Patent Publication Number: US-11664716-B2

Title: Adaptive switch driving

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 63/027,291, filed 19 May 2020, the disclosure of which is hereby incorporated by reference in its entirety herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to switch-mode power supplies and, more specifically, to driving a switch of a switch-mode power supply. 
     BACKGROUND 
     A switch-mode power supply (SMPS) uses switches to transfer power between a power source and a load. Large input currents or large DC supply voltages can stress the switch-mode power supply during operation. In some cases, this stress can lead to switch degradation and premature failure of the power supply. 
     SUMMARY 
     An apparatus is disclosed that implements adaptive switch driving. In particular, the apparatus includes a switching circuit with at least one switch that interrupts the flow of an input current. The switching circuit also includes a driver circuit and a driver controller. The driver circuit provides a driver current to charge or discharge an intrinsic capacitor of the switch and control a transition period of the switch. The driver controller indirectly or directly monitors one or more parameters that affect a voltage at a terminal of the switch. These parameters can include an input current and/or a direct-current (DC) supply voltage. The driver controller adjusts the magnitude of the driver current responsive to detecting a change in one or more of these parameters. 
     For example, if one or more of these parameters decreases, a likelihood of the peak voltage exceeding a breakdown voltage of the switch decreases. Therefore, the driver controller can increase the driver current to decrease the transition period of the switch and improve efficiency. Alternatively, if one or more of these parameters increases, there is a higher likelihood that the peak voltage can exceed the breakdown voltage of the switch. In response, the driver circuit can increase the transition period of the switch to reduce the peak voltage and improve reliability. In these ways, the driver circuit can readily adapt to balance reliability and efficiency in various situations. 
     In an example aspect, an apparatus is disclosed. The apparatus includes a switching circuit including an input and an output. The input is configured to accept an input voltage and an input current. The input voltage includes a direct-current supply voltage. The output is configured to provide an output voltage. The switching circuit is configured to selectively be in a first state that provides the input voltage as the output voltage, be in a second state that provides a ground voltage as the output voltage, or be in a third state that causes the output voltage to change from the input voltage to the ground voltage according to a slew rate. The third state enables the switching circuit to transition from the first state to the second state. The switching circuit is also configured to adjust the slew rate of the output voltage for the third state responsive to at least one of the following: a change in a magnitude of the direct-current supply voltage or a change in a magnitude of the input current. 
     In an example aspect, an apparatus is disclosed. The apparatus includes switch-mode means for transferring power between a power source and a load. The switch-mode means includes switching means for selectively operating in a closed state to connect the power source to the load or an open state to disconnect the power source from the load. The switch-mode means also includes driver means for controlling a transition period associated with the switching means transitioning from the closed state to the open state. The switch-mode means additionally includes monitor means for detecting a change in a magnitude of an input current or a change in a magnitude of a direct-current supply voltage provided by the power source. The switch-mode means further includes control means for adjusting the transition period responsive to the monitor means detecting the change in the magnitude of the input current or the change in the magnitude of the direct-current supply voltage. 
     In an example aspect, a method for adaptive switch driving is disclosed. The method includes accepting an input voltage and an input current at an input of a switching circuit. The input voltage includes a direct-current supply voltage. The method also includes operating the switching circuit in a first state to provide the input voltage as an output voltage at an output of the switching circuit. The method additionally includes operating the switching circuit in a second state to provide a ground voltage as the output voltage at the output. The method further includes operating the switching circuit in a third state to transition from the first state to the second state. The third state causes the output voltage to change from the input voltage to the ground voltage according to a slew rate. The method also includes adjusting the slew rate of the output voltage responsive to at least one of the following: a change in a magnitude of the direct-current supply voltage or a change in a magnitude of the input current. 
     In an example aspect, an apparatus is disclosed. The apparatus includes a switching circuit with an input, at least one switch, at least one driver circuit, and at least one driver controller. The input is configured to accept an input voltage. The at least one switch is coupled between the input and an output of the switching circuit. The at least one switch is configured to selectively be in a closed state to connect the input to the output or be in an open state to disconnect the input from the output. The at least one driver circuit is coupled to the at least one switch. The at least one driver circuit is configured to provide a driver current to enable the at least one switch to transition from the closed state to the open state. The at least one driver controller is coupled to the at least one driver circuit and configured to monitor at least one parameter associated with the input voltage. The at least one driver controller is also configured to detect a change in the at least one parameter and adjust a magnitude of the driver current provided by the at least one driver circuit based on the detected change in the at least one parameter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    illustrates an example operating environment for adaptive switch driving. 
         FIG.  2    illustrates an example switch-mode power supply, an example power source, and an example load for adaptive switch driving. 
         FIG.  3 - 1    illustrates an example switching circuit for adaptive switch driving. 
         FIG.  3 - 2    illustrates example states of a switching circuit for adaptive switch driving. 
         FIG.  3 - 3    illustrates changes in an output voltage of a switching circuit for different modes associated with adaptive switch driving. 
         FIG.  3 - 4    illustrates another example state of a switching circuit for adaptive switch driving. 
         FIG.  4    illustrates an example driver controller for adaptive switch driving. 
         FIG.  5 - 1    illustrates a first example implementation of a driver controller for adaptive switch driving. 
         FIG.  5 - 2    illustrates a second example implementation of a driver controller for adaptive switch driving. 
         FIG.  5 - 3    illustrates a third example implementation of a driver controller for adaptive switch driving. 
         FIG.  5 - 4    illustrates a fourth example implementation of a driver controller for adaptive switch driving. 
         FIG.  6    illustrates a flow diagram illustrating an example process for adaptive switch driving. 
     
    
    
