PATENT DOCUMENT

Publication Number: US-10644531-B1
Application Number: US-201715468001-A
Country: US
Kind Code: B1

Title: Adaptable power rectifier for wireless charger system

Abstract:
A power converter including a rectifier circuit and a method for rectifying an incoming alternating current. The rectifier circuit may alter its output voltage according to varying conditions of the power converter. The variations may include voltage changes at the input or output.

Claims:
What is claimed is: 
     
       1. A power converter, comprising:
 a first inductive coil configured to output a first induced current; 
 a second inductive coil configured to output a second induced current; 
 a rectifier circuit coupled to the first inductive coil and the second inductive coil and comprising a set of voltage-controlled switches, the rectifier circuit configured to operate in a full-wave rectifying mode and a voltage doubler rectifying mode; and 
 processing circuitry configured to:
 cause the rectifier circuit to switch between the full-wave rectifying mode and the voltage doubler rectifying mode; 
 monitor a voltage at the first inductive coil; and 
 cause the rectifier circuit to switch to the voltage doubler rectifying mode in response to the voltage being below a threshold; 
 
 wherein the rectifier circuit is configured to switch between the full-wave rectifying mode and the voltage doubler rectifying mode by selectively controlling a conduction state of each voltage-controlled switch of the set of voltage-controlled switches. 
 
     
     
       2. The power converter of  claim 1 , wherein the processing circuitry is further configured to:
 cause the rectifier circuit to switch to the full-wave rectifying mode in response to the voltage exceeding the threshold. 
 
     
     
       3. The power converter of  claim 1 , wherein the rectifier circuit is configured to:
 controllably pass the first induced current through a full-wave bridge rectifying circuit or a first voltage doubler rectifying circuit; and 
 pass the second induced current through a second voltage doubler rectifying circuit. 
 
     
     
       4. The power converter of  claim 1 , wherein the rectifier circuit is configured to:
 controllably pass the first induced current through a first full-wave bridge rectifying circuit or a first voltage doubler rectifying circuit; and 
 controllably pass the second induced current through a second full-wave bridge rectifying circuit or a second voltage doubler rectifying circuit. 
 
     
     
       5. The power converter of  claim 4 , wherein the rectifier circuit is configured to simultaneously pass the first induced current through the first full-wave bridge rectifying circuit and pass the second induced current through the second full-wave bridge rectifying circuit. 
     
     
       6. The power converter of  claim 1 , wherein the rectifier circuit is configured to:
 controllably pass the first induced current through a full-wave bridge rectifying circuit or a first voltage doubler rectifying circuit; and 
 controllably pass the second induced current through a second voltage doubler rectifying circuit or an impedance matching voltage doubler rectifying circuit. 
 
     
     
       7. The power converter of  claim 1 , wherein each of the set of voltage-controlled switches comprises a MOSFET. 
     
     
       8. The power converter of  claim 7 , wherein:
 the processing circuitry is configured to cause the rectifier circuit to switch to the voltage doubler rectifying mode by toggling and holding one of the set of voltage-controlled switches in an on-state. 
 
     
     
       9. The power converter of  claim 1 , wherein:
 the rectifier circuit further comprises a capacitor coupled to a high-side lead of an input to the rectifier circuit; 
 the set of voltage-controlled switches comprises:
 a first voltage-controlled switch coupled to the capacitor and a low-side lead of the input; and 
 a second voltage-controlled switch coupled to the capacitor and a high-side lead of an output capacitor; and 
 
 the processing circuitry is configured to operate a turn-on timing and a turn-off timing of the first voltage-controlled switch and the second voltage-controlled switch; wherein
 the first voltage-controlled switch is turned off while the second voltage-controlled switch is turned on; and 
 the second voltage-controlled switch is turned on during at least half of a voltage cycle of an alternating current input signal applied to the rectifier circuit. 
 
 
     
     
       10. The power converter of  claim 9 , wherein the processing circuitry is further configured to monitor an output voltage from the rectifier circuit. 
     
     
       11. The power converter of  claim 10 , wherein in response to an increase in the output voltage the second voltage-controlled switch is turned on for a longer duration. 
     
     
       12. The power converter of  claim 10 , wherein in response to a decrease in the output voltage the second voltage-controlled switch is turned on for a shorter duration. 
     
     
       13. The power converter of  claim 9 , wherein each of the first voltage-controlled switch and the second voltage-controlled switch comprises a MOSFET. 
     
     
       14. The power converter of  claim 1 , wherein the first inductive coil and the second inductive coil comprise wireless power receivers. 
     
     
       15. A method of rectifying an alternating current, comprising:
 operating a first inductive coil to output a first induced current; 
 operating a second inductive coil to output a second induced current; 
 operating a rectifier circuit, coupled to the first inductive coil and the second inductive coil, in a full-wave rectifying mode or a voltage doubler rectifying mode; 
 measuring an incoming voltage to a rectifier; 
 operating the rectifier in the full-wave rectifying mode in response to the measured incoming voltage exceeding a first threshold; and 
 operating the rectifier in the voltage doubler rectifying mode in response to the measured incoming voltage falling below a second threshold. 
 
     
     
       16. The method of  claim 15 , wherein the first threshold is the same as the second threshold. 
     
     
       17. The method of  claim 15 , wherein the first threshold is higher than the second threshold. 
     
     
       18. The method of  claim 15 , wherein the voltage doubler rectifying mode is an impedance matching voltage doubler rectifying mode. 
     
     
       19. The method of  claim 15 , wherein the rectifier comprises a set of voltage-controlled switches. 
     
     
       20. The method of  claim 19 , wherein the operating the rectifier circuit in the voltage doubler rectifying mode comprises toggling and holding one of the set of voltage-controlled switches in an on-state.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a nonprovisional patent application of U.S. Patent Application No. 62/398,127, filed Sep. 22, 2016 and titled “Adaptable Power Rectifier for Wireless Charger System,” the disclosure of which is hereby incorporated herein by reference in its entirety. 
     FIELD 
     Embodiments described herein generally relate to power converters and, in particular, to systems and methods for operating rectifying circuitry adaptable to the characteristics of incoming power. 
     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 rectifier circuit. A rectifier circuit typically operates in a single mode, such as a half-wave rectifier, a full-wave rectifier circuit, or a voltage doubler rectifier. 
     SUMMARY 
     Embodiments described herein generally relate to a power converter including a rectifier circuit. The rectifier circuit is configured to adaptably rectify an alternating current into a direct current, under varying conditions such as a changing input voltage or changing load demands. In an example embodiment, the power converter includes a first inductive coil configured to output a first induced current and a second inductive coil configured to output a second induced current. The power converter further includes a rectifier circuit, which includes a set of voltage-controlled switches coupled to the first inductive coil and the second inductive coil. 
     The rectifier circuit is configured to switch between a full-wave rectifying mode and a voltage doubler rectifying mode by selectively controlling the conduction state of each voltage-controlled switch of the set of voltage-controlled switches. Processing circuitry is configured to cause the rectifier circuit to switch between the full-wave rectifying mode and the voltage doubler rectifying mode. 
     In some examples, the processing circuitry is configured to monitor a voltage at the first inductive coil and cause the rectifier circuit to switch to the voltage doubler rectifying mode in response to the voltage being below a threshold. In other examples, the processing circuitry is configured to monitor a voltage at the first inductive coil and cause the rectifier circuit to switch to the full-wave rectifying mode in response to the voltage exceeding a threshold. 
     In another embodiment, a voltage rectifier includes an output. The output is connected parallel to: a first voltage-controlled switch connected in series with a second voltage-controlled switch; a third voltage-controlled switch connected in series with a fourth voltage-controlled switch; and a fifth voltage-controlled switch connected in series with a sixth voltage-controlled switch. The voltage rectifier includes a first alternating current input and a second alternating current input. The first alternating current input has a first node connected between the third voltage-controlled switch and the fourth voltage-controlled switch and a second node connected between the fifth voltage-controlled switch and the sixth voltage-controlled switch. The second alternating current input has a third node connected between the fifth voltage-controlled switch and the sixth voltage-controlled switch and a fourth node connected between the first voltage-controlled switch and the second voltage-controlled switch. Processing circuitry is configured to operate the sixth voltage-controlled switch to operate the voltage rectifier in a secondary mode. 
     In still another embodiment, a voltage rectifier includes an output. The output is connected parallel to: a first voltage-controlled switch connected in series with a second voltage-controlled switch; a third voltage-controlled switch connected in series with a fourth voltage-controlled switch; and a fifth voltage-controlled switch connected in series with a sixth voltage-controlled switch. The voltage rectifier includes a first alternating current input and a second alternating current input. The first alternating current input has a first node connected between the third voltage-controlled switch and the fourth voltage-controlled switch and a second node connected between the fifth voltage-controlled switch and the sixth voltage-controlled switch. The second alternating current input has a third node connected between the first voltage-controlled switch and the second voltage-controlled switch and a fourth node connected to a common voltage node of the second voltage-controlled switch and the output. Processing circuitry is configured to operate the sixth voltage-controlled switch to operate the voltage rectifier in a secondary mode. 
     In still another embodiment, a voltage rectifier includes an output. The output is connected parallel to: a first voltage-controlled switch connected in series with a second voltage-controlled switch; a third voltage-controlled switch connected in series with a fourth voltage-controlled switch; and a fifth voltage-controlled switch connected in series with a sixth voltage-controlled switch. The voltage rectifier includes an alternating current input having a first node connected between the first voltage-controlled switch and the second voltage-controlled switch and a second node connected between the fifth voltage-controlled switch and the sixth voltage-controlled switch. A first capacitor is connected in series between the first node and the connection point between the first voltage-controlled switch and the second voltage-controlled switch. A second capacitor is connected to the first node and between the third voltage-controlled switch and the fourth voltage-controlled switch. Processing circuitry is configured to operate the fourth voltage-controlled switch to operate the voltage rectifier in a primary mode or a secondary mode. 
     In still another embodiment, a method of rectifying an alternating current is provided. The method includes the operation of measuring an incoming voltage to a rectifier. The rectifier is operated in a full-wave rectifying mode in response to the measured incoming voltage exceeding a first threshold. The rectifier is operated in a voltage doubler rectifying mode in response to the measured incoming voltage falling below a second threshold. 
     In still another embodiment, a voltage rectifier includes a capacitor, a first voltage-controlled switch, a second voltage-controlled switch, and processing circuitry. The capacitor is coupled to a high-side lead of an input to the voltage rectifier. The first voltage-controlled switch is coupled to the capacitor and a low-side lead of the input, while the second voltage-controlled switch is coupled to the capacitor and a high-side lead of an output capacitor. The processing circuitry is configured to operate the turn-on timing and the turn-off timing of the first voltage-controlled switch and the second voltage-controlled switch. The first voltage-controlled switch is turned off while the second voltage-controlled switch is turned on, and the second voltage-controlled switch is turned on during at least half of a voltage cycle of an alternating current input signal. 
    
