Patent Publication Number: US-2017373600-A1

Title: Multi-mode switching power converter

Description:
FIELD OF DISCLOSURE 
     The present disclosure relates in general to circuits for audio devices, including without limitation personal audio devices such as wireless telephones and media players, and more specifically, to a switch mode amplifier including a reconfigurable switched mode converter for driving an audio transducer of an audio device. 
     BACKGROUND 
     Personal audio devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuitry often includes a speaker driver including a power amplifier for driving an audio output signal to headphones or speakers. 
     One existing approach to driving an audio output signal is to employ a speaker driver, such as speaker driver  100  depicted in  FIG. 1 . Speaker driver  100  may include an envelope-tracking boost converter  102  (e.g., a Class H amplifier) followed by a full-bridge output stage  104  (e.g., a Class D amplifier) which effectively operates as another converter stage. Boost converter  102  may include a power inductor  105 , switches  106 ,  108 , and a capacitor  110  arranged as shown. Full-bridge output stage  104  may include switches  112 ,  114 ,  116 , and  118 , inductors  120  and  124 , and capacitors  122  and  126  as shown. 
     Speaker drivers such as speaker driver  100  suffer from numerous disadvantages. One disadvantage is that due to switching in output stage  104 , such a speaker driver  100  may give rise to large amounts of radiated electromagnetic radiation, which may cause interference with other electromagnetic signals. Such radiated electromagnetic interference may be mitigated by LC or resonant filters formed using inductor  120  and capacitor  122  and inductor  124  and capacitor  126 . However, such LC filters are often quite large in size, and coupling capacitors  122  and  126  to the terminals of the output transducer may have a negative impact on the power efficiency of speaker driver  100 . Another disadvantage is that boost converter  102  may operate at switching frequencies up to several megahertz, and full-bridge output stage may operate at switching frequencies up to several hundred kilohertz to generate an audio band frequency signal, which may result in high switching power loss. However, reducing switching frequency may reduce switching loss but may require increases in physical dimension sizes of boost inductor  105  and output inductive-capacitive filters (not shown). To further reduce common-mode electromagnetic interference of full-bridge output stage  104 , a typical edge slew rate control may be applied to full-bridge output stage  104 , causing even higher switching loss. 
     In addition, such architectures often do not handle large impulsive signals. To reduce power consumption, an output voltage V BST  generated by boost converter  102  may be varied in accordance with the output signal, such that output voltage V BST  may operate at lower voltage levels for lower output signal magnitudes. Thus, if a signal quickly increases, adequate time may not be present to increase voltage V BST , thus leading to signal clipping unless a delay is placed in the signal path. However, adding a delay to a signal path may cause incompatibility with other types of audio circuits, such as adaptive noise cancellation circuits. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, one or more disadvantages and problems associated with existing approaches to driving an audio output signal to an audio transducer may be reduced or eliminated. 
     In accordance with embodiments of the present disclosure, a multi-mode switching power converter may include a power inductor, a first switch coupled between a first terminal of the power inductor and a first supply terminal having a first voltage, a second switch coupled between the first terminal of the power inductor and a second supply terminal having a second voltage, a full bridge comprising a plurality of switches and having an output for producing the output voltage comprising a first output terminal and a second output terminal, wherein a first input of the full bridge is coupled to a second terminal of the power inductor and a second input of the full bridge is coupled to one of the first supply terminal and the second supply terminal, and a capacitor coupled between the first output terminal and the second output terminal. 
     In accordance with these and other embodiments of the present disclosure, a method may include, in a multi-mode switching power converter comprising a power inductor, a first switch coupled between a first terminal of the power inductor and a first supply terminal having a first voltage, a second switch coupled between the first terminal of the power inductor and a second supply terminal having a second voltage, a full bridge comprising a plurality of switches and having an output for producing the output voltage comprising a first output terminal and a second output terminal, wherein a first input of the full bridge is coupled to a second terminal of the power inductor and a second input of the full bridge is coupled to one of the first supply terminal and the second supply terminal, and a capacitor coupled between the first output terminal and the second output terminal, sequentially operating the first switch, the second switch, and the plurality of switches in a plurality of switch configurations in accordance with a selected operational mode of the power converter, the selected operational mode selected from a plurality of operational modes. 