     DETAILED DESCRIPTION 
     A switch-mode power supply uses switches to transfer power between a power source and a load. At least one of the switches within the switch-mode power supply can control the flow of current from the power source to the load. Parasitic and non-parasitic inductors within the switch-mode power supply and package, however, resist the change in current flow. Consequently, these inductors can cause voltage ringing at one or more terminals of the switch in response to the switch opening to interrupt the flow of current. In some situations, a peak voltage caused by the voltage ringing can exceed a breakdown voltage of the switch. Left unchecked, the reliability of the switch can degrade over time due to this peak voltage. 
     This problem can be exacerbated in some operating conditions or implementations. For example, larger currents or larger direct-current supply voltages supplied by the power source can increase the peak voltage observed by the switch. As another example, some types of interconnections and packaging can increase the amount of parasitic inductance seen by the switch, which can increase the peak voltage caused by the voltage ringing. 
     To reduce the peak voltage, some techniques add a capacitor or a clamp circuit at the input node of the switch-mode power supply to dampen the voltage ringing. Other techniques can apply routing or printed-circuit-board (PCB) layout constraints to reduce the parasitic inductance seen by the switch and therefore decrease the peak voltage. Still other techniques can sacrifice efficiency for reliability by permanently operating the switch with a longer switching period to decrease the peak voltage. 
     In contrast, techniques for adaptive switch driving are described herein. An apparatus includes a switching circuit with at least one switch that interrupts the flow of an input current. The switching circuit also includes a driver circuit and a driver controller. The driver circuit provides a driver current to charge or discharge an intrinsic capacitor of the switch and control a transition period of the switch. The driver controller indirectly or directly monitors one or more parameters that affect a voltage at a terminal of the switch. These parameters can include an input current and/or a direct-current (DC) supply voltage. The driver controller adjusts the magnitude of the driver current responsive to detecting a change in one or more of these parameters. 
     For example, if one or more of these parameters decreases, a likelihood of the peak voltage exceeding a breakdown voltage of the switch decreases. Therefore, the driver controller can increase the driver current to decrease the transition period of the switch and improve efficiency. Alternatively, if one or more of these parameters increases, there is a higher likelihood that the peak voltage can exceed the breakdown voltage of the switch. In response, the driver circuit can increase the transition period of the switch to reduce the peak voltage and improve reliability. In these ways, the driver circuit can readily adapt to balance reliability and efficiency in various situations. 
       FIG.  1    illustrates an example environment  100  for adaptive switch driving. In the environment  100 , a computing device  102  communicates with a base station  104  through a wireless communication link  106  (wireless link  106 ). In this example, the computing device  102  is depicted as a smartphone. However, the computing device  102  can be implemented as any suitable computing or electronic device, such as a modem, a cellular base station, a broadband router, an access point, a cellular phone, a gaming device, a navigation device, a media device, a laptop computer, a desktop computer, a tablet computer, a wearable computer, a server, a network-attached storage (NAS) device, a smart appliance or other internet of things (IoT) device, a medical device, a vehicle-based communication system, a radar, a radio apparatus, and so forth. 
     The base station  104  communicates with the computing device  102  via the wireless link  106 , which can be implemented as any suitable type of wireless link. Although depicted as a tower of a cellular network, the base station  104  can represent or be implemented as another device, such as a satellite, a server device, a terrestrial television broadcast tower, an access point, a peer-to-peer device, a mesh network node, a fiber optic line, and so forth. Therefore, the computing device  102  may communicate with the base station  104  or another device via a wired connection, a wireless connection, or a combination thereof. 
     The wireless link  106  can include a downlink of data or control information communicated from the base station  104  to the computing device  102 , an uplink of other data or control information communicated from the computing device  102  to the base station  104 , or both a downlink and an uplink. The wireless link  106  can be implemented using any suitable communication protocol or standard, such as 2nd-generation (2G), 3rd-generation (3G), 4th-generation (4G), or 5th-generation (5G) cellular; IEEE 802.11 (e.g., Wi-Fi™); IEEE 802.15 (e.g., Bluetooth™); IEEE 802.16 (e.g., WiMAX™); and so forth. In some implementations, the wireless link  106  may wirelessly provide power and the base station  104  may comprise a power source. 
     As shown, the computing device  102  includes an application processor  108  and a computer-readable storage medium  110  (CRM  110 ). The application processor  108  can include any type of processor, such as a multi-core processor, that executes processor-executable code stored by the CRM  110 . The CRM  110  can include any suitable type of data storage media, such as volatile memory (e.g., random access memory (RAM)), non-volatile memory (e.g., Flash memory), optical media, magnetic media (e.g., disk), and so forth. In the context of this disclosure, the CRM  110  is implemented to store instructions  112 , data  114 , and other information of the computing device  102 , and thus does not include transitory propagating signals or carrier waves. 
     The computing device  102  can also include input/output ports  116  (I/O ports  116 ) and a display  118 . The I/O ports  116  enable data exchanges or interaction with other devices, networks, or users. The I/O ports  116  can include serial ports (e.g., universal serial bus (USB) ports), parallel ports, audio ports, infrared (IR) ports, user interface ports such as a touchscreen, and so forth. The display  118  presents graphics of the computing device  102 , such as a user interface associated with an operating system, program, or application. Alternatively or additionally, the display  118  can be implemented as a display port or virtual interface, through which graphical content of the computing device  102  is presented. 
     A wireless transceiver  120  of the computing device  102  provides connectivity to respective networks and other electronic devices connected therewith. Alternatively or additionally, the computing device  102  can include a wired transceiver, such as an Ethernet or fiber optic interface for communicating over a local network, intranet, or the Internet. The wireless transceiver  120  can facilitate communication over any suitable type of wireless network, such as a wireless local area network (WLAN), peer-to-peer (P2P) network, mesh network, cellular network, wireless wide-area-network (WWAN), and/or wireless personal-area-network (WPAN). In the context of the example environment  100 , the wireless transceiver  120  enables the computing device  102  to communicate with the base station  104  and networks connected therewith. However, the wireless transceiver  120  can also enable the computing device  102  to communicate “directly” with other devices or networks. 
     The wireless transceiver  120  includes circuitry and logic for transmitting and receiving communication signals via an antenna  122 . Components of the wireless transceiver  120  can include amplifiers, switches, mixers, analog-to-digital converters, filters, and so forth for conditioning the communication signals (e.g., for generating or processing signals). The wireless transceiver  120  can also include logic to perform in-phase/quadrature (I/Q) operations, such as synthesis, encoding, modulation, decoding, demodulation, and so forth. In some cases, components of the wireless transceiver  120  are implemented as separate transmitter and receiver entities. Additionally or alternatively, the wireless transceiver  120  can be realized using multiple or different sections to implement respective transmitting and receiving operations (e.g., separate transmit and receive chains). In general, the wireless transceiver  120  processes data and/or signals associated with communicating data of the computing device  102  over the antenna  122 . 
     The computing device  102  also includes at least one power source  124 , at least one load  126 , and at least one power transfer circuit  128 . The power source  124  can represent a variety of different types of power sources, including a wired power source, a solar charger, a portable charging station, a wireless charger, a battery, and so forth. In general, the power source  124  can be an internal power source that is internal to the computing device  102  or an external power source that is external from the computing device  102 . Depending on the type of computing device  102 , the battery may comprise a lithium-ion battery, a lithium polymer battery, a nickel-metal hydride battery, a nickel-cadmium battery, a lead acid battery, and so forth. In some cases, the battery can include multiple batteries, such as a main battery and a supplemental battery, and/or multiple battery cell combinations. 
     The power transfer circuit  128  transfers power from the power source  124  to one or more loads  126  of the computing device  102 . Generally, the power level provided via the power transfer circuit  128  and the power source  124  is at a level sufficient to power the one or more loads  126 . For example, the power level may be on the order of milliwatts (mW) for powering loads associated with a smartphone, or on the order of watts to kilowatts (kW) for powering loads associated with an electric vehicle. Example types of loads include a variable load, a load associated with a component of the computing device  102  (e.g., the application processor  108 , an amplifier within the wireless transceiver  120 , the display  118 , a battery, or a power converter), a load that is external from the computing device  102  (e.g., another battery), and so forth. The power transfer circuit  128  can be a stand-alone component or integrated within another component, such as a power management integrated circuit (PMIC) (not shown). 
     The power transfer circuit  128  includes at least one switch-mode power supply  130 , which can be implemented as a buck power converter, a buck-boost power converter, and so forth. The switch-mode power supply  130  includes at least one switching circuit  132  to enable DC-to-DC power conversion. The switching circuit  132  includes at least one switch  134 , at least one driver circuit  136 , and at least one driver controller  138 . In addition to the switching circuit  132 , the switch-mode power supply  130  can include other energy storage components, including at least one inductor or at least one capacitor. 
     The switch  134  can interrupt an input current that is provided from the power source  124  to the switch-mode power supply  130  by transitioning from a closed state to an open state. The switch  134  can be implemented using a transistor, such as a metal-oxide-semiconductor field-effect transistor (MOSFET) (e.g., n-type MOSFET or p-type MOSFET), a junction field-effect transistor (JFET), a bipolar junction transistor (BJT), an insulated gate bipolar transistor (IGBT), and so forth. The switch  134  includes an intrinsic capacitor, which prevents the switch  134  from instantaneously switching between the closed state and the open state. In particular, the intrinsic capacitor, such as a gate capacitor associated with a MOSFET, resists a change in voltage at a gate terminal of the switch  134 . 
     The driver circuit  136  is coupled to the switch  134  and enables the switch  134  to transition between the closed state and the open state. In particular, the driver circuit  136  provides a driver current to assist with charging or discharging the intrinsic capacitor of the switch  134 . The rate at which the switch  134  transitions between states is dependent upon the rate at which the intrinsic capacitor is charged or discharged by the driver current. As such, increasing the driver current increases the transition rate (e.g., decreases the transition period of the switch  134 ), and decreasing the driver current decreases the transition rate (e.g., increases the transition period of the switch  134 ). 
     The driver controller  138  is coupled to the driver circuit  136  and can at least partially implement adaptive switch driving. The driver controller  138  indirectly or directly monitors one or more parameters that can affect a voltage at a terminal of the switch  134  and adjusts the magnitude of the driver current based on these parameters. In particular, the driver controller  138  adapts the driver current and therefore the switch  134 &#39;s transition rate to balance reliability with efficiency. For example, the driver controller can increase the transition rate to improve efficiency of the switch  134  or decrease the transition rate to reduce a peak voltage at the terminal of the switch and protect the switch  134  from voltage ringing. Through adaptive switch driving, the switching circuit  132  is able to appropriately configure itself to enhance a balancing of reliability versus efficiency in different operating conditions. 
     In some implementations, the switching circuit  132  is implemented within an integrated circuit. In the depicted configuration, the switching circuit  132  is integrated within the switch-mode power supply  130 . In other implementations, the switching circuit  132  (or a portion of the switching circuitry  132  such as the driver controller  138 ) can be external to the switch-mode power supply  130 . For example, the driver controller  138  can be implemented by the PMIC, the application processor  108 , a main processor, a secondary processor, or a low-power digital signal processor (DSP) of the computing device  102 . 
     Although not shown, the power transfer circuit  128  can include other types of control circuitry (not shown) that controls operation of the switch-mode power supply  130 . For example, this control circuitry can monitor operation of the switch-mode power supply  130  and control the pulse-width modulation of the switching circuit  132 . An example switch-mode power supply  130  is further described with respect to  FIG.  2   . 
       FIG.  2    illustrates an example switch-mode power supply  130 , an example power source  124 , and an example load  126  for adaptive switch driving. The switch-mode power supply  130  is coupled between the power source  124  and the load  126 . In the depicted configuration, the switch-mode power supply  130  is implemented as a buck converter, and includes the switching circuit  132 , at least one inductor  202 , and at least one capacitor  204 . 
     The switching circuit  132  includes an input (e.g., an input node  206 ), an output (e.g., an output node  208 ), and a ground node  210 . The input node  206  is coupled to the power source  124  and accepts both an input voltage (V in )  212  and an input current (I in )  214  from the power source  124 . The output node  208  is coupled to the inductor  202  and provides an output voltage (V out )  216  and an output current (I out )  218 . The ground node  210  is coupled to a ground  220  and accepts a ground voltage  222  (e.g., a reference voltage associated with the ground  220 ). The inductor  202  is coupled between the output node  208  and the load  126 . The capacitor  204  is coupled between the load and the ground  220  (e.g., the ground node  210 ). 
     The switch-mode power supply  130  is implemented on a package or printed circuit board (PCB). Parasitic inductances resulting from interconnections (e.g., routing) and layout of the package or printed circuit board are seen by the switching circuit  132 . These parasitic inductances are represented by a first parasitic inductor  224 - 1 , which exists between a power node  226  associated with the power source  124  and the input node  206 , and a second parasitic inductor  224 - 2 , which exists between the ground node  210  and the ground  220 . As an example, inductances of the parasitic inductances  224 - 1  and  224 - 2  can each be on the order of 1 or 2 nanohenries (nH). 
     The parasitic inductors  224 - 1  and  224 - 2  and the inductor  202  oppose changes in current. If the current changes through any of the inductors  224 - 1 ,  224 - 2 , or  202 , an opposing voltage is induced within the affected inductor, which prevents the current from changing instantaneously. The induced voltage is proportional to the rate at which the current changes and the inductance (e.g., self-inductance) of the inductor, as shown by Equation 1 below: 
                   V   =     L   ⁢     di   dt               Equation   ⁢           ⁢   1               
where V represents the inducted voltage in volts, L represents the inductance of the inductor in henries, and di/dt represents the rate of change of the current in amperes per second. A polarity of the induced voltage opposes the change in the current.
 
