Patent Publication Number: US-9419607-B2

Title: Gate drive circuit

Description:
TECHNICAL FIELD 
     This disclosure relates generally to a gate drive circuit. 
     BACKGROUND 
     A gate drive circuit may be used to drive semiconductor switches (e.g., transistors) that drive a load, which may be part of a switching amplifier. For example, the gate drive circuit may control operation of sets of transistors to provide power to the load. 
     SUMMARY 
     Example circuitry may include: a transformer circuit having first windings and second windings, where the second windings are magnetically orthogonal to the first windings; first transistors to provide a first voltage to a load, where each of the first transistors is responsive to a first control signal that is based on a first signal through a first winding; second transistors to provide a second voltage to the load, where each of the second transistors is responsive to a second control signal that is based on the first signal through the first winding, and where the first and second control signals cause the first transistors to operate in a different switching state than the second transistors; and control circuitry responsive to signals received through the second windings to control the first transistors and the second transistors to operate in a same switching state. The example circuitry may include one or more of the following features, either alone or in combination. 
     A control circuit may be between each first winding and each first and second transistor, where each circuit may be configured to generate either the first control signal or the second control signal. The control circuitry may include circuits, each of which may be between a secondary winding and a corresponding transistor. 
     The first transistors may include a first transistor connected between the first voltage and the load and a second transistor connected between the load and a reference voltage. The second transistors may include a third transistor connected between the first voltage and the load and a fourth transistor connected between the load voltage and the reference voltage. The first transistor and the fourth transistor may be operational in a same switching state to apply the first voltage to the load, and the second transistor and the third transistor may be operational in a same switching state to apply the second voltage to the load, where the second voltage is equal in magnitude and opposite in polarity to the first voltage. The first transistor and the fourth transistor may be conductive while the second transistor and the third transistor are not conductive, and the first transistor and the fourth transistor may not be conductive while the second transistor and the third transistor are conductive. The first transistor, the second transistor, the third transistor, and the fourth transistor may be field effect transistors (FETs), with each FET having a control terminal for receiving either the first control signal or the second control signal. 
     The control circuitry may be configured to generate a third control signal that is applicable to gates of the first and second transistors. Control of the first transistors and the second transistors to be in a same switching state may occur, at most, within 200 nanoseconds of a command instructing that the transistors operate in a same switching state. Control of the first transistors and the second transistors to be in a same switching state may occur, at most, within 100 nanoseconds of a command instructing that the transistors operate in a same switching state. 
     The example circuitry may include compensation circuitry to reduce noise resulting from lack of symmetry in magnetic structures making up the transformer circuit. The first windings and the second windings may be secondary windings of a transformer circuit having at least one primary winding. The transformer circuit may include a main primary winding and an orthogonal primary winding, with the main primary winding for inducing signals in the first windings and the orthogonal primary winding for inducing signals in the second windings. The load may be part of an audio amplifier. The control circuitry may be configured to override the first control signal and the second control signal to cause the first transistors and the second transistors to be in a same switching state. The control circuitry may be configured to override the first control signal and the second control signal to cause the first transistors and the second transistors to be non-conductive. 
     Example circuitry may include: a transformer circuit having first windings and second windings, where the second windings are magnetically orthogonal to the first windings; and control circuitry (i) responsive to signals in the first windings, to cause application of a first voltage and a second voltage to a load, where the application of the first voltage and the second voltage is applied at different times and in opposite polarity, and (ii) responsive to signals in the second windings to prevent application of either the first voltage or the second voltage to the load. The example circuitry may include one or more of the following features, either alone or in combination. 
     The example circuitry may include switches that are controllable based on the signals in the first windings to enable application of either the first voltage or the second voltage to the load. The switches may also be controllable to open based on the signals in the second windings, thereby preventing application of either the first voltage or the second voltage to the load. The first and second windings may be secondary windings of the transformer circuit, and the transformer circuit may have one or more primary windings to receive control signals for controlling the circuitry. 
