Driving apparatus

Provided is a driving apparatus that drives a switching device, the driving apparatus including a reference potential line, a first switching control unit configured to switch whether to connect a control terminal of the switching device to the reference potential line, a first resistor element arranged in series to the first switching control unit in a path from the control terminal of the switching device to the reference potential line, a first capacitor provided in parallel with the first resistor element in the path from the control terminal of the switching device to the reference potential line, and a discharge control unit configured to control whether to discharge the first capacitor.

The contents of the following Japanese patent application is incorporated herein by reference:2020-216718 filed in JP on Dec. 25, 2020

BACKGROUND

1. Technical Field

The present invention relates to a driving apparatus that drives a switching device.

2. Related Art

Up to now, a driving apparatus that controls a switching device such as a transistor has been proposed (for example, see Patent document 1.Patent document 1: Japanese Patent Application Publication No. 2000-324801

The driving apparatus can preferably cope with a high speed operation of the switching device.

SUMMARY

To address the above-described issue, according to one aspect of the present invention, there is provided a driving apparatus that drives a switching device. The driving apparatus may include a reference potential line. The driving apparatus may include a first switching control unit configured to switch whether to connect a control terminal of the switching device to the reference potential line. The driving apparatus may include a first resistor element arranged in series to the first switching control unit in a path from the control terminal of the switching device to the reference potential line. The driving apparatus may include a first capacitor provided in parallel with the first resistor element in the path from the control terminal of the switching device to the reference potential line. The driving apparatus may include a discharge control unit configured to control whether to discharge the first capacitor.

The discharge control unit may discharge the first capacitor under a condition that a control voltage at the control terminal of the switching device is lower than or equal to a first threshold voltage. The first threshold voltage may be lower than a plateau voltage of the switching device.

The switching device may be any element of a pair of switching devices configured to operate in a complementary manner. The discharge control unit may discharge the first capacitor from completion of turn-off to start of next turn-on.

The first resistor element may be arranged between the control terminal of the switching device and the first switching control unit. The first capacitor may be arranged in parallel with the first resistor element between the control terminal of the switching device and the first switching control unit.

The driving apparatus may include a first diode arranged in parallel with the first resistor element between the control terminal of the switching device and the first capacitor.

The discharge control unit may include a first transistor arranged between a connection point of the first diode and the first capacitor and the reference potential line.

The driving apparatus may include a second resistor element arranged in series to the first diode between a connection point of the first capacitor and the first transistor and the control terminal of the switching device.

The driving apparatus may include a third resistor element arranged in series to the first transistor between the connection point of the first capacitor and the first transistor and the reference potential line.

The driving apparatus may include a fourth resistor element arranged in series to the first capacitor between a connection point of the first switching control unit and the first resistor element and a connection point of the first diode and the first transistor.

The first diode may be a Zener diode.

A capacitance of the first capacitor may be variable. The driving apparatus may include a capacitance control unit configured to control the capacitance of the first capacitor.

A resistance value of the second resistor element may be variable. A resistance value of the third resistor element may be variable. A resistance value of the fourth resistor element may be variable. The driving apparatus may include a resistance control unit configured to control a resistance value of a resistor element.

The switching device may be a wide bandgap semiconductor device using at least one of silicon carbide, gallium nitride, gallium oxide, and diamond as a main material. The first capacitor may have a capacitance in which electric charge of the control terminal can be moved and accumulated until a control voltage at the control terminal of the switching device turns to a plateau voltage.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the present invention will be described by way of embodiments of the invention, but the following embodiments are not intended to restrict the invention according to the claims. In addition, not all combinations of features described in the embodiments necessarily have to be essential to solving means of the invention. Note that in the present specification and drawings, an element having a substantially identical function or configuration is assigned with the identical reference sign, so that duplicated description will be omitted, and an illustration of an element that is not directly related to the present invention will be omitted. In addition, in one drawing, a representative element among elements having the identical function or configuration is assigned with a reference sign, and reference signs for the others may be omitted.

In the present specification, when such a term “identical” or “equal” is used, a case where an error derived from a production tolerance or the like is present may also be included. The error is, for example, within 10%. In addition, when the term like “identical” or “equal” is used, approximate values may be set due to costs. With regard to the approximate values, for example, an E-series value is adopted from among non-series values as in “3.1Ω is set as 3.3Ω” or the like.

FIG.1is a diagram illustrating one example of a power supply circuit200according to a reference example. The power supply circuit200is configured to supply power to a load. The power supply circuit200of the present example includes switching devices112-1and112-2, driving apparatuses210-1and210-2, a control circuit114, a high potential line120, and a reference potential line122.