     During operation, the switching circuit  132  selectively passes the input current  214  from the input node  206  to the output node  208  or interrupts (e.g., prevents or stops) the flow of the input current  214  from the input node  206  to the output node  208 . For example, in a first state, the switching circuit  132  connects the input node  206  to the output node  208  and disconnects the ground node  210  from the output node  208 . As such, the switching circuit  132  provides the input voltage  212  as the output voltage  216  and provides the input current  214  as the output current  218  to charge the inductor  202 . The output current  218  enables the inductor  202  to increase the amount of energy stored by its magnetic field. 
     In a second state, the switching circuit  132  disconnects the input node  206  from the output node  208  and connects the ground node  210  to the output node  208 . This effectively disconnects the power source  124  from the load  126 . The switching circuit  132  provides the ground voltage  222  as the output voltage  216  and the inductor  202  operates as a current source to provide the output current  218  to the load  126 . The output current  218  generated by the inductor  202  discharges the inductor (e.g., decreases the amount of energy stored by the magnetic field). 
     Due to intrinsic capacitors, the switching circuit  132  is unable to instantaneously transition between the first state and the second state. As such, the switching circuit  132  can be in a third state (e.g., a transition state) while transitioning from the first state to the second state. A duration of time that the switching circuit  132  operates in the third state is referred to as a transition period. 
     In the third state, the switching circuit  132  decreases the flow of the input current  214  from the input node  206  to the output node  208  and increases the flow of a current from the ground node  210  to the output node  208 . This causes the parasitic inductor  224 - 1  to resist the change to the input current  214 , the inductor  202  to resist the change to the output current  218 , and the parasitic inductor  224 - 2  to resist the change in current from the ground  220  to the ground node  210 . This opposition causes voltage ringing to occur at the input node  206 , the output node  208 , and the ground node  210 . In some cases, the voltage ringing can have a peak voltage that reduces reliability of the switching circuit  132  and damages one or more switches  134  within the switching circuit  132 . 
     Consider the input voltage  212  at the input node  206 . While the switching circuit  132  operates in the third state, the voltage ringing caused by the parasitic inductor  224 - 1  can affect a peak of the input voltage  212 , as represented by Equation 2 below: 
                     V   in_peak     =       L   ⁢     di   dt       +     V     D   ⁢   C                 Equation   ⁢           ⁢   2               
wherein V in_peak  represents a peak of the input voltage  212 , L represents the inductance of the parasitic inductor  224 - 1 , di represents the change in the input current  214  due to the switching circuit  132  interrupting the flow of the input current  214 , dt represents the transition period of the switching circuit  132 , and V DC  represents a direct current (DC) supply voltage  228  provided by the power source  124  at the power node  226 . In some cases, the peak of the input voltage  212  can be approximately twice the DC supply voltage  228 . In general, the inductance L is a fixed value. In some situations, the input current  214  and the DC supply voltage  228  can vary depending on the type of power source  124  that is connected to the switch-mode power supply  130 . As an example, the input current  214  can vary between two and four amperes and the DC supply voltage  228  can be greater than or equal to 4.5 volts, such as 5.25 volts. In some cases, the peak of the input voltage  212  can be between approximately 8 and 10 volts while a breakdown voltage of the switch  134  within the switching circuit  132  can be between approximately 9 and 10 V.
 
