Abstract:
Embodiment of the inventive subject matter include an apparatus comprising a first switch, a second switch, a third switch, and a transistor. The first switch is coupled to a first voltage device and the transistor to selectively electrically connect the first voltage device to the transistor to provide a first charge to the transistor. The second switch is coupled to a second voltage device and the transistor to selectively electrically connect the second voltage device to the transistor to remove charge from the transistor. The third switch is coupled to the third voltage device and the transistor to selectively couple the third voltage device to the transistor to provide a second charge to the transistor.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This continuation application claims priority to U.S. patent application Ser. No. 14/970,694, filed Dec. 16, 2015, which application is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates generally to circuitry and more specifically to supplying and draining charge from a transistor. 
       BACKGROUND 
       [0003]    Transistors are commonly used in circuitry as switches and to amplify an electrical signal, among other uses. Many transistors, such as field effect transistors and bipolar junction transistors, have three terminals: a gate, a source, and a drain. The source and drain terminals can be coupled to a first potential, supplied, for example by a voltage device such as a battery. The gate terminal can be connected to a second potential, supplied, for example, by a second voltage device. Supplying the second potential to the gate of the transistor applies charge to the gate. Once the applied charge increases above a threshold, the gate opens to allow current to flow through the source and drain terminals as provided by the first potential. When current is flowing through the source and drain terminals, the transistor can be referred to as “on.” When the second potential is no longer applied to the gate terminal and the charge is removed from the gate, current ceases to flow through the source and drain terminals. When current is not flowing through the source and drain terminals, the transistor can be referred to as “off.” 
         [0004]    Typically, when switching a transistor from being on to off, the charge that was applied to the gate is actively drained from the gate. For example, an electrical ground can be electrically connected to the gate which pulls charge that was applied to the gate from the gate. This charge is then lost, becoming effectively lost energy. In applications where transistors are rapidly switched between on and off states, the energy lost through draining the charge can become significant. 
       SUMMARY 
       [0005]    Generally speaking, and pursuant to these various embodiments, a circuit and method are provided that sequentially apply and/or remove charge to a transistor as part of respectively turning the gate on and off. When charge applied to a switch&#39;s gate is removed from the gate, at least part of that charge can be removed to a storage device and used again instead of being drained to a ground. For example, a capacitor can be used to provide a potential through which charge is applied to a transistor&#39;s gate. When draining that charge, the charge can be at least partially drained back to that capacitor before connecting the gate to an electric ground, which removes sufficient charge to fully turn off the transistor. So configured, the charge drained to the capacitor instead of to the ground can be reused the next time that the transistor is switched back on. These and other benefits can be understood with reference to the drawings and following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Embodiments of the invention are illustrated in the figures of the accompanying drawings in which: 
           [0007]      FIG. 1  depicts an example circuit  100  in which potential is applied to, and or drained from, a gate  116  of a transistor  114  in stages where charge is reclaimed from the gate  116  of the transistor  114 , according to some embodiments of the inventive subject matter. 
           [0008]      FIG. 2  is a chart  200  depicting potential difference across a gate of a transistor over time when the potential is applied to, and drained from, the gate of the transistor in stages, according to some embodiments of the inventive subject matter. 
           [0009]      FIG. 3  depicts an example circuit  300  including a first transistor  304 , a second transistor  306 , and a third transistor  302  coupled to a gate  318  of a driven transistor  308  in which potential can be applied to, and/or drained from, the gate  318  of the driven transistor  308  in steps and that allows for reclamation of potential from the gate  318  of the driven transistor  308 , according to some embodiments of the inventive subject matter. 
           [0010]      FIG. 4  is a flow chart of example operations for supplying charge to a gate of a transistor, according to some embodiments of the inventive subject matter. 
           [0011]      FIG. 5  is a flow chart of example operations for draining charge from a gate of a transistor, according to some embodiments of the inventive subject matter. 
