JP7240835B2 - switching circuit - Google Patents

Description

The present invention relates to a switching circuit that drives a semiconductor switching element using a drive circuit.

The conduction state of the semiconductor switching element is controlled by a drive signal input to the control electrode, and the main current flows between the main electrodes in the ON state. At this time, a surge voltage is generated due to the switching operation, and the semiconductor switching element may be damaged or malfunction. In order to suppress the surge voltage, it is effective to moderate the voltage fluctuation in the switching operation, but this increases the switching loss. Thus, there is a trade-off relationship between suppression of surge voltage and switching loss.

Therefore, methods for speeding up the operation of the switching element and suppressing the surge voltage are being studied. For example, a method of connecting a branch circuit section composed of a resistance element or a diode between a driving circuit for driving a semiconductor switching element and a gate terminal of the semiconductor switching element is being studied (see Patent Document 1). In this method, the branch circuit section slows down the rising speed or falling speed of the gate voltage during a period that affects the generation of a surge voltage in the switching operation.

JP 2012-147591 A

However, in the above configuration, the current path connected to the gate terminal contains a resistance component. Therefore, discharge of electric charges accumulated in the gate terminal is inhibited by the resistance element or the diode connected to the gate terminal. As a result, high-speed operation of the semiconductor switching element is hindered, and switching loss increases.

An object of the present invention is to provide a switching circuit in which switching loss and surge voltage are suppressed.

In a switching circuit according to an aspect of the present invention, for a driving transistor that controls a semiconductor switching element, one main electrode is connected to a control electrode of the semiconductor switching element, and a resistor element is connected between the other main electrode and a power supply terminal. and a capacitor are connected in parallel.

According to the present invention, it is possible to provide a switching circuit in which switching loss and surge voltage are suppressed.

1 is a schematic diagram showing the configuration of a switching circuit according to a first embodiment of the present invention; FIG. FIG. 5 is a schematic diagram showing the configuration of a switching circuit according to a modification of the first embodiment of the present invention; FIG. 10 is a schematic diagram showing another configuration of the switching circuit according to the modification of the first embodiment of the present invention; FIG. 5 is a schematic diagram showing still another configuration of a switching circuit according to a modification of the first embodiment of the present invention; It is a schematic diagram showing the configuration of a switching circuit according to a second embodiment of the present invention. It is a schematic diagram showing the configuration of a switching circuit according to a third embodiment of the present invention. It is a schematic diagram which shows the structure of the switching circuit based on the modification of the 3rd Embodiment of this invention. FIG. 11 is a schematic diagram showing another configuration of a switching circuit according to a modification of the third embodiment of the present invention; FIG. 11 is a schematic diagram showing still another configuration of a switching circuit according to a modification of the third embodiment of the present invention;

Embodiments will be described below with reference to the drawings. In the description of the drawings, the same parts are denoted by the same reference numerals, and the description thereof is omitted.

(First embodiment)
A switching circuit according to a first embodiment of the present invention comprises, as shown in FIG. 20.

Driving power for driving the driving circuit 20 is supplied by a driving power supply 30 having a pair of power terminals consisting of a high potential terminal 31 and a low potential terminal 32 . For example, a DC power supply or the like is used as the driving power supply 30 .

In the ON state, a main current flows between the high potential main electrode 11 and the low potential main electrode 12 of the semiconductor switching element 10 . At this time, the high potential main electrode 11 is set to a relatively high potential, and the low potential main electrode 12 is set to a relatively low potential. FIG. 1 exemplarily shows a case where the semiconductor switching element 10 is a MOSFET (metal-oxide-semiconductor field-effect transistor). That is, the high potential main electrode 11 is the drain electrode, the low potential main electrode 12 is the source electrode, and the control electrode 13 is the gate electrode. The high potential main electrode 11 is connected to the power supply terminal 50 and the low potential main electrode 12 is connected to the low potential terminal 32 . The potential of the power supply terminal 50 may be set higher than the potential of the high potential terminal 31, for example. Note that the semiconductor switching element 10 is not limited to a MOSFET.