     The switching circuit  132 , however, can dynamically adjust the transition period (dt) based on the input current  214  and/or the DC supply voltage  228  to control the peak of the input voltage  212  during the third state. For example, the switching circuit  132  can decrease the transition period at the expense of increasing the peak of the input voltage  212  to improve efficiency in situations in which the peak of the input voltage  212  is not likely to be significantly large to damage the switching circuit  132 . Alternatively, the switching circuit  132  can increase the transition period to decrease the peak of the input voltage  212  to improve reliability in situations in which the peak of the input voltage  212  would otherwise exceed a breakdown voltage associated with the switch  134 . In this manner, the switching circuit  132  can adapt the transition period in real-time to manage reliability and efficiency. 
     The adjustment to the transition period of the switching circuit  132  can be observed at the output node  208 . In particular, a slew rate of the output voltage  216  is dependent upon the transition period of the switching circuit  132 . In this manner, the slew rate of the output voltage  216  changes in response to a change in the transition period. For example, increasing the transition period decreases the slew rate. Alternatively, decreasing the transition period increases the slew rate. The slew rate characterizes the rate at which the output voltage  216  changes from the input voltage  212  to the ground voltage  222  as the switching circuit  132  transitions from the first state to the second state (e.g., operates in the third state) during the transition period. In other words, the slew rate represents an amount of change in the output voltage  216  per unit of time. 
     The switching circuit  132  can also be in a fourth state (e.g., another transition state) while transitioning from the second state to the first state. In the fourth state, the switching circuit  132  increases the flow of the input current  214  from the input node  206  to the output node  208  and decreases the flow of the current from the ground node  210  to the output node  208 . The switching circuit  132  is further described with respect to  FIG.  3 - 1   . 
       FIG.  3 - 1    illustrates an example switching circuit  132  for adaptive switch driving. In the depicted configuration, the switching circuit  132  includes a first switch  134 - 1  and a second switch  134 - 2 . The first switch  134 - 1  is coupled between the input and the output of the switching circuit  132  (e.g., between the input node  206  and the output node  208 ). The second switch  134 - 2  is coupled between the ground node  210  and the output node  208 . The first switch  134 - 1  and the second switch  134 - 2  enable the switch-mode power supply  130  of  FIG.  2    to implement a buck converter. 
     In an example implementation, the switch  134 - 1  is implemented using a p-type MOSFET  302  and the switch  134 - 2  is implemented using an n-type MOSFET  304 . A gate terminal of the switch  134 - 1  is coupled to the driver circuit  136 , a source terminal of the switch  134 - 1  is coupled to the input node  206 , and a drain terminal of the switch  134 - 1  is coupled to the output node  208 . A gate terminal of the switch  134 - 2  is coupled to the driver circuit  136 , a source terminal of the switch  134 - 2  is coupled to the ground node  210 , and a drain terminal of the switch  134 - 2  is coupled to the output node  208 . 
     The driver circuit  136  provides respective driver currents  308 - 1  and  308 - 2  to the switches  134 - 1  and  134 - 2 . The driver circuit  136  has a variable strength, which means it can vary magnitudes of the driver currents  308 - 1  and  308 - 2 . For example, the driver circuit  136  can include a first set of parallel branches with respective buffers or switches coupled between a current generator and the gate of the switch  134 - 1 . Likewise, the driver circuit  136  can include a second set of parallel branches with respective buffers or switches coupled between the current generator and the gate of the switch  134 - 2 . The current generator can be internal to the driver circuit  136  or external from the driver circuit  136 . By enabling different quantities of the buffers within the parallel branches, the strength of the driver circuit  136  can be adjusted. 
     As an example, consider that the driver circuit  136  can selectively have a first strength associated with a reliability mode  312 - 1  or a second strength associated with an efficiency mode  312 - 2 . In this case, the first strength is less than the second strength in order to increase the transition period and improve reliability by decreasing the peak of the input voltage  212 . In contrast, the second strength is greater than the first strength to decrease the transition period and increase efficiency at the expense of increasing the peak of the input voltage  212 . 
     Although not shown, the gates of the switches  134 - 1  and  134 - 2  can also be coupled to a voltage generator, which can be included as part of the driver circuit  136  or as part of the power transfer circuit  128 . The voltage generator provides a bias voltage at the gates of the switches  134 - 1  and  134 - 2  to enable the switches  134 - 1  and  134 - 2  to operate in the open state or the closed state. 
     The driver controller  138  generates a control signal  310 , which adjusts the strength or operational mode of the driver circuit  136 . Using the control signal  310 , the driver controller  138  controls the magnitude of the driver currents  308 - 1  and  308 - 2 . In this way, the driver controller  138  controls the transition periods of the switches  134 - 1  and  134 - 2 . As described above, the driver controller  138  adjusts the driver currents  308 - 1  and  308 - 2  based on information regarding the input current  214  and the DC supply voltage  228 . 
     The control signal  310  can be a binary signal that indicates whether or not the driver circuit  136  operates at according to the reliability mode  312 - 1  or the efficiency mode  312 - 2 . In other situations, the control signal  310  can include multiple bits to specify the quantity of buffers that are enabled within the driver circuit  136 , which affects the magnitude of the driver currents  308 - 1  and  308 - 2 . 
     In some cases, the driver controller  138  can cause the driver circuit  136  to have a same strength to open and close the switch  134 - 1  or  134 - 2 . In other implementations, the driver controller  138  can cause the driver circuit  136  to operate at different strengths to open and close the switch  134 - 1  or  134 - 2 . For example, the driver circuit  136 &#39;s strength can be decreased to enable the switch  134 - 1  to safely transition from the closed state to the open state and the driver circuit  136 &#39;s strength can be increased to enable the switch  134  to efficiently transition from the open state to the closed state. The driver controller  138  can include a variety of different types of monitoring circuits, as further described with respect to  FIG.  4   . The driver controller  138  can cause the switching circuit  132  to selectively be in one of a variety of different states, which are further described with respect to  FIG.  3 - 2   . 
       FIG.  3 - 2    illustrates example states of the switching circuit  132  for adaptive switch driving. In particular, the switching circuit  132  can selectively be in a first state  314 - 1 , a second state  314 - 2 , a third state  314 - 3 , or a fourth state  314 - 4  (shown in  FIG.  3 - 4   ). In the first state  314 - 1 , the switch  134 - 1  is in a closed state and the switch  134 - 2  is in an open state. As such, the switching circuit  132  connects the input node  206  to the output node  208  using the switch  134 - 1  and disconnects the output node  208  from the ground node  210  using the switch  134 - 2 . 
     In the second state  314 - 2 , the switch  134 - 1  is in the open state and the switch  134 - 2  is in the closed state. As such, the switching circuit  132  disconnects the input node  206  from the output node  208  using the switch  134 - 1  and connects the output node  208  to the ground node  210  using the switch  134 - 2 . 
     In the third state  314 - 3 , the switching circuit  132  is in the process of transitioning from the first state  314 - 1  to the second state  314 - 2 . In particular, the switch  134 - 1  is transitioning from the closed state to the open state, and the switch  134 - 2  is transitioning from the open state to the closed state. As such, the switching circuit  132  partially connects the input node  206  to the output node  208  using the switch  134 - 1  and partially connects the ground node  210  to the output node  208  using the switch  134 - 2 . Although not illustrated in  FIG.  3 - 2   , the switching circuit  132  can also selectively be in a fourth state, which is further described with respect to  FIG.  3 - 4   . 
     A graph  316  illustrates the impact of the different states  314 - 1  to  314 - 3  of the switching circuit  132  on the output voltage  216 . During time interval T 1 , the first state  314 - 1  causes the output voltage  216  to be approximately equal to the input voltage  212 . During time interval T 2 , the third state  314 - 3  causes the output voltage  216  to decrease from an amount that is approximately equal to the input voltage  212  to another amount that is approximately equal to the ground voltage  222 . The rate at which the output voltage  216  changes is referred to as a slew rate  318 . The slew rate  318  is equal to a ratio of a difference between the input voltage  212  and the ground voltage  222  and a duration of the time interval T 2 . The time interval T 2  represents a transition period  320  of the switching circuit  132 . During time interval T 3 , the second state  314 - 2  causes the output voltage  216  to be approximately equal to the ground voltage  222 . The slew rate  318  and the transition period  320  can vary depending on the operational mode of the driver circuit  136 , as further described with respect to  FIG.  3 - 3   . 
       FIG.  3 - 3    illustrates examples graphs  322  and  324 , which show changes in the output voltage  216  of the switching circuit  132  for different modes associated with adaptive switch driving. The graphs  322  and  324  illustrate changes in the output voltage  216  over time in accordance with the reliability mode  312 - 1  and the efficiency mode  312 - 2 , respectively. The graphs  322  and  324  are similar to the graph  316  of  FIG.  3 - 2   . In particular, the switching circuit  132  operates in a first state  314 - 1  during the time interval T 1 , operates in a third state  314 - 3  during the time interval T 2 , and operates in a second state  314 - 2  during the time interval T 3 . 
     The reliability mode  312 - 1  and the efficiency mode  312 - 2  differ in terms of transition periods  320 - 1  and  320 - 2  and slew rates  318 - 1  and  318 - 2  observed during the time interval T 2  while the switching circuit  132  is in the third state  314 - 3 . For example, the reliability mode  312 - 1  has a longer transition period  320 - 1  than the transition period  320 - 2  of the efficiency mode  312 - 2 . As a result, an absolute value of the slew rate  318 - 1  is smaller than an absolute value of the slew rate  318 - 2 . This causes the slope of the output voltage  216  to be less steep during the reliability mode  312 - 1  and steeper during the efficiency mode  312 - 2 . 
     By having a longer transition period  320 - 1  and a smaller slew rate  318 - 1 , the reliability mode  312 - 1  can improve reliability of the switching circuit  132  by reducing voltage peaks caused by the third state  314 - 3 . In contrast, the efficiency mode  312 - 2  improves an efficiency of the switching circuit  132  relative to the reliability mode  312 - 1  by having a shorter transition period  320 - 2  and a larger slew rate  318 - 2 , which enables a faster transition from the first state  314 - 1  to the second state  314 - 2  relative to the reliability mode  312 - 1 . A driver controller  138  controls whether the switching circuit  132  operates in the reliability mode  312 - 1  or the efficiency mode  312 - 2 , as further described with respect to  FIGS.  4  to  5 - 4   . 