The switching device112-1and the switching device112-2are each a transistor such as a MOSFET as one example, but are not limited to this. Each of the switching devices112may have a drain terminal, a source terminal, and a gate terminal. When the switching device112is an insulated gate bipolar transistor (IGBT) or the like, the drain terminal and the source terminal may also be referred to as a collector terminal and an emitter terminal. The gate terminal is one example of a control terminal that controls an on/off state of the switching device112.

The switching device112-1and the switching device112-2of the present example may be connected in series to each other between a high potential line120and a reference potential line122. A reference potential such as a ground potential is applied to the reference potential line122. A high potential higher than the reference potential is applied to the high potential line120. An external power source may be connected to the reference potential line122and the high potential line120. In addition, a capacitor116may be connected between the reference potential line122and the high potential line120.

According to the present example, the drain terminal of the switching device112-2is connected to the high potential line120, and the drain terminal of the switching device112-1is connected to the source terminal of the switching device112-2. In addition, the source terminal of the switching device112-1is connected to the reference potential line122.

The power supply circuit200supplies the power to the load from a connection point118of the switching device112-1and the switching device112-2. The on/off states of the switching device112-1and the switching device112-2are mutually switched in a complementary manner. That is, when one of the switching devices112is in the on state, the other switching device112is controlled to be in the off state. With this configuration, whether the load is connected to the high potential line120or connected to the reference potential line122is switched.

A driving apparatus210-1controls the switching device112-1to switch the on state and the off state. A driving apparatus210-2controls the switching device112-2to switch the on state and the off state. The driving apparatus210-2may have a similar function and structure to the driving apparatus210-1. According to the present example, the structure and operation of the driving apparatus210-1will be described, and description of the driving apparatus210-2will be omitted. In addition, in the present specification, the driving apparatus210-1may be simply referred to as the driving apparatus210.

The driving apparatus210generates a control signal to be input to the gate terminal of the switching device112. The driving apparatus210includes a first switching control unit11, a second switching control unit12, a first resistor element21, a resistor element22, a first power source31, a second power source32, and a first capacitor50.

The first power source31and the second power source32are arranged in series to each other between a high potential line40and a reference potential line42. The first power source31and the second power source32generate a voltage between the high potential line40and the reference potential line42. A connection point91of the first power source31and the second power source32may be connected to the source terminal of the switching device112.

The first switching control unit11and the second switching control unit12control switching of the on/off state of the switching device112. The first switching control unit11and the second switching control unit12of the present example are transistors arranged in series to each other between the high potential line40and the reference potential line42and configured to operate in a complementary manner. Each of the transistors illustrated in the present specification and the drawings may be a bipolar transistor, may be a MOSFET, may be an IGBT, may be a wide bandgap semiconductor device using at least one of silicon carbide, gallium nitride, gallium oxide, and diamond as a main material, or may be another semiconductor switching device. A connection point92of the first switching control unit11and the second switching control unit12is connected to the control terminal (gate terminal) of the switching device112.

The first switching control unit11controls whether to connect the control terminal of the switching device112to the reference potential line42. According to the present example, when the first switching control unit11is in the on state, the control terminal of the switching device112is connected to the reference potential line42. The second switching control unit12controls whether to connect the control terminal of the switching device112to the high potential line40. According to the present example, when the second switching control unit12is in the on state, the control terminal of the switching device112is connected to the high potential line40

The control circuit114controls the on/off states of the first switching control unit11and the second switching control unit12. The control circuit114may generate control signals applied to control terminals of the first switching control unit11and the second switching control unit12.

The first resistor element21is provided in series to the first switching control unit11in a path between the control terminal of the switching device112and the reference potential line42. The first resistor element21of the present example is arranged between the first switching control unit11and the reference potential line42, but may be arranged between the connection point92and the first switching control unit11. When the first switching control unit11turns on, electric charge accumulated in a gate capacitance of the switching device112is drawn to the reference potential line42through the first resistor element21. For this reason, a speed of turn-off by the switching device112is adjusted by a resistance value of the first resistor element21, and a time rate of change (which may also be referred to as di/dt) of a main current (in the present example, a drain current Id) of the switching device112can be adjusted. Note that when the switching device112performs a turn-off operation, a surge voltage in accordance with the time rate of change of the main current of the switching device112is generated at main terminals (in the present example, the source terminal and the drain terminal) of the switching device112.