The drive circuit 20 has a high potential side element 21 and a low potential side element 22 cascaded between a high potential terminal 31 and a low potential terminal 32 . A connection point between the high potential side element 21 and the low potential side element 22 is an output terminal for outputting a drive signal, and the output terminal is connected to the control electrode 13 of the semiconductor switching element 10 .

The drive circuit 20 shown in FIG. 1 has a push-pull circuit in which a first drive transistor T21 as a high potential side element 21 and a second drive transistor T22 as a low potential side element 22 are cascaded.

The first driving transistor T21 is an NPN bipolar transistor. An emitter electrode, which is one main electrode of the first driving transistor T21, is connected to the control electrode 13 of the semiconductor switching element 10. As shown in FIG. A collector electrode, which is the other main electrode of the first driving transistor T21, is connected to the high-potential terminal 31 . A control signal SH for controlling the conductive state of the first driving transistor T21 is input to the base electrode of the first driving transistor T21.

The second driving transistor T22 is a PNP bipolar transistor. An emitter electrode, which is one main electrode of the second driving transistor T22, is connected to the control electrode 13 of the semiconductor switching element 10 and the emitter electrode of the first driving transistor T21. A collector electrode, which is the other main electrode of the second driving transistor T22, is connected to one terminal of a low potential side parallel circuit 23 in which a parallel resistor 231 and a parallel capacitor 232 are connected in parallel. The other terminal of the low potential side parallel circuit 23 is connected to the low potential terminal 32 and the low potential main electrode 12 of the semiconductor switching element 10 . A control signal SL for controlling the conductive state of the second driving transistor T22 is input to the base electrode of the second driving transistor T22.

To turn on the semiconductor switching element 10, the first driving transistor T21 is turned on and the second driving transistor T22 is turned off. As a result, charge is supplied to the control electrode 13 of the semiconductor switching element 10 via the first driving transistor T21, and the semiconductor switching element 10 turns on. When the voltage of control electrode 13 exceeds the threshold voltage, semiconductor switching element 10 is turned on.

On the other hand, when the semiconductor switching element 10 is to be turned off, the first driving transistor T21 is turned off and the second driving transistor T22 is turned on. As a result, the supply of charge to the control electrode 13 of the semiconductor switching element 10 is stopped, and the semiconductor switching element 10 turns off. Then, electric charge is discharged from the control electrode 13 of the semiconductor switching element 10 through the second driving transistor T22. When the voltage of control electrode 13 falls below the threshold voltage, semiconductor switching element 10 is turned off.

As described above, in the drive circuit 20 shown in FIG. 1, both the high potential side element 21 and the low potential side element 22 are drive transistors. The semiconductor switching element 10 is controlled according to the conducting states of the first driving transistor T21 and the second driving transistor T22. The conduction state of the semiconductor switching element 10 is controlled by using the charge supplied to the control electrode 13 as a drive signal. A control signal SH for controlling the first driving transistor T21 and a control signal SL for controlling the second driving transistor T22 are output from the control circuit 40. FIG.

In the switching circuit shown in FIG. 1, when the semiconductor switching element 10 is turned off, the second driving transistor T22 is turned on, and the impedance between the emitter electrode and the collector electrode becomes low. As a result, the capacitance of the control electrode 13 of the semiconductor switching element 10 and the parallel capacitor 232 forming the low potential side parallel circuit 23 are connected in series. Therefore, the charge accumulated in the control electrode 13 moves to the parallel capacitor 232 at high speed.

As a result, the time required for the turn-off operation of semiconductor switching element 10 is shortened. That is, the switching operation of the semiconductor switching element 10 is performed at high speed, and switching loss can be suppressed.

Furthermore, due to the charging operation of the parallel capacitor 232 by the charge moving from the control electrode 13, the potential of the collector electrode of the second driving transistor T22 becomes higher than the potential of the low potential terminal 32. FIG. Therefore, a current flows into the base electrode of the second driving transistor T22. The contribution of the current flowing into the base electrode causes the charge to move faster from the control electrode 13 to the parallel capacitor 232 .