       FIG.  3 - 4    illustrates an example fourth state  314 - 4  of the switching circuit  132  for adaptive switch driving. In the fourth state, the switching circuit  132  is in the process of transitioning from the second state  314 - 2  to the first state  314 - 1 . In particular, the switch  134 - 1  is transitioning from the open state to the closed state, and the switch  134 - 2  is transitioning from the closed state to the open state. As such, the switching circuit  132  partially connects the input node  206  to the output node  208  using the switch  134 - 1  and partially connects the ground node  210  to the output node  208  using the switch  134 - 2 . 
     A graph  326  illustrates the impact of the different states  314 - 1 ,  314 - 2 , and  314 - 4  of the switching circuit  132  on the output voltage  216 . During time interval T 3 , the second state  314 - 2  causes the output voltage  216  to be approximately equal to the ground voltage  222 . The time interval T 3  of  FIG.  3 - 4    can represent the time interval T 3  of in  FIG.  3 - 2   . 
     During time interval T 4 , the fourth state  314 - 4  causes the output voltage  216  to increase from an amount that is approximately equal to the ground voltage  222  to another amount that is approximately equal to the input voltage  212 . The rate at which the output voltage  216  changes is referred to as a slew rate  328 . The slew rate  328  is equal to a ratio of a difference between the input voltage  212  and the ground voltage  222  and a duration of the time interval T 4 . The time interval T 4  represents a transition period  330  of the switching circuit  132 . During time interval T 5 , the first state  314 - 1  causes the output voltage  216  to be approximately equal to the input voltage  212 . 
     In some implementations, a magnitude of the slew rate  328  of  FIG.  3 - 4    can be similar to a magnitude of the slew rate  318  of  FIG.  3 - 2   . In other implementations, a magnitude of the slew rate  328  of  FIG.  3 - 4    can differ from a magnitude of the slew rate  318  of  FIG.  3 - 2   . Likewise, the transition period  330  of  FIG.  3 - 4    can be similar to or different than the transition period  320  of  FIG.  3 - 2   . 
       FIG.  4    illustrates an example driver controller  138  for adaptive switch driving. In the depicted example, the driver controller  138  can include at least one voltage monitor circuit  402  and/or at least one current monitor circuit  404 . The voltage monitor circuit  402  indirectly or directly determines information regarding the DC supply voltage  228  (e.g., indirectly or directly measures the DC supply voltage  228 ). In contrast, the current monitor circuit  404  indirectly or directly determines information regarding the input current  214  (e.g., indirectly or directly measures the input current  214 ). 
     The voltage monitor circuit  402  can include at least one a supply voltage sensor  406  and/or at least one power-source-type indicator  408 . The supply voltage sensor  406  directly measures the DC supply voltage  228 . The power-source-type indicator  408  provides an indication regarding the type of power source  124  that supplies the DC supply voltage  228  to the switch-mode power supply  130 . This can include a generic classification of whether the power source  124  is external from the computing device  102  (e.g., a universal serial bus (USB) charger, an external solar panel, an external battery bank) or internal to the computing device  102  (e.g., an internal battery). 
     In some cases, the power-source-type indicator  408  can further specify the type of power source  124  that is coupled to the switch-mode power supply  130 . In general, different types of power sources  124  can provide different DC supply voltages  228  or different input current  214 . Therefore, the driver controller  138  can assume a particular amount or range of the DC supply voltage  228  or the input current  214  based on the type of power source  124  identified by the power-source-type indicator  408 . For example, the driver controller  138  can indirectly determine that the DC supply voltage  228  is greater than approximately four volts responsive to the power-source-type indicator  408  indicating that the power source  124  comprises the USB charger. In some cases, the power-source-type indicator  408  obtains information about the power source  124  from the power transfer circuit  128 . 
     The current monitor circuit  404  can include at least one direct input current sensor  410 , at least one mode indicator  412 , at least one zero-crossing comparator  414 , or some combination thereof. The direct input current sensor  410  directly measures the input current  214 . The mode indicator  412  indirectly determines information regarding the input current  214  based on an operating mode of the switch-mode power supply  130 . As an example, the operating mode can be a pulse-width modulation mode or a skip mode. In the pulse-width modulation mode, the switching circuit  132  cycles between the first state  314 - 1  and the second state  314 - 2  according to a duty cycle, which can be varied to regulate the output voltage  216 . In the skip mode, the switching circuit  132  remains in the second state  314 - 2  and does not transition to the first state  314 - 1  during one or more cycles. The zero-crossing comparator  414  analyzes zero-crossings of the output current  218  to estimate a magnitude of the input current  214 . Example implementations of the driver controller  138  are further described with respect to  FIGS.  5 - 1  to  5 - 4   . 
       FIG.  5 - 1    illustrates a first example implementation of the driver controller  138  for adaptive switch driving. In the depicted configuration, the driver controller  138  includes the DC supply voltage sensor  406 , the input current sensor  410 , a logic circuit  502 , and an output node  504 . The DC supply voltage sensor  406  is coupled between the power node  226  (of  FIG.  2   ) and the logic circuit  502 . The input current sensor  410  is coupled between the input node  206  and the logic circuit  502 . The logic circuit  502  is coupled to an output of the DC supply voltage sensor  406 , an output of the input current sensor  410 , and the output node  504 . The logic circuit  502  can be implemented using one or more logic gates, such as an AND gate, an OR gate, a NAND gate, or a NOR gate. In the depicted configuration, the logic circuit  502  is implemented using an AND gate. The output node  504  is coupled to the driver circuit  136  of  FIG.  1   . 
     The DC supply voltage sensor  406  includes a voltage sensor  506 , a threshold voltage  508 , and a comparator  510 . The voltage sensor  506  is coupled between the power node  226  and an input of the comparator  510 . The threshold voltage  508  is provided to another input of the comparator  510  and can be generated by the power transfer circuit  128 . As an example, the threshold voltage  508  can be approximately equal to four volts. 
     The input current sensor  410  includes a current sensor  512 , a reference current  514 , and a comparator  516 . The current sensor  512  is coupled between the input node  206  and an input of the comparator  516 . The reference current  514  is provided to another input of the comparator  510  and can be generated by the power transfer circuit  128 . As an example, the reference current can be approximately equal to one ampere. 
     During operation, the DC supply voltage sensor  406  senses the DC supply voltage  228  at the power node  226  and compares the DC supply voltage  228  to the threshold voltage  508 . The comparator  510  generates a first voltage to indicate that the DC supply voltage  228  is greater than the threshold voltage  508  or generates a second voltage to indicate that the DC supply voltage  228  is less than or equal to the threshold voltage  508 . The input current sensor  410  senses the input current  214  at the input node  206  and compares the measured input current  214  to the threshold current  514 . The comparator  516  generates the first voltage to indicate that the input current  214  is greater than the threshold current  514  or generates the second voltage to indicate that the input current  214  is less than or equal to the threshold current  514 . 
     The logic circuit  502  generates the control signal  310  (of  FIG.  3 - 1   ) based on the voltages provided by the DC supply voltage sensor  406  and the input current sensor  410 . In this example, the logic circuit  502  generates the control signal  310  to decrease the strength of the driver circuit  136  (e.g., cause the driver circuit  136  to operate according to the reliability mode  312 - 1 ) responsive to the DC supply voltage  228  being greater than the threshold voltage  508  and the input current  214  being greater than the threshold current. Alternatively, the logic circuit  502  generates the control signal  310  to increase the strength of the driver circuit  136  (e.g., cause the driver circuit  136  to operate according to the efficiency mode  312 - 2 ) responsive to either the DC supply voltage  228  being less than or equal to the threshold voltage  508  or the input current  214  being less than or equal to the threshold current  514 . 
     In this example implementation, the driver controller  138  has direct measurements regarding the DC supply voltage  228  and the input current  214 . As such, the driver controller  138  can perform additional steps to specify an optimal amount of the driver current  308 - 1  to limit the peak of the input voltage  212  below the breakdown voltage of the switch  134 - 1  according to Equation 2. While this can be advantageous to enable finer control of the driver current  308 - 1 , this implementation can be more expensive and have a larger footprint. In an alternative implementations, cost, size, and/or complexity can be reduced by replacing the input current sensor  410  with the mode indicator  412  (shown in  FIG.  5 - 2   ), the zero-crossing comparator  414  (shown in  FIG.  5 - 3   ), or the power-source-type indicator  408  (shown in  FIG.  5 - 4   ). 
       FIG.  5 - 2    illustrates a second example implementation of the driver controller  138  for adaptive switch driving. In the depicted configuration, the driver controller  138  includes the DC supply voltage sensor  406  (of  FIG.  5 - 1   ) and the logic circuit  502  (of  FIG.  5 - 1   ). Instead of the input current sensor  410  of  FIG.  5 - 1   , the driver controller  138  of  FIG.  5 - 2    includes the mode indicator  412  (of  FIG.  4   ). 
     The mode indicator  412  is coupled to the logic circuit  502 . The mode indicator  412  provides a mode signal  518  to the logic circuit  502 . The mode signal  518  indicates whether the switch-mode power supply  130  entered the pulse-width modulation mode (e.g., transitioned from the skip mode to the pulse-width modulation mode). Generally, this transition happens if the input current  214  exceeds a threshold current, which can be between approximately 600 and 900 milliamperes. In this way, the mode signal  518  provides an indirect estimate of the input current  214 . In some cases, the mode signal  518  is generated by other components within the power transfer circuit  128  and the mode indicator  412  passes the mode signal  518  (with or without modification) to the logic circuit  502 . 
