Gate drive device, switch device

Abstract

When the change speed of the gate voltage is reduced, the turn-off loss will increase. The gate driving device of the present invention includes: a gate driving unit for driving the gate of a switching element; a peak detection unit for detecting that the main terminal voltage applied between the main terminals of the switching element during the turn-off period of the switching element is a peak value; and a driving condition changing unit for increasing the change speed of the gate voltage of the switching element based on the gate driving unit according to the detection of the main terminal voltage being a peak value.

Description

Technical Field

[0001] The invention relates to a gate driving device and a switch device. Background Art

[0002] Conventionally, in a gate driving device that drives the gate of a switching element, a gate voltage change speed is reduced to reduce a surge voltage at the time of turn-off (for example, refer to Patent Documents 1 to 3).

[0003] Patent Document 1: Japanese Patent No. 6290118

[0004] Patent Document 2: Japanese Patent No. 6266478

[0005] Patent Document 3: Japanese Patent No. 4935266 Summary of the invention

[0007] Technical Problems to be Solved by the Invention

[0008] When the gate voltage change speed is reduced, the turn-off loss will increase. Summary of the invention

[0009] In a first aspect of the present invention, a gate drive device is provided. The gate drive device may include a gate drive unit that drives the gate of a switching element. The gate drive device may include a peak detection unit that detects that a main terminal voltage applied between main terminals of the switching element during a cut-off period of the switching element is a peak value. The gate drive device may include a drive condition change unit that increases a change speed of a gate voltage of the switching element based on the gate drive unit in response to detecting that the main terminal voltage is a peak value.

[0010] The peak detection unit may include a voltage detection circuit for detecting the voltage between the main terminals. The peak detection unit may include a comparator for comparing a parameter corresponding to the voltage between the main terminals with a reference value. The peak detection unit may include a detection unit for detecting that the voltage between the main terminals is a peak value based on a comparison result obtained by the comparator.

[0011] The peak detection unit may further include a differentiation processing unit that detects a value corresponding to the rate of change of the voltage between the main terminals as a parameter. The comparator may compare the parameter with a reference value indicating that the rate of change is zero or less.

[0012] The peak detection section may further include a low-pass filter at a stage before or after the differential processing section.

[0013] The comparator can compare the parameter with a reference value indicating that the voltage between the main terminals is at a peak value.

[0014] When the voltage between the main terminals is detected to be at a peak value, the drive condition changing section may reduce the resistance value of the gate resistor connected to the gate, compared to when the voltage between the main terminals is not detected to be at a peak value.

[0015] The driving condition changing unit may reduce the resistance value of the gate resistor connected to the gate after detecting that the voltage between the main terminals is at a peak value and at least before the current between the main terminals of the switching element is cut off or before the voltage between the main terminals becomes a DC voltage applied between the main terminals.

[0016] The drive condition changing section may increase the gate current of the switching element when the peak value of the voltage between the main terminals is detected, compared to when the peak value of the voltage between the main terminals is not detected.

[0017] The gate driving device may include a temperature sensor for measuring the temperature of the switching element. The gate driving device may include an enabling unit for activating the peak detection unit and the driving condition change unit when the temperature is higher than a reference temperature.

[0018] In a second aspect of the present invention, a switching device is provided. The switching device may include the gate driving device according to the first aspect. The switching device may include a switching element whose gate is driven by the gate driving device.

[0019] The switching element may be a wide bandgap semiconductor element.

[0020] The above summary of the invention does not list all the features of the present invention, and variations of these feature groups may also constitute inventions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A switch device 100 according to this embodiment is shown.

[0022] Figure 2 The operation of the switch device 100 is shown.

[0023] Figure 3 The operation waveform when the main switching element 2 is turned off is shown.

[0024] Figure 4 A switch device 100A according to a modified example is shown. DETAILED DESCRIPTION

[0025] The present invention is described below by way of the embodiments of the invention, but the following embodiments do not limit the invention involved in the claims. In addition, the combination of features described in the embodiments is not necessarily a technical means for solving the technical problem of the invention. In addition, the same reference numerals are used for common structures in the embodiments, and their repeated descriptions are omitted.

[0026] [1. Structure of switch device 100]

[0027] Figure 1 The switch device 100 according to the present embodiment is shown. In the figure, blank arrows indicate voltages.

