JP2012039790A - Power conversion equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax bias of a cut-off current between power semiconductor elements connected in parallel which is caused by a difference in turning on/off operation time caused by a difference in characteristic of power switching elements connected in parallel, for improved reliability, to allow application of elements of low current rating and breakdown strength, with lower cost.SOLUTION: A figure shows a circuit of single phase amount of a power conversion equipment that converts DC to AC, which is an example of a circuit configuration in which power switching elements are used in bi-parallel. Although each energization current is ILa≠ILb if there is a difference of characteristics in power semiconductor elements 6a and 6b, by presenting such gate drive circuit configuration as gate currents IGa and IGb appropriate for the characteristic of 6a and 6b are made to flow, a time lag required for turning on/off is relaxed to provide ILa≒ILb, which allows suppressing concentration of a main circuit current to one power semiconductor element connected in parallel. The figure shows an example of bi-parallel, and the present invention is effective regardless of the number of parallel connections.

Description

  The present invention relates to a power conversion device, and more particularly to a method of driving a power switching element used in the power conversion device.

In recent years, power converters such as inverters and converters are mainly configured using semiconductor power switching elements.
FIG. 7 shows a configuration example of a main circuit and a gate drive circuit of a general power conversion device using a power switching element such as an IGBT.

  In the configuration of FIG. 7, a circuit for one phase of the power conversion device in which the power switching elements 6 a and 6 b are connected in parallel is shown. The circuit shown in FIG. 7 converts the power supplied from the DC power source 1 and supplies it to the load M. Hereinafter, the circuit of FIG. 7 having the DC power source 1 and the power switching elements 6a and 6b is referred to as a main circuit. Note that the DC power supply 1 may be obtained from an AC power supply through a diode rectifier circuit and a smoothing capacitor.

  The gate drive power supply 2 is based on an ON / OFF signal S1 from a control circuit (not shown), and gate terminals of the power switching elements 6a and 6b through gate resistors 3a and 3b connected in parallel with the gate drive signal, respectively. To communicate. The emitter wirings of the power switching elements 6 a and 6 b are connected to the emitter terminal of the gate drive power supply 2.

  Hereinafter, a circuit in which the gate terminals of the power switching elements 6a and 6b are connected from the gate driving power supply 2 through the gate resistors 3a and 3b and the emitter terminals of the power switching elements 6a and 6b are returned to the gate driving power supply is referred to as a gate driving circuit.

  In FIG. 7, the power switching elements 6a and 6b perform turn-on / turn-off operations according to the gate drive signal transmitted from the gate drive power source 2, convert the power supplied from the DC power source 1 into arbitrary energy, and load M For example, DC / AC conversion, motor drive by frequency conversion, step-up / step-down, braking energy processing, and the like are intended.

  The gate drive power supply 2 uses the emitter terminal voltage as a reference potential, and based on the signal S1 input from the control circuit, the gate terminal potential of the power switching elements 6a and 6b is a positive potential at the time of turn-on operation, and at the time of turn-off operation. Operates to have a negative potential. Due to this potential difference, current flows from the gate drive power supply 2 to the gate terminals of the power switching elements 6a and 6b during the turn-on operation, and conversely current flows from the gate terminals of the power switching elements 6a and 6b to the gate drive power supply 2 during the turn-off operation. Shed. Hereinafter, this current is referred to as a gate current.

FIG. 8 shows an example of a gate drive circuit of the power conversion apparatus in the case where the power switching elements 6a and 6b shown in FIG. 7 are connected in parallel.
The gate drive circuit of FIG. 8 is the same as that shown in FIG. 7, and FIG. 8 omits the main circuit from FIG. The power switching elements 6a and 6b are part of the main circuit shown in FIG.

  The dotted arrows in FIG. 8 indicate the direction of the gate current during the turn-on operation, and the direction of the arrow during the turn-off operation is opposite to the direction of the arrow. Ideally, IG = IGa + IGb and IG = IE = IEa + IEb.

  In the above description, the operation of the upper half power switching elements 6a and 6b and the upper half gate drive circuit in FIG. 7 connected in series has been described. The same description applies to the operation of the switching element and the gate drive circuit.