     Example circuitry may include: a transformer circuit having first windings and second windings, with the second windings being magnetically orthogonal to the first windings; means responsive to first control signals that are based on first signals through first windings to provide a first voltage to a load; means responsive to second control signals that are based on the first signals through the first windings to provide a second voltage to the load, where the first control signals and the second controls signal cause output of the first voltage to be opposite in polarity to the second voltage; and means responsive to third signals received via second windings to override the first signals to cease output of the first voltage or the second voltage from the circuitry. 
     Two or more of the features described in this disclosure/specification, including this summary section, can be combined to form implementations not specifically described herein. 
     The circuitry described herein, or portions thereof, can be controlled by a computer program product that includes instructions that are stored on one or more non-transitory machine-readable storage media, and that are executable on one or more processing devices. The systems and techniques described herein, or portions thereof, can be implemented as an apparatus, method, or electronic system that can include one or more processing devices and memory to store executable instructions to control the circuitry described herein. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram including an example gate drive circuit. 
         FIGS. 2 and 3  are circuit diagrams showing current paths through the example circuitry of  FIG. 1  in different modes of operation. 
         FIG. 4  is a circuit diagram of a transformer circuit having main and orthogonal windings that may be incorporated into a gate drive circuit. 
         FIG. 5  is a circuit diagram including an example gate drive circuit that includes the transformer circuit of  FIG. 4 . 
         FIG. 6  is a circuit diagram of an example compensation circuit. 
         FIGS. 7A through 7G  show structures of an example orthogonal transformer that may be used in the circuitry described herein. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  shows example of circuitry  100 , which includes a gate drive circuit, switches driven by the gate drive circuit, and an associated load. Circuitry  100  includes a transformer circuit, in this example, transformer  101  having primary winding  102  and secondary windings  103 ,  104 ,  105 ,  106 . In this example, four transistors  110 ,  111 ,  112 ,  113  are used to drive a load  116 , here an RLC (resistive-capacitive-inductive load). Transistors  110 ,  111 ,  112 ,  113  are metal oxide field-effect transistors (MOSFETs); however, any appropriate type of transistor may be used (e.g., bipolar junction transistors (BJTs) or IGBT&#39;s). A single pulse command into the primary winding of the transformer simultaneously provides outputs to gate drive circuitry for all switching transistors. 
     Transistor  110  has a drain connected to the high side terminal of voltage source V 1   120 , and a source connected to a first terminal  121  of output circuit  122 . Transistor  111  has a drain connected to the high side terminal of voltage source V 1   120 , and a source connected to a second terminal  124  of output circuit  122 . Transistor  112  has a drain connected to top terminal  121  of output circuit  122 , and a source connected to a reference, in this example, ground  126 . Transistor  113  has a drain connected to bottom terminal  124  of output circuit  122 , and a source connected to a reference, in this example, ground  126 . 
     Transistors  110 ,  111 ,  112 ,  113  also have control terminals, namely respective gates  110   a,    111   a,    112   a,    113   a.  Applying an appropriate voltage to a gate drives the corresponding transistor to conduction, thereby allowing current to flow between source and drain. In this example, gate  110   a  is controlled by applying a signal from secondary winding  103 , gate  111   a  is controlled by applying a signal from secondary winding  104 , gate  112   a  is controlled by applying a signal from secondary winding  105 , and gate  113   a  is controlled by applying a signal from secondary winding  106 . In one state of operation shown in  FIG. 2 , transistors  110  and  113  are driven to conduction (with transistors  111  and  112  non-conducting), thereby creating an electrical path  201  from voltage V 1   120 , through transistor  110 , through load  116 , through transistor  113 , to ground  126 . In another state of operation shown in  FIG. 3 , transistors  111  and  112  are driven to conduction (with transistors  110  and  113  non-conducting), thereby creating an electrical path  301  from voltage V 1   120 , through transistor  111 , through load  116 , through transistor  112 , to ground  126 . Thus, voltages applied to the load in the different switching states are opposite in polarity. 
