PATENT DOCUMENT

Publication Number: US-10148178-B2
Application Number: US-201715646035-A
Country: US
Kind Code: B2

Title: Synchronous buck converter with current sensing

Abstract:
A power converter includes a buck converter with a low-side switch. During a discharge mode, current passes through the low-side switch to form a current loop. The low-side switch is typically closed synchronously with the opening of a high-side switch coupled to an input voltage level to the buck converter. The power converter also includes a high-side controller and a low-side controller, which together are configured to adjust the timing of the operation mode of the high-side controller between a storage mode and the discharge mode.

Claims:
What is claimed is: 
     
       1. A step-down voltage converter comprising:
 a tank inductor; 
 an output capacitor in series with the tank inductor; 
 a first voltage-controlled switch in series with the tank inductor and an input signal; 
 a second voltage-controlled switch in series with the tank inductor and a reference signal; and 
 a low-side controller operably connected to the second voltage-controlled switch and configured to detect a current associated with the second voltage-controlled switch; wherein
 the low-side controller is configured to open the second voltage-controlled switch in response to the current crossing a threshold. 
 
 
     
     
       2. The step-down voltage converter of  claim 1 , wherein:
 the current is a first current; 
 the threshold is a first threshold; 
 the step-down voltage converter further comprises a high-side controller operably connected to the first voltage-controlled switch and configured to detect a second current associated with the first voltage-controlled switch; and 
 the high-side controller is configured to open the first voltage-controlled switch in response to the second current crossing a second threshold. 
 
     
     
       3. The step-down voltage converter of  claim 2 , further comprising:
 a first resistor connected in series between the first voltage-controlled switch and the tank inductor; 
 a second resistor connected in parallel with the second voltage-controlled switch; wherein
 the second current is detected by measuring a first voltage across the first resistor; and 
 the first current is detected by measuring a second voltage across the second resistor. 
 
 
     
     
       4. The step-down voltage converter of  claim 2 , wherein the low-side controller is configured to close the second voltage-controlled switch upon measuring the second voltage exceeding a voltage threshold. 
     
     
       5. The step-down voltage converter of  claim 2 , wherein the high-side controller is configured to close the first voltage-controlled switch substantially synchronously with the low-side controller opening the second voltage-controlled switch. 
     
     
       6. The step-down voltage converter of  claim 2 , wherein the high-side controller is configured to close the first voltage-controlled switch a delayed time after the low-side controller opens the second voltage-controlled switch. 
     
     
       7. The step-down voltage converter of  claim 1 , further comprising a third voltage-controlled switch in series with a resistor, the third voltage controlled switch and the resistor coupled parallel to the second voltage-controlled switch; wherein
 the low-side controller is configured to detect the current as a voltage across the resistor. 
 
     
     
       8. The step-down voltage converter of  claim 7 , wherein:
 the third voltage-controlled switch comprises a MOSFET; and 
 the third voltage-controlled switch is biased with a gate voltage level sufficient to cause the third voltage-controlled switch to close substantially synchronously with the first voltage-controlled switch opening and to cause the third voltage-controlled switch to open substantially synchronously with the first voltage-controlled switch closing. 
 
     
     
       9. The step-down voltage converter of  claim 7 , wherein the low-side controller is configured to close the second voltage-controlled switch upon measuring the voltage exceeding a voltage threshold. 
     
     
       10. A power converter within a housing of an electronic device, the power converter comprising:
 a buck converter comprising:
 a high-side MOSFET connected in series with a tank inductor forming a first current loop in a storage mode; 
 a low-side MOSFET connected in series with the tank inductor forming a second current loop in a discharge mode; 
 
 a first current monitoring circuit associated with a first current through the tank inductor during the storage mode; 
 a second current monitoring circuit associated with a second current through the tank inductor during the discharge mode; and 
 a high-side controller configured to decrease a gate voltage of the high-side MOSFET below a switching threshold of the high-side MOSFET, when a first voltage output from the first current monitoring circuit exceeds a first predetermined threshold. 
 
     
     
       11. The power converter of  claim 10 , further comprising a low-side controller configured to decrease a gate voltage of the low-side MOSFET below a switching threshold of the low-side MOSFET, when a second voltage output from the second current monitoring circuit drops below a second predetermined threshold. 
     
     
       12. The power converter of  claim 11 , wherein the low-side controller is further configured to increase the gate voltage of the low-side MOSFET above the switching threshold of the low-side MOSFET, when the second voltage output from the second current monitoring circuit exceeds a third predetermined threshold. 
     
     
       13. The power converter of  claim 11 , wherein the high-side controller is further configured to increase the gate voltage of the high-side MOSFET above the switching threshold of the high-side MOSFET, substantially synchronously, when the low-side controller decreases the gate voltage of the low-side MOSFET below the switching threshold of the low-side MOSFET. 
     
     
       14. The power converter of  claim 11 , wherein the high-side controller is further configured to increase the gate voltage of the high-side MOSFET above the switching threshold of the high-side MOSFET, after a predetermined delay, when the second voltage output from the second current monitoring circuit drops below the second predetermined threshold. 
     
     
       15. The power converter of  claim 10 , wherein the high-side MOSFET is coupled to an input signal to the buck converter. 
     
     
       16. The power converter of  claim 10 , wherein the first current monitoring circuit comprises a resistor connected in series between the tank inductor and the high-side MOSFET. 
     
     
       17. The power converter of  claim 10 , wherein the second current monitoring circuit comprises a resistor and an auxiliary MOSFET connected in parallel with the low-side MOSFET. 
     
     
       18. A method of reducing voltage in a power converter, the method comprising:
 receiving a voltage at an input of a buck converter comprising a tank inductor and a high-side switch; 
 monitoring current through the tank inductor; 
 upon determining that the current through the tank inductor has reached a predetermined value, opening the high-side switch; and 
 after opening the high-side switch and upon determining that current through the tank inductor exceeds zero, closing a low-side switch; wherein
 the opening of the high-side switch disconnects the input from the tank inductor; and 
 the closing of the low-side switch passes current through the tank inductor. 
 
 
     
     
       19. The method of  claim 18 , further comprising:
 upon determining that the current through the tank inductor has dropped to zero, opening the low-side switch; and 
 upon opening the low-side switch, closing the high-side switch; wherein
 the closing of the high-side switch connects the input to the tank inductor. 
 
 
     
     
       20. The method of  claim 18 , further comprising:
 upon determining that the current through the tank inductor has dropped to zero, opening the low-side switch and initiating a predetermined delay; and 
 after the predetermined delay, closing the high-side switch to connect the input to the tank inductor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/399,038, filed on Sep. 23, 2016, and entitled “Synchronous Buck Converter with Current Sensing” and U.S. Provisional Patent Application No. 62/399,194, filed on Sep. 23, 2016, and entitled “Synchronous Buck Converter with Current Sensing” each of which is incorporated by reference as if fully disclosed herein. 
    