[0028] As an example, the switching device 100 shows a phase of a power conversion device for motor driving or power supply, switching the connection between the positive power line 101 and the negative power line 102 and the power output terminal 105, and outputting the converted voltage from the power output terminal 105.

[0029] Here, for example, a DC voltage Ed of 600 to 800 V is applied between the positive power line 101 and the negative power line 102, and the negative power line 102 is connected to the reference potential (for example, the ground potential) of the entire switch device 100. An inductive load 106 may be connected to the power output terminal 105. The switch device 100 includes: a positive main switch element 1 and a negative main switch element 2; return diodes 3 and 4 connected in reverse parallel to the main switch elements 1 and 2; and a positive gate drive device 5 and a negative gate drive device 6.

[0030] [1-1. Main switching elements 1, 2]

[0031] The main switch elements 1 and 2 are each an example of a switch element, and are electrically connected or disconnected between the drain terminal and the source terminal. For example, the main switch elements 1 and 2 are switched on (also called connected) / off (also called disconnected) using the gate drive devices 5 and 6 described later. Here, in this embodiment, as an example, the main switch elements 1 and 2 are connected in series between the negative power supply line 102 and the positive power supply line 101 in sequence, forming the upper arm and the lower arm in the power conversion device. The power output terminal 105 is connected to the midpoint of the main switch elements 1 and 2.

[0032] The main switch elements 1 and 2 are silicon semiconductor elements with silicon as the substrate. Alternatively, at least one of the main switch elements 1 and 2 may also be a wide bandgap semiconductor element. A wide bandgap semiconductor element refers to a semiconductor element with a larger bandgap than a silicon semiconductor element, such as a semiconductor element containing SiC, GaN, diamond, gallium nitride materials, gallium oxide materials, AlN, AlGaN or ZnO. A wide bandgap semiconductor element can increase the switching speed more than a silicon semiconductor element. In addition, in the present embodiment, the main switch elements 1 and 2 are MOSFETs (Metal Oxide Semiconductor Field Effect Transistor), and the positive side power line 101 may have a parasitic diode (not shown) as a cathode.

[0033] [1-2. Reflux diodes 3, 4]

[0034] The return diodes 3 and 4 are connected in antiparallel to the main switch elements 1 and 2. The return diodes 3 and 4 may be Schottky barrier diodes or parasitic diodes of MOSFET. The return diodes 3 and 4 may be silicon semiconductor elements or wide bandgap semiconductor elements.

[0035] [1-3. Gate driving devices 5, 6]

[0036] The gate drive devices 5 and 6 drive the gates of the corresponding main switch elements 1 and 2 based on the input signal input from the outside. For the input signal, the main switch elements 1 and 2 can be controlled by PWM control, and a substantially sinusoidal AC current can be output from the power supply output terminal 105. The input signal can be input separately to the main switch element 1 and the main switch element 2. In addition, in the present embodiment, as an example, when the input signal is high (on command signal), it indicates that the main switch element 2 is set to the on state, and when the input signal is low (off command signal), it indicates that the main switch element 2 is set to the off state.

[0037] The positive side gate driving device 5 drives the gate of the main switching element 1, and the negative side gate driving device 6 drives the gate of the main switching element 2. In addition, the gate driving devices 5 and 6 have the same structure, so in this embodiment, the negative side gate driving device 6 is described, and the description of the positive side gate driving device 5 is omitted.

[0038] The gate drive device 6 includes a peak detection unit 61, a gate drive unit 62, a drive condition change unit 63, a temperature sensor 64, and an enable unit 65. In this embodiment, as an example, each part of the gate drive device 6 is described as an analog circuit. In addition, the temperature sensor 64 and the enable unit 65 do not necessarily have to be included in the gate drive device 6.

[0039] [1-3-1. Peak detection unit 61]

[0040] The peak detection unit 61 detects that the voltage between the main terminals of the main switching element 2 during the off period of the main switching element 2 is at a peak value. In the present embodiment, as an example, the peak detection unit 61 detects that the voltage V applied between the drain terminal and the source terminal of the main switching element 2 is at a peak value. ds The peak detection unit 61 detects that the voltage V ds When it is a peak value, a flag signal for changing the gate driving condition of the main switching element 2 is provided to the driving condition changing unit 63. The peak detection unit 61 includes a voltage detection circuit 610, a low pass filter 615, a differential processing unit 616, a comparator 617, and a detection unit 618.

