JP7543638B2 - Driving device, switching device, and driving method - Google Patents

Description

The present invention relates to a drive device, a switch device, and a drive method.

2. Description of the Related Art Active gate control, which dynamically controls a gate current, has been known as a technique for reducing a surge voltage that occurs during a switching operation of a power switching element (see, for example, Japanese Patent Application Laid-Open No. 2003-233664).
[Prior Art Literature]
[Patent Documents]
[Patent Document 1] JP2015-195699

In the drive device of Patent Document 1, when turning off the IGBT, the drive capacity for drawing out the gate current while the collector voltage is rising is reduced, and the collector voltage is converged to a steady value, thereby reducing the surge voltage. However, in driving a switching element, it is desirable to reduce the switching loss while reducing the surge voltage.

In order to solve the above problem, a first aspect of the present invention provides a drive device. The drive device may include a drive unit that drives a control terminal to turn on and off a switching element having a control terminal, a first main terminal, and a second main terminal. The drive device may include a drive control unit that controls a control current that the drive unit passes between the control terminal and the control terminal. In response to receiving an instruction to switch the switching element from on to off, the drive control unit may set the control current from the on state to the off state of the switching element to a first off current for turning off the switching element, and then reduce and increase the control current again.

After reducing the control current, the drive control unit may increase the control current again after a predetermined time has elapsed.

After reducing the control current, the drive control unit may increase the control current again in response to a reduction in the voltage between the first main terminal and the second main terminal.

After reducing the control current, the drive control unit may increase the control current again in response to a change in polarity of the time change in the voltage between the first main terminal and the second main terminal.

After reducing the control current, the drive control unit may increase the control current again to the first off current.

After reducing the control current, the drive control unit may increase the control current again to a third off current that is different from the first off current.

The switching element may be a wide bandgap semiconductor element.

The wide band gap semiconductor element may be at least one of SiC and GaN.

In a second aspect of the present invention, a switch device is provided. The switch device may include a drive device. The switch device may include a switching element.

In a third aspect of the present invention, a driving method is provided. The driving method may be a driving method for driving a switching element having a control terminal, a first main terminal, and a second main terminal. In response to receiving an instruction to switch the switching element from on to off, during a transition period from an on state to an off state of the switching element, a driving unit that drives the control terminal to turn the switching element on and off may flow a control current between the control terminal and the control terminal as a first current for turning off the switching element, and then the control current may be decreased and increased again.

Note that the above summary of the invention does not list all of the necessary features of the present invention. Also, subcombinations of these features may also be inventions.

1 shows a configuration of a switch device 10 according to the present embodiment. 4 shows various waveforms when the driving device 100 according to the present embodiment turns off the switching element 20. 1 shows an example of a block diagram in which the drive control unit 120 according to the present embodiment determines whether or not to increase the gate current. 1 shows an example of a block diagram in which a drive control unit 120 according to a modified example of the present embodiment determines whether or not to increase a gate current. 1 shows an example of a block diagram in which the drive control unit 120 according to another modified example of the present embodiment determines whether or not to increase the gate current.

The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

Figure 1 shows the configuration of a switch device 10 according to this embodiment. The switch device 10 includes a switching element 20, a control current detector 30, a main terminal voltage detector 40, and a drive device 100.

The switching element 20 may be a power semiconductor element. As an example, the switching element 20 may be a wide band gap semiconductor element, which may be, for example, at least one of SiC and GaN. By driving such an element with a high switching speed, the driving device 100 can further enhance the effect of this embodiment.

The switching element 20 has a control terminal 22, a first main terminal 24, and a second main terminal 26, and electrically connects (ON) or disconnects (OFF) between the first main terminal 24 and the second main terminal 26 depending on the voltage or current input to the control terminal 22. As an example, in this embodiment, the switching element 20 is an nMOS transistor having a gate as the control terminal 22, a drain as the first main terminal 24, and a source as the second main terminal 26, and is turned OFF when the voltage of the control terminal 22 based on the second main terminal 26 (also referred to as the "bias voltage"), i.e., for example, the gate-source voltage Vgs, is equal to or lower than the threshold voltage Vth, and is turned ON when the gate-source voltage Vgs exceeds the threshold voltage Vth.

The following description will be given taking an example in which the switching element 20 is an nMOS transistor, but each embodiment can be applied to various types of switching elements 20, such as a MOS transistor with a control terminal called the gate and two main terminals called the drain and source, an IGBT (insulated gate bipolar transistor) with a control terminal called the gate and two main terminals called the collector and emitter, and a bipolar transistor with a control electrode called the base and two main electrodes called the collector and emitter.