The resistor element22is provided in series to the second switching control unit12in a path between the control terminal of the switching device112and the high potential line40. The resistor element22of the present example is arranged between the second switching control unit12and the high potential line40, but may be arranged between the connection point92and the second switching control unit12. When the second switching control unit12turns on, the gate capacitance of the switching device112is charged with the electric charge from the high potential line40through the resistor element22. For this reason, a speed of turn-on by the switching device112is adjusted by a resistance value of the resistor element22, and the time rate of change (which may also be referred to as di/dt) of the main current (in the present example, the drain current Id) of the switching device112can be adjusted.

As described above, when the resistance value of the first resistor element21is increased, the surge voltage can be suppressed by decreasing the time rate of change of the main current. However, when the resistance value of the first resistor element21is increased, a discharge time of gate charge of the switching device112is lengthened, and a period of time (in the present specification, which will be referred to as a turn-off time) from start to completion of a turn-off operation of the switching device112is increased. For this reason, a turn-off loss of the switching device112is increased. Note that the completion of the turn-off may be timing at which interruption of the main current of the switching device112is completed, or timing at which a voltage between the main terminals after the generation of the surge voltage is matched with a voltage of the capacitor116.

On the other hand, when the resistance value of the first resistor element21is decreased, the turn-off loss can be reduced by shortening the turn-off time of the switching device112. However, the surge voltage is increased.

Since an operating frequency of a semiconductor device in recent years has been increased, the switching device112can preferably perform a high speed operation. To cause the switching device112to perform the high speed operation, suppression of the surge voltage and suppression of the turn-off time and the turn-off loss are preferably balanced.

The power supply circuit200includes the first capacitor50provided in parallel with the first resistor element21in a path from the control terminal of the switching device112to the reference potential line42. The first capacitor50of the present example is provided in parallel with the first resistor element21between a connection point93of the first switching control unit11and the first resistor element21and the reference potential line42.

When the first capacitor50is provided, immediately after the first switching control unit11is put into the on state, the gate charge of the switching device112is moved to the first capacitor50via the first switching control unit11. In this case, the gate charge does not pass through the first resistor element21. For this reason, the gate voltage of the switching device112promptly falls. For this reason, the turn-off time of the switching device112can be shortened.

After the first capacitor50is sufficiently charged with the electric charge, the gate charge of the switching device112is moved to the reference potential line42mainly through the first switching control unit11and the first resistor element21. For this reason, the time rate of change of the main current can be adjusted by the first resistor element21, and the surge voltage can be suppressed.

In this manner, when the first capacitor50is provided, the turn-off time of the switching device112is shortened, and also, the surge voltage can be suppressed. However, in a case where turn-on and turn-off of the switching device112are repeated, when the electric charge accumulated in the first capacitor50at the time of the previous turn-off is not sufficiently discharged by the next turn-off, the sufficient gate charge cannot be moved to the first capacitor50at the time of the next turn-off. In this case, the turn-off time cannot be shortened.

According to the present example, the first resistor element21also functions as a discharge circuit of the first capacitor50. Thus, the electric charge accumulated in the first capacitor50is discharged via the first resistor element21. For this reason, when the resistance value of the first resistor element21is increased for a purpose of suppressing the surge voltage, the discharge of the accumulated charge of the first capacitor50is slowed down, and a case may occur that the accumulated charge cannot be sufficiently discharged by the next turn-off. In particular, when the switching device112performs the high speed operation, the discharge of the first capacitor50might be too late. When the resistance value of the first resistor element21is decreased, the discharge time of the first capacitor50is shortened, but it becomes difficult to suppress the surge voltage.

FIG.2is a diagram illustrating a configuration example of a power supply circuit100according to one embodiment of the present invention. The power supply circuit100includes driving apparatuses110-1and110-2instead of the driving apparatuses210-1and210-2illustrated inFIG.1. A configuration other than the driving apparatus110is similar to the power supply circuit200illustrated inFIG.1. The driving apparatus110-2has a similar function and configuration to the driving apparatus110-1. According to the present example, a structure and operation of the driving apparatus110-1will be described, and description of the driving apparatus110-2will be omitted. In addition, in the present specification, the driving apparatus110-1may be simply referred to as the driving apparatus110.

The driving apparatus110is configured to drive the switching device112. Similarly as in the driving apparatus210, the driving apparatus110includes the first power source31, the second power source32, the first switching control unit11, the second switching control unit12, the first resistor element21, the resistor element22, and the first capacitor50. In the example ofFIG.2, the first resistor element21is arranged between the connection point92and the first switching control unit11, and the resistor element22is arranged between the connection point92and the second switching control unit12. In another example, the first resistor element21may be arranged between the first switching control unit11and the reference potential line42. In addition, the resistor element22may be arranged between the second switching control unit12and the high potential line40.