[0041] [1-3-1-1. Voltage detection circuit 610]

[0042] The voltage detection circuit 610 detects the voltage V ds For example, the voltage detection circuit 610 has a voltage V ds Resistors 611 and 612 for voltage division. The midpoint of the resistors 611 and 612 is connected to a low-pass filter 615, and the detected voltage is supplied to the low-pass filter 615. In this embodiment, the detection voltage is a positive voltage when the potential on the drain terminal side is higher than that on the source terminal side.

[0043] [1-3-1-2. Low-pass filter 615]

[0044] The low-pass filter 615 performs filtering to remove frequency components higher than a preset cutoff frequency from the voltage signal detected by the voltage detection circuit 610. The cutoff frequency may be greater than the switching frequency of the main switching elements 1 and 2. The low-pass filter 615 provides the filtered voltage signal to the differential processing unit 616.

[0045] [1-3-1-3. Differential Processing Unit 616]

[0046] The differential processing unit 616 detects the voltage V ds The differential processing unit 616 can be a differential circuit, and as an example, it can be a passive differential circuit (also called an RC circuit) including a resistor and a capacitor, or it can be an active differential circuit including an operational amplifier, a resistor and a capacitor. The differential processing unit 616 provides the detected parameter to the comparator 617.

[0047] [1-3-1-4. Comparator 617]

[0048] The comparator 617 compares the parameter detected by the differential processing unit 616 with the reference value, and provides a comparison signal indicating the comparison result to the detection unit 618. In this embodiment, as an example, a voltage indicating the parameter detected by the differential processing unit 616 is input to the non-inverting input terminal of the comparator 617, and a voltage indicating the reference value is input to the inverting input terminal. The reference value may be a voltage indicating V ds The rate of change is the value of the reference rate of change (in this embodiment, as an example, zero). Since the reference rate of change is zero, the comparison signal indicates the inversion of the positive and negative polarity of the parameter, that is, the voltage V ds Become the largest or smallest peak.

[0049] [1-3-1-5. Detection unit 618]

[0050] The detection unit 618 detects the voltage V based on the comparison result of the comparator 617. ds For example, the detection unit 618 can detect the voltage V according to the rise or fall of the comparison signal. ds The detection unit 618 detects the voltage V ds A signal (also referred to as a flag signal) which becomes a peak and becomes a high level is provided to the driving condition changing section 63 .

[0051] [1-3-2. Gate driving unit 62]

[0052] The gate driving unit 62 drives the gate of the main switching element 2 based on an on signal and an off signal included in an input signal from the outside. The gate driving unit 62 includes a first switching element 621 , a second switching element 622 , and a power source 623 .

[0053] The first switching element 621 and the second switching element 622 are connected in series. The first switching element 621 and the second switching element 622 provide a gate drive signal (on command signal / off command signal) instructing on / off to the gate terminal of the main switching element 2 .

[0054] For example, the first switch element 621 is connected between a first potential (20V as an example) higher than the reference potential of the negative power supply line 102 and the gate terminal of the main switch element 2. Thus, when the first switch element 621 is turned on, the gate drive signal driving the gate of the main switch element 2 becomes high, and the main switch element 2 is turned on. In the present embodiment, as an example, the first switch element 621 is a P-type MOSFET, with a source terminal connected to the first potential side, a drain terminal connected to the gate terminal side of the main switch element 2, and a gate terminal connected to the input terminal side of the input signal. Thus, the first switch element 621 becomes turned on due to the input signal becoming high.

[0055] The second switch element 622 is connected between a second potential (-5V as an example) lower than the reference potential and the gate terminal of the main switch element 2. Thus, when the second switch element 622 is turned on, the gate drive signal becomes low, and the main switch element 2 is turned off. In the present embodiment, as an example, the second switch element 622 is an N-type MOSFET, with a source terminal connected to the second potential side, a drain terminal connected to the gate terminal side of the main switch element 2, and a gate terminal connected to the input terminal side of the input signal. Thus, the second switch element 622 becomes conductive due to the input signal becoming low.

[0056] Furthermore, the first switching element 621 and the second switching element 622 are not limited to MOSFETs, and may be semiconductor elements of other structures such as bipolar transistors.