    
     FIELD 
     Embodiments described herein generally relate to power converters and, in particular, to systems and methods for reducing conduction losses in power converters. 
     BACKGROUND 
     An electronic device can receive electric power from a power source. The electronic device can include a power conversion and/or regulation circuit to change one or more characteristics of power received from the power source into a form usable by one or more components of the electronic device. In many examples, the power conversion and/or regulation circuit includes a power converter, such as a buck converter, boost converter, or a boost-buck converter. 
     Many conventional power converters include one or more diodes that exhibit a voltage drop when in forward conduction mode. This voltage drop results in power loss (e.g., conduction loss) that reduces the operational efficiency of the power converter. 
     SUMMARY 
     Embodiments described herein generally reference a power converter including a step-down voltage converter. The step-down voltage converter can include a tank inductor, an output capacitor and a voltage-controlled switch. Typically, the voltage-controlled switch is coupled in series with the tank inductor to selectively couple the tank inductor to an input voltage signal. The voltage-controlled switch receives a switching signal from a state controller. In response to the switching signal, the voltage-controlled switch connects or disconnects the tank inductor from the input voltage signal. 
     The power converter can also include a second voltage-controlled switch that selectively couples the output capacitor to the tank inductor. The second voltage-controlled switch receives a different switching signal from a second state controller. In response to the second switching signal, the second voltage-controlled switch connects or disconnects the tank inductor from the output capacitor. 
     The power converter also includes current monitoring circuitry that selectively switches the state of the first voltage-controlled switch and the state of the second voltage-controlled switch based on a measurement of current through the tank inductor. In some embodiments the second voltage-controlled switch is turned off when current through the tank inductor falls below a threshold. 
     Other embodiments described herein reference a power converter disposed within a housing of an electronic device. The power converter includes a buck converter formed with a MOSFET (e.g., high-side MOSFET) connected in series with a tank inductor forming a first current loop. A second MOSFET (e.g., a low-side MOSFET) is connected in series with the tank inductor forming a second current loop. A first current monitoring circuit is associated with a first current through the tank inductor when the high-side MOSFET is in an on-state and the second MOSFET is in an off-state (e.g., the buck converter is in a storage mode). A second current monitoring circuit is associated with a second current through the tank inductor when the low-side MOSFET is in an on-state and the high-side MOSFET is in an off-state (e.g., the buck converter is in a discharge mode). 
     Still further embodiments described herein reference a method of reducing voltage in a power converter. The method includes the operations of receiving a voltage at an input of a buck converter defined by a tank inductor and a voltage-controlled switch and monitoring current through the tank inductor. Upon determining that current through the tank inductor has reached or crossed a predetermined value, the voltage-controlled switch is opened and a second voltage-controlled switch is closed. The opening of the first voltage-controlled switch disconnects the input from the tank inductor, and the closing of the second voltage-controlled switch passes current through the tank inductor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIG. 1A  is a simplified depiction of an electronic device coupled to a stand-alone power converter. 
         FIG. 1B  depicts a stand-alone power converter configured for use with a wireless power transfer system. 
         FIG. 1C  depicts another stand-alone power converter configured for use with a wireless power transfer system. 
         FIG. 2  is a simplified system diagram of a power converter that incorporates a step-down voltage converter (e.g., buck converter) such as described herein. 
         FIG. 3  is a simplified system diagram of a power converter that incorporates a step-down voltage converter, a high-side controller, and a low-side controller, such as described herein. 
         FIG. 4  is a simplified schematic diagram of a power converter incorporating a buck converter, a high-side controller, and a low-side controller, such as described herein. 
         FIG. 5  is a simplified flow chart depicting a method of operating a low-side controller, such as described herein. 
         FIG. 6  is a simplified flow chart depicting a method of operating a high-side controller, such as described herein. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, they are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     Embodiments described herein reference systems and methods for operating a power converter in a manner that efficiently converts one or more characteristics of electric power received from an electric power source (more generally, “power source”). More specifically, the power converter can be configured to receive unregulated or otherwise noisy voltage (herein, the “input voltage” or the “input voltage level”) into a regulated voltage level (herein, the “output voltage”). For example, the power converter can be configured to regulate mains voltage (e.g., 90 VAC-265 VAC at 50-60 Hz) to a level such as 3.3 VDC, 5.0 VDC, 12 VDC, 50 VDC or any other suitable voltage. 
     In many embodiments, the power converter includes at least one buck converter (or other suitable step-down voltage converter) operated at a duty cycle selected to reduce the input voltage level to the output voltage level. The buck converter includes a tank inductor, an output capacitor, and at least one voltage-controlled switch. The output of the buck converter is coupled to a load, such as an electronic device. A feedback circuit (e.g., a compensation network) can be interposed between the buck converter and the load, although the feedback circuit may not be shown in all embodiments. The feedback circuit may be used to regulate the output voltage level in response to changes in the power consumption of the load and/or in response to changes in the input voltage level. In some embodiments, the buck converter can be operated with peak current control in order to provide overcurrent protection to the load, although this may not be required. 
     For many embodiments described herein, the buck converter is configured for synchronous operation. More specifically, the buck converter is implemented with a voltage-controlled switch (e.g., a MOSFET) in the place of a conventional return diode. In other words, a buck converter such as described herein includes two voltage-controlled switches arranged in a bridge configuration. Herein, these switches are referred to as a “high-side switch” and a “low-side switch” respectively, the low-side switch replacing the conventional return diode. The voltage-controlled switches are configured to alternate the buck converter between a “storage mode” (in which energy is stored in the tank inductor and/or the output capacitor), and a “discharge mode” (in which energy is discharged from the tank inductor and/or the output capacitor). 
     When in the storage mode, the high-side switch is closed (i.e., conducting current) and the low-side switch is open (i.e., not conducting current). In this configuration, the buck converter couples the input voltage level to the load through the tank inductor, defining a first current loop. Similarly, when in the discharge mode, the high-side switch is opened (i.e., not conducting current) and the low-side switch is closed (i.e., conducting current). In this configuration, the buck converter decouples the input voltage level from the load, coupling a ground reference of the load back to the tank inductor, defining a second current loop. In the discharge mode, energy stored in one or both the tank inductor and/or output capacitor is discharged into the load. 