The two effects of the charge operation of the parallel capacitor 232 and the flow of current into the base electrode of the second drive transistor T22 caused by the charge operation of the parallel capacitor 232 speed up the turn-off operation of the semiconductor switching element 10. is performed on

In order to perform the turn-off operation at high speed, it is preferable that the capacitance value of the parallel capacitor 232 is large. However, as described below, the magnitude of the capacitance of parallel capacitor 232 is limited in order to suppress surge voltages. By reducing the capacitance value of the parallel capacitor 232, charging of the parallel capacitor 232 progresses before the turn-off operation is completed, thereby slowing the transfer of charge from the control electrode 13 to the parallel capacitor 232. At this time, since the electric charge is transferred from the control electrode 13 mainly by the current flowing through the parallel resistor 231, the transfer speed of the electric charge discharged from the control electrode 13 decreases.

Therefore, at the beginning of the turn-off operation, the charge moves quickly, causing the voltage to fluctuate abruptly, but from the middle of the turn-off operation, the voltage fluctuations become gentle. As a result, ringing at the control electrode 13 is suppressed in the latter half of the turn-off operation, and surge voltage is suppressed.

By reducing the capacitance value of the parallel capacitor 232 and advancing the timing for slowing the charge transfer, the time during which the voltage fluctuates slowly in the turn-off operation is lengthened. As a result, the effect of suppressing the surge voltage can be increased. However, the earlier the timing for slowing down the charge transfer, the greater the switching loss. In other words, in order to suppress switching loss, the larger the capacitance value of the parallel capacitor 232 is, the better. Therefore, the capacitance value of parallel capacitor 232 is set in consideration of the switching loss required for the switching circuit and the allowable magnitude of surge voltage.

For example, depending on the capacitance value Cg of the parasitic capacitance Cgs between the control electrode 13 and the low potential main electrode 12 of the semiconductor switching element 10, the power supply voltage Vd which is the potential difference between the high potential terminal 31 and the low potential terminal 32, etc., the parallel capacitor 232 capacitance values C1 are set. As a result of repeated studies, the present inventors have found that when the value of Cg×Vd/(C1+Cg) is approximately the same as the threshold voltage Vth of the semiconductor switching element 10, damage and malfunction of the semiconductor switching element 10 due to surge voltage can be prevented. It was also found that the switching loss can be suppressed.

Considering a margin for characteristic variations of components used in the semiconductor switching element 10 and the drive circuit 20, the capacitance value C1 of the parallel capacitor 232 may be set so as to satisfy the following equation (1). :

Vth≧Cg×Vd/(3×(C1+Cg)) (1)

By setting the capacitance value C1 so as to satisfy the relationship of expression (1), the switching operation can be performed at high speed, and the switching loss can be suppressed.

Also, the capacitance value C1 may be set so as to satisfy the following equation (2):

Vth≦3×Cg×Vd/(C1+Cg) (2)

By setting the capacitance value C1 so as to satisfy the relationship of equation (2), the voltage fluctuation in the latter half of the turn-off operation can be reduced so as to suppress damage and malfunction of the semiconductor switching element 10 due to surge voltage. In other words, the switching loss is suppressed by performing the switching operation at high speed until halfway through the turn-off operation, and the surge voltage can be suppressed by reducing the switching operation speed after that.

As described above, in the switching circuit according to the first embodiment, the charge accumulated in the control electrode 13 is rapidly discharged during the turn-off operation. Furthermore, the capacitance value C1 of the parallel capacitor 232 is set so that the speed of charge transfer from the control electrode 13 decreases during the turn-off operation. Therefore, the voltage fluctuation in the second half of the turn-off operation becomes moderate. As a result, the switching circuit shown in FIG. 1 can suppress switching loss and surge voltage.

<Modification>
FIG. 2 shows a switching circuit according to a modification of the first embodiment. In the switching circuit shown in FIG. 2, a drive resistor R21 is used for the high potential side element 21. In the switching circuit shown in FIG. That is, one terminal of the drive resistor R21 is connected to the high potential terminal 31, and the other terminal is connected to the control electrode 13 of the semiconductor switching element 10. FIG. The low-potential-side element 22 uses a PNP transistor as the second driving transistor T22, as in the switching circuit shown in FIG.