       
    
    
     DETAILED DESCRIPTION 
     Introduction 
       [0012]    This section provides an introduction to some embodiments of the inventive subject matter. Embodiments of the inventive subject matter efficiently drive a transistor through a process of applying charge to, and or draining charge from, a transistor in stages. Additionally, in some embodiments, charge is reclaimed from the gate of the driven transistor during this process. Through such a process, the reclaimed charge can be used in subsequent drive cycles to at least partially drive the gate of the transistor. One such example of a circuit is depicted in  FIG. 1 . 
         [0013]      FIG. 1  depicts an example circuit  100  in which potential is applied to, and/or drained from, a gate  116  of a transistor  114  in stages where charge is reclaimed from the gate  116  of the transistor  114 , according to some embodiments of the inventive subject matter. The circuit  100  of  FIG. 1  includes a first switch  110 , a second switch  112 , a third switch  108 , and a transistor  114 . The circuit  100  also includes a first voltage device  104 , a second voltage device  106 , and a third voltage device  102 . The first switch  110  is coupled to the first voltage device  104  (having a potential difference of “V high ”) and a gate  116  of the transistor  114 . The second switch  112  is coupled to the second voltage device  106  (having a potential difference of “V low ”) and the gate  116  of the transistor  114 . The third switch  108  is coupled to the third voltage device  102  (having a potential difference of “V int ”) and the gate  116  of the transistor  114 . 
         [0014]    Each of the voltage devices (i.e., the first voltage device  104 , the second voltage device  106 , and the third voltage device  102 ) is operable to provide a potential difference (i.e., supply and/or drain charge) to the gate  116  of the transistor  114 . For example, the voltage devices can be AC voltage sources, DC voltage sources (e.g., batteries, capacitors, etc.), grounds, or any other device able to provide a potential difference. Consequently, each of the voltage devices can be used to drive the transistor  114  via the gate  116  to allow current to flow through the source and drain of the transistor  114 . Although each of the voltage devices can be used to drive the transistor  114 , in some embodiments, only the first voltage device  104  (i.e., V high ) is able to provide a potential to the gate  116  of the transistor  114  that is sufficient to allow current to flow through the source and the drain of the transistor  114 . In some embodiments, the second voltage device  106  (i.e., V low ) and the third voltage device  102  (i.e., V int ) are not able to provide a potential to the gate  116  of the transistor  114  that is sufficient to allow current to flow through the source and the drain of the transistor  114 . Furthermore, in the example provided, the potential difference of the third voltage device  102  (i.e., V it ) is greater than that of the second voltage device  106  (i.e., V low ). 
         [0015]    Because the third voltage device  102  may not able to provide a potential sufficient to allow current to flow through the source and drain of the transistor  114 , the third switch  108  can be closed (while the first switch  110  and the second switch  112  are open) to apply a potential difference of V int  to the gate  116  of the transistor  114  to partially drive the transistor. That is, the potential difference of V int  can be applied to the gate  116  of the transistor  114  without turning the transistor  114  on. In other embodiments, the third voltage device  102  may be able to provide a potential sufficient to allow current to flow through the source and drain of the transistor  114 . In either case, the third switch  108  can be considered a pre-charge switch because although closing the pre-charge switch applies some charge from the third voltage device  102  to a transistor  114 , the charge is less than the final charge applied to the transistor  114 . Next, the third switch  108  can be opened and the first switch  110  closed. Closing the first switch  110  applies a potential difference of V high  to the gate  116  of the transistor  114 . Regardless of whether the third voltage device  102  is able to provide a potential sufficient to allow current to flow through the source and drain of the transistor  114 , the potential difference V high  is sufficient to allow current to flow through the source and drain of the transistor  114 . Because the potential difference of V high  is sufficient to allow current to flow through the source and drain of the transistor  114 , when the potential difference of V high  is applied to the gate  116  of the transistor  114 , the transistor  114  is turned on. Thus, in this sense, the first switch  110  can be considered an “on switch” because closing the on switch applies a charge from the first voltage device  104  to a transistor  114  that is sufficient to allow current to flow through the transistor  114 . 