     In many embodiments described herein, the high-side switch is coupled to a current-monitoring controller which is referred to herein as a “high-side controller.” Similarly, the low-side switch is coupled to a current-monitoring controller which is referred to herein as a “low-side controller.” The high-side controller provides high-side peak-current control to the buck converter by detecting current through the high-side switch (e.g., measuring voltage across a resistor in series with the high-side switch). The low-side controller detects a condition, namely, when the tank inductor current starts to flow into a body diode of the low side switch. The low-side controller may detect this condition, for example, by measuring a voltage across the low side switch. When the condition occurs, the low-side controller turns on the low side switch and reduces or minimizes a voltage drop across the body diode of the low-side switch. The low-side controller further detects the condition when current through the tank inductor reaches zero to trigger the time at which the high-side switch should be turned on for a subsequent cycle. 
     As a result of this topology, a buck converter such as described herein can operate in the same manner as a conventional buck converter without the conduction losses associated with the use of the conventional return diode. Further, a buck converter such as described herein can efficiently operate with input voltage that is substantially higher than the output voltage. Conversely, a conventional return diode of a conventional buck converter experiences increased conduction losses and voltage stress effects as the input voltage level increases. 
     These and other embodiments are discussed below with reference to  FIGS. 1A-6 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanation only and should not be construed as limiting. 
     Generally and broadly,  FIGS. 1A-1C  depict various simplified profiles of electronic devices that may incorporate, or may be associated with or coupled to, one or more power converters such as described herein. It will be appreciated, however, that the depicted examples are not exhaustive; the various embodiments described with reference to  FIGS. 1A-1C  may be modified or combined in any number of suitable or implementation-specific ways. 
     For example,  FIG. 1A  depicts an electronic device coupled to a stand-alone power converter configured to change one or more characteristics of power received from a power source into a form usable by the electronic device. 
     More particularly, the electronic device  100   a  includes a housing  102  to retain, support, and/or enclose various components of the electronic device  100   a  such as a rechargeable battery (not shown). The electronic device  100   a  can also include a processor, memory, power converter and/or battery, network connections, sensors, input/output ports, acoustic elements, haptic elements, digital and/or analog circuits for performing and/or coordinating tasks of the electronic device  100   a , and so on. For simplicity of illustration, the electronic device  100   a  is depicted in  FIG. 1A  without many of these elements, each of which may be included, partially and/or entirely, within the housing  102  and may be operationally or functionally associated with the internal battery. 
     In one example, the internal battery of the electronic device  100   a  can be recharged by physically connecting the electronic device  100   a  to a power converter  104 . More specifically, a power cable  106  can provide a direct electrical connection between the power converter  104  and the electronic device  100   a . In some cases, the power cable  106  is connected to the electronic device  100   a  via a connector  108 . 
     In these embodiments, the power converter  104  can be configured to accept power at mains voltage and output that power in a form usable by one or more circuits configured to facilitate recharging of the internal battery. In one particular example, the power converter  104  accepts 120 VAC as input and outputs 5 VDC, which can be accepted by the electronic device  100   a  and used to recharge the internal battery. More broadly, the power converter  104  can be configured to accept high-voltage AC and can be configured to output a lower-voltage DC. 
     In another example, the power converter  104  can be configured to accept power at mains voltage and output that power in a form that is subsequently converted again by the electronic device  100   a  prior to being used to charge the internal battery. More specifically, in this example, the power converter  104  can be configured to accept 120 VAC as input and can be configured to output 50 VDC. In these examples, the power converter  104  may also include an inverter (not shown). Thereafter, the electronic device  100   a  can accept 50 VDC and further convert, by a second power converter within the electronic device  100   a , to 5 VDC. 
     More broadly, the power converter  104  can be configured in this example to accept high-voltage AC and can be configured to output lower-voltage DC. In addition, the second power converter (which can be enclosed within the housing  102 ) can be configured to accept relatively high-voltage DC and can be configured to output low-voltage DC. 
     It may be appreciated that the limited examples provided above are not exhaustive. For example, the power converter  104  may be configured to perform an AC-to-AC or AC-to-DC conversion to different voltages than those provided above. Similarly, a power converter enclosed within the housing of the electronic device  100   a  may be appropriately configured to provide AC-to-AC, AC-to-DC, DC-to-AC, or DC-to-DC conversion. 
     It may be appreciated that the electronic device  100   a  can be any suitable electronic device that is either stationary or mobile, taking a larger or smaller form factor than illustrated. For example, in certain embodiments, the electronic device  100   a  can be, without limitation: a laptop computer; a tablet computer; a cellular phone; a wearable device; a health monitoring device; a personal or commercial automation device; a personal or commercial appliance; a craft or vehicle entertainment control, power, and/or information system; a navigation device; and so on. 
     In still further embodiments, a power converter (such as the power converter  104 ) can be configured to operate with an inductive or resonant wireless power transfer system. For example,  FIG. 1B  depicts a stand-alone power converter, identified as the power converter  100   b , configured to change one or more characteristics of power received from a power source into a form that may be wirelessly transferred to an electronic device (not shown). In this example, the power converter  100   b  can be configured to convert alternating current received via a connector end  110  into alternating current (at the same or different frequency) that can be used by a transmitter end of the power converter  100   b  to generate one or more time-varying magnetic fields that can be used to wirelessly transfer power to an electronic device placed on or near the transmitter end. In this example, the power converter  100   b  can directly convert alternating current at one frequency and peak-to-peak voltage into alternating current at a second frequency and peak-to-peak voltage. In this manner, the power converter  100   b  may operate more efficiently; an intermediate conversion to direct current is not required. 
     Another example of an inductive or resonant wireless power transfer system is depicted in  FIG. 1C . More specifically, a power converter  100   c  can be configured to change one or more characteristics of power received from a power source into a form that may be wirelessly transferred to more than one electronic device is illustrated. As with the example described above, the power converter  100   c  can be configured to convert alternating current received via a connector end  110  into alternating current (at the same or different frequency) that can be used by a transmitter end of the power converter  100   c  to generate one or more time-varying magnetic fields that can be used to wirelessly transfer power to multiple electronic devices each placed on or near the transmitter end. In this example, the power converter  100   c  directly converts alternating current at one frequency and peak-to-peak voltage into alternating current at a second frequency and peak to peak voltage. In this manner, and as noted with respect to some embodiments described herein, the power converter  100   c  may operate more efficiently; an intermediate conversion to direct current is not required. 
