JP2004282806A - Drive circuit of voltage drive element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive circuit of a voltage drive element in which a switching speed is improved. <P>SOLUTION: An IGBT 10 is driven by alternately turning on and off a P-channel type MOSFET 20 and an N-channel type MOSFET 30. When the MOSFET 20 and the MOSFT 30 are turned on simultaneously when the IGBT 10 is turned on, a voltage drop occurs at a current limiting resistor 31 via feedthrough current I. Since a MOSFET 40 is turned on by this voltage, gate current Ig is generated at the IGBT 10 via the MOSFET 40 from a gate power source Vcc. Accordingly, a switching time for turning on can be shortened by increasing the gate current by setting the resistance value of a gate resistor 33 to a small value. The switching speed is improved as compared with the case of routing a current limiting resistor 31 which cannot reduce the resistance value to limit the feedthrough current. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a driving circuit for a voltage driving element.
[0002]
[Prior art]
For example, a push-pull circuit disclosed in Japanese Patent Application Laid-Open No. 2002-333476 is known as a driving circuit of a voltage driving element.
The push-pull circuit connects the two switching elements in series between the operating power supply of the voltage driving element and the ground, and connects the connection midpoint of the two switching elements to the gate terminal of the voltage driving element. By turning on the switching element on the operation power supply side and turning off the switching element on the ground side, the voltage at the gate terminal of the voltage driving element is raised to turn on the voltage driving element. In addition, while the switching element on the operating power supply side is turned off, the switching element on the ground side is turned on, thereby lowering the voltage of the gate terminal of the voltage driving element to drive the voltage driving element so as to turn off the voltage driving element.
[0003]
In a drive circuit of this type, when the switching element on the operating power supply side and the switching element on the ground side are simultaneously turned on due to a difference in threshold voltage, an excessive current flows through the switching element, and the life of the switching element is reduced. In general, the switching element on the operating power supply side and the switching element on the ground side are not turned on at the same time, so that the switching element that is turned on is turned after the other switching element is surely turned off, so that there is a possibility of affecting the switching element. An off time for turning off both of the two switching elements is provided. However, in such control, there is a period during which both the switching element on the operating power supply side and the switching element on the ground side are simultaneously turned off, and the voltage driving element cannot be switched at high speed.
[0004]
[Problems to be solved by the invention]
In order to solve this, instead of providing an off period in which both switching elements are turned off, for example, a resistance element is connected in series between an operation power supply and a switching element on the operation power supply side, or between a switching element on the ground side and ground. It is conceivable to reduce the through current when the switching element on the operating power supply side and the switching element on the ground side are simultaneously turned on by connecting. However, in this case, for example, when a resistance element is simply provided between the operation power supply and the switching element on the operation power supply side, the resistance element restricts the current flowing from the operation power supply to the gate terminal of the voltage drive element, and the voltage drive element is operated at high speed. There was a problem that it was not possible to operate from off to on.
[0005]
In addition, when a resistance element connected in series between the switching element on the ground side and the ground is provided, the current flowing from the gate terminal of the voltage driving element to the ground decreases, so that the voltage driving element is quickly turned on. There was a problem that could not be turned off.
The present invention has been made in view of the above-described conventional problems, and has been made in view of the above circumstances. A voltage capable of rapidly turning on and off a voltage driving element while reducing a through current when a switching element on an operating power supply side and a switching element on a ground side are simultaneously turned on. It is an object of the present invention to provide a drive circuit for a drive element.
[0006]
[Means for Solving the Problems]
According to the present invention, a first switching element and a second switching element are connected in series between a first power supply and a ground via a first resistance element, and the first switching element and the second switching element are connected. In the drive circuit of the voltage drive element, the connection midpoint of which is connected to the gate terminal of the voltage drive element, one terminal is connected to the second power supply, and the other terminal is connected to the gate terminal of the voltage drive element; A third switching element that performs a switching operation based on the voltage of the first resistor element side terminal of the first switching element is provided.
[0007]
【The invention's effect】
According to the present invention, the first resistance element limits the through current when the first switching element and the second switching element are simultaneously turned on, and the first resistance element uses a voltage drop generated in the first resistance element by the through current. , The third switching element is turned on. When the third switching element is turned on, a current flows from the second power supply to the gate terminal of the voltage driving element via the third switching element. Therefore, a large current flows through the voltage driving element without passing through the first resistance element. The gate can be charged with a gate charge.