The first capacitor50is provided in parallel with the first resistor element21in the path from the control terminal of the switching device112to the reference potential line42. The first capacitor50of the present example is arranged in parallel with the first resistor element21between the control terminal of the switching device112and the first switching control unit11(or the connection point93). The connection point93is a connection point of the first resistor element21and the first switching control unit11.

The driving apparatus110further includes a discharge control unit52configured to control whether to discharge the first capacitor50. The discharge control unit52is provided to be separate from the first switching control unit11. The discharge control unit52of the present example is a first transistor configured to switch whether to connect an electrode on the switching device112side of the first capacitor50to the reference potential line42. When the first switching control unit11is in the on state and also the discharge control unit52is put into the on state, both ends of the first capacitor50are connected to the reference potential line42. With this configuration, the first capacitor50is discharged without the intermediation of the first resistor element21. Note that on resistances of the first switching control unit11and the discharge control unit52are sufficiently smaller than the first resistor element21.

The discharge control unit52is put into the on state after the timing at which the first switching control unit11is put into the on state. With this configuration, during a predetermined period since the first switching control unit11is put into the on state, the gate charge of the switching device112is moved to the first capacitor50, and the gate voltage of the switching device112promptly falls. For this reason, the turn-off time of the switching device112can be shortened. Then, since the discharge control unit52is put into the on state, the accumulated charge of the first capacitor50is discharged without the intermediation of the first resistor element21. With this configuration, the accumulated charge of the first capacitor50can be promptly discharged, and even when the switching device112performs the high speed operation, the discharge of the first capacitor50can be sufficiently performed. In addition, the surge voltage can be suppressed by adjusting the resistance value of the first resistor element21.

The control circuit114may control the on/off state of the discharge control unit52. The control circuit114may control the discharge control unit52based on the timing at which the first switching control unit11is put into the on state. For example, the discharge control unit52may be put into the on state after a predetermined period of time elapses since the first switching control unit11is put into the on state. In addition, the control circuit114may control the discharge control unit52based on a state of any of the driving apparatus110-1, the driving apparatus110-2, the switching device112-1, and the switching device112-2. A state of each of the apparatuses and the devices may be an instantaneous value or a temporal waveform of a voltage or a current in a predetermined position on a circuit.

The driving apparatus110may further include a first diode54. The first diode54is arranged in parallel with the first resistor element21between the control terminal of the switching device112and the first capacitor50. The first diode54is arranged such that a direction from the switching device112towards the first capacitor50is set as a forward direction. When the first diode54is provided, the discharge of the accumulated charge of the first capacitor50via the first resistor element21can be avoided. The discharge control unit52of the present example is arranged between a connection point95of the first diode54and the first capacitor50and the reference potential line42.

FIG.3is a drawing illustrating an operation example of the switching device112-1and the driving apparatus110-1. A horizontal axis inFIG.3represents time, and a vertical axis represents a magnitude of a voltage or a current. In addition, the gate voltage (gate-source voltage) of the switching device112is denoted by Vgs, a gate current is denoted by Ig, the voltage between the main terminals is denoted by Vds, the main current is denoted by Id, and a voltage of the first capacitor50is denoted by Vc.

In an initial state ofFIG.3, the switching device112is in the on state. At timing t1, the first switching control unit11shifts from the off state to the on state. With this configuration, the gate current Ig flows, and the gate charge of the switching device112is moved to the first capacitor50. The gate voltage Vgs promptly falls, and the capacitor voltage Vc rises. InFIG.3, the gate current Ig flowing to the control terminal of the switching device112is set as positive, and the gate current Ig flowing from the control terminal is set as negative. The gate charge is moved to the first capacitor50until timing t2at which the gate voltage Vgs falls to a plateau voltage of the switching device112. The plateau voltage will be described below. The first capacitor50may have a capacitance in which the gate charge can be moved and accumulated such that the gate voltage Vgs of the switching device112is matched with the plateau voltage, or may have a capacitance in which the gate charge can be moved and accumulated such that the gate voltage Vgs of the switching device112turns to the plateau voltage. That is, the capacitance of the first capacitor50may be a capacitance or larger in which a total amount of the moved gate charge can be accumulated when the gate charge is moved from the switching device112such that the gate voltage Vgs of the switching device112is matched with the plateau voltage.

When the gate voltage Vgs falls to the plateau voltage and thereafter (at t2and thereafter), the gate charge of the switching device112flows to the reference potential line42through the first resistor element21and the first switching control unit11. The gate current Ig is relatively decreased by the resistance value of the first resistor element21. In addition, the voltage Vds between the main terminals gradually rises since the switching device112starts to turn off.

