Patent Publication Number: US-2022231602-A1

Title: Buck voltage regulator device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Patent Application Ser. No. 63/139,241, filed Jan. 19, 2021, the entirety of which is hereby incorporated herein by reference for all purposes. 
    
    
     GOVERNMENT LICENSE RIGHTS 
     This invention was made with Government support under FA8808-10-C-0001 awarded by the Department of Defense. The government has certain rights in this invention. 
    
    
     FIELD 
     This invention relates generally to power supply devices, and more specifically, to a buck voltage regulator device. 
     BACKGROUND 
     A power supply device is configured to transfer electrical energy from an electrical energy source to an electrical load, while converting voltage and current characteristics of the electrical energy. As one example, a power supply device may comprise a buck voltage regulator device that is configured to step down voltage (while stepping up current) from an electrical energy source to an electrical load. 
     SUMMARY 
     According to one aspect of the present disclosure, a buck voltage regulator device is provided. The buck voltage regulator device comprises a coupled inductor including a primary winding and one or more auxiliary windings including a first auxiliary winding. A high-side switch is electrically connected between an electrical energy source and a starting end of the primary winding. A first low-side switch is electrically connected between the starting end of the primary winding and a ground node. A second low-side switch is electrically connected between a starting end of the first auxiliary winding and the ground node. A first output node is electrically connected to a terminal end of the primary winding. A second output node is electrically connected to a terminal end of the first auxiliary winding. A first output storage capacitor is electrically connected to the terminal end of the primary winding and electrically connected between the first output node and the ground node. A second output storage capacitor is electrically connected to the terminal end of the first auxiliary winding and electrically connected between the second output node and the ground node. 
     The features and functions that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example embodiment of a synchronous buck voltage regulator device with synchronous rectified output. 
         FIG. 2  shows an example embodiment of a two-phase synchronous buck voltage regulator device with synchronous rectified output. 
         FIGS. 3A-3D  show four operating states of the two-phase synchronous buck voltage regulator device of  FIG. 2 . 
         FIGS. 4-5  show graphs indicating example operation of the two-phase synchronous buck voltage regulator device of  FIG. 2  throughout the different operating states shown in  FIGS. 3A-3D . 
     
    
    
