Patent Publication Number: US-11646689-B2

Title: External adjustment of a drive control of a switch

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/570,419, filed Sep. 23, 2019, currently pending. U.S. application Ser. No. 16/570,419 is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a switch controller for a semiconductor switch, and more specifically to a switch controller which may be controlled by a user or a system controller. 
     2. Discussion of the Related Art 
     Household and industrial appliances such as ventilation fans, cooling systems, refrigerators, dishwashers, washer/dryer machines, and many other white products/goods typically utilize electric motors that transfer energy from an electrical source to a mechanical load. Electrical energy for driving the electric motors is provided through a drive system, which draws electrical energy from an electrical source (e.g., from an ac low frequency source). The electrical energy received from the electrical source is processed through a power converter, and converted to a desired form of electrical energy that is supplied to the motor to achieve the desired mechanical output. The desired mechanical output of the motor may be for example the speed of the motor, the torque, or the position of a motor shaft. 
     Motors and their related circuitries such as motor drives represent a large portion of utility network loads. The functionality, efficiency, size, and price of motor drives are challenging and are competitive factors that suppliers of these products consider. The function of a power converter in a motor drive includes providing the input electrical signals to the motor such as voltage, current, frequency, and phase for a desired mechanical output load motion (e.g., spin/force) on the motor shaft. The power converter in one example may be an inverter transferring a dc input to an ac output of desired voltage, current, frequency, and phase and generally includes one or more switches to control the transfer of energy. Each switch is controlled by a switch controller for the power converter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG.  1    is a functional block diagram of a system with a system controller which adjusts the drive characteristics of a switch in accordance with embodiments of the present disclosure. 
         FIG.  2 A  is a timing diagram of various waveforms of the system of  FIG.  1    during a switch turn on event, in accordance with embodiments of the present disclosure. 
         FIG.  2 B  is another timing diagram of various waveforms of the system of  FIG.  1    during a switch turn off event, in accordance with embodiments of the present disclosure. 
         FIG.  3    is a functional block diagram of the system controller and switch controller of  FIG.  1    illustrating example commands from the system controller to adjust the switch, in accordance with embodiments of the present disclosure. 
         FIG.  4    is a functional block diagram of a switch controller illustrating receiving commands from a user, in accordance with embodiments of the present disclosure. 
         FIG.  5 A  is a functional block diagram of a motor driver with a system controller to adjust one or more switches of various half-bridge modules, in accordance with embodiments of the present disclosure. 
         FIG.  5 B  is a functional block diagram of the system controller and half-bridge module of  FIG.  5 A , in accordance with embodiments of the present disclosure. 
         FIG.  6 A  is a functional block diagram of one example of a power converter in a half-bridge configuration with a system controller to adjust one or more switches, in accordance with embodiments of the present disclosure. 
         FIG.  6 B  is a functional block diagram of another example of a power converter in a half-bridge configuration with a system controller to adjust one or more switches, in accordance with embodiments of the present disclosure. 
         FIG.  6 C  is a functional block diagram of the system controller, interface, and switch controller of  FIGS.  6 A and  6 B , in accordance with embodiments of the present disclosure. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention. 
     Reference throughout this specification to “one embodiment”, “an embodiment”, “one example” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, “one example” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or subcombinations in one or more embodiments or examples. Particular features, structures or characteristics may be included in an integrated circuit, an electronic circuit, a combinational logic circuit, or other suitable components that provide the described functionality. In addition, it is appreciated that the figures provided herewith are for explanation purposes to persons ordinarily skilled in the art and that the drawings are not necessarily drawn to scale. 
     In the context of the present application, when a transistor is in an “off state”, or “off”, the transistor does not substantially conduct current. Conversely, when a transistor is in an “on state”, or “on”, the transistor is able to substantially conduct current. By way of example, in one embodiment, a high-voltage transistor comprises an N-channel metal-oxide-semiconductor field-effect transistor (NMOS) with the high-voltage being supported between the first terminal, a drain, and the second terminal, a source. In another embodiment, a high-voltage transistor comprises an insulated-gate bipolar transistor (IGBT) with the high-voltage being supported between the first terminal, a collector, and the second terminal, an emitter. For purposes of this disclosure, “ground” or “ground potential” refers to a reference voltage or potential against which all other voltages or potentials of an electronic circuit or integrated circuit (IC) are defined or measured. In one example, the transistor or switch may also be referred to as a conductivity modulated device which may be controlled to conduct various amounts of current. 
     Inverters with half-bridge switching configurations are commonly used with motor drives. Instead of implementing a full bridge switching configuration, utilizing a half-bridge switching circuit with low-side and high-side control blocks (also referred to as a low-side switch controller and high-side switch controller) inside one single package (e.g., a module) allows support for multiphase inverters, such as single-phase and 3-phase inverters, that provide increased layout flexibility as well as simplified thermal management for each module. Utilization of a modular half-bridge circuit structure for a motor drive inverter may reduce overall system cost because of a variety of reasons. Each switch of the half-bridge circuit structure is generally controlled by a switch controller which in turn is controlled by a system controller. The switches are controlled by the switch controllers to regulate the energy delivery in response to signals received from the system controller and/or a user. 
     Conductivity modulated devices, such as transistors, maybe be utilized for the one or more switches in a power converter, such as an inverter. Typical losses related to conductivity modulated devices are conduction losses and switching losses (also referred to as crossover losses). When the conductivity modulated device conducts current, the voltage across the conductivity modulated device in response to the current through the conductivity modulated device generates conduction loss. Switching losses are generally associated with the losses, which occur while the conductivity modulated device is transitioning between an ON state and an OFF state or vice versa. 
     In general, a conductivity modulated device takes time to transition from an ON state to an OFF state and vice versa in response to a drive signal that is provided to a control terminal of the conductivity modulated device. The control terminal of a field effect transistor (FET), insulated-gate bipolar transistor, or a SiC based transistor is generally referred to as the gate terminal. The control terminal of a bipolar junction transistor (BJT) is generally referred to as the base terminal. The time for the conductivity modulated device to transition from an OFF state to an ON state may be referred to as the turn-on time whereas the time for the conductivity modulated device to transition from an ON state to an OFF state may be referred to as the turn-off time. Switching/crossover losses occur during this transition time, and they may be lessened by reducing the duration of the turn-on and turn-off times. In addition, shorter turn-on and turn-off times generally correspond to reduced temperature of the conductivity modulated device (and therefore the system). However, shorter turn-on and turn-off times also generally correspond with increased system level electromagnetic interference (EMI). As such, there is generally a trade-off between EMI, switching losses, and temperature. 
     The duration of the turn-on and turn-off time of a conductivity modulated device is related to the characteristics of the drive signal provided to the control terminal of the conductivity modulated device. It should be appreciated that conductivity modulated devices may be voltage controlled or current controlled at the gate terminal. Voltage controlled conductivity modulated devices typically would be controlled with a voltage source and a drive resistor (also referred to as a gate resistor) and the drive current for the conductivity modulated device is determined by the voltage drop across the control resistor. In other words, the value of the voltage source controls the drive characteristics of the conductivity modulated device. Current controlled conductivity devices could include a current source and the drive current for the conductivity modulated device is determined by the charge delivered by the current source. In other words, the value of the current source controls the drive characteristics of the conductivity modulated device. In one example, the drive signal is a current characterized by its magnitude, direction, and rate of change. The characteristics of the drive current determine the electric charge that passes through the control terminal of the conductivity modulated device, and it is the electric charge that ultimately modulates the conductivity of the conductivity modulated device. Drive current of higher magnitude corresponds to more charge in less time at the control terminal, resulting in shorter turn-on and/or turn-off time and lower switching/crossover losses. There may be conditions in a system, such as a motor drive, where the system controller could determine a need to deliver more power temporarily to a load without exceeding a maximum allowable temperature of the switching devices. The controller can reduce the turn-on and/or turn-off times of the switching devices to provide the temporary increase in power. Further, the system can be configured to tolerate higher electrical noise for the time the higher power is required. In embodiments of the present invention, the characteristics of a driver for a conductivity modulated device may be adjusted by a system controller and/or a user through the switch controller and/or a dedicated hardware sensor. The adjusted drive could increase or decrease the power delivered to the load within the bounds of other system parameters. In other words, a user and/or a system controller could adjust the drive characteristics of a conductivity modulated device to meet changing requirements. This could be accomplished by a switch controller which includes a drive characteristic control which can receive a drive characteristic signal representative of one or more drive characteristics of the conductivity modulated device. Further, in one embodiment, the conductivity modulated device may be adjusted in real time by a system controller and/or a user and as such, the drive characteristics of a conductivity modulated device may be adjusted on demand to meet changing requirements. 
