Patent Publication Number: US-2023136279-A1

Title: Controller for controlling a resonant converter

Description:
BACKGROUND 
     A conventional resonant converter converts an input voltage to an output voltage by controlling a frequency of a switching circuit in the resonant converter. When the resonant converter is operated in the inductive region, the output voltage of the resonant converter decreases when the frequency increases because a gain of the resonant converter decreases as the frequency increases, where the gain is a ratio of the output voltage to the input voltage. On the other hand, the rate of decrease of the gain becomes less significant when the frequency further increases, which means it is difficult to decrease the output voltage if the frequency is above a certain level, e.g., greater than 100 KHz, when a lower output voltage is desired. As a result, if the resonant converter receives a relatively high input voltage while a low output voltage is required, the resonant converter may not be able to efficiently regulate its output voltage to a target level. Therefore, a conventional resonant converter is only suitable to operate within a narrow input voltage range (e.g., 90 V AC  to 145 V AC ). 
     SUMMARY 
     Disclosed are embodiments of a controller for controlling a resonant converter. The controller includes a first sensing pin, a second sensing pin, a feedback pin, a first driving pin and a second driving pin. The first driving pin is operable for receiving a first sensing signal indicating a level of an input voltage of the resonant converter provided by a power source. The resonant converter receives the input voltage and provides an output voltage. The second sensing pin is operable for receiving a second sensing signal indicating a level of an input current of the resonant converter. The feedback pin is operable for receiving a feedback signal indicating a level of the output voltage. The first driving pin and the second driving pin are operable for controlling a high side switch and a low side switch of the resonant converter, respectively. The controller is operable for generating a compensated signal based on the first sensing signal, comparing the compensated signal with a peak value of the second sensing signal to generate a first comparison result, comparing the feedback signal with a threshold to generate a second comparison result, and controlling the high side switch and the low side switch based on the first and the second comparison results. 
     In other embodiments, a controller for controlling a resonant converter includes a mode selection unit, a peak detector and a compensation unit. The mode selection unit is operable for selecting a mode among a first, a second and a third mode based on a first sensing signal and a second sensing signal and for controlling the controller to operate in the selected mode, where the first sensing signal indicates a level of an input voltage of the resonant converter, and where the second sensing signal indicates a level of an input current of the resonant converter. The peak detector is operable for detecting a peak value of the second sensing signal. The compensation unit is operable for generating a compensated signal based on the first sensing signal, where the compensated signal is inversely proportional to the first sensing signal if the input voltage of the resonant converter is within a predetermined range. The mode selection unit is operable for comparing the compensated signal with the peak value of the second sensing signal to generate a first comparison result, comparing a feedback signal with a threshold to generate a second comparison result, and determining the selected mode based on the first and the second comparison results. The feedback signal indicates a level of an output voltage of the resonant converter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of embodiments of the claimed subject matter will become apparent as the following detailed description proceeds, and upon reference to the drawings, wherein like numerals depict like parts, and in which: 
         FIG.  1    shows a resonant converter controlled by a controller, in accordance with embodiments of the present invention. 
         FIG.  2    shows a block diagram of a controller for controlling a resonant converter, in accordance with embodiments of the present invention. 
         FIG.  3    shows a flowchart illustrating operations of a controller for controlling a resonant converter, in accordance with embodiments of the present invention. 
         FIG.  4 A  shows components in a controller associated with a first mode, in accordance with embodiments of the present invention. 
         FIG.  4 B  shows signal waveforms of a controller associated with a first mode, in accordance with embodiments of the present invention. 
         FIG.  5 A  shows components in a controller associated with a second mode, in accordance with embodiments of the present invention. 
         FIG.  5 B  shows signal waveforms of a controller associated with a second mode, in accordance with embodiments of the present invention. 
         FIG.  6 A  shows components in a controller associated with a third mode, in accordance with embodiments of the present invention. 
         FIG.  6 B  shows signal waveforms of a controller associated with a third mode, in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present invention. While the invention will be described in combination with these embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail to avoid obscuring aspects of the present invention. 