     In accordance with these and other embodiments of the present disclosure, a switching power stage for producing an output voltage to a load may include a multi-mode switching power converter and a controller. The multi-mode switching power converter may include a power inductor, a first switch coupled between a first terminal of the power inductor and a first supply terminal having a first voltage, a second switch coupled between the first terminal of the power inductor and a second supply terminal having a second voltage, a full bridge comprising a plurality of switches and having an output for producing the output voltage comprising a first output terminal and a second output terminal, wherein a first input of the full bridge is coupled to a second terminal of the power inductor and a second input of the full bridge is coupled to one of the first supply terminal and the second supply terminal, and a capacitor coupled between the first output terminal and the second output terminal. The controller may be configured to sequentially operate the first switch, the second switch, and the plurality of switches in a plurality of switch configurations in accordance with a selected operational mode of the power converter, the selected operational mode selected from a plurality of operational modes. 
     Technical advantages of the present disclosure may be readily apparent to one skilled in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the claims set forth in this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
         FIG. 1  illustrates an example speaker driver, as is known in the relevant art; 
         FIG. 2  illustrates an example personal audio device, in accordance with embodiments of the present disclosure; 
         FIG. 3  illustrates a block diagram of selected components of an example audio integrated circuit of a personal audio device, in accordance with embodiments of the present disclosure; 
         FIG. 4  illustrates a block and circuit diagram of selected components of an example switched mode amplifier, in accordance with embodiments of the present disclosure; 
         FIG. 5  illustrates a circuit diagram of selected components of an example power converter, in accordance with embodiments of the present disclosure; 
         FIG. 6  illustrates a switch timing table setting forth switch configurations of the power converter of  FIG. 5  when operating in a buck mode, in accordance with embodiments of the present disclosure; 
         FIGS. 7A-7D  illustrate equivalent circuit diagrams of selected components of the power converter of  FIG. 5  operating in various phases of a buck mode in accordance with the switch timing table of  FIG. 6 , in accordance with embodiments of the present disclosure; 
         FIG. 8  illustrates a switch timing table setting forth switch configurations of the power converter of  FIG. 5  when operating in a boost mode, in accordance with embodiments of the present disclosure; 
         FIGS. 9A-9D  illustrate equivalent circuit diagrams of selected components of the power converter of  FIG. 5  operating in various phases of a boost mode in accordance with the switch timing table of  FIG. 8 , in accordance with embodiments of the present disclosure; 
         FIG. 10  illustrates a switch timing table setting forth switch configurations of the power converter of  FIG. 5  when operating in a differential buck-boost mode, in accordance with embodiments of the present disclosure; 
         FIGS. 11A-11C  illustrate equivalent circuit diagrams of selected components of the power converter of  FIG. 5  operating in various phases of a differential buck-boost in accordance with the switch timing table of  FIG. 10 , in accordance with embodiments of the present disclosure; 
         FIG. 12  illustrates a circuit diagram of selected components of another example power converter, in accordance with embodiments of the present disclosure; 
         FIG. 13  illustrates a circuit diagram of selected components of another example power converter, in accordance with embodiments of the present disclosure; 
         FIG. 14  illustrates a switch timing table setting forth switch configurations of the power converter of  FIG. 13  when operating in a buck mode, in accordance with embodiments of the present disclosure; 
         FIGS. 15A-15D  illustrate equivalent circuit diagrams of selected components of the power converter of  FIG. 13  operating in various phases of a buck mode in accordance with the switch timing table of  FIG. 14 , in accordance with embodiments of the present disclosure; 
         FIG. 16  illustrates a table setting forth switch configurations of the power converter of  FIG. 13  when operating in a boost mode, in accordance with embodiments of the present disclosure; 
         FIGS. 17A-17D  illustrate equivalent circuit diagrams of selected components of the power converter of  FIG. 13  operating in various phases of a boost mode, in accordance with embodiments of the present disclosure; 
         FIG. 18  illustrates a switch timing table setting forth switch configurations of the power converter of  FIG. 13  when operating in a buck-boost mode, in accordance with embodiments of the present disclosure; 