     The foregoing embodiments depicted in  FIGS. 1A-1C  and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate an understanding of various possible electronic devices or accessory devices that can incorporate, or be otherwise coupled to, one or more power converters such as described herein. More specifically,  FIGS. 1A-1C  are presented to illustrate that a power converter such as described herein can be incorporated, either entirely or partially, into the housing of an electronic device, into a separate power accessory that couples to an electronic device via a cable, into a separate power accessory that provides wireless power to one or more electronic devices, and so on. 
     Generally and broadly,  FIGS. 2-3  reference a power converter that may be incorporated within, coupled to or otherwise associated with, an electronic device or stand-alone power converter such as the electronic devices and/or stand-alone power converters depicted in  FIGS. 1A-1C . 
     For example,  FIG. 2  depicts a simplified system diagram of a power converter that incorporates a step-down voltage converter such as described herein. The power converter  200  can be configured to accept power from an alternating current power source  202 . 
     The alternating current power source  202  can deliver alternating current with any suitable amplitude or frequency. In one example, the alternating current power source  202  is connected to the output of a step-up converter (not shown) which can be configured to accept variable mains voltage as input (e.g., 110 VAC-265 VAC). In this case, the step-up converter may be configured to increase mains voltage to 400 VDC, or any other suitable voltage level that is reliably higher than the maximum expected mains voltage level (e.g., 265 VAC). 
     In other examples, the alternating current power source  202  can be implemented in another way. For example, the alternating current power source  202  can be a receiving element (or more than one receiving element) of a wireless power transfer system. More specifically, a wireless power transfer system may be implemented as an inductive or resonant power transfer system with a transmit coil (e.g., transmitting element) and a receive coil (e.g., receiving element) that, when positioned in proximity of one another, form a primary coil and a secondary coil of an air-gap transformer. When power transfers from the primary coil to the secondary coil, the secondary coil outputs alternating current. 
     However, for simplicity of illustration and description, the embodiments that follow are described in reference to an alternating current power source  202  configured to output high voltage alternating current, such as 90 VAC or 265 VAC, although as noted with respect to some embodiments described herein (e.g., wireless power transfer embodiments), any suitable alternating current power source can be stepped down or otherwise adjusted using the techniques, methods, and circuit topologies described below. 
     The power converter  200  can include multiple distinct and interconnected circuits or blocks, such as, but not limited to: a rectifier  204 , a step-down voltage converter  206 , and a low voltage output  208  (which may be coupled to a compensation network). In some cases, the power converter  200  can also include or be associated with one or more of a processor, memory, sensors, digital and/or analog circuits for performing and/or coordinating tasks of the power converter  200 . For simplicity of illustration and description, the power converter  200  is depicted in  FIG. 2  without many of these elements. 
     The rectifier  204  of the power converter  200  receives alternating current from the alternating current power source  202  and rectifies the received current into a rippled direct current. The rectifier  204  can be a half-bridge rectifier, although in many embodiments a full-bridge rectifier is used. In many cases, a filter can be added in parallel to the output of the rectifier to further smooth the rippled direct current waveform. The filter can be any suitable low-pass filter (e.g., a capacitor or capacitor network parallel to the output of the rectifier or an inductor-capacitor choke or filter). The rectifier  204  can be implemented in any number of suitable ways. For example, the rectifier  204  can be a synchronous or asynchronous rectifier. For embodiments in which the alternating current power source  202  outputs ˜265 VAC, the rectifier  204  outputs rippled direct current having an average bias of (up to or beyond) 400 VDC. 
     The step-down voltage converter  206  of the power converter  200  receives the rippled direct current from the rectifier  204 . In many embodiments, the step-down voltage converter  206  is implemented with a buck converter topology. 
     In one example, a buck converter can include a tank inductor and an output capacitor. A low-side lead of the tank inductor is coupled to a high-side lead of the output capacitor, which, in turn, is connected to a high-side output lead of the buck converter. The output leads of the buck converter are typically connected to a load. In many cases, a compensation network or other regulator is positioned between the output leads of the buck converter and the input leads of the load. The compensation network can provide regulation and ripple smoothing to the voltage received by the load. For simplicity of illustration, these components are not shown in  FIG. 2 . 
     Returning to the buck converter, a voltage-controlled switch (e.g., a high-side switch) couples the high-side lead of the tank inductor to an input lead of the buck converter. The input lead of the buck converter receives the input voltage, which in the illustrated example is the rippled direct current output from the rectifier  204 . The buck converter also includes an additional voltage-controlled switch (e.g., a low-side switch), which couples the high-side lead of the tank inductor to a common ground reference (e.g., a reference signal). The buck converter can be switched between a storage mode and a discharge mode by oppositely toggling the high-side switch and the low-side switch. 
     When the buck converter is in the storage mode, the high-side switch is closed and a first current loop is defined from the input voltage source, through the tank inductor, and to the load. In this mode, voltage across the tank inductor sharply increases to a voltage level equal to the difference between the voltage across the load and the input voltage. This voltage across the tank inductor induces current through the tank inductor to linearly increase. As a result of the topology of the circuit, the current flowing through the tank inductor also flows to the output capacitor and to the load. 
     Alternatively, when the buck converter transitions to the discharge mode, the high-side switch is opened and a second current loop is defined through the low-side switch. In this mode, voltage across the tank inductor sharply decreases to a voltage level equal to the difference between the voltage across the output leads of the buck converter and reference ground. This voltage across the tank inductor is lower than when in the storage mode, so current within the tank inductor linearly decreases in magnitude. The decreasing current flowing through the tank inductor also flows to the output capacitor and to the load connected across the output leads of the buck converter. In this manner, the output capacitor functions as a low-pass filter, generally reducing ripple in the voltage delivered from the output of the buck converter to the load. 
     The buck converter can be efficiently operated by switching between the storage mode and the discharge mode by toggling the voltage-controlled switch at a duty cycle selected based on the desired output voltage. The voltage output from the buck converter is proportionately related to the input voltage by the duty cycle. This relationship can be modeled by Equation 1: 
     