     DETAILED DESCRIPTION 
     A synchronous buck voltage regulator device typically comprises one or more energy storage elements, such as an inductor, a capacitor, or both that are controlled by two or more switches to step down voltage from an electrical energy source to an electrical load. A magnitude of a stepdown voltage of the synchronous buck voltage regulator device may be limited by an amount of current that flows across the switches. 
     In some examples, a synchronous buck voltage regulator may comprise a coupled inductor in place of a single inductor in order to provide different voltages at different outputs. The coupled inductor may comprise a primary winding and an auxiliary winding that is rectified by a diode. The addition of the auxiliary winding steps down a turn ratio of the coupled inductor relative to a single inductor, such that less current flows through the switches and more current flows through the windings of the coupled inductor when the switches are turned on. This allows for the synchronous buck voltage regulator device to handle a larger step down in voltage. Moreover, the auxiliary winding acts as a direct current (DC)-DC voltage regulator for an auxiliary output. In particular, the synchronous buck voltage regulator device outputs an intermediate voltage at a primary output electrically connected to the primary winding and outputs a lower voltage at the auxiliary output electrically connected to the auxiliary winding. 
     However, such a synchronous buck voltage regulator device lacks operational flexibility because the synchronous buck voltage regulator device is configured such that electrical energy has to be provided to both the primary and auxiliary outputs. In other words, more electrical energy cannot be provided to the auxiliary output than the primary output (i.e., the primary output cannot be zero volts). 
     To address the above and other issues, according to one aspect of the present disclosure, a buck voltage regulator device is provided. The buck voltage regulator device comprises a coupled inductor including a primary winding and an auxiliary winding. A high-side switch is electrically connected between an electrical energy source and a starting end of the primary winding. A first low-side switch is electrically connected between the starting end of the primary winding and a ground node. A second low-side switch is electrically connected between a starting end of the auxiliary winding and the ground node. A first output node is electrically connected to a terminal end of the primary winding. A second output node is electrically connected to a terminal end of the auxiliary winding. A first output storage capacitor is electrically connected to the terminal end of the primary winding and electrically connected between the first output node and the ground node. A second output storage capacitor is electrically connected to the terminal end of the auxiliary winding and electrically connected between the second output node and the ground node. 
     Such a circuit topology of the buck voltage regulator device allows for synchronous rectification of electrical energy to the second output node without necessarily having to provide electrical energy to the first output node. Instead, the first output storage capacitor can be used along with the primary winding to store electrical energy that can be subsequently supplied to the second output node. This allows the buck voltage regulator device to have a large step down in voltage between the electrical energy source and the second output node in a single stage. Moreover, such a circuit topology of the buck voltage regulator device has greater operational flexibility relative to a conventional buck voltage regulator device because either output can be designated to receive a greater amount of power as desired based on the particular implementation. 
       FIG. 1  shows an example embodiment of a synchronous buck voltage regulator device  100  with synchronous rectified output. The buck voltage regulator device  100  is configured to transfer electrical energy from an electrical energy source  102  to one or more electrical loads  104 ,  106 , while converting voltage and current characteristics of the electrical energy. The buck voltage regulator device  100  may be employed in any suitable application. As one non-limiting example, the buck voltage regulator device  100  may be employed as an integrated power converter. As another non-limiting example, the buck voltage regulator device  100  may be employed as a point-of-load regulator. 
     The electrical energy source  102  may take any suitable form. In some examples, the electrical energy source  102  may comprise a rectified alternating current (AC) power source. In other examples, the electrical energy source  102  may comprise a DC power source. In some examples, the electrical energy source  102  may comprise an electrical bus. In some examples, the electrical energy source  102  may comprise an electrical energy storage device, such as a battery. 
     Additionally, a first electrical load  104  and a second electrical load  106  may take any suitable form of electrical component that consumes electrical energy. In some embodiments, a single electrical load may be electrically connected to the synchronous buck voltage regulator device  100  (e.g., either of the first electrical load  104  or the second electrical load  106  may be omitted). 
     The buck voltage regulator device  100  comprises a coupled inductor  108  including a primary winding  110  and an auxiliary winding  112 . The primary winding  110  has a starting end  114  and a terminal end  116 . The auxiliary winding  112  has a starting end  118  and a terminal end  120 . In the illustrated embodiment, the coupled inductor  108  has a single auxiliary winding  112  to accommodate a second output node  150  electrically connected to the second electrical load  106 . In some embodiments, the coupled inductor may include more than one auxiliary winding to accommodate additional auxiliary output nodes that are electrically connected to additional electrical loads. The coupled inductor may include any suitable number of windings to transfer electrical energy to any suitable number of electrical loads. 
     A high-side switch  122  is electrically connected between the electrical energy source  102  and the starting end  114  of the primary winding  110 . The high-side switch  122  comprises a drain  124 , a gate  126 , and a source  128 . The drain  124  is electrically connected to the electrical energy source  102 . The source  128  is electrically connected to the starting end  114  of the primary winding  110 . 
     A first low-side switch  130  is electrically connected between the starting end  114  of the primary winding  110  and a ground node  138 . The first low-side switch  130  comprises a drain  132 , a gate  134 , and a source  136 . The drain  132  is electrically connected to the starting end  114  of the primary winding  110 . The source  136  is electrically connected to the ground node  138 . 