         FIGS. 19A-19D  illustrate equivalent circuit diagrams of selected components of the power converter of  FIG. 13  operating in various phases of a buck-boost mode in accordance with the switch timing table of  FIG. 18 , in accordance with embodiments of the present disclosure; 
         FIG. 20  illustrates a circuit diagram of selected components of another example power converter, in accordance with embodiments of the present disclosure; and 
         FIG. 21  illustrates a circuit diagram of selected components of another example power converter, in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  illustrates an example personal audio device  1 , in accordance with embodiments of the present disclosure.  FIG. 2  depicts personal audio device  1  coupled to a headset  3  in the form of a pair of earbud speakers  8 A and  8 B. Headset  3  depicted in  FIG. 2  is merely an example, and it is understood that personal audio device  1  may be used in connection with a variety of audio transducers, including without limitation, headphones, earbuds, in-ear earphones, and external speakers. A plug  4  may provide for connection of headset  3  to an electrical terminal of personal audio device  1 . Personal audio device  1  may provide a display to a user and receive user input using a touch screen  2 , or alternatively, a standard liquid crystal display (LCD) may be combined with various buttons, sliders, and/or dials disposed on the face and/or sides of personal audio device  1 . As also shown in  FIG. 2 , personal audio device  1  may include an audio integrated circuit (IC)  9  for generating an analog audio signal for transmission to headset  3  and/or another audio transducer. 
       FIG. 3  illustrates a block diagram of selected components of an example audio IC  9  of a personal audio device, in accordance with embodiments of the present disclosure. As shown in  FIG. 3 , a microcontroller core  18  may supply a digital audio input signal DIG_IN to a digital-to-analog converter (DAC)  14 , which may convert the digital audio input signal to an analog signal Y IN . DAC  14  may supply analog signal Y IN  to an amplifier  16  which may amplify or attenuate audio input signal Y IN  to provide an audio output signal V OUT , which may operate a speaker, a headphone transducer, a line level signal output, and/or other suitable output. In some embodiments, DAC  14  may be an integral component of amplifier  16 . A power supply  10  may provide the power supply rail inputs of amplifier  16 . In some embodiments, power supply  10  may comprise a battery. Although  FIGS. 2 and 3  contemplate that audio IC  9  resides in a personal audio device, systems and methods described herein may also be applied to electrical and electronic systems and devices other than a personal audio device, including audio systems for use in a computing device larger than a personal audio device, an automobile, a building, or other structure. 
       FIG. 4  illustrates a block and circuit diagram of selected components of an example switched mode amplifier  20 , in accordance with embodiments of the present disclosure. In some embodiments, switched mode amplifier  20  may implement all or a portion of amplifier  16  described with respect to  FIG. 3 . As shown in  FIG. 4 , switched mode amplifier  20  may comprise a loop filter  22 , a converter controller  24 , and a power converter  26 . 
     Loop filter  22  may comprise any system, device, or apparatus configured to receive an input signal (e.g., audio input signal Y IN  or a derivative thereof) and a feedback signal (e.g., audio output signal V OUT , a derivative thereof, or other signal indicative of audio output signal V OUT ) and based on such input signal and feedback signal, generate a controller input signal to be communicated to converter controller  24 . In some embodiments, such controller input signal may comprise a signal indicative of an integrated error between the input signal and the feedback signal. In other embodiments, such controller input signal may comprise a signal indicative of a target current signal to be driven as an output current I OUT  or a target voltage signal to be driven as an output voltage V OUT  to a load coupled to the output terminals of power converter  26 . 
     Converter controller  24  may comprise any system, device, or apparatus configured to, based on the controller input signal, sequentially select among a plurality of switch configurations of power converter  26  and based on an input signal (e.g., input signal INPUT), output signal V OUT , and/or other characteristics of switched mode amplifier  20 , communicate a plurality of control signals to power converter  26  to apply a switch configuration from a plurality of switch configurations of switches of power converter  26  to selectively activate or deactivate each of the plurality of switches in order to transfer electrical energy from a power supply V SUPPLY  to the load of switched mode amplifier  20  in accordance with the input signal. Examples of switch configurations associated with each are described in greater detail elsewhere in this disclosure. In addition, in some embodiments, converter controller  24  may control switches of a power converter  26  in order to regulate a common mode voltage of the output terminals of power converter  26 , as described in greater detail below. 