When a predetermined period elapses since the gate voltage Vgs falls to the plateau voltage, the gate voltage Vgs starts to be lower than the plateau voltage (timing t3). For example, when discharge of electric charge of a feedback capacitance Crss (or a gate-drain capacitance Cgd) of the switching device112is finished, the gate voltage Vgs starts to fall. A duration of a period from t2to t3may be 0. The time rate of change (di/dt) of the main current Id affecting a magnitude of the surge voltage is determined by a magnitude of the gate current Ig during the period from t2to t3. According to the present example, since the gate current Ig during the period can be adjusted by the first resistor element21, the surge voltage can be suppressed.

According to the embodiment ofFIG.2, the discharge control unit52discharges the first capacitor50at predetermined timing t4at or after the timing t3. In the example ofFIG.3, the discharge control unit52is put into the on state under a condition that the gate voltage Vgs is lower than or equal to a first threshold voltage. The first threshold voltage is lower than the plateau voltage. With this configuration, since the capacitor voltage Vc promptly falls, even when the switching device112performs the high speed operation, the first capacitor50can be sufficiently discharged. In addition, the gate current Ig of the switching device112also flows to the reference potential line42through the discharge control unit52. For this reason, it is possible to cause the gate voltage Vgs to promptly fall. Note that, the gate current Ig is increased when the discharge control unit52is put into the on state at the timing t4, which however does not affect the magnitude of the surge voltage generated at the timing t3.

As described above, according to the embodiment illustrated inFIG.2andFIG.3, it is possible to provide the driving apparatus110that balances the suppression of the surge voltage of the switching device112and the shortening of the turn-off time and further can cope with the increase in the operating frequency of the switching device112.

Note that the plateau voltage may be a voltage that satisfies at least any one or more of the following conditions (1) to (3).

(1) The gate-source voltage Vgs in a region between inflexion points on a gate charge-Vgs characteristic curve of the switching device112.

(2) The gate voltage Vgs during a period in which the main current Id does not change but the drain-source voltage Vds changes in a switching operation of the switching device.

(3) The gate voltage Vgs while the feedback capacitance Crss (or the gate-drain capacitance Cgd) in the MOSFET is discharged. When a specification value of the plateau voltage is set by a manufacturer or the like of the switching device112, the specification value may be used.

In addition, the first threshold voltage may be a voltage defined by any of the following (4) to (6), and when a specification value of a threshold voltage is set by the manufacturer or the like of the switching device112, the specification value may be used.

(4) The gate voltage Vgs in a case where the main current Id is 0. The case where the main current Id is 0 includes a case where the main current Id turns to substantially 0 like a case where the main current is lower than or equal to measuring power of measurement equipment.

(5) The gate voltage Vgs in a case where the main current Id that is 0.1% of a rated current of the switching device112flows. It is sufficient when the value of the main current Id used herein is sufficiently lower than the rated current as in 1% or below, and is not limited to 0.1% of the rated current.

(6) The gate voltage Vgs in a case where the main current Id flowing to the switching device112is equal to a leakage current at the time of interruption in the off state. The case where the main current is equal to the leakage current at the time of interruption includes a case where the main current is substantially equal to the leakage current at the time of interruption like a case where a difference is lower than or equal to the measuring power of the measurement equipment.

At the timing t4and thereafter, since the discharge control unit52is in the on state, a short-circuit state equivalently occurs between the gate and the source of the switching device112. For this reason, the gate-source voltage Vgs of the switching device112is fixed to a reverse bias voltage, and it is possible to avoid a situation where the switching device112is erroneously put into the on state. For this reason, the discharge control unit52also functions as an active mirror clamp circuit that avoids the erroneous on state of the switching device112.

Therefore, it is sufficient when the discharge of the first capacitor50is completed at latest by the next turn-on of the switching device. By the next turn-on of the switching device, the first capacitor50may be discharged during a dead time period of the pair of switching devices112-1and112-2configured to operate in a complementary manner. The dead time period refers to a period in which both the switching devices112are in the off state (or controlled to be put in the off state).

Note that the discharge control unit52can also function as the active mirror clamp circuit by turning on the discharge control unit52at timing at which the gate voltage of the switching device is lower than the first threshold voltage.

The control circuit114may control the discharge control unit52based on at least one of the gate voltage Vgs, the gate current Ig, the voltage Vds between the main terminals, and the main current Id. Based on at least one of these, the control circuit114may estimate the timing t3at which the gate voltage Vgs starts to be lower than the plateau voltage. For example, the control circuit114may detect timing at which the voltage Vds between the main terminals indicates a peak as t3, and may also detect timing at which the main current Id starts to fall from a steady state value as t3. The control circuit114may control the discharge control unit52to be in the on state at predetermined timing at or after the timing t3.

