JPH06335232A - Snubber circuit for switching element and switching circuit - Google Patents

Abstract

PURPOSE:To reduce the number of components of the snubber circuit of a plurality of IGBTs which are connected in parallel without sacrificing surge absorption capacity and surge absorption recovery capacity. CONSTITUTION:A series circuit consisting of diodes 6a and 6b and capacitors 7a and 7b is connected in parallel between a collector C and an emitter E of a plurality of IGBTs 1a and 1b which are connected between DC buses 4 and 5 and at the same time the connection points of the diodes 6a and 6b and the capacitors 7a and 7b are commonly connected by a conductor 14 and a resistor 11 is connected in parallel to the diode 6.

Description

Detailed Description of the Invention

[0001]

This invention relates to a switching element,
In particular, the present invention relates to a snubber circuit of a switching element that protects the IGBT when the IGBT operates, and a switching circuit including the snubber circuit.

[0002]

2. Description of the Related Art FIG. 7 shows a switching element such as an IGBT (hereinafter, simply referred to as an IGBT) commonly referred to as RC.
FIG. 6 is a circuit diagram of a switching circuit configured by connecting a −D snubber circuit. This switching circuit is used particularly in power converters such as inverters and converters or chopper devices. In the figure, 1a and 1b are modularized IGBTs, and 2 and 3 are IGBTs 1a and 1b.
Conductors for commonly connecting the collectors C and the emitters E of the above, and reference numerals 4 and 5 are DC bus bars for supplying a DC voltage to the IGBTs 1a and 1b.

Reference numeral 6 is a diode for guiding a surge voltage to the capacitor 7 when the IGBTs 1a, 1b are off, and the anode of this diode 6 is connected to the collector of the IGBT 1b by a conductive wire 8.
, The cathode is connected to one end of the capacitor 7 by a conductor 9, and the other end of the capacitor 7 is connected to the emitter of the IGBT 1b by a conductor 10.
A resistor 11 is connected to the lead wires 12, 13 of the diode 6.
Are connected in parallel by. The diode 6, the capacitor 7, and the resistor 11 are used to connect the R- of the IGBTs 1a and 1b
CD snubber circuit (hereinafter simply referred to as snubber circuit)
Make up.

Next, the operation will be described. IGBT1
When a and 1b are turned off by a gate control circuit (not shown), the surge voltage generated in the IGBT 1a becomes
Conductor 8 → Diode 6 → Conductor 9 → Capacitor 7 → Conductor 1
It is absorbed by the capacitor 7 along the path of 0 → conductor 3. On the other hand, the surge voltage generated in the IGBT 1b is absorbed by the capacitor 7 along the route of the conductor wire 8 → the diode 6 → the conductor wire 9 → the capacitor 7 → the conductor wire 10. Thereby, the IGBTs 1a, 1
The surge voltage generated due to the jump of the voltage between the collector C and the emitter E of b is absorbed by the capacitor 7 and suppressed to protect the IGBTs 1a and 1b from destruction.

When the IGBTs 1a and 1b are turned on, the charge of the capacitor 7 charged by the surge voltage is in the route of the conductor wire 9 → lead wire 13 → resistor 11 → lead wire 12 → conductor wire 8 → IGBT 1b → conductor wire 10. Discharged by the resistor 11, and further the conductor 9 → the lead 13 → the resistor 11 → the lead 12 → the conductor 8 → the conductor 2 → the IGBT 1a → the conductor 3 → the conductor 1
Even in the 0 path, the electric charge is discharged by the resistor 11 to restore the surge absorbing capability of the capacitor 7.