     Power converter  26  may receive a voltage V SUPPLY  (e.g., provided by power supply  10 ) at its input, and may generate at its output audio output signal V OUT . Although not explicitly shown in  FIG. 3 , in some embodiments, voltage V SUPPLY  may be received via input terminals including a positive input terminal and a negative input terminal which may be coupled to a ground voltage. As described in greater detail in this disclosure, power converter  26  may comprise a power inductor and a plurality of switches that are controlled by control signals received from converter controller  24  in order to convert voltage V SUPPLY  to audio output signal V OUT , such that audio output signal V OUT  is a function of the input signal to loop filter  22 . Examples of power converter  26  are described in greater detail elsewhere in this disclosure. 
       FIG. 5  illustrates a circuit diagram of selected components of an example power converter  26 A, in accordance with embodiments of the present disclosure. In some embodiments, power converter  26 A depicted in  FIG. 5  may implement all or a portion of power converter  26  described with respect to  FIG. 4 . As shown in  FIG. 5 , power converter  26 A may receive a voltage V SUPPLY  (e.g., provided by power supply  10 ) at input terminals, including a positive input terminal and a negative input terminal (which may in some embodiments be coupled to a ground voltage), and may generate at its output an output voltage V OUT . Power converter  26 A may comprise a power inductor  62  and plurality of switches  51 - 60 . Power inductor  62  may comprise any passive two-terminal electrical component which resists changes in electrical current passing through it and such that when electrical current flowing through it changes, a time-varying magnetic field induces a voltage in power inductor  62 , in accordance with Faraday&#39;s law of electromagnetic induction, which opposes the change in current that created the magnetic field. 
     Each switch  51 - 60  may comprise any suitable device, system, or apparatus for making a connection in an electric circuit when the switch is enabled (e.g., activated, closed, or on) and breaking the connection when the switch is disabled (e.g., deactivated, open, or off) in response to a control signal received by the switch. For purposes of clarity and exposition, control signals for switches  51 - 60  (e.g., control signals communicated from converter controller  24 ) are not depicted although such control signals would be present to selectively enable and disable switches  51 - 60 . In some embodiments, a switch  51 - 60  may comprise an n-type metal-oxide-semiconductor field-effect transistor. Switch  51  may be coupled between a positive input terminal of the supply voltage V SUPPLY  and a first terminal of power inductor  62  such that an anode of a body diode of switch  51  is coupled to the first terminal of power inductor  62  and a cathode of the body diode of switch  51  is coupled to the positive input terminal of the supply voltage V SUPPLY . Switch  52  may be coupled between a negative input terminal of the supply voltage V SUPPLY  and the first terminal of power inductor  62  such that a cathode of a body diode of switch  52  is coupled to the first terminal of power inductor  62  and an anode of the body diode of switch  52  is coupled to the negative input terminal of the supply voltage V SUPPLY . Together, switch  51  and switch  52  may form a half bridge. 
     Switch  53  may be coupled between a second terminal of power inductor  62  and a terminal of switch  54 . Switch  54  may be coupled between a first output terminal of power converter  26 A and a terminal of switch  53 . Switches  53  and  54  may be arranged such that their respective body diodes are coupled together via the respective cathodes of such respective body diodes. In some embodiments, switches  53  and  54  may be combined into a single switch. 
     Switch  55  may be coupled between the first output terminal of power converter  26 A and a terminal of switch  56 . Switch  56  may be coupled between the negative input terminal of the supply voltage V SUPPLY  and a terminal of switch  55 . Switches  55  and  56  may be arranged such that their respective body diodes are coupled together via the respective cathodes of such respective body diodes. In some embodiments, switches  55  and  56  may be combined into a single switch. 
     Switch  57  may be coupled between the second terminal of power inductor  62  and a terminal of switch  58 . Switch  58  may be coupled between a second output terminal of power converter  26 A and a terminal of switch  57 . Switches  57  and  58  may be arranged such that their respective body diodes are coupled together via the respective cathodes of such respective body diodes. In some embodiments, switches  57  and  58  may be combined into a single switch. 