FIG.4is a diagram illustrating another configuration example of the driving apparatus110. The driving apparatus110of the present example further includes a second resistor element24in addition to the configuration of the driving apparatus110described with reference toFIG.2. The second resistor element24is arranged in series to the first diode54between the connection point95of the first capacitor50and the discharge control unit52and the control terminal of the switching device112. In the example ofFIG.4, the second resistor element24is arranged between the first diode54and the connection point95, but in another example, the second resistor element24may be arranged between the first diode54and the control terminal of the switching device112. When the second resistor element24is arranged in this manner, a discharge speed of the first capacitor50is not decreased, and it is possible to set a current flowing to the first diode54to be within a limit value of the first diode54.

When the second resistor element24is provided, the current flowing to the first diode54can be adjusted. For example, when the second resistor element24is provided, it is possible to avoid a situation where a current exceeding the rated value flows to the first diode54. Note that, to shorten the turn-off time, a resistance value of the second resistor element24is preferably lower than the resistance value of the first resistor element21.

In addition, when the resistance value of the second resistor element24is adjusted, the current flowing to the first capacitor50from the control terminal of the switching device112can be adjusted. With this configuration, the time rate of change of the voltage Vds between the main terminals can be adjusted. Furthermore, when the resistance value of the first resistor element21is adjusted, the current flowing to the reference potential line42from the control terminal of the switching device112through the first resistor element21and the first switching control unit11can be adjusted. With this configuration, the time rate of change of the main current Id can be adjusted. That is, in the present example, since the first resistor element21and the second resistor element24are separately adjusted, it is possible to independently adjust the time rate of change of the voltage Vds between the main terminals and the time rate of change of the main current Id. With this configuration, the switching speed can be increased without increasing the surge voltage, and the switching loss can be reduced.

FIG.5is a diagram illustrating another configuration example of the driving apparatus110. The driving apparatus110of the present example further includes a third resistor element26in addition to the configuration of any of the driving apparatuses110described with reference toFIG.2toFIG.4. As illustrated inFIG.4, the driving apparatus110may include the second resistor element24. The third resistor element26is arranged in series to the discharge control unit52between the connection point95and the reference potential line42. In the example ofFIG.5, the third resistor element26is arranged between the discharge control unit52and the connection point95, but in another example, the third resistor element26may be arranged between the discharge control unit52and the reference potential line42. In this manner, when the third resistor element26is arranged, it is possible to set the current flowing to the discharge control unit52to be within a limit value of the discharge control unit52without lengthening the turn-off time.

When the third resistor element26is provided, the current flowing to the discharge control unit52can be adjusted. For example, when the third resistor element26is provided, it is possible to avoid a situation where a current exceeding the rated value flows to the discharge control unit52. Note that, to shorten the turn-off time, a resistance value of the third resistor element26is preferably lower than the resistance value of the first resistor element21.

FIG.6is a diagram illustrating another configuration example of the driving apparatus110. The driving apparatus110of the present example further includes a fourth resistor element28in addition to the configuration of any of the driving apparatuses110described with reference toFIG.2toFIG.5. As illustrated inFIG.4andFIG.5, the driving apparatus110may include at least one of the second resistor element24and the third resistor element26. The fourth resistor element28is arranged in series to the first capacitor50between the connection point93and the connection point95. In the example ofFIG.6, the fourth resistor element28is arranged between the connection point95and the first capacitor50, but in another example, the fourth resistor element28may be arranged between the connection point93and the first capacitor50. When the fourth resistor element28is arranged in this manner, it is possible to set the current flowing to the first capacitor50to be within the limit value of the first capacitor50without reducing an effect of the active mirror clamp circuit included in the discharge control unit52.

When the fourth resistor element28is provided, the current flowing to the first capacitor50can be adjusted. For example, when the fourth resistor element28is provided, it is possible to avoid a situation where a current exceeding the rated value flows to the first capacitor50or the first diode54. Note that, to shorten the turn-off time, a resistance value of the fourth resistor element28is preferably lower than the resistance value of the first resistor element21.