The control current detector 30 is provided between the drive device 100 and the control terminal 22 of the switching element 20, and detects the control current, for example, the gate current Ig, flowing between the drive device 100 and the control terminal 22. In this specification, expressions such as "provided between... and..." do not limit the physical arrangement, but rather mean "electrically connected to... and...". In addition, "connected" here is not limited to being directly connected without going through other elements, but also includes being indirectly connected through other elements. The control current detector 30 supplies the detected control current, for example the value of the gate current Ig, to the drive device 100.

The main terminal voltage detector 40 detects the main terminal voltage, for example, the drain-source voltage Vds, which indicates the potential difference between the first main terminal 24 and the second main terminal 26. The main terminal voltage detector 40 supplies the detected main terminal voltage value to the drive device 100.

The driving device 100 receives a power supply voltage from a power supply (not shown) and drives the control terminal 22 of the switching element 20, for example, the gate, in response to a driving signal input from the outside. As a result, the driving device 100 switches on/off between the first main terminal 24 and the second main terminal 26 of the switching element 20, for example, between the drain and the source. The driving device 100 may be realized by one or more integrated circuits having the control terminal 22 of the switching element 20, the positive terminal and the negative terminal of the power supply, and multiple terminals for inputting or outputting the driving signal, the value of the control current, and the value of the voltage between the main terminals, or may be realized by a combination of multiple discrete components. The driving device 100 includes a driving unit 110 and a driving control unit 120.

The drive unit 110 is provided between the drive control unit 120 and the control terminal 22 of the switching element 20, and drives the control terminal 22 to turn on and off the switching element 20, which has the control terminal 22, the first main terminal 24, and the second main terminal 26, in response to a command from the drive control unit 120. The drive unit 110 has an on-current control unit 112 and an off-current control unit 114.

The on-current control unit 112 is provided between the drive control unit 120 and the control terminal 22 of the switching element 20, and controls the control current (on-current) to turn on the switching element 20 in response to an on-current command from the drive control unit 120. For example, the on-current control unit 112 applies a gate current Ig to the control terminal 22, which is the gate, and makes the gate-source voltage Vgs greater than the threshold voltage Vth, thereby turning on the switching element 20. At this time, the on-current control unit 112 may be configured to be able to control the magnitude of the gate current Ig applied to the control terminal 22. Note that the on-current control unit 112 can also use the value of the gate current Ig detected by the control current detector 30 as feedback when controlling the gate current Ig to a predetermined magnitude.

The off-current control unit 114 is provided between the drive control unit 120 and the control terminal 22 of the switching element 20, and controls the control current (off-current) to turn off the switching element 20 in response to an off-current command from the drive control unit 120. For example, the off-current control unit 114 draws the gate current Ig from the control terminal 22, which is the gate, and turns off the switching element 20 by making the gate-source voltage Vgs equal to or lower than the threshold voltage Vth. At this time, the off-current control unit 114 may be configured to be able to control the magnitude of the gate current Ig drawn from the control terminal 22. Note that the off-current control unit 114 can also use the value of the gate current Ig detected by the control current detector 30 as feedback when controlling the gate current Ig to a predetermined magnitude.

The drive control unit 120 controls the control current that the drive unit 110 passes between the control terminal 22. In the drive device 100 according to this embodiment, in response to receiving an instruction to switch the switching element 20 from on to off, the drive control unit 120 reduces and then increases the control current again during the transition period from the on state to the off state of the switching element 20 after setting the control current to a first off current for switching the switching element 20 off. This will be explained in detail using waveforms.

Figure 2 shows various waveforms when the driving device 100 according to this embodiment turns off the switching element 20.

At time t1, the drive device 100 obtains an off command (OFF command) from, for example, a control board (not shown) that instructs switching the switching element 20 from on to off. In response to receiving the command to switch the switching element 20 from on to off, the drive control unit 120 controls the control current to be a first off current for turning off the switching element 20 during the transition period from the on state to the off state of the switching element 20. That is, the drive control unit 120 supplies an off current command to the off current control unit 114 to draw the gate current Ig of the switching element 20 with the first off current. When the off current control unit 114 controls the gate current Ig according to the off current command from the drive control unit 120 and starts drawing current from the control terminal 22 of the switching element 20, i.e., the gate, the gate voltage Vgs decreases.

At time t2, when the gate voltage Vgs drops to a certain level, the drain-source voltage Vds of the switching element 20 starts to rise.

At time t3, when the drain-source voltage Vds rises to the DC intermediate voltage, the drain current Id of the switching element 20 begins to decrease.