     Transistors  110 ,  111 ,  112 ,  113  are controlled by transformer  101 . In this example, secondary windings  103 ,  106  are opposite in orientation to secondary windings  104 ,  105 . When primary winding  102  is excited with a positive voltage with respect to the dot, secondary windings  103 ,  106  will have a positive voltage (with respect to the dot) induced in them. This will put a positive voltage on gates  110   a,    113   a,  causing transistors  110 ,  113  to conduct. That same signal results in a negative voltage being applied to the gates  111   a  and  112   a,  and, as a result, transistors  111 ,  112  do not conduct. This results in current flow along path  201  of  FIG. 2 . When primary winding  102  is controlled to have a negative voltage with respect to the dot, secondary windings  104 ,  105  will have a negative voltage (with respect to the dot) induced in them. This will put a positive voltage on to gates  111   a,    112   a,  causing transistors  111 ,  112  to conduct. That same signal results in a negative voltage being applied to gates  110   a  and  113   a  and, as a result, transistors  110 ,  114  do not conduct. This results in current flow along path  301  of  FIG. 3 . 
     Circuitry  100 , however, does not provide a mechanism for quickly turning-off (e.g., preventing conduction through) all four transistors  110 ,  111 ,  112 ,  113  at the same time or at about the same time. In some cases, a significant amount of additional circuitry may be included to turn-off all transistors at the same time as part of the gate drive circuit. A downside to this approach is that this amount of additional circuitry increases overall circuit complexity and system cost. By contrast, the examples described herein, which use orthogonal windings, may be simpler, smaller, less expensive, and require less additional circuitry. 
     Turning-off all four transistors can be beneficial in response to fault conditions, or at normal shutdown to reduce transient noise generation. In this regard, it may be possible to provide no signal through primary winding  102 , which will eventually result in all transistors settling into a non-conductive state. However, if transistors are conducting, removal of the signal from the primary winding may not result in the transistors transitioning to a non-conductive state quickly enough. Instead, there can be a lag, during which time the conducting transistors remain at least partly conductive. In this regard, it takes time for their gate drive to drop sufficiently to allow the devices to open. This time is uncontrolled, and possible unwanted states may exist (such as having all transistors conducting). Also, uncontrolled gate drive voltage might result in an intermediate drive being applied for a short period of time placing the transistors in a partially conducting state. This can damage or destroy the devices as large power may be dissipated in the transistors. 
     A transformer having orthogonal windings may be incorporated into a gate drive circuit, such as that included in  FIG. 1 , to turn-off all transistors controlled by the gate drive circuit at about the same time. The orthogonality of the windings, as described below, can ensure the orthogonal inputs and corresponding outputs do not interfere with each other. As described below, in example implementations, there are multiple primary and corresponding secondary windings in the transformer. One set of primary and corresponding secondary windings (a first set) is orthogonal to another set of primary and corresponding secondary windings (a second set). Thus, inputs and corresponding outputs of the first set to do interfere, or substantially interfere, with inputs and corresponding outputs of the second set 
     For example, an input to a primary winding of the second set (e.g., a turn off pulse) results in output signals in secondary windings of the second set to drive gate turn-off circuitry, but does not produce outputs in any of the windings of the first set. Similarly, in this example, an input to a primary winding of the first set results in output signals in secondary windings of the first set, but does not produce outputs in any of the windings of the second set. 
     In an example implementation, the transformer having orthogonal windings may include two magnetic circuits wound around a single E-core, which are configured to operate relatively independently. In the examples described herein, the “orthogonal” part of transformer is configured to produce one or more signals that are used to operate all transistors in a same switching state, e.g., to enable all of the transistors to be turned-off at about the same time. 
     In some implementations, the responsiveness to signals produced by the orthogonal windings may be on the order of tens or hundreds of nanoseconds (ns). For example, in some implementations, the transistors may be turned off (e.g., driven to non-conduction) within that period. In some implementations, the transistors all may be turned-off within 200 ns, 100 ns, 50 ns, or less following application of a turn off command signal to the transformer. In other implementations, the transistors may be turned-off within a different period of time that is greater than 200 ns. Thus, the use of orthogonal windings and the gate drive circuit described herein may result in a reduced turn-off time compared to the case if a signal is simply removed from the primary winding of the transformer, which could result in turn-off times in 100 s of μs to 100 s of ms. 