     Switch  59  may be coupled between the second output terminal of power converter  26 A and a terminal of switch  60 . Switch  60  may be coupled between the negative input terminal of the supply voltage V SUPPLY  and a terminal of switch  59 . Switches  59  and  60  may be arranged such that their respective body diodes are coupled together via the respective cathodes of such respective body diodes. In some embodiments, switches  59  and  60  may be combined into a single switch. 
     Together, switches  53 - 60  may comprise a full bridge having a first terminal coupled to the second terminal of power inductor  62  and a second terminal coupled to the second terminal of the supply voltage V SUPPLY . 
     In addition to switches  51 - 60  and power inductor  62 , power converter  26 A may include an output capacitor  64  coupled between the first output terminal of power converter  26 A and the second output terminal of power converter  26 A. In order to generate a rectified audio signal at the terminal labeled with voltage V OSW1  in  FIG. 5 , switches  51  and  52  may switch at a switching frequency up to several megahertz while the full-bridge output stage comprising switches  53 - 60  may switch at an audio-band frequency (e.g., 20 Hz to 20 KHz) in order to rectify output voltage VOUT, resulting in a substantial reduction in switching loss as compared with full-bridge output stage  104  depicted in  FIG. 1 . 
     As described above, a power converter  26 A may operate in a plurality of different switch configurations.  FIG. 6  illustrates a table setting forth switch configurations of the power converter of  FIG. 5  when operating in a buck mode, in accordance with embodiments of the present disclosure. Power converter  26 A may operate in a buck mode when output voltage V OUT  has a magnitude lower than that for which the duration of a charging phase T 1  becomes too small to operate power converter  26 A in a boost mode (e.g., |V OUT |&lt;V SUPPLY ). As shown in  FIG. 6 , during a charging phase T 1  of power converter  26 A, when output voltage V OUT  is positive, converter controller  24  may enable switches  51 ,  53 ,  54 ,  59 , and  60  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 7A  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 A, when output voltage V OUT  is positive, converter controller  24  may enable switches  52 ,  53 ,  54 ,  59 , and  60  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 7B  (closed switches shown, open switches removed). Similarly, during a charging phase T 1  of power converter  26 A, when output voltage V OUT  is negative, converter controller  24  may enable switches  51 ,  55 ,  56 ,  57 , and  58  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 7C  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 A, when output voltage V OUT  is negative, converter controller  24  may enable switches  52 ,  55 ,  56 ,  57 , and  58  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 7D  (closed switches shown, open switches removed). 
       FIG. 8  illustrates a switch timing table setting forth switch configurations of the power converter of  FIG. 5  when operating in a boost mode, in accordance with embodiments of the present disclosure. In accordance with the switch timing table of  FIG. 8 , switches  51  and  52  may switch at a switching frequency of several megahertz, while switches  53 - 60  may switch at an audio band frequency of approximately 20 Hz to 20 KHz. Power converter  26 A may operate in a boost mode when output voltage V OUT  has a magnitude higher than that for which the duration of a charging phase T 1  becomes too large to operate power converter  26 A in a buck mode (e.g., |V OUT |&gt;V SUPPLY ). As shown in  FIG. 8 , during a charging phase T 1  of power converter  26 A, when output voltage V OUT  is positive, converter controller  24  may enable switches  51 ,  53 ,  54 ,  55 , and  56  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 9A  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 A, when output voltage V OUT  is positive, converter controller  24  may enable switches  51 ,  53 ,  54 ,  59 , and  60  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 9B  (closed switches shown, open switches removed). Similarly, during a charging phase T 1  of power converter  26 A, when output voltage V OUT  is negative, converter controller  24  may enable switches  51 ,  57 ,  58 ,  59 , and  60  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 9C  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 A, when output voltage V OUT  is negative, converter controller  24  may enable switches  51 ,  55 ,  56 ,  57 , and  58  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 9D  (closed switches shown, open switches removed). 