       FIG.  1    illustrates a system  100  with a system controller  102  which adjusts the drive characteristics of a conductivity modulated device  106 , in accordance with embodiments of the present disclosure. System  100  includes a system controller  102  and a power switching array  104 . The power switching array  104  can include one or more conductivity modulated devices. As shown, the power switching array  104  includes conductivity modulated devices  106 ,  108 ,  110 , and  112 . The conductivity modulated devices  106 ,  108 ,  110 , and  112  are illustrated as coupled together by dotted lines to emphasize that the power switching array  104  could be coupled in various configurations. For example, the conductivity modulated devices in the power switching array  104  could be representative of transistors of one or more inverters with half-bridge switching configurations or other power converter topologies. In another example, the conductivity modulated devices in the power switching array  104  could be representative of one or more inverter transistors with full-bridge switching configurations. 
     Each conductivity modulated device  106 ,  108 ,  110 , and  112  is controlled by a switch controller, however for ease of explanation, only the switch controller  114  for conductivity modulated device  106  is illustrated. The voltage across the conductivity modulated device  106  is shown as voltage V DS    150  (also referred to as drain-source voltage V DS    150 ) while the conducted current of the conductivity modulated device  106  is current I D    148  (also referred to as drain current I D    148 ). In the example shown, the conductivity modulated device  106  is a current controlled device. The control current for the conductivity modulated device  106  is shown as current I G    146  (also referred to as gate current I G    146 ). The conductivity modulated device may be a transistor, such as a metal-oxide-semiconductor field-effect transistor (MOSFET), bipolar transistor, injection enhancement gate transistors (IEGT), insulated-gate bipolar transistor (IGBT) and gate turn-off thyristor (GTO). Further, the conductivity modulated device may be based on silicon (Si), gallium nitride (GaN), or silicon carbide (SiC) semiconductors. 
     The system controller  102  couples to the switch controller  114  through interface  120 . In one example, the interface  120  galvanically isolates the system controller  102  from the switch controller  114 . In another example, the interface  120  does not galvanically isolate the system controller  102  from the switch controller  114 . As shown, the system controller  102  receives a sense signal  116  representative of a power event. In one example, the power event may be an indication to the system controller  102  to provide increased power to a load, such as a motor. In one embodiment, the sensed power event may indicate to the system controller  102  to adjust the drive characteristics of the conductivity modulated device  106 . In on example, the system controller  102  adjusts the drive characteristics of the conductivity modulated device  106  by increasing the magnitude of the drive current (e.g. gate current I G    146 ) of the conductivity modulated device  106 . Further, in one embodiment the system controller  102  adjusts the drive characteristics of the conductivity modulated device  106  by increasing the magnitude of the drive current during either the turn-on time, the turn-off time, or both. In one example, the drive current may also be referred to as the drive strength with greater magnitude of drive currents corresponding to greater drive strength. Or in other words, the power event may indicate to the system controller  102  to decrease turn-on time and/or turn-off time by increasing the magnitude of the gate current I G    146  to decrease the rise time and/or fall time of the drain current I D    148  of the conductivity modulated device  106 . In some embodiments, the power event may indicate to the system controller  102  to decrease turn-on time and/or turn-off time by increasing the magnitude of the gate current I G    146  to decrease the fall time and/or rise time of the drain-source voltage V DS    150 . For example, the system controller  102  decreases turn-on time and/or turn-off time by modulating the value of currents I EN  and I DIS  of current sources  140  and  144 . One example of a sensed power event which would increase the magnitude of the gate current I G    146  could include an outdoor air conditioning fan during startup that may have to overcome possible wind blowing conditions. Another example of a sensed power event could include a dishwasher water pump which has to pump a large amount of water in case the drain for the dishwasher has unexpectedly flooded. A further example of a sensed power event could include a refrigerator during initial installation to cool itself to the desired temperature, also known as a cool-down period. 
     In the embodiment shown in  FIG.  1   , system controller  102  outputs a command signal  118  to the switch controller  114 . In one example, the command signal  118  is outputted in response to the received sense signal  116 . The command signal  118  is representative of one or more commands for the switch controller  114  by the system controller  102  and vice versa. In one example, the communication between the system controller  102  and the switch controller  114  is bidirectional. Example commands communicated by and/or to the system controller  102  could include a “status inquiry” command in which the system controller  102  pings the switch controller  114  for the “status” of the switch controller  114 , such as the information stored in a status register of the switch controller. Another example command communicated with the system controller  102  could include a “fault” command in which the switch controller  114  has sensed a fault condition (such as overcurrent, overvoltage, overheating, etc) in the system  100  and communicates the fault to the system controller  102 . In general, the switch controller  114  responds to a sensed fault by turning off the conductivity modulated device  106 . A further example command communicated by the system controller  102  could include a “reset” command in which the switch controller  114  is restarted or turned on. In embodiments of the present disclosure, the system controller  102  communicates an adjustment command representative of adjusting one or more drive characteristics of conductivity modulated device  106 . An example drive characteristic includes the magnitude of the gate current I G    146  (e.g. drive strength) which is related to the rise time and/or fall time of the drain current I D    148  and the drain-source voltage V DS    150 . The magnitude of the gate current I G    146  may be varied by modulating the values of currents I EN  and I DIS  by current sources  140  and  144 . Another example drive characteristic could include the duration which the conductivity modulated device  106  is driven by the gate current I G    146 . A further example drive characteristic could include the frequency which the conductivity modulated device  106  is driven by the gate current I G    146 . For example, the gate current I G    146  could be a pulsed signal which may be pulse width modulated (PWM) or pulse frequency modulated (PFM) in response to the command signal  118 . In some embodiments, the command signal  118  could be representative of driving the conductivity modulated device  106  at a first magnitude of gate current I G    146  or a second magnitude of gate current I G    146 , where the second magnitude is greater than the first magnitude. The command signal  118  could be a voltage signal or a current signal. In one example, the command signal  118  could be representative of a digital word. Further, the system controller  102  could apply coding to the command signal  118 . 
     The interface  120  receives the command signal  118  and interprets/demodulates the command signal  118  to output the drive characteristic signal  128 . In embodiments, the drive characteristic signal  128  is representative of one or more drive characteristics for the conductivity modulated device  106 . The switch controller  114  also includes a drive characteristic control  122  and drive elements  124  and  126 . As shown, the interface  120  is coupled to and outputs the drive characteristic signal  128  to the drive characteristic control  122 . Drive characteristic control  122  is coupled to drive elements  124 ,  126  and controls drive elements  124 ,  126  to enable or disable (i.e. turn on or turn off) the conductivity modulated device  106 . In embodiments, the drive characteristic control  122  controls drive elements  124 ,  126  in response to the drive characteristic signal  128 . Further, the drive characteristic control  122  controls drive elements  124 ,  126  to enable or disable (i.e. turn on or turn off) the conductivity modulated device  106  with the one or more drive characteristics provided by the drive characteristic signal  128 . As shown in  FIG.  1   , the drive characteristic control  122  outputs an enable signal EN  130  and disable signal DIS  134  to turn on or turn off the conductivity modulated device  106 . 
