Patent Publication Number: US-8970200-B2

Title: Systems and methods for light-load efficiency in displays

Description:
BACKGROUND 
     The present disclosure relates generally to systems and methods for improving the efficiency of a display panel, and more specifically, to improving the efficiency of a boost converter in the display panel while operating under light-load conditions. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     A backlight driver circuit in a light-emitting diode (LED) display may use a boost converter to provide a range of direct current (DC) voltages to a string of light-emitting diodes (LEDs) in the LED display. Generally, the string of LEDs provides various amounts of white light to the screen of the LED display such that the range of DC voltages corresponds to a range of brightness levels or white light provided to the screen. To control the range of voltages provided to the string of LEDs, the backlight driver circuit may use the boost converter to adjust (e.g., increase) an input voltage provided by a voltage supply and couple the adjusted voltage to the string of LEDs. Generally, the boost converter adjusts the voltage of the voltage supply by turning a switch (e.g., metal-oxide-semiconductor field-effect transistor) on and off such that an inductor coupled in series with the voltage supply and the string of LEDs may maintain a voltage, which may increase a total voltage available to the string of LEDs. 
     In conventional backlight driver circuits, the boost converter is configured to switch a metal-oxide-semiconductor field-effect transistor (MOSFET) using a fixed gate drive voltage to minimize a power loss in the MOSFET. That is, the backlight driver circuit may provide a fixed gate drive voltage to the gate of the MOSFET to switch the MOSFET off and on such that an on-resistance R ds (on) between the drain and the source in the MOSFET is minimized, thereby decreasing conduction losses of the MOSFET due to the on-resistance R ds (on). However, during light-load conditions, a large portion of the power loss of the MOSFET may no longer be attributed to the power lost via the on-resistance R ds (on). Instead, during light-load conditions, a large portion of the power loss of the MOSFET may be attributed to driving the gate of the MOSFET when the MOSFET switches. As such, by using the fixed gated drive voltage for all load conditions (i.e., including light-load conditions), the boost converter may be less efficient due to the power loss via the gate of the MOSFET. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     The present disclosure relates generally to systems and methods for improving the efficiency of a boost converter in the display panel while operating under light-load conditions. In certain embodiments, a backlight driver circuit may adjust a gate drive voltage provided to a gate of a metal-oxide-semiconductor field-effect transistor (MOSFET) in the boost converter based on the load conditions of light-emitting diodes used to illuminate the display panel. Moreover, the backlight driver circuit may switch between two different voltage sources to further broaden a range of gate drive voltages available to drive the gate of the MOSFET in the boost converter. As a result, the backlight driver circuit may decrease gate drive losses associated with the MOSFET, thereby increasing the efficiency of the boost converter. For example, the backlight driver may use a low voltage power source (e.g., 5V) to provide a range of low voltages to the gate of the MOSFET during light-load conditions and may use a high voltage power source (e.g., 12V) to provide a range of higher voltages to the gate of the MOSFET during non-light load conditions. By using the low voltage source to provide low voltages to the MOSFET gate for light-load conditions, the backlight driver circuit may improve the efficiency of the boost converter by decreasing the power losses associated with gate drive of the MOSFET. That is, by using a lower gate drive voltage to switch the MOSFET during light-load conditions, the backlight driver circuit may decrease the gate drive losses of the MOSFET as compared to switching the MOSFET with a higher gate drive voltage. 