At time t4, when the drain-source voltage Vds reaches a predetermined voltage, the drive control unit 120 determines that it is necessary to suppress the surge and sets a surge suppression flag. At this time, the drive control unit 120 may determine that it is necessary to suppress the surge when, for example, the drain-source voltage Vds reaches a predetermined percentage (for example, 95%) or more of the withstand voltage of the switching element 20. When the drive control unit 120 sets the surge suppression flag, it controls to reduce the control current. That is, the drive control unit 120 supplies an off current command to the off current control unit 114 so that the gate current Ig of the switching element 20 is drawn with a second off current (|first off current|>|second off current|) that is smaller than the first off current. When the off current control unit 114 reduces the drive capacity by the off current command from the drive control unit 120 and reduces the amount of current drawn from the control terminal 22, i.e., the gate, the discharge speed of the gate charge decreases, thereby suppressing the rise in the drain-source voltage Vds.

The drive control unit 120 may set the second off current to a magnitude such that the drain-source voltage Vds becomes approximately constant (flat) until time t5 after the transient response that occurs when the gate current Ig is changed from the first off current to the second off current at time t4 has converged. Note that the magnitude of such a second off current may be empirically determined based on actually measured values, etc. This allows the drive control unit 120 to reliably suppress the occurrence of a surge.

When a predetermined delay time has elapsed from time t4, at time t5, the drive control unit 120 determines that the control current may be increased again and sets the gate current increase flag. Here, the delay time may be a time that is preset so that a surge does not occur even if the control current is increased again. Such a delay time may be empirically determined based on an actually measured value, etc., and may be set to a different time depending on what kind of device is used as the switching element 20. When the drive control unit 120 sets the gate current increase flag, it controls the control current to be increased again. That is, the drive control unit 120 supplies an off current command to the off current control unit 114 so that the gate current Ig of the switching element 20 is drawn with a third off current (|second off current|<|third off current|) that is larger than the second off current.

In this way, after the drive control unit 120 reduces the control current, it increases the control current again in response to the passage of a predetermined time. When the off-current control unit 114 increases the drive capacity again in response to an off-current command from the drive control unit 120 and increases the amount of current drawn from the control terminal 22, i.e., the gate, the discharge rate of the gate charge increases.

At this time, the drive control unit 120 may set the third off current to the same magnitude as the first off current. That is, after reducing the control current, the drive control unit 120 may increase the control current again to the first off current. As a result, the drive device 100 uses only two off currents, the first off current (= third off current) and the second off current, and therefore the circuit configuration of the drive device 100 can be simplified.

Alternatively, the drive control unit 120 may set the third off current to a different magnitude than the first off current. That is, the drive control unit 120 may reduce the control current and then increase the control current again to a third off current that is different from the first off current. This allows the drive device 100 to flexibly set the magnitude of the off current after surge suppression, and to more precisely control the reduction of switching loss.

At time T6', the drive control unit 120 determines that the gate voltage Vgs has fallen sufficiently below the threshold voltage Vth, and controls the gate current Ig to be released. That is, the drive control unit 120 supplies an off current command to the off current control unit 114 to set the gate current Ig of the switching element 20 to zero. This allows the drive device 100 to turn off the switching element 20 at an earlier timing (time T6') than when the gate current Ig is turned off while remaining at the second off current (time t6).

In this way, according to the driving device 100 of this embodiment, in response to receiving an instruction to switch the switching element 20 from on to off, the driving control unit 120 sets the control current to a first off current for turning off the switching element 20 during the transition period from the on state to the off state of the switching element 20, and then reduces and increases the control current again. As a result, the driving device 100 reduces the control current when the drain-source voltage Vds reaches a predetermined voltage, and the discharge rate of the gate charge decreases, thereby suppressing the rise of the drain-source voltage Vds. In addition, since the driving device 100 reduces and increases the control current again, the discharge rate of the gate charge increases again, making it possible to finish charging the gate input capacitance in a short time compared to the case where the control current is not increased again, and the turn-off loss can be reduced. In this way, the driving device 100 of this embodiment can reduce the switching loss while reducing the surge voltage in driving the switching element 20.

Figure 3 shows an example of a block diagram in which the drive control unit 120 according to this embodiment determines whether to increase the gate current. In the above description, a case has been described as an example in which the drive control unit 120 determines whether to increase the control current when a predetermined time has elapsed after reducing the control current. In this case, the drive control unit 120 may determine whether to increase the gate current using, for example, a block diagram as shown in Figure 3.