The switching circuit shown in FIG. 7 is an IGBT1.
A snubber circuit was provided only in b, and the surge voltage generated in the IGBT 1a was led to the snubber circuit through conductors 2 and 8.
As shown in FIG. 8, a snubber circuit including a diode 6a, a capacitor 7a, and a resistor 11a may be connected in parallel to the IGBT 1a between the collector C and the emitter E of the IGBT 1a by the shortest paths by the conductors 8a and 10a. . By connecting the snubber circuit in this way, the IG
Since the inductance of the conducting wires 8a and 10a connecting the BT1a and the snubber circuit is reduced, the surge absorbing capability of the IGBT1a is improved. A snubber circuit including a diode 6b, a capacitor 7b, and a resistor 11b is also connected to the IGBT 1b by conducting wires 8b and 9b.

Next, the operation will be described. IGBT1
When a and 1b are turned off, the surge voltage generated in the IGBT 1a is absorbed by the capacitor 7a in the route of the conductor 8a → diode 6a → conductor 9a → capacitor 7a → conductor 10a, while the surge voltage generated in the IGBT 1b is conductor 8b. → Diode 6b → Conductor 9b → Capacitor 7b → Conductor 10b is absorbed by the capacitor 7b in the path of each IGB.
The jump of the voltage between the collector C and the emitter E of T1a and 1b is suppressed.

When the IGBTs 1a and 1b are turned on, the charge charged in the capacitor 7a by the surge voltage in the IGBT 1a is changed from the lead wire 9a to the lead wire 13a.
-> Resistor 11a-> lead wire 12a-> conductor wire 8a-> IGBT1
a → The conductor 10a is discharged through the resistor 11a, while I
In the GBT 1b, the electric charge charged in the capacitor 7b is the lead wire 9b → the lead wire 13b → the resistor 11b → the lead wire 1
2b → conductor 8b → IGBT 1b → conductor 10b is discharged through the resistor 11b to recover the surge absorbing ability.

[0009]

Since the conventional switching circuit is configured as described above, for example, the switching circuit shown in FIG. 7 has a single snubber circuit which absorbs surges and surges of two IGBTs. Although the capability can be restored, if the outer shape becomes larger as the power capacity of each IGBT increases and the conductor wire connecting the IGBTs in parallel becomes longer accordingly, the influence of the internal impedance of the conductor wire on the surge voltage cannot be ignored. Therefore, the IGBT
There is a problem that the action of the capacitor that absorbs the surge voltage generated in 1a is reduced.

Further, in order to solve the above problems, a snubber circuit may be connected to each IGBT by a shortest conductor wire as shown in FIG. 8, but a switching circuit is added as the snubber circuit is added. However, there is a problem in that the number of parts of the device is increased and the device using the switching circuit is inevitably increased in size.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a snubber circuit and a switching circuit of a switching element that can prevent the apparatus from becoming large in size.

[0012]

According to a first aspect of the present invention, there is provided a snubber circuit for a switching element, wherein a diode and a capacitor are provided between a first electrode and a second electrode of each switching element connected in parallel between DC busbars. Is connected in parallel, the connection points of the diodes and the capacitors are commonly connected, and a resistor is connected in parallel to either one of the diodes.

In a snubber circuit for a switching element according to a second aspect of the present invention, one end of a capacitor is connected to either one of the first electrode or the second electrode of each switching element connected in parallel between DC busbars. The other end of the capacitor is commonly connected to the DC bus via a single resistor.

According to a third aspect of the present invention, there is provided a switching circuit, wherein a first switching element and a second switching element connected in parallel between DC busbars and the second switching element after the first switching element is turned off. Control means for turning off the switching element and a snubber circuit between the first electrode and the second electrode of the second switching element are provided.

[0015]

In the snubber circuit of the switching element according to the invention of claim 1, the surge voltage charged in the capacitor in the series circuit provided corresponding to each switching element is discharged by a single resistor. It is not necessary to provide the number of resistors according to the number.

In the snubber circuit of the switching element according to the second aspect of the present invention, each capacitor is charged with a surge voltage generated when the switching element is turned off through a single resistor, and each capacitor is charged when the switching element is turned on. Since the electric charge is discharged by a single resistor, it is not necessary to provide the number of resistors corresponding to the number of switching elements.