[0057] The power supply 623 supplies a DC voltage to the series circuit of the first switching element 621 and the second switching element 622. In the present embodiment, as an example, the power supply 623 sets the first switching element 621 side to the first potential and sets the second switching element 622 side to the second potential. In addition, as long as the source terminal of the first switching element 621 is connected to the first potential side and the source terminal of the second switching element 622 is connected to the second potential side, the power supply 623 may not be provided.

[0058] [1-3-3. Driving Condition Changing Unit 63]

[0059] The driving condition changing unit 63 detects the voltage V ds The driving condition is changed to a peak value so that the change speed of the gate voltage of the main switching element 2 by the gate driving unit 62 is increased. The driving condition changing unit 63 includes a gate resistor 630 and a connection switching unit 631 .

[0060] The gate resistor 630 has two gate resistors 6301 and 6302 having different resistance values. The resistance value of the gate resistor 6301 may be greater than the resistance value of the gate resistor 6302. In the present embodiment, as an example, one end of each of the gate resistors 6301 and 6302 is connected to the gate of the main switch element 2, and the other end is connected to the connection switching unit 631. In addition, as long as the resistance value can be changed during the off period of the main switch element 2, the gate resistor 630 may also adopt other structures. As an example, the gate resistors 6301 and 6302 may be connected in parallel between the second switch element 622 and the power supply 623.

[0061] The connection switching unit 631 selectively connects one of the two gate resistors 6301 and 6302 to the gate. The connection switching unit 631 can electrically connect the other end (the end opposite to the gate side) of the gate resistors 6301 and 6302 to the gate driving unit 62 according to the flag signal. ds The connection switching unit 631 can detect the voltage V ds When the voltage V is the peak value, that is, when the flag signal is a high voltage, the connection switching unit 631 switches to reduce the resistance value of the gate resistor 630 connected to the gate. In the present embodiment, as an example, when the high-level flag signal is not received from the detection unit 618 during the off-period of the main switch element 2, the connection switching unit 631 connects the gate resistor 6301 with a larger resistance value to the gate. In addition, when the high-level flag signal is received from the detection unit 618 during the off-period of the main switch element 2, the connection switching unit 631 connects the gate resistor 6302 with a smaller resistance value to the gate. Thus, the change speed of the gate voltage of the main switch element 2 is adjusted according to the detected voltage V ds Increase for peak value.

[0062] [1-3-4. Temperature sensor 64]

[0063] The temperature sensor 64 measures the temperature of the main switching element 2. The temperature sensor 64 can supply the enabling unit 65 with a current or a voltage corresponding to the measured temperature.

[0064] [1-3-5. Enabling unit 65]

[0065] The enabling unit 65 sets the peak detection unit 61 and the driving condition change unit 63 to be valid (enable) according to the fact that the measured temperature obtained by the temperature sensor 64 is higher than the reference temperature. The enabling unit 65 can provide an enable signal to the peak detection unit 61 and the driving condition change unit 63 when the measured temperature is higher than the reference temperature. In the case where the main switch element 2 is a silicon semiconductor element, the reference temperature can be 125 degrees, and in the case where the main switch element 2 is a wide bandgap semiconductor element such as SiC, the reference temperature can be 175 degrees. In addition, when the measured temperature is below the reference temperature, the peak detection unit 61 and the driving condition change unit 63 can be maintained in a disabled state. In this case, the connection switching unit 631 of the driving condition change unit 63 can electrically connect the gate resistor 6301 with a larger resistance value to the main switch element 2.

[0066] According to the switching device 100, the change speed of the gate voltage of the main switching element 2 is determined by detecting the voltage V during the off period of the main switching element 2. ds As the peak value increases, so the voltage V dsThe turn-off after the gate voltage reaches the peak value can be completed quickly. Therefore, compared with the case where the gate voltage change speed does not increase, the turn-off time can be shortened and the turn-off loss can be reduced. In addition, the gate voltage change speed is V ds The peak value increases afterwards, thus preventing the peak voltage from increasing, and further preventing the surge voltage from increasing.

[0067] In addition, the undetected voltage V ds Compared with the peak value, the detected voltage V ds When the voltage is at a peak value, the resistance value of the gate resistor 630 becomes small, so the change speed of the gate voltage can be increased reliably.