The drive control unit 120 may include, for example, a first AND operator 310 and a delay operator 320. The first AND operator 310 has two input terminals, outputs the logical product of the inputs at the two input terminals, and supplies it to the delay operator 320. The first AND operator 310 inputs an OFF command to one input terminal and a surge suppression flag to the other input terminal. Here, as described above, the OFF command becomes high at time t1, and the surge suppression flag becomes high at time t4. Therefore, the first AND operator 310 outputs high at time t4.

The delay operator 320 has a predetermined delay time and delays the input signal by the predetermined time. Therefore, the drive control unit 120 determines that the gate current has increased after the first AND operator 310 outputs high, that is, after the predetermined delay time has elapsed from time t4. In this way, the drive control unit 120 may use, for example, a block diagram as shown in this figure, to decrease the control current and then increase the control current again in response to the elapse of a predetermined time. This allows the drive device 100 to determine an increase in the control current using a relatively simple circuit.

Figure 4 shows an example of a block diagram in which the drive control unit 120 according to a modified example of this embodiment determines whether to increase the gate current. In Figure 4, the same reference numerals are used for components having the same functions and configurations as those in Figure 3, and descriptions are omitted except for the following differences. In the above description, an example has been described in which the drive control unit 120 determines whether to increase the control current when a predetermined time has elapsed after reducing the control current. However, the drive control unit 120 may, for example, increase the control current again using a block diagram such as the one shown in this figure in response to a decrease in the voltage between the first main terminal 24 and the second main terminal 26 after reducing the control current.

The drive control unit 120 may include, for example, a first AND operator 310, a previous value operator 410, an addition operator 420, a comparator 430, and a second AND operator 440. The first AND operator 310 outputs the logical product of the OFF command and the surge suppression flag, and supplies it to one input terminal of the second AND operator 440.

The previous value operator 410 inputs the drain-source voltage Vds and supplies the previous value of the drain-source voltage Vds to the negative terminal of the addition operator 420.

The addition operator 420 has two input terminals, and outputs the sum of the two inputs and supplies it to the negative terminal of the comparator 430. The addition operator 420 inputs the current value of the drain-source voltage Vds to the positive terminal and the previous value of the drain-source voltage Vds to the negative terminal. Thus, if the current value of the drain-source voltage Vds is greater than the previous value, the addition operator 420 outputs a positive value. On the other hand, if the current value of the drain-source voltage Vds is less than the previous value, the addition operator 420 outputs a negative value.

The comparator 430 has two input terminals, and outputs a comparison of the two inputs and supplies it to the other input terminal of the second AND operator 440. The comparator 430 inputs 0 to the positive terminal and the output of the addition operator 420 to the negative terminal. Thus, when the addition operator 420 outputs a positive value, the comparator 430 outputs low. On the other hand, when the addition operator 420 outputs a negative value, the comparator 430 outputs high.

The second AND operator 440 has two input terminals and outputs the logical product of the inputs at the two input terminals. The second AND operator 440 inputs the output of the first AND operator 310 to one input terminal and the output of the comparator 430 to the other input terminal. Therefore, the second AND operator 440 determines that the gate current is increased when the drain-source voltage Vds decreases after time t4. In this way, the drive control unit 120 may use a block diagram such as that shown in this figure to reduce the control current and then increase the control current again in response to the reduction in the voltage between the first main terminal 24 and the second main terminal 26. This allows the drive device 100 to determine an increase in the control current using an actual reduction in the value of the drain-source voltage Vds as a trigger, without relying on empirical rules, etc.

Figure 5 shows an example of a block diagram in which the drive control unit 120 according to another modified example of this embodiment determines whether to increase the gate current. In Figure 5, the same reference numerals are used for components having the same functions and configurations as those in Figure 4, and descriptions are omitted except for the differences below. In the above description, a case in which the drive control unit 120 determines whether to increase the control current in response to a decrease in the voltage between the first main terminal 24 and the second main terminal 26 after reducing the control current has been described as an example. However, the drive control unit 120 may, for example, increase the control current again in response to a change in the polarity of the time change in the voltage between the first main terminal 24 and the second main terminal 26 after reducing the control current, using a block diagram such as the one shown in this figure.

The drive control unit 120 may include, for example, a first AND operator 310, a comparator 430, a second AND operator 440, and a dV/dt calculation unit 510. The dV/dt calculation unit 510 inputs the drain-source voltage Vds, outputs the time change of the drain-source voltage Vds, i.e., the dV/dt value, and supplies it to the negative terminal of the comparator 430. As an example, the dV/dt calculation unit 510 may be a differentiation circuit, which may be, for example, a CR differentiation circuit, etc.