     A second low-side switch  140  is electrically connected between the starting end  118  of the auxiliary winding  112  and the ground node  138 . The second low-side switch  140  comprises a drain  142 , a gate  144 , and a source  146 . The drain  142  is electrically connected to the starting end  118  of the auxiliary winding  112 . The source  146  is electrically connected to the ground node  138 . 
     In some embodiments, the primary winding  110  and the auxiliary winding  112  may be referenced to the same ground node. In other embodiments, the primary winding  110  and the auxiliary winding  112  may be referenced to different ground nodes (e.g., chassis ground, signal ground, or power ground). 
     The high-side switch  122 , the first low-side switch  130 , and the second low-side switch  140  may be any suitable type of switching device or combination of switching devices capable of conducting current in a manner that be controlled via synchronous rectification. In one example, the switches comprise Gallium Nitride Field Effect Transistors (GaNFETs). GaNFETs may provide relatively low drain-source resistance that facilitates transfer of high circulating energy with high efficiency at a relatively high frequency (e.g., 500 kHz). In other non-limiting examples the switches may comprise Metal Oxide Silicon Field Effect Transistors (MOSFETs) and/or Schottky or silicon rectifiers. 
     A first output node  148  is electrically connected to the terminal end  116  of the primary winding  110 . In some examples, the first output node  148  may be electrically connected to the first electrical load  104 , such that electrical energy is transferred from the electrical energy source  102  to the first electrical load  104  and the second electrical load  106 . In other examples, the first electrical load  104  may be omitted. 
     A second output node  150  is electrically connected to the terminal end  120  of the auxiliary winding  112 . The second output node  150  may be electrically connected to the second electrical load  106 . In one example, the second electrical load  106  may be used in a single-load application where electrical energy is transferred from the electrical energy source  102  to the second electrical load  106 . In another example, electrical energy is transferred from the electrical energy source  102  to the first electrical load  104  and the second electrical load  106 . Note that under conditions where the electrical load current at the second output node  150  is zero, the voltage would still be regulated by the buck voltage regulator device  100 . 
     In the illustrated embodiment, the buck voltage regulator device  100  includes the first output node  148  and the second output node  150 . In other embodiments, the buck voltage regulator device may include more than two output nodes. Further, in some embodiments, different output nodes may be referenced to different ground nodes (e.g., chassis ground, signal ground, or power ground). 
     A first output storage capacitor  152  is electrically connected to the terminal end  116  of the primary winding  110  and electrically connected between the first output node  148  and the ground node  138 . A second output storage capacitor  154  is electrically connected to the terminal end  120  of the auxiliary winding  112  and electrically connected between the second output node  150  and the ground node  138 . The first and second output storage capacitors  152 ,  154  are configured to store electrical energy that can be transferred to either of the first or second output nodes  148 ,  150  depending on the control scheme of the buck voltage regulator device  100 . 
     In some embodiments, the buck voltage regulator device  100  optionally may comprise an input-side noise filter capacitor  156  that is electrically connected between the electrical energy source  102  and the ground node  138 . The input-noise filter capacitor  156  is configured to filter electromagnetic interference at the electrical energy source  102 . 
     The buck voltage regulator device  100  comprises a controller  158  that is configured to control the state of the first high-side switch  122 , the first low-side switch  130 , and the second low-side switch  140  according to a desired control scheme. The control scheme may vary depending on the load(s) on the first and second output nodes  148 ,  150  and the voltage desired at the first and second output nodes  148 ,  150 . 
     In one example, the controller  158  is configured to operate the high-side switch  122  with a drive signal  160  and operate the first low-side switch  130  and the second low-side switch  140  with an inverse drive signal  162  to adjust an output voltage at the second output node  150  relative to an input voltage at the electrical energy source  102 . The inverse drive signal  162  may be the same waveform as the drive signal  160  but inverted. In other words, the high-side switch  122  may be turned on when the first low-side switch  130  and the second low-side switch  140  are turned off and vice versa. When the high-side switch  122  is turned on and the first and second low-side switches  130 ,  140  are turned off, current flows from the electrical energy source  102  through the primary winding  110  of the coupled inductor  108  and electrical energy is stored in the primary winding  110  and the first output storage capacitor  152 . When the high-side switch  122  is turned off and the first and second low-side switches  130 ,  140  are turned on, electrical energy stored in the primary winding  110  and in the first output storage capacitor  152  is transferred through the auxiliary winding  112  to the second output node  150 . Such synchronous rectification of the switches according to the control scheme allows for bidirectional transfer of electrical energy across the buck voltage regulator device  100 . In particular, electrical energy is stored in the first output storage capacitor  152  when the high-side switch  122  is turned on and current flows through the primary winding  110 . Subsequently, when the high-side switch  122  is turned off and the first and second low-side switches  130 ,  140  are turned on, the electrical energy that is stored in the first output storage capacitor  152  changes direction and flows back to the coupled inductor  108  where the electrical energy is transferred through the auxiliary winding  112  to the second output node  150 . In this way, the coupled inductor  108  acts as a transformer. Moreover, such synchronous rectification of the switches according to the control scheme allows for the first output node  148  to be unloaded while still being able to transfer electrical energy to the second output node  150 . 
     The controller  158  may operate the switches according to a control scheme that is based on a duty cycle of the drive signal and a turns ratio of the coupled inductor  108 . In one example, the control scheme may conform to the DC transfer function: 
     
