Controller for controlling a resonant converter

Abstract

The present invention discloses a controller for controlling a resonant converter. The controller includes: a first sensing pin coupled to a power supply for receiving a first sensing signal indicating the level of the input voltage of the resonant converter; a second sensing pin coupled to the resonant converter for receiving a second sensing signal indicating the level of the input current of the resonant converter; a feedback pin coupled to the resonant converter via a feedback circuit for receiving a feedback signal indicating the level of the output voltage of the resonant converter; and a first drive pin and a second drive pin coupled to the resonant converter for controlling the high-side switch and the low-side switch of the resonant converter, respectively. The controller is configured to: generate a compensation signal based on the first sensing signal, compare the compensation signal with a peak value of the second sensing signal to generate a first comparison result, compare the feedback signal with a threshold to generate a second comparison result, and control the high-side switch and the low-side switch based on the first and second comparison results.

Description

Technical Field

[0001] The present invention relates to the field of electronic device control, and in particular to a controller for controlling a resonant converter. Background Art

[0002] Conventional resonant converters convert input voltage into output voltage by controlling the frequency of the switching circuit in the resonant converter. When the resonant converter operates in the inductive region, the output voltage of the resonant converter decreases as the frequency increases because the gain of the resonant converter decreases as the frequency increases, where the gain is the ratio of the output voltage to the input voltage. On the other hand, when the frequency increases further, the rate of decrease in the gain becomes less obvious, which means that when a lower output voltage is required, it is difficult to reduce the output voltage under conditions where the frequency is higher than a certain value (for example, greater than 100KHz). Therefore, if the input voltage received by the resonant converter is high but a lower output voltage is required, the resonant converter may not be able to effectively regulate its output voltage to the target level. Therefore, conventional resonant converters are only suitable for operating within a narrow input voltage range (for example, 90V AC Up to 145V AC ). Summary of the Invention

[0003] In view of this, an object of the present invention is to provide a controller for controlling a resonant converter, which can enable the resonant converter to operate under a wider input voltage range and can reduce or eliminate audio noise.

[0004] In order to achieve the above objectives, the technical solutions adopted in the embodiments of the present invention are as follows:

[0005] In a first aspect, the present invention provides a controller for controlling a resonant converter. The controller includes: a first sensing pin coupled to a power supply, the first sensing pin being configured to receive a first sensing signal, the first sensing signal being configured to indicate the level of an input voltage of the resonant converter, the input voltage being provided by the power supply; a second sensing pin coupled to the resonant converter, the second sensing pin being configured to receive a second sensing signal, the second sensing signal being configured to indicate the level of an input current of the resonant converter; a feedback pin coupled to the resonant converter via a feedback circuit, the feedback pin being configured to receive a feedback signal, the feedback signal being configured to indicate the level of an output voltage of the resonant converter; a first driving pin coupled to the resonant converter, the first driving pin being configured to control a high-side switch of the resonant converter; and a second driving pin coupled to the resonant converter, the second driving pin being configured to control a low-side switch of the resonant converter. The controller is configured to: generate a compensation signal based on the first sensing signal, compare the compensation signal with a peak value of a second sensing signal to generate a first comparison result, compare the feedback signal with a threshold to generate a second comparison result, and control the high-side switch and the low-side switch based on the first comparison result and the second comparison result.

[0006] In a second aspect, the present invention provides a controller for controlling a resonant converter. The controller of the second aspect includes: a mode selection unit for selecting a mode from a first mode, a second mode, and a third mode based on a first sensing signal and a second sensing signal, and controlling the controller to operate in the selected mode, wherein the first sensing signal is used to indicate the level of the input voltage of the resonant converter, wherein the second sensing signal is used to indicate the level of the input current of the resonant converter; a peak detector coupled to the mode selection unit for detecting the peak value of the second sensing signal; and a compensation unit coupled to the mode selection unit for generating a compensation signal based on the first sensing signal, wherein if the input voltage of the resonant converter is within a preset range, the compensation signal is negatively correlated with the first sensing signal, wherein the mode selection unit is further used to compare the compensation signal with the peak value of the second sensing signal to generate a first comparison result, compare the feedback signal with a threshold value to generate a second comparison result, and determine the selected mode based on the first comparison result and the second comparison result, and wherein the feedback signal is used to indicate the level of the output voltage of the resonant converter.