Therefore, the second AND operator 440 determines that the gate current has increased when the polarity of the dV/dt value of the drain-source voltage Vds changes to negative after time t4. In this way, the drive control unit 120 may use, for example, a block diagram as shown in this figure, to reduce the control current and then increase the control current again in response to a change in the polarity of the time change in the voltage between the first main terminal 24 and the second main terminal 26. This allows the drive device 100 to determine an increase in the control current using an actual change in polarity of the dV/dt value of the drain-source voltage Vds as a trigger, without relying on empirical rules, etc.

In the above description, the dV/dt calculation unit 510 is included in the drive control unit 120, but the present invention is not limited to this. The dV/dt calculation unit 510 may be provided as a functional unit different from the drive control unit 120 in the drive device 100. The dV/dt calculation unit 510 may be provided as a functional unit different from the drive device 100 in the switch device 10.

The present invention has been described above using an embodiment, but the technical scope of the present invention is not limited to the scope described in the above embodiment. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiment. It is clear from the claims that forms incorporating such modifications or improvements can also be included in the technical scope of the present invention.

The order of execution of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically stated as "before" or "prior to," and it should be noted that the processes may be performed in any order, unless the output of a previous process is used in a later process. Even if the operational flow in the claims, specifications, and drawings is explained using "first," "next," etc. for convenience, it does not mean that it is necessary to perform the processes in this order.

REFERENCE SIGNS LIST 10 Switch device 20 Switching element 22 Control terminal 24 First main terminal 26 Second main terminal 30 Control current detector 40 Main terminal voltage detector 100 Drive device 110 Drive section 112 ON current control section 114 OFF current control section 120 Drive control section 310 First AND operator 320 Delay operator 410 Previous value operator 420 Addition operator 430 Comparator 440 Second AND operator 510 dV/dt calculation section

Claims (10)

a drive unit that drives a control terminal to turn on and off a switching element having a control terminal, a first main terminal, and a second main terminal;
a drive control unit that controls a control current that the drive unit passes between the control terminal and the control terminal;
The drive control unit is
in response to receiving an instruction to switch the switching element from on to off, during a transition period from an on state to an off state of the switching element, the control current is set to a first off current for switching off the switching element, and then the control current is reduced;
After the control current is reduced, the control current is increased again in response to a trigger that a voltage between the first main terminal and the second main terminal is reduced.
Drive unit. a drive unit that drives a control terminal to turn on and off a switching element having a control terminal, a first main terminal, and a second main terminal;
a drive control unit that controls a control current that the drive unit passes between the control terminal and the control terminal;
The drive control unit is
in response to receiving an instruction to switch the switching element from on to off, during a transition period from an on state to an off state of the switching element, the control current is set to a first off current for switching off the switching element, and then the control current is reduced;
After the control current is reduced, the control current is increased again in response to a change in polarity of the time change in the voltage between the first main terminal and the second main terminal.
Drive unit. The drive device according to claim 1 or 2, wherein the drive control unit cancels the extraction of the control current from the control terminal after increasing the control current again. The drive device according to any one of claims 1 to 3, wherein the drive control unit increases the control current again to the first off current after decreasing the control current. The drive device according to any one of claims 1 to 3, wherein the drive control unit, after reducing the control current, increases the control current again to a third off current different from the first off current. The drive device according to any one of claims 1 to 5, wherein the switching element is a wide band gap semiconductor element. The drive device according to claim 6, wherein the wide band gap semiconductor element is at least one of SiC and GaN. A drive device according to any one of claims 1 to 7;
A switch device comprising the switching element. A method for driving a switching element having a control terminal, a first main terminal, and a second main terminal, comprising the steps of:
in response to receiving an instruction to switch the switching element from on to off, during a transition period from an on state to an off state of the switching element, a control current that a drive unit drives the control terminal to turn the switching element on and off is caused to flow between the control terminal and the control terminal to a first current for turning off the switching element, and then the control current is reduced;
After the control current is reduced, the control current is increased again in response to a trigger that a voltage between the first main terminal and the second main terminal is reduced.
Drive method. A method for driving a switching element having a control terminal, a first main terminal, and a second main terminal, comprising the steps of:
in response to receiving an instruction to switch the switching element from on to off, during a transition period from an on state to an off state of the switching element, a control current that a drive unit drives the control terminal to turn the switching element on and off is caused to flow between the control terminal and the control terminal to a first current for turning off the switching element, and then the control current is reduced;
After the control current is reduced, the control current is increased again in response to a change in polarity of the time change in the voltage between the first main terminal and the second main terminal.
Drive method.