       FIG. 10  illustrates a switch timing table setting forth switch configurations of the power converter of  FIG. 5  when operating in a differential buck-boost mode, in accordance with embodiments of the present disclosure. In accordance with the switch timing table of  FIG. 10 , switches  51  and  52  may switch at a switching frequency of several megahertz, while switches  53 - 60  may switch at an audio band frequency of approximately 20 Hz to 20 KHz. Power converter  26 A may operate in the differential buck-boost mode for very low magnitudes (e.g., |V OUT |≈0). As shown in  FIG. 10 , during a first phase T 1  of power converter  26 A, converter controller  24  may enable switches  52 ,  53 ,  54 ,  59 , and  60  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 11A  (closed switches shown, open switches removed). During a second phase T 2  of power converter  26 A, converter controller  24  may enable switches  51 ,  57 ,  58 ,  59 , and  60  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 11B  (closed switches shown, open switches removed). During a third phase T 3  of power converter  26 A, converter controller  24  may enable switches  52 ,  55 ,  56 ,  57 , and  58  of power converter  26 A, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 11C  (closed switches shown, open switches removed). Accordingly, output voltage V OUT  may be regulated by adjusting an on-time difference between phases T 1  and T 3 , including regulating at a voltage of zero when the on-times of phases T 1  and T 3  are the same. 
       FIG. 12  illustrates a circuit diagram of selected components of another example power converter  26 B, in accordance with embodiments of the present disclosure. In some embodiments, power converter  26 B depicted in  FIG. 12  may implement all or a portion of power converter  26  described with respect to  FIG. 4 . Power converter  26 B depicted in  FIG. 12  may in many respects be identical to power converter  26 A of  FIG. 5 , and thus only the differences between power converter  26 B and power converter  26 A are discussed. The main difference between power converter  26 B and power converter  26 A is that power converter  26 B includes another switch  61  coupled between the second terminal of power inductor  62  and the second terminal of supply voltage V SUPPLY . In addition, switch  61  may be arranged such that an anode of its body diode is coupled to the second terminal of supply voltage V SUPPLY  and a diode of its body diode is coupled to the second terminal of power inductor  62 . Switch  61  may be enabled at certain times (e.g., when switches  53 ,  54 ,  55 , and  56  are enabled or when switches  57 ,  58 ,  59 , and  60  are enabled, so as to reduce a conduction resistance to minimize power loss in either of the boost mode or buck mode. 
       FIG. 13  illustrates a circuit diagram of selected components of another example power converter  26 C, in accordance with embodiments of the present disclosure. In some embodiments, power converter  26 C depicted in  FIG. 13  may implement all or a portion of power converter  26  described with respect to  FIG. 4 . As shown in  FIG. 13 , power converter  26 C may receive a voltage V SUPPLY  (e.g., provided by power supply  10 ) at input terminals, including a positive input terminal and a negative input terminal (which may in some embodiments be coupled to a ground voltage), and may generate at its output an output voltage V OUT . Power converter  26 C may comprise a power inductor  82  and plurality of switches  71 - 78 . Power inductor  82  may comprise any passive two-terminal electrical component which resists changes in electrical current passing through it and such that when electrical current flowing through it changes, a time-varying magnetic field induces a voltage in power inductor  82 , in accordance with Faraday&#39;s law of electromagnetic induction, which opposes the change in current that created the magnetic field. 
     Each switch  71 - 78  may comprise any suitable device, system, or apparatus for making a connection in an electric circuit when the switch is enabled (e.g., activated, closed, or on) and breaking the connection when the switch is disabled (e.g., deactivated, open, or off) in response to a control signal received by the switch. For purposes of clarity and exposition, control signals for switches  71 - 78  (e.g., control signals communicated from converter controller  24 ) are not depicted although such control signals would be present to selectively enable and disable switches  71 - 78 . In some embodiments, a switch  71 - 78  may comprise an n-type metal-oxide-semiconductor field-effect transistor. Switch  71  may be coupled between a positive input terminal of the supply voltage V SUPPLY  and a first terminal of power inductor  82  such that an anode of a body diode of switch  71  is coupled to the first terminal of power inductor  82  and a cathode of the body diode of switch  71  is coupled to the positive input terminal of the supply voltage V SUPPLY . Switch  72  may be coupled between a negative input terminal of the supply voltage V SUPPLY  and the first terminal of power inductor  72  such that a cathode of a body diode of switch  72  is coupled to the first terminal of power inductor  72  and an anode of the body diode of switch  72  is coupled to the negative input terminal of the supply voltage V SUPPLY . Together, switch  71  and switch  72  may form a half bridge. 