     In one example, the enable signal EN  130  and the disable signal DIS  134  could be outputted in response to the command signal  118  from the system controller  102  via the drive characteristic signal  128 . In another example, the enable signal EN  130  and the disable signal DIS  134  could be outputted in response to one or more signals, separate from command signal  118 , received by the switch controller  114 . Further, the drive characteristic control  122  could receive the one or more signals, separate from the command signal  118 , and outputs the applicable enable signal EN  130  or disable signal DIS  134  to turn on or turn off the conductivity modulated device  106   
     As will be discussed further, in one embodiment the drive characteristic control  122  adjusts the drive strength (e.g. drive current) of the conductivity modulated device  106  by adjusting the current provided by drive elements  124 ,  126 . As shown, the drive characteristic control  122  outputs the enable trim signal  132  and the disable trim signal  136  to the drive elements  124  and  126 , respectively, which adjusts the magnitude of the gate current I G    146  and the subsequent turn-on and turn-off times of the conductivity modulated device  106 . 
     Drive element  124  includes switch  138  and current source  140  with current I EN  to enable the conductivity modulated device  106 . Current source  140  is coupled to the conductivity modulated device  106  to provide current to the control terminal (e.g. gate). Drive element  126  includes switch  142  and current source  144  with current I DIS  to disable the conductivity modulated device  106 . Current source  144  is coupled to the conductivity modulated device  106  to sink current from the control terminal (e.g. gate). In some embodiments, current sources  140  and  144  are trimmable current sources in which the magnitudes of current I EN  and current I DIS  are responsive to the drive characteristic signal  128 . 
     Drive characteristic control  122  is coupled to output an enable signal EN  130  and an enable trim signal  132  to drive element  124 . To enable the conductivity modulated device  106  to conduct (i.e. turn on), the drive characteristic control  122  outputs the enable signal EN  130  to turn on the switch  138  and turns off switch  140 . The current I EN  is sourced to the control terminal of the conductivity modulated device  106  and the magnitude of the gate current I G    146  of the conductivity modulated device  106  is substantially equal to current I EN . In one example, the enable signal EN  130  may be a rectangular pulse waveform with varying lengths of logic high and logic low sections. Logic high sections could correspond to the switch  138  being on while logic low sections could correspond to the switch  138  being off (or vice versa). In one embodiment, the drive characteristic control  122  outputs the enable signal EN  130  in response to a signal separate from the command signal  118  and the drive characteristic signal  128 . Drive characteristic control  122  outputs an enable trim signal  132  to adjust the value of the current I EN  and therefore the magnitude of the gate current I G    146 . In embodiments of the present disclosure enable trim signal  132  is responsive to the drive characteristic signal  128 . The enable trim signal  132  may be a voltage or current signal, with the magnitude of the current I EN  corresponding to the value of the enable trim signal. In one example of the present disclosure, the enable trim signal  132  can trim the value of the current I EN  to a first current value I 1  or a second current value I 2 , however it should be appreciated that the enable trim signal  132  can trim the value of the current I EN  to a plurality of current values. The magnitude of the gate current I G    146  controls the fall time of the drain-source voltage VDS  150  and the turn-on time of the conductivity modulated device  106  when switch  138  is on and current source  140  is providing current to the conductivity modulated device  106  while switch  142  is off. As such, the system controller  102  can adjust the drive characteristics, such as the rise time of the drain current I D    148  and/or the fall time of the drain-source voltage V DS    150  and the turn-on time, of a conductivity modulated device  106 . 
     Similarly, the drive characteristic control  122  is configured to output a disable signal DIS  134  and disable trim signal  136  to drive element  126 . To disable the conductivity modulated device  106  from conducting (i.e. turn off), the drive characteristic control  122  outputs the disable signal DIS  134  to turn on the switch  142  and turns off switch  138 . The amount of current sinked from the control terminal of the conductivity modulated device  106  is limited by the value of current I DIS  provided by current source  144 . In one example, the disable signal DIS  134  is a rectangular pulse waveform with varying lengths of logic high or logic low sections. Logic high sections could correspond to the switch  142  being on while logic low sections could correspond to the switch  142  being off (or vice versa). In one example, the disable signal DIS  134  is substantially the inverse of the enable signal EN  130 . In one embodiment, the drive characteristic control  122  outputs the disable signal DIS  136  in response to a signal separate from the command signal  118  and the drive characteristic signal  128 . The drive characteristic control  122  outputs the disable trim signal  136  to adjust the value of the current I DIS  and therefore the magnitude of the gate current I G    146 . In embodiments of the present disclosure, disable trim signal  136  is responsive to the drive characteristic signal  128 . The disable trim signal  136  may be a voltage or current signal, with the magnitude of the current I DIS  corresponding to the value of the disable trim signal  136 . In one example of the present disclosure, the disable trim signal  136  can trim the value of the current I DIS  to a first current I 1  value or a second current value I 2 , however it should be appreciated that the disable trim signal  132  can trim the value of the current I DIS  to a plurality of current values. The magnitude of the gate current I G    146  controls the fall time of the drain current I D    148  and the subsequent turn-off time of the conductivity modulated device  106 . As such, the system controller  102  can adjust the drive characteristics, such as the fall time of the drain current I D    148  and the subsequent turn-off time, of a conductivity modulated device  106 . 
     In another embodiment, the drive characteristic control  122  may adjust the drive characteristics for the conductivity modulated device  106  by pulse width modulating or pulse frequency modulating the enable signal EN  130  or the disable signal DIS  134 . By pulse width modulating or pulse frequency modulating the enable signal EN  130  or the disable signal DIS  134 , the drive characteristic control  122  adjusts the average magnitude of the gate current I G    146 . As such the rise time and/or fall time of the drain-source voltage V DS    150  or the drain current I D    148  may be adjusted and subsequent turn-on and/or turn-off times of the conductivity modulated device  106 . 
       FIG.  2 A  illustrates an example timing diagram  200  of the enable signal EN  130 , gate current I G    146 , the drain-source voltage V DS    150  and drain current I D    148  during a turn-on transition of the conductivity modulated device  106  of  FIG.  1   . The example waveforms for the gate current I G    146 , drain current I D    148 , and drain-source voltage V DS    150  shown in  FIG.  2 A  are straight-line approximations. Further,  FIG.  2 A  illustrates example waveforms for the gate current I G    146 , drain current I D    148 , and drain-source voltage V DS    150  for different drive strengths. The example waveforms on the right hand side of the page illustrate providing the conductivity modulated device  106  with greater drive current than the examples waveforms on the left hand side of the page. 
     In the example shown, the enable signal EN  130  transitions from logic low to logic high to turn-on the switch  138  of drive element  124 . Similarly, the disable signal (not shown) would transition from logic high to logic low to turn off switch  142 . As such, the conductivity modulated device  106  is enabled to conduct a drive current I D    148 . 
     Once the switch  138  is turned on (and switch  142  is turned off) by the enable signal EN  130 , the gate current I G    146  increases to the magnitude of current I EN  of current source  140 . On the left hand side of the page, current I EN  of current source  140  is substantially equal to a first current value L. 