[0068] In addition, one of the two gate resistors 6301 and 6302 having different resistance values ​​is selectively connected to the gate of the main switching element 2. Therefore, according to the detected voltage V ds By connecting the gate resistor 6302 with a smaller resistance value to the gate to increase the peak value, the change speed of the gate voltage can be reliably increased.

[0069] In addition, the voltage V ds The voltage detection circuit 610 detects the voltage V ds The comparison result between the corresponding parameter and the reference value is used to detect the voltage V ds The peak value can therefore be reliably ds Detection of the peak condition.

[0070] In addition, with V ds The value corresponding to the rate of change of V is used as a parameter and compared with a reference value indicating a zero rate of change, so that the voltage V can be reliably ds Detect the peak value.

[0071] In addition, a low-pass filter 615 is provided at the front stage of the differential processing unit 616, so that the influence of noise can be reduced and the voltage V ds Detect the peak value.

[0072] In addition, the peak detection unit 61 and the driving condition change unit 63 are enabled based on the fact that the element temperature of the main switching element 2 is higher than the reference temperature. Therefore, the peak detection unit 61 and the driving condition change unit 63 can be prevented from operating when the cut-off loss is originally small due to the low element temperature and the effect is small due to the change in driving conditions, thereby extending the life of the switching device 100.

[0073] [2.Action]

[0074] Figure 2The operation of the switching device 100 is shown. The switching device 100 changes the driving conditions by performing the processes of steps S101 to S111 during the off period of the main switching element 2.

[0075] In step S101, the voltage detection circuit 610 detects the voltage V applied between the drain terminal and the source terminal of the main switching element 2. ds Conduct testing.

[0076] In step S103 , the low-pass filter 615 performs filtering on the detected voltage signal to remove high-frequency components.

[0077] In step S105, the differential processing unit 616 detects the voltage V ds In this embodiment, as an example, the differential processing unit 616 detects the voltage V ds The rate of change dV ds / dt as a parameter, but it can also detect dV ds / dt uses the value obtained by performing addition, subtraction, multiplication, division and other operations as a parameter.

[0078] In step S107, the comparator 617 compares the parameter detected by the differential processing unit 616 with the reference value. In this embodiment, as an example, the comparator 617 compares the voltage V ds The rate of change dV ds The parameter of / dt is compared with zero. In addition, the processing of the above steps S101 to S107 can be continued in step S109 described later until the voltage V ds peak value.

[0079] In step S109, the detection unit 618 detects the voltage V based on the comparison result of the comparator 617. ds In this embodiment, as an example, the detection unit 618 detects the voltage V according to the decrease of the comparison signal. ds The detection unit 618 detects the peak value and outputs a high-level flag signal. ds After reaching the peak value, the flag signal can be maintained at a high level at least until the current between the drain and source of the main switching element 2 is cut off. ds After the peak value, the voltage V ds The flag signal is maintained at a high level before the DC voltage Ed is reached. The detection unit 618 may switch the flag signal to a low level before the main switch element 2 is turned off next time. As an example, the detection unit 618 may switch the flag signal to a low level when the voltage V dsThe flag signal is switched to a low level when the peak voltage decreases and reaches the DC voltage Ed, or when a reference time (as an example, half the switching cycle of the main switching elements 1 and 2) has passed since the peak voltage decreases, or when a reference time (as an example, half the switching cycle of the main switching elements 1 and 2) has passed since the peak voltage decreases. Alternatively, the detection unit 618 may switch the flag signal to a low level when the flag signal continues to be a high level for more than the reference time.

[0080] In step S111, the driving condition changing unit 63 increases the speed of change of the gate voltage of the main switching element 2 by the gate driving unit 62. For example, the driving condition changing unit 63 switches the connection object of the gate from the gate resistor 6301 with a larger resistance value to the gate resistor 6302 with a smaller resistance value. ds After the voltage reaches the peak value, the flag signal is maintained at a high level at least before the current between the drain and source of the main switch element 2 is cut off. Therefore, the driving condition changing unit 63 can connect the gate resistor 6302 to the gate at least before the current between the drain and source of the main switch element 2 is cut off. The driving condition changing unit 63 can switch the connection object of the gate from the gate resistor 6302 to the gate resistor 6301 before the main switch element 2 is turned off next time.