     Switch  73  may be coupled between the second terminal of power inductor  82  and the second terminal of supply voltage V SUPPLY . In addition, switch  73  may be arranged such that an anode of its body diode is coupled to the second terminal of supply voltage V SUPPLY  and a diode of its body diode is coupled to the second terminal of power inductor  82 . 
     Switch  74  may be coupled between the second terminal of power inductor  82  and terminals of switches  75  and  77 . In addition, switch  74  may be arranged such that an anode of its body diode is coupled to the second terminal of power inductor  82  and a cathode of its body diode is coupled to terminals of switches  75  and  77 . 
     Switch  75  may be coupled between a terminal of switch  74  and a first output terminal of power converter  26 C. In addition, switch  75  may be arranged such that an anode of its body diode is coupled to the first output terminal of power converter  26 C and a cathode of its body diode is coupled to terminals of switches  74  and  77 . 
     Switch  76  may be coupled between the second terminal of supply voltage V SUPPLY  and the first output terminal of power converter  26 C. In addition, switch  76  may be arranged such that an anode of its body diode is coupled to the second terminal of supply voltage V SUPPLY  and a cathode of its body diode is coupled to the first output terminal of power converter  26 C. 
     Switch  77  may be coupled between a terminal of switch  74  and a second output terminal of power converter  26 C. In addition, switch  77  may be arranged such that an anode of its body diode is coupled to the second output terminal of power converter  26 C and a cathode of its body diode is coupled to terminals of switches  74  and  75 . 
     Switch  78  may be coupled between the second terminal of supply voltage V SUPPLY  and the second output terminal of power converter  26 C. In addition, switch  78  may be arranged such that an anode of its body diode is coupled to the second terminal of supply voltage V SUPPLY  and a cathode of its body diode is coupled to the second output terminal of power converter  26 C. 
     Together, switches  75 - 78  may comprise a full bridge having a first terminal coupled to the second terminal of power inductor  82  via switch  74  and a second terminal coupled to the second terminal of the supply voltage V SUPPLY . 
     In addition to switches  71 - 78  and power inductor  82 , power converter  26 C may include an output capacitor  84  coupled between the first output terminal of power converter  26 C and the second output terminal of power converter  26 C. In order to generate a rectified audio signal at the terminal labeled with voltage V OSW2  in  FIG. 13 , switches  71 - 74  may switch at a switching frequency up to several megahertz while the full-bridge output stage comprising switches  53 - 60  may switch at an audio-band frequency (e.g., 20 Hz to 20 KHz) in order to rectify output voltage VOUT, resulting in a substantial reduction in switching loss as compared with full-bridge output stage  104  depicted in  FIG. 1 . 
     As described above, a power converter  26 C may operate in a plurality of different switch configurations.  FIG. 14  illustrates a switch table setting forth switch configurations of the power converter of  FIG. 13  when operating in a buck mode, in accordance with embodiments of the present disclosure. Power converter  26 C may operate in a buck mode when output voltage V OUT  has a magnitude lower than that for which the duration of a charging phase T 1  becomes too small to operate power converter  26 C in a boost mode (e.g., |V OUT |&lt;V SUPPLY ). As shown in  FIG. 14 , during a charging phase T 1  of power converter  26 C, when output voltage V OUT  is positive, converter controller  24  may enable switches  71 ,  74 ,  75 , and  78  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 15A  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 C, when output voltage V OUT  is positive, converter controller  24  may enable switches  72 ,  74 ,  75 , and  78 , of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 15B  (closed switches shown, open switches removed). Similarly, during a charging phase T 1  of power converter  26 C, when output voltage V OUT  is negative, converter controller  24  may enable switches  71 ,  74 ,  76 , and  77  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 15C  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 C, when output voltage V OUT  is negative, converter controller  24  may enable switches  72 ,  74 ,  76 , and  77  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 15D  (closed switches shown, open switches removed). 