     After the switch  138  is turned on, the drain current I D    148  of the conductivity modulated device  106  increases from zero with slope m 1 . For the example shown, the drain current ID  148  increases to a peak value and then decreases to its conduction value. In the embodiment shown in  FIG.  2 A , the drain-source voltage V DS    150  of the conductivity modulated device  106  begins to decrease to zero with a slope m 2  once the drain current ID  148  reaches its peak value. The magnitude of slopes m 1  and m 2  are related to the magnitude of the gate current I G , which for the example on the left hand side is substantially equal to the first current value I 1  of current source I EN    140 . For the example shown, the turn-on time  252  begins when the enable signal EN  130  transitions to a logic high value and ends when the drain-source voltage V DS    150  is substantially zero and the drain current I D    148  of the conductivity modulated device  160  has reached its conduction value. 
     On the right hand side of the page, current I EN  of current source  140  is substantially equal to a second current value I 2 . As shown, the second current value I 2  is greater than the first current value I 1 . The magnitudes of slopes m 1  (for the drain current I D    148 ) and m 2  (for the drain-source voltage V DS    150 ) are greater as compared to the magnitudes of slopes m 1  and m 2  shown on the left hand side of the page. As such, the rise time of for the drain current I D    148  is shorter (and the fall time for the drain-source voltage V DS    150  is shorter) resulting in an overall shorter turn-on time  254  for the operation of the conductivity modulated device  106  on the right hand side as compared to the turn-on time  252  shown on the left-hand side of the page. In other words, varying the value of the current I EN  of the current source  140  and subsequently the gate current I G    146  of the conductivity modulated device  106  varies the turn-on time of the conductivity modulated device  106 . The shaded area under the waveforms for the drain current I D    148  and the drain-source voltage V DS    150  represents the crossover energy loss during the turn-on of the conductivity modulated device  106 . As shown the shaded area on the left hand side of the page is larger than the right hand side of the page, indicating that the crossover losses for the conductivity modulated device  106  on the left hand side of the page is greater than on the right hand side of the page. Shorter turn-on times reduce switching/crossover losses, which also reduces the amount of dissipated heat and increases the amount of power delivery by the system  100 . However, shorter turn-on times may lead to increase EMI. 
       FIG.  2 B  illustrates an example timing diagram  201  of the disable signal DIS  134 , gate current I G    146 , the drain-source voltage V DS    150  and drain current I D    148  during a turn-off transition of the conductivity modulated device  106  of  FIG.  1   . Similar to  FIG.  2 A , the example waveforms for the gate current I G    146 , drain current I D    148 , and drain-source voltage V DS    150  shown are straight-line approximations. Further,  FIG.  2 B  illustrates the example waveforms for the gate current I G    146 , drain current I D    148 , and drain-source voltage V DS    150  for different drive strengths. The example waveforms for the gate current I G    146 , drain current I D    148 , and drain-source voltage V DS    150  on the right hand side of the page has a greater drive current than the example waveforms for gate current I G    146 , drain current I D    148 , and drain-source voltage V DS    150  on the left hand side of the page. 
     The disable signal DIS  134  transitions from logic low to logic high to turn-on the switch  142  of drive element  126 . Similarly, the enable signal (not shown) would transition from logic high to logic low to turn off switch  138 . As such, the conductivity modulated device  106  is disabled from conducting a drive current I D    148 . 
     Once the switch  142  is turned on (and switch  138  is turned off) by the disable signal DIS  134 , the magnitude of the gate current I G    146  is substantially the magnitude of current I DIS  of current source  144 . For the drive element  126  shown in  FIG.  1   , once the switch  142  is turned on (and switch  138  is off) the gate current I G    146  is flowing to return  127 . Due to the direction of current, the gate current I G    146  shown in  FIG.  2 B  decreases. Further, the maximum magnitude of the gate current I G    146  is responsive to the magnitude of current I DIS  of current source  144 . On the left hand side of the page, current I DIS  of current source  144  is substantially equal to a first current value I 1 . 
     After the switch  142  is turned on, the drain-source voltage V DS    150  of the conductivity modulated device  106  begins to increase from zero with a slope m 2 . For the example shown, the drain current I D    148  of the conductivity modulated device  106  decreases to zero with slope m 1  once the drain-source voltage V DS    150  has reached its peak value. The magnitude of slopes m 1  and m 2  are related to the magnitude of the gate current I G , which for the example on the left hand side is substantially equal to the first current value I 1  of current source I DIS    144 . For the example shown, the turn-off time  256  begins when the disable signal DIS  134  transitions to a logic high value and ends when the drain current I D    148  is substantially zero and the drain-source voltage V DS    150  of the conductivity modulated device  160  has reached its non-conducting value. 
     On the right hand side of the page, current I DIS  of current source  144  is substantially equal to a second current value I 2 . As shown, the second current value I 2  is greater than the first current value I 1 . The magnitudes of slopes m 1  (for the drain current I D    148 ) and m 2  (for the drain-source voltage V DS    150 ) are greater as compared to the magnitudes of slopes m 1  and m 2  shown on the left hand side of the page. As such, the fall time of for the drain current I D    148  is shorter (and the rise time for the drain-source voltage V DS    150  is shorter) resulting in an overall shorter turn-off time  258  for the operation of the conductivity modulated device  106  on the right hand side as compared to the turn-off time  256  shown on the left-hand side of the page. In other words, varying the value of the current I DIS  of the current source  144  and subsequently of the gate current I G    146  of the conductivity modulated device  106 , the turn-off time of the conductivity modulated device  106  is shortened. The shaded area under the waveforms for the drain current I D    148  and the drain-source voltage V DS    150  represents the crossover loss during the turn-on of the conductivity modulated device  106 . As shown the shaded area on the left hand side of the page is larger than the right hand side of the page, indicating that the crossover losses for the conductivity modulated device  106  on the left hand side of the page is greater than on the right hand side of the page. Shorter turn-off times reduce switching/crossover losses, which also reduces the amount of dissipated heat and increases the amount of power delivery by the system  100 . 
       FIG.  3    is a functional block diagram of the system controller  102  and switch controller  114  of  FIG.  1    illustrating example command signals  118  from the system controller for different commands to adjust the conductivity modulated device  106  and/or the switch controller  114 . It should be appreciated that the system controller  102 , switch controller  114  and their respective elements couple and function as described above. 
     As shown, the command signal  118  is a rectangular pulse waveform with high and low sections. As will be discussed, the duration of the low sections corresponds with which command is being transmitted by the system controller  102 , referred to as active low pulse duration encoding. Under default conditions or steady state conditions, when no command is being sent, the command signal  118  is substantially equal to the high value. In one example, the high value could be substantially 5 volts (V). When the system controller  102  sends a command to the switch controller  114  via the command signal  118 , the command signal transitions to a low value. In one example, the low value could be substantially 0V. The duration of the low value section of the command signal  118  corresponds to which command is being sent by the system controller  102 . The example command signal  118  in  FIG.  3    is an “active low” signal in which the duration of the low section corresponds to which command is being transmitted. However, it should be appreciated that the command signal  118  may be an “active high” signal in which the duration of the high section corresponds to which command is being transmitted. 
     For example, a first command  360  corresponds to the command signal  118  being substantially the low value for a period T. For a second command  361 , the command signal  118  could be substantially the low value for a period  2 T. In the example shown, the low section of the second command  361  is twice as long as the low section for the first command  360 . Similarly for the third command  362  and the fourth command  363 . The command signal  118  could be substantially the low value for a period  3 T for the third command  362 , which is three times as long as the low section of the first command  360 . For the fourth command  363 , the command signal  118  could be substantially the low value for a period  4 T, which is four times as long as the low section of the first command  360 . In other words, the duration of each command could be a period T longer than the duration of the previous command. In one example, the interface  120  could include a timer or counter to measure the durations of the low value sections in the command signal  118  to determine which command has been received. 