         [0016]    Dependent upon the componentry of the circuit, when the first switch  110  is opened, the flow of current through the source and drain of the transistor  114  may stop. That is, in some embodiments, opening the first switch  110  may cause the transistor  114  to turn off, while in other embodiments the transistor  114  may not turn off until charge is actively drained from the gate  116  of the transistor  114 . Regardless of whether current is flowing through the source and drain of the transistor  114  after the first switch  110  is opened, there still exists a potential difference across the gate  116  of the transistor  114  (i.e., charge accumulated on the gate  116  of the transistor  114 ). In some embodiments, the third voltage device  102  is operable to drain this potential difference from the gate  116  of the transistor  114 . In such embodiments, the third switch  108  is closed while the first switch  104  and the second switch  106  remain open. If the potential of the third voltage device  102  is less than the potential difference that exists across the gate  116  of the transistor  114 , the third voltage device  102  will drain charge from the gate  116  of the transistor  114 . After draining charge from the gate  116  of the transistor  114  to the third voltage device  102 , any remaining charge can be drained to the second voltage device  106 . Any remaining charge can be drained to the second voltage device  106  by opening the third switch  108  and then closing the second switch  112 . In this sense, the second switch  112  can be considered an off switch because closing the off switch allows any charge remaining on the transistor  114  to dissipate, fully closing off movement of current through the transistor  114 . 
         [0017]    Although the above text describes the pre-charge as being applied by only one voltage device (i.e., the third voltage device  102 ), certain embodiments are not so limited. In some embodiments, multiple voltage devices can be used to apply the pre-charge. For example, as depicted in  FIG. 1  with dashed lines, two additional voltage devices (i.e., a fourth voltage device  122  and a fifth voltage device  124 ) can be used. In such embodiments, a fifth switch  120  can be closed first, applying a potential difference of V int-2  to the gate  116  of the transistor  114 . Once the potential across the gate  116  of the transistor  114  has stabilized, the fifth switch  120  is opened and the fourth switch  118  is closed. Closing the fourth switch  118  applies a potential difference of V int-1  to the gate  116  of the transistor  114 . Once the potential difference across the gate  116  of the transistor  114  has stabilized, the fourth switch  118  can be opened and the third switch  108  closed. As can be seen, any number of voltage devices can be used as pre-charge voltage devices. For ease of reading, portions of this specification will refer to only a single pre-charge switch and pre-charge voltage device. However, it should be noted that embodiments of the inventive subject matter can utilize a greater number of pre-charge switches and pre-charge voltage devices. 
         [0018]    Although the discussion of  FIG. 1  describes driving a transistor via a gate of the transistor, in some embodiments, the transistor can be driven by terminals other than the gate. For example, in some embodiments, the transistor can be driven by a back gate (or any other terminal) in lieu of, or in addition to, the gate. 
         [0019]    While  FIG. 1  depicts an example circuit for increased efficiency in driving a gate of a transistor,  FIG. 2  depicts potential difference across a gate of a transistor in an example circuit, such as that described in  FIG. 1 . 
         [0020]      FIG. 2  is a chart  200  depicting potential difference across a gate of a transistor over time when the potential is applied to, and drained from, the gate of the transistor in stages, according to some embodiments of the inventive subject matter. The potential difference across the gate of the transistor (i.e., voltage across the gate of the transistor) is denoted as “V gate ” and is depicted on the Y-axis of the chart. Time is depicted on the X-axis of the chart. As described in the discussion of  FIG. 1 , the gate of the transistor is coupled to three voltage devices: a first voltage device having a potential difference of V high , a second voltage device having a potential difference of V low , and a third voltage device having a potential difference of V int . At a time before t=0, V gate ≦V low  and the first switch, second switch, and third switch are open. 