[0081] According to the above operation, since the voltage V is detected ds After the peak value, at least before the current between the drain and source is cut off, or at the voltage V ds Since the gate resistor 6302 is connected to the gate before the DC voltage Ed is reached, the time required for turning off can be reliably shortened compared to the case where the gate resistor 6301 is connected to the gate during the turning off process.

[0082] [3. Action waveform]

[0083] Figure 3 2 shows the operation waveform when the main switch element 2 is turned off. In addition, the horizontal axis in the figure shows time, and the vertical axis shows the input signal of the main switch element 2, the gate-source voltage V gs , drain-source voltage V ds , drain current Id, etc.

[0084] [3-1. Operation waveform of switch device of comparative example]

[0085] First, the operation waveform of the switch device of the comparative example of the present embodiment during the off period is described. The switch device of the comparative example does not include the peak detection unit 61 and the drive condition change unit 63, and does not change the change speed of the gate voltage during the off period. In addition, the operation waveform of the switch device of the comparative example is shown by a dotted line in the figure, and partially overlaps with the solid line operation waveform of the switch device 100 described later.

[0086] When the input signal for controlling the main switch element 2 is switched from high (on command) to low (off command), at time t1, the gate drive signal from the gate drive unit 62 becomes low, and a negative gate current Ig (i.e., a current not shown flowing from the gate of the main switch element 2 to the ground of the gate drive device 6 via the second switch element 622) begins to flow. As a result, the gate drive signal indicating the off state is output from the gate drive unit 62, and the gate charge begins to be injected in the reverse bias direction into the main switch element 2. Then, during the period from time t1 to t2, the gate input capacitance Cgs of the main switch element 2 is charged in the reverse bias direction, and the gate-source voltage V gs reduce.

[0087] Next, when the gate-source voltage V gs When the gate voltage decreases to the mirror voltage (time t2), most of the gate charge is used to charge the feedback capacitor (gate-drain capacitor) Cgd, and the gate-source voltage V gs The change of V between the drain and source of the main switching element 2 becomes flat (the so-called mirror period), and the ds Increase.

[0088] The drain-source voltage V of the main switching element 1 relative to the main switching element 2 ds As a result, the discharge current flows from the parasitic capacitance Cds, so that the drain current Id of the main switching element 2 decreases, and a voltage VL corresponding to the current change rate is applied to the main switching element 2 .

[0089] Next, at time t3, in the main switch element 2, the mirror period ends and the drain current Id decreases sharply (becomes zero at time t5). As a result, the voltage applied to the wiring inductance of the positive power line 101 increases instantaneously, and the drain-source voltage V ds The drain-source voltage V ds The gate-source voltage V gs Below the gate threshold voltage V gs(th) .

[0090] Then, the charging of the gate input capacitance Cgs of the main switch element 2 is completed, and the main switch element 2 is turned off. In this comparative example, a turn-off loss Eoff schematically shown by the shaded area of ​​the oblique lines and dots is generated. In addition, when the turn-off of the main switch element 2 is completed, the main switch element 1 can be turned on.

[0091] [3-2. Operation waveform of the switch device 100 according to the embodiment]

[0092] Next, the operation waveform of the switch device 100 of this embodiment at the time of OFF is described. In addition, the operation waveform of the switch device 100 is shown by a solid line. The description of the same operation waveform as the comparative example is omitted.

[0093] In the switch device 100 according to the present embodiment, when the drain-source voltage V ds , the differential processing unit 616 detects a parameter indicating that the rate of change is positive. In addition, a high-level comparison signal indicating that the parameter is greater than a reference value (in this operation example, as an example, a value indicating that the rate of change is zero) is output from the comparator 617.

[0094] In addition, when the drain-source voltage V ds When the peak voltage Vp starts to decrease, the differential processing unit 616 detects the voltage V ds In addition, a low-level comparison signal indicating that the parameter is smaller than a reference value (in this operation example, a value indicating that the rate of change is zero, for example) is output from the comparator 617. Thus, based on the decrease in the comparison signal, the detection unit 618 detects that the voltage V ds When the gate source voltage V gs The change speed of the voltage V between the drain and the source increases, and the decrease is more rapid than that of the action waveform of the comparative example. Therefore, in this action example, unlike the comparative example, at time t10 before time t5, the voltage V between the drain and the source is ds The DC voltage Ed is the gate-source voltage V gs Below the gate threshold voltage V gs(th) .