  If there is some variation in the switching characteristics of the power switching elements 6a and 6b connected in parallel shown in FIG. 8, the time required for turn-on / turn-off differs between the power switching elements 6a and 6b. This difference is caused by, for example, a difference in gate capacitance or threshold voltage caused by variations in the manufacturing process of the power switching elements 6a and 6b.

  Due to this difference in switching characteristics, the power switching element that is turned on more quickly at the time of turn-on operation cuts off a larger current than the other power switching element connected in parallel, and is turned off later at the time of turn-off operation. The other large current to which the power switching elements are connected in parallel is cut off.

  The shared current generated by the variation of the power semiconductor switching element is balanced. In order to cope with this point, Patent Document 1 discloses a configuration in which a common mode coil is inserted between the gate drive circuit and the gate of the power switching element.

JP-A-8-19246

FIG. 9 is a diagram showing a main circuit for one phase of the power conversion device in which the power switching elements 6a and 6b are connected in parallel.
FIG. 9 omits the description of the gate drive circuit from the circuit shown in FIG. 7 and adds the flow of current and voltage.

  In FIG. 9, the current IL flowing through the parasitic inductance 10 of the emitter wiring is IL = ILa + ILb. If the switching characteristics of the power switching elements 6a and 6b are the same, ideally ILa = ILb.

  Here, it is assumed that the switching characteristics of the power switching elements 6a and 6b are different. For example, it is assumed that the power switching element 6a has a larger gate capacity than the power switching element 6b, and the time required for switching is slower for the power switching element 6a than for the power switching element 6b. In this case, the power switching element 6b is turned on before the power switching element 6a is turned on.

  Since the power switching element 6a is turned on with a delay, only the power switching element 6b is turned on until the power switching element 6a is turned on. Therefore, as an extreme example, ILa = 0 and ILb = IL. . Further, due to the same phenomenon, current concentrates on the power switching element 6b that turns off with a delay during the turn-off operation, and ILa = IL and ILb = 0.

  Due to this phenomenon, a current exceeding the safe operating region flows through the power switching elements 6a and 6b during turn-on and turn-off, and the surge voltage applied to the power switching elements 6a and 6b exceeds the withstand voltage of the power switching elements 6a and 6b. This causes damage to the power switching elements 6a and 6b.

  For the surge voltage, the parasitic inductance 10 of the wiring from the DC power source 1 to the power switching elements 6a and 6b is L (for the sake of simplicity, the parasitic inductance of the wiring between the DC power source 1 and the power switching element 6a, and the DC power source 1 and the parasitic inductance of the wiring between the power switching element 6b is L). A voltage ΔVa due to the voltage EDC of the DC power source 1 + parasitic inductance 10 is applied to the power switching element 6a, and a voltage ΔVb due to EDC + parasitic inductance 10 is applied to the power switching element 6b.

  Here, ΔVa = L × dILa / dt and ΔVb = dILb / dt. DILa / dt and dILb / dt indicate the amount of time change of the current flowing through the power switching elements 6a and 6b, and generally increase as the excessive current flows relative to the rated current of the power switching elements 6a and 6b. For this reason, the surge voltage also becomes a large value with this current change amount.

  Although this point is also taken into consideration in the configuration of Patent Document 1, in the configuration of Patent Document 1, it is necessary to insert a common mode coil between the gate drive circuit and the gate of the power switching element. And the circuit scale becomes large.

  Therefore, an object of the present invention is to provide a power conversion device that reduces the bias of current flowing in the turn-on / off operation caused by a difference in switching characteristics of power switching elements connected in parallel with a simple configuration.

  It is another object of the present invention to provide a power conversion device that improves reliability, enables application of an element with a low current rating and withstand voltage, and realizes cost reduction.

  The power converter includes a configuration in which at least two sets of series circuits in which a first power switching element and a second power switching element are connected in series are connected in parallel, the first power switching element, In a power conversion device for converting power applied by switching a second power switching element and supplying energy to a load, a gate drive signal for switching the first power switching element A first gate drive power source that outputs to the gate of the first power switching element, and a gate drive signal that switches the second power switching element to the gate of each second power switching element. 2 gate drive power supplies, between the first power switching element and the first gate drive power supply. A first gate current adjustment unit that adjusts the first power switching element to flow a gate current suitable for its electrical characteristics when each of the first switching elements is turned on / off; The second power switching element is provided between the second power switching element and the second gate driving power source, and is suitable for the electrical characteristics of the second power switching element when the second switching element is turned on / off. And a second gate current adjusting unit that adjusts the gate current to flow.