       
         
           
             
               V 
               o 
             
             = 
             
               D 
               × 
               
                 
                   V 
                   
                     i 
                     ⁢ 
                     n 
                   
                 
                 ⁡ 
                 
                   ( 
                   
                     
                       N 
                       a 
                     
                     
                       N 
                       p 
                     
                   
                   ) 
                 
               
             
           
         
       
     
     where V o  is the output voltage, D is the duty cycle, V in  is the input voltage, N a  is a number of turns of the auxiliary winding  112 , N p  is a number of turns of the primary winding  110 , and 
     
       
         
           
             ( 
             
               
                 N 
                 a 
               
               
                 N 
                 p 
               
             
             ) 
           
         
       
     
     is the turns ratio of the coupled inductor  108 . 
     In some examples, the duty cycle of the drive signal is less than 50% and the number of turns of the primary winding is greater than a number of turns of the auxiliary winding such that the output voltage at the second output node  150  is stepped down relative to the input voltage at the electrical energy source. In one example, the duty cycle is set to ˜27% on high side and ˜73% on the low side. By setting the duty cycle to less than 50%, efficiency of the buck voltage regulator device  100  may be increased relative to a buck voltage regulator device that relies on diodes for rectification. 
     The buck voltage regulator device  100  may be configured to transfer electrical energy to either or both of the first and second output node at desired voltage levels by changing the turns ratio of the coupled inductor  108  and the duty cycle. Such a circuit topology of the buck voltage regulator device has greater operational flexibility relative to a conventional buck voltage regulator device because either output can be designated to receive a greater amount of power as desired based on the particular implementation. 
     The above-described buck voltage regulator device is configured to transfer electrical energy to the output(s) that is pulsed in accordance with the duty cycle. Such pulsating output may cause output current ripple where the output current rises during the on-state and falls during the off-state. Such output current ripple may be affected by switching frequency, output capacitance, inductor, load, and/or any other current limiting features of the buck voltage regulator device. Such output current ripple may be filtered via one or more noise-filtering components, such as a noise filtering capacitor. 
       FIG. 2  shows an example embodiment of a two-phase synchronous buck voltage regulator device  200  with synchronous rectified output. The two-phase synchronous buck voltage regulator device  200  may have reduced output current ripple relative to the buck voltage regulator device  100  shown in  FIG. 1 . The two-phase synchronous buck voltage regulator device  200  is configured to transfer electrical energy from an electrical energy source  202  to one or more electrical loads  204 ,  206 , while converting voltage and current characteristics of the electrical energy. The buck voltage regulator device  200  may be employed in any suitable application. As one non-limiting example, the buck voltage regulator device  200  may be employed as an integrated power converter. As another non-limiting example, the buck voltage regulator device  200  may be employed as a point-of-load regulator. As used herein, the term “two-phase” refers to the configuration and control of two coupled inductors and two sets of associated high-side and low-side switches of the two-phase synchronous buck voltage regulator device  200 . In this context, the buck voltage regulator device  100  of  FIG. 1  may be considered a “single-phase” buck voltage regulator device. 
     The electrical energy source  202  may take any suitable form. In some examples, the electrical energy source  202  may comprise a rectified AC power source. In other examples, the electrical energy source  202  may comprise a DC power source. In some examples, the electrical energy source  202  may comprise an electrical bus. In some examples, the electrical energy source  202  may comprise an electrical energy storage device, such as a battery. 
     A first electrical load  204  and a second electrical load  206  may take any suitable form of electrical component that consumes electrical energy. In some embodiments, a single electrical load may be electrically connected to the two-phase synchronous buck voltage regulator device  200  (e.g., either of the first electrical load  204  or the second electrical load  206  may be omitted). 
     The two-phase synchronous buck voltage regulator device  200  comprises a first coupled inductor  208  including a first primary winding  210  and a first auxiliary winding  212 . The first primary winding  210  has a starting end  214  and a terminal end  216 . The first auxiliary winding  212  has a starting end  218  and a terminal end  220 . 
     A first high-side switch  222  is electrically connected between the electrical energy source  202  and the starting end  214  of the first primary winding  210 . The first high-side switch  222  comprises a drain  224 , a gate  226 , and a source  228 . The drain  224  is electrically connected to the electrical energy source  202 . The source  228  is electrically connected to the starting end  214  of the first primary winding  210 . 
     A first low-side switch  230  is electrically connected between the starting end  214  of the first primary winding  210  and a ground node  238 . The first low-side switch  230  comprises a drain  232 , a gate  234 , and a source  236 . The drain  232  is electrically connected to the starting end  214  of the primary winding  210 . The source  236  is electrically connected to the ground node  238 . 
     A second low-side switch  240  is electrically connected between the starting end  218  of the first auxiliary winding  212  and the ground node  238 . The second low-side switch  240  comprises a drain  242 , a gate  244 , and a source  246 . The drain  242  is electrically connected to the starting end  218  of the first auxiliary winding  212 . The source  246  is electrically connected to the ground node  238 . 
     The two-phase synchronous buck voltage regulator device  200  comprises a second coupled inductor  248  including a second primary winding  250  and a second auxiliary winding  252 . The second primary winding  250  has a starting end  254  and a terminal end  256 . The second auxiliary winding  252  has a starting end  258  and a terminal end  260 . 
     A second high-side switch  262  is electrically connected between the electrical energy source  202  and the starting end  254  of the second primary winding  250  of the second coupled inductor  248 . The second high-side switch  262  comprises a drain  264 , a gate  266 , and a source  268 . The drain  264  is electrically connected to the electrical energy source  202 . The source  268  is electrically connected to the starting end  254  of the second primary winding  250 . 
     A third low-side switch  270  is electrically connected between the starting end  254  of the second primary winding  250  of the second coupled inductor  248  and the ground node  238 . The third low-side switch  270  comprises a drain  272 , a gate  274 , and a source  276 . The drain  272  is electrically connected to the starting end  254  of the second primary winding  250 . The source  276  is electrically connected to the ground node  238 . 
     A fourth low-side switch  278  is electrically connected between the starting end  258  of the second auxiliary winding  252  of the second coupled inductor  248  and the ground node  238 . The fourth low-side switch  278  comprises a drain  280 , a gate  282 , and a source  284 . The drain  280  is electrically connected to the starting end  258  of the second auxiliary winding  252  of the second coupled inductor  248 . The source  284  is electrically connected to the ground node  238 . 