In addition, when the resistance value of the fourth resistor element28is adjusted, the current flowing to the first capacitor50from the control terminal of the switching device112can be adjusted. With this configuration, the time rate of change of the voltage Vds between the main terminals can be adjusted. Furthermore, when the resistance value of the first resistor element21is adjusted, the current flowing to the reference potential line42from the control terminal of the switching device112through the first resistor element21and the first switching control unit11can be adjusted. With this configuration, the time rate of change of the main current Id can be adjusted. That is, in the present example, when the first resistor element21and the fourth resistor element28are separately adjusted, the time rate of change of the voltage Vds between the main terminals and the time rate of change of the main current Id can be independently adjusted. With this configuration, the switching speed can be increased without increasing the surge voltage, and the switching loss can be reduced.

FIG.7is a diagram illustrating another configuration example of the driving apparatus110. With regard to the driving apparatus110of the present example, in the configuration of any of the driving apparatuses110described with reference toFIG.2toFIG.6, the capacitance of the first capacitor50is variable. In addition, the driving apparatus110may include a capacitance control unit124configured to control the capacitance of the first capacitor50. A configuration other than the first capacitor50and the capacitance control unit124is similar to any of the examples described with reference toFIG.2toFIG.6.

The capacitance control unit124may adjust the capacitance of the first capacitor50such that a period from t1to t3illustrated inFIG.3approaches 0. With this configuration, the timing t3at which the gate voltage Vgs turns to be lower than the plateau voltage can be expedited, and the turn-off time of the switching device112can be shortened.

For example, when the capacitance of the first capacitor50is increased, the still more gate charge can be moved to the first capacitor50. During the period from t2to t3, since the gate charge that is not moved to the first capacitor50is discharged via the first resistor element21, the period from t2to t3can be shortened by increasing the capacitance of the first capacitor50. It is noted however that when the capacitance of the first capacitor50is set to be too large, since the large gate current Ig flows even after the voltage Vds between the main terminals rises, the surge voltage is increased.

The capacitance control unit124may adjust the capacitance of the first capacitor50in such a range that the surge voltage is not increased. The capacitance control unit124may adjust the capacitance of the first capacitor50using operation information of the circuit (such as the gate voltage Vgs, the gate current Ig, the voltage Vds between the main terminals, the main current Id, and the capacitor voltage Vc), control information of a driving target device (such as an on time and an off time of the driving target device, and a signal to be input to the driving apparatus110from the control circuit114). In addition, the capacitance of the first capacitor50may be adjusted such that the period from t2to t3is shortened.

FIG.8is a diagram illustrating another configuration example of the driving apparatus110. With regard to the driving apparatus110of the present example, in the configuration of the driving apparatus110illustrated inFIG.4, the resistance value of the second resistor element24is variable. In addition, the driving apparatus110may include a resistance control unit126configured to control the resistance value of the second resistor element24. A configuration other than the second resistor element24and the resistance control unit126is similar to the example described with reference toFIG.4.

According to the present example, the current flowing to the first diode54can be adjusted. In addition, when the resistance value of the second resistor element24is adjusted, the current flowing to the first capacitor50from the control terminal of the switching device112and the current flowing to the reference potential line42from the control terminal of the switching device112via the discharge control unit52can be adjusted. The resistance control unit126may adjust the resistance value of the second resistor element24such that a conduction current of the first diode54is set to be within a limit value.

FIG.9is a diagram illustrating another configuration example of the driving apparatus110. With regard to the driving apparatus110of the present example, in the configuration of the driving apparatus110illustrated inFIG.5, the resistance value of the third resistor element26is variable. In addition, the driving apparatus110may include the resistance control unit126configured to control the resistance value of the third resistor element26. A configuration other than the third resistor element26and the resistance control unit126is similar to the example described with reference toFIG.5.

According to the present example, the current flowing to the discharge control unit52can be adjusted. In addition, when the resistance value of the third resistor element26is adjusted, the current flowing to the reference potential line42from the first capacitor50and the current flowing to the reference potential line42from the switching device112via the third resistor element26can be adjusted. The resistance control unit126may adjust the resistance value of the third resistor element26such that the conduction current of the first diode54is set to be within the limit value.

FIG.10is a diagram illustrating another configuration example of the driving apparatus110. With regard to the driving apparatus110of the present example, in the configuration of the driving apparatus110illustrated inFIG.6, the resistance value of the fourth resistor element28is variable. In addition, the driving apparatus110may include the resistance control unit126configured to control the resistance value of the fourth resistor element28. A configuration other than the fourth resistor element28and the resistance control unit126is similar to the example described with reference toFIG.6.

According to the present example, the current flowing to the first capacitor50can be adjusted. In addition, when the resistance value of the fourth resistor element28is adjusted, the current flowing to the first capacitor50from the control terminal of the switching device112and the current flowing to the reference potential line42from the first capacitor50can be adjusted. The resistance control unit126may adjust the resistance value of the fourth resistor element28such that the conduction current of the first diode54is set to be within the limit value.