         [0021]    At t=0, the third switch is closed and the potential difference of V int  is applied to the gate of the transistor. During the first time period  202 , the potential difference across the gate of the transistor and the potential difference of the third voltage device move toward an equilibrium such that V gate =V int  at the end of the first time period  202 . At the end of the first time period  202 , the third switch is opened. 
         [0022]    At the beginning of the second time period  204 , the first switch is closed. When the first switch is closed, the potential difference of V high  is applied to the gate of the transistor. During the second time period,  204 , the potential difference across the gate of the transistor and the potential difference of the first voltage device move toward an equilibrium such that V gate =V high  at the end of the second time period  204 . At the end of the second time period  204  (i.e., when V gate =V high ), the potential difference across the gate of the transistor is sufficient to allow current to flow through the source and drain of the transistor (i.e., the transistor is “on”). It should be noted that in some embodiments, V high  may be large enough (and the source/drain voltage low enough) that V high  is greater than the minimum voltage necessary to achieve the threshold voltage for the transistor. In such embodiments, V gate  may never reach V high . Nevertheless, assuming that V high  is sufficient to allow current to flow through the drain and source of the transistor, while V gate  may not be equal to V high  at the end of the end of the second time period  204 , V gate  will at least be great enough that the threshold voltage is achieved. Whether equilibrium is reached, the potential difference across the gate of the transistor remains sufficient to allow current to flow through the source and drain of the transistor so long as the first switch is closed (assuming that the first voltage device can continuously provide the requisite potential difference). This state lasts for the duration of the third time period  206 . At the end of the third time period  206 , the first switch is opened. 
         [0023]    After the first switch is opened, the potential difference across the gate of the transistor may be nonzero. According to some embodiments of the inventive subject matter, just as the potential difference across the gate of the transistor is applied in steps, the potential difference across the gate of the transistor can be drained in steps. For example, after the first switch is opened, the third switch can be closed. As depicted in  FIG. 2 , the third switch is closed at the beginning of the fourth time period  208 . During the fourth time period  208 , charge is drained from the gate of the transistor to the third voltage device. Put simply, during the fourth time period  208  the potential difference across the gate of the transistor and the potential difference of the third voltage device move toward an equilibrium such that V gate =V int  at the end of the fourth time period  208 . At the end of the fourth time period  208 , the third switch is opened. 
         [0024]    At the beginning of the fifth time period  210 , the second switch is closed. During the fifth time period, charge is drained from the gate of the transistor to the second voltage device. In some embodiments, the second voltage device is a ground. In such embodiments, all (or a majority of) the remaining charge is drained to the second voltage device and the potential difference across the gate of the transistor reaches zero at the end of the fifth time period  210 . 
       Example Circuit 
       [0025]    While  FIGS. 1 and 2  provide introductory information about a generic circuit having multiple switches and voltage devices used to drive the gate of a transistor,  FIG. 3  and the accompanying text describe a more specific exemplary circuit in which a number of transistors are used as switches to control application of potential differences from multiple voltage devices to drive the gate of a transistor. 
         [0026]      FIG. 3  depicts an example circuit  300  including a first transistor  304 , a second transistor  306 , and a third transistor  302  coupled to a gate  318  of a driven transistor  308  in which potential can be applied to, and/or drained from, the gate  318  of the driven transistor  308  in steps and that allows for reclamation of potential from the gate  318  of the driven transistor  308 , according to some embodiments of the inventive subject matter. A source of the first transistor  304  is coupled to a first voltage device  316 , the drain of the first transistor  304  is coupled to a gate  318  of the switch transistor  308 , and a gate of the first transistor is coupled to a controller  310 . A source of the second transistor  306  is coupled the gate  318  of the driven transistor  308 , a drain of the second transistor  306  is coupled to a second voltage device (in this example, ground), and a gate of the second transistor  306  is coupled to the controller  310 . A source of the third transistor  302  is coupled to a third voltage device  320  (e.g., a capacitor, as depicted in  FIG. 3 ), a drain of the third transistor  302  is coupled to the gate  318  of the driven transistor, and a gate of the third transistor  302  is coupled to the controller  310 . The third voltage device  320  is used to both apply charge to, and drain charge from, the gate  318  of the driven transistor  308 . Consequently, charge remaining on the gate  318  of the driven transistor  308  that would otherwise be drained to ground is reclaimed by the third voltage device  320  and applied to the gate  318  of the driven transistor  308  in subsequent cycles to aid in driving the gate  308  of the driven transistor  308 . 