       FIG.  1    shows a circuit  100  including a resonant converter controlled by a controller  110 , in accordance with embodiments of the present invention. The resonant converter receives an input voltage V AC  from a power source  101  and converts the input voltage V AC  to an output voltage V O . The resonant converter includes a switching circuit, a resonant tank and a transformer T 1 . The switching circuit includes a high side switch Q 1  and a low side switch Q 2 . In operation, a conductance status of the high side switch Q 1  and a conductance status of the low side switch Q 2  are complementary. In other words, when switch Q 1  is turned on, switch Q 2  is off, and vice versa. The resonant tank includes a first resonant inductor LR 1 , a second resonant inductor LR 2  and a resonant capacitor CR. 
     In an embodiment, the controller  110  includes a first sensing pin HV, a second sensing pin CS, a feedback pin VFB, a first driving pin DRVH and a second driving pin DRVL. The first sensing pin HV is coupled to the power source  101  for receiving a first sensing signal HVIN indicating a level of the input voltage V AC  that is provided by the power source  101 . The second sensing pin CS is coupled to the resonant converter through a current detecting circuit  120 . The second sensing pin CS receives a second sensing signal INS. The second sensing signal INS indicates a level of an input current I IN  of the resonant converter and further indicates a load condition. The feedback pin VFB is coupled to an output terminal of the resonant converter through a feedback circuit  140  for receiving a feedback signal FB indicating a level of the output voltage V O  of the resonant converter. In an embodiment, the feedback circuit  140  includes an amplifier  102  and an optical coupler  104 . The first driving pin DRVH and the second driving pin DRVL are coupled to the high side switch Q 1  and the low side switch Q 2 , and is operable for controlling (e.g., turning on or off) the high side switch Q 1  and the low side switch Q 2 , respectively. The controller  110  is operable for adjusting a frequency of the high side switch Q 1  and a frequency of the low side switch Q 2  based on the feedback signal FB. 
     In operation, the controller  110  is operable for: generating a compensated signal VP based on the first sensing signal HVIN, comparing the compensated signal VP with a peak value INSPK of the second sensing signal INS to generate a first comparison result, comparing the feedback signal FB with a threshold VH to generate a second comparison result, and controlling the high side switch Q 1  and the low side switch Q 2  based on the first and the second comparison results. 
       FIG.  2    shows a block diagram of the controller  110  in  FIG.  1   , in accordance with embodiments of the present invention. In the  FIG.  2    embodiments, 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 generation unit  280 , a duty control unit  212  and a driving signal generation unit  214 . 
     The sawtooth generation unit  280  is operable for generating a first sawtooth signal SAW 1  and a second sawtooth signal SAW 2 . The peak detector  202  is coupled to the second sensing pin CS, and includes circuitry that is operable 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 operable for generating the compensation signal VP based on the first sensing signal HVIN, where the compensation signal VP is inversely related to (e.g., inversely proportional to) the first sensing signal HVIN if the input voltage of the resonant converter is within a predetermined range (e.g., 90 Vac to 265 Vac). Here, inversely related or proportional to means if the first sensing signal HVIN increases, then the compensation signal VP decreases, and vice versa. In an embodiment, the voltage level of the compensation signal VP can be obtained according to equation (1), 
       VP= K−F ×HV   (1),
 
     where K and F are constants that are empirically determined. The mode selection unit  204  is coupled to the first sensing pin HV through the compensation unit  290  and coupled to the second sensing pin CS through the peak detector  202 . The mode selection unit  204  is operable for selecting 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 the first sensing signal HVIN and the second sensing signal INS, and is also operable for controlling the controller  110  to operate in the selected mode. 
     More specifically, the mode selection unit  204  selects the first mode if the peak value INSPK of the second sensing signal INS is greater than the compensated signal VP and the feedback signal FB is greater than a threshold VH. In an embodiment, the threshold VH is a peak value of the first sawtooth signal SAW 1  generated by the sawtooth generation unit  280 . The mode selection unit  204  selects the second mode if the peak value INSPK of the second sensing signal INS is greater than the compensated signal VP and the feedback signal FB is less than the threshold VH. The mode selection unit  204  selects the third mode if the peak value INSPK of the second sensing signal INS is less than the compensated signal VP. 
       FIG.  3    shows a flowchart illustrating operations of the controller  110  in  FIG.  2   , in accordance with embodiments of the present invention. 
     In step  302 , the controller  110  detects a level of the first sensing signal HVIN and a level of the second sensing signal INS. The first sensing signal HVIN indicates a level of an input voltage V AC  of a resonant converter. The second sensing signal INS indicates a level of an input current I IN  of the resonant converter. The controller  110  further generates the compensated signal VP based on the first sensing signal HVIN, and detects a peak value INSPK of the second sensing signal INS. 