     Example commands could include: status inquiry, reset, increase drive current, and decrease drive current. The increase drive current and decrease drive current commands are adjustment commands/signals to adjust the drive characteristics of the conductivity modulated device  106 . For the first command  360 , the system controller  102  could send a “status inquiry” command in which the system controller  102  pings the switch controller  114  for the “status” of. of the switch controller  114 , such as the information stored in a status register of the switch controller 
     For the second command  361 , the system controller  102  could send a “reset” command in which the system controller  102  allows the switch controller  114  to be restarted or turned on. 
     For the third command  362 , the system controller  102  could send an adjustment command to “increase drive current” in which the system controller  102  indicates that the switch controller  114  should increase either the current I EN  of current source  140  or current I DIS  of current source  144 , or both, to decrease the rise time of the drain current I D    148  or the fall time of the drain current I D    148 , or both (i.e. the fall time of the drain-source voltage V DS    150  or the rise time of the drain-source voltage V DS    150 , or both). The decreased rise time or fall time would shorten the turn-on time or turn-off time, respectively, of the conductivity modulated device  106 . Under normal operating conditions, the drive characteristic control  122  outputs the enable trim signal  132  and the disable trim signal  136  such that the current I EN  of current source  140  and current I DIS  of current source  144  are substantially equal to the first current value I 1  (of  FIGS.  2 A and  2 B ). In one example, the system controller  102  outputs the third command  362  in response to the sense signal  115  indicating that there is a power event in the system  100  in which the system controller  102  may want to deliver more power. In response to the third command  362 , the drive characteristic controller  122  could output either the enable trim signal  132  or the disable trim signal (or both) to adjust the value of current I EN  of current source  140  or current I DIS  of current source  144  (or both) to the second current value I 2  (as shown in  FIGS.  2 A and  2 B ) and increasing the drive current of the conductivity modulated device  106 . 
     For the fourth command  363 , the system controller  102  could send an adjustment command to “decrease drive current” (or in other words a “return drive current” command) in which the system controller  102  indicates that the switch controller  114  should decrease (or return) either the current I EN  of current source  140  or current I DIS  of current source  144 , or both, to increase the rise time of the drain current I D    148  or the fall time of the drain current I D    148 , or both (i.e. increase the fall time of the drain-source voltage V DS    150  of the rise time of the drain-source voltage V DS    150 , or both). Or in other words, the system controller  102  indicates that the switch controller  114  should return the value of current I EN  of current source  140  or current I DIS  of current source  144 , or both, to the first current value I 1  of  FIGS.  2 A and  2 B . In one example, the sense signal  115  indicates to the system controller  102  that the increased power event in the system  100  has passed. In response to the fourth command  363 , the drive characteristic controller  122  could output either the enable trim signal  132  or the disable trim signal (or both) to adjust the value of current I EN  of current source  140  or current I DIS  of current source  144  (or both) to the first current value I 1  of  FIGS.  2 A and  2 B  and decreases (or returns) the drive current of the conductivity modulated device  106  to its default current value. Although for this example, the commands: status inquiry, reset, increase drive current, and decrease drive current are the first, second, third, and fourth commands  360 ,  361 ,  362 , and  363 , respectively, it should be appreciated that the commands could be in any order. 
     In some embodiments, the communication between the system controller  102  and the switch controller  114  may be bidirectional. For example, the switch controller  114  may sense a fault condition (such as overcurrent, overvoltage, overheating, etc) in the system  100  and communicates the fault to the system controller  102 . The fault communication from the switch controller  114  may be encoded as a multi-bit word to the system controller  102 . 
       FIG.  4    illustrates the switch controller  114  receiving the command signal  118  in response to a toggle  465 , in accordance with embodiments of the present disclosure. In one embodiment, the toggle  465  could be in response to a user. In another embodiment, the toggle  465  could be in response to a dedicated hardware sensor which senses the power event. It should be appreciated that the switch controller  114  and its elements couple and function as described above. In one example, the switch controller  114  may receive commands from both the system controller (not shown) and the toggle  465 . In another example, the switch controller  114  receives the command signal  118  in response to just the toggle  465 . 
     The toggle  465  may be a rectangular pulse waveform of logic high and logic low sections. In one embodiment, the toggle  465  is representative of a user manually selecting from two choices, such as a mechanical switch. A logic low value for the toggle  465  corresponds to the rise time/fall time of the drain current I D    148  (rise time/fall time of the drain-source voltage V DS    150 ) substantially equal to a first value, as for example, the gate current I G    146  substantially equal to the first current value I 1  as shown in  FIGS.  2 A and  2 B . A logic high value for the toggle  465  could correspond to the rise/fall time of the drain current I D    148  (rise time/fall time of the drain-source voltage V DS    150 ) substantially equal to a second value, as for example, the gate current I G    146  substantially equal to the second current value I 2  as shown in  FIGS.  2 A and  2 B . 
     As shown in one embodiment, a transistor  464  is coupled to the interface  120  of the switch controller  114  and the return  127 . The control terminal of the transistor  464  is configured to receive the toggle  465 . In the embodiment shown, the transistor  464  is a bipolar junction transistor (BJT). The base of the transistor  464  is configured to receive the toggle  465 , the emitter of transistor  464  is coupled to the return  127  and the collector of the transistor  464  is coupled to the interface  120 . For the embodiment shown, the command signal  118  is a voltage signal and is the collector voltage or the collector-emitter voltage of transistor  464 . In operation, when the toggle  465  is low, the transistor  464  is off and the command signal  118  is high. As such, a high value for the command signal  118  corresponds to the rise time/fall time of the drain current I D    148  (rise time/fall time of the drain-source voltage V DS    150 ) substantially equal to the first value. When the toggle  465  is high, the transistor  464  is on and the command signal  118  is substantially equal to the return  127  (i.e. low value). As such, a low value for the command signal  118  corresponds to the rise time/fall time of the drain current I D    148  (rise time/fall time of the drain-source voltage V DS    150 ) substantially equal to the second value. 
       FIG.  5 A  illustrates a multi-phase motor drive system  500  including three half-bridge inverter modules  566 ,  567 , and  568 , coupled individually to a high-voltage (HV) bus  576  and controlled with a single system controller  102  to drive a motor  569 , such as for example a single-phase or 3-phase motor. As shown, each half-bridge inverter modules  566 ,  567 , and  568  and the system controller  102  are referenced to return  127 . Further, the system controller  102  can adjust the drive characteristics of one or more switches of the various half-bridge inverter modules  566 ,  567 , and  568 , in accordance with the teachings of the present disclosure. As shown, each switch is represented by an n-type metal-oxide-semiconductor field effect transistor (MOSFET) and is a conductivity modulated device as discussed above. 
     Each half-bridge module  566 ,  567 ,  568  are individually coupled to the HV bus  576 . Each half-bridge module  566 ,  567 ,  568 , includes a high side switch  570 ,  571 ,  572 , and a low side switch  573 ,  574 ,  575 , respectively coupled together as a power converter or an inverter in a full-bridge configuration. Each switch  570 ,  571 ,  572 ,  573 ,  574 , and  575  is controlled by its own switch controller (shown further in  FIG.  5 B ) and form a power switching array. The half-bridge mid-point terminals HB 1 , HB 2 , HB 3  between each high side and low side switch of their respective half-bridge modules  566 ,  567 ,  568 , are coupled to the three phase terminals A, B, and C of the multiphase motor  569 . In one example, the motor  569  is a brushless 3-phase DC motor, which may be included in for example an electric appliance, power tool, fan, or the like. In operation, the half-bridge modules  566 ,  567 , and  568  provides the input electrical signals (such as voltage, current, frequency, and phase for the desired mechanical output load motion) to the motor  569  from the electrical energy supplied by the HV bus  576 . The switching properties of switches  570 ,  570 ,  571 ,  572 ,  573 ,  574 , and  575  are controlled by their respective switch controllers to regulate the energy flow to the motor  569 . In other words, the switch controllers adjust the output to the motor  569  to maintain the target operation of the motor  569 . 