In the switching circuit according to the third aspect of the present invention, the surge voltage generated in the first switching element which is first turned off is commutated by the second switching element which is in the on state, and the switching of the younger brother 2 is turned off. Since the surge voltage generated at that time is absorbed by the snubber circuit provided in the second switching element, it is not necessary to provide the number of snubber circuits according to the number of switching elements.

[0018]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of the snubber circuit of the switching element in this embodiment. In the figure, the same reference numerals as those in FIG. 8 indicate the same or corresponding parts. Figure 8
The difference from the conventional snubber circuit shown in FIG.
The common connection of the cathode of 6b by the conductor 14 and the elimination of the resistor 11a connected in parallel to the diode 6a,
This is because the resistor 11 is connected in parallel only to the diode 6b to reduce the number of parts in the circuit.

Next, the operation of this embodiment will be described.
First, when the IGBTs 1a and 1b are controlled to be off, the surge voltage generated in the IGBT 1a is absorbed by the capacitor 7a along the route of the conductor 8a → the diode 6a → the conductor 9a → the capacitor 7a → the conductor 10a, as in the conventional circuit.
The surge voltage generated in the BT1b is absorbed by the capacitor 7b along the route of the conducting wire 8b → the diode 6b → the conducting wire 9b → the capacitor 7b → the conducting wire 10b, and the jumping of the voltage between the collector C and the emitter E of each IGBT 1a, 1b is suppressed.

When the IGBTs 1a and 1b are turned on, the charge charged in the capacitor 7a by the surge voltage in the IGBT 1a is the conductor 9a → the conductor 14 → the lead 13 → the resistor 11 → the lead 12 → the conductor 8b → the conductor 8b. Two
→ IGBT1a → lead wire 10a is discharged through the resistor 11 while the electric charge charged in the capacitor 7b in the IGBT1b is lead wire 9b → lead wire 13 → resistor 11 → lead wire 12 → lead wire 8b → IGBT1b → lead wire 10b. The resistor 11 is discharged to recover the surge absorbing ability. Therefore, it is possible to recover the surge absorbing ability by discharging the electric charges of the capacitors 7a and 7b in the snubber circuits of the respective IGBTs 1a and 1b with only the single resistor 11.

Example 2. In the first embodiment, the IGBT 1
Although the operation of the snubber circuit in the case where two a and 1b are connected in parallel has been described, even in the case of a switching circuit in which three IGBTs are connected in parallel as shown in FIG.
By commonly connecting the cathodes of the diodes, a single resistor can be connected in parallel with the diodes.

The snubber circuit according to this embodiment will be described below with reference to FIG. In the figure, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts. In the figure, 1c is an IGBT 1a,
Is a third IGBT connected in parallel with 1b,
Between the collector C and the emitter E of the IGBT 1c, a snubber circuit composed of a series circuit of a diode 6c and a capacitor 7c is connected in parallel by conductors 8c and 10c. The resistor 11 is connected in parallel only to the diode 6c. Further, the cathode of the diode 6c is commonly connected to the cathode of the diode 6b by the conductor wire 14b.

Further, the collector C of the IGBT 1b and the IGBT
The collector C of T1a is commonly connected by a conductor 2a, the collector C of the IGBT1b and the collector C of IGBT1c are commonly connected by a conductor 2b, and the emitter E and IG of the IGBT1b are connected.
The emitter E of the BT1a is connected to the IGBT1b by the conductor 3a.
The emitter E of the IGBT 1c and the emitter E of the IGBT 1c are commonly connected by the conductor 3b, so that the IGBTs 1a, 1b, 1c
Are commonly connected in parallel. Further, the diodes 6a, 6b
The cathodes are commonly connected by a conductor 14a.