[0095] Then, the charging of the gate input capacitance Cgs of the main switch element 2 is completed, and the main switch element 2 is turned off. In addition, in this operation example, after time t10, the drain-source voltage V ds The voltage increases again to become the DC voltage Ed. Therefore, although the comparison signal rises and falls, the connection of the gate resistor 6302 to the gate is maintained after time t4.

[0096] As described above, according to this operation example, the gate-source voltage V gsThe change rate of gate voltage increases, and the drop is more rapid than the action waveform of the comparative example. Therefore, the time required for cutoff is shortened from the period between time t1 and t5 to the period between time t1 and t10. Therefore, the cutoff loss Eoff schematically shown by the oblique line shaded area in the figure is lower than that of the comparative example. In addition, the change rate of gate voltage is ds The peak value increases afterwards, thus preventing the peak voltage from increasing, and further preventing the surge voltage from increasing.

[0097] [4. Modifications]

[0098] Figure 4 A switch device 100A according to a modification example is shown. The switch device 100A includes a peak detection unit 61A.

[0099] The peak detection unit 61A includes a comparator 617A. The comparator 617A compares the peak value with the voltage V ds The corresponding parameters and the voltage V ds In this embodiment, as an example, a voltage V is input to the non-inverting input terminal of the comparator 617A. ds , a voltage representing a reference value is input to the inverting input terminal.

[0100] According to the above-mentioned switch device 100A, the voltage V ds The corresponding value is set as the parameter, which will show the voltage V ds The value of the peak voltage Vp is set as a reference value and used for comparison to detect the voltage V ds The peak value can therefore be reliably ds In addition, compared with the case where the differential processing unit 616 is used, the structure can be simplified.

[0101] [5. Other Modifications]

[0102] In addition, in the above-mentioned embodiment and modification, the low-pass filter 615 is provided in the front stage of the differential processing unit 616, but it can also be provided in the rear stage of the differential processing unit 616 (as an example, between the differential processing unit 616 and the comparator 617). In this case, the influence of noise can be reduced, and the voltage V ds Detection of the peak condition.

[0103] In addition, the reference value used by the comparator 617 is used as the voltage V ds The value of the case where the rate of change is zero is described above, but it can also be set to a value indicating the case where the rate of change is a negative reference rate of change. In this case, since the voltage V is detected dsThe rate of change is sharply reduced compared to the reference rate, so it is possible to prevent the voltage V from being affected by noise, etc. ds When the voltage gradually reaches a local maximum value smaller than the peak voltage Vp before reaching the peak voltage Vp, the peak value is erroneously detected.

[0104] Alternatively, the reference value may be a voltage V ds The rate of change of the positive reference rate of change (as an example, the voltage V ds The value of the change rate when the peak voltage Vp increases slowly near the peak voltage Vp) is shown in the figure. In this case, in fact, due to the voltage V ds The voltage V is detected before the peak timing. ds As a peak value, the delay from the fall (or rise) of the comparison signal until the driving condition is changed can be taken into account, so that the change timing of the driving condition matches the peak timing. ds Although the value of the peak voltage Vp has been described, a value smaller than the peak voltage Vp may be used.

[0105] In addition, for the undetected voltage V ds The driving condition changing unit 63 detects the voltage V ds In the case of a peak value, the resistance value of the gate resistor 630 connected to the gate is reduced. Alternatively / in addition, the voltage V is not detected. ds The driving condition changing unit 63 may also detect the voltage V ds When the voltage is at a peak value, the gate current of the main switching element 2 is increased. In this case, the change speed of the gate voltage can be increased during the off period of the main switching element 2.

[0106] Furthermore, the switch devices 100 and 200 are described as including a group of the positive-side main switching element 1 and the drive device 5 and a group of the negative-side main switching element 2 and the drive device 6 , but may include only one of the groups.

[0107] In addition, although each part of the gate driving device 6 is described as an analog circuit, at least one of the low-pass filter 615, the differential processing unit 616, the detection unit 618, and the enable unit 65 may be a digital circuit.

[0108] In the above embodiment, the main switch element 1 on the positive side and the main switch element 2 on the negative side are each set as one element for explanation, but they can also be set as two or more switch elements connected in parallel. In this case, the drive device 5 (or 6) can be independently provided on each of the two or more switch elements on the positive side (or negative side), or can be provided together with respect to the two or more switch elements on the positive side (or negative side).