[0008]
Then, when the through current disappears, the third switching element is turned off, and at this time, a current flows to the gate terminal of the voltage driving element via the first resistance element, so that the charging speed of the gate charge becomes slow. As a result, the switching time and the loss can be reduced, and for example, when a freewheel diode is connected to the load of the voltage driving element, the recovery current flowing through the freewheel diode can be reduced.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the invention will be described with reference to examples.
FIG. 1 is a diagram illustrating a drive circuit of a load using a power semiconductor element IGBT, which is one of voltage drive elements.
The load 50 is connected between the power supply VB and the collector terminal C of the IGBT 10, and the emitter terminal E of the IGBT 10 is grounded. A drive signal is input to the gate terminal G of the IGBT 10, and the IGBT 10 is turned on / off according to the drive signal, and the load 50 is driven. A free wheel diode 60 is connected to both ends of the load 50, and is configured to regenerate energy stored in the load 50.
[0010]
As a drive circuit of the IGBT 10, a push-pull circuit 100 is connected between a gate drive power supply Vcc and the ground via a current limiting resistor 31. The push-pull circuit 100 includes a P-channel MOSFET 20 and an N-channel MOSFET 30. A source terminal S of the P-channel MOSFET 20 is connected to a gate power supply Vcc via a current limiting resistor 31, and a drain terminal D is an N-channel MOSFET. Connected to drain terminal D of MOSFET 30. The source terminal S of the N-channel MOSFET 30 is grounded.
[0011]
Gate terminals G of the P-channel MOSFET 20 and the N-channel MOSFET 30 are connected to the input terminal T, respectively. A connection point b between the drain terminal D of the P-channel MOSFET 20 and the drain terminal D of the N-channel MOSFET 30 is connected to the gate terminal G of the IGBT 10 via a gate resistor 32 and a gate resistor 33 connected in series. The drive pulse input by the push-pull circuit 100 is inverted and amplified, and a drive signal is output to the gate terminal G of the IGBT 10. The resistance value of the gate resistor 33 is set smaller than the resistance value of the gate resistor 32.
[0012]
In this embodiment, in the process of turning on the IGBT 10, a P-channel MOSFET 40 is provided as a third switching element so as to shorten the charge time of the gate. The source terminal S of the P-channel MOSFET 40 is connected to the gate power supply Vcc, and the drain terminal D is connected to a connection point a between the gate resistors 32 and 33. Gate terminal G is connected between P-channel MOSFET 20 and current limiting resistor 31. As a result, the P-channel MOSFET 40 operates by the voltage generated across the current limiting resistor 31, and allows the gate current Ig to flow to the gate terminal G of the IGBT 10 without passing through the current limiting resistor 31.
[0013]
FIG. 2 is a time chart showing the operation of each part of the circuit when the IGBT is turned on.
(1) is a drive pulse applied to the input terminal of the push-pull circuit 100. As shown in the figure, an on-threshold (threshold) L20 at which the P-channel MOSFET 20 turns from off to on is larger than an off-threshold L30 at which the N-channel MOSFET 30 turns from on to off.
At the time of turning on, at time t1 when the potential of the drive pulse becomes lower than the threshold L20 from the Hi level, the P-channel MOSFET 20 is turned on as shown in (2), but the N-channel MOSFET 30 is turned off. This occurs at time t2 when the potential of the drive pulse becomes equal to or lower than the threshold L30 as shown in (3). Therefore, between time t1 and time t2, both MOSFETs are simultaneously turned on, and a through current I is generated.
[0014]
(4) shows the through current I. At time t1, when the P-channel MOSFET 20 is turned on, a through current I is generated from the gate power supply Vcc to the ground. However, since the current value of the through current I is limited by the current limiting resistor 31, the P-channel MOSFET 20 and the N-channel MOSFET 30 are not affected by the current.
[0015]
The maximum value Imax of the through current I is determined by the following equation using the voltage value V of the gate power supply Vcc and the resistance value R1 of the current limiting resistor 31.
Imax = V / R1
When the current limiting resistor 31 is not provided, the through current I rises until the N-channel MOSFET 30 is turned off at time t2 as indicated by a dashed line. At this time, the P-channel MOSFET 20 and the N-channel MOSFET 30 may be thermally damaged due to an excessive current rise.