         [0027]    When applying a potential difference to the gate  318  of the driven transistor  308 , the controller  310  applies a potential difference to the gate of the third transistor  302  so as to allow current from the third voltage device  320  to flow through the source and drain of the third transistor  302  and to the gate  318  of the driven transistor  308 . Put simply, the controller  310  turns the third transistor  302  on. After the third voltage device  320  has applied its potential difference to the gate  318  of the driven transistor  308 , the controller  310  turns the third transistor  302  off. In one embodiment, the controller  310  can monitor the potential of the third voltage device  320  and turn the third transistor  302  off when the third voltage device  320  has been discharged. Additionally or alternatively, the controller  310  can monitor the potential difference across the gate  318  of the driven transistor  308 . For example, a sensor  322  can be electrically coupled to the gate  318  of the driven transistor  308  and in communication with the controller  310 . In such embodiments, the controller  310  can monitor the sensor  322  to determine when the third transistor  302  should be turned off. For example, the controller  310  can turn the third transistor  302  off when the potential difference across the gate  318  of the driven transistor  318  has stabilized. In the embodiment depicted in  FIG. 3 , the potential difference of the third voltage device  320  is insufficient to allow current to flow through the source and drain of the driven transistor  308 . 
         [0028]    After the third transistor  302  is turned off, the controller  310  applies a potential difference to the gate of the first transistor  304  to turn the first transistor  304  on. When the first transistor  304  is on, the potential difference from the first voltage device  316  is applied to the gate  318  of the driven transistor  308 . In the embodiment depicted in  FIG. 3 , the potential difference of the first voltage device  316  is sufficient to allow current to flow through the source and drain of the driven transistor  308 . The controller  310  continues to provide a potential difference to the gate of the first transistor  304  until it is time to turn the driven transistor  308  off. When it is time to turn the driven transistor  308  off, the controller  310  ceases providing a potential difference to the gate of the first transistor  304 . That is, the controller  310  turns the first transistor  304  off. 
         [0029]    After turning the first transistor  304  off, the controller  310  provides a potential difference to the gate of the third transistor  302 . This turns the third transistor  302  on. If the potential difference across the gate  318  of the driven transistor  308  is greater than the potential difference of the third voltage device  320  (i.e., the potential difference across the gate  318  of the driven transistor  308  is greater than the potential difference across plates of the capacitor), charge is drained from the gate  318  of the driven transistor  308  to the third voltage device  320 . This charge is reclaimed by the third voltage device  320  and can be used in subsequent drive cycles to at least partially drive the gate  318  of the driven transistor  308 . After the third voltage device  320  drains the charge from the gate  318  of the driven transistor  308 , the controller  310  turns the third transistor  302  off. The controller  310  can monitor the potential of the third voltage device  320  and/or the potential difference across the gate  318  of the driven transistor  308  while charge is draining from the gate  318  of the driven transistor  308  to the third voltage device  320 . For example, the controller  310  can monitor the potential difference across the gate  318  of the driven transistor  308  via the sensor  322 . In some embodiments, the controller  310  turns the third transistor  302  off when the potential difference of the third voltage device  320  is in equilibrium with the potential difference across the gate  318  of the driven transistor  308 . 
         [0030]    After turning off the third transistor  302 , the controller  310  applies a potential difference to the gate of the second transistor  306  to turn the second transistor  306  on. When the second transistor  306  is on, some or all of the charge remaining on gate  318  of the driven transistor  308 , if any, can be drained to the second voltage device. In the embodiment depicted in  FIG. 3 , the second voltage device is a ground. 