       
         
           
             
               
                 
                   
                     D 
                     cycle 
                   
                   = 
                   
                     
                       V 
                       out 
                     
                     
                       V 
                       
                         i 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         n 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     In one example, if direct current output from the rectifier  204  is 400 VDC and the desired output voltage is 50 VDC, a duty cycle of 12.5% may be selected. 
     In still further embodiments, the step-down voltage converter  206  can be implemented in another manner; it is appreciated that the example topology described above is merely one example of a suitable or appropriate step-down voltage converter. 
     In many examples, the output of the step-down voltage converter  206  of the power converter  200  is a rippled direct current having a voltage defined by the duty cycle at which the step-down voltage converter  206  is operated. In many cases, the rippled direct current may not be preferred. As such, a compensation network (or other voltage regulator) may be positioned between the output of the step-down voltage converter  206  and the low voltage output  208  to the load. The compensation network can be configured to reduce ripple within the voltage output from the step-down voltage converter  206  and, additionally, provide feedback to a shunt voltage regulator coupled to the step-down voltage converter  206  so that the duty cycle of the step-down voltage converter  206  can be adjusted in real-time. 
     In many embodiments, the power converter  200  can incorporate a low-side controller (not shown) that is configured to control the conduction state of the low-side switch and adjust the storage mode timing of the step-down voltage converter  206 . More specifically, the low-side controller monitors current through the low-side switch (see, e.g.,  FIG. 3 ) during the discharge mode. During the discharge mode, the low-side controller detects when current begins to conduct through a body diode of the low-side switch and also through the tank inductor. Thus, the low-side controller can trigger a turn-on of the low-side switch to reduce voltage loss across the body diode. Once current through the low-side switch, and thus the tank inductor, reaches zero, the low-side controller can trigger a turn-off of the low-side switch. 
     The power converter  200  also incorporates a high-side controller (not shown) that is configured to adjust the discharge mode timing of the step-down voltage converter  206 . More specifically, the high-side controller typically operates to synchronously or near-synchronously trigger a turn-on of the high-side switch when the low-side switch is not conducting. The high-side controller can also provide peak-current control to the power converter  200 . 
     The high-side controller monitors current through the high-side switch (see, e.g.,  FIG. 3 ) during the storage mode. Once current through the high-side switch, and thus the tank inductor, crosses a threshold, the high-side controller can trigger a turn-off of the high-side switch (e.g., a current control loop). In other cases, the high-side controller can turn on or turn off the high-side switch in response to feedback from a compensation network (e.g., a voltage control loop). 
       FIG. 3  depicts a simplified system diagram of another example power converter, identified as the power converter  300 . The power converter  300  can include multiple distinct and interconnected circuits or blocks, such as, but not limited to: a voltage level controller  304 , a compensation network or regulator (identified as the compensation network  306 ), a high-side controller  318 , and a low-side controller  320 . As with some embodiments described herein, the power converter  300  can also include or be associated with one or more of a processor, memory, sensors, and digital and/or analog circuits for performing and/or coordinating tasks of the power converter  300 . For simplicity of illustration and description, the power converter  300  is depicted in  FIG. 3  without many of these elements. Further, while the high-side controller  318  and low-side controller  320  are illustrated as separate components, in some embodiments the high-side controller  318  and low-side controller  320  may be implemented in a single component. 
     The voltage level controller  304  of the power converter  300  receives the rippled direct current from a rippled direct current source  302 . In many embodiments, the voltage level controller  304  is implemented with a buck converter topology. For example, a buck converter includes a high-side MOSFET  310 , which couples the rippled direct current source  302  to a high-side lead of a tank inductor  312 . The low-side lead of the tank inductor  312  is coupled to the high-side lead of an output capacitor  314 . The output capacitor  314 , in turn, is coupled to the load  308  via the compensation network  306 . The high-side MOSFET  310  accordingly defines a first current path through the tank inductor to the load when the buck converter is in a storage mode. 
     A low-side MOSFET  316  defines a second current path through the tank inductor  312  to the load  308  when the buck converter is in a discharge mode. The low-side MOSFET  316  can be used to couple the high-side lead of the tank inductor  312  to a ground reference (e.g., a reference signal) of the buck converter. 
     The voltage level controller  304 , implemented as a buck converter, can be switched between a storage mode and a discharge mode by toggling the high-side MOSFET  310  and the low-side MOSFET  316 . More specifically, when the voltage level controller  304  is in the storage mode, the high-side MOSFET  310  is closed and the low-side MOSFET  316  is opened, defining a first current loop from the rippled direct current source  302 , through the tank inductor  312 , and to the load  308 . In this mode, voltage across the tank inductor  312  sharply increases to a voltage level equal to the difference between the voltage across the load  308  and the input voltage. This voltage across the tank inductor  312  induces current through the tank inductor  312  to linearly increase. As a result of the topology of the circuit, the current flowing through the tank inductor  312  also flows to the output capacitor  314  and to the load  308 . 
     Alternatively, when the voltage level controller  304  transitions to the discharge mode, the high-side MOSFET  310  is opened and the low-side MOSFET  316  is closed, defining a second current loop through the low-side MOSFET  316 , through the tank inductor  312 , and to the load  308 . In this mode, voltage across the tank inductor  312  sharply decreases to a voltage level equal to the difference between the voltage across the load  308  and reference ground. This voltage across the tank inductor  312  is accordingly negative when compared to the positive voltage of the storage mode, so current within the tank inductor  312  linearly decreases in magnitude. The decreasing current flowing through the tank inductor  312  also flows to the output capacitor  314  and to the load  308  connected across the output leads of the voltage level controller  304 . In this manner, the output capacitor  314  functions as a low-pass filter, generally reducing ripple in the voltage delivered from the output of the voltage level controller  304  to the load  308 . The compensation network  306  further reduces remaining ripple in the voltage signal. 
     As noted with respect to some embodiments described herein, the voltage level controller  304  can be efficiently operated by switching between the storage mode and the discharge mode by toggling the high-side MOSFET  310  and/or the low-side MOSFET  316  at a duty cycle selected based on the desired output voltage. The high-side MOSFET  310  can be controlled by drive circuitry  322 , which may be incorporated into a high-side controller  318 . The drive circuitry  322  is configured to selectively apply a voltage to the gate of the high-side MOSFET  310  to toggle the discharge mode of the voltage level controller  304 . The low-side MOSFET  316  can be controlled by additional drive circuitry  328 , which may be incorporated into a low-side controller  320 . The drive circuitry  328  is configured to selectively apply a voltage to the gate of the low-side MOSFET  316  to toggle the storage mode of the voltage level controller  304 . 