     Referring, to  FIG. 4 , an example transformer circuit, including transformer  400 , that may be used in a gate drive circuit is shown. In this example, transformer  400  includes primary windings  401 . Primary windings  401  are designated as primary main windings, since signals sent through those windings induce signals in corresponding secondary main windings to control the operation of a first set of transistors and a second set of transistors so that the first set of transistors are operational (e.g., conductive) when the second set of transistors are non-operational (e.g., non-conductive), and vice versa. In this example, transformer  400  includes secondary windings  404 . Secondary windings  404  are designated as secondary main windings, since signals in those windings are induced by signals the primary main windings to control the operation of the first set of transistors and the second set of transistors so that the first set of transistors are operational (e.g., conductive) when the second set of transistors are non-operational (e.g., non-conductive), and vice versa. 
     In the example of  FIG. 1  above, for example, transistors  110 ,  113  are driven to conduction when transistors  111 ,  112  are non-conductive, and transistors  111 ,  112  are driven to conduction when transistors  110 ,  113  are non-conductive. Thus, transistors  110 ,  111  and  112 ,  113  are operated in different switching states from each other by control signals generated via the main windings. 
     In this example, transformer  400  also includes primary winding  409 . Primary winding  409  is designated as a primary orthogonal winding, since primary orthogonal winding  409  defines a magnetic flux path that is orthogonal (or substantially orthogonal) to the magnetic flux path of primary main windings  401 . Signals sent through primary orthogonal winding  409  induce signals in corresponding secondary orthogonal windings to control the operation of transistors controlled by the gate drive circuit so that all transistors are in a same switching state. Secondary windings  410  are designated as secondary orthogonal windings, since each secondary orthogonal winding  410  is coupled to a magnetic flux path that is orthogonal to the magnetic flux path coupling secondary main windings  404 . Signals in secondary orthogonal windings  410  are induced by signals in the primary orthogonal winding  409  to control the operation of all transistors to be in a same switching state. In this regard, in some implementations, all of the transistors controlled by the gate drive circuit are driven to a non-conducing state (a same switching state) by control signals generated via the orthogonal windings, thereby turning-off the gate drive circuit, and preventing an output from the corresponding controlled circuitry. Other types of switching state operation may also be commanded using the circuitry described herein or variants thereof. 
     Examples of the construction of transformers having orthogonal windings are described in U.S. patent application Ser. No. 13/076,923, filed on Mar. 31, 2011, which is incorporated herein by reference. 
     In the example implementations described herein, there may be little or no magnetic coupling between the main windings and the orthogonal windings. As such, each set can be operated independently without inducing significant voltages in the other set of windings. In some implementations, signals from the orthogonal windings override signals from the main windings. As described below, even if signals from the main windings instruct different switching state operation of different sets of transistors, if a signal from the orthogonal windings instructing a same switching state operation is generated, the signal from the orthogonal windings overrides the signals from the main windings, and causes in a same switching state operation of all transistors in the circuit. 
     A transformer having orthogonal windings may be incorporated into circuitry such as that of  FIG. 1 , and operated in the manner described herein to control various switches, and turn all off, or operate all in a same switching state, at about the same time. For example,  FIG. 5  shows example transformer  400  of  FIG. 4  in an example circuitry  500 , including a gate drive circuit, switches (e.g., transistors), and an associated load. However, the concepts described herein are not limited to use with the structures of transformer  400  or circuitry  500 . 
     In the example of  FIG. 5 , primary main winding  401  is excited by a main pulse command associated with different switching state operation of transistors  501 ,  502 ,  503 ,  504 . Primary orthogonal winding  409  is excited by a shutdown command, e.g., when this shutdown command is received, all four transistors  501 ,  502 ,  503 ,  504  are turned off (e.g., placed in an open circuit state) at about the same time (e.g., simultaneously). The orthogonal nature of these two sets of windings allows the main windings to command two of the gate drive signals applied to transistors to be in different switching states with the other two, while the orthogonal windings output voltages to all four gate drive circuits to apply gate drive signals to transistors with identical phase (and required magnitude to cause all transistors to enter a non-conducting state). 