Next, the operation will be described. IGBT1
When a to 1c are turned off, the surge voltage generated in the IGBT 1a is absorbed by the capacitor 7a in the route of the conductor 8a → diode 6a → conductor 9a → capacitor 7a → conductor 10a, and the surge voltage generated in the IGBT 1b is conductor 8b.
→ diode 6b → conductor 9b → capacitor 7b → conductor 1
It is absorbed by the capacitor 7b in the path of 0b. Further IGB
The surge voltage generated at T1c is the conductor 8c → diode 6
It is absorbed by the capacitor 7c along the route of c → conductor 9c → capacitor 7c → conductor 10c.

When the IGBTs 1a to 1c are turned on, the charges stored in the capacitor 7a are transferred to the conductor 9
a → conductor wire 14a → conductor wire 14b → lead wire 13 → resistor 11
→ lead wire 12 → conductor wire 8c → conductor wire 2b → conductor wire 2a → IG
Discharged by the resistor 11 along the path of BT1a → conductor 3a,
The electric charge stored in the capacitor 7b is discharged by the resistor 11 along the route of the conductor 9b → the conductor 14b → the lead 13 → the resistor 11 → the lead 12 → the conductor 8c → the conductor 2b → the IGBT 1b → the conductor 3b. Further, the electric charge charged in the capacitor 7c is discharged by the resistor 11 along the route of the conductor wire 9c → the lead wire 13 → the resistor 11 → the lead wire 12 → the conductor wire 8c → the IGBT 1c → the conductor wire 3b.

Example 3. In the snubber circuits of Examples 1 and 2, a series circuit in which a diode and a capacitor are connected in this order between the collector C and the emitter E of each IGBT 1a and 1b is connected in parallel. However, the connection order is not limited, and a snubber circuit in which a capacitor 7a (7b) and a diode 6a (6b) are serially connected in this order as shown in FIG. 3 is connected in parallel between the collector C and the emitter E of each IGBT 1a, 1b. However, the same effect can be obtained. Example 1 above
It is needless to say that in the snubber circuits (1) to (3), the points where the diode and the capacitor are connected are geometrically the shortest, and at least all the potentials at the connection points are the same.

Example 4. The above Examples 1 to 3 are R-C-D.
Although the snubber circuit has been described, the number of components of the RC snubber circuit can be reduced even in a switching circuit provided with a so-called RC snubber circuit configured by connecting a resistor and a capacitor in series.

Here, to put the role of the resistor of the RC snubber circuit into consideration, if the snubber circuit is composed of only a capacitor, the surge voltage generated can be efficiently absorbed by the capacitor. However, when a switching element such as an IGBT is turned off, a resonance phenomenon occurs due to the capacitor and the stray inductance of the switching circuit. Since this resonance phenomenon induces inconveniences such as generation of noise, a resistor is connected in series to the capacitor in order to suppress resonance.

Further, since the charge accumulated in the capacitor is charged and discharged through the resistor, energy loss is large and the resistor becomes large. Therefore, when an RC snubber circuit is provided in a plurality of switching elements like an inverter device, the size of the device can be reduced by reducing the number of resistors.

FIG. 4 is a circuit diagram showing a switching circuit using the RC snubber circuit in this embodiment. In the figure, the same reference numerals as those in FIGS. 1 to 3 indicate the same or corresponding parts. The structure of this RC snubber circuit is, as is clear from the figure, each IGBT1 connected in parallel by conductors 2 and 3.
One ends of the capacitors 7a and 7b are connected to the emitters E of a and 1b by the conductive wires 10a and 10b, and the other ends are connected to the conductive wire 9
a and 9b commonly connect to the lead wire 13 at one end of the resistor 11a. Further, the lead wire 12 at the other end of the resistor 11 is connected to the high voltage side conductor wire 2. In this way, each IGB
By using the same resistance in the RC snubber circuits provided in the respective T1a and 1b, the number of parts can be reduced and the device can be downsized.