       Example Operations 
       [0031]    While  FIG. 3  depicts an example circuit, according to some embodiments of the inventive subject matter,  FIGS. 4 and 5  are flow charts of example operations for supplying charge to, and draining charge from, a transistor. Specifically,  FIG. 4  is a flow chart of example operations for supplying charge to a transistor in stages and  FIG. 5  is a flow chart of example operations for draining charge from a transistor in stages. The flow charts of  FIGS. 4 and 5  are based on a circuit similar to those presented in  FIGS. 1 and 3 . For example, the flow charts of  FIGS. 4 and 5  are based on a circuit having a first switch, a second switch, a third switch, and a driven transistor. The first switch is coupled to a first voltage device (having a potential difference V high ) and a gate of the transistor. The second switch is coupled to a second voltage device (having a potential difference V low ) and the gate of the transistor. The third switch is coupled to a third voltage device (having a potential difference V int ) and the gate of the transistor. The potential difference V high  is greater than the potential difference V int , and the potential difference V int  is greater than the potential difference V low . The potential difference V high  is great enough that, when applied to the gate of the transistor, current is able to flow through the drain and supply of the transistor. 
         [0032]      FIG. 4  is a flow chart of example operations for supplying charge to a gate of a transistor, according to some embodiments of the inventive subject matter. At the beginning of the flow of  FIG. 4 , all three switches are open. The flow begins at block  402 . 
         [0033]    At block  402 , a third switch is closed. The third switch is coupled to the gate of the transistor and the third voltage device. The third voltage device has a potential difference of V int . Closing the third switch allows charge to flow from the third voltage device to the gate of the transistor. In some embodiments, charge flows to the gate of the transistor from the third voltage device until the potential difference across the gate of the transistor is in equilibrium with the potential difference of the third voltage device. For example, charge can flow from the third voltage device to the gate of the transistor until the potential difference across the gate of the transistor reaches V int . The flow continues at block  404 . In some embodiments, (e.g., as depicted in  FIG. 3  and described in the associated text), the potential difference across the gate of the transistor can be monitored. For example, a sensor can be used to monitor the potential difference across the gate of the transistor. In such embodiments, the flow proceeds from block  402  to block  408  (before proceeding to block  404 ). At block  408 , the potential difference across the gate of the transistor is monitored. The flow continues at decision diamond  410 . At decision diamond  410 , if the potential difference across the gate of the transistor has not stabilized, the flow continues at block  408  where the potential difference across the gate of the transistor is monitored. If the potential difference across the gate of the transistor has stabilized, the flow continues at block  404 . 
         [0034]    At block  404 , the third switch is opened. When the third switch is opened, charge ceases to flow between the third voltage device and the gate of the transistor. Assuming no loses, the potential difference across the gate of the transistor remains V int  after the third switch is opened. Because the potential difference V int  is not sufficient to allow current to flow through the source and drain of the transistor, the transistor remains off. The flow continues at block  406 . 
         [0035]    At block  406 , the first switch is closed. The first switch is coupled to the gate of the transistor and the first voltage source. The first voltage source has a potential difference of V high . Closing the first switch allows charge to flow from the first voltage device to the gate of the transistor. Once the potential difference across the gate of the transistor is sufficient to allow current to flow through the source and drain of the transistor, the transistor turns on. In some embodiments, the potential difference across the gate of the transistor may reach V high , although this is not required. 
         [0036]    In some embodiments, after block  406 , the flow ends. However, in other embodiments, a cyclical on and off routine for the transistor may be desired. In such embodiments, the example operations of  FIG. 4  can be followed by the example operations presented in  FIG. 5 , which turn the transistor off. 
         [0037]      FIG. 5  is a flow chart of example operations for draining charge from a gate of a transistor, according to some embodiments of the inventive subject matter. The flow begins at block  502 . 