     Various refinements of the features noted above may exist in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. The brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a block diagram of exemplary components of an electronic device, in accordance with an embodiment; 
         FIG. 2  is a front view of a handheld electronic device, in accordance with an embodiment; 
         FIG. 3  is a view of a computer, in accordance with an embodiment; 
         FIG. 4  is a block diagram of a boost converter in a display in the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 5  is a flow chart that depicts a method for adjusting a gate drive voltage provided to a metal-oxide-semiconductor field-effect transistor (MOSFET) in the boost converter of  FIG. 4 , in accordance with an embodiment; 
         FIG. 6  is a graph of gate drive voltage profiles that may be provided to the MOSFET in the boost converter of  FIG. 4 , in accordance with an embodiment; 
         FIG. 7  is a graph of boost converter efficiency with respect to current provided to the display in the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 8  is a flow chart that depicts a method for adjusting a gate drive voltage provided to the MOSFET in the boost converter of  FIG. 4  using two voltage sources, in accordance with an embodiment; 
         FIG. 9  is a graph of a gate drive voltage profile that may be provided to the MOSFET in the boost converter of  FIG. 4  using the method of  FIG. 8 , in accordance with an embodiment; 
         FIG. 10  is a graph of boost converter efficiency with respect to current provided to the display in the electronic device of  FIG. 1 , in accordance with an embodiment; and 
         FIG. 11  is a flow chart that depicts a method for adjusting a gate drive voltage provided to the MOSFET in the boost converter of  FIG. 4  using two voltage sources and based in part on a change in brightness levels that occur in the display of the electronic device of  FIG. 1 , in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     The present disclosure relates generally to systems and methods for improving the efficiency of a boost converter in the display panel while operating under light-load conditions. Generally, conventional boost converters use a fixed gate drive voltage to switch a metal-oxide-semiconductor field-effect transistor (MOSFET) such that an on-resistance R ds (on) between the drain and the source in the MOSFET may be controlled (e.g., minimized). However, during light-load conditions, a large portion of power losses that occur in the boost converter may be attributed to a gate drive loss in the MOSFET of the boost converter. To decrease the gate drive loss in the MOSFET of the boost converter during light-load conditions, a backlight driver circuit may use lower gate drive voltages to switch the MOSFET. 
     With this in mind, a variety of electronic devices may incorporate systems and methods for improving the efficiency of a boost converter in a display panel. An example of a suitable electronic device may include various internal and/or external components, which contribute to the function of the device.  FIG. 1  is a block diagram illustrating the components that may be present in such an electronic device  10  and which may allow the electronic device  10  to function in accordance with the methods discussed herein. Those of ordinary skill in the art will appreciate that the various functional blocks shown in  FIG. 1  may include hardware elements (including circuitry), software elements (including computer code stored on a computer-readable medium), or a combination of both hardware and software elements. It should further be noted that  FIG. 1  is merely one example of a particular implementation and is merely intended to illustrate the types of components that may be present in the electronic device  10 . For example, in the presently illustrated embodiment, these components may include a display  12 , I/O ports  14 , input structures  16 , one or more processors  18 , a memory device  20 , a non-volatile storage  22 , a networking device  24 , a power source  26 , a backlight driver circuit  28 , and the like. 
     With regard to each of these components, the display  12  may be used to display various images generated by the electronic device  10 . Moreover, the display  12  may be a light-emitting diode (LED) display and may be a touch-screen display, for example, which may enable users to interact with a user interface of the electronic device  10 . In some embodiments, the display  12  may be a MultiTouch™ display that can detect multiple touches at once. 
     The I/O ports  14  may include ports configured to connect to a variety of external I/O devices, such as a power source, headset or headphones, peripheral devices such as keyboards or mice, or other electronic devices  10  (such as handheld devices and/or computers, printers, projectors, external displays, modems, docking stations, and so forth). 
     The input structures  16  may include the various devices, circuitry, and pathways by which user input or feedback is provided to the processor  18 . Such input structures  16  may be configured to control a function of the electronic device  10 , applications running on the electronic device  10 , and/or any interfaces or devices connected to or used by the electronic device  10 . 
     The processor(s)  18  may provide the processing capability to execute the operating system, programs, user and application interfaces, and any other functions of the electronic device  10 . The instructions or data to be processed by the processor(s)  18  may be stored in a computer-readable medium, such as the memory  20 . The memory  20  may be provided as a volatile memory, such as random access memory (RAM), and/or as a non-volatile memory, such as read-only memory (ROM). The components may further include other forms of computer-readable media, such as the non-volatile storage  22 , for persistent storage of data and/or instructions. The non-volatile storage  22  may include flash memory, a hard drive, or any other optical, magnetic, and/or solid-state storage media. The non-volatile storage  22  may be used to store firmware, data files, software, wireless connection information, and any other suitable data. In certain embodiments, the processor  18  may control the operation of various switches and hardware components that may be located within the electronic device  10  including the backlight driver circuit  28 . 