[0007] Based on the embodiments provided in the above aspects, the embodiments provided by the present invention can enable the resonant converter to operate under a wider input voltage range, while reducing or eliminating audio noise.

[0008] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0010] Figure 1 According to an embodiment of the present invention, a circuit 100 including a resonant converter controlled by a controller 110 is shown;

[0011] Figure 2 According to an embodiment of the present invention, Figure 1 A block diagram of the controller 110 in FIG.

[0012] Figure 3 According to an embodiment of the present invention, the Figure 2 Flowchart of the operation of the controller 110;

[0013] Figure 4A According to an embodiment of the present invention, components in the controller 110 related to the first mode are shown;

[0014] Figure 4B According to an embodiment of the present invention, the signal waveform of the controller 110 related to the first mode is shown;

[0015] Figure 5A According to an embodiment of the present invention, components in the controller 110 related to the second mode are shown;

[0016] Figure 5B According to an embodiment of the present invention, the signal waveform of the controller 110 related to the second mode is shown;

[0017] Figure 6A According to an embodiment of the present invention, components in the controller 110 related to the third mode are shown;

[0018] Figure 6B According to an embodiment of the present invention, signal waveforms of the controller 110 associated with the third mode are shown. DETAILED DESCRIPTION

[0019] The following will provide detailed reference to the embodiments of the present invention. Although the present invention is described and illustrated by these embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, the present invention covers all alternatives, modifications and equivalents within the spirit and scope of the invention as defined by the appended claims.

[0020] In addition, numerous specific details are provided in the following detailed description to better illustrate the present invention. Those skilled in the art will appreciate that the present invention can be practiced without these specific details. In other instances, well-known methods, means, components, and circuits are not described in detail in order to highlight the main points of the present invention.

[0021] Figure 1 According to an embodiment of the present invention, a circuit 100 is shown including a resonant converter controlled by a controller 110. The resonant converter receives an input voltage V from a power source 101. AC and the input voltage V AC Converted to output voltage V O The resonant converter includes a switching circuit, a resonant tank, and a transformer T1. The switching circuit includes a high-side switch Q1 and a low-side switch Q2. During operation, the on-state of the high-side switch Q1 and the on-state of the low-side switch Q2 are complementary. In other words, when switch Q1 is on, switch Q2 is off, and vice versa. The resonant tank includes a first resonant inductor LR1, a second resonant inductor LR2, and a resonant capacitor CR.

[0022] In one embodiment, the controller 110 includes a first sensing pin HV, a second sensing pin CS, a feedback pin VFB, a first drive pin DRVH, and a second drive pin DRVL. The first sensing pin HV is coupled to the power supply 101 for receiving a first sensing signal HVIN, which is used to indicate the input voltage V provided by the power supply 101. AC The second sensing pin CS is coupled to the resonant converter via the current detection circuit 120. The second sensing pin CS receives a second sensing signal INS. The second sensing signal INS is used to indicate the input current I IN The feedback pin VFB is coupled to the output terminal of the resonant converter through the feedback circuit 140 and is used to receive the feedback signal FB. The feedback signal FB is used to indicate the output voltage V O In one embodiment, the feedback circuit 140 includes an amplifier 102 and an optocoupler 104. A first drive pin DRVH and a second drive pin DRVL are coupled to the high-side switch Q1 and the low-side switch Q2, respectively, for controlling (e.g., turning on or off) the high-side switch Q1 and the low-side switch Q2. The controller 110 is configured to adjust the frequency of the high-side switch Q1 and the frequency of the low-side switch Q2 according to the feedback signal FB.

[0023] During operation, the controller 110 is used to: generate a compensation signal VP based on the first sensing signal HVIN, compare the compensation signal VP with the peak value INSPK of the second sensing signal INS to generate a first comparison result, compare the feedback signal FB with the threshold value VH to generate a second comparison result, and control the high-side switch Q1 and the low-side switch Q2 according to the first comparison result and the second comparison result.