[0109] The present invention has been described above using the embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. Those skilled in the art will appreciate that various changes or improvements can be made to the above embodiments. According to the claims, the various changes or improvements made are also included in the technical scope of the present invention.

[0110] Please note that the execution order of the actions, processes, steps, and stages of the devices, systems, programs, and methods shown in the claims, specifications, and drawings can be implemented in any order unless "before", "previously", etc. are specifically stated, and the output of the previous processing is not used in the subsequent processing. In the action flow in the claims, specifications, and drawings, "first", "then", etc. are used for convenience of explanation, but it does not mean that it must be implemented in this order.

[0111] Description of symbols

[0112] 1 Main switching element

[0113] 2 Main switching elements

[0114] 3. Recirculation diode

[0115] 4 Return diode

[0116] 5. Drive device

[0117] 6 Drive device

[0118] 61 Peak detection unit

[0119] 62 Gate drive unit

[0120] 63 Driving condition change section

[0121] 64 Temperature Sensor

[0122] 65 Enabling Department

[0123] 100 Switchgear

[0124] 101 Positive power line

[0125] 102 Negative power line

[0126] 105 Power output terminal

[0127] 106 Inductive load

[0128] 610 Voltage Detection Circuit

[0129] 611 Resistor

[0130] 612 Resistors

[0131] 615 Low-pass filter

[0132] 616 Differential Processing Unit

[0133] 617 Comparator

[0134] 618 Testing Department

[0135] 621 1st switch element

[0136] 622 Second switch element

[0137] 623 Power Supply

[0138] 630 Gate resistor

[0139] 631 Connection Switching Unit

[0140] 6301 Gate resistor

[0141] 6302 Gate resistor.

Claims

1. A gate driving device, characterized in that: include: a gate driving unit that drives a gate of the switching element; a peak detection unit configured to detect that a main terminal voltage applied between the main terminals of the switching element during an off period of the switching element reaches a peak value; as well as A driving condition changing unit increases a speed of change of a gate voltage of the switching element by the gate driving unit, based on detection that the voltage between the main terminals reaches a peak value.

2. The gate driving device according to claim 1, wherein: The peak detection unit has: A voltage detection circuit, which detects the voltage between the main terminals; a comparator for comparing a parameter corresponding to the voltage between the main terminals with a reference value; as well as A detection unit detects that the voltage between the main terminals reaches a peak value based on a comparison result of the comparator.

3. The gate driving device according to claim 2, wherein: The peak detection unit further includes a differential processing unit that detects a value corresponding to a rate of change of the voltage between the main terminals as the parameter. The comparator compares the parameter with the reference value indicating that the change rate is a reference change rate of zero or less.

4. The gate driving device according to claim 3, characterized in that: The peak detection section further includes a low-pass filter at a stage before or after the differential processing section.

5. The gate driving device according to claim 2, wherein: The comparator compares the parameter with the reference value indicating that the voltage between the main terminals is at a peak value.

6. The gate driving device according to any one of claims 1 to 5, characterized in that: When the voltage between the main terminals is detected to have reached a peak value, the drive condition changing section reduces the resistance value of the gate resistor connected to the gate, compared to when the voltage between the main terminals is not detected to have reached a peak value.

7. The gate driving device according to claim 6, wherein: After detecting that the voltage between the main terminals reaches a peak value, the driving condition changing unit reduces the resistance value of the gate resistor connected to the gate at least before the current between the main terminals of the switching element is cut off or before the voltage between the main terminals becomes a DC voltage applied between the main terminals.

8. The gate driving device according to any one of claims 1 to 5, characterized in that: The drive condition changing section increases the gate current of the switching element when the voltage between the main terminals is detected to be at a peak value, compared to when the voltage between the main terminals is not detected to be at a peak value.

9. The gate driving device according to any one of claims 1 to 5, characterized in that: Further including: a temperature sensor, which measures the temperature of the switching element; as well as An enabling unit that enables the peak detection unit and the drive condition change unit in response to the temperature being higher than a reference temperature.

10. A switch device, characterized in that: include: The gate driving device according to any one of claims 1 to 9; as well as The switching element has its gate driven by the gate driving device.

11. The switch device according to claim 10, characterized in that The switching element is a wide bandgap semiconductor element.

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