     The network device  24  may include a network controller or a network interface card (NIC). Additionally, the network device  24  may be a Wi-Fi device, a radio frequency device, a Bluetooth® device, a cellular communication device, or the like. The network device  24  may allow the electronic device  10  to communicate over a network, such as a Local Area Network (LAN), Wide Area Network (WAN), or the Internet. The power source  26  may include a variety of power types such as a battery or AC power. 
     The backlight driver circuit  28  may be used to control an amount of white light or brightness level that may be produced by a number of light-emitting diodes (LEDs) in the display  12 . As such, the backlight driver circuit  28  may alter a direct current (DC) voltage provided to the LEDs using a boost converter within the display  12 . Additional details with regard to the backlight driver circuit  28  will be described below with reference to  FIG. 4 . 
     With the foregoing in mind,  FIG. 2  illustrates an electronic device  10  in the form of a handheld device  34  and a tablet device  40 , respectively.  FIG. 2  illustrates a cellular telephone, but it should be noted that while the depicted handheld device  34  is provided in the context of a cellular telephone, other types of handheld devices (such as media players for playing music and/or video, personal data organizers, handheld game platforms, tablet devices, and/or combinations of such devices) may also be suitably provided as the electronic device  10 . As discussed with respect to the general electronic device  10  of  FIG. 1 , the handheld device  34  may allow a user to connect to and communicate through the Internet or through other networks, such as local or wide area networks. The handheld electronic device  34  may also communicate with other devices using short-range connections, such as Bluetooth® and near field communication. By way of example, the handheld device  34  may be a model of an iPod®, iPhone®, or iPad® available from Apple Inc. of Cupertino, Calif. 
     The handheld device  34  may include an enclosure or body that protects the interior components from physical damage and shields them from electromagnetic interference. The enclosure may be formed from any suitable material such as plastic, metal or a composite material and may allow certain frequencies of electromagnetic radiation to pass through to wireless communication circuitry within the handheld device  34  to facilitate wireless communication. In the depicted embodiment, the enclosure includes user input structures  16  through which a user may interface with the device. Each user input structure  16  may be configured to help control a device function when actuated. 
     In the depicted embodiment, the handheld device  34  includes the display  12 . The display  12  may be a touch-screen LED display used to display a graphical user interface (GUI) that allows a user to interact with the handheld device  34 . The handheld electronic device  34  also may include various input and output (I/O) ports that allow connection of the handheld device  34  to external devices. 
     In addition to handheld device  34 , the electronic device  10  may also take the form of a computer or other type of electronic device. Such computers may include computers that are generally portable (such as laptop, notebook, and tablet computers) as well as computers that are generally used in one place (such as conventional desktop computers, workstations, and/or servers). In certain embodiments, the electronic device  10  in the form of a computer may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, iPad® or Mac Pro® available from Apple Inc. By way of example, an electronic device  10  in the form of a laptop computer  50  is illustrated in  FIG. 3  in accordance with one embodiment. The depicted computer  50  includes a housing  52 , a display  12 , input structures  16 , and input/output ports  14 . 
     In one embodiment, the input structures  16  (such as a keyboard and/or touchpad) may be used to interact with the computer  50 , such as to start, control, or operate a GUI or applications running on the computer  50 . For example, a keyboard and/or touchpad may allow a user to navigate a user interface or application interface displayed on the display  12 . 
     As depicted, the electronic device  10  in the form of the computer  50  may also include various input and output ports  14  to allow connection of additional devices. For example, the computer  50  may include an I/O port  14 , such as a USB port or other port, suitable for connecting to another electronic device, a projector, a supplemental display, and so forth. The computer  50  may include network connectivity, memory, and storage capabilities, as described with respect to  FIG. 1 . As a result, the computer  50  may store and execute a GUI and other applications. 