[0024] Figure 2 According to an embodiment of the present invention, Figure 1 A block diagram of the controller 110 is shown in FIG. Figure 2 In the embodiment of the present invention, the controller 110 includes a peak detector 202, a compensation unit 290, a mode selection unit 204, a soft on / off unit 206, a frequency control unit 208, a voltage-controlled oscillator 210, a sawtooth wave generation unit 280, a duty cycle control unit 212 and a drive signal generation unit 214.

[0025] The sawtooth wave generating unit 280 is used to generate a first sawtooth wave signal SAW1 and a second sawtooth wave signal SAW2. The peak detector 202 is coupled to the second sensing pin CS and includes a circuit for detecting the peak value INSPK of the second sensing signal INS. The compensation unit 290 is coupled to the first sensing pin HV and is used to generate a compensation signal VP based on the first sensing signal HVIN. If the input voltage of the resonant converter is within a preset range (e.g., 90Vac to 265Vac), the compensation signal VP is negatively correlated (e.g., inversely proportional) to the first sensing signal HVIN. Here, negative correlation or inverse proportional means that if the first sensing signal HVIN increases, the compensation signal VP decreases, and vice versa. In one embodiment, the voltage level of the compensation signal VP can be obtained according to equation (1),

[0026] VP=KF×HVIN (1),

[0027] Where K and F are constants determined empirically. Mode selection unit 204 is coupled to first sensing pin HV via compensation unit 290 and to second sensing pin CS via peak detector 202. Mode selection unit 204 is configured to select a mode among a first mode (normal mode), a second mode (high-frequency burst mode), and a third mode (low-frequency burst mode) based on first sensing signal HVIN and second sensing signal INS. Mode selection unit 204 is also configured to control controller 110 to operate in the selected mode.

[0028] Specifically, if the peak value INSPK of the second sensing signal INS is greater than the compensation signal VP and the feedback signal FB is greater than the threshold value VH, the mode selection unit 204 selects the first mode. In one embodiment, the threshold value VH is the peak value of the first sawtooth wave signal SAW1 generated by the sawtooth wave generation unit 280. If the peak value INSPK of the second sensing signal INS is greater than the compensation signal VP and the feedback signal FB is less than the threshold value VH, the mode selection unit 204 selects the second mode. If the peak value INSPK of the second sensing signal INS is less than the compensation signal VP, the mode selection unit 204 selects the third mode.

[0029] Figure 3 According to an embodiment of the present invention, the Figure 2 Flowchart of the operation of the controller 110 in FIG.

[0030] In step 302, the controller 110 detects the level of the first sensing signal HVIN and the level of the second sensing signal INS. The first sensing signal HVIN is used to indicate the input voltage V AC The second sensing signal INS is used to indicate the input current I IN The controller 110 also generates a compensation signal VP according to the first sensing signal HVIN and detects a peak value INSPK of the second sensing signal INS.

[0031] In step 304, the controller 110 compares the peak value INSPK with the compensation signal VP. If the peak value INSPK is greater than the compensation signal VP, the process proceeds to step 306; otherwise, the process proceeds to step 312. In step 312, the controller 110 enters the third mode.

[0032] In step 306, the controller 110 indicates the output voltage V O The feedback signal FB of the level is compared with the threshold value VH. If the feedback signal FB is greater than the threshold value VH, the process proceeds to step 308; otherwise, the process proceeds to step 310. In step 308, the controller 110 enters the first mode. In step 310, the controller 110 enters the second mode.

[0033] Figure 3 Steps 304-312 shown can be performed by Figure 2 The mode selection unit 204 in FIG. 2 may include a plurality of comparators and logic circuits (not shown) to generate comparison results and perform the mode selection step.

[0034] Figure 4A According to an embodiment of the present invention, components in the controller 110 related to the first mode are shown. Figure 4BAccording to an embodiment of the present invention, signal waveforms of the controller 110 associated with the first mode are shown. Figure 4A and Figure 4B Will combine Figure 2 Provide explanation.