     The high-side MOSFET  310  and the low-side MOSFET  316  can each be associated with a respective diode. The diodes are placed across the respective source and drain of the MOSFETs  310 ,  316  such that one diode is associated with the high-side MOSFET  310  and one with the low-side MOSFET  316 . In some embodiments, the diodes can be discrete and separate elements from the high-side MOSFET  310  and low-side MOSFET  316 , although this is not required. For example, in one embodiment the diodes are implemented as body diodes within the high-side MOSFET  310  and low-side MOSFET  316 . In other examples, the diodes can be implemented as external diodes. 
     In many examples, a body diode is incorporated within the low-side MOSFET  316 . When the voltage level controller  304  begins to enter the discharge mode, the high-side MOSFET  310  may be turned off. Once the high-side MOSFET  310  is off, current may begin flowing through the body diode of the low-side MOSFET  316 . The voltage across the low-side MOSFET  316  may increase rapidly when the diode begins conducting current. This voltage may be measured in order to control the turn-on timing of the low-side MOSFET  316 . 
     The power converter  300  incorporates a high-side controller  318  that is configured to adjust the discharge mode timing of the voltage level controller  304  by controlling a time at which the drive circuitry  322  is disabled. More specifically, the high-side controller  318  typically monitors a current through the high-side MOSFET  310  and the tank inductor  312 . The high-side controller  318  may include peak current detection circuitry  324 , which is configured to monitor for a given peak current through the tank inductor  312 . When the peak current is reached, the high-side controller  318  may cause the drive circuitry  322  to trigger a discharge mode of the voltage level controller  304 . 
     During the discharge mode, the high-side MOSFET  310  may be opened while the low-side MOSFET  316  is closed. The synchronous or near-synchronous switching of both MOSFETs may reduce power losses typical in circuits incorporating a diode in the place of the low-side MOSFET  316 . The low-side MOSFET  316  may be near-synchronously switched with the high-side MOSFET  310  by closing the low-side MOSFET  316  after the high-side MOSFET  310  has ceased conducting and current begins to flow through the body diode of the low-side MOSFET  316 . 
     More specifically, during the storage mode of the voltage level controller  304 , a resistor may be connected in series between the high-side MOSFET  310  and the tank inductor  312 . During the storage mode the high-side MOSFET  310  is closed, and current through the tank inductor  312  increases linearly. As the current through the inductor increases, a voltage measured across the resistor can increase. The peak current detection circuitry  324  within the high-side controller  318  can measure the voltage across the resistor to determine the current through the tank inductor  312 . The detected voltage signal across the resister can be used to control the drive circuitry  322  and control the turn-off timing of the high-side MOSFET  310 . In this manner, generally and broadly, the high-side controller  318  can be used to facilitate peak current and/or peak voltage switching of the high-side MOSFET  310 . 
     The power converter  300  further incorporates a low-side controller  320  that is configured to turn on the low-side MOSFET  316  during the discharge mode and adjust the storage mode timing of the voltage level controller  304 . The low-side controller  320  may do this by controlling a time at which the drive circuitry  328  is enabled and disabled, respectively. More specifically, the low-side controller  320  typically monitors a voltage across the low-side MOSFET  316  to detect a current through the tank inductor  312 . The low-side controller  320  may include current detection circuitry  326 , which is configured to monitor for a zero-current condition through the tank inductor  312 . When current begins to flow through the body diode of the low-side MOSFET  316  during the discharge mode, the low-side controller  320  may detect a voltage (or voltage change) across the low-side MOSFET  316  and cause the drive circuitry  322  to trigger a turn-on of the low-side MOSFET  316 , thereby reducing conduction losses through the body diode. 
     When the current through the low-side MOSFET  316  reaches zero amps, the low-side controller  320  may cause the drive circuitry  322  to trigger a storage mode of the voltage level controller  304  by turning off the low-side MOSFET  316 . In some embodiments, there may be a delay between the current reaching zero amps and the triggering of the storage mode. During the storage mode the high-side MOSFET  310  may be closed while the low-side MOSFET  316  is opened. In many cases, the low-side MOSFET  316  is opened when the low-side controller  320  detects a zero current condition, while the high-side MOSFET  310  may be closed after a delay. 
     More specifically, during the discharge mode of the voltage level controller  304 , a resistor may be coupled in parallel with the low-side MOSFET  316  and in series with an auxiliary MOSFET (which is shown as element  420  in  FIG. 4 ) and the tank inductor  312 . Since this resistor is inserted into a parallel current path through the tank inductor  312 , when the body diode of the low-side MOSFET  316  begins conducting, current through the low-side MOSFET  316  can be measured as a voltage across the parallel resistor (barring any relatively negligible voltage loss across the auxiliary MOSFET). This voltage signal can be used to control the turn-on timing of the low-side MOSFET  316 . In this manner, generally and broadly, the low-side controller  320  can be used to reduce or minimize the power loss caused by the voltage drop of the body diode conduction of the low-side MOSFET  316  before the low side MOSFET  316  is turned on which, in turn, can reduce dynamic conduction losses. 
     The voltage across the resistor that is in parallel with the low-side MOSFET  316  can also be used to control the turn-off timing of the low-side MOSFET  316  as current through the tank inductor  312  decreases, which causes the voltage across the resistor to decrease. In this manner, generally and broadly, the low-side controller  320  can be used to facilitate zero-current and/or zero-voltage switching (or near-zero current and/or voltage switching) of the voltage level controller  304  which may further reduce dynamic switching losses. 
     In many cases, the power converter is configured to reduce a relatively high voltage to a low voltage, such that the voltage level controller  304  is operated a majority of a duty cycle in the discharge mode. In these cases, the resistor by which current is measured may have a high resistance level such that, when the resistor is connected in parallel with the low-side MOSFET  316  current detection power losses are minimized. 
     Additional control circuitry may interconnect the high-side controller  318  and the low-side controller  320  in order to facilitate synchronous or near-synchronous operation of the high-side MOSFET  310  and the low-side MOSFET  316 . In some embodiments, an inverter control may interconnect the high-side controller  318  and the low-side controller  320  such that when the high-side MOSFET  310  is opened, the low-side MOSFET  316  is closed, and vice versa. In other embodiments, additional circuitry, such as a delay between the turn-off of the low-side MOSFET  316  and the turn-on of the high-side MOSFET  310 , may be implemented as appropriate. 
     The foregoing embodiments depicted in  FIGS. 2-3  and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate a thorough understanding of various possible configurations and circuit topologies of a power converter that incorporates a high-side controller and a low-side controller that facilitate efficient synchronous or near synchronous operation. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof. 
     Generally and broadly,  FIG. 4  depicts a simplified schematic diagram of an example power converter, which may incorporate a buck converter (e.g., a voltage level controller) as described herein. In particular, the power converter  400  is configured to receive rippled high-voltage DC and configured to output reduced voltage DC. The power converter  400  can include a low-side controller  424  that assists in timing the conduction mode of a low-side MOSFET  412  and the storage mode timing of the buck converter. The power converter  400  can also include a high-side controller  416  that assists in timing the discharge mode of the buck converter. In some embodiments, the high-side controller can facilitate timing the storage mode of the buck converter, or both modes. It should be appreciated that discussions herein relating to timing or affecting a “discharge” mode may be readily configured to timing or affecting a “storage” mode. Accordingly, embodiments herein that discuss controlling timing of a discharge mode are meant to encompass controlling timing of a storage mode, and vice versa. 