     The first high-side switch  222 , the second high-side switch  262 , the first low-side switch  230 , the second low-side switch  240 , the third low-side switch  270 , and the fourth low-side switch  278  may be any suitable type of switching device or combination of switching devices capable of conducting current in a manner that be controlled via synchronous rectification. Non-limiting examples of such switches comprise MOSFETs, GaNFETs, and Schottky or silicon rectifiers. 
     A first output node  286  is electrically connected to the terminal end  216  of the first primary winding  210  of the first coupled inductor  208  and the terminal end  256  of the second primary winding  250  of the second coupled inductor  248 . A second output node  288  is electrically connected to the terminal end  220  of the first auxiliary winding  212  of the first coupled inductor  208  and the terminal end  260  of the second auxiliary winding  252  of the second coupled inductor  248 . In some examples, electrical loads may be electrically connected to both the first and second output nodes  286 ,  288 . In other examples, a single electrical load may be electrically connected to either of the first output node  286  or the second output node  288 . 
     In the illustrated embodiment, the two-phase synchronous buck voltage regulator device  200  includes two coupled inductors and two sets of associated high-side and low-side switches. In other embodiments, a synchronous buck voltage regulator device may include more than two phases of inductors and associates sets of switches to accommodate more than two output nodes. A synchronous buck voltage regulator device may include any suitable number of phases of coupled inductors and associated sets of switches. 
     A first output storage capacitor  290  is electrically connected to the terminal end  216  of the first primary winding  210  of the first coupled inductor  208  and the terminal end  256  of the second primary winding  250  of the second coupled inductor  248 . Further. the first output storage capacitor  290  is electrically connected between the first output node  286  and the ground node  238 . 
     A second output storage capacitor  292  is electrically connected to the terminal end  220  of the first auxiliary winding  212  of the first coupled inductor  208  and the terminal end  260  of the second auxiliary winding  252  of the second coupled inductor  248 . Further, the second output storage capacitor  292  is electrically connected between the second output node  288  and the ground node  238 . 
     In some embodiments, the two-phase synchronous buck voltage regulator device  200  optionally may comprise an output ripple-reducing inductor  294  including a starting end  295  and a terminal end  297 . The starting end  295  of the output ripple-reducing inductor  294  is electrically connected to the terminal end  220  of the first auxiliary winding  212  of the first coupled inductor  208  and the terminal end  260  of the second auxiliary winding  252  of the second coupled inductor  248 . The terminal end  297  of the output ripple-reducing inductor  294  is electrically connected to the second output storage capacitor  292  and the second output node  288 . Further, in some embodiments, the two-phase synchronous buck voltage regulator device  200  optionally may comprise an output-side noise filter capacitor  296  that is electrically connected between the first auxiliary winding  212  of the first coupled inductor  208 , the terminal end  260  of the second auxiliary winding  252  of the second coupled inductor  248 , the starting end  295  of the output ripple-reducing inductor  294  and the ground node  238 . The output ripple-reducing inductor  294  and the output-side noise filter capacitor  296  may collectively act as a filter to reduce ripple current at the second output node  288 . 
     In some embodiments, the two-phase synchronous buck voltage regulator device  200  optionally may comprise an input-side noise filter capacitor  298  that is electrically connected between the electrical energy source  202  and the ground node  238 . The input-side noise filter capacitor  298  is configured to filter electromagnetic interference at the electrical energy source  202 . 
     The two-phase synchronous buck voltage regulator device  200  comprises a controller  299  configured to control the state of the first high-side switch  222 , the second high-side switch  262 , the first low-side switch  230 , the second low-side switch  240 , the third low-side switch  270 , and the fourth low-side switch  278  according to a desired control scheme. The control scheme may vary depending on the load(s) on the first and second output nodes  286 ,  288  and the voltage desired at the first and second output nodes  286 ,  288 . 
     In one example, the controller  299  is configured to operate the two-phase synchronous voltage regulator device  200  in four states to adjust an output voltage at the second output node  288  relative to an input voltage at the electrical energy source  202  based, at least in part, on a first turns ratio of the first coupled inductor and a second turns ratio of the second coupled inductor. For example, the control scheme may conform to the DC transfer function described above. 
       FIGS. 3A-3D  show four example operating states of the two-phase synchronous buck voltage regulator device  200  of  FIG. 2  during an operating cycle. In  FIG. 3A , during a first state of the four states, the controller  299  is configured to turn on the first high-side switch  222 , turn on the third low-side switch  270 , and turn on the fourth low-side switch  278 . Further, the controller  299  is configured to turn off the second high-side switch  262 , turn off the first low-side switch  230 , and turn off the second low-side switch  240 . In this first operating state, electrical energy is transferred from the electrical energy source  202  and stored in the first primary winding  210  of the first coupled inductor  208  and the first output storage capacitor  290  and electrical energy stored in the second primary winding  250  of the second coupled inductor  248  is transferred through the second auxiliary winding  252  of second coupled inductor  248  to the second output node  288 . 
     In  FIG. 3B , during a second state of the four states, the controller  299  is configured to turn on the first low-side switch  230 , turn on the second low-side switch  240 , turn on the third low-side switch  270 , and turn on the fourth low-side switch  278 . Further, the controller  299  is configured to turn off the first high-side switch  222  and turn off the second high-side switch  262 . In this second operating state, electrical energy is transferred from the first primary winding  210  of the first coupled inductor  208  through the first auxiliary winding  212  of the first coupled inductor  208  to the second output node  288  and electrical energy stored in the second primary winding  250  of the second coupled inductor  248  is transferred through the second auxiliary winding  252  of second coupled inductor  248  to the second output node  288 . 
     In  FIG. 3C , during a third state of the four states, the controller  299  is configured to turn on the second high-side switch  262 , turn on the first low-side switch  230 , and turn on the second low-side switch  240 . Further, the controller  299  is configured to turn off the first high-side switch  222 , turn off the third low-side switch  270 , and turn off the fourth low-side switch  278 . In this third operating state, electrical energy stored in the first primary winding  210  of the first coupled inductor  208  is transferred through the first auxiliary winding  212  of the first coupled inductor  208  to the second output node  288  and electrical energy is transferred from the electrical energy source  202  and stored in the second primary winding  250  of the second coupled inductor  248  and the first output storage capacitor  290 . 