[0035] In the first mode (normal mode), the frequency control unit 208 receives the feedback signal FB from the feedback pin VFB and generates a frequency control signal VFBE according to the feedback signal FB. The voltage controlled oscillator 210 is coupled to the frequency control unit 208. The voltage controlled oscillator 210 is used to generate a switching signal FS having a frequency according to the frequency control signal VFBE, and the switching signal FS controls the high-side switch Q1 and the low-side switch Q2 according to the frequency control signal VFBE. In one embodiment, the frequency of the switching signal FS is inversely proportional to the level of the frequency control signal VFBE. The drive signal generation unit 214 receives the switching signal FS and generates a first drive signal HDR and a second drive signal LDR to control the high-side switch Q1 and the low-side switch Q2, respectively. In one embodiment, as Figure 4B As shown, the first drive signal HDR and the second drive signal LDR have the same frequency as the switching signal FS, and the second drive signal LDR is inverted relative to the first drive signal HDR, so that the high-side switch Q1 and the low-side switch Q2 are alternately turned on, and the on state of the high-side switch Q1 and the on state of the low-side switch Q2 are complementary.

[0036] Figure 5A According to an embodiment of the present invention, components in the controller 110 related to the second mode are shown. Figure 5B According to an embodiment of the present invention, signal waveforms of the controller 110 associated with the second mode are shown. Figure 5A and Figure 5B Will combine Figure 2 Provide explanation.

[0037] In the second mode (high-frequency burst mode), the frequency control unit 208 and the voltage-controlled oscillator 210 operate in a manner similar to that in the first mode. The duty cycle control unit 212 generates a duty cycle control signal DT by comparing the feedback signal FB with the first sawtooth wave signal SAW1 having a first frequency. In one embodiment, the duty cycle control unit 212 includes a comparator 502. The duty cycle control signal DT may be a pulse-width modulated signal having the same frequency as the sawtooth wave signal SAW1. In each cycle, the duty cycle control signal DT is in a first state (e.g., a logic high level) during a first time period T1 and in a second state (e.g., a logic low level) during a second time period T2 following the first time period T1. The drive signal generation unit 214 generates a first drive signal HDR and a second drive signal LDR based on the switching signal FS from the voltage-controlled oscillator 210 and the duty cycle control signal DT. Specifically, the drive signal generation unit 214 multiplies the switching signal FS by the duty cycle control signal DT to generate the first drive signal HDR and the second drive signal LDR. In one embodiment, the drive signal generation unit 214 includes an AND gate. According to the first driving signal HDR and the second driving signal LDR, Figure 5B As shown, the high-side switch Q1 and the low-side switch Q2 are alternately turned on and off (one switch is on while the other is off) during a first time period T1. Both the high-side switch Q1 and the low-side switch Q2 are turned off during a second time period T2 following the first time period T1. The lengths of the first time period T1 and the second time period T2 are determined by comparing the feedback signal FB with a first sawtooth wave signal SAW1 having a first frequency. In one embodiment, the first frequency is configured to be no less than 20 kHz so that the resonant converter does not generate audible noise during operation.

[0038] Figure 6A According to an embodiment of the present invention, components in the controller 110 related to the third mode are shown. Figure 6B According to an embodiment of the present invention, signal waveforms of the controller 110 associated with the third mode are shown. Figure 6A and Figure 6B Will combine Figure 2 Provide explanation.

[0039] In the third mode (low-frequency burst mode), the duty cycle control unit 212 generates a duty cycle control signal DT by comparing the feedback signal FB with the second sawtooth wave signal SAW2 having a second frequency. The duty cycle control signal DT may be a pulse-width modulated signal having the same frequency as the sawtooth wave signal SAW2. If the feedback signal FB is greater than the second sawtooth wave signal SAW2, the duty cycle control signal DT is in a first state (e.g., a logic high level). If the feedback signal FB is less than the second sawtooth wave signal SAW2, the duty cycle control signal DT is in a second state (e.g., a logic low level). In the third mode, the soft on / off unit 206, coupled to the voltage-controlled oscillator 210 via the frequency control unit 208, is enabled. During a time period TR after the duty cycle control signal DT transitions from the second state to the first state, the soft on / off unit 206 gradually decreases the frequency of the switching signal FS. During a time period TF after the duty cycle control signal DT transitions from the first state to the second state, the soft on / off unit 206 gradually increases the frequency of the switching signal FS. Specifically, the soft on / off unit 206 generates an adjustment signal ADJ to adjust the frequency control unit 208 so that the frequency control signal VFBE gradually increases during the time period TR and gradually decreases during the time period TF. The voltage controlled oscillator 210 generates a switching signal FS based on the frequency control signal VFBE. In one embodiment, the frequency of the switching signal FS is inversely proportional to the level of the frequency control signal VFBE. The drive signal generation unit 214 generates a first drive signal HDR and a second drive signal LDR based on the frequency control signal VFBE and the switching signal FS. The frequency control signal VFBE is adjusted by the duty cycle control signal DT. Specifically, in the third time period T3, the frequency control signal VFBE is higher than the threshold value (for example, the initial level V TH ), the driving signal generating unit 214 is enabled to generate the first driving signal HDR (in phase with the switching signal FS) and the second driving signal LDR (in phase opposite to the first driving signal HDR). During the fourth time period T4, the frequency control signal VFBE is not higher than the threshold value (for example, the initial level V TH ), the driving signal generating unit 214 maintains the first driving signal HDR and the second driving signal LDR in the second state (eg, a logic low level).