     The low-side controller  424  and high-side controller  416  may be operated in a synchronous or near-synchronous manner to reduce conduction losses. The output of the power converter  400  can be regulated by a compensation/feedback network (not shown) at positive output terminal V OUT    410 . Feedback received from the compensation/feedback network can be implemented as additional control to the low-side controller  424  and/or the high-side controller  416 . 
     As with other power converters described herein, the power converter  400  is implemented with a buck converter that includes an output capacitor  408  and a tank inductor  406 . In this topology, the low-side lead of the tank inductor  406  is coupled to a high-side lead of the output capacitor  408 , which, in turn, is connected to a positive output terminal  410  (V OUT ) of the buck converter. The negative output of the buck converter may be a common ground reference. 
     A high-side MOSFET  404  can be used to couple a high-side lead of the tank inductor  406  to a positive input terminal  402  to the power converter  400 . The high-side MOSFET  404  defines a first current path from the positive input terminal  402 , through the tank inductor  406 , and to the positive output terminal  410  when the buck converter is in a storage mode. 
     A low-side MOSFET  412  couples a high-side lead of the tank inductor  406  to a common ground reference (e.g., a reference signal). The low-side MOSFET  412  defines a second current path from the ground reference, through the tank inductor  406 , and to the positive output terminal  410  when the buck converter is in a discharge mode. 
     The buck converter can be switched between a storage mode and a discharge mode by toggling the high-side MOSFET  404  and/or the low-side MOSFET  412 . More specifically, when the buck converter is in the storage mode, the high-side MOSFET  404  is closed while the low-side MOSFET  412  is opened, and a first current loop is defined from the positive input terminal  402 , through the tank inductor  406 , to the positive output terminal  410 . 
     In the storage mode, voltage across the tank inductor  406  sharply increases to a positive voltage level equal to the difference between the voltage across the output capacitor  408  and the input voltage V IN . This voltage across the tank inductor  406  induces current i L  through the tank inductor  406  to linearly increase. As a result of the topology of the circuit, the current i L  flowing through the tank inductor  406  also flows to the output capacitor  408  and to the positive output terminal  410 . 
     When the buck converter transitions to the discharge mode, the high-side MOSFET  404  is opened while the low-side MOSFET  412  is closed, and a second current loop is defined through the low-side MOSFET  412 . In this mode, voltage across the tank inductor  406  sharply decreases to a voltage level equal to the voltage across the output capacitor  408 . This voltage across the tank inductor  406  is accordingly negative when compared to the positive voltage of the storage mode, so the current i L  within the tank inductor  406  linearly decreases in magnitude. The decreasing current i L  flowing through the tank inductor  406  also flows to the output capacitor  408  and to the positive output terminal  410  of the power converter  400 . In this manner, the output capacitor  408  functions as a low-pass filter, generally reducing ripple in the voltage delivered from the output of the buck converter to the positive output terminal  410  of the power converter  400 . 
     More particularly, as noted with respect to some embodiments described herein, the buck converter can be efficiently operated by switching between the storage mode and the discharge mode by toggling the gate voltage of the high-side MOSFET  404  and/or the low-side MOSFET  412  at a duty cycle selected based on the desired output voltage. More specifically, increasing the voltage at the gate of the high-side MOSFET  404  can cause the high-side MOSFET  404  to conduct current, and increasing the voltage at the gate of the low-side MOSFET  412  can cause the low-side MOSFET  412  to conduct current. 
     The buck converter can be toggled from the storage mode to the discharge mode in a manner that is responsive to changes in impedance of a load. More particularly, the power converter  400  can include a feedback controller (not shown). The feedback controller may monitor the output voltage V OUT  of the power converter  400  implementing the buck converter. If the output voltage of the power converter  400  drops, the feedback controller may compensate for the voltage drop by increasing the per-cycle on-time of the high-side MOSFET  404 . In this manner, the output voltage of the power converter  400  can be regulated independent of the load current and independent of the input voltage. 
     The output of the power converter  400  can further be coupled to a compensation network and/or a regulation network (not shown) in order to regulate V OUT  against any load variation. The compensation network can be formed in any number of suitable ways to provide stable operation of the voltage output from the power converter  400  and to provide an isolated node suitable for providing feedback to the feedback controller. 
     In many cases, the power converter  400  incorporates a high-side controller  416  that is configured to adjust the discharge mode timing of the buck converter by controlling a time at which the low-side MOSFET  412  and/or the high-side MOSFET  404  is toggled. 
     More specifically, the high-side controller  416  typically monitors a voltage across a resistor  414  coupled in series between the high-side MOSFET  404  and the tank inductor  406 . When the buck converter is in the storage mode, the high-side MOSFET  404  is closed, while the low-side MOSFET  412  is opened, creating a first current loop through the resistor  414  and the tank inductor  406 . As the resistor  414  is coupled in series with the tank inductor  406 , the current through the tank inductor i L  may be measured by the high-side controller  416  as a voltage across the resistor  414 . 
     In this manner, the measurement of voltage across the resistor  414  is configured to directly detect a given peak current through the tank inductor  406 . As noted above, once current through the resistor  414 , and thus the tank inductor  406 , reaches the given peak value, the high-side controller  416  can trigger a turn-off of the high-side MOSFET  404 . The high-side controller  416  can trigger a turn-off of the high-side MOSFET  404  by lowering the voltage at the gate of the high-side MOSFET  404 . The low-side controller  424  may synchronously or near-synchronously trigger a turn-on of the low-side MOSFET  412  (e.g., via a signal causing the low-side controller  424  to increase the gate voltage of the low-side MOSFET  412 ). Accordingly, the high-side controller  416  triggers the buck converter to change to a discharge mode. 
     The low-side MOSFET  412  may be near-synchronously switched with the high-side MOSFET  404  by causing a turn-on of the low-side MOSFET  412 . This may be done by increasing the gate voltage of the low-side MOSFET  412  after the high-side MOSFET  404  has ceased conducting and/or current begins to flow through the body diode of the low-side MOSFET  412 . By synchronously or near-synchronously switching the high-side MOSFET  404  and the low-side MOSFET  412 , the power converter  400  may reduce switching losses due to cut-in voltages and/or delays in topologies incorporating a return diode in place of the low-side MOSFET  412 . 
     The power converter  400  further incorporates a low-side controller  424  that is configured to optimize or otherwise facilitate the turn-on timing of the low-side MOSFET  412  and adjust the storage timing of the buck converter by controlling a time at which the low-side MOSFET  412  and/or the high-side MOSFET  404  is toggled. 
     More specifically, the low-side controller  424 , through the auxiliary MOSFET  420  and series resistor  422 , typically monitors a voltage across the low side MOSFET  412 . The auxiliary MOSFET  420  and the resistor  422  are coupled in parallel with the low-side MOSFET  412 . Generally, the gate of the auxiliary MOSFET  420  is biased with a fixed low voltage VCC2, as shown in  FIG. 4 . When the low-side MOSFET  412  is conducting during the discharge mode, the drain voltage and source voltage of the auxiliary MOSFET  420  become zero (or near-zero), and the auxiliary MOSFET  420  begins conducting as well. 