According to the switching circuit shown in FIG. 2, the manufacturing cost of the switching circuit can be reduced by using a resistive element that is cheaper than a transistor for the high-potential side element 21 . By adjusting the resistance value of drive resistor R21, the amount of charge supplied to control electrode 13 of semiconductor switching element 10 in the turn-on operation is adjusted. That is, the speed of the turn-on operation can be set by the drive resistor R21.

In the switching circuit shown in FIG. 2 as well, the low potential side parallel circuit 23 is connected to the low potential side element 22 . As a result, electric charge moves from the control electrode 13 to the parallel capacitor 232, and current flows into the base electrode of the second driving transistor T22 due to the charge operation of the parallel capacitor 232 caused by this electric charge movement. By these two actions, the turn-off operation of the semiconductor switching element 10 is performed at high speed.

Also, like the switching circuit shown in FIG. 1, by satisfying the expression (1), the semiconductor switching element 10 can perform high-speed switching operation. By satisfying the expression (2), the surge voltage can be suppressed by slowing down the switching operation in the second half of the turn-off operation.

A first driving transistor T21 may be connected between the driving resistor R21 and the high potential terminal 31, as shown in FIG. That is, the high potential terminal 31 is connected to the collector electrode of the first driving transistor T21, which is an NPN transistor, and the driving resistor R21 is connected to the emitter electrode.

According to the switching circuit shown in FIG. 3, leakage current flowing from the high-potential terminal 31 is suppressed when the semiconductor switching element 10 is in the OFF state. Therefore, a low-loss drive circuit 20 can be realized.

Furthermore, as shown in FIG. 4, a capacitor C21 may be connected in parallel with the drive resistor R21. The switching circuit shown in FIG. 4 has a configuration in which the capacitor C21 and the capacitance of the control electrode 13 of the semiconductor switching element 10 are connected in series. Therefore, at the beginning of the turn-on operation, the capacitance of the control electrode 13 is rapidly charged. Therefore, semiconductor switching element 10 performs high-speed switching operation until halfway through the turn-on operation, and switching loss can be suppressed.

(Second embodiment)
A switching circuit according to the second embodiment of the present invention, as shown in FIG. A potential side parallel circuit 24 is connected. The switching circuit shown in FIG. 5 differs from FIG. 1 in that it further includes a high potential side parallel circuit 24 . Other configurations are the same as those of the first embodiment shown in FIG.

The collector electrode of the NPN bipolar transistor, which is the first driving transistor T21, is connected to one terminal of the high potential side parallel circuit 24, and the emitter electrode is connected to the control electrode 13 of the semiconductor switching element 10. FIG. The other terminal of the high potential side parallel circuit 24 is connected to the high potential terminal 31 .

In the switching circuit shown in FIG. 5, when the semiconductor switching element 10 is turned on, the first driving transistor T21 is turned on, and the impedance between the emitter electrode and the collector electrode becomes low. As a result, the capacitance of the control electrode 13 of the semiconductor switching element 10 and the parallel capacitor 242 are connected in series. Therefore, the charge moves to the control electrode 13 at high speed via the parallel capacitor 242 .

That is, in the turn-on operation, charges are rapidly supplied to the control electrode 13 . As a result, the semiconductor switching element 10 turns on at high speed. Therefore, the switching operation of the semiconductor switching element 10 is performed at high speed, and switching loss can be suppressed.

Furthermore, due to the transfer of charge to the control electrode 13 via the parallel capacitor 242, the potential of the collector electrode of the first driving transistor T21 becomes lower than the potential of the high potential terminal 31. FIG. As a result, a current flows into the base electrode of the first driving transistor T21, and the charge is more rapidly supplied to the control electrode 13 by the first driving transistor T21.

As described above, in the switching circuit shown in FIG. 5, charge transfer through the parallel capacitor 242 and current flow into the base electrode of the first driving transistor T21 due to the charge transfer occur. By these two actions, the turn-on operation of the semiconductor switching element 10 is performed at high speed.