[0016]
Since the voltage generated at both ends of the current limiting resistor 31 by the through current I is input to the gate of the P-channel MOSFET 40, the P-channel MOSFET 40 is turned off at the same time when the through current I is generated as shown in (5). Turns on. As a result, a gate current Ig flows from the gate power supply Vcc to the gate terminal G of the IGBT 10 via the P-channel MOSFET 40 and the gate resistor 33.
[0017]
That is, the gate charge of the IGBT 10 can be charged by the P-channel MOSFET 40 at the same time when the through current I is generated, so that the IGBT 10 is turned on at high speed without delay in charging the gate charge of the IGBT 10. be able to.
(6) shows the gate current Ig. The maximum value Igmax of the gate current Ig is determined from the gate resistance 33 by the following equation.
Igmax = V / R3
Here, R3 is the resistance value of the gate resistor 33.
[0018]
Therefore, by setting the resistance value R3 of the gate resistor 33 low, the IGBT can be charged with the gate charge at high speed, and the gate voltage VGE of the IGBT 10 can be rapidly increased as shown in (7). As a result, the turn-on time of the IGBT 10 is shortened, and the switching speed is improved.
During the ON period of the P-channel MOSFET 40, the current flowing from the gate power supply Vcc to the ground via the N-channel MOSFET 30 is limited by the gate resistor 32, and thus does not affect the gate charging operation of the IGBT 10.
[0019]
Thereafter, when the potential of the driving pulse reaches the threshold value L20 of the N-channel MOSFET 30 at time t2, the N-channel MOSFET 30 is turned off and the through current I is cut off, so that the current value corresponds to the threshold value L40. When the current falls below the current, the P-channel MOSFET 40 is turned off.
[0020]
After the time t2, after the P-channel MOSFET 40 is turned off, the gate current Ig flows through the current limiting resistor 31, the P-channel MOSFET 20, the gate resistor 32, and the gate resistor 33. The gate current Igs at this time can be calculated by the following equation.
Igs = V / (R1 + R2 + R3)
Here, R1 is the resistance value of the current limiting resistor 31, R2 is the resistance value of the gate resistor 32, and R3 is the resistance value of the gate resistor 33.
[0021]
Since the gate current Igs is smaller than Igmax, the charging speed of the gate charge decreases at time t2, the rate of increase of the gate voltage VGE becomes slow, and the switching speed of the IGBT is moderated. When the drive pulse becomes Lo, the gate current Ig becomes zero, and the turn-on of the IGBT 10 is completed.
[0022]
The present embodiment is configured as described above, and by providing the P-channel MOSFET 40, a gate current Ig of a large current can flow immediately after the start of turn-on to quickly charge the gate of the IGBT 10 with a gate charge. At the same time as the current is cut off, the gate current Ig is reduced and the charge of the gate charge is reduced, so that the switching time for turning on the IGBT 10 can be reduced, the charge loss of the gate charge can be reduced, and the recovery current flowing through the freewheel diode 60 can be reduced. The effect of relaxing is obtained.
Although the source terminal S of the P-channel MOSFET 40 as the third switching element is connected to the gate power supply Vcc, it is also possible to provide another second power supply to generate a gate current for the IGBT 10. However, in this case, it is necessary to control the voltage of the second power supply connected to the source terminal of the MOSFET 40 to be substantially the same as the voltage of the gate power supply Vcc. Therefore, it is desirable to use the same power supply as in this embodiment. .
[0023]
In this embodiment, the P-channel MOSFET 40 is used as the third switching element, but a PNP transistor may be used instead. In the case of a PNP transistor, as shown in FIG. 3, the drain terminal D, the source terminal S, and the gate terminal G of the N-channel MOSFET 40 are connected to the collector C, the emitter E, and the base B of the PNP transistor 40 ', respectively. do it.
[0024]
Next, a second embodiment will be described.
FIG. 4 is another example of a drive circuit using the power semiconductor element IGBT.
In the first embodiment, the charge charging time to the gate is reduced in the turn-on process of the IGBT 10, but in the present embodiment, the reduction of the charge discharge time to the gate in the turn-off process will be described.
In the first embodiment, the current limiting resistor 31 is connected to the gate power supply Vcc side. However, in this embodiment, a current limiting resistor 31a is connected between the ground and the N-channel MOSFET 30 instead. Has become.
[0025]
An N-channel MOSFET 40a is used as a third switching element, the source terminal S is grounded, and the drain terminal D is connected to a connection point a between the gate resistor 32 and the gate resistor 33. The gate terminal G is connected between the current limiting resistor 31a and the N-channel MOSFET 30.