[0040] Therefore, if Figure 6BAs shown, the high-side switch Q1 and the low-side switch Q2 alternately turn on and off (one switch is on while the other is off) during a third time period T3, and both are off during a fourth time period T4 following the third time period T3. The lengths of the third time period T3 and the fourth time period T4 are determined by comparing the feedback signal FB with a second sawtooth wave signal SAW2 having a second frequency. In one embodiment, the first frequency is greater than the second frequency (e.g., the first frequency is 100 times the second frequency). For example, the first frequency is 20 kHz and the second frequency is 200 Hz. In addition, the frequencies of the high-side switch Q1 and the low-side switch Q2 gradually decrease at the beginning of the third time period T3 and gradually increase at the end of the third time period T3. With this configuration, the audible noise generated by the resonant converter can be significantly reduced or eliminated.

[0041] As described above, embodiments of the present invention disclose a controller for controlling a resonant converter. In addition to a normal mode, the controller also includes a high-frequency burst mode and a low-frequency burst mode with a soft on / off function. If the input voltage received by the resonant converter is high and a lower output voltage needs to be generated, the controller can operate in the high-frequency burst mode or the low-frequency burst mode. In the high-frequency burst mode, in addition to adjusting the switching signal FS according to the feedback signal FB to reduce the output voltage, the controller can further reduce the output voltage by using the duty cycle control signal DT. The duty cycle control signal DT is configured to have a higher frequency than the human audible frequency (e.g., not less than 20 kHz). In the low-frequency burst mode, although the frequency of the duty cycle control signal DT is relatively low (e.g., 200 Hz), the soft on / off function can reduce or eliminate audible noise. The controller can dynamically switch between the normal mode, the high-frequency burst mode, and the low-frequency burst mode according to the input voltage level and load conditions. Advantageously, the controller according to the present invention can enable the resonant converter to operate over a wider input voltage range (e.g., 90V AC to 265V AC ) while reducing or eliminating audio noise.

[0042] Although the foregoing description and drawings represent embodiments of the present invention, it should be understood that various additions, modifications, and substitutions may be made therein without departing from the spirit and scope of the principles of the present invention as defined in the appended claims. Those skilled in the art will appreciate that the present invention can be used with many modifications of form, structure, arrangement, proportion, materials, elements and components, and other aspects, and that other aspects herein are particularly suitable for specific environments and operating requirements in the practice of the present invention without departing from the principles of the present invention. Therefore, the presently disclosed embodiments are to be considered in all respects as illustrative and not restrictive, and the scope of the invention is indicated by the appended claims and their legal equivalents, and is not limited to the foregoing description.