  According to the present invention, it is possible to reduce the bias of the current flowing in the turn-on / off operation caused by the difference in switching characteristics of the power switching elements connected in parallel with a simple configuration.

  As a result, the reliability of the apparatus can be improved, and an element having a low current rating and a low withstand voltage can be applied, and cost reduction can be realized.

It is a figure which shows the structural example of the power converter device of this embodiment. It is a figure which shows 1st Embodiment of a gate current adjustment part. It is the figure which extracted a part of main circuit and gate drive circuit part at the time of providing the gate current adjustment part of 1st Embodiment. It is a figure which shows the structure of the power converter device provided with the gate current adjustment part of 2nd Embodiment. It is a figure which shows the structural example at the time of applying 3rd Embodiment to the gate current adjustment part of 1st Embodiment. It is a figure which shows the structural example at the time of applying 3rd Embodiment to the gate current adjustment part of 2nd Embodiment. A configuration example of a main circuit and a gate drive circuit of a power conversion device using a general power switching element is shown. It is a figure which shows the gate drive circuit example of the power converter device in the case of the structure where the switching element for electric power was connected in 2 parallel. It is a figure which shows the main circuit for 1 phase of the power converter device with which the switching element for electric power was connected 2 parallelly.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration example of a power conversion device according to the present embodiment. The configuration of the figure is for one phase for converting the power supplied from the DC power source 1 into arbitrary energy for the purposes of DC / AC conversion, motor drive by frequency conversion, step-up / step-down, braking energy processing, etc. This is a circuit configuration example in which two power switching elements are used in parallel, and the converted energy is supplied to the load M.

  The DC power source 1 has a rectifier circuit and a smoothing circuit when the power conversion device of the present embodiment is an AC input type, and a smoothing circuit when the DC power source is a DC input type. Hereinafter, the circuit having the DC power supply 1 and the power switching elements 6a and 6b in the circuit of FIG. 1 is referred to as a main circuit.

  The gate drive power supply 2a is a gate drive power supply for the power switching elements 6a and 6b, and includes a DC power supply circuit, an insulator, and a switch element. Based on an on / off signal S1 output from a control circuit (not shown), the gate drive power supply 2a is connected from the gate terminal 2G to the gate terminals 6aG and 6bG of the power switching elements 6a and 6b via the gate resistors 3a and 3b. A gate drive signal is output. The gate drive signal output from the gate drive power supply 2a uses the voltage at the emitter terminal 2E as a reference voltage, and sets the potential at the gate terminals of the power switching elements 6a and 6b to a positive potential during the turn-on operation and to a negative potential during the turn-off operation. Current.

  The gate drive power supply 2b is a gate drive power supply for the power switching elements 6c and 6c. A gate drive signal based on an ON / OFF signal S2 from a control circuit (not shown) is supplied to the power via the gate resistors 3 and 3d. Output to the gate terminals 6cG and 6dG of the switching elements 6c and 6c. Due to the potential difference generated by the gate drive signal, current flows from the gate drive power supply 2 to the gate terminals of the power switching elements 6a and 6b during the turn-on operation, and conversely during the turn-off operation, the gate drive from the gate terminals of the power switching elements 6a and 6b. A current is passed through the power supply 2. Hereinafter, this current is referred to as a gate current.

  The power switching elements 6a to 6d are semiconductor switching elements such as IGBTs, and perform switching based on the inputs of the gate terminals 6aG to 6dG. The diodes 8a to 8d are free wheeling diodes (FWD) for commutating the load current of the power switching element 6a.

  The operation of the upper half power switching elements 6a and 6b and the operation of the lower half power switching elements 6c and 6d are basically the same, so in the following description, the upper half power switching elements 6a and 6d and The operation of 6b will be mainly described. Hereinafter, a circuit having the gate drive power supply 2a, the wirings 4, 4a and 4b, the gate resistors 3a and 3b, the power switching elements 6a and 6b, the gate terminals 6aG and 6bG, and the emitter terminals 6aE and 6bE is referred to as a gate drive circuit.