Next, the operation of this embodiment will be described.
When the IGBTs 1a and 1b are turned off, the IGBT 1a
The surge voltage generated at is lead wire 2 → lead wire 12 → resistance 1
1 → lead wire 13 → conductor wire 9a → capacitor 7a → conductor wire 1
The capacitor 7a is charged and absorbed through the path of 0a. The surge voltage generated in the IGBT 1b passes through the path of the lead wire 2 → the lead wire 12 → the resistor 11 → the lead wire 13 → the lead wire 9b → the capacitor 7b → the lead wire 10b and the capacitor 7b.
Is charged and absorbed.

Further, when the IGBTs 1a and 1b are controlled to be turned on, the charges charged in the capacitor 7a are transferred to the conductor 9a.
→ Lead wire 13 → Resistor 11 → Lead wire 12 → Conductor wire 2 → I
It is discharged by the resistor 11 through the path from the GBT 1a to the conducting wire 10a. Further, the electric charge charged in the capacitor 7b is the conductor wire 9b → the lead wire 13 → the resistor 11 → the lead wire 12 →
It is discharged by the resistor 11 through the path of the conductor 2 → the IGBT 1b → the conductor 10b. In this way, each capacitor 7
The charged electric charges of a and 7b are charged and discharged by the single resistor 11.

Example 5. In the above Examples 1 to 4, the IGBT is used.
A snubber circuit is provided in each IGBT connected in parallel in order to further shorten the path to the snubber circuit. However, the IGBT
After connecting two of these in parallel and turning on these IGBTs,
When the switching circuit by the IGBT is applied to the chopper device or the like in which the order of turning off is determined, the snubber circuit is provided only in the IGBT to be turned off later, so that the number of parts of the device can be reduced.

FIG. 5 is a circuit diagram showing the configuration of the switching circuit in this embodiment. In the same figure, (a) is a circuit diagram showing the main body of the switching circuit, and the circuit configuration is the same as that of the conventional switching circuit. In addition, in the figure, (b) is a block diagram of a control means for performing on / off control of the IGBTs 1a and 1b. In this figure, GT is IG
A gate signal generator that outputs gate on / off signals G1 and G for BT1a and 1b, an AND circuit that outputs a high level signal S when the gate on / off signals G1 and G are at a high level (when on), and TD is a delay Circuit,
The delay circuit TD outputs the high-level control signal ST without delay when the signal S output from the AND circuit AN is at the high level, and when the signal S is inverted to the low level (when off), the control signal after a predetermined time T. Invert ST to a low level signal.

OR is an OR circuit, and this OR circuit OR
Is IG while signal S or control signal ST is at high level
The high level gate signal G2 that turns on BT1b is IG
The signal is output to the gate of BT1b, and when the control signal ST is inverted to the low level as the signal S is inverted to the low level, the gate signal G2 is set to the low level and output to the gate of the IGBT1b.

Next, the operation of this embodiment will be described with reference to the timing chart of FIG. First, when the high-level gate on / off signals G and G1 are output from the gate signal generator GT, the gate on / off signal G1 becomes a gate signal and is input to the gate of the IGBT1b to turn on the IGBT1b. Since the gate on / off signal G1 is input to the AND circuit AN together with the gate on / off signal G, a high level signal S is input from the AND circuit AN to the OR circuit OR and the delay circuit TD. Then, the gate signal G2 is output from the OR circuit OR to the gate of the IGBT 1b and I
The GBT 1b is turned on.

As described above, when the IGBTs 1a and 1b are turned on at the same time, the total current 2I flowing through the DC bus 4 is the path of the DC bus 4 → IGBT 1a → DC bus 5, the DC bus 4
→ Conductor 2 → IGBT 1b → Conductor 3 → DC bus 5 is divided into I halves and flows as a collector current Ic in each IGBT 1a, 1b. After turning on each of the IGBTs 1a and 1b, when the gate signal G1 is set to a low level (off) to turn off the IGBTs 1a and 1b in this order, the IGBT 1a first turns off. The total current 2I flowing through the DC bus 4 is the DC bus 4 → conductor 2 → IGB
All are commutated to the IGBT 1b in the route of T1b → conductor 3 → DC bus 5.