     In step  304 , the controller  110  compares the peak value INSPK with the compensated signal VP. If the peak value INSPK is greater than the compensated signal VP, the flowchart goes to step  306 ; otherwise, the flowchart goes to step  312 . In step  312 , the controller  110  enters the third mode. 
     In step  306 , the controller  110  compares the feedback signal FB indicating a level of the output voltage V O  of the resonant converter with the threshold VH. If the feedback signal FB is greater than the threshold VH, the flowchart goes to step  308 ; otherwise, the flowchart goes to step  310 . In step  308 , the controller  110  enters the first mode. In step  310 , the controller  110  enters the second mode. 
     The steps  304 - 312  shown in  FIG.  3    can be performed by the mode selection unit  204  in  FIG.  2   . The mode selection unit  204  can include multiple comparators and logic circuit (not shown) to generate the comparison results and perform mode selection steps. 
       FIG.  4 A  shows components in the controller  110  associated with the first mode, in accordance with embodiments of the present invention.  FIG.  4 B  shows signal waveforms of the controller  110  associated with the first mode, in accordance with embodiments of the present invention.  FIGS.  4 A and  4 B  are described in combination with  FIG.  2   . 
     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 based on the feedback signal FB. The voltage-controlled oscillator  210  is coupled to the frequency control unit  208 , and generates a switching signal FS having a frequency for controlling the high side switch Q 1  and the low side switch Q 2  based on the frequency control signal VFBE. In an embodiment, the frequency of the switching signal FS is inversely proportional to a level of the frequency control signal VFBE. The driving signal generation unit  214  receives the switching signal FS, and generates the first driving signal HDR and the second driving signal LDR to control the high side switch Q 1  and the low side switch Q 2 , respectively. In an embodiment, as shown in  FIG.  4 B , the first driving signal HDR and the second driving signal LDR have the same frequency as that of the switching signal FS, while the second driving signal LDR is phase-inverted relative to the first driving signal HDR, such that the high side switch Q 1  and the low side switch Q 2  are alternately turned on and a conductance status of the high side switch Q 1  and a conductance status of the low side switch Q 2  are complementary. 
       FIG.  5 A  shows components in the controller  110  associated with the second mode, in accordance with embodiments of the present invention.  FIG.  5 B  shows signal waveforms of the controller  110  associated with the second mode, in accordance with embodiments of the present invention.  FIGS.  5 A and  5 B  are described in combination with  FIG.  2   . 
     In the second mode (high frequency burst mode), operation of the frequency control unit  208  and the voltage-controlled oscillator  210  is similar to that of the first mode. The duty control unit  212  generates a duty control signal DT by comparing the feedback signal FB with the first sawtooth signal SAW 1  having a first frequency. In an embodiment, the duty control unit  212  includes a comparator  502 . The duty control signal DT can be a pulse-width modulation signal having a same frequency as that of the sawtooth signal SAW 1 . In each cycle, the duty control signal DT is in a first state (e.g., logic high) during a first time period T 1  and is in a second state (e.g., logic low) during a second time period T 2  successive to the first time period T 1 . The driving signal generation unit  214  generates the first driving signal HDR and the second driving signal LDR based on the switching signal FS from the voltage-controlled oscillator  210  and the duty control signal DT. More specifically, the driving signal generation unit  214  multiplies the switching signal FS with the duty control signal DT to generate the first driving signal HDR and the second driving signal LDR. In an embodiment, the driving signal generation unit  214  includes an AND gate. According to the first driving signal HDR and the second driving signal LDR, as shown in  FIG.  5 B , the high side switch Q 1  and the low side switch Q 2  are alternately turned on and off during the first time period T 1  (one switch is on while the other switch is off), and are both off during the second time period T 2  successive to the first time period T 1 . A length of the first time period T 1  and a length of the second time period T 2  are determined by comparing the feedback signal FB with the first sawtooth signal SAW 1  having the first frequency. In an embodiment, the first frequency is configured to be not less than 20 KHz, such that the resonant converter will not produce audible noise in operation. 