    
     
       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 elements. 
         FIG. 1A  depicts a wireless power transmission system, including a portable electronic device incorporating a rectifier. 
         FIG. 1B  depicts a wireless power transmission system, including a portable electronic device incorporating a rectifier. 
         FIG. 1C  depicts a wireless power transmission system, including a portable electronic device incorporating a rectifier. 
         FIG. 2  depicts a simplified schematic view of components of a wireless charging system. 
         FIG. 3  depicts a simplified schematic diagram of an example rectifier of a power converter. 
         FIG. 4  depicts a simplified schematic diagram of another example rectifier of a power converter. 
         FIG. 5  depicts a simplified schematic diagram of another example rectifier of a power converter. 
         FIG. 6  depicts a simplified schematic diagram of another example rectifier of a power converter. 
         FIG. 7  depicts a simplified schematic diagram of another example rectifier of a power converter. 
         FIG. 8  depicts a simplified schematic diagram of another example rectifier of a power converter. 
         FIG. 9  depicts an example process for rectifying an alternating current. 
         FIG. 10  depicts another example process for rectifying an alternating current. 
     
    
    
     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 implementation. To the contrary, the described embodiments are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the disclosure and 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”) into a form usable by one or more components of an electronic device. The electronic device may be any stationary or portable electronic device including a desktop computer, a laptop computer, a tablet computer, a cellular telephone, a peripheral device, an accessory device, a wearable device, a vehicle or aeronautical control system, an industrial control system, an appliance, and so on. 
     Generally, a power converter, such as described herein, is configured to convert voltage from an unregulated or otherwise noisy voltage source (herein, “input voltage”) into a regulated voltage level (herein, “output voltage”) suitable for use by one or more electronic devices. For example, a power converter can be configured to regulate mains voltage (e.g., 90 VAC-265 VAC at 50-60 Hz) to a reference level such as 3.3 VDC, 5.0 VDC, 12 VDC, 50 VDC or any other suitable reference voltage. In some examples, the output of the power converter can be boosted to a higher level after being regulated to the reference level. 
     For simplicity and consistency of the description provided herein, many embodiments are presented and described with reference to power converters configured to reduce a high voltage alternating current (e.g., 265 VAC) to a relatively lower voltage direct current (e.g., 50 VDC). It may be appreciated, however, that the various techniques, circuit topologies, operations and/or methods presented with respect to this particular implementation can be equivalently applied to power converters configured to regulate power in another manner. For example, a power converter such as described herein can be suitably configured in any implementation-specific manner to convert an arbitrary input voltage to any selected or desired output voltage, whether such operation requires DC-to-DC conversion stages, AC-to-DC conversion stages, DC-to-AC conversion stages, AC-to-AC conversion stages, or any combination or sequence thereof. 
     As noted above, some embodiments described herein reference a power converter configured to regulate an alternating current input voltage to a particular direct current output voltage level. In these examples, the power converter includes at least one rectifier operated in a manner to efficiently rectify the input voltage to a rippled or steady direct current output voltage level. In many cases, the output of the rectifier is connected to additional power conditioning circuitry, such as a buck converter, a boost converter, a buck-boost converter, and/or a compensation network. The output of the rectifier can thereafter be connected to a load, such as an electronic device. 
     In some cases, a power converter includes a rectifier configured to regulate an alternating current input with a voltage which may be unpredictable or variable (e.g., 0.1 VAC-50 VAC). The rectifier may additionally or alternatively be connected to a load having a variable demand or impedance, but which requires the output voltage of the rectifier to have a voltage level with little or no variance, such as 3.3 VDC, 5.0 VDC, or 12 VDC (e.g., a constant or rippled direct current voltage). 
     For example, the power converter may be implemented in a portable electronic device configured to receive power wirelessly from a power transmitting source, such as a wireless charging mat. The portable electronic device may be configured to receive power wirelessly through a resonant inductive coupling, capacitive coupling, optical, acoustic, contact array, and so on. It should be understood that these and other wireless charging methods and systems may be employed within the scope of the present disclosure. For simplicity of description, the following embodiments are described in reference to resonant inductive systems and methods employing a receive coil in an electronic device coupled with a transmit coil in a wireless charging mat. 
     A wireless charging mat typically includes at least one transmit coil and an electronic device that can receive power from the wireless charging mat typically includes at least one receive coil. In operation, the transmit coil is energized with an alternating current; a time-varying magnetic flux field is produced by the transmit coil in response. The magnetic flux field induces an alternating current within the receive coil of the electronic device. 
     In such embodiments, the voltage induced at the receive coil of the electronic device may vary depending on the proximity between and the relative alignment of the receive coil with the transmit coil in the wireless charging mat. For example, if the receive coil is located away from the transmit coil, it may be subject to attenuated magnetic flux, resulting in a reduced induced voltage at the receive coil. Similarly, some orientations of the electronic device may reduce the induced voltage, for example due to interference introduced by objects, such as other components of the electronic device. 
     The power demands of the electronic device may also vary over time, which may result in a varying impedance across output leads of the power converter. For example, the demands of a processor or other circuitry may increase and decrease, placing a varying power demand on the power converter. The varying power demand results in a varying impedance across the output of the power converter, causing increases and decreases in the voltage output of the power converter from a desired constant output voltage. 
     Accordingly, the power converter may include a rectifier circuit configured to convert a variable alternating current input voltage to a substantially constant direct current output voltage (e.g., a rippled direct current voltage). In some examples, the rectifier circuit includes multiple operating modes to compensate for the varying input voltage and the varying impedance of the connected load. A first operating mode may be formed from a full-wave rectifying sub-circuit. A second operating mode may be formed from an additional rectifying sub-circuit, such as a voltage doubler rectifying circuit. A voltage-controlled switch within the rectifier circuit may controllably adjust the operating mode (e.g., based on the input voltage level, a desired output voltage and/or current, and so on). 
     In these examples, the rectifier circuit may be coupled to processing circuitry which is configured to monitor a power condition associated with the power converter (e.g., an input voltage level, an output voltage level, an impedance at the output, etc.) and affect the operation of the rectifier circuit based on the condition. For example, the processing circuitry may monitor an input voltage level. If the input voltage is above a first threshold level, the processing circuitry may cause the rectifier circuit to be operated in a full-wave rectifying mode. In the full-wave rectifying mode the current delivered to a connected load (e.g., a battery or other component of the electronic device) may be higher than in other operating modes. However, if the input voltage falls below a second threshold level (e.g., the same or a lower level from the first threshold level), the processing circuitry may cause the rectifier circuit to be operated in a voltage doubler rectifying mode. In the voltage doubler rectifying mode the output voltage may be double the full-wave rectifying mode to compensate for the lower input voltage, while the current delivered to a connected load may be reduced. 
     In other examples, the rectifier circuit includes a boost rectifier topology. In a boost rectifier topology, the rectifier circuit can variably adjust a direct current output voltage up to double the peak input alternating current voltage. In these examples, the boost rectifier circuit may include two voltage-controlled switches connected similar to a voltage doubler configuration. The output voltage of the boost rectifier circuit may be controlled as a function of the operation timing of the voltage-controlled switches. The output voltage may thus be controllably adjusted to boost levels up to double the peak input voltage. 
     In these examples, the boost rectifier circuit may be coupled to processing circuitry which is configured to monitor a power condition associated with the power converter (e.g., an input voltage level, an output voltage level, an impedance at the output, etc.) and affect the operation of the boost rectifier circuit based on the condition. For example, the processing circuitry may monitor an output voltage level. If the output voltage level drops (e.g., due to an increased impedance across the output terminals), the processing circuitry may change the turn-on and turn-off timing of the voltage-controlled switches to boost the output voltage from the boost rectifier circuit. 
     These and other embodiments are discussed below with reference to  FIGS. 1A-7 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
     Generally and broadly,  FIGS. 1A-1C  reference various example 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  108  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  108  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  103 . More specifically, a power cable  105  can provide a direct electrical connection between the power converter  103  and the electronic device  100   a . In some cases, the power cable  105  is connected to the electronic device  100   a  via a connector  107 . 
     In these embodiments, the power converter  103  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  103  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  103  can be configured to accept high-voltage AC and can be configured to output a lower-voltage DC. 
     In another example, the power converter  103  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  103  can be configured to accept 120 VAC as input and can be configured to output 50 VDC. In these examples, the power converter  103  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  103  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  108 ) 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  103  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. 