     During operation, the logic circuit  502  generates the control signal  310  (of  FIG.  3 - 1   ) based on the voltage provided by the DC supply voltage sensor  406  and the mode signal  518  provided by the mode indicator  412 . In this example, the logic circuit  502  generates the control signal  310  to decrease the strength of the driver circuit  136  (e.g., cause the driver circuit  136  to operate according to the reliability mode  312 - 1 ) responsive to the DC supply voltage  228  being greater than the threshold voltage  508  and the mode signal  518  indicating that that the switch-mode power supply  130  entered the pulse-width modulation mode. Alternatively, the logic circuit  502  generates the control signal  310  to increase the strength of the driver circuit  136  (e.g., cause the driver circuit  136  to operate according to the efficiency mode  312 - 2 ) responsive to either the DC supply voltage  228  being less than or equal to the threshold voltage  508  or the mode signal  518  indicating that the switch-mode power supply  130  has not transitioned from the skip mode to the pulse-width modulation mode. 
       FIG.  5 - 3    illustrates a third example implementation of the driver controller  138  for adaptive switch driving. In the depicted configuration, the driver controller  138  includes the DC supply voltage sensor  406  (of  FIG.  5 - 1   ) and the logic circuit  502  (of  FIG.  5 - 1   ). Instead of the input current sensor  410  of  FIG.  5 - 1    or the mode indicator  412  of  FIG.  5 - 2   , the driver controller  138  of  FIG.  5 - 3    includes the zero-crossing comparator  414  (of  FIG.  4   ). In some implementations, the zero-crossing comparator  414  is already implemented as part of the switch-mode power supply  130 . 
     The zero-crossing comparator  414  is coupled to the logic circuit  502  and the output node  208 . The zero-crossing comparator  414  includes a current sensor  520 , a ground reference  522 , and a comparator  524 . The current sensor  520  measures the output current  218  at the output node  208 . The comparator  524  determines instances at which the output current  218  crosses zero (e.g., crosses the ground reference  522 ). At these instances, the zero-crossing comparator  414  can indirectly determine the input current  214 . For example, the zero-crossing comparator  414  can indicate that the input current  214  is estimated to be less than or equal to a particular threshold amount. 
     During operation, the logic circuit  502  generates the control signal  310  (of  FIG.  3 - 1   ) based on the voltages provided by the DC supply voltage sensor  406  and the zero-crossing comparator  414 . In this example, the logic circuit  502  generates the control signal  310  to decrease the strength of the driver circuit  136  (e.g., cause the driver circuit  136  to operate according to the reliability mode  312 - 1 ) responsive to the DC supply voltage  228  being greater than the threshold voltage  508  and the estimated input current  214  being greater than the threshold amount. Alternatively, the logic circuit  502  generates the control signal  310  to increase the strength of the driver circuit  136  (e.g., cause the driver circuit  136  to operate according to the efficiency mode  312 - 2 ) responsive to either the DC supply voltage  228  being less than or equal to the threshold voltage  508  or the estimated input current  214  being less than or equal to the threshold amount. 
       FIG.  5 - 4    illustrates a fourth example implementation of the driver controller  138  for adaptive switch driving. In the depicted configuration, the driver controller  138  includes the DC supply voltage sensor  406  (of  FIG.  5 - 1   ) and the logic circuit  502  (of  FIG.  5 - 1   ). Instead of the input current sensor  410  of  FIG.  5 - 1   , the mode indicator  412  of  FIG.  5 - 2   , or the zero-crossing comparator  414  of  FIG.  5 - 3   , the driver controller  138  of  FIG.  5 - 4    includes the power-source-type indicator  408  (of  FIG.  4   ). 
     The power-source-type indicator  408  is coupled to the logic circuit  502 . The power-source-type indicator  408  provides a power-source-type signal  526  to the logic circuit  502 . The power-source-type signal  526  indicates a type or classification associated with the power source  124 . In some cases, the power-source-type signal  526  is generated by other components within the power transfer circuit  128  or the computing device  102 , and the power-source-type indicator  408  passes the power-source-type signal  526  to the logic circuit  502 . 
     During operation, the logic circuit  502  generates the control signal  310  (of  FIG.  3 - 1   ) based on the voltage provided by the DC supply voltage sensor  406  and the power-source-type signal  526  provided by the power-source-type indicator  408 . In this example, the logic circuit  502  generates the control signal  310  to decrease the strength of the driver circuit  136  (e.g., cause the driver circuit  136  to operate according to the reliability mode  312 - 1 ) responsive to the DC supply voltage  228  being greater than the threshold voltage  508  and the power-source-type signal  526  indicating that that the power source  124  is associated with a type of power source  124  that is external from the computing device  102 , such as the USB charger. Alternatively, the logic circuit  502  generates the control signal  310  to increase the strength of the driver circuit  136  (e.g., cause the driver circuit  136  to operate according to the efficiency mode  312 - 2 ) responsive to either the DC supply voltage  228  being less than or equal to the threshold voltage  508  or the power-source-type signal  526  indicating that the power source  124  is internal to the computing device  102 , such as a battery of the computing device  102 . 
       FIG.  6    is a flow diagram illustrating an example process  600  for adaptive switch driving. The process  600  is described in the form of a set of blocks  602 - 610  that specify operations that can be performed. However, operations are not necessarily limited to the order shown in  FIG.  6    or described herein, for the operations may be implemented in alternative orders or in fully or partially overlapping manners. Also, more, fewer, and/or different operations may be implemented to perform the process  600 , or an alternative process. Operations represented by the illustrated blocks of the process  600  may be performed by a switch-mode power supply  130  (e.g., of  FIG.  1  or  2   ). More specifically, the operations of the process  600  may be performed by a switching circuit  132  as shown in  FIGS.  1  to  3 - 1   . 
     At block  602 , an input voltage and an input current are accepted at an input of a switching circuit. The input voltage comprises a direct-current supply voltage. For example, the switching circuit  132  can accept the input voltage  212  and the input current  214  at the input of thereof (e.g., at the input node  206 ), as shown in  FIG.  2   . The input voltage  212  can be a direct-current supply voltage. Thus, the power source  124  may provide the input voltage  212  and the input current  214  to the input node  206  of the switching circuit  132 . 
     At block  604 , the switching circuit operates in a first state to provide the input voltage as an output voltage at an output of the switching circuit. For example, the switching circuit  132  can operate in the first state  314 - 1  to provide the input voltage  212  as the output voltage  216  at the output of the switch circuit  132  (e.g., the output node  208 ), as shown in  FIG.  3 - 2   . The first state  314 - 1  may cause the switch  134 - 1  to be in a closed state, which connects the input node  206  to the output node  208 . 
     At block  606 , the switching circuit operates in a second state to provide a ground voltage as the output voltage at the output. For example, the switching circuit  132  can operate in the second state  314 - 2  to provide the ground voltage  222  as the output voltage  216  at the output of the switching circuit (e.g., at the output node  208 ), as shown in  FIG.  3 - 2   . The second state  314 - 2  may cause the switch  134 - 1  to be in an open state, which disconnects the input node  206  from the output node  208 . 
     At block  608 , the switching circuit operates in a third state to transition from the first state to the second state. The third state causes the output voltage to change from the input voltage to the ground voltage according to a slew rate. For example, the switching circuit  132  can operate in the third state  314 - 3  to transition from the first state  314 - 1  to the second state  314 - 2 , as shown in  FIG.  3 - 2   . The third state  314 - 3  may cause the switch  134 - 1  to transition from the closed state to the open state. A duration that the switching circuit  132  operates in the third state  314 - 3  is referred to as the transition period  320 . The third state  314 - 3  can cause the output voltage  216  to change from the input voltage  212  to the ground voltage  222  according to the slew rate  318 . 
     The switching circuit can also operate in a fourth state  314 - 4  to transition from the second state  314 - 2  to the first state  314 - 1 . The fourth state  314 - 4  causes the output voltage  216  to change from the ground voltage  222  to the input voltage  212 . The fourth state  314 - 4  may cause the switch  134 - 1  to transition from the open state to the closed state. 
     At block  610 , the slew rate of the output voltage is adjusted responsive to at least one of the following: a change in a magnitude of the direct-current supply voltage or a change in a magnitude of the input current. For example, the switching circuit  132  can adjust the slew rate of the output voltage  216  responsive to a change in a magnitude of the direct-current supply voltage  228  (of  FIG.  2   ) or a change in a magnitude of the input current  214  (of  FIG.  2   ). In particular, the switching circuit  132  may decrease the slew rate  318  (e.g., increase the transition period  320 ) according to the reliability mode  312 - 1  or increase the slew rate  318  (e.g., decrease the transition period  320 ) according to the efficiency mode  312 - 2 , as shown in  FIG.  3 - 2   . 
     As an example, the switching circuit  132  can operate according to the reliability mode  312 - 1  responsive to detecting an increase in the direct-current supply voltage  228  or an increase in the input current  214 . In this mode, the driver circuit  136  decreases the slew rate  318  to improve reliability by decreasing the peak of the input voltage  212 . Alternatively, the switching circuit  132  can operate according to the efficiency mode  312 - 2  responsive to detecting a decrease in the magnitude of the direct-current supply voltage  228  or a decrease in the magnitude of the input current  214 . In this mode, the driver circuit  136  increases the slew rate  318  to increase efficiency of the switching circuit  132  at the expense of increasing the peak of the input voltage  212 . Through adaptive switch driving, the switching circuit  132  is able to appropriately configure itself to balance reliability versus efficiency in different operating conditions. 
     Unless context dictates otherwise, use herein of the word “or” may be considered use of an “inclusive or,” or a term that permits inclusion or application of one or more items that are linked by the word “or” (e.g., a phrase “A or B” may be interpreted as permitting just “A,” as permitting just “B,” or as permitting both “A” and “B”). Further, items represented in the accompanying figures and terms discussed herein may be indicative of one or more items or terms, and thus reference may be made interchangeably to single or plural forms of the items and terms in this written description. Finally, although subject matter has been described in language specific to structural features or methodological operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or operations described above, including not necessarily being limited to the organizations in which features are arranged or the orders in which operations are performed. 
     Some aspects are described below: 
     Aspect 1: An apparatus comprising: 
     a switching circuit comprising:
         an input configured to accept an input voltage and an input current,       