  Comparing the power conversion device of this embodiment of FIG. 1 with the general power conversion device of FIG. 7, the device of FIG. 1 is further provided with gate current adjustment units 7a and 7b as compared with the device of FIG. . The gate current adjusting unit 7a is provided on the wirings 4a, 4b, 5a, and 5b between the gate driving power source 2a, the gate resistors 3a and 3b, and the power switching elements 6a and 6b. Similarly, the gate current adjusting unit 7b is provided between the gate drive power supply 2b, the gate resistors 3c and 3d, and the power switching elements 6c and 6d.

  The gate current adjusting unit 7a adjusts the gate currents IGa and IGb suitable for the electrical characteristics of the power switching elements 6a and 6b to flow at turn-on / off. The gate current adjusting unit 7a alleviates the time difference required for turning on / off the power switching elements 6a and 6b, and the current ILa flowing between the collector and the emitter of the power switching element 6a≈the power switching element 6b. The current ILb flowing between the collector and the emitter is used. As a result, current concentration on one of power switching elements 6a and 6b connected in parallel can be suppressed.

FIG. 2 is a diagram illustrating a first embodiment of the gate current adjusting unit 7a.
In the figure, the gate current adjusting unit 7a includes a wiring 4c and a wiring 5c. The wiring 4c physically connects the wiring 4a connecting the gate resistance 3a and the gate terminal 6aG and the wiring 4b connecting the gate resistance 3b and the gate terminal 6bG to the gate terminal 6aG of the power switching element 6a and the gate terminal 6bG of the power switching element 6b. Wiring that is connected at the nearest position. That is, the wiring 4c is connected so that the distance from the gate terminal 6aG to the gate terminal 6bG is the shortest, and the wiring impedance therebetween is reduced. The wiring 5c includes a wiring 5a connecting the emitter terminal 2E of the gate drive power supply 2a and the emitter terminal 6aE of the power switching element 6a, and a wiring 5b connecting the emitter terminal 2E of the gate drive power supply 2a and the emitter terminal 6bE of the power switching element 6b. Is connected to the emitter terminal 6aE of the power switching element 6a and the emitter terminal 6bE of the power switching element 6b at a physically closest position. That is, the wiring 5c is connected so that the distance from the emitter terminal 6aE to the emitter terminal 6bE is the shortest, and the wiring impedance therebetween is reduced. In this way, the wiring 4c and the wiring 5c are connected at positions physically close to the gate terminal 6aG, the gate terminal 6bG, the emitter terminal 6aE, and the emitter terminal 6bE, respectively. Can be reduced.

  In the circuit of FIG. 2, for example, consider a case where the power switching element 6a has a larger gate capacity than the power switching element 6b and the switching time of the power switching element 6a is slower. In this case, the gate current IGb flowing to the gate terminal 6bG is partly passed to the gate terminal 6aG as the current IGc through the wiring 4c because the power switching element 6b performs a fast switching operation. Therefore, an IGa + IGc current flows through the gate terminal 6aG, and an IGb-IGc current flows through 6bG.

  Therefore, the gate power supply adjustment unit 7a as shown in FIG. 2 allows a large current to flow through the gate of the power switching element 6 having a large gate capacity and a small current to flow through the gate of the power switching element 6 having a small gate capacity. Adjust the gate current. As a result, the time required for switching can be made uniform between the power switching elements 6a and 6b connected in parallel.

  According to the gate current adjusting unit 7a of the first embodiment, the unbalance between the current ILa flowing between the collector and the emitter of the power switching element 6a and the current ILb flowing between the collector and the emitter of the power switching element 6b is Improved. Therefore, the power switching elements 6a and 6b can be prevented from being damaged due to energization of a current exceeding the above-described safe operation region and the surge voltage exceeding the withstand voltage. Therefore, a power converter with high credibility can be provided, and since the power switching element 6 with a low current rating and withstand voltage can be used, the power converter can be realized with a low-cost configuration. .

FIG. 3 is a diagram in which a part of the main circuit and the gate drive circuit part are extracted when the gate current adjustment unit 7a of the first embodiment is provided.
In the figure, 8 is the main circuit wiring, 9a is the wiring 5b2, 9b is the wiring 5c, and 9c is the parasitic inductance of the wirings 5a1 and 5b1. The parasitic inductances 8, 9a, 9b, and 9c are assumed to be L, La, Lb, and Lc.