     Furthermore, although illustrated as a cellular phone, it may be appreciated that the electronic device  100   a  can be another 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 a laptop computer, a tablet computer, a cellular phone, a wearable device, a health monitoring device, a home or building automation device, a home or building appliance, a craft or vehicle entertainment, control, power, and/or information system, a navigation device, and so on. 
     In other embodiments, a power converter can be implemented within a wireless power transfer system  100   b . For example,  FIGS. 1B and 1C  depict a wireless charging mat  104 , configured to wirelessly transfer power to an electronic device  102 . An electronic device  102  includes a housing  108  enclosing one or more power receivers configured to receive an alternating current input voltage from the wireless charging mat  104  through a resonant inductive coupling, capacitive coupling, optical, acoustic, contact array, or similar system or method. For simplicity, the following embodiments are described in reference to resonant inductive systems and methods employing one or more receive coils  110   a ,  110   b  in the electronic device  102 . The receive coils  110   a ,  110   b  are configured to interact with a transmit coil  112  in the charging mat  104  to receive power, and may further power components of the electronic device  102  and/or recharge a battery of the electronic device  102 . 
     A receive coil  110   a  may be any inductive coil suitable for forming an inductive coupling with a nearby transmit coil  112 . The receive coil  110   a  may be configured to respond to the presence of a magnetic flux field (e.g., a field generated by a transmit coil  112 ), by which the field may induce a current in the receive coil  110   a . Generally, the induced current is an alternating current, and the electronic device  102  includes a power converter with a rectifier configured to convert an alternating current input voltage to a direct current output voltage. 
     The charging mat  104  includes a housing to enclose electronic, mechanical, and/or structural components. For example, the housing may enclose one or more inductive transmit coils  112 . Generally, a wireless charging mat  104  is configured to transfer power to an electronic device  102  on or near a charging surface  106  without use of wires. The charging mat  104  may draw power from a power source, such as a wall receptacle, condition the power, and transmit the conditioned power to the electronic device  102  using the transmit coil  112 . The transmit coil  112  may be energized with an alternating current, which may produce a magnetic flux field in response. If an electronic device  102  that incorporates a corresponding receive coil  110   a ,  110   b  is brought within the flux field, a current is induced within the receive coil  110   a ,  110   b.    
     In many cases, the voltage of the power induced in the receive coil  110   a ,  110   b  by the transmit coil  112  may vary. For example, the voltage may decrease due to a reduced coupling between a receive coil  110   b  in the electronic device  102  and the transmit coil  112  in the wireless charging mat  104 . For example, as depicted in  FIG. 1C , the electronic device  102  includes a first receive coil  110   a  and a second receive coil  110   b . Each of the receive coils  110   a ,  110   b  is positioned over a corresponding transmit coil  112 . When the transmit coil is energized, it produces a magnetic flux field. The first receive coil  110   a  overlaps the transmit coil  112  more than the second receive coil  110   b  does, and may accordingly have a stronger response to the magnetic flux field, such as a higher induced voltage. The second receive coil  110   b  may have a weaker response to the magnetic flux field, such as a lower induced voltage. 
     A power converter (such as the power converter depicted below with respect to  FIG. 2 .) within the electronic device  102  includes a rectifier circuit configured to convert an alternating current input voltage to a substantially constant direct current output voltage (e.g., a rippled direct current voltage). In these examples, the rectifier circuit is configured to adapt to conditions which affect its output voltage, such as a reduced input voltage (e.g., due to a reduced coupling between a receive coil  110   b  and a transmit coil  112 ) or a varying impedance across the output of the power converter (e.g., due to a load with varying power demands). In some examples, a rectifier circuit includes at least two operating modes, such as a full-wave rectifying mode and a voltage doubler rectifying mode. A voltage-controlled switch coupled with processing circuitry may controllably adjust the operating mode of the rectifier circuit (e.g., based on the input voltage level, a desired output voltage and/or current, and so on). Example embodiments are further described below with respect to  FIGS. 3-6 . 
     In other examples, the rectifier circuit includes a boost rectifier topology. The boost rectifier includes two voltage-controlled switches, which may be dynamically controlled to output a boosted voltage up to double the peak input alternating current voltage. The output voltage of the boost rectifier circuit may be controlled as a function of the operation timing of the voltage-controlled switches. Example embodiments are further described below with respect to  FIGS. 7-8 . 
     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. 
       FIG. 2  depicts a simplified schematic view of components of a wireless charging system  200 . The wireless charging system  200  includes a wireless charging mat  204  configured to transmit power to an electronic device  202 . The wireless charging mat  204  includes a power supply  214 , which may provide alternating current power. The alternating current power supply  214  can deliver alternating current with any suitable amplitude or frequency. In one example, the alternating current power supply  214  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-250 VAC). In this case, the step-up converter may be configured to increase mains voltage to 400 VAC, or any other suitable voltage level that is reliably higher than the maximum expected mains voltage level (e.g., 250 VAC). 
     Incoming power may pass from the power supply  214  through conditioning circuitry  216 . The conditioning circuitry  216  may alter the power according to the requirements for output at an inductive transmit coil  212 . For example, the conditioning circuitry  216  may alter the voltage, current, frequency, phase, and/or other aspects of the incoming power in order to arrive at a desired output for the transmit coil  212 . The transmit coil  212  may be configured to wirelessly transfer power to one or more receive coils  210   a ,  210   b  via resonant inductive power transfer. The transmit coil  212  may be energized with an alternating current signal received from the conditioning circuitry  216  to induce an alternating current in a coupled receive coil  210   a ,  210   b . The conditioning circuitry  216  may include a number of other components, such as a rectifier, a buck converter, boost converter, filters, boost/buck converter, and so forth, which have been omitted from  FIG. 2  for clarity. In some cases, the incoming power from the power supply  214  may be a direct current. In such cases, the conditioning circuitry  216  may additionally convert the direct current to an appropriate alternating current for the transmit coil  212 . 
     In some embodiments, elements of the power supply  214  and/or conditioning circuitry  216  may form part of the wireless charging mat  204 . In other embodiments, one or both of the power supply  214  and conditioning circuitry  216  may be separate from the wireless charging mat  204 . 
     The electronic device  202  may receive power wirelessly via an induced current in one or more receive coils  210   a ,  210   b . For example, the transmit coil  212  in the wireless charging mat  204  may be energized with an alternating current, causing the transmit coil  212  to generate a magnetic flux field. The magnetic flux field may in turn induce an alternating current in the receive coils  210   a ,  210   b  of the electronic device  202 . The induced current in each receive coil  210   a ,  210   b  has a voltage, which voltage may vary depending on the coupling between each receive coil  210   a ,  210   b  and the transmit coil  212  in the wireless charging mat  204 . The induced current may pass from the receive coils  210   a ,  210   b  through a power converter, including a rectifier circuit  220 . 
     The rectifier circuit  220  is configured to convert an alternating current input voltage to a substantially constant direct current output voltage (e.g., a rippled direct current voltage). The power converter may include additional conditioning circuitry  224  to further alter the power according to the requirements for output to the load  226 . For example, the conditioning circuitry  224  may alter the voltage, current, frequency, phase, and/or other aspects of the incoming power in order to arrive at a desired output to the load  226 . The conditioning circuitry  224  may include a number of other components, such as a buck converter, boost converter, filters, boost/buck converter, a compensation network, and so forth, which have been omitted from  FIG. 2  for clarity. In other embodiments the rectifier circuit  220  may be directly coupled to the load  226  and/or the one or more receive coils  210   a ,  210   b.    
     The conditioning circuitry  224  may be further coupled to a load  226 . The load  226  may be any appropriate load, and may require a substantially constant direct current input voltage. In many embodiments, the load  226  may have an impedance which varies over time. For example, the load  226  may include components of the electronic device  202 , such as processing circuits, battery charging components, a display, and so on. These components may consume power at varying levels and times, altering the power requirements and, consequently, an impedance across output terminals of the power converter. 
     Accordingly, the rectifier circuit  220  may be configured to compensate for the varying input voltage levels and/or output impedance noted above. In some embodiments, the rectifier circuit  220  includes at least two operating modes to compensate for the varying input voltage and/or impedance. In many cases, a first operating mode may be formed from a full-wave rectifying sub-circuit. A second operating mode may be formed from an additional rectifying sub-circuit, such as a voltage doubler rectifying circuit. One or more switches within the rectifier circuit  220  may controllably switch the operating mode. 
     In these embodiments, the rectifier circuit  220  may be coupled to processing circuitry  222 . The processing circuitry  222  may control the operation of one or more switches within the rectifier circuit  220 , including to cause the rectifier circuit  220  to switch between modes. While the processing circuitry  222  is depicted outside the line of power transmission to the load  226 , in other embodiments the processing circuitry  222  may be within the power transmission line. However implemented, the processing circuitry  222  is configured to monitor a condition of the input voltage and affect the operation of the rectifier circuit  220  based on the condition. 
     For example, the processing circuitry  222  may monitor an input voltage level received from one or more receive coils  210   a ,  210   b . If the input voltage level is above a first threshold, the processing circuitry  222  may cause the rectifier circuit  220  to be operated in a full-wave rectifying mode. However, if the input voltage falls below a second threshold level (e.g., the same or a different level from the first threshold), the processing circuitry  222  may cause the rectifier circuit  220  to be operated in a voltage doubler rectifying mode. In the voltage doubler rectifying mode the output voltage to the load  226  may be doubled in order to compensate for the reduced input voltage level. 