     the input voltage comprising a direct-current supply voltage; and
         an output configured to provide an output voltage;       

     the switching circuit configured to selectively:
         be in a first state that provides the input voltage as the output voltage,   be in a second state that provides a ground voltage as the output voltage, or   be in a third state that causes the output voltage to change from the input voltage to the ground voltage according to a slew rate, the third state enabling the switching circuit to transition from the first state to the second state; and       

     the switching circuit configured to adjust the slew rate of the output voltage for the third state responsive to at least one of the following: a change in a magnitude of the direct-current supply voltage or a change in a magnitude of the input current. 
     Aspect 2: The apparatus of aspect 1, wherein: 
     the switching circuit is configured to transition between the first state and the second state according to a transition period; 
     the slew rate of the output voltage is dependent upon the transition period; and 
     the switching circuit is configured to adjust the transition period responsive to at least one of the change in the magnitude of the direct-current supply voltage or the change in the magnitude of the input current. 
     Aspect 3: The apparatus of aspect 1 or 2, wherein the switching circuit is configured to: 
     decrease the slew rate responsive to at least one of an increase in the magnitude of the direct-current supply voltage or an increase in the magnitude of the input current; and 
     increase the slew rate responsive to at least one of a decrease in the magnitude of the direct-current supply voltage or a decrease in the magnitude of the input current. 
     Aspect 4: The apparatus of aspect 3, wherein: 
     the switching circuit comprises a switch coupled between the input and the output; and 
     the switching circuit is configured to cause a peak of the input voltage at the input to be less than a breakdown voltage of the switch by decreasing the slew rate of the output voltage. 
     Aspect 5: The apparatus of aspect 3 or 4, wherein the switching circuit is configured to: 
     operate at a first efficiency responsive to decreasing the slew rate of the output voltage; and 
     operate at a second efficiency responsive to increasing the slew rate of the output voltage, the second efficiency being greater than the first efficiency. 
     Aspect 6: The apparatus of any previous aspect, further comprising: 
     a switch-mode power supply configured to be coupled between a power source and a load, the switch-mode power supply comprising:
         the switching circuit; and   at least one inductor coupled between the output of the switching circuit and the load,       

     wherein the input of the switching circuit is configured to be coupled to the power source. 
     Aspect 7: The apparatus of aspect 6, wherein: 
     the load comprises at least one battery; and 
     the switch-mode power supply is configured to transfer power from the power source to the at least one battery. 
     Aspect 8: The apparatus of aspects 1-3, 6, or 7, wherein the switching circuit comprises: 
     a first switch coupled between the input and the output, the first switch configured to selectively:
         be in a closed state according to the first state to connect the input to the output; or   be in an open state according to the second state to disconnect the input from the output; and       

     a second switch coupled between the output and a ground, the second switch configured to selectively:
         be in the open state according to the first state to disconnect the ground from the output; or   be in the closed state according to the second state to connect the ground to the output.       