     In  FIG. 3D , during a fourth state of the four states, the controller  299  is configured to turn on the first low-side switch  230 , turn on the second low-side switch  240 , turn on the third low-side switch  270 , and turn on the fourth low-side switch  278 . Further, the controller  299  is configured to turn off the first high-side switch  222  and turn off the second high-side switch  262 . In this fourth operating state, electrical energy stored in the first primary winding  210  of the first coupled inductor  208  is transferred through the first auxiliary winding  212  of the first coupled inductor  208  to the second output node  288  and electrical energy stored in the second primary winding  250  of the second coupled inductor  248  is transferred through the second auxiliary winding  252  of the second coupled inductor  248  to the second output node  288 . 
     The above-described control scheme may be repeated each operating cycle to adjust an output voltage at the second output node relative to an input voltage at the electrical energy source. The control scheme is provided as a non-limiting example, and the controller may be configured to employ other controls schemes without departing from the scope of the present disclosure. In general, the duty cycle and the turns ratios of the coupled inductors may be modified depending on the application to provide any suitable output voltage(s) to either of the first or second output nodes. 
     In one example, the control scheme may dictate that the high-side switches are switched 180 degrees out of phase. Further, each high-side switch may have ˜27% duty cycle. Correspondingly, the low-side switches may have a ˜73% duty cycle. The switches may be switched at a switching frequency of 500 KHz. This complimentary timing of the high-side and low-side switches results in no phase shift between charging/discharging of the first and second coupled inductors. Moreover, since the second and fourth operating states are the same, both phases of the device deliver electrical energy to the output 50% of the operating cycle. Additionally, each single phase of the device delivers electrical energy to the output 25% of the operating cycle. In other examples, the two-phase synchronous buck voltage regulator device may operate using different duty cycles and different switching frequencies without departing from the scope of the present disclosure. 
     Furthermore, in some embodiments, the order of the operating states may be switched within an operating cycle. For example, an alternate order may include the third state (e.g. shown in  FIG. 3C ), the fourth state (shown in  FIG. 3D ), the first state (e.g., shown in  FIG. 3A ), and the second state (e.g., shown in  FIG. 3B ). 
     According to the topology of the two-phase synchronous buck voltage regulator device  200  and the corresponding control scheme, the coupled inductors not only function as inductors but also provide transformer action that allows for electrical energy to be transferred to the output node(s) during both on and off phases of the duty cycles of the switches. Moreover, the topology of the two-phase synchronous buck voltage regulator device  200  allows for relatively high ripple current on the primary side of the coupled inductors without introducing a correspondingly high ripple current on the output side of the coupled inductors. In other words, electrical energy transferred through the auxiliary side of the coupled inductors to the output node(s) may have reduced ripple current relative to the ripple current on the primary side of the coupled inductors. 
     In some embodiments, the two-phase synchronous buck voltage regulator device  200  optionally may be configured to perform zero-voltage switching of the switches using such high ripple current on the primary side of the coupled inductors. Zero-voltage switching may be performed when ripple current flows backwards into the low-side switch and applies a voltage on the gate that pulls the current low to change the state of the switch. Such zero-voltage switching using inductive energy may reduce energy losses of the switch and thus may increase efficiency of the two-phase synchronous buck voltage regulator device  200 . In other embodiments, the two-phase synchronous buck voltage regulator device  200  may operate without performing zero-voltage switching. 
       FIGS. 4-5  show graphs indicating example operation of the two-phase synchronous buck voltage regulator device  200  of  FIG. 2  throughout the different operating states shown in  FIGS. 3A-3D .  FIG. 4  shows operation of the first and second high-side switches and the drain-to-source voltage across the first and third low-side switches throughout the four operating states. The current and voltage levels of the illustrated graphs are provided as non-limiting examples. The buck voltage regulator device may be configured to operate within any suitable range of current/voltage levels depending on the implementation. The graph  400  shows the second high-side switch current over time. The current remains at zero in the first and second states of the operating cycle since the second high-side switch is turned off. In the third state, the second high-side switch is turned on and the current ramps up. Note at  406 , current ripple occurs when the second high-side switch is initially turned on. In the fourth state, the second high-side switch is turned off and the current returns to zero. 
     The graph  402  shows the current across the first high-side switch over time. In the first state, the first high-side switch is turned on and the current ramps up. Note at  408 , current ripple occurs when the first high-side switch is initially turned on. In the second state, the first high-side switch is turned off and the current returns to zero. The current remains at zero in the third and fourth states since the first high-side switch is turned off. 
     The graph  404  shows the drain-to-source voltage across the first and third low-side switches. The voltage waveform is a square wave that alternates between high and low voltages with the voltage going high in the first and third states and low in the second and fourth states. Note that the current ripple at  406  and  408  minimally impacts the voltage waveform. 
       FIG. 5  shows operation of the first, second, third, and fourth low-side switches and the drain-to-source voltage across the first and third low-side switches throughout the four operating states. The graph  500  shows the fourth low-side switch current over time. In the first state, the fourth low-side switch is turned on and the current steps up to a peak level. In the second state, the fourth low-side switch remains turned on and the current level steps down because current flows through the auxiliary winding to the second output node. In the third state, the fourth low-side switch is turned off and the current steps down to zero. In the fourth state, the fourth low-side switch is turned on and the current steps up again. 
     The graph  502  shows the second low-side switch current over time. The second low-side switch current mirrors the behavior of the fourth low-side switch current throughout the four operating states. 
     The graph  504  shows the third low-side switch current over time. In the first state, the third low-side switch is turned on and the current ramps up. In the second state, the third low-side switch remains turned on and the current again ramps up. In the third state, the third low-side switch is turned off and the current steps down to zero. Note at  510 , current ripple occurs when the third low-side switch transitions from the off state to the on state. 
     The graph  506  shows the first low-side switch current over time. In the first state, the first low-side switch is turned off and the current is zero. In the second state, the first low-side switch is turned on and the current ramps up. Note at  512 , current ripple occurs when the first low-side switch transitions from the off state to the one state. In the second state, the first low-side switch is turned on and the current again ramps. In the third state and the fourth state, the first low-side switch remains turned on and the current ramps up. 
     The graph  508  shows the drain-to-source voltage across the first and third low-side switches. The voltage waveform is a square wave that alternates between high and low voltages with the voltage going high in the first and third states and low in the second and fourth states. Note that the current ripple at  510  and  512  minimally impacts the voltage waveform. 