     In other embodiments, the rectifier circuit  220  includes a boost rectifier topology. In a boost rectifier topology, the rectifier circuit  220  can variably adjust a direct current output voltage up to double the peak input alternating current voltage. The rectifier circuit  220  may include two voltage-controlled switches, which may be dynamically controlled to output a boosted voltage up to double the peak input alternating current voltage. The output voltage of the boost rectifier circuit may be controlled as a function of the operation timing of the voltage-controlled switches. 
     In these embodiments, the rectifier circuit  220  may be coupled to processing circuitry  222 . The processing circuitry  222  is configured to monitor a power condition associated with the power converter (e.g., an input voltage level, an output voltage level, or an impedance at the output) and affect the operation of the rectifier circuit  220   
     For example, the processing circuitry  222  may monitor an output voltage level to the load  226 . If the impedance of the load  226  increases, the output voltage level to the load  226  may also drop. In response to the detected voltage drop, the processing circuitry  222  may alter the turn-on and turn-off timing of the voltage-controlled switches to boost the output voltage from the boost rectifier circuit. 
     The processing circuitry  222  may include one or more computer processors or microcontrollers that are configured to perform, interrupt, or coordinate operations in response to computer-readable instructions. Additionally or alternatively, the processing circuitry  222  may include other processors including application specific integrated chips and other microcontroller devices. 
     In some embodiments, the processing circuitry  222  may further be operatively connected to computer memory via an electronic bus or bridge. The memory may include a variety of types of non-transitory computer-readable storage media, including, for example, read access memory, read-only memory, erasable programmable memory, or flash memory. The memory is configured to store computer-readable instructions, sensor values, and other persistent software elements. 
     In this example, the processing circuitry  222  may be operable to read computer-readable instructions stored on the memory. The computer-readable instructions may adapt the processing circuitry  222  to perform the operations or functions described herein, such as switching the operating mode of the rectifier circuit  220 . In some embodiments, the processing circuitry  222  may affect the operations of other components, such as the conditioning circuitry  224 . The computer-readable instructions may be provided as a computer-program product, software application, or the like. 
     Generally and broadly,  FIGS. 3-8  reference certain example rectifier circuits that can be implemented within a power converter such as described herein. It will be appreciated, however, that the depicted examples are not exhaustive; the various embodiments depicted and described with reference to  FIGS. 3-8  may be implemented, interconnected, or otherwise modified in any number of suitable or appropriate ways. 
     For example,  FIG. 3  depicts a simplified schematic diagram of an example rectifier of a power converter such as described herein. The rectifier circuit  320  receives input power from two alternating current power sources  310   a ,  310   b  and rectifies the received current into a direct current output voltage having a substantially constant voltage (e.g., a rippled direct current voltage). The alternating current power sources  310   a ,  310   b  may be inductive receive coils such as depicted above with respect to  FIGS. 1A-2 , while in other embodiments the power sources  310   a ,  310   b  may receive power through another source. In some embodiments each alternating current power source  310   a ,  310   b  is a separate receive coil, while in other embodiments the power sources  310   a ,  310   b  may represent portions of a center-tapped receive coil. 
     The rectifier circuit  320  includes a set of voltage-controlled switches  331 - 336 . The set may include six voltage-controlled switches  331 - 336 , and a conduction state of each voltage-controlled switch  331 - 336  may be toggled between an on-state and an off-state in order to rectify the input voltage. The voltage-controlled switches  331 - 336  are connected in parallel with the load  344  in pairs. A first voltage-controlled switch  331  and second voltage-controlled switch  332  are connected in series, with the pair being connected in parallel to the load  344 . A third voltage-controlled switch  333  and fourth voltage-controlled switch  334  are connected in series, with the pair being connected in parallel to the load  344 . A fifth voltage-controlled switch  335  and sixth voltage-controlled switch  336  are connected in series, with the pair being connected in parallel to the load  344 . 
     The load  344  may be any arbitrary load configured to receive the rectified output voltage of the rectifier circuit  320  (e.g., the conditioning circuitry  224  and/or the load  226  as depicted in  FIG. 2 ). In many cases, the output of the rectifier circuit  320  may be a rippled direct current voltage. An output capacitor  342  can be added in parallel to the load  344  to further smooth the rippled direct current waveform. The output capacitor  342  functions as a low-pass filter. 
     The alternating current power sources  310   a ,  310   b  are coupled to the set of voltage-controlled switches of the rectifier circuit  320 . A high-side lead of a first alternating current power source  310   a  is coupled to a low-side lead of the third voltage-controlled switch  333  and a high-side lead of the fourth voltage-controlled switch  334 . A low-side lead of the first alternating current power source  310   a  is coupled to a low-side lead of the fifth voltage-controlled switch  335  and a high-side lead of the sixth voltage-controlled switch  336 . In some embodiments, a capacitor  338  may be connected in series between the high-side lead of the first alternating current power source  310   a  and the low-side lead of the third voltage-controlled switch  333 . 
     A high-side lead of a second alternating current power source  310   b  is coupled to a low-side lead of the fifth voltage-controlled switch  335  and a high-side lead of the sixth voltage-controlled switch  336 . A low-side lead of the second alternating current power source  310   b  is coupled to a low-side lead of the first voltage-controlled switch  331  and a high-side lead of the second voltage-controlled switch  332 . In some embodiments, a capacitor  340  may be connected in series between the low-side lead of the second alternating current power source  310   b  and the low-side lead of the first voltage-controlled switch  331 . 
     The set of voltage-controlled switches of the rectifier circuit  320  may be operated in a full-wave rectifier mode and a voltage doubler mode. The sixth voltage-controlled switch  336  may controllably switch the rectifier circuit  320  between modes. For example, the sixth voltage-controlled switch  336  may be operably coupled to processing circuitry (e.g., processing circuitry  222  such as depicted in  FIG. 2 ). The processing circuitry may monitor a condition of the power converter and operate the sixth voltage-controlled switch  336  according to the condition. 
     For example, the processing circuitry may monitor a voltage across one or both alternating current power sources  310   a ,  310   b . If the voltage across one or both alternating current power sources  310   a ,  310   b  exceeds a threshold (e.g., due to strong coupling with a transmit coil), the processing circuit may operate the sixth voltage-controlled switch  336  in a full-wave rectifying mode. In the full-wave rectifying mode, the first alternating current power source  310   a  may pass current through a full-wave bridge rectifier circuit formed with the third voltage-controlled switch  333 , the fourth voltage-controlled switch  334 , the fifth voltage-controlled switch  335 , and the sixth voltage-controlled switch  336 . 
     In this example, during a positive voltage half-cycle of the first alternating current power source  310   a , the processing circuitry causes the third voltage-controlled switch  333  and the sixth voltage-controlled switch  336  to be closed while the fourth voltage-controlled switch  334  and the fifth voltage-controlled switch  335  are opened. This passes a positive-voltage current to the high-side lead of the output capacitor  342  and the load  344 . During a negative voltage half-cycle of the first alternating current power source  310   a , the processing circuitry causes the fourth voltage-controlled switch  334  and the fifth voltage-controlled switch  335  to be closed while the third voltage-controlled switch  333  and the sixth voltage-controlled switch  336  are opened. This passes a negative-voltage current to the low-side lead of the output capacitor  342  and the load  344 . In this manner, the first alternating current power source  310   a  is rectified during its full cycle. 
     In the full-wave rectifying mode, the second alternating current power source  310   b  may simultaneously pass current through a full-wave bridge rectifier circuit formed with the first voltage-controlled switch  331 , the second voltage-controlled switch  332 , the fifth voltage-controlled switch  335 , and the sixth voltage-controlled switch  336 . 
     In this example, during a positive voltage half-cycle of the second alternating current power source  310   b , the processing circuitry causes the second voltage-controlled switch  332  and the fifth voltage-controlled switch  335  to be closed while the sixth voltage-controlled switch  336  and the first voltage-controlled switch  331  are opened. This passes a positive-voltage current to the high-side lead of the output capacitor  342  and the load  344 . During a negative voltage half-cycle of the second alternating current power source  310   b , the processing circuitry causes the first voltage-controlled switch  331  and the sixth voltage-controlled switch  336  to be closed while the second voltage-controlled switch  332  and the fifth voltage-controlled switch  335  are opened. This passes a negative-voltage current to the low-side lead of the output capacitor  342  and the load  344 . In this manner, the second alternating current power source  310   a  is rectified during its full cycle. 
     If the voltage across one or both alternating current power sources  310   a ,  310   b  falls below a threshold (e.g., due to weak coupling with a transmit coil), the processing circuit may operate the sixth voltage-controlled switch  336  in a voltage doubler rectifying mode. In the voltage doubler rectifying mode, the sixth voltage-controlled switch  336  is pulled to ground and the first alternating current power source  310   a  may pass current through a voltage doubler rectifier circuit formed with the third voltage-controlled switch  333  and the fourth voltage-controlled switch  334 . 