Claims

1. A controller for controlling a resonant converter, characterized in that: The controller includes: a first sensing pin coupled to a power supply, the first sensing pin being configured to receive a first sensing signal, the first sensing signal being configured to indicate a level of an input voltage of the resonant converter, the input voltage being provided by the power supply; a second sensing pin coupled to the resonant converter, the second sensing pin being configured to receive a second sensing signal, the second sensing signal being configured to indicate a level of an input current of the resonant converter; coupled to a feedback pin of the resonant converter via a feedback circuit, the feedback pin being configured to receive a feedback signal, the feedback signal being configured to indicate a level of an output voltage of the resonant converter; coupled to a first drive pin of the resonant converter, the first drive pin being configured to control a high-side switch of the resonant converter; and coupled to a second drive pin of the resonant converter, the second drive pin being used to control a low-side switch of the resonant converter, wherein: The controller is configured to: generate a compensation signal according to the first sensing signal, compare the compensation signal with a peak value of the second sensing signal to generate a first comparison result, compare the feedback signal with a threshold to generate a second comparison result, and control the high-side switch and the low-side switch according to the first comparison result and the second comparison result. The controller is further configured to adjust the frequencies of the high-side switch and the low-side switch according to the feedback signal, and control the resonant converter to operate in a first mode, a second mode, and a third mode according to the first comparison result and the second comparison result. Wherein, in the first mode, the high-side switch and the low-side switch are alternately turned on and off, wherein, in the second mode, the high-side switch and the low-side switch are alternately turned on and off in a first time period, and the high-side switch and the low-side switch are turned off in a second time period after the first time period, and wherein the controller is further configured to determine the length of the first time period and the length of the second time period by comparing the feedback signal with a first sawtooth wave signal having a first frequency, wherein, in the third mode, the high-side switch and the low-side switch are alternately turned on and off in a third time period, and the high-side switch and the low-side switch are turned off in a fourth time period after the third time period, and wherein the controller is further configured to determine the length of the third time period and the length of the fourth time period by comparing the feedback signal with a second sawtooth wave signal having a second frequency, The first frequency is greater than the second frequency, and the threshold is a peak value of the first sawtooth wave signal.

2. The controller according to claim 1, characterized in that Also includes: A peak detector is coupled to the second sensing pin, and is configured to detect a peak value of the second sensing signal.

3. The controller according to claim 1, wherein: Also includes: A compensation unit is coupled to the first sensing pin, the compensation unit being configured to generate the compensation signal according to the first sensing signal, wherein if the input voltage of the resonant converter is within a preset range, the compensation signal is negatively correlated with the first sensing signal.

4. The controller according to claim 1, wherein: Also includes: a mode selection unit coupled to the first sensing pin and the second sensing pin, the mode selection unit being configured to select a mode among the first mode, the second mode, and the third mode according to the first sensing signal and the second sensing signal, and to control the controller to operate in the selected mode; If the peak value of the second sensing signal is greater than the compensation signal and the feedback signal is greater than the threshold, the mode selection unit selects the first mode. If the peak value of the second sensing signal is greater than the compensation signal and the feedback signal is less than the threshold, the mode selection unit selects the second mode, and If the peak value of the second sensing signal is smaller than the compensation signal, the mode selection unit selects the third mode.

5. The controller according to claim 1, wherein: The first frequency is 100 times the second frequency.

6. The controller according to claim 1, characterized in that The first frequency is not less than 20KHz.

7. The controller according to claim 1 or 4, characterized in that: Also includes: a frequency control unit coupled to the feedback pin, the frequency control unit being configured to generate a frequency control signal according to the feedback signal; as well as A voltage controlled oscillator is coupled to the frequency control unit, and is configured to generate a switching signal having a frequency of the high-side switch and the low-side switch according to the frequency control signal.

8. The controller according to claim 7, characterized in that Also includes: a soft on / off unit coupled to the voltage controlled oscillator, Wherein, in the third mode, the soft on / off unit is configured to gradually reduce the frequency of the switching signal at the beginning of the third time period, and gradually increase the frequency of the switching signal at the end of the third time period.

9. The controller according to claim 4, characterized in that Also includes: a frequency control unit coupled to the feedback pin, the frequency control unit being configured to generate a frequency control signal according to the feedback signal; a voltage-controlled oscillator coupled to the frequency control unit, the voltage-controlled oscillator configured to generate a switching signal having frequencies of the high-side switch and the low-side switch according to the frequency control signal; a duty cycle control unit coupled to the mode selection unit; as well as a driving signal generating unit coupled to the duty cycle control unit and the voltage controlled oscillator, In the second mode, the duty cycle control unit is used to generate a duty cycle control signal by comparing the feedback signal with the first sawtooth wave signal, and the drive signal generating unit is used to generate a first drive signal and a second drive signal according to the switching signal and the duty cycle control signal. Wherein, in the third mode, the duty cycle control unit is used to generate the duty cycle control signal by comparing the feedback signal with the second sawtooth wave signal, and the drive signal generation unit is used to generate the first drive signal and the second drive signal according to the switching signal and the frequency control signal, wherein the frequency control signal is adjusted by the duty cycle control signal. The first drive signal is output from the first drive pin to control the high-side switch, and the second drive signal is output from the second drive pin to control the low-side switch.