     The sum of the fourth low-side switch current and the second low-side switch current remains the same across all four states of the operating cycle. Such behavior indicates that the current ripple on the primary side of the coupled inductors at  406 ,  408 ,  510 , and  512  minimally affects or is not introduced to the output side of the coupled inductors. Accordingly, the two-phase synchronous buck voltage regulator device  200  may have minimal ripple at the output node(s). 
     The control scheme described above with reference to  FIGS. 3A-3D, 4 , and  5  is provided as an exemplary control scheme. Parameters of the control scheme (e.g., duty cycle, input voltage, output voltage, input current, output current, turns ratio, switching frequency) may vary without departing from the scope of this disclosure. Further, in other embodiments, the buck voltage regulator device  200  of  FIG. 2  may be controlled using a different control scheme. For example, another control scheme may employ a different number of operating states per operating cycle. 
     The topology of the synchronous buck voltage regulator device is not restricted to one or two phases. A synchronous buck voltage regulator device may include any suitable number of phases including one, two, three, or more coupled inductors and associated sets of switches based on the capabilities of the controller that operates the synchronous buck voltage regulator device. 
     The topology of the synchronous buck voltage regulator device and corresponding control scheme described herein may allow for a significant step up or down in voltage in a single stage with high efficiency. Such a buck voltage regulator device may be used in place of a multi-stage, step-down converter. Since the buck voltage regulator device has a single stage, the buck voltage regulator device may have a smaller device footprint and reduced weight relative to other multi-stage converter implementations. Moreover, such a single-stage buck voltage regulator device may have reduced heat generation relative to other multi-stage converter implementations. The synchronous buck voltage regulator concepts described herein may be broadly applicable to any suitable power supply device that is configured to transfer electrical energy from an electrical energy source to an electrical load, while converting voltage and current characteristics of the electrical energy. 
     In an example, a buck voltage regulator device comprises a coupled inductor including a primary winding and one or more auxiliary windings including a first auxiliary winding, a high-side switch electrically connected between an electrical energy source and a starting end of the primary winding, a first low-side switch electrically connected between the starting end of the primary winding and a ground node, a second low-side switch electrically connected between a starting end of the first auxiliary winding and the ground node, a first output node electrically connected to a terminal end of the primary winding, a second output node electrically connected to a terminal end of the first auxiliary winding, a first output storage capacitor electrically connected to the terminal end of the primary winding and electrically connected between the first output node and the ground node, and a second output storage capacitor electrically connected to the terminal end of the first auxiliary winding and electrically connected between the second output node and the ground node. In this example and/or other examples, the buck voltage regulator device may further comprise a controller configured to operate the high-side switch with a drive signal and operate the first low-side switch and the second low-side switch with an inverse of the drive signal to adjust an output voltage at the second output node relative to an input voltage at the electrical energy source based on a duty cycle of the drive signal and a turns ratio of the coupled inductor. In this example and/or other examples, the duty cycle of the drive signal may be less than 50% and a number of turns of the primary winding may be greater than a number of turns of the first auxiliary winding such that the output voltage at the second output node is stepped down relative to the input voltage. In this example and/or other examples, the coupled inductor may be a first coupled inductor, the primary winding may be a first primary winding, the high-side switch may be a first high-side switch, and the buck voltage regulator device may further comprise a second coupled inductor including a second primary winding and one or more auxiliary windings including a second auxiliary winding, a second high-side switch electrically connected between the electrical energy source and a starting end of the second primary winding of the second coupled inductor, a third low-side switch electrically connected between the starting end of the second primary winding of the second coupled inductor and the ground node, and a fourth low-side switch electrically connected between a starting end of the second auxiliary winding of the second coupled inductor and the ground node. In this example and/or other examples, the buck voltage regulator device may further comprise an output ripple-reducing inductor electrically connected between the terminal end of the first auxiliary winding of the first coupled inductor, the terminal end of the second auxiliary winding of the second coupled inductor, and the second output node, an input-side noise filter capacitor electrically connected between the electrical energy source and the ground node, and an output-side noise filter capacitor electrically connected between the output ripple-reducing inductor and the ground node. In this example and/or other examples, the first high-side switch, the second high-side switch, the first low-side switch, the second low-side switch, the third low-side switch, and the fourth low-side switch may comprise Gallium Nitride Field Effect Transistors (GaNFETS). In this example and/or other examples, the buck voltage regulator device may further comprise a controller configured to operate the buck voltage regulator device in four states to adjust an output voltage at the second output node relative to an input voltage at the electrical energy source based on a first turns ratio of the first coupled inductor and a second turns ratio of the second coupled inductor. In this example and/or other examples, during a first state of the four states, the controller may be configured to turn on the first high-side switch, turn on the third low-side switch, and turn on the fourth low-side switch, such that electrical energy is transferred from the electrical energy source and stored in the first primary winding of the first coupled inductor and the first output storage capacitor and electrical energy stored in the second primary winding of the second coupled inductor is transferred through the second auxiliary winding of second coupled inductor to the second output node. In this example and/or other examples, during a second state of the four states, the controller may be configured to turn on the first low-side switch, turn on the second low-side switch, turn on the third low-side switch, and turn on the fourth low-side switch, such that electrical energy is transferred from the first primary winding of the first coupled inductor through the first auxiliary winding of the first coupled inductor to the second output node and electrical energy stored in the second primary winding of the second coupled inductor is transferred through the second auxiliary winding of second coupled inductor to the second output node. In this example and/or other examples, during a third state of the four states, the controller may be configured to turn on the second high-side switch, turn on the first low-side switch, and turn on the second low-side switch, such that electrical energy stored in the first primary winding of the first coupled inductor is transferred through the first auxiliary winding of the first coupled inductor to the second output node and electrical energy is transferred from the electrical energy source and stored in the second primary winding of the second coupled inductor and the first output storage capacitor. In this example and/or other examples, during a fourth state of the four states, the controller may be configured to turn on the first low-side switch, turn on the second low-side switch, turn on the third low-side switch, and turn on the fourth low-side switch, such that electrical energy stored in the first primary winding of the first coupled inductor is transferred through the first auxiliary winding of the first coupled inductor to the second output node and electrical energy stored in the second primary winding of the second coupled inductor is transferred through the second auxiliary winding of the second coupled inductor to the second output node. 