Note that the capacitance value C2 of the parallel capacitor 242 is set so that the speed of the charges moving to the control electrode 13 during the turn-on operation is reduced. Thereby, surge voltage can be suppressed. Therefore, the capacitance value of the parallel capacitor 242 is set in consideration of the switching loss required for the switching circuit and the magnitude of the allowable surge voltage.

For example, the capacitance value C2 of the parallel capacitor 242 is set according to the capacitance value Cg of the parasitic capacitance Cgs, the power supply voltage Vd, and the like. As a result of repeated studies, the present inventors have found that when the value of C2×Vd/(C2+Cg) is approximately the same as the threshold voltage Vth of the semiconductor switching element 10, damage and malfunction of the semiconductor switching element 10 due to surge voltage can be prevented. It was also found that the switching loss can be suppressed.

Considering a margin for characteristic variations of components used in the semiconductor switching element 10 and the drive circuit 20, the capacitance value C2 of the parallel capacitor 242 may be set so as to satisfy the following equation (3). :

Vth≦3×C2×Vd/(C2+Cg) (3)

By setting the capacitance value C2 so as to satisfy the expression (3), the switching loss of the semiconductor switching element 10 can be suppressed.

Also, the capacitance value C2 may be set so as to satisfy the following equation (4):

Vth≧C2×Vd/(3×(C2+Cg)) (4)

By setting the capacitance value C2 so as to satisfy the equation (4), charges are supplied from the high potential terminal 31 to the control electrode 13 mainly by the current flowing through the parallel resistor 241 from the middle of the turn-on operation. As a result, the speed of charge transfer becomes slower than that at the beginning of the turn-on operation, and the voltage fluctuation in the latter half of the turn-on operation, which affects the occurrence of ringing, can be moderated. Thereby, surge voltage can be suppressed.

As described above, according to the switching circuit according to the second embodiment, the turn-on operation of the semiconductor switching element 10 is performed at high speed. Furthermore, surge voltage in turn-on operation can be suppressed.

Others are substantially the same as the first embodiment. That is, in the switching circuit shown in FIG. 5, the low potential side parallel circuit 23 is connected between the second driving transistor T22 and the low potential terminal 32, like the switching circuit shown in FIG. Therefore, the turn-off operation of the semiconductor switching element 10 can be performed at high speed, and the surge voltage in the turn-off operation can be suppressed.

Therefore, according to the switching circuit according to the second embodiment, the semiconductor switching element 10 can be switched at high speed and the surge voltage can be suppressed in both the turn-on operation and the turn-off operation.

(Third embodiment)
FIG. 6 shows a switching circuit according to a third embodiment of the invention. The switching circuit shown in FIG. 6 differs from the switching circuit shown in FIG. 5 in that the low potential side parallel circuit 23 is not connected to the second driving transistor T22. Other configurations are the same as those of the second embodiment shown in FIG.

According to the switching circuit shown in FIG. 6, the high-potential side parallel circuit 24 is connected between the first driving transistor T21 and the high-potential terminal 31, so that high-speed turn-on operation and surge during turn-on operation Voltage suppression is possible. In addition, since the drive circuit 20 does not have the low-potential side parallel circuit 23, it is possible to reduce the size of the drive circuit 20, reduce the number of components, and reduce the rate of defects and the manufacturing cost.

For example, the switching circuit shown in FIG. 6 is preferably used for the semiconductor switching element 10 that has low resistance to surge voltage during turn-on operation and high resistance to surge voltage during turn-off operation. On the other hand, the switching circuit shown in FIG. 1 is preferably used for the semiconductor switching element 10 that has high resistance to surge voltage during turn-on operation and low resistance to surge voltage during turn-off operation.

Others are substantially the same as the above-described embodiment, and redundant description is omitted. For example, similarly to the switching circuit shown in FIG. 5, high-speed switching operation of the semiconductor switching element 10 is possible by satisfying the expression (3). Moreover, by satisfying the expression (4), the surge voltage can be suppressed.

<Modification>
FIG. 7 shows a switching circuit according to a modification of the third embodiment. The switching circuit shown in FIG. 7 uses a drive resistor R22 for the low potential side element 22. The switching circuit shown in FIG. The high potential side element 21 uses an NPN transistor as the first driving transistor T21.