At this time, since the collector C and the emitter E of the IGBT 1a are short-circuited by the IGBT 1b,
When the IGBT 1a is off, its own collector C-emitter E
There is no voltage jump. Therefore, it is not necessary to provide the snubber circuit in the IGBT 1a.

On the other hand, when the gate signal G1 is inverted to low level, the signal S output from the AND circuit AN becomes low level and is input to the delay circuit TD and the OR circuit OR.
However, since the delay circuit TD outputs the control signal ST inverted from the high level to the low level after the predetermined time T even when the input signal S becomes the low level, it outputs to the OR circuit OR.
During a predetermined time T, the high level gate signal G2 is IGB
It keeps outputting to the gate of T1b and keeps the IGBT1b in the ON state. Then, during this predetermined time T, the total current 2A is I
Commute at GBT1b.

However, when the predetermined time T elapses, the control signal ST is inverted to the low level, so that the gate signal G2 output from the OR circuit OR is inverted to the low level and turned off. As a result, the IGBT 1b is turned off, and the introduced total current 2I is turned off. Then, the surge voltage generated in the IGBT 1b due to the off operation is absorbed by the capacitor 7 through the route of the conducting wire 8 → the diode 6 → the conducting wire 9 → the capacitor 7 → the conducting wire 10 → the conducting wire 3.

When the IGBTs 1a and 1b return to the ON operation, the charges charged in the capacitor are the conductive wire 9 → the lead wire 13 → the resistor 11 → the lead wire 12 → the conductive wire 8 → the IGBT.
1b → route of conductor 10 and conductor 9 → lead 13 →
Resistor 11 → Lead wire 12 → Conductor wire 8 → Conductor wire 2 → IGBT1
It is distributed in the path of a → conductor 3 → conductor 10 and discharged by the resistor 11.

In this embodiment, the collector current flowing in one IGBT is reduced in consideration of the life of the IGBT and the like.
This is effective in suppressing the junction temperature ΔTj inside the GBT.

[0043]

A snubber circuit for a switching element according to a first aspect of the invention is a series circuit including a diode and a capacitor between a first electrode and a second electrode of each switching element connected in parallel between DC busbars. Are connected in parallel, the connection points of the diodes and the capacitors are commonly connected, and the resistor is connected in parallel to any one of the diodes, so that the surge in the capacitors charged in each series circuit is increased. By discharging the voltage with the resistance common to each switching element, there is an effect that the number of resistances corresponding to the number of switching elements is not necessary and the size of the device using the switching elements can be reduced.

In the snubber circuit of the switching element according to the second aspect of the present invention, one end of the capacitor is connected to either one of the first electrode or the second electrode of each switching element connected in parallel between the DC buses. Since the other end of the capacitor is commonly connected to the DC bus via a single resistor, the surge voltage generated when the switching element is turned off is charged to each capacitor through a single resistor, and switching is performed. When the element is turned on, the electric charge charged in each capacitor is discharged with a single resistor, so it is not necessary to have the number of resistors according to the number of switching elements, the circuit configuration is simplified and the switching element is used. There is an effect that the device can be downsized.

According to a third aspect of the present invention, there is provided a switching circuit comprising: a first switching element and a second switching element connected in parallel between DC busbars; and the second switching element after the first switching element is turned off. Since the control means for controlling the switching element to be turned off and the first electrode and the second electrode of the second switching element are provided with the snubber circuit, the surge voltage generated in the first switching element which is turned off first is turned on. The second switching element is used for commutation, and the surge voltage generated when the switching of the younger brother 2 is turned off can be absorbed by the snubber circuit provided in the second switching element. There is an effect that it is possible to provide a miniaturized switching circuit that does not need to have the snubber circuits according to the number.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a snubber circuit for a switching element according to the present invention.

FIG. 2 is a circuit diagram showing a configuration of a modified example of the snubber circuit of the switching element according to the present embodiment.