     In this example, during a negative voltage half-cycle of the first alternating current power source  310   a , the processing circuitry causes the third voltage-controlled switch  333  to be opened while the fourth voltage-controlled switch  334  is closed. This places the capacitor  338  in parallel with the first alternating current power source  310   a , charging the capacitor  338  with a negative voltage. During a positive voltage half-cycle of the first alternating current power source  310   a , the processing circuitry causes the fourth voltage-controlled switch  334  to be opened while the third voltage-controlled switch  333  is closed. This places the capacitor  338  in series with the first alternating current power source  310   a  both of which are in parallel with the output capacitor  342 . This charges the output capacitor  342  with the combined voltage of the first alternating current power source  310   a  and the capacitor  338 , doubling the output voltage of the rectifier circuit  320 . 
     In the voltage doubler rectifying mode, the second alternating current power source  310   b  may simultaneously pass current through a voltage doubler rectifier circuit formed with the first voltage-controlled switch  331  and the second voltage-controlled switch  332 . 
     Continuing the example, during a negative voltage half-cycle of the second alternating current power source  310   b , the processing circuitry causes the first voltage-controlled switch  331  to be opened while the second voltage-controlled switch  332  is closed. This places the capacitor  340  in parallel with the first alternating current power source  310   a , charging the capacitor  340  with a negative voltage. During a positive voltage half-cycle of the second alternating current power source  310   b , the processing circuitry causes the second voltage-controlled switch  332  to be opened while the first voltage-controlled switch  331  is closed. This places the capacitor  340  in series with the second alternating current power source  310   b , both of which are in parallel with the output capacitor  342 . This charges the output capacitor  342  with the combined voltage of the second alternating current power source  310   b  and the capacitor  340 , doubling the output voltage of the rectifier circuit  320 . 
     Each voltage-controlled switch  331 - 336  may be a suitable switch, such as a MOSFET. In some embodiments, the voltage-controlled switches  331 - 336  can each be associated with a diode. The diodes are placed across the respective source and drain of the voltage-controlled switches  331 - 336  such that one diode is associated with each voltage-controlled switch. In some embodiments, the diodes can be discrete and separate elements from the voltage-controlled switches  331 - 336 , although this is not required. For example, in one embodiment the diodes are implemented as body diodes within the voltage-controlled switches  331 - 336 . In other examples, the diodes can be implemented as external diodes, such as Schottky diodes. The diodes of the voltage-controlled switches  331 - 336  can be used as supplemental current paths during the operation of the rectifier circuit  320 . More specifically, in certain embodiments, the rectifier circuit  320  may briefly pause between switching between the separate electrical paths of each rectifier sub-circuit (e.g., between positive and negative half-cycles of a full-wave rectifier sub-circuit). This “dead time” between rectifier cycles may be included in order to prevent “shoot-through” current which may occur if the voltage-controlled switches of the distinct rectifier half-cycles are in the on-state at the same time. During the dead time between rectifier half-cycles, current within a receive coil  310   a ,  310   b  may be conducted through one or more of the diodes, thereby preventing said current from causing damage to one or more of the voltage-controlled switches  331 - 336  during the dead time period. As may be appreciated, the voltage across an inverter diode may increase rapidly when said diode begins conducting current during a dead time period. The forward voltage of the conducting diodes may be observed as a voltage spike when measured across a receive coil  310   a ,  310   b.    
       FIG. 4  depicts a simplified schematic diagram of an example rectifier of a power converter such as described herein. The rectifier circuit  420  receives input power from two alternating current power sources  410   a ,  410   b  and rectifies the received current into a direct current output voltage having a substantially constant voltage (e.g., a rippled direct current voltage). The alternating current power sources  410   a ,  410   b  may be inductive receive coils such as depicted above with respect to  FIGS. 1A-2 , while in other embodiments the rectifier power sources  410   a ,  410   b  may receive power through another source. 
     The rectifier circuit  420  includes a set of voltage-controlled switches  431 - 436 . The set may include six voltage-controlled switches  431 - 436 , and a conduction state of each voltage-controlled switch  431 - 436  may be toggled between an on-state and an off-state in order to rectify the input voltage. The voltage-controlled switches  431 - 436  are connected in parallel with the load  444  in pairs. A first voltage-controlled switch  431  and second voltage-controlled switch  432  are connected in series, with the pair being connected in parallel to the load  444 . A third voltage-controlled switch  433  and fourth voltage-controlled switch  434  are connected in series, with the pair being connected in parallel to the load  444 . A fifth voltage-controlled switch  435  and sixth voltage-controlled switch  436  are connected in series, with the pair being connected in parallel to the load  444 . 
     The load  444  may be any arbitrary load configured to receive the rectified output voltage of the rectifier circuit  420  (e.g., the conditioning circuitry  224  and/or the load  226  as depicted in  FIG. 2 ). In many cases, the output of the rectifier circuit  420  may be a rippled direct current voltage. An output capacitor  442  can be added in parallel to the load  444  to further smooth the rippled direct current waveform. The output capacitor  442  functions as a low-pass filter. 
     The alternating current power sources  410   a ,  410   b  are coupled to the set of voltage-controlled switches of the rectifier circuit  420 . A high-side lead of a first alternating current power source  410   a  is coupled to a low-side lead of the third voltage-controlled switch  433  and a high-side lead of the fourth voltage-controlled switch  434 . A low-side lead of the first alternating current power source  410   a  is coupled to a low-side lead of the fifth voltage-controlled switch  435  and a high-side lead of the sixth voltage-controlled switch  436 . In some embodiments, a capacitor  438  may be connected in series between the high-side lead of the first alternating current power source  410   a  and the low-side lead of the third voltage-controlled switch  433 . 
     A high-side lead of a second alternating current power source  410   b  is coupled to a low-side lead of the first voltage-controlled switch  431  and a high-side lead of the second voltage-controlled switch  432 . A low-side lead of the second alternating current power source  410   b  is coupled to a low-side lead of the second voltage-controlled switch  432  (e.g., a common ground reference of the rectifier circuit  420 ). In some embodiments, a capacitor  440  may be connected in series between the high-side lead of the second alternating current power source  410   b  and the low-side lead of the first voltage-controlled switch  431 . 
     The first alternating current power source  410   a  may be operated in a full-wave rectifier mode and a voltage doubler mode, while the second alternating current power source  410   b  may be operated in a voltage doubler mode (e.g., by passing current through a voltage doubler rectifying circuit formed with the first voltage-controlled switch  431  and second voltage-controlled switch  432 ). The sixth voltage-controlled switch  436  may controllably switch the rectifier circuit  420  between modes for the first alternating current power source  410   a . For example, the sixth voltage-controlled switch  436  may be operably coupled to processing circuitry (e.g., processing circuitry  222  such as depicted in  FIG. 2 ). The processing circuitry may monitor a condition of the power converter and operate the sixth voltage-controlled switch  436  according to the condition. 
     For example, the processing circuitry may monitor a voltage across the first alternating current power source  410   a . If the voltage across the first alternating current power source  410   a  exceeds a threshold (e.g., due to strong coupling with a transmit coil), the processing circuit may operate the sixth voltage-controlled switch  436  in a full-wave rectifying mode. In the full-wave rectifying mode, the first alternating current power source  410   a  may pass current through a full-wave bridge rectifier circuit formed with the third voltage-controlled switch  433 , the fourth voltage-controlled switch  434 , the fifth voltage-controlled switch  435 , and the sixth voltage-controlled switch  436 . 
     If the voltage across the first alternating current power source  410   a  falls below a threshold (e.g., due to weak coupling with a transmit coil), the processing circuit may operate the sixth voltage-controlled switch  436  in a voltage doubler rectifying mode. In the voltage doubler rectifying mode, the sixth voltage-controlled switch  436  is pulled to ground and the first alternating current power source  410   a  may pass current through a voltage doubler rectifier circuit formed with the third voltage-controlled switch  433  and the fourth voltage-controlled switch  434 . 
     Similar to the example rectifier circuit of  FIG. 3 , each voltage-controlled switch  431 - 436  may be a suitable switch, such as a MOSFET. In some embodiments, the voltage-controlled switches  431 - 436  can each be associated with a diode. The diodes may be discrete and separate elements from the voltage-controlled switches, while in other embodiments the diodes are implemented as body diodes within the voltage-controlled switches  431 - 436 . 
       FIG. 5  depicts a simplified schematic diagram of an example rectifier of a power converter such as described herein. The rectifier circuit  520  receives input power from two alternating current power sources  510   a ,  510   b  and rectifies the received current into a direct current output voltage having a substantially constant voltage (e.g., a rippled direct current voltage). The alternating current power sources  510   a ,  510   b  may be inductive receive coils such as depicted above with respect to  FIGS. 1A-2 , while in other embodiments the rectifier power sources  510   a ,  510   b  may receive power through another source. 
     The rectifier circuit  520  includes a set of voltage-controlled switches  531 - 536 . The set may include six voltage-controlled switches  531 - 536 , and a conduction state of each voltage-controlled switch  531 - 536  may be toggled between an on-state and an off-state in order to rectify the input voltage. The voltage-controlled switches  531 - 536  are connected in parallel with the load  544  in pairs. A first voltage-controlled switch  531  and second voltage-controlled switch  532  are connected in series, with the pair being connected in parallel to the load  544 . A third voltage-controlled switch  533  and fourth voltage-controlled switch  534  are connected in series, with the pair being connected in parallel to the load  544 . A fifth voltage-controlled switch  535  and sixth voltage-controlled switch  536  are connected in series, with the pair being connected in parallel to the load  544 . 