     The system controller  102  couples to each half-bridge module  566 ,  567 , and  568  through the communication bus  577 . Similar to above, in embodiments the system controller  102  receives a sense signal  116  representative of a power event. In one embodiment, the power event may be an indication to the system controller  102  to adjust one or more drive characteristics of one or more of switches  570 ,  570 ,  571 ,  572 ,  573 ,  574 , and  575 . For embodiments, the system controller adjusts the drive current of one or more of switches  570 ,  570 ,  571 ,  572 ,  573 ,  574 , and  575  in response to the sensed power event  116 . Or in other words, the power event may indicate to the system controller  102  to decrease switch turn-on time and/or turn-off time by increasing the magnitude of the gate current I G    146  of one or more of switches  570 ,  570 ,  571 ,  572 ,  573 ,  574 , and  575  to increase the rise time and/or fall time of the drain current I D    148  of one or more of switches  570 ,  570 ,  571 ,  572 ,  573 ,  574 , and  575 . One example of a sensed power event which would increase the magnitude of the gate current I G    146  could include an outdoor air conditioning fan during startup that may have to overcome possible wind blowing conditions. Another example of a sensed power event could include a dishwasher water pump which has to pump a large amount of water in case the drain for the dishwasher has unexpectedly flooded. A further example of a sensed power event could include a refrigerator during initial installation to cool itself to the desired temperature. 
     The system controller  102  is configured to output a command signal to one or more half-bridge modules  566 ,  567 , and  568 . In one embodiment, the system controller  102  can send the command signal via the communication bus  577 . In another embodiment, the system controller  102  sends the command signal via a separate connection. The command signal  118  could be a voltage signal or a current signal. In one example, the command signal  118  could be representative of a digital word. Further, the system controller  102  could apply coding to the command signal  118 . As will be further illustrated with respect to  FIG.  5 B , the system controller  102  outputs a command signal  118  to at least one switch controller of one or more half-bridge modules  566 ,  567 , and  568  via the communication bus  577 . In one embodiment, the command signal is outputted in response to the received sense signal  116  and may be representative of commands by the system controller  102  for the respective switch controller. Example commands communicated by the system controller  102  could include a “status inquiry” command for one or more of the half-bridge modules  566 ,  567 , and  568 . Another example command communicated by the system controller  102  could include a “fault” command in which the system controller  102  has sensed a fault condition (such as overcurrent, overvoltage, overheating, etc) in the system  100  and communicates the fault to half-bridge modules  566 ,  567 , and  568 . In general, the half-bridge modules  566 ,  567 , and  568  respond to the fault command by turning off their respective high-side and low-side switches. 
     In embodiments of the present disclosure, the system controller  102  communicates a command signal  118 , representative of the drive characteristics of one or more of the high-side switches  570 ,  571 ,  572  and low-side switches  573 ,  574 , and  575 . An example drive characteristic includes the magnitude of the gate current I G    146  for the respective switch, which is related to the rise time and/or fall time of the drain current I D    148  and drain-to-source voltage  150  for the respective switch. Another example drive characteristic could include the duration which one or more of switches  570 ,  571 ,  572   573 ,  574 , and  575  is driven by the gate current I G    146 . For example, the command communicated via the communication bus  577  could be representative of driving one or more of switches  570 ,  571 ,  572   573 ,  574 , and  575  at a first magnitude of gate current I G  or a second magnitude of gate current I G , where the second magnitude is greater than the first magnitude. Although it should be appreciated that the command signal  118  could represent driving one or more of switches  570 ,  571 ,  572   573 ,  574 , and  575  with more than two magnitudes of gate current I G . 
     Half-bridge modules  566 ,  567 , and  568  are coupled to a communication bus  577 , which is also coupled to system controller  102 . The communication bus  577 , which in one example is an open collector configuration, is coupled to a supply voltage V UP  through a pull up resistor R UP . Further, the communication bus  577  may be in one example, a single-wire communication bus. As mentioned above, the communication bus  577  may be utilized by the system controller  102  to communicate commands to one or more half-bridge modules  566 ,  567 , and  568 . In one example, the communication bus  577  in normal steady state condition is pulled up to supply voltage V UP , and during any communication can be pulled down by the system controller  102  for sending a command to half-bridge modules  566 ,  567 , and  568 . In one embodiment, the communication bus  577  can be pulled down for a detection of a command through a digital multi-bit word. In another embodiment, the communication bus  577  can be pulled down to communicate a command as discussed with respect to  FIG.  3   . In some embodiments, the duration which the communication bus  577  is pulled down corresponds with the command sent by the system controller  102 . 
       FIG.  5 B  provides increased detail of the half-bridge modules in accordance with embodiments of the present disclosure. Specifically,  FIG.  5 B  illustrates the half-bridge module  566 , but it should be appreciated that the other half-bridge modules  567 ,  568 , although present, are not shown in detail. Further the elements included in half-bridge modules  567 ,  568  are similar to what is shown in  FIG.  5 B  with regards to half-bridge module  566 . 
     Half-bridge module  566  includes high-side switch  570  and low-side switch  537  coupled together in series. The high-side switch  570  and low-side switch  537  are exemplified by n-type MOSFETs with their respective body diodes. The drain of the high-side switch  570  is coupled to the HV bus  576  and the source of the source of low-side switch  573  is coupled to return  127 . The half-bridge mid-point HB 1  is coupled to phase A of motor  569 . 
     Half-bridge module  566  further includes switch controllers  114  and  515 . Switch controller  114  is coupled to control the low-side switch  573  while switch controller  515  is coupled to control the high-side switch  570 . Both switch controllers  114 ,  515  include drive characteristic control for their respective switches, as discussed above and in accordance with embodiments of the present disclosure. The switch controllers  114  and  515  can also include interfaces to receive the command signal  118 , as will be further discussed. Similar to above, switch controllers  114 ,  515  control the enabling and disabling, along with the turn-on time and turn-off time of their respective switches. Further, the switch controllers  114 ,  515  can adjust the drive characteristics of the low-side switch  573  and the high-side switch  570 , respectively, in response to the system controller  102 . 
     The system controller  102  is coupled to half-bridge module  566  and switch controller  114 . As shown, the system controller  102  outputs the command signal  118  to the switch controller  114 . In response to the command signal  118  received from the system controller  102 , the switch controller  114  adjusts the drive characteristics of the low-side switch  537 . In one embodiment, the interface (not shown) of the switch controller  114  receives the command signal  118  and outputs the drive characteristic signal to the drive characteristic control of switch controller  114 . The drive characteristic control then outputs signals to the drive elements which enable and disable the low-side switch  573 . The system controller  102  may send the command signal  118  via the communication bus  577  or by another coupling to switch controller  114 . 
     As shown in a dashed line, in some embodiments the system controller  102  can optionally be coupled to switch controller  515  to provide the command signal  118  rather than providing the command signal  118  via the switch controller  114 . In response to the command signal  118 , the switch controller  515  adjusts the drive characteristics of the high-side switch  570 . In one embodiment, the interface (not shown) of the switch controller  515  receives the command signal  118  and outputs the drive characteristic signal to the drive characteristic control of switch controller  515 . The drive characteristic control then outputs signals to the drive elements which enable and disable the high-side switch  570 . The system controller  102  may send the command signal  118  by another coupling to switch controller  515  or via the communication bus  577 . 
