up control circuit as described in any one of claims 1-6, wherein the driving circuit is electrically connected to the logic operation modules in the resonant converter circuit and the start-up control circuit, respectively. The driving circuit is used to output a first driving instruction and a second driving instruction according to the first logic signal and the second logic signal output by the logic operation module. The resonant converter circuit is used to adjust the output voltage according to the first driving command and the second driving command.

8. The resonant converter according to claim 7, characterized in that, The driving circuit includes a first arithmetic unit, a trigger unit, and a signal output unit. The first arithmetic unit is electrically connected to the logic arithmetic module and the trigger unit, respectively. The signal output unit is electrically connected to the trigger unit and the resonant conversion circuit, respectively. The first arithmetic unit is configured to output a first arithmetic voltage and a second arithmetic voltage based on the resonant capacitor voltage, the first logic signal, and the second logic signal; the triggering unit is configured to output a first level signal and a second level signal based on the first arithmetic voltage and the second arithmetic voltage; the signal output unit is configured to output a second driving instruction based on the first level signal, and also to output the first driving instruction based on the second level signal.

9. The resonant converter according to claim 7, characterized in that, The resonant converter further includes a compensation circuit, which is electrically connected to the resonant capacitors in the driving circuit and the resonant converter circuit, respectively. The compensation circuit is used to divide the voltage of the resonant capacitor and inject compensation current into the midpoint of the voltage-dividing capacitor.

10. The resonant converter according to claim 9, characterized in that, The compensation circuit includes a first voltage divider capacitor, a second voltage divider capacitor, a first driving current source, and a second driving current source. The first terminal of the first voltage divider capacitor is electrically connected to the resonant capacitor in the resonant conversion circuit. The second terminal of the first voltage divider capacitor is electrically connected to the first terminal of the second voltage divider capacitor, the control terminal of the first driving current source, and the control terminal of the second driving current source, respectively. The second terminal of the second voltage divider capacitor is grounded. The input terminal of the first driving current source is used to receive the first driving command, and the input terminal of the second driving current source is used to receive the second driving command.

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