     With the foregoing discussion in mind,  FIG. 4  depicts a block diagram of a boost converter  70  that may be employed in the display  12  of the electronic device  10 . As shown in  FIG. 4 , the boost converter  70  may include the backlight driver circuit  28 , a switch such as a metal-oxide-semiconductor field-effect transistor (MOSFET)  74 , a string of light-emitting diodes (LEDs)  76 , and an inductor  78 . The backlight driver circuit  28  may include control logic  86  that may control an operation of each component in the backlight drive circuit  28 . For example, the control logic  86  may control how a voltage may be provided to the string of LEDs  76  via a direct current (DC) voltage source  80 . In certain embodiments, the control logic  86  may be a controller, processor, microprocessor, or the like. In any case, the control logic  86  may control the brightness or amount of white light generated by the string of LEDs  76  by adjusting the voltage provided to the string of LEDs  76  using the boost converter  70 . That is, the control logic  86  may control the switching of the MOSFET  74  such that the inductor  78  maintains a charge or voltage, which may be combined with the voltage from the DC voltage source  80  and provided to the string of LEDs  76 . 
     To control the switching of the MOSFET  74 , the control logic  86  may couple a gate drive voltage to the gate of the MOSFET  74  via the DC voltage source  80 . In certain embodiments, the backlight driver circuit  28  may include a variable gate drive linear drop-out (LDO) regulator  84 , which may receive the voltage from the DC voltage source  80 . The variable gate drive LDO regulator  84  may adjust the voltage provided by the DC voltage source  80  using resistors arranged as a voltage divider, using a variable resistor, or the like. In one embodiment, the control logic  86  may be configured to provide a fixed gate drive voltage to the MOSFET  74 . 
     The fixed gate drive voltage may be calculated based on a function designed to minimize an on-resistance R ds (on) between the drain and the source of the MOSFET  74  when the string of LEDS  74  are operating under full-load or near full-load conditions. While operating under full-load or near full-load conditions, a significant portion of the total power loss experienced by the boost converter  70  may include energy dissipated through the on-resistance R ds (on) of the MOSFET  74 . However, when the string of LEDs  74  are not driven at full-load or near full-load conditions (e.g., during light-load condition), the total power loss experienced by the boost converter  70  may no longer be dominated by the energy dissipated through the on-resistance R ds (on) of the MOSFET  74 . Instead, the gate drive loss of the MOSFET  74  may become a more significant portion of the total power loss of the boost converter  70 , as opposed to the power loss via the on-resistance R ds (on) of the MOSFET  74 . 
     Keeping this in mind, the gate drive loss in the boost converter  70  may be expressed by the following equation:
 
 P   gate     —     loss   =C   gate   ×V   2   ×f   (1)
 
where P gate     —     loss  represents an amount of power loss experienced by the gate of the MOSFET  74  (gate drive loss), C gate  represents a capacitance of the gate of the MOSFET  74 , V represents the gate drive voltage provided to the gate of the MOSFET  74 , and f represents a switching frequency of the MOSFET  74 . In certain embodiments, to reduce the gate drive loss of the MOSFET  74  during light-load conditions, the control logic  86  may lower the gate drive voltage provided to the gate of the MOSFET  74 . Although lowering the gate drive voltage may subsequently increase the on-resistance R ds (on) of the MOSFET  74 , during light-load conditions, the power loss in the MOSFET  74  via the on-resistance R ds (on) consists of a small portion of the total power loss of the boost converter  70 , as compared to the power loss due to the gate drive voltage. Accordingly, to improve the efficiency of the boost converter  70  during light-load conditions, the control logic  86  may decrease the gate drive voltage used to switch the MOSFET  74 . That is, by lowering the gate drive voltage during light-load conditions, the control logic  86  may significantly reduce the gate drive loss of the MOSFET  74  since the gate drive voltage variable V is a significant contributor to the total gate drive loss P gate     —     loss , as indicated in Equation 1. In certain embodiments, to enable the MOSFET  74  to switch with lower gate drive voltages the MOSFET  74  may be a logic level MOSFET.