     In another alternative embodiment shown by the dashed line, switch controller  114  couples to switch controller  515 . The switch controller  114  sends either the received command signal  118  or the drive characteristic signal  128  to switch controller  515  rather than the switch controller  515  receiving the command signal  118  from the system controller  102 . Communication from the low-side switch controller  114  to the high-side switch controller  515  may be accomplished through communication links between the low-side switch controller  114  and the high-side controller  515 . For example, the control signals for controlling both the high-side switch  570  and low-side switch  573  may be received by the low-side switch controller  114  from the system controller  102 . The control signal for switching the high-side switch  570  may be communicated to the high-side controller  515  from the low-side switch controller  114  via communication links. 
     In one embodiment, the low-side switch controller  114  relays the command signal  118  received from the system controller  102  to adjust the drive characteristics of the high side switch  570 , such as the high-side drive current, to the high-side switch controller  515 . For this example, the high-side switch controller  515  includes the interface (not shown) to receive the command signal  118  from the low-side switch controller  114  and outputs the drive characteristic signal to the drive characteristic control of switch controller  515 . The drive characteristic control then outputs signals to drive elements which enable and disable the high-side switch  570 . 
     In another embodiment, the low-side switch controller  114  receives the command signal  118  to adjust the drive characteristics of the high side switch  570 , such as the high-side drive current, at an interface (not shown). The interface (not shown) outputs the drive characteristic signal  128  to adjust the drive characteristics of the high side switch  570  and the drive characteristic signal  128  of the low-side switch controller  114  is communicated to the high-side switch controller  515 . For this example, the high-side switch controller  515  includes its own drive characteristic control which is coupled to and receives the drive characteristic signal  128  of the low-side switch controller  114 . The drive characteristic control of switch controller  515  then outputs signals to drive elements which enable and disable the high-side switch  570 . 
       FIG.  6 A  illustrates an example power converter  600  with switch controllers  114 ,  615  which include drive characteristic control in accordance with embodiments of the present disclosure. Switch controllers  114 ,  615  include drive characteristic control which is responsive to the system controller  102 . Further, the system controller  102  can adjust the drive characteristics of switches  679 ,  680 , in accordance with embodiments of the present disclosure. Power converter  600  receives an input voltage V IN    602  and is designed to transfer electrical energy form an input to a load  682  through an energy transfer element L 1   681  by controlling the switching of power switches  679 ,  680 . In various implementations, the power converter  600  can control the voltage, current, or power levels of the energy output to the load  682 . In the example shown in  FIG.  6 A , the energy transfer element L 1   681  and two power switches  679 ,  680  are coupled together in a half-bridge configuration, however other topologies can be used. The power switches  679 ,  680  form a power switching array. Switch controller  114  may be referred to as a low-side switch controller while switch controller  615  may be referred to as a high-side switch controller. 
     In the example shown, power switches  679 ,  680  are IGBTs. However, examples of the present invention can also be used in combination with other power switch technologies. For example, metal-oxide-semiconductor field-effect transistors (MOSFETs), bipolar transistors, injection enhancement gate transistors (TEGTs) and gate turn-off thyristors (GTOs) can be used. In addition, power converter  600  can be used with power switches which are based on gallium nitride (GaN) semiconductors or silicon carbide (SiC) semiconductors. 
     System controller  102  is coupled to receive system inputs  699 , sense signal  116  and provides the command signal  118 . The system controller  102  determines whether the switch controllers  114 ,  615  should turn on or turn off the power switches  679 ,  680  based on system inputs  699 . Example system inputs  699  include pulse width modulated (PWM) signal for a general purpose motor drive, a turn-on and turn-off sequence of a multi-level power converter, or a system fault turn-off request. The sense signal  116  is also a system input and in one embodiment is representative of a power event. In one embodiment, the power event may be an indication to the system controller  102  to adjust the drive characteristic of either power switch  679 ,  680  or both. In one example of adjusting the drive characteristic of either power switch  679 ,  680 , the power event may be an indication to increase the drive current of either power switch  679 ,  680  or both. Or in other words, the power event may indicate to the system controller  102  to decrease turn-on time and/or turn-off time by increasing the magnitude of the control current for either power switch  679 ,  680  or both to increase the rise time and/or fall time of the current conducted by either power switch  679 ,  680  or both. 
     In the illustrated example, system controller  102  outputs a command signal  118  representative of one or more commands to the interface  120  of switch controllers  114 ,  615 . Example commands include enabling or disabling power switches  679 ,  680 , reset, fault notification, and adjust the drive current (i.e. rise time and/or fall time of conducted current) of power switches  679 ,  680 . The command signal  118  could be a voltage signal or a current signal. In one example, the command signal  118  could be representative of an N-bit digital word. Further, the system controller  102  could apply coding to the command signal  118 . In one example, the communication between the system controller  102  and the interface  120  may be bidirectional. Interface  120  is coupled to the system controller  102  and receives the command signal  118 .  FIG.  6 A  illustrates a single interface  120  for both the switch controllers  114 ,  615 . However, it should be appreciated that each switch controller  114 ,  615  may have its own interface and as such the system controller  102  would output the command signal  118  to both interfaces. The interface  120  and the system controller  102  are both referenced to a primary reference potential  683  while the switch controller  114  is referenced to a secondary reference potential  684  and the switch controller  615  is referenced to a secondary reference potential  685 . Secondary reference potentials  684 ,  685  are different potentials. In one example, reference potential  685  is coupled to the half-bridge point between the high-side switch  679  and the low-side switch  680  while reference potential  684  is coupled to the emitter of low-side switch  680 . The switch controllers  114 ,  615  are galvanically isolated from the interface  120  by isolated communication links  678 . The isolated communication links  678  may be implemented as an inductive coupling, such as a signal transformer or coupled inductor, optical coupling, or capacitive coupling. Further, the switch controllers  114 ,  615  may bidirectionally communicate with the interface  120  via the communication links  678 . 
     Interface  120  interprets the command signal  118  sent by the system controller  102  and sends the drive characteristic signal to switch controllers  114 ,  615  to drive the power switches  679 ,  680  and further, to adjust the drive current of power switches  679 ,  680 . The switch controllers  114 ,  615  receive their respective drive characteristic signals and generate drive signals to control the power switches  670 ,  680 . As discussed above, the switch controllers  114 ,  615  include drive characteristic control circuits and enable and disable drive elements to control the drive current (i.e. drive strength) of power switches  680 ,  679 . As such, the system controller  102  adjusts the drive strength of power switches  680 ,  679 . 
       FIG.  6 B  illustrates another example of a power converter  601  in a half-bridge configuration with a system controller  102  to adjust the drive characteristics, such as for example the drive current, of power switches  679 ,  680 . It should be appreciated that the power converter  601  shares many similarities with the power converter  600  shown in  FIG.  6 B . At least one difference however, is the interface  120  couples to switch controller  114  through isolation interface  678  and does not couple to the switch controller  615 . For the example shown in  FIG.  6 B , interface  120  interprets the command signal  118  and outputs the drive characteristic signal  128  to the switch controller  114 . The switch controller  114  sends the drive characteristic signal  128  to switch controller  615  rather than the switch controller  815  receiving the drive characteristic signal from interface  120 . Communication from the low-side switch controller  114  to the high-side switch controller  615  may be accomplished through communication links between the low-side switch controller  114  and the high-side controller  615 . For this example, the high-side switch controller  615  includes its own drive characteristic control which is coupled to and receives the drive characteristic signal  128  of the low-side switch controller  114 . The drive characteristic control of switch controller  615  then outputs signals to drive elements which enable and disable the high-side switch  679 . 