10. A controller for controlling a resonant converter, characterized in that: The controller includes: a mode selection unit, configured to select a mode among a first mode, a second mode, and a third mode according to a first sensing signal and a second sensing signal, and control the controller to operate in the selected mode, wherein the first sensing signal is used to indicate a level of an input voltage of the resonant converter, and the second sensing signal is used to indicate a level of an input current of the resonant converter; a peak detector coupled to the mode selection unit, configured to detect a peak value of the second sensing signal; and a compensation unit coupled to the mode selection unit, configured to generate a compensation signal according to the first sensing signal, wherein if the input voltage of the resonant converter is within a preset range, the compensation signal is negatively correlated with the first sensing signal, The mode selection unit is further configured to: compare the compensation signal with a peak value of the second sensing signal to generate a first comparison result, compare the feedback signal with a threshold to generate a second comparison result, and determine the selected mode according to the first comparison result and the second comparison result; and The feedback signal is used to indicate the level of the output voltage of the resonant converter. If the peak value of the second sensing signal is greater than the compensation signal and the feedback signal is greater than the threshold, the mode selection unit selects the first mode, If the peak value of the second sensing signal is greater than the compensation signal and the feedback signal is less than the threshold, the mode selection unit selects the second mode, and If the peak value of the second sensing signal is smaller than the compensation signal, the mode selection unit selects the third mode. In the first mode, the high-side switch and the low-side switch of the resonant converter are alternately turned on and off. In the second mode, the high-side switch and the low-side switch are alternately turned on and off in a first time period, and the high-side switch and the low-side switch are turned off in a second time period after the first time period, and wherein the controller is further configured to determine the length of the first time period and the length of the second time period by comparing the feedback signal with a first sawtooth wave signal having a first frequency, In the third mode, the high-side switch and the low-side switch are alternately turned on and off in a third time period, and the high-side switch and the low-side switch are turned off in a fourth time period after the third time period, and wherein the controller is further configured to determine the length of the third time period and the length of the fourth time period by comparing the feedback signal with a second sawtooth wave signal having a second frequency, The first frequency is greater than the second frequency, and the threshold is a peak value of the first sawtooth wave signal.

11. The controller according to claim 10, characterized in that The first frequency is 100 times the second frequency.

12. The controller according to claim 10, characterized in that The first frequency is not less than 20KHz.

13. The controller according to claim 10, characterized in that Also includes: a frequency control unit coupled to the mode selection unit, configured to generate a frequency control signal according to the feedback signal; as well as A voltage-controlled oscillator coupled to the frequency control unit is configured to generate a switching signal having a frequency according to the frequency control signal, wherein the switching signal is configured to control the high-side switch and the low-side switch.

14. The controller according to claim 13, characterized in that Also includes: a soft on / off unit coupled to the voltage controlled oscillator, Wherein, in the third mode, the soft on / off unit is configured to gradually reduce the frequency of the switching signal at the beginning of the third time period, and gradually increase the frequency of the switching signal at the end of the third time period.

15. The controller according to claim 13, characterized in that Also includes: a duty cycle control unit coupled to the mode selection unit; as well as a driving signal generating unit coupled to the duty cycle control unit and the voltage controlled oscillator, In the second mode, the duty cycle control unit is used to generate a duty cycle control signal by comparing the feedback signal with the first sawtooth wave signal, and the drive signal generating unit is used to generate a first drive signal and a second drive signal according to the switching signal and the duty cycle control signal. Wherein, in the third mode, the duty cycle control unit is used to generate the duty cycle control signal by comparing the feedback signal with the second sawtooth wave signal, and the drive signal generation unit is used to generate the first drive signal and the second drive signal according to the switching signal and the frequency control signal, wherein the frequency control signal is adjusted by the duty cycle control signal, and The first drive signal controls the high-side switch, and the second drive signal controls the low-side switch.

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