       FIG.  6 A  shows components in the controller  110  associated with the third mode, in accordance with embodiments of the present invention.  FIG.  6 B  shows signal waveforms of the controller  110  associated with the third mode, in accordance with embodiments of the present invention.  FIGS.  6 A and  6 B  are described in combination with  FIG.  2   . 
     In the third mode (low frequency burst mode), the duty control unit  212  generates a duty control signal DT by comparing the feedback signal FB with the second sawtooth signal SAW 2  having a second frequency. The duty control signal DT can be a pulse-width modulation signal having a same frequency as that of the sawtooth signal SAW 2 . The duty control signal DT is in a first state (e.g., logic high) if the feedback signal FB is greater than the second sawtooth signal SAW 2 , and is in a second state (e.g., logic low) if the feedback signal FB is less than the second sawtooth signal SAW 2 . In the third mode, the soft on/off unit  206 , which is coupled to the voltage-controlled oscillator  210  through the frequency control unit  208 , is enabled to gradually decrease the frequency of the switching signal FS during a time period TR after the duty control signal DT changes from the second state to the first state, and to gradually increase the frequency of the switching signal FS during a time period TF after the duty control signal DT changes from the first state to the second state. More specifically, the soft on/off unit  206  generates an adjustment signal ADJ to adjust the frequency control unit  208  such 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 the switching signal FS based on the frequency control signal VFBE. In an embodiment, the frequency of the switching signal FS is inversely proportional to a level of the frequency control signal VFBE. The driving signal generation unit  214  generates the first driving signal HDR and the second driving signal LDR based on the frequency control signal VFBE and the switching signal FS. The frequency control signal VFBE is adjusted by the duty control signal DT. More specifically, during a third time period T 3 , the frequency control signal VFBE is above a threshold (e.g., an initial level V TH ), and the driving signal generation unit  214  is enabled to generate the first driving signal HDR (which is in phase with the switching signal FS) and to generate the second driving signal LDR (which is phase-inverted of the first driving signal HDR). During a fourth time period T 4 , the frequency control signal VFBE is not above the threshold (e.g., the initial level V TH ), and the driving signal generation unit  214  keeps the first driving signal HDR the second driving signal LDR in a second state (e.g., logic low). 
     Accordingly, as shown in  FIG.  6 B , the high side switch Q 1  and the low side switch Q 2  are alternately turned on and off during the third time period T 3  (one switch is on while the other is off), and both are off during the fourth time period T 4  successive to the third time period T 3 . A length of the third time period T 3  and a length of the fourth time period T 4  is determined by comparing the feedback signal FB with the second sawtooth signal SAW 2  having the second frequency. In one embodiment, the first frequency is greater than (e.g., 100 times) the second frequency. For example, the first frequency is 20 KHz and the second frequency is 200 Hz. Moreover, the frequency of the high side switch Q 1  and the frequency of the low side switch Q 2  gradually decrease at the beginning of the third time period T 3  and gradually increase at the end of the third time period T 3 . With such configuration, the audible noise produced by the resonant converter can be significantly reduced or eliminated. 
     As described above, disclosed is a controller for controlling a resonant converter. In addition to a normal mode, the controller further includes a high frequency burst mode and low frequency burst mode with soft on/off function. If the resonant converter receives a relatively high input voltage, and a low output voltage is required, the controller can operate in the high frequency burst mode or in the low frequency burst mode. In the high frequency burst mode, beside decreasing the output voltage by the switching signal FS according to the feedback FB, the controller can further decrease the output voltage by using a duty control signal DT. The duty control signal DT is configured to have a relatively high frequency (e.g., not less than 20 KHz) that is beyond the audible frequency of humans. In the low frequency burst mode, although the duty control signal DT has a relatively low frequency (e.g., 200 Hz), the soft on/off function can reduce or eliminate audible noise. The controller can dynamically switch among the normal mode, the high frequency burst mode, and the low frequency burst mode according to the input voltage level and the load condition. Advantageously, a controller according to present invention can enable the resonant converter to operate with a broader input voltage range (e.g., 90 V AC  to 265 V AC  ) and meanwhile the audible noise can be reduced or eliminated. 
     While the foregoing description and drawings represent embodiments of the present invention, it will 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 accompanying claims. One skilled in the art will appreciate that the invention may be used with many modifications of form, structure, arrangement, proportions, materials, elements, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims and their legal equivalents, and not limited to the foregoing description.