     In the example implementation of  FIG. 5 , transistor  501  corresponds to transistor  110  of  FIG. 1 , transistor  502  corresponds to transistor  111  of  FIG. 1 , transistor  503  corresponds to transistor  112  of  FIG. 1 , and transistor  504  corresponds to transistor  113  of  FIG. 1 . Accordingly, in an example operation, transistors  501 ,  504  are driven to conduction while transistors  502 ,  503  are non-conductive; and transistors  502 ,  503  are driven to conduction while transistors  501 ,  504  are non-conductive. Thus, the operation of transistors  501 ,  502 ,  503 ,  504  when providing signals to load  508  (in this example, the load is included in an audio amplifier) is, conceptually, the same as the operation of transistors  110 ,  111 ,  112 ,  113  of  FIG. 1  when providing signals to the load. For example, the voltage provided to the load via transistors  501 ,  504  is in different switching states from, and opposite in polarity to, the voltage applied to the load via transistors  502 ,  503 . In the example of  FIG. 5 , the voltage references are +B and −B, which may be any appropriate different voltages, such as V 1  and ground. 
     In the example implementation of  FIG. 5 , there is additional control circuitry electrically connected between each secondary winding and each corresponding transistor. Taking transistor  501  as an example, control circuitry  510  includes gate turn-on circuit  511  and gate turn-off circuit  512 . In operation, gate turn-on circuit  511  generates a first control signal that is based on a signal through secondary main winding  404   a.  This first control signal is applied to the gate (the control terminal) of transistor  501  to drive transistor  501  to conduction. In operation, gate turn-off circuit  412  generates a second control signal that is based on a different signal through secondary main winding  404   b.  This second control signal is applied to the gate (the control terminal) of transistor  501  to cause transistor  501  not to conduct. The gate turn-on and gate turn-off circuits of  FIG. 5  are operated to generate appropriate control signals for transistors  501 ,  502 ,  503 ,  504  so that transistors  501 ,  504  are conductive while transistors  502 ,  503  are not conductive, and so that transistors  502 ,  503  are conductive while transistors  501 ,  504  are not conductive (conceptually, the same manner of operation as the circuitry described with respect to  FIG. 1 ). 
     In this example implementation, each gate turn-off circuit (e.g., gate turn-off circuit  512 ) is also responsive to a signal that is based on the output of a corresponding secondary orthogonal winding (e.g., winding  410   a ). In response to the signal from the secondary orthogonal winding, the gate turn-off circuit generates a control signal that overrides any control signal from gate turn-on circuit  511 . This control signal from gate turn-off circuit  512  drives transistor  501  to a non-conductive state (e.g., turns-off transistor  501 ). In some implementations, each gate turn-off circuit (four shown in this example) generates a control signal at about the same time, responsive to the same signal through primary orthogonal winding  409 , to operate its corresponding transistor in a same switching state will all other transistors controlled by the gate drive circuit (e.g., to turn off-each transistor at about the same time). As was the case above, in some implementations, the transistors all may be turned-off within 200 ns, 100 ns, 50 ns, or less following application of a signal to primary orthogonal winding  409  of the transformer  400 . In other implementations, the transistors may be turned-off within a period of time that is greater than 200 ns. 
     In some implementations, a gate drive circuit employing primary and secondary orthogonal windings, such as the gate drive included in circuit  500 , also includes compensation circuitry (not shown specifically in  FIG. 5 ) to reduce noise in the orthogonal signals, which may result from lack of symmetry in magnetic structures comprising the transformers. For example, if there is more than a specified amount of asymmetry in the structure of a transformer, the magnetic flux path of the main windings may not be entirely orthogonal to the magnetic flux path of orthogonal windings. In this case, there may be stray signals, such as noise, induced in the main or orthogonal windings at inappropriate times, adversely affecting the operation of the gate drive circuit. The compensation circuit may be configured to reduce these stray signals or the effects of the stray signals, thereby compensating for the lack of symmetry in magnetic structures comprising the transformer. 