       FIG. 16  illustrates a switching timing table setting forth switch configurations of the power converter of  FIG. 13  when operating in a boost mode, in accordance with embodiments of the present disclosure. Power converter  26 C may operate in a buck mode when output voltage V OUT  has a magnitude lower than that for which the duration of a charging phase T 1  becomes too large to operate power converter  26 C in a buck mode (e.g., |V OUT |&gt;V SUPPLY ). As shown in  FIG. 16 , during a charging phase T 1  of power converter  26 C, when output voltage V OUT  is positive, converter controller  24  may enable switches  71  and  73  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 17A  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 C, when output voltage V OUT  is positive, converter controller  24  may enable switches  71 ,  74 ,  75 , and  78 , of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 17B  (closed switches shown, open switches removed). Similarly, during a charging phase T 1  of power converter  26 C, when output voltage V OUT  is negative, converter controller  24  may enable switches  71  and  73  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 17C  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 C, when output voltage V OUT  is negative, converter controller  24  may enable switches  71 ,  74 ,  76 , and  77  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 17D  (closed switches shown, open switches removed). 
       FIG. 18  illustrates a switching timing table setting forth switch configurations of the power converter of  FIG. 13  when operating in a buck-boost mode, in accordance with embodiments of the present disclosure. As shown in  FIG. 18 , during a charging phase T 1  of power converter  26 C, when output voltage V OUT  is positive, converter controller  24  may enable switches  71  and  73  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 19A  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 C, when output voltage V OUT  is positive, converter controller  24  may enable switches  72 ,  74 ,  75 , and  78 , of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 19B  (closed switches shown, open switches removed). Similarly, during a charging phase T 1  of power converter  26 C, when output voltage V OUT  is negative, converter controller  24  may enable switches  71  and  73  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 19C  (closed switches shown, open switches removed). During a discharge phase T 2  of power converter  26 C, when output voltage V OUT  is negative, converter controller  24  may enable switches  72 ,  74 ,  76 , and  77  of power converter  26 C, with such switch configuration resulting in the equivalent circuit depicted in  FIG. 19D  (closed switches shown, open switches removed). 
       FIG. 20  illustrates a circuit diagram of selected components of another example power converter  26 D, in accordance with embodiments of the present disclosure. In some embodiments, power converter  26 D depicted in  FIG. 20  may implement all or a portion of power converter  26  described with respect to  FIG. 4 . Power converter  26 D depicted in  FIG. 20  may in many respects be identical to power converter  26 C of  FIG. 13 , and thus only the differences between power converter  26 D and power converter  26 C are discussed. The main differences between power converter  26 D and power converter  26 C are that: 
     (a) switch  74  present in power converter  26 C is not present in power converter  26 D and is replaced with a short; 
     (b) switch  74 A is added in series with switch  75 ; and 
     (c) switch  74 B is added in series with switch  77 . 
     Power converter  26 D may have the same operating modes as described above with respect to power converter  26 C. When output voltage V OUT  is positive, switch  74 A may have the same function as and operate like switch  74  of power converter  26 C and switch  74 B may be disabled. When output voltage V OUT  is negative, switch  74 B may have the same function as and operate like switch  74  of power converter  26 C and switch  74 A may be disabled. 
       FIG. 21  illustrates a circuit diagram of selected components of another example power converter  26 E, in accordance with embodiments of the present disclosure. In some embodiments, power converter  26 E depicted in  FIG. 21  may implement all or a portion of power converter  26  described with respect to  FIG. 4 . Power converter  26 E depicted in  FIG. 21  may in many respects be identical to power converter  26 C of  FIG. 13 , and thus only the differences between power converter  26 E and power converter  26 C are discussed. The main differences between power converter  26 E and power converter  26 C are that: 
     (a) switch  73  present in power converter  26 C is not present in power converter  26 D and is replaced with an open; 
     (b) switch  74  present in power converter  26 C is not present in power converter  26 D and is replaced with a short; 
     (c) switch  74 A is added in series with switch  76 ; and 
     (d) switch  74 B is added in series with switch  78 . 
     Power converter  26 E may have the same operating modes as power converter  26 D, but with fewer components. 
     As used herein, when two or more elements are referred to as “coupled” to one another, such term indicates that such two or more elements are in electronic communication or mechanical communication, as applicable, whether connected indirectly or directly, with or without intervening elements. 
     This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. 
     All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present inventions have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.