         [0038]    At block  502 , the first switch is opened. As previously discussed, the first switch is coupled to a first voltage device and the gate of the transistor such that when the first switch is closed, charge can flow from the first voltage device to the gate of the transistor. The flow continues at block  504 . 
         [0039]    At block  504 , the third switch is closed. Although the first switch is opened at block  502 , the potential difference across the gate of the transistor is nonzero. When the third switch is closed, charge can flow between the gate of the transistor and the third voltage device. If the potential difference across the gate of the transistor is greater than the potential difference of the third voltage device, charge can flow from the gate of the transistor to the third voltage device. The charge on the gate of the transistor is being reclaimed by the third voltage device. This charge can be used in subsequent drive cycles to at least partially drive the gate of the transistor. The flow continues at block  506 . In some embodiments, (e.g., as depicted in  FIG. 3  and described in the associated text), the potential difference across the gate of the transistor can be monitored. For example, a sensor can be used to monitor the potential difference across the gate of the transistor. In such embodiments, the flow proceeds from block  504  to block  510  (before proceeding to block  506 ). At block  510 , the potential difference across the gate of the transistor is monitored. The flow continues at decision diamond  512 . At decision diamond  512 , if the potential difference across the gate of the transistor has not stabilized, the flow continues at block  510  where the potential difference across the gate of the transistor is monitored. If the potential difference across the gate of the transistor has stabilized, the flow continues at block  506 . 
         [0040]    At block  506 , the third switch is opened. When the third switch is open, current cannot flow between the third voltage device and the gate of the transistor. The flow continues at block  508 . 
         [0041]    At block  508 , the second switch is closed. When the second switch is closed, the second voltage device is coupled to the gate of the transistor. Accordingly, any charge remaining on the gate of the transistor can drain to the second voltage device. In some embodiments, the potential difference of the third voltage device is regulated by the circuit. For example, if the third voltage device currently has a voltage of zero, during the off cycle (i.e., during the example operations depicted in  FIG. 5 ) when the third switch is closed, charge can flow from the gate of the transistor up to the capacity of the third voltage device (i.e., V int ). At the other extreme, if the potential difference of the third voltage device is equal to, or above, V int , any excess charge that cannot drain from the gate of the transistor to the third voltage device is drained to the second voltage device. For example, in some embodiments, any excess charge can drain to ground via the second switch. After block  508 , the flow ends. However, in embodiments described above in which the transistor is cycled between on and off states, the flow can continue with the example operations of  FIG. 4 . 
       General 
       [0042]    Although the figures and description describe three switches/transistors and three voltage devices coupled to the gate of a driven transistor, embodiments are not so limited. For example, the third switch/transistor and third voltage device can be replaced by two or more switches/transistors and voltage devices. In such embodiments, each of the two or more switches/transistors and voltage devices would be coupled to the gate of the driven transistor. Each of the two or more voltage devices would have a capacity that is insufficient to allow current to flow through the source and drain of the driven transistor. Consequently, each of the two or more voltage devices would be able to partially drive the gate of the driven transistor. Likewise, each of the two or more voltage devices would be able to reclaim/drain charge from the gate of the driven transistor. 
         [0043]    Although  FIG. 3  depicts a single controller coupled to the gates of the first, second, and third transistors, embodiments are not so limited. In some embodiments, each of the first, second, and third transistors may have separate and/or independent controllers, or two of the transistors may have a common controller. Additionally, in some embodiments, the controller may be able to monitor the potential difference of one or more of the first, second, or third voltage device and/or the gate of the driven transistor. In such embodiments, the controller can make determinations as to when each transistor/switch should be on/closed or off/open based on a potential difference reading from one or more of the first, second, or third voltage devices and/or the gate of the driven transistor. Additionally, in some embodiments, the controller may base such a determination on time. 
         [0044]    In some embodiments, the driven transistor is transistor that is designed to operate under significant power levels. For example, the transistor can be a power MOSFET. Because of the high power levels under which the driven transistor operates, efficiency gains realized from recovering charge from the gate of the driven transistor can be significant.