     Aspect 9: The apparatus of aspect 8, wherein the switching circuit comprises: 
     at least one driver circuit coupled to the first switch and the second switch, the at least one driver circuit configured to:
         provide a first driver current to the first switch to enable the first switch to transition from the closed state to the open state; and   provide a second driver current to the second switch to enable the second switch to transition from the open state to the closed state; and       

     at least one driver controller coupled to the at least one driver circuit, the at least one driver controller configured to:
         detect at least one of the change in the magnitude of the direct-current supply voltage or the change in the magnitude of the input current; and   adjust a magnitude of the first driver current and a magnitude of the second driver current based on the detected change to adjust the slew rate of the output voltage.       

     Aspect 10: An apparatus comprising: 
     switch-mode means for transferring power between a power source and a load, the switch-mode means comprising:
         switching means for selectively operating in a closed state to connect the power source to the load or an open state to disconnect the power source from the load;   driver means for controlling a transition period associated with the switching means transitioning from the closed state to the open state;   monitor means for detecting a change in a magnitude of an input current or a change in a magnitude of a direct-current supply voltage provided by the power source; and   control means for adjusting the transition period responsive to the monitor means detecting the change in the magnitude of the input current or the change in the magnitude of the direct-current supply voltage.       

     Aspect 11: The apparatus of aspect 10, wherein the controls means is configured to: 
     increase the transition period responsive to the monitor means detecting at least one of an increase in the magnitude of the direct-current supply voltage or an increase in the magnitude of the input current; and 
     decrease the transition period responsive to the monitor means detecting at least one of a decrease in the magnitude of the direct-current supply voltage or a decrease in the magnitude of the input current. 
     Aspect 12: The apparatus of aspect 10 or 11, wherein: 
     the control means is configured to cause a peak of an input voltage at an input of the switching means to be less than a breakdown voltage of the switching means by increasing the transition period. 
     Aspect 13: The apparatus of any one of aspects 10-12, wherein the switching means is configured to: 
     operate at a first efficiency responsive to the control means increasing the transition period; and 
     operate at a second efficiency responsive to the control means decreasing the transition period, the second efficiency being greater than the first efficiency. 
     Aspect 14: A method comprising: 
     accepting an input voltage and an input current at an input of a switching circuit, the input voltage comprising a direct-current supply voltage; 
     operating the switching circuit in a first state to provide the input voltage as an output voltage at an output of the switching circuit; 
     operating the switching circuit in a second state to provide a ground voltage as the output voltage at the output; 
     operating the switching circuit in a third state to transition from the first state to the second state, the third state causing the output voltage to change from the input voltage to the ground voltage according to a slew rate; and 
     adjusting the slew rate of the output voltage responsive to at least one of the following: a change in a magnitude of the direct-current supply voltage or a change in a magnitude of the input current. 
     Aspect 15: The method of aspect 14, wherein the adjusting of the slew rate comprises: 
     decreasing the slew rate responsive to at least one of an increase in the magnitude of the direct-current supply voltage or an increase in the magnitude of the input current; and 
     increasing the slew rate responsive to at least one of a decrease in the magnitude of the direct-current supply voltage or a decrease in the magnitude of the input current. 
     Aspect 16: The method of aspect 15, wherein the decreasing of the slew rate comprises causing a peak of the input voltage at the input to be less than a breakdown voltage associated with the switching circuit. 
     Aspect 17: The method of aspect 15 or 16, wherein: 
     the decreasing of the slew rate comprises operating the switching circuit at a first efficiency; and 
     the increasing of the slew rate comprises operating the switching circuit at a second efficiency, the second efficiency being greater than the first efficiency. 
     Aspect 18: An apparatus comprising: 
     a switching circuit comprising:
         an input configured to accept an input voltage;   at least one switch coupled between the input of the switching circuit and an output of the switching circuit, the at least one switch configured to selectively:
           be in a closed state to connect the input to the output; or   be in an open state to disconnect the input from the output;   
           at least one driver circuit coupled to the at least one switch, the at least one driver circuit configured to provide a driver current to enable the at least one switch to transition from the closed state to the open state; and   at least one driver controller coupled to the at least one driver circuit, the at least one driver controller configured to:
           monitor at least one parameter associated with the input voltage;   detect a change in the at least one parameter; and   adjust a magnitude of the driver current provided by the at least one driver circuit based on the detected change in the at least one parameter.   
               

     Aspect 19: The apparatus of aspect 18, wherein a transition period of the at least one switch is dependent upon the magnitude of the driver current. 
     Aspect 20: The apparatus of aspect 18 or 19, wherein: 
     the at least one parameter is configured to selectively have a first magnitude or a second magnitude that is smaller than the first magnitude; 
     the at least one driver circuit is configured to selectively:
         provide a first driver current as the driver current; or       

     provide a second driver current as the driver current, the second driver current being smaller than the first driver current; and 
     the at least one driver controller is configured to selectively:
         cause the at least one driver circuit to provide the second driver current responsive to the at least one parameter having the first magnitude; or   cause the at least one driver circuit to provide the first driver current responsive to the at least one parameter having the second magnitude.       

     Aspect 21: The apparatus of aspect 20, wherein: 
     the input is configured to accept an input current; 
     the input voltage comprises a direct-current supply voltage; and 
     the at least one parameter includes the input current and the direct-current supply voltage. 
     Aspect 22: The apparatus of aspect 21, wherein the driver controller comprises at least one of the following: 
     a voltage monitor circuit configured to measure the direct-current supply voltage indirectly or directly; and 
     a current monitor circuit configured to measure the input current indirectly or directly. 
     Aspect 23: The apparatus of aspect 22, wherein the voltage monitor circuit comprises a direct-current supply voltage sensor. 
     Aspect 24: The apparatus of aspect 22 or 23, wherein the voltage monitor circuit comprises a power-source-type indicator. 
     Aspect 25: The apparatus of any one of aspects 22-24, wherein the current monitor circuit comprises an input current sensor. 
     Aspect 26: The apparatus of any one of aspects 22-25, wherein the current monitor circuit comprises a mode indicator. 
     Aspect 27: The apparatus of any one of aspects 22-26, wherein the current monitor circuit comprises a zero-crossing comparator. 
     Aspect 28: The apparatus of any one of aspects 18-26, wherein the at least one driver controller is configured to: 
     detect an increase in a magnitude of the at least one parameter; and 
     responsive to the detection, cause the at least one driver circuit to decrease the driver current. 
     Aspect 29: The apparatus of aspect 28, wherein the at least one driver controller is configured to decrease the driver current by an amount that enables a peak of the input voltage to be less than a breakdown voltage of the at least one switch. 
     Aspect 30: The apparatus of any one of aspects 18-29, wherein the at least one driver controller is configured to: 
     detect a decrease in the magnitude of at least one parameter; and 
     responsive to the detection, cause the at least one driver circuit to increase the driver current. 
     Aspect 31: The apparatus of aspect 30, wherein the at least one driver controller is configured to increase an efficiency of the at least one switch by increasing the driver current. 
     Aspect 32: The apparatus of any one of aspects 18-31, further comprising a switch-mode power supply, wherein: 
     the switch-mode power supply comprises the switching circuit; 
     the at least one parameter comprises a mode signal, the mode signal indicating an operational mode of the switch-mode power supply; and 
     the at least one driver controller is configured to cause the at least one driver circuit to decrease the driver current responsive to the mode signal changing from indicating a skip mode to indicating a pulse-width modulation mode. 
     Aspect 33: The apparatus of claim any one of aspects 18-32, further comprising an internal power source, wherein: 
     the apparatus is configured to selectively utilize power from an external power source or the internal power source; 
     the at least one parameter comprises a power-source-type signal, the power-source-type signal indicating whether the apparatus utilizes power from the external power source or the internal power source; and 
     the at least one driver controller is configured to cause the at least one driver circuit to selectively:
         decrease the driver current responsive to the power-source-type signal changing from indicating that the apparatus is utilizing the power from the internal power source to indicating that the apparatus is utilizing the power from the external power source; or   increase the driver current responsive to the power-source-type signal changing from indicating that the apparatus is utilizing the power from the external power source to indicating that the apparatus is utilizing the power from the internal power source.