  During the turn-on / off operation, a current change of dILd / dt occurs in the main circuit wiring between the power switching elements 6a and 6b, and an electromotive voltage ΔVc is applied by the main circuit wiring inductance 8 between the power switching elements 6a and 6b. Is done. This voltage ΔVc is also applied to the parasitic inductances 9b and 9c of the parallel circuit wirings 5a2, 5b2 and 5c of the circuit having the parasitic inductance 8 of the main circuit wiring. Due to the potential difference caused thereby, a current change of dILc / dt occurs, and the voltage ΔVd is applied to the parasitic inductance 9b of the wiring 5c by ΔILc / dt. This voltage ΔVd causes a current change of dILe / dt in the parasitic inductance 9c of the wirings 5a1 and 5b1.

  The switching time of the power switching elements 6a and 6b is about several tens [ns] to several hundreds [ns] (about several tens [MHz]), and the current change amount of the main circuit is about 800 [A] at the maximum. is there. Therefore, although greatly different depending on the types of power switching elements 6a and 6b, the dILe / dt of the emitter wiring due to the steep main circuit current change dILd / dt of about several [kA / μs] is applied to the wirings 5a1, 5b1, and 5c. It flows as a common mode current. This current acts on the gate drive power supply 2a, causing malfunction of the gate drive power supply 2a, damage to parts, and the like.

This point is addressed by the gate current adjustment unit 7 of the second embodiment.
FIG. 4 is a diagram illustrating a configuration of a power conversion device including the gate current adjusting unit 7a according to the second embodiment.

  In FIG. 4, the gate current adjusting section 7a connects the gate wirings 4a1 and 4b1 at the downstream ends of the gate resistors 3a and 3b on the gate wiring side, and also exits from the gate terminals 6aG and 6bG of the power switching elements 6a and 6b. The gate wirings 4a2 and 4b2 are connected. And it has the structure which connects between these two connection points by the wiring 4d. In the emitter wiring, emitter wirings 5a1 and 5b1 are connected, and emitter wirings 5a2 and 5b2 are connected. And it has the structure which connects these connection points with the wiring 5d.

  In other words, in the gate current adjusting unit 7a of the second embodiment, the gate terminal 2E of the gate drive power supply 2a and the gate terminals 6aG of the power switching elements 6a and 6b provided individually for each power switching element 6, respectively. And 6bG are connected at a plurality of locations. Also, the emitter wiring 2a of the gate drive power source 2a and the emitter wiring 6aE and 6bE of the power switching elements 6a and 6b, which are individually provided for each power switching element 6, are connected at a plurality of locations. It has become.

  With this configuration, in the gate current adjusting unit 7a of the second embodiment, the gate wiring and the emitter wiring are provided with a single line. Then, the current path of the common mode current dILe / dt generated in the first embodiment can be cut off at this single line portion, and the inflow of the common mode current to the gate drive power supply 2a can be suppressed. Note that the connection point between the gate wiring 4a2 and the gate wiring 4b2 is physically located close to the gate terminal 6aG and the gate terminal 6bG, and the connection point between the emitter wiring 5a2 and the emitter wiring 5b2 is the emitter terminal 6aE and the emitter terminal. It is preferable that the wiring distance between the gate terminal 6aG and the gate terminal 6bG and the wiring distance between the emitter terminal 6aE and the emitter terminal 6bE be shortest at a position physically close to 6bE.

Next, the gate current adjusting unit 7 of the third embodiment will be described.
In the gate current adjustment unit 7 of the third embodiment, the magnetic body 10 that is effective in suppressing the common mode current is disposed in the gate current adjustment unit 7 of the first embodiment or the second embodiment.

FIG. 5 is a diagram illustrating a configuration example in the case where the third embodiment is applied to the gate current adjusting unit 7 of the first embodiment.
In the figure, the gate current adjusting unit 7a is effective in suppressing the common mode current at the position between the gate wirings 4a1 and 5a1 and between the emitter wirings 4b1 and 5b1 in the configuration of the first embodiment of FIG. A certain magnetic body 10a and 10b are provided.

  With this configuration, the common mode current dILf / dt of several tens [MHz] can be reduced by the effect of the impedance of the magnetic bodies 10a and 10b, and the inflow of the common mode current to the gate drive power supply 2a can be suppressed.