 
     In one embodiment, the control logic  86  may use the variable gate drive LDO regulator  84  to lower the gate drive voltage provided to the MOSFET  74  during light-load conditions. As such, the control logic  86  may receive a brightness command  88  from the processor  18  or the like via a pulse-width modulation (PWM) duty cycle or an inter-integrated circuit (I2C) control. The brightness command  88  may indicate a brightness level or amount of white light that corresponds to a frame of image data depicted on the display  12 . The brightness level indicated by the brightness command  88  may be directly related to the voltage applied to the string of LEDs  76 . As such, the control logic  86  may determine a voltage value to provide to the string of LEDs  76  that corresponds to the brightness command  88 . After determining this voltage value, the control logic  86  may send the resulting voltage value to the variable gate drive LDO regulator  84 , which may convert a voltage received from the DC voltage source  80  such that it matches the voltage value. The resulting voltage may then be used as a gate drive voltage to the MOSFET  74 . In one embodiment, the control logic  86  may determine the gate drive voltage value based on a gate drive voltage profile and the brightness level specified by the brightness command  88 . 
     Keeping the foregoing in mind,  FIG. 5  illustrates a flow chart of a method  100  for adjusting the gate drive voltage provided to the MOSFET  74  in the boost converter  70  based on the brightness command  88 . At block  102 , the control logic  86  may receive the brightness command  88 , as described above. The brightness command  88  may indicate a percentage of the total load voltage applied to the string of LEDs  76 . In one embodiment, the brightness command  88  may be received for each frame of image data depicted on the display  12 . 
     At block  104 , the control logic  86  may receive a gate drive voltage profile. The gate drive voltage profile may be based on a type of MOSFET used in the boost converter  70 , an arrangement of the string of LEDs  76 , and the like. Generally, the gate drive voltage profiles may be determined such that the efficiency of the boost converter  70  may be optimized according to load conditions (e.g., brightness). For instance, the gate drive voltage profiles may be designed to improve the efficiency of the boost converter  70  as a function of the load on the string of LEDs  76 . 
     By way of example,  FIG. 6  illustrates a graph  110  that depicts different gate drive voltage profiles for the MOSFET  76 . Namely, the graph  110  depicts a linear gate drive voltage profile  112 , a step gate drive voltage profile  114 , and a non-linear gate drive voltage profile  116  that may be used to determine a gate drive voltage for the MOSFET  76  during various load conditions. Depending on various factors such as the type of MOSFET used in the boost converter  70  or the arrangement of the string of LEDs  76 , a gate drive voltage profile may be defined for a respective boost converter  70  and provided to the control logic  86 . 
     After receiving the brightness command and gate drive voltage profile, at block  106 , the control logic  86  may adjust an input voltage based on the brightness command  88  and gate drive voltage profile. That is, the control logic  86  may determine a gate drive voltage for the MOSFET  74  based on an intersection between a brightness level that corresponds to the brightness command  88  and the gate drive voltage profile. For instance, referring to  FIG. 6 , if the brightness command  88  corresponds to a brightness level that is less than 45% and the gate drive voltage profile corresponds to the gate drive voltage profile  114 , the variable gate drive LDO regulator  84  may convert the voltage received from the DC voltage source  80  such that the voltage provided to the gate of the MOSFET  74  corresponds to a minimum gate drive voltage (VG(min)) for the MOSFET  74 , as indicated in the gate drive voltage profile  114 . 
     After adjusting the voltage received from the DC voltage source  80  based on the brightness command and the gate drive voltage profile, the variable gate drive LDO regulator  84  may switch the MOSFET  74  using the adjusted voltage of block  106 . As a result, the control logic  86  may improve the efficiency of the boost converter  70  by decreasing gate drive losses in the MOSFET  74  during light-load conditions, as compared to using a fixed gate drive voltage for all load conditions.  FIG. 7  depicts a graph  120  that compares the efficiency of the boost converter  70  operating using a standard gate drive voltage profile and an adaptive gate drive voltage profile for switching the MOSFET  74 . The standard gate drive voltage profile may corresponds to a fixed gate drive voltage, whereas the adaptive gate drive voltage profile may correspond to the linear gate drive voltage profile  112  depicted in  FIG. 6 . As shown in the graph  120 , the boost converter  70  is more efficient during light-load conditions (e.g., 0.01 A-0.10 A) when operating using the adaptive gate drive voltage profile as compared to the standard gate drive voltage profile. 