     In another example, a buck voltage regulator device, comprises a first coupled inductor including a first primary winding and one or more auxiliary windings including a first auxiliary winding, a first high-side switch electrically connected between an electrical energy source and a starting end of the first primary winding of the first coupled inductor, a first low-side switch electrically connected between the starting end of the first primary winding of the first coupled inductor and a ground node, a second low-side switch electrically connected between a starting end of the first auxiliary winding of the first coupled inductor and the ground node, a second coupled inductor including a second primary winding and one or more auxiliary windings including a second auxiliary winding, a second high-side switch electrically connected between the electrical energy source and a starting end of the second primary winding of the second coupled inductor, a third low-side switch electrically connected between the starting end of the second primary winding of the second coupled inductor and the ground node, a fourth low-side switch electrically connected between a starting end of the second auxiliary winding of the second coupled inductor and the ground node, a first output node electrically connected to a terminal end of the first primary winding and the second primary winding, a second output node electrically connected to a terminal end of the first auxiliary winding and the second auxiliary winding, a first output storage capacitor electrically connected to the terminal end of the first primary winding and the terminal end of the second primary winding and electrically connected between the first output node and the ground node, and a second output storage capacitor electrically connected to the terminal end of the first auxiliary winding and the terminal end of the second auxiliary winding and electrically connected between the second output node and the ground node. In this example and/or other examples, the buck voltage regulator device further comprises an output ripple-reducing inductor electrically connected between the terminal end of the first auxiliary winding of the first coupled inductor, the terminal end of the second auxiliary winding of the second coupled inductor, and the second output node, an input-side noise filter capacitor electrically connected between the electrical energy source and the ground node, and an output-side noise filter capacitor electrically connected between the output ripple-reducing inductor and the ground node. In this example and/or other examples, the first high-side switch, the second high-side switch, the first low-side switch, the second low-side switch, the third low-side switch, and the fourth low-side switch may comprise Gallium Nitride Field Effect Transistors (GaNFETS). In this example and/or other examples, the buck voltage regulator device may further comprise a controller configured to operate the buck voltage regulator device in four states to adjust an output voltage at the second output node relative to an input voltage at the electrical energy source based on a first turns ratio of the first coupled inductor and a second turns ratio of the second coupled inductor. In this example and/or other examples, during a first state of the four states, the controller may be configured to turn on the first high-side switch, turn on the third low-side switch, and turn on the fourth low-side switch, such that electrical energy is transferred from the electrical energy source and stored in the first primary winding of the first coupled inductor and the first output storage capacitor and electrical energy stored in the second primary winding of the second coupled inductor is transferred through the second auxiliary winding of second coupled inductor to the second output node. In this example and/or other examples, during a second state of the four states, the controller may be configured to turn on the first low-side switch, turn on the second low-side switch, turn on the third low-side switch, and turn on the fourth low-side switch, such that electrical energy is transferred from the first primary winding of the first coupled inductor through the first auxiliary winding of the first coupled inductor to the second output node and electrical energy stored in the second primary winding of the second coupled inductor is transferred through the second auxiliary winding of second coupled inductor to the second output node. In this example and/or other examples, during a third state of the four states, the controller may be configured to turn on the second high-side switch, turn on the first low-side switch, and turn on the second low-side switch, such that electrical energy stored in the first primary winding of the first coupled inductor is transferred through the first auxiliary winding of the first coupled inductor to the second output node and electrical energy is transferred from the electrical energy source and stored in the second primary winding of the second coupled inductor and the first output storage capacitor. In this example and/or other examples, during a fourth state of the four states, the controller may be configured to turn on the first low-side switch, turn on the second low-side switch, turn on the third low-side switch, and turn on the fourth low-side switch, such that electrical energy stored in the first primary winding of the first coupled inductor is transferred through the first auxiliary winding of the first coupled inductor and electrical energy stored in the second primary winding of the second coupled inductor is transferred through the second auxiliary winding of the second coupled inductor to the second output node. 
     In yet another example, a buck voltage regulator device, comprises a coupled inductor including a primary winding and one or more auxiliary windings including a first auxiliary winding, a high-side switch electrically connected between an electrical energy source and a starting end of the primary winding, a first low-side switch electrically connected between the starting end of the primary winding and a ground node, a second low-side switch electrically connected between a starting end of the first auxiliary winding and the ground node, a first output node electrically connected to a terminal end of the primary winding, a second output node electrically connected to a terminal end of the first auxiliary winding, a first output storage capacitor electrically connected to the terminal end of the primary winding and electrically connected between the first output node and the ground node, a second output storage capacitor electrically connected to the terminal end of the first auxiliary winding and electrically connected between the second output node and the ground node, and a controller configured to operate the high-side switch with a drive signal and further configured to operate the first low-side switch and the second low-side switch with an inverse of the drive signal to adjust an output voltage at the second output node relative to an input voltage at the electrical energy source. 
     The present disclosure includes all novel and non-obvious combinations and subcombinations of the various features and techniques disclosed herein. The various features and techniques disclosed herein are not necessarily required of all examples of the present disclosure. Furthermore, the various features and techniques disclosed herein may define patentable subject matter apart from the disclosed examples and may find utility in other implementations not expressly disclosed herein.