     In this regard,  FIG. 6  shows an example implementation of a portion  600  of circuitry  500  of  FIG. 5 , which includes a compensation circuit. In this example implementation, the compensation circuit includes resistors  601 , which are selected and configured to set noise thresholds to filter out coupling resulting from stray fields. The stray fields may be caused by transformer windings that are not entirely orthogonal. Other types of compensation circuits may be used in addition to, or instead of, the example depicted in  FIG. 6 . 
     In some implementations, the load is, or includes, an audio amplifier or components thereof. However, the gate drive circuit may be used to drive switches to control any appropriate electrical or electro-mechanical load or loads. 
       FIGS. 7A through 7G  show structures of an example orthogonal transformer that may be used in the circuitry described herein. However, the circuitry is not limited to use with the structures shown in  FIGS. 7A through 7G , and may be used with any appropriate transformer structure. 
     Referring to  FIG. 7A , a conventional transformer is shown, which is represented in  FIG. 5  by primary winding  401  (“primary”) and secondary windings  404   a  and  404   b  (“secondaries”) (other secondaries are shown in  FIG. 5 , but only one is depicted in  FIG. 7A  for simplicity). In operation, if current is forced into the dot side of primary  401  (thus is shown the tail of the arrow representing current), current will come out of the dot sides of secondaries  404   a  and  404   b  (thus is shown a point representing the tip of the current arrow). This reflects conventional transformer operation. Referring to  FIG. 7B , the resulting flux path for this operation is shown. 
     To the structure of  FIG. 7A  is added a set of a set of orthogonal windings, such as are represented by orthogonal primary  409  and orthogonal secondary  410   a  shown in  FIG. 7C . Referring to  FIG. 7D , assuming that the flux from primary  401  induced in the center leg of the transformer splits evenly between the two outer legs of the transformer, when the two windings which comprise  409  are connected as shown, the change in magnetic field (dB/dt) resulting from voltage applied across primary  401  induces equal and opposite EMFs in the two windings, such that the voltage seen across orthogonal primary  409  is zero. Likewise, the voltage seen across orthogonal secondary  410   a  is zero. 
     When current flows through orthogonal primary  409 , the resulting flux is shown in  FIG. 7E . It can be seen that the fluxes in the center lag cancel, while those in the outer legs reinforce, resulting in a net flux of  FIG. 7F . Because there is no flux in the center leg resulting from current in orthogonal primary  409  or orthogonal secondary  410 A, voltages applied to orthogonal primary  409  or orthogonal secondary  410   a  will not result in any voltage induced in windings  401 ,  404   a  or  404   b.  This is the reciprocal to the behavior described previously. Furthermore, windings  409  and  410   a  together comprise a transformer, e.g., if current flows into  409  on the dot side, current will flow out of  410  on the dot side, giving conventional transformer operation with the two windings coupled through the flux path shown in  FIG. 7F . This results in the magnetic system coupling:  401 ,  404   a  and  404   b;  and  409  and  410   a.  Being orthogonal, these sets of windings are independent and can transmit information and power independent of one another. 
     Referring to  FIG. 7G , it can also be seen that if the transformer is not perfectly symmetrical, the center leg flux does not split exactly into the two outer legs. This asymmetry results in the two magnetic systems not being perfectly orthogonal, resulting in some bleed-through of signals between the two. Circuitry to filter or otherwise ignore this coupling is described with respect to  FIG. 6 . 
     The circuitry described above is not limited to the specific implementations described herein. For example, the transistors may be replaced with any appropriate circuitry or other controllable switch or switching element. There may be different numbers of primary main windings, secondary main windings, primary orthogonal windings, and secondary orthogonal windings than those described herein. There also may be different numbers of transistors, and they may be in different configurations, than in the example implementations described herein. Any appropriate control circuitry, and numbers of control circuits, may be used. 
     Any “electrical connection” as used herein may imply a direct physical connection or a connection that includes intervening components but that nevertheless allows electrical signals (including wireless signals) to flow between connected components. Any “connection” involving electrical circuitry mentioned herein, unless stated otherwise, is an electrical connection and not necessarily a direct physical connection regardless of whether the word “electrical” is used to modify “connection”. 
     Elements of different implementations described herein can be combined to form other implementations not specifically set forth above. 
     Other implementations not specifically described herein are also within the scope of the following claims.