     Referring back to  FIG. 4 , in certain embodiments, the backlight driver circuit  28  may also include a rail switch component  90  that may be coupled to a DC voltage source  92  as well as the DC voltage source  80 . In some embodiments, the DC voltage source  80  may have a higher DC voltage as compared to the DC voltage source  92 . As such, the control logic  86  may further improve the light-load efficiency of the boost converter  70  by directing the rail switch component  90  to provide voltage to the variable gate drive LDO regulator  84  from either the low DC voltage source  80  (e.g., 5V) or the high DC voltage source  92  (e.g., 12V). 
     In general, the control logic  86  may further improve the light-load efficiency of the boost converter  70  by receiving the brightness command  88  and determining a load percentage of the total load voltage being applied to the string of LEDs  76  based on the brightness command  88 . If the load percentage is greater than some value, the control logic  86  may send a signal to the rail switch component  90  to couple the variable gate drive LDO regulator  94  to the high DC voltage source  80 . If, however, the load percentage is not greater than some value, the control logic  86  may send a signal to the rail switch component  90  to couple the variable gate drive LDO regulator  94  to the low DC voltage source  92 . As such, during light-load conditions, the control logic  86  may use the low DC voltage source  92  to provide relatively low gate drive voltages to the MOSFET  74 . As a result, the control logic  86  may decrease the power loss experienced by the variable gate drive LDO regulator  84  when adjusting the high DC voltage source  80  into relatively low DC voltages to provide as gate drive voltages. 
     Keeping this in mind,  FIG. 8  illustrates a flow chart of a method  130  for adjusting the gate drive voltage provided to the MOSFET  74  in the boost converter  70  based on the brightness command  88  and using two DC voltage sources. At block  132  and block  134 , the control logic  86  may receive the brightness command  88  and a gate drive voltage profile, as described above with respect to block  102  and block  104  of  FIG. 5 . In addition to these inputs, at block  136 , the control logic  86  may receive a brightness threshold that may correspond to a brightness level or load percentage for the string of LEDs  76 . The brightness threshold may be determined based on efficiency characteristics of the voltage gate drive LDO regulator  84  with respect to its voltage outputs. 
     At block  138 , the control logic  86  may determine whether the brightness level that corresponds to the brightness command  88  is greater than the brightness threshold. If the brightness level is greater than the brightness threshold, the control logic  86  may proceed to block  140 . At block  140 , the control logic  86  may convert an input voltage from the high DC voltage source  80  to a gate drive voltage based on the brightness command  88  and the gate drive voltage profile, as discussed above with respect to block  108  of  FIG. 5 . That is, the control logic  86  may send a signal to the rail switch  90  to couple the high DC voltage source  80  to the variable gate drive LDO regulator  84  and send a signal to the variable gate drive LDO regulator  84  to convert the voltage received from the rail switch  90  into the gate drive voltage. The control logic  86  may then proceed to block  142  and send a signal to the variable gate drive LDO regulator  84  to switch the MOSFET  74  using the adjusted voltage determined at block  140 . 
     If, however, the control logic  86  determines that the brightness level is not greater than the brightness threshold, the control logic  86  may proceed to block  144 . At block  144 , the control logic  86  may adjust an input voltage from the low DC voltage source  92  to a gate drive voltage based on the brightness command  88  and the gate drive voltage profile, as discussed above with respect to block  108  of  FIG. 5 . That is, the control logic  86  may send a signal to the rail switch  90  to couple the low DC voltage source  92  to the variable gate drive LDO regulator  84  and send a signal to the variable gate drive LDO regulator  84  to convert the voltage received from the rail switch  90  into the gate drive voltage. The control logic  86  may then proceed to block  142  and send a signal to the variable gate drive LDO regulator  84  to switch the MOSFET  74  using the adjusted voltage determined at block  144 . 