FIG. 3 is a circuit diagram showing a configuration of another modification of the snubber circuit for the switching element according to the present embodiment.

FIG. 4 is a circuit diagram showing a configuration of a snubber circuit of a switching element according to another embodiment.

FIG. 5 is a circuit diagram showing a configuration of an embodiment of a switching circuit according to the present invention.

FIG. 6 is a timing chart illustrating the operation of the switching circuit according to the present embodiment.

FIG. 7 is a circuit diagram showing a configuration of a snubber circuit of a conventional switching element.

FIG. 8 is a circuit diagram showing a configuration of a snubber circuit of a conventional switching element.

[Explanation of symbols]

 1a, 1b, 1c IGBT 4,5 DC bus 6a, 6b, 6c Diode 7a, 7b, 7c Capacitor 11 Resistor 14a, 14b Conductor

[Procedure amendment]

[Submission date] August 3, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction content]

Example 5. In the above Examples 1 to 4, the IGBT is used.
A snubber circuit is provided in each IGBT connected in parallel in order to further shorten the path to the snubber circuit. However, the IGBT
After connecting two of these in parallel and turning on these IGBTs,
If the order of turning off operation of applying the switching circuit of the IGBT device that have been established, the snubber circuit by providing only the IGBT to turn off the operation after, it is possible to reduce the number of parts of the apparatus.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

FIG. 5 is a circuit diagram showing the configuration of the switching circuit in this embodiment. In the same figure, (a) is a circuit diagram showing the main body of the switching circuit, and the circuit configuration is the same as that of the conventional switching circuit. In addition, in the figure, (b) is a block diagram of a control means for controlling the on / off of the IGBT 1a. In this figure, GT is IGBT1
a gate signal generator for outputting a gate-off signal G 1 against the a, T D is the delay circuit, the control signal ST of the delay circuit TD signals G1 outputted Ri by the AND circuits has a high level when the high level Is output without delay, and the signal G1
Is inverted to a low level (when off), the control signal ST is inverted to a low level signal after a predetermined time T.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

OR is an OR circuit, and this OR circuit OR
Is I while the signal G1 or the control signal ST is at a high level.
The high level gate signal G2 that turns on the GBT1b is I
The signal is output to the gate of the GBT 1b, and when the control signal ST is inverted to the low level as the signal G1 is inverted to the low level, the gate signal G2 is set to the low level and output to the gate of the IGBT 1b.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction content]

According to a third aspect of the present invention, there is provided a switching circuit comprising: a first switching element and a second switching element connected in parallel between DC busbars; and the second switching element after the first switching element is turned off. Since the control means for controlling the switching element to be turned off and the first electrode and the second electrode of the second switching element are provided with the snubber circuit, the surge voltage generated in the first switching element which is turned off first is turned on. The second switching element is a commutator, and the surge voltage generated when the second switching is turned off can be absorbed by the snubber circuit provided in the second switching element. There is an effect that it is possible to provide a miniaturized switching circuit that does not need to have the snubber circuits according to the number.

[Procedure Amendment 5]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

Claims (3)

[Claims] 1. A series circuit including a diode and a capacitor is connected in parallel between a first electrode and a second electrode of each switching element connected in parallel between DC busbars, and a connection point between each diode and the capacitor. A snubber circuit of a switching element, characterized in that the resistors are connected in parallel to any one of the diodes, with a common connection between them. 2. One end of a capacitor is connected to either one of the first electrode or the second electrode of each switching element connected in parallel between DC busbars, and the other end of the capacitor is connected to a single resistor. A snubber circuit of a switching element, wherein the snubber circuit is commonly connected to the DC bus via the DC bus. 3. A first switching element and a second switching element connected in parallel between a DC bus and the first switching element.
Control circuit for controlling the second switching element to be off after controlling the second switching element to be off, and a snubber circuit for the first electrode and the second electrode of the second switching element. .