FIG. 6 is a diagram illustrating a configuration example in the case where the third embodiment is applied to the gate current adjusting unit 7 of the second embodiment.
In the configuration of FIG. 6, the gate current adjusting unit 7 a has a configuration in which a magnetic body 10 c effective for suppressing common mode current is provided between the gate wirings 4 d and 5 d in the configuration of the second embodiment of FIG. 5. It has become.

According to the configuration of FIG. 6, the energization path of the common mode current dILe / dt can be cut off, and the common mode current can be prevented from flowing into the gate drive power supply 2a.
As described above, according to the power conversion device of the present embodiment, it is possible to improve the unbalance between the main circuit currents ILa and ILb flowing between the collectors and the emitters of the power switching elements 6a and 6b. Therefore, it is possible to prevent current exceeding the safe operation region from flowing through the power switching elements 6a and 6b, damage due to the surge voltage exceeding the withstand voltage, and malfunction of the gate drive circuit.

  Further, by removing the factor that damages the power switching elements 6a and 6b, a highly reliable power conversion device can be realized. Furthermore, power switching elements having a small current rating and withstand voltage can be used for the components used in the power converter, and the cost can be reduced.

  In the above example, for simplification of explanation, an example is shown in which the power conversion device is a circuit having two parallel configurations of the power switching elements 6a and 6c and the power switching elements 6b and 6d. The power converter according to the embodiment can be applied to a circuit configuration of three or more parallel circuits.

DESCRIPTION OF SYMBOLS 1 DC power supply 2a, 2b Gate drive power supply 3a, 3b Gate resistance 4 Gate wiring 5 Emitter wiring 6a, 6b Power switching element 7 Gate current adjustment part 7 Diode 8, 9, 11 Inductance 10 Magnetic body

Claims (5)

A first power switching element and a second power switching element, wherein the first power switching element and the second power switching element have a configuration in which at least two sets of series circuits in which a first power switching element and a second power switching element are connected in series are connected in parallel; In a power conversion device that converts power applied by switching elements and supplies energy to a load,
A first gate drive power supply that outputs a gate drive signal for switching the first power switching element to the gate of each first power switching element;
A second gate drive power supply for outputting a gate drive signal for switching the second power switching element to the gate of each second power switching element;
The first power switching element is provided between the first power switching element and the first gate drive power source, and the electrical characteristics of the first power switching element are changed when each first switching element is turned on / off. A first gate current adjustment unit for adjusting a suitable gate current to flow;
The second power switching element is provided between the second power switching element and the second gate drive power source, and the second power switching element has an electrical characteristic when the second switching element is turned on / off. A second gate current adjusting unit that adjusts so that a suitable gate current flows; and a power conversion device comprising: The first gate current adjustment unit includes a connection wiring that connects a plurality of gate wirings that connect the first gate drive power supply and the gate terminals of the first power switching elements, and the first gate drive. A connection wiring for connecting a plurality of emitter wirings for connecting a power source and each of the emitter terminals of the first power switching element;
The second gate current adjusting unit includes a connection wiring that connects a plurality of gate wirings that connect the second gate drive power supply and the gate terminals of the second power switching elements, and the second gate drive. The power conversion device according to claim 1, comprising a connection wiring that connects a plurality of emitter wirings that connect a power source and each of the emitter terminals of the second power switching element.   The power converter according to claim 2, wherein the connection wires are connected in close proximity to the gate terminal and the emitter terminal, respectively. The first gate current adjustment unit provides a single line portion by connecting a plurality of gate wirings connecting the first gate driving power source and the gate terminals of the first power switching elements at two or more locations, A plurality of emitter wirings connecting the first gate drive power supply and the emitter terminals of the first power switching element are connected at two or more locations to provide a single line portion;
The second gate current adjustment unit provides a single line portion by connecting a plurality of gate wirings connecting the second gate driving power source and the gate terminals of the second power switching elements at two or more locations, 2. A configuration in which a plurality of emitter wirings respectively connecting the second gate driving power source and the emitter terminal of the second power switching element are connected at two or more locations to provide a single line portion. The power converter device described in 1.   5. The power conversion device according to claim 1, wherein a magnetic material having an effect as an inductance with respect to a common mode is disposed between the emitter wirings or between the gate wirings. 6.

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