     The load  544  may be any arbitrary load configured to receive the rectified output voltage of the rectifier circuit  520  (e.g., the conditioning circuitry  224  and/or the load  226  as depicted in  FIG. 2 ). In many cases, the output of the rectifier circuit  520  may be a rippled direct current voltage. An output capacitor  542  can be added in parallel to the load  544  to further smooth the rippled direct current waveform. The output capacitor  542  functions as a low-pass filter. 
     The alternating current power sources  510   a ,  510   b  are coupled to the set of voltage-controlled switches of the rectifier circuit  520 . A high-side lead of a first alternating current power source  510   a  is coupled to a low-side lead of the third voltage-controlled switch  533  and a high-side lead of the fourth voltage-controlled switch  534 . A low-side lead of the first alternating current power source  510   a  is coupled to a low-side lead of the fifth voltage-controlled switch  535  and a high-side lead of the sixth voltage-controlled switch  536 . In some embodiments, a capacitor  538  may be connected in series between the high-side lead of the first alternating current power source  510   a  and the low-side lead of the third voltage-controlled switch  533 . 
     A high-side lead of a second alternating current power source  510   b  is coupled to a low-side lead of the first voltage-controlled switch  531  and a high-side lead of the second voltage-controlled switch  532 . A low-side lead of the second alternating current power source  510   b  is coupled to a low-side lead of the second voltage-controlled switch  532  (e.g., a common ground reference of the rectifier circuit  520 ). In some embodiments, a capacitor  540  may be connected in series between the high-side lead of the second alternating current power source  510   b  and the low-side lead of the first voltage-controlled switch  531 . Another capacitor  546  may be coupled to the low-side lead of the first alternating current power source  510   a  and the high-side lead of the second alternating current power source  510   b.    
     The set of voltage-controlled switches of the rectifier circuit  520  may be operated in two modes. The sixth voltage-controlled switch  536  may controllably switch the rectifier circuit  520  between modes. For example, the sixth voltage-controlled switch  536  may be operably coupled to processing circuitry (e.g., processing circuitry  222  such as depicted in  FIG. 2 ). The processing circuitry may monitor a condition of the power converter and operate the sixth voltage-controlled switch  536  according to the condition. 
     For example, in a first mode the first alternating current power source  510   a  may pass current through a full-wave bridge rectifier circuit formed with the third voltage-controlled switch  533 , the fourth voltage-controlled switch  534 , the fifth voltage-controlled switch  535 , and the sixth voltage-controlled switch  536 . The second alternating current power source  510   b  may simultaneously pass current through a voltage doubler rectifier circuit formed with the first voltage-controlled switch  531  and the second voltage-controlled switch  532 . 
     In a second mode, the processing circuit causes the sixth voltage-controlled switch  536  to be pulled to ground. In this mode, the first alternating current power source  510   a  may pass current through a voltage doubler rectifier circuit formed with the third voltage-controlled switch  533  and the fourth voltage-controlled switch  534 . The second alternating current power source  510   b  may simultaneously pass current through an impedance matching voltage doubler rectifier circuit formed with the two capacitors  546 ,  540 , the first voltage-controlled switch  531 , and the second voltage-controlled switch  532 . 
     Accordingly, when the rectifier circuit  520  depicted in  FIG. 5  switches to the second mode, the voltage output of the first alternating current power source  510   a  may be doubled, while the power output of the second alternating current power source  510   b  may be changed (e.g., increased). Therefore, the processing circuitry may control the interval and frequency of pulling the sixth voltage-controlled switch  536  to ground in order to control voltage and/or power output to the load  544 . The interval and frequency may be controlled according to a monitored condition of the power converter, such as a voltage across one or both power sources  510   a ,  510   b , a voltage at the load  544 , a current at the load  544 , a combination of these conditions, and so on. 
     Similar to the example rectifier circuit of  FIG. 3 , each voltage-controlled switch  531 - 536  may be a suitable switch, such as a MOSFET. In some embodiments, the voltage-controlled switches  531 - 536  can each be associated with a diode. The diodes may be discrete and separate elements from the voltage-controlled switches, while in other embodiments the diodes are implemented as body diodes within the voltage-controlled switches  531 - 536 . 
       FIG. 6  depicts a simplified schematic diagram of an example rectifier of a power converter such as described herein. The rectifier circuit  620  receives input power from an alternating current power source  610  and rectifies the received current into a direct current output voltage having a substantially constant voltage (e.g., a rippled direct current voltage). The alternating current power source  610  may be an inductive receive coil such as depicted above with respect to  FIGS. 1A-2 , while in other embodiments the rectifier circuit  620  may receive input power through another source. 
     The rectifier circuit  620  includes a set of voltage-controlled switches  631 - 636 . The set may include six voltage-controlled switches  631 - 636 , and a conduction state of each voltage-controlled switch  631 - 636  may be toggled between an on-state and an off-state in order to rectify the input voltage. The voltage-controlled switches  631 - 636  are connected in parallel with the load  644  in pairs. A first voltage-controlled switch  631  and second voltage-controlled switch  632  are connected in series, with the pair being connected in parallel to the load  644 . A third voltage-controlled switch  633  and fourth voltage-controlled switch  634  are connected in series, with the pair being connected in parallel to the load  644 . A fifth voltage-controlled switch  635  and sixth voltage-controlled switch  636  are connected in series, with the pair being connected in parallel to the load  644 . 
     The load  644  may be any arbitrary load configured to receive the rectified output voltage of the rectifier circuit  620  (e.g., the conditioning circuitry  224  and/or the load  226  as depicted in  FIG. 2 ). In many cases, the output of the rectifier circuit  620  may be a rippled direct current voltage. An output capacitor  642  can be added in parallel to the load  644  to further smooth the rippled direct current waveform. The output capacitor  642  functions as a low-pass filter. 
     The alternating current power source  610  is coupled to the set of voltage-controlled switches of the rectifier circuit  620 . A high-side lead of the alternating current power source  610  is coupled to a low-side lead of the first voltage-controlled switch  631  and a high-side lead of the second voltage-controlled switch  632 . A low-side lead of the alternating current power source  610  is coupled to a low-side lead of the fifth voltage-controlled switch  635  and a high-side lead of the sixth voltage-controlled switch  636 . A capacitor  638  is connected in series between the high-side lead of the alternating current power source  610  and the low-side lead of the first voltage-controlled switch  631 . Another capacitor  646  is connected to the high-side lead of the alternating current power source  610  and the low-side lead of the third voltage-controlled switch  633 . In some embodiments, yet another capacitor  640  may be connected in series between the low-side lead of the alternating current power source  610  and the low-side lead of the fifth voltage-controlled switch  635 , though this is not required. 
     The set of voltage-controlled switches of the rectifier circuit  620  may be operated in multiple modes. Processing circuitry (e.g., processing circuitry  222  such as depicted in  FIG. 2 ) may be coupled to one or more voltage-controlled switches to controllably switch the rectifier circuit  620  between modes. For example, the fourth voltage-controlled switch  634  and/or sixth voltage-controlled switch  636  may be toggled on or off to switch the mode of the rectifier circuit  620 . The processing circuitry may monitor a condition of the power converter and operate the voltage-controlled switches  634 ,  636  according to the condition. 
     For example, in a first mode the alternating current power source  610  may pass current through a full-wave bridge rectifier circuit formed with the first voltage-controlled switch  631 , the second voltage-controlled switch  632 , the fifth voltage-controlled switch  635 , and the sixth voltage-controlled switch  636 . The capacitor  646  may be parallel to the capacitor  638 , resulting in a first full-wave bridge rectifier circuit. 
     In a second mode the fourth voltage-controlled switch  634  may be pulled to ground. The alternating current power source  610  may again pass current through a full-wave bridge rectifier circuit formed with the first voltage-controlled switch  631 , the second voltage-controlled switch  632 , the fifth voltage-controlled switch  635 , and the sixth voltage-controlled switch  636 . The capacitor  646 , however, may be parallel to the alternating current power source  610 , resulting in a second full-wave bridge rectifier circuit having a different power output (e.g., an increased or decreased power output). Accordingly, the processing circuitry may control the interval and frequency of pulling the fourth voltage-controlled switch  634  to ground in order to control the power output to the load  644 . 
     In a third mode the sixth voltage-controlled switch  636  may be pulled to ground. The alternating current power source  610  may pass current through a voltage doubler rectifier circuit formed with the first voltage-controlled switch  631  and the second voltage-controlled switch  632 . Accordingly, the processing circuitry may control the interval and frequency of pulling the sixth voltage-controlled switch  636  to ground in order to control the voltage output to the load  644 . 
     In a fourth mode the fourth voltage-controlled switch  634  and the sixth voltage-controlled switch  636  may be pulled to ground. The alternating current power source  610  may pass current through an impedance matching voltage doubler rectifier circuit formed with the capacitors  638 ,  646 , the first voltage-controlled switch  631 , and the second voltage-controlled switch  632 . Accordingly, the processing circuitry may control the interval and frequency of pulling the fourth voltage-controlled switch  634  and/or the sixth voltage-controlled switch  636  to ground in order to control the voltage and/or power output to the load  644 . 
     The processing circuitry may control the interval and frequency of toggling one or more of the voltage-controlled switches  631 - 636  in order to control voltage and/or power output to the load  644 . The interval and frequency may be controlled according to a monitored condition of the power converter, such as a voltage across the alternating current power source  610 , a voltage at the load  644 , a current at the load  644 , a combination of these conditions, and so on. 
     Similar to the example rectifier circuit of  FIG. 3 , each voltage-controlled switch  631 - 636  may be a suitable switch, such as a MOSFET. In some embodiments, the voltage-controlled switches  631 - 636  can each be associated with a diode. The diodes may be discrete and separate elements from the voltage-controlled switches, while in other embodiments the diodes are implemented as body diodes within the voltage-controlled switches  631 - 636 . 