     Keeping the foregoing in mind,  FIG. 9  illustrates a graph  150  of an example flexible gate drive voltage profile  152  as a function of brightness. If the brightness threshold of block  136  is 40%, the control logic  86  may use the input voltage V IN  from the high DC voltage source  80  to provide a range of gate drive voltages between 5V and 12V. In the same manner, the control logic  86  may use the input voltage V DD  from the low DC voltage source  92  to provide a range of gate drive voltages between 4V and 5V. 
     By using the high DC voltage source  80  to provide the gate drive voltages to the MOSFET  74  for higher load conditions and the low DC voltage source  92  to provide the gate drive voltages to the MOSFET  74  for lighter load conditions, the control logic  86  may further improve the efficiency of the boost converter  70 . That is, the control logic  86  may use the high DC voltage source  80  to provide the MOSFET  74  with a first range of gate drive voltages and the low DC voltage source to provide the MOSFET  74  with a second range of gate drive voltages such that the power loss of the variable gate drive LDO regulator  84  may be improved from using the high DC voltage source  80  to provide the MOSFET  74  with gate drive voltages encompassing both ranges of gate drive voltages. For instance, the variable gate drive LDO regulator  84  may dissipate a significantly larger amount of energy via its resistors when adjusting a 12V DC voltage (i.e., from the high DC voltage source  80 ) to a 4V DC voltage as compared to adjusting a 5V DC voltage (i.e., from the low DC voltage source  92 ) to the 4V DC voltage. 
     The improved efficiency of the boost converter  70  is illustrated in a graph  160  of  FIG. 10 . The graph  160  illustrates a comparison of the efficiency of the boost converter  70  operating using a standard gate drive voltage profile and a flexible gate drive voltage profile for switching the MOSFET  74  as described above with respect to the method  130 . The standard gate drive voltage profile may be a fixed gate drive voltage as discussed above, and the flexible gate drive voltage profile may correspond to the flexible gate drive voltage profile  152  of  FIG. 9 . As shown in the graph  160 , the boost converter is more efficient during light-load conditions (e.g., 0.01 A-0.10 A) when operating using the flexible gate drive voltage profile as compared to the standard gate drive voltage profile. 
     In certain embodiments, since the brightness command  88  may be passed through a PWM duty cycle control or I2C control, the load condition for the string of LEDs  76  may be known prior to the load actually being applied to the string of LEDs  76 . As such, the control logic  86  may have a sufficient amount of time to change the gate drive voltage provided to the MOSFET  74  using the rail switch  90  and the variable gate drive LDO regulator  84 . However, to further increase the response time of the backlight driver circuit  28 , the control logic  86  may bypass switching between DC voltage sources when a transition between two brightness levels for two consecutive frames of image data is greater than some threshold. 
     For example,  FIG. 11  illustrates a flow chart of a method  170  for bypassing the switching between DC voltage sources when a transition between two brightness levels for two consecutive frames of image data is greater than some threshold. At block  172 , block  174 , and block  176 , the control logic  86  may receive the brightness command  88 , the gate drive voltage profile, and the brightness threshold as described above. At block  178 , the control logic  86  may receive a brightness change threshold, which may correspond to a significant load change that may cause the control logic  74  to switch DC voltage sources to provide the MOSFET its corresponding gate drive voltage as discussed above. 
     At block  180 , the control logic  86  may determine whether the brightness level change between the current brightness level, as indicated by the brightness command  88 , and the previous brightness level is greater than the brightness change threshold. If the brightness level change is greater than the brightness change threshold, the control logic  86  may not determine a new gate drive voltage. That is, the control logic  86  may proceed to block  182  and continue switching the MOSFET  74  using the same gate drive voltage used previously. The control logic  86  may then, at block  184 , receive the next brightness command  88  and return to block  180 . 
     If, however, the brightness level change is not greater than the brightness change threshold at block  180 , the control logic  86  may proceed to block  138  in the method  130  of  FIG. 8 . That is, the control logic  86  may switch the MOSFET  74  using a gate drive voltage that may be obtained from the high DC voltage source  80  or the low DC voltage  92  as described above. As such, once the load condition of the string of LEDs  76  is in a steady-state or near steady-state condition, the control logic  86  may resume operating the boost converter  70  efficiently as per the method  130  described above with respect to  FIG. 8 . 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.