       FIG.  6 C  illustrates an example isolated communication link  678 . For simplicity, only the isolated communication link  678  between interface  120  and switch controller  114  is shown. The interface  120  and the system controller  102  are both referenced to a primary reference potential  683  while the switch controller  114  is referenced to a secondary reference potential  684 . The switch controller  114  is galvanically isolated from the interface  120  by isolated communication links  678 . 
     The isolated communication links  678  illustrated is a signal transformer with a primary winding  687  and a secondary winding  689 . The interface  120  is coupled to the primary winding  687  and outputs the drive characteristic signal  128 . The switch controller  114  is coupled to the secondary winding  689  and receives the drive characteristic signal  128  multiplied by the turns ratio of the primary and secondary windings  687 ,  689 . 
     The above description of illustrated examples of the present invention, including what is described in the Abstract, are not intended to be exhaustive or to be limitation to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible without departing from the broader spirit and scope of the present invention. Indeed, it is appreciated that the specific example voltages, currents, frequencies, power range values, times, etc., are provided for explanation purposes and that other values may also be employed in other embodiments and examples in accordance with the teachings of the present invention. 
     Although the present invention is defined in the claims, it should be understood that the present invention can alternatively be defined in accordance with the following examples: 
     Example 1. A control system configured to control a conductivity modulated device of a power switching array that is configured to control energy delivery to a load, comprising a system controller configured to sense a power event in the control system and to output a command signal to adjust a drive characteristic of the conductivity modulated device in response to the sensed power event; and a switch controller coupled to the system controller and configured to receive the command signal, the switch controller further configured to control energy delivery to the load by controlling the turn on and turn off of the conductivity modulated device, wherein the switch controller comprises an adjustable drive element configured to control a rise time and/or a fall time of a voltage across the conductivity modulated device; and a drive characteristic control configured to receive the command signal and vary the drive characteristic of the conductivity modulated device, the drive characteristic control further configured to vary the adjustable drive element to adjust the rise time and/or the fall time of the voltage across the conductivity modulated device in response to the command signal generated by the system controller. 
     Example 2. The control system of example 1, the drive characteristic control configured to adjust a rise time and/or a fall time of a current conducted by the conductivity modulated device. 
     Example 3. The control system of examples 1 or 2, wherein the adjustable drive element comprises a switch coupled to the drive characteristic control, the switch configured to be turned on or off to enable or disable the conduction of current by the conductivity modulated device; and a trimmable current source coupled to the drive characteristic control and coupled in series with the switch, the drive characteristic control being further configured to control a current provided by the trimmable current source in response to the command signal to vary the rise time and/or the fall time of the voltage across the conductivity modulated device. 
     Example 4. The control system of any one of examples 1 to 3, the drive characteristic control further configured to control the current provided by the trimmable current source to vary a rise time and/or a fall time of the current conducted by the conductivity modulated device. 
     Example 5. The control system of any one of examples 1 to 4, wherein the drive characteristic control is further configured to control a magnitude of the current provided by the trimmable current source. 
     Example 6. The control system of any one of examples 1 to 5, wherein the drive characteristic control is further configured to control a duration of the current provided by the trimmable current source. 
     Example 7. The control system of any one of examples 1 to 6, wherein the drive characteristic control is further configured to control a frequency of the current provided by the trimmable current source. 
     Example 8. The control system of any one of examples 1 to 7, wherein the switch controller further comprises an interface coupled to the system controller and configured to receive a command signal, the interface further configured to interpret the command signal and output a drive characteristic signal to the drive characteristic control to adjust the rise time and/or fall time of conductivity modulated device. 
     Example 9. The control system of any one of examples 1 to 8, wherein the interface is galvanically isolated from the drive characteristic control. 
     Example 10. The control system of any one of examples 1 to 9, wherein the control system controls energy delivery to a motor. 
     Example 11. The control system of any one of examples 1 to 10, wherein the conductivity modulated device is a transistor. 
     Example 12. The control system of any one of examples 1 to 11, wherein the command signal is a rectangular pulse waveform of logic high and logic low sections, wherein a duration of the logic low section corresponds to a command of the command signal. 
     Example 13. The control system of any one of examples 1 to 12, wherein the system controller is configured to output the command signal to adjust the conductivity modulated device on demand. 
     Example 14. A control system configured to control a conductivity modulated device which is configured to control energy delivery to a load, comprising a system controller configured to sense a power event in the control system and to assert a command signal in response to the sensed power event; and a switch controller coupled to the system controller and configured to receive the command signal, the switch controller further configured to control the turn on and the turn off of the conductivity modulated device to control the energy delivery to the load by variation of a rise time, a fall time, or both of a voltage across the conductivity modulated device in response to a first command in the command signal, wherein the switch controller is configured to not vary the rise time, the fall time, or both in response to a second command in the command signal. 
     Example 15. The control system of example 14, wherein the switch controller further comprises: an adjustable drive element configured to control the rise time, the fall time or both of the voltage across the conductivity modulated device; an interface coupled to the system controller and configured to receive the command signal, wherein the interface is configured to interpret the command signal and output a drive characteristic signal; and a drive characteristic control configured to receive the drive characteristic signal and vary the adjustable drive element to adjust the rise time, the fall time, or both of the voltage across the conductivity modulated device from a default value in response to the first command in the command signal, the drive characteristic control is configured to not vary the rise time, the fall time, or both from the default value in response to the second command in the command signal. 
     Example 16. The control system of example 14 or 15, wherein the adjustable drive element further comprises: a switch coupled to the drive characteristic control, wherein the drive characteristic control is configured to turn the switch ON or OFF to enable or disable the conduction of the conductivity modulated device; and a trimmable current source coupled to the drive characteristic control and coupled in series with the switch, wherein the drive characteristic control is configured to control a magnitude of current provided by the trimmable current source is controlled by the drive characteristic control in response to the drive characteristic signal to vary the rise time, the fall time, or both of the voltage across the conductivity modulated device. 
     Example 17. The control system of any one of examples 14 to 16, wherein the magnitude of current provided by the trimmable current source increases in response to the first command. 
     Example 18. A switch controller configured to control energy delivery to a load by controlling the turn on and turn off of a conductivity modulated device, the switch controller comprising: a drive characteristic control configured to receive drive characteristics from a command signal, wherein the command signal is provided to actively adjust a drive current of the conductivity modulated device; and a first drive element coupled to the drive characteristic control comprising a first switch coupled to the drive characteristic control and configured to be turned on or off to transition the conductivity modulated device from a first state to a second state; and a first trimmable current source coupled to the drive characteristic control and coupled in series with the first switch, the first trimmable current source configured to provide current for the conductivity modulated device to transition the conductivity modulated device from the first state to the second state at a first rate in response to a first command of the command signal and to provide current for the conductivity modulated device to transition the conductivity modulated device from the first state to the second state at a second rate in response to a second command of the command signal. 
     Example 19. The switch controller of example 18, further comprising a second drive element coupled to the drive characteristic control, wherein the second drive element comprises: a second switch coupled to the drive characteristic control and configured to be turned on or off to transition the conductivity modulated device from the second state to the first state; and a second trimmable current source coupled to the drive characteristic control and coupled in series with the second switch, the second trimmable current source is configured to provide current for the conductivity modulated device to transition the conductivity modulated device from the second state to the first state at the first rate in response to the first command of the command signal and to provide current for the conductivity modulated device to transition the conductivity modulated device from the second state to the first state at the second rate in response to the second command of the command signal. 
     Example 20. The switch controller of example 18 or 19, wherein the command signal is received from a system controller. 
     Example 21. The switch controller of any one of examples 18 to 20, wherein the command signal is received from a user toggle. 
     Example 22. The switch controller of any one of examples 18 to 21, wherein the command signal is received from a sensor.