According to the switching circuit shown in FIG. 7, the manufacturing cost of the switching circuit can be reduced by using a resistive element that is cheaper than a transistor for the low potential side element 22 . The speed of the turn-off operation can be adjusted by the resistance value of the drive resistor R22. In the switching circuit shown in FIG. 7 as well, the charge moves at high speed to the control electrode 13 via the parallel capacitor 242, and current flows into the base electrode of the first driving transistor T21 due to this charge movement. occurs. By these two actions, the turn-on operation of the semiconductor switching element 10 is performed at high speed.

In addition, as in the switching circuit shown in FIG. 5, high-speed switching operation of the semiconductor switching element 10 is possible by satisfying the expression (3). By satisfying the expression (4), the surge voltage can be suppressed by slowing down the switching operation in the second half of the turn-on operation.

A second driving transistor T22 may be connected between the driving resistor R22 and the low potential terminal 32, as shown in FIG. That is, the emitter electrode of the second driving transistor T22, which is a PNP transistor, is connected to the driving resistor R22, and the collector electrode is connected to the low potential terminal 32. FIG.

According to the switching circuit shown in FIG. 8, leakage current flowing through the low potential terminal 32 is suppressed when the semiconductor switching element 10 is in the ON state. Therefore, a low-loss drive circuit 20 can be realized.

Furthermore, as shown in FIG. 9, a capacitor C22 may be connected in parallel with the drive resistor R22. The switching circuit shown in FIG. 9 has a configuration in which the capacitor C22 and the capacitance of the control electrode 13 of the semiconductor switching element 10 are connected in series. Therefore, the charge is rapidly discharged from the control electrode 13 at the beginning of the turn-off operation. Therefore, the semiconductor switching element 10 performs high-speed switching operation until halfway through the turn-off operation, and switching loss can be suppressed.

(Other embodiments)
While embodiments of the present invention have been described above, the discussion and drawings forming part of this disclosure should not be construed as limiting the invention. Various alternative embodiments, implementations and operational techniques will become apparent to those skilled in the art from this disclosure.

For example, the case where the semiconductor switching element 10 is a MOSFET has been exemplified above. However, semiconductor switching element 10 may be another transistor. That is, the semiconductor switching element 10 may be a unipolar transistor or a bipolar transistor. Also, the semiconductor switching element 10 may be composed of a silicon semiconductor, or may be composed of a wide bandgap semiconductor.

DESCRIPTION OF SYMBOLS 10... Semiconductor switching element 11... High potential main electrode 12... Low potential main electrode 13... Control electrode 20... Drive circuit 21... High potential side element 22... Low potential side element 23... Low potential side parallel circuit 24... High potential side parallel Circuit 30 Drive power supply 31 High potential terminal 32 Low potential terminal T21 First drive transistor T22 Second drive transistor

Claims (5)