       FIG. 7  depicts a simplified schematic diagram of an example rectifier of a power converter such as described herein. The rectifier circuit  720  is in the form of a boost rectifier circuit. The boost rectifier circuit  720  receives input power from an alternating current power source  710  and rectifies the received current into a direct current output voltage having a substantially constant voltage (e.g., a rippled direct current voltage). The alternating current power source  710  may be an inductive receive coil such as depicted above with respect to  FIGS. 1A-2 , while in other embodiments the boost rectifier circuit  720  may receive input power through another source. 
     The boost rectifier circuit  720  includes an output capacitor  742  coupled in parallel with two voltage-controlled switches  731 ,  732 . A high-side lead of a first voltage-controlled switch  731  is coupled to a high-side lead of the output capacitor  742 . A low-side lead of the first voltage-controlled switch  731  is coupled to a high-side lead of a second voltage-controlled switch  732 . A low-side lead of the second voltage-controlled switch  732  is coupled to a low-side lead of the output capacitor  742 . The boost rectifier circuit  720  may provide a rectified output to a load  744  across the leads of the output capacitor. 
     An alternating current input voltage may be supplied to the boost rectifier circuit  720  by an alternating current power source  710 . The alternating current power source  710  may be an inductive receive coil such as depicted above with respect to  FIGS. 1A-2 , while in other embodiments the boost rectifier circuit  720  may receive input power through another source. A high-side lead of the alternating current power source  710  is coupled in series with a resistor  739  and a capacitor  738 , which is in turn coupled to the low-side lead of the first voltage-controlled switch  731  and the high-side lead of the second voltage-controlled switch  732 . 
     A load  744  is coupled to the output capacitor  742 . The load  744  may be any arbitrary load configured to receive the rectified output voltage of the rectifier circuit  720  (e.g., the conditioning circuitry  224  and/or the load  226  as depicted in  FIG. 2 ). In many cases, the load  744  has an impedance which varies over time (e.g., due to changing power consumption). The input voltage from the alternating current power source  710  may also vary (e.g., according to the coupling of the inductive receive coil with a transmit coil). Generally, the electronic device requires the voltage output to the load have a substantially constant voltage level (e.g., a rippled direct current voltage having a substantially constant voltage level). 
     Accordingly, the boost rectifier circuit  720  may controllably boost the output voltage up to double the peak input voltage. The level of the output voltage may be controlled by altering the operation timing (e.g., conduction state timing) of the voltage-controlled switches  731 ,  732 . The voltage-controlled switches  731 ,  732  define two current paths. A first current path is defined when the first voltage-controlled switch  731  is opened and the second voltage-controlled switch  732  is closed. The first current path passes current through the resistor  739  and through the capacitor  738  to a ground reference (e.g., a local ground of the boost rectifier circuit  720  or a common ground of the electronic device). 
     At a full voltage doubling operation, the first current path may be operated during a negative voltage half-cycle of the alternating current input. Accordingly, during the negative half-cycle the capacitor  738  may be charged. After one or more voltage cycles of the alternating current input, the capacitor  738  may be charged up to the peak voltage of the alternating current input voltage. 
     A second current path through the boost rectifier circuit  720  is defined when the first voltage-controlled switch  731  is closed and the second voltage-controlled switch  732  is opened. The second current path passes current through the resistor  739  and through the capacitor  738  and outputs to the load  744 . 
     Continuing the example of full voltage doubling operation, the second current path may be operated during a positive voltage half-cycle of the alternating current input. The boost rectifier circuit  720  may synchronously or near-synchronously cause the second voltage-controlled switch  732  to open and the first voltage-controlled switch  731  to close when the voltage level of the alternating current power source  710  crosses zero volts between the negative half-cycle and the positive half-cycle (and vice versa when switching from the positive half-cycle to the negative half-cycle). During the positive half-cycle the alternating current power source  710  and the capacitor  738  may be placed in parallel to the output capacitor  742 . As a result, the output capacitor  742  may be charged, and after one or more voltage cycles of the alternating current input the output capacitor  742  may be charged up to double the peak voltage of the alternating current input voltage. 
     In order to control the boost level of the boost rectifier circuit  720 , the timing of operating the first current path and the second current path may be adjusted. For example, the first current path may be operated through the negative half-cycle and a portion of the positive half-cycle. This may charge the capacitor  738  to a voltage below the peak voltage level of the alternating current input after one or more voltage cycles. The second current path may be operated through the remaining portion of the positive half-cycle, and may consequently charge the output capacitor to a voltage level that is less than double the peak voltage of the alternating current input. 
     The timing of operating the first current path and the second current path of the boost rectifier circuit  720  may be controlled by processing circuitry (e.g., processing circuitry  222  such as depicted in  FIG. 2 ). The processing circuitry may monitor a power condition associated with the power converter incorporating the boost rectifier circuit  720  (e.g., an input voltage level, an output voltage level, an impedance at the output, etc.) and adjust the operation timing accordingly. For example, if the processing circuitry detects a drop in voltage across the load  744  (e.g., due to an increased impedance of the load  744 ), the timing may be adjusted to increase the output voltage across the output capacitor  742 . 
     Similar to the example rectifier circuit of  FIG. 3 , each voltage-controlled switch  731 ,  732  may be a suitable switch, such as a MOSFET. In some embodiments, the voltage-controlled switches  731 ,  732  can each be associated with a diode. The diodes may be discrete and separate elements from the voltage-controlled switches, while in other embodiments the diodes are implemented as body diodes within the voltage-controlled switches  731 ,  732 . 
       FIG. 8  depicts a simplified schematic diagram of an example rectifier of a power converter such as described herein. The rectifier circuit  820  may be a multi-mode rectifier, such as depicted above with respect to  FIG. 3 , and in one of the modes the rectifier circuit  820  may operate as a boost rectifier, such as depicted above with respect to  FIG. 7 . Accordingly, the rectifier circuit  820  receives input power from two alternating current power sources  810   a ,  810   b  and rectifies the received current into a direct current output voltage having a substantially constant voltage (e.g., a rippled direct current voltage). The alternating current power sources  810   a ,  810   b  may be inductive receive coils such as depicted above with respect to  FIGS. 1A-2 , while in other embodiments the power sources  810   a ,  810   b  may receive power through another source. In some embodiments each alternating current power source  810   a ,  810   b  is a separate receive coil, while in other embodiments the power sources  810   a ,  810   b  may represent portions of a center-tapped receive coil. 
     The rectifier circuit  820  includes a set of voltage-controlled switches  831 - 836 . The set may include six voltage-controlled switches  831 - 836 , and a conduction state of each voltage-controlled switch  831 - 836  may be toggled between an on-state and an off-state in order to rectify the input voltage. The voltage-controlled switches  831 - 836  are connected in parallel with the load  844  in pairs. A first voltage-controlled switch  831  and second voltage-controlled switch  832  are connected in series, with the pair being connected in parallel to the load  844 . A third voltage-controlled switch  833  and fourth voltage-controlled switch  834  are connected in series, with the pair being connected in parallel to the load  844 . A fifth voltage-controlled switch  835  and sixth voltage-controlled switch  836  are connected in series, with the pair being connected in parallel to the load  844 . 
     The load  844  may be any arbitrary load configured to receive the rectified output voltage of the rectifier circuit  820  (e.g., the conditioning circuitry  224  and/or the load  226  as depicted in  FIG. 2 ). In many cases, the output of the rectifier circuit  820  may be a rippled direct current voltage. An output capacitor  842  can be added in parallel to the load  844  to further smooth the rippled direct current waveform. The output capacitor  842  functions as a low-pass filter. 
     The alternating current power sources  810   a ,  810   b  are coupled to the set of voltage-controlled switches of the rectifier circuit  820 . A high-side lead of a first alternating current power source  810   a  is coupled to a low-side lead of the third voltage-controlled switch  833  and a high-side lead of the fourth voltage-controlled switch  834 . A low-side lead of the first alternating current power source  810   a  is coupled to a low-side lead of the fifth voltage-controlled switch  835  and a high-side lead of the sixth voltage-controlled switch  836 . A resistor  839  and a capacitor  838  are connected in series between the high-side lead of the first alternating current power source  810   a  and the low-side lead of the third voltage-controlled switch  833 . 
     A high-side lead of a second alternating current power source  810   b  is coupled to a low-side lead of the fifth voltage-controlled switch  835  and a high-side lead of the sixth voltage-controlled switch  836 . A low-side lead of the second alternating current power source  810   b  is coupled to a low-side lead of the first voltage-controlled switch  831  and a high-side lead of the second voltage-controlled switch  832 . A resistor  841  and a capacitor  840  are connected in series between the low-side lead of the second alternating current power source  810   b  and the low-side lead of the first voltage-controlled switch  831 . 
     The set of voltage-controlled switches of the rectifier circuit  820  may be operated in a full-wave rectifier mode and a boost rectifier mode. The sixth voltage-controlled switch  836  may controllably switch the rectifier circuit  820  between modes. For example, the sixth voltage-controlled switch  836  may be operably coupled to processing circuitry (e.g., processing circuitry  222  such as depicted in  FIG. 2 ). The processing circuitry may monitor a condition of the power converter and operate the sixth voltage-controlled switch  836  according to the condition. 