The resistance control unit126described with reference toFIG.8toFIG.10may control one or more resistances among the second resistor element24, the third resistor element26, and the fourth resistor element28. In addition, the resistance control unit126may control the resistance value of the first resistor element21. In this case, an inclination of the gate voltage Vgs during a period from t3to t4which is illustrated inFIG.3can be adjusted.

FIG.11is a diagram illustrating another configuration example of the driving apparatus110. The driving apparatus110of the present example further includes the discharge control unit52in addition to the configuration of the driving apparatus210-1illustrated inFIG.1. The discharge control unit52of the present example also controls whether to discharge the first capacitor50. Timing at which the discharge control unit52discharges the first capacitor50is similar to the examples described with reference toFIG.2toFIG.10.

The discharge control unit52of the present example is provided in parallel with the first capacitor50. The discharge control unit52of the present example is a transistor configured to control whether to connect both electrodes of the first capacitor50. It is noted however that the configuration of the discharge control unit52is not limited to this. It is sufficient when the discharge control unit52can discharge the first capacitor50at any timing independently from the first switching control unit11. In the present example too, the suppression of the surge voltage, the shortening of the turn-off time, and the high speed discharge of the first capacitor50can be realized.

FIG.12is a diagram illustrating another configuration example of the driving apparatus110. With regard to the driving apparatus110of the present example, in any of the driving apparatuses110described with reference toFIG.2toFIG.10, the first diode54is a Zener diode. A structure other than the first diode54is similar to any of the examples described with reference toFIG.2toFIG.10. According to the present example, while the switching device112turns off, it is possible to suppress variation of the gate voltage Vgs in a negative direction.

In a state where the switching device112-1turns off, when the switching of the other switching device112-2to the on or off state is performed, the gate voltage Vgs of the switching device112-1may vary in a positive direction or the negative direction. When the gate voltage Vgs varies in the negative direction, dielectric breakdown may occur between the gate and the source. On the other hand, when the gate voltage Vgs varies in the positive direction, the switching device112-1may erroneously shift to the on state, and a short-circuit state may occur in which both the switching device112-1and the switching device112-2turn on.

As described with reference toFIG.2and the like, since the discharge control unit52functions as the active mirror clamp circuit, the erroneous shift of the switching device112-1to the on state can be avoided. In addition, since the Zener diode is used as the first diode54, the variation of the gate voltage Vgs in the negative direction can be suppressed.

FIG.13illustrates an equivalent circuit of the driving apparatus110and the switching device112-1which are illustrated inFIG.12.FIG.13illustrates the capacitances Cgd, Cds, and Cgs between the respective terminals of the switching device112-1. In addition,FIG.13illustrates an equivalent circuit in a case where the switching device112shifts to the off state and is put into the steady state. Both the first switching control unit11and the discharge control unit52are in the on state. In this case, the first capacitor50is in the short-circuit state in which electrodes at both ends are connected, and is therefore not taken into account in the equivalent circuit ofFIG.13. In the steady state, the gate voltage Vgs of the capacitance Cgs is substantially equal to the voltage Vg generated by the first power source31.

In this state, when the switching of the other switching device112-2is performed, and the gate voltage Vgs rises in the negative direction, a voltage Vgs-Vg in accordance with the variation is applied to the first diode54. Note that the similar voltage Vgs-Vg is also applied to the first resistor element21.

When the voltage Vgs-Vg exceeds a breakdown voltage of the first diode54, the first diode54turns on, and the first power source31and the capacitance Cgs are connected in parallel with each other. At this time, the voltage applied to the first resistor element21falls to 0 V. Note that the breakdown voltage of the first diode54is preferably designed such that the gate voltage Vgs does not exceed a gate-source withhold voltage.

Since the first power source31and the capacitance Cgs are connected in parallel with each other, the gate voltage Vgs is set to be equal to the voltage Vg. With this configuration, it is possible to avoid the excessive rise of the gate voltage Vgs in the negative direction.

EXPLANATION OF REFERENCES

11: first switching control unit,12: second switching control unit,21: first resistor element,22: resistor element,24: second resistor element,26: third resistor element,28: fourth resistor element,31: first power source,32: second power source,40: high potential line,42: reference potential line,50: first capacitor,52: discharge control unit,54: first diode,91,92,93,95,118: connection point,100: power supply circuit,110,210: driving apparatus,112: switching device,114: control circuit,116: capacitor,120: high potential line,122: reference potential line,124: capacitance control unit,126: resistance control unit,200: power supply circuit