a driving power supply having a high potential terminal and a low potential terminal;
A semiconductor switching element having a low-potential main electrode connected to the low-potential terminal, a high-potential main electrode set to a higher potential than the low-potential main electrode, and a control electrode to which a drive signal for controlling conduction state is input. and,
A high-potential side element and a low-potential side element are cascade-connected between the high-potential terminal and the low-potential terminal, and the drive signal is output from a connection point between the high-potential side element and the low-potential side element. with a drive circuit and
at least one of the high potential side element and the low potential side element is a driving transistor having one main electrode connected to the control electrode of the semiconductor switching element;
wherein the drive circuit comprises a parallel circuit of a resistive element and a capacitor connected to the other main electrode of the drive transistor ;
the low-potential-side element is the driving transistor;
one main electrode of the low potential side element is connected to the control electrode of the semiconductor switching element;
the parallel circuit is connected between the other main electrode of the low potential side element and the low potential terminal and the low potential main electrode of the semiconductor switching element;
a power supply voltage Vd which is a potential difference between the high potential terminal and the low potential terminal; a capacitance value C1 of the capacitor in the parallel circuit connected to the other main electrode of the low potential side element; and the control of the semiconductor switching element The capacitance value Cg of the parasitic capacitance between the electrode and the low-potential main electrode and the threshold voltage Vth of the semiconductor switching element satisfy the relationship Vth≦3×Cg×Vd/(C1+Cg).
A switching circuit characterized by: a power supply voltage Vd which is a potential difference between the high potential terminal and the low potential terminal; a capacitance value C1 of the capacitor in the parallel circuit connected to the other main electrode of the low potential side element; and the control of the semiconductor switching element The capacitance value Cg of the parasitic capacitance between the electrode and the low-potential main electrode and the threshold voltage Vth of the semiconductor switching element satisfy the relationship Vth≧Cg×Vd/(3×(C1+Cg)). 2. A switching circuit as claimed in claim 1 . a driving power supply having a high potential terminal and a low potential terminal;
A semiconductor switching element having a low-potential main electrode connected to the low-potential terminal, a high-potential main electrode set to a higher potential than the low-potential main electrode, and a control electrode to which a drive signal for controlling conduction state is input. and,
A high-potential side element and a low-potential side element are cascade-connected between the high-potential terminal and the low-potential terminal, and the drive signal is output from a connection point between the high-potential side element and the low-potential side element. drive circuit and
with
at least one of the high potential side element and the low potential side element is a driving transistor having one main electrode connected to the control electrode of the semiconductor switching element;
wherein the drive circuit comprises a parallel circuit of a resistive element and a capacitor connected to the other main electrode of the drive transistor;
the high-potential-side element is the driving transistor;
one main electrode of the high potential side element is connected to the control electrode of the semiconductor switching element;
the parallel circuit is connected between the other main electrode of the high potential side element and the high potential terminal;
a power supply voltage Vd that is a potential difference between the high potential terminal and the low potential terminal, a capacitance value C2 of the capacitor in the parallel circuit connected to the other main electrode of the high potential side element, and the control of the semiconductor switching element A capacitance value Cg of a parasitic capacitance between an electrode and the low-potential main electrode and a threshold voltage Vth of the semiconductor switching element satisfy a relationship of Vth≦3×C2×Vd/(C2+Cg) . switching circuit. a power supply voltage Vd that is a potential difference between the high potential terminal and the low potential terminal, a capacitance value C2 of the capacitor in the parallel circuit connected to the other main electrode of the high potential side element, and the control of the semiconductor switching element The capacitance value Cg of the parasitic capacitance between the electrode and the low-potential main electrode and the threshold voltage Vth of the semiconductor switching element satisfy the relationship Vth≧C2×Vd/(3×(C2+Cg)). 4. A switching circuit as claimed in claim 3 . a driving power supply having a high potential terminal and a low potential terminal;
A semiconductor switching element having a low-potential main electrode connected to the low-potential terminal, a high-potential main electrode set to a higher potential than the low-potential main electrode, and a control electrode to which a drive signal for controlling conduction state is input. and,
A high-potential side element and a low-potential side element are cascade-connected between the high-potential terminal and the low-potential terminal, and the drive signal is output from a connection point between the high-potential side element and the low-potential side element. drive circuit and
with
at least one of the high potential side element and the low potential side element is a driving transistor having one main electrode connected to the control electrode of the semiconductor switching element;
wherein the drive circuit comprises a parallel circuit of a resistive element and a capacitor connected to the other main electrode of the drive transistor;
the high-potential-side element is the driving transistor;
one main electrode of the high potential side element is connected to the control electrode of the semiconductor switching element;
the parallel circuit is connected between the other main electrode of the high potential side element and the high potential terminal;
a power supply voltage Vd that is a potential difference between the high potential terminal and the low potential terminal, a capacitance value C2 of the capacitor in the parallel circuit connected to the other main electrode of the high potential side element, and the control of the semiconductor switching element The capacitance value Cg of the parasitic capacitance between the electrode and the low-potential main electrode and the threshold voltage Vth of the semiconductor switching element satisfy the relationship Vth≧C2×Vd/(3×(C2+Cg)).
A switching circuit characterized by:

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