     Once the low-side MOSFET  412  is turned off during the storage mode, the drain voltage of the low-side MOSFET  412  becomes high, causing the drain voltage of the auxiliary MOSFET  420  to increase and become high as well. Accordingly, the gate to source voltage of the auxiliary MOSFET  420  falls below the gate threshold voltage level, causing the auxiliary MOSFET  420  to turn off and cease conducting. 
     When the low side MOSFET  412  begins conducting (e.g., the body diode of the low-side MOSFET  412  begins conducting), the auxiliary MOSFET is closed as well, coupling the resistor  422  to the tank inductor  406  in an auxiliary current loop. As current is conducted through the low-side MOSFET  412 , a small parallel current is induced in the auxiliary current loop through the resistor  422 . The current of the auxiliary current loop through the resistor  422  may be measured by the low-side controller  424  as a voltage across the resistor  422 . The current measured through the resistor  422  is thus proportional to the current in the second current loop through the tank inductor  406 . The resistance value of the resistor  422  may be selected as appropriate to adjust the current sensing amplitude measured at the low-side controller  424 . 
     As the buck converter completes a transition to the discharge mode, the low-side controller  424  detects a voltage across the low-side MOSFET  412 . The low-side voltage controller  424  then increases the gate voltage of the low-side MOSFET  412 , closing the low-side MOSFET  412  and reducing the conduction loss due to the body diode. The low-side MOSFET  412  then permits current flow through the tank inductor  406  and to the positive output terminal  410  of the power converter  400 . 
     In this manner, the measurement of voltage across the resistor  422  is also configured to indirectly detect zero or near-zero current through the tank inductor  406 . As noted above, once current through the resistor  422 , and thus the tank inductor  406 , reaches zero amps, the low-side controller  424  can trigger a turn-off of the low-side MOSFET  412 . The low-side controller  424  can trigger a turn-off of the low-side MOSFET  412  by lowering the voltage at the gate of the low-side MOSFET  412 . The low-side controller  424  may synchronously or sequentially trigger a turn-on of the high-side MOSFET  404  (e.g., via a signal to the high-side controller  416 ). In some embodiments, the turn-on of the high-side MOSFET  404  may be delayed after a detected zero-voltage or near-zero voltage condition. Once the high-side MOSFET  404  is turned on, a voltage at the high-side lead of the tank inductor  406  can cause a turn-off of the auxiliary MOSFET  420 . 
     In many cases, the power converter  400  is configured to convert a relatively high voltage to a low voltage, such that the buck converter is operated a majority of each duty cycle in the discharge mode. In these cases, reducing the voltage stress of the low-side controller  424  from the high-side lead of the tank inductor may allow a low voltage controller to be used in high voltage conversion. 
     The foregoing embodiment depicted in  FIG. 4  and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate a thorough understanding of various possible configurations of circuits that may be used to implement a power converter such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof. 
       FIG. 5  is a simplified flow chart depicting example operations of a method of operating a high-side controller such as described herein. The method depicted can, in some embodiments, be performed (at least in part) by one or more portions of a power converter such as depicted in  FIG. 4 . In other cases, the method is performed by another processor or circuit, or combination of processors or circuits. 
     The method  500  begins at operation  502  in which a current is monitored through a tank inductor of a buck converter. In some cases, a resistor can be positioned in series with the tank inductor. Current through the resistor is the same as current through the tank inductor, and can be measured as a voltage across the resistor. In other cases, a different current can be measured. For example, current can be measured by an inductor or Hall effect sensor positioned around or adjacent a conductor, such as a lead or trace associated with a buck converter of a power converter. Accordingly, it may be appreciated that a current through the tank inductor can be measured or obtained in any number of suitable ways. 
     Next, at operation  504 , a peak current is detected. In some cases, the peak current may be a fixed threshold value. In other cases, the peak current may be a variable threshold value. In cases where the threshold value is variable, it may be set according to feedback values generated in other processes and/or components of the power converter. 
     At operation  506 , a high-side MOSFET of the buck converter is turned off. The high-side MOSFET may be turned off by lowering a voltage applied at the gate of the high-side MOSFET. Lastly, at operation  508 , a low-side MOSFET of the buck converter is turned on. In many cases, the low-side MOSFET of the buck converter is turned on synchronously or near-synchronously with the turn-off of the high-side MOSFET. The low-side MOSFET may be turned on in response to detecting that a body diode of the low-side MOSFET begins to conduct. 
     One may appreciate that although many embodiments are disclosed above, that the operations and steps presented with respect to methods and techniques described herein are meant as exemplary and accordingly are not exhaustive. One may further appreciate that alternate step order or fewer or additional operations may be required or desired for particular embodiments. 
       FIG. 6  is a simplified flow chart depicting example operations of a method of operating a low-side controller such as described herein. The method depicted can, in some embodiments, be performed (at least in part) by one or more portions of a power converter such as depicted in  FIG. 4 . In other cases, the method is performed by another processor or circuit, or combination of processors or circuits. 
     The method  600  begins at operation  602 , in which a current is monitored through a tank inductor of a buck converter. In some cases, a resistor can be positioned in parallel to a low-side MOSFET conducting current through the tank inductor. Current through the resistor is proportional to current through the tank inductor, and can be measured as a voltage across the resistor. In other cases, a different current can be measured. For example, current can be measured by an inductor or Hall effect sensor positioned around or adjacent a conductor, such as a lead or trace associated with a buck converter of a power converter. Accordingly, it may be appreciated that a current through the tank inductor can be measured or obtained in any number of suitable ways. 
     Next, at operation  604 , a zero-current or zero crossing of current is detected. At operation  606 , a low-side MOSFET of the buck converter is turned off. The low-side MOSFET may be turned off by lowering a voltage applied at the gate of the low-side MOSFET. 
     Lastly, at operation  508 , a high-side MOSFET of the buck converter is turned on. In some cases, the high-side MOSFET of the buck converter is turned on synchronously with the turn-off of the low-side MOSFET. In other cases, the high-side MOSFET is turned on after a delay. The delay can be based on a characteristic associated with the power converter and/or a detected state or pattern of the current through the tank inductor. 
     One may appreciate that although many embodiments are disclosed above, that the operations and steps presented with respect to methods and techniques described herein are meant as exemplary and accordingly are not exhaustive. One may further appreciate that alternate step order or fewer or additional operations may be required or desired for particular embodiments. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20170710
Publication Date: 20181204
Grant Date: 20181204
Priority Date: 20160923
Inventors: OH, InHwan
PANDYA, MANISHA P.
MOHTASHEMI, BEHZAD
Assignee: APPLE INC
CPC Classifications: [{"code": "H02M2001/0009", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02M1/083", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/1588", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/158", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M3/1588", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M1/0009", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02M1/0009", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02B70/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02B70/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02M3/158", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M1/083", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/1588", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 61686660