     For example, the processing circuitry may monitor a voltage across the load  844 . The processing circuitry may typically operate the sixth voltage-controlled switch  836  in a full-wave rectifying mode. In the full-wave rectifying mode, the first alternating current power source  810   a  may pass current through a full-wave bridge rectifier circuit formed with the third voltage-controlled switch  833 , the fourth voltage-controlled switch  834 , the fifth voltage-controlled switch  835 , and the sixth voltage-controlled switch  836 . 
     In the full-wave rectifying mode, the second alternating current power source  810   b  may simultaneously pass current through a full-wave bridge rectifier circuit formed with the first voltage-controlled switch  831 , the second voltage-controlled switch  832 , the fifth voltage-controlled switch  835 , and the sixth voltage-controlled switch  836 . 
     If the voltage across the load  844  falls below a threshold (e.g., due to an increased impedance at the load  844 ), the processing circuit may operate the sixth voltage-controlled switch  836  in a boost rectifier mode. In the boost rectifier mode, the sixth voltage-controlled switch  836  is pulled to ground and the first alternating current power source  810   a  may pass current through a boost rectifier circuit formed with the third voltage-controlled switch  833  and the fourth voltage-controlled switch  835 . 
     In the boost rectifier mode, the second alternating current power source  810   b  may simultaneously pass current through a boost rectifier circuit formed with the first voltage-controlled switch  831  and the second voltage-controlled switch  832 . The boost rectifiers may be operated in a manner as discussed above in  FIG. 7 . In some cases, the boost rectifiers are operated with the same boost level, while in other embodiments each boost rectifier is operated independently. 
     Similar to the example rectifier circuit of  FIG. 3 , each voltage-controlled switch  831 ,  832  may be a suitable switch, such as a MOSFET. In some embodiments, the voltage-controlled switches  831 ,  832  can each be associated with a diode. The diodes may be discrete and separate elements from the voltage-controlled switches, while in other embodiments the diodes are implemented as body diodes within the voltage-controlled switches  831 ,  832 . 
       FIG. 9  depicts an example process  900  for rectifying an alternating current. The process  900  may be implemented on any of the example power converters and/or devices discussed above with respect to  FIGS. 1-8 . The following process  900  may be used to convert voltage from one or more alternating current sources into a regulated direct current voltage level suitable for use by an electronic device using, for example, the rectifier circuit described with respect to  FIGS. 2-8  and/or the processing circuitry described with respect to  FIG. 2 . In some embodiments, the process  900  may be implemented as processor-executable instructions that are stored within a memory of an electronic device having a rectifier circuit. 
     In operation  902 , an incoming voltage is measured. The incoming voltage may be a single voltage from a single source, or multiple voltages may be measured from multiple sources. In many cases, the incoming voltage is from one or more alternating current sources. The incoming voltage may be measured by a sensor, circuit, or similar element associated with the alternating current source. In many embodiments, the alternating current source is an inductive receive coil or similar element configured to receive wirelessly transmitted power. For example, the incoming voltage may be measured by coupling a voltage measuring circuit to a pair of nodes of the inductive receive coil. In some embodiments, the voltage measuring circuit forms part of processing circuitry. 
     In operation  904 , a determination is made whether the measured voltage exceeds a first threshold value. In many embodiments, the measured voltage may be monitored by processing circuitry (e.g., the processing circuitry  222  such as depicted in  FIG. 2 ). In operation  904  the processing circuitry may determine whether the measured voltage exceeds a first threshold value (e.g., a fixed or variable/programmable threshold). If the voltage exceeds the first threshold value, the method may move to operation  906 . If the voltage does not exceed the first threshold value, the method may move to operation  908 . 
     In operation  906 , in response to determining that the measured voltage exceeds the first threshold value, the incoming voltage is rectified in a full-wave rectifying mode. In many embodiments, the processing circuitry may further cause a rectifying circuit (e.g., the rectifying circuit such as depicted in  FIG. 3 ,  FIG. 4 ,  FIG. 5 ,  FIG. 6 , or  FIG. 8 ) to operate in a full-wave rectifying mode. For example, the processing circuitry may cause the incoming alternating current to pass through a full-wave bridge rectifying circuit. 
     In operation  908 , in response to determining that the measured voltage does not exceed the first threshold value, a determination is made whether the measured voltage falls below a second threshold value. In some embodiments, the first threshold value and the second threshold value may be the same value. In these embodiments, there may be no additional determination at operation  908 , and the method may directly move to operation  910 . In other embodiments, the processing circuitry may make a further determination whether the measured voltage falls below a second threshold value (e.g., a fixed or variable/programmable threshold). If the voltage falls below the first threshold value, the method may move to operation  910 . If the voltage does not fall below the first threshold value, the method may move to operation  912 . 
     In operation  910 , in response to determining that the measured voltage falls below the first threshold value, the incoming voltage is rectified in a voltage doubler rectifying mode. In many embodiments, the processing circuitry may further cause a rectifying circuit (e.g., the rectifying circuit such as depicted in  FIG. 3 ,  FIG. 4 ,  FIG. 5 , or  FIG. 6 ) to operate in a voltage doubler rectifying mode. For example, the processing circuitry may cause the incoming alternating current to pass through a voltage doubler rectifying circuit. 
     In operation  912 , in response to determining that the measured voltage does not fall below the threshold value, the incoming voltage may be rectified in another mode. In some cases, the rectifier circuit may at the time of the determination be operating in a full-wave rectifying mode. In these cases the full-wave rectifying mode may be maintained, or the rectifier circuit may be temporarily operated in another mode, such as a voltage doubler rectifying mode, then operated in the full-wave rectifying mode. In this manner, the rectifier circuit may be controlled to maintain a constant output voltage. 
     In other cases, the rectifier circuit may at the time of the determination be operating in a voltage doubler rectifying mode. In these cases the voltage doubler rectifying mode may be maintained, or the rectifier circuit may be temporarily operated in another mode, such as a full-wave rectifying mode, then operated in the voltage doubler rectifying mode. In this manner, the rectifier circuit may be controlled to maintain a constant output voltage. 
     Many embodiments of the foregoing disclosure may include or may be described in relation to various methods of operation, use, manufacture, and so on. Notably, the operations of methods presented herein are meant only to be exemplary and, accordingly, are not necessarily exhaustive. For example an alternate operation order or fewer or additional steps may be required or desired for particular embodiments. 
       FIG. 10  depicts another example process  1000  for rectifying an alternating current. The process  1000  may be implemented on any of the example power converters and/or devices discussed above with respect to  FIGS. 1-8 . The following process  1000  may be used to convert voltage from one or more alternating current sources into a regulated direct current voltage level suitable for use by an electronic device using, for example, the rectifier circuit described with respect to  FIGS. 2-8  and/or the processing circuitry described with respect to  FIG. 2 . In some embodiments, the process  1000  may be implemented as processor-executable instructions that are stored within a memory of an electronic device having a rectifier circuit. 
     In operation  1002 , a voltage associated with a power converter is measured. The measured voltage may be an input voltage to the power converter, or an output voltage from the power converter. An input voltage may be a single voltage from a single source, or multiple voltages may be measured from multiple sources. In many cases, the input voltage is from one or more alternating current sources. The output voltage may be connected to a load with a variable impedance. In either case, the voltage may be measured by a sensor, circuit, or similar element associated with the power converter. For example, the voltage may be measured by coupling a voltage measuring circuit to a pair of input or output nodes of the power converter. In some embodiments, the voltage measuring circuit forms part of processing circuitry. 
     In operation  1004 , a determination is made whether the measured voltage is at a desired level. In many embodiments, the measured voltage may be monitored by processing circuitry (e.g., the processing circuitry  222  such as depicted in  FIG. 2 ). In operation  1004  the processing circuitry may determine whether the measured voltage is at a desired level (e.g., whether it falls within a particular range). If the voltage is above or below the desired level, the method may move to operation  1006 . 
     In operation  1006 , in response to determining whether the measured voltage is above or below the desired voltage level, switch timing for rectifying the input voltage is determined. The input voltage may be boost rectified by adjusting the timing of one or more rectifying switches. The rectifying switches may be implemented in a rectifying circuit (e.g., the rectifying circuit such as depicted in  FIG. 7  or  FIG. 8 ). For example, if the measured voltage is below the desired voltage level, one of the switches may be held closed for a longer portion of each input current cycle, while another is held closed for a shorter portion of each input current cycle. This may cause an increase in a rectified output voltage level. The switch timing may be determined as a function of the desired rectified output voltage level relative to the measured voltage level. 
     In operation  1008 , in response to determining the switch timing, the one or more rectifying switches are operated according to the determined switch timing. Accordingly, the output voltage level may be boosted or have its boost level reduced. 
     Many embodiments of the foregoing disclosure may include or may be described in relation to various methods of operation, use, manufacture, and so on. Notably, the operations of methods presented herein are meant only to be exemplary and, accordingly, are not necessarily exhaustive. For example an alternate operation order or fewer or additional steps 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: 20170323
Publication Date: 20200505
Grant Date: 20200505
Priority Date: 20160922
Inventors: QIU, WEIHONG
DAYAL, ROHAN
MOUSSAOUI, ZAKI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/045", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M7/219", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M7/219", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M7/25", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M7/219", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M1/32", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 70461586