With this connection, the N-channel MOSFET 40a can be turned on by a voltage drop on the current limiting resistor 31a, as in the first embodiment.
The connections of the IGBT 10, the load 50, and the like are the same as in the first embodiment.
[0026]
FIG. 5 is a time chart showing the operation of each section of the circuit when the IGBT is turned off.
(1) is a drive pulse input to the push-pull circuit 100. In the process in which the drive pulse changes from the Lo level to the Hi level, the off threshold L20 at which the P-channel MOSFET 20 turns from on to off as shown is the on threshold L30 at which the N-channel MOSFET 30 turns from off to on. Therefore, only the N-channel MOSFET 30 is turned on at time t1 as shown in (3). On the other hand, the P-channel MOSFET 20 is turned off at time t2 when the potential of the driving pulse becomes equal to or higher than the threshold L20 as shown in (2), so that both MOSFETs are simultaneously turned on between time t1 and time t2, The current I flows.
[0027]
These operations are the same as those in the first embodiment. The through current I is limited by the current limiting resistor 31a, and the voltage generated at both ends of the current limiting resistor 31a is as shown in (5). Since the N-channel MOSFET 40a is turned on, a gate current Ig is generated via the N-channel MOSFET 40a. The gate current Ig at this time is a discharge current of the gate charge.
[0028]
As described above, since the gate charge can be discharged from the IGBT 10 by the N-channel MOSFET 40 at the same time when the through current I occurs, the gate charge can be discharged without delay.
(6) shows the gate current Ig.
At this time, the maximum value Igmax of the gate current is determined by the following equation from the gate resistance 33 as in the first embodiment.
Igmax = V / R3
[0029]
Also, while the N-channel MOSFET 40a is on, a relatively large gate current Ig can be generated by selecting the gate resistor 33, so that the gate discharge from the IGBT 10 is rapidly performed, and (7) As shown, the gate voltage VGE of the IGBT 10 can be rapidly decreased, and the switching time for turning off is shortened.
During the ON period of the N-channel MOSFET 40a, the current flowing from the gate power supply Vcc to the ground via the P-channel MOSFET 20 is limited by the gate resistor 32, so that the IGBT 10 does not affect the discharging operation of the gate charge. Absent.
[0030]
Thereafter, at time t2 when the P-channel MOSFET 20 turns off, the through current I is cut off, and the gate voltage of the N-channel MOSFET 40a decreases.
After the time t2, when the N-channel MOSFET 40a is turned off, the gate current Ig flows to the ground via the gate resistor 33, the gate resistor 32 and the N-channel MOSFET 30, so that the discharge speed of the gate charge is small and the gate voltage VGE falls. The switching speed of the IGBT 10 is reduced, and the switching speed of the IGBT 10 is reduced.
The gate current Igs at this time can be calculated from the gate resistance 32 as in the first embodiment.
[0031]
The present embodiment is configured as described above, and by providing the N-channel MOSFET 40a, even at the time of turn-on, the gate charge can be rapidly discharged immediately after the start, and the discharge of the gate charge can be slowed at the same time when the through current disappears. Accordingly, the switching time for turning off and the discharge loss of the gate charge can be reduced, and the surge voltage generated in the load 50 can be reduced.
[0032]
In this embodiment, the N-channel MOSFET 40a is used as the third switching element, but an NPN transistor may be used instead. In the case of an NPN transistor, as shown in FIG. 6, the drain terminal D, the source terminal S, and the gate terminal G of the N-channel MOSFET 40a are replaced by the collector C, the emitter E, and the base B of the NPN transistor 40a ', respectively. Just fine.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment.
FIG. 2 is a time chart showing the operation of each section of the circuit when the IGBT is turned on.
FIG. 3 is a diagram showing a modification.
FIG. 4 is a diagram showing a second embodiment.
FIG. 5 is a time chart showing the operation of each section of the circuit when the IGBT is turned off.
FIG. 6 is a diagram showing a modification.
[Explanation of symbols]
10 IGBT
20 P-channel MOSFET
30 N-channel MOSFET
31, 31a Current limiting resistors 32, 33 Gate resistor 40 P-channel MOSFET
40a N-channel type MOSFET
40 'PNP transistor 40a' NPN transistor 50 IGBT
60 Freewheel diode 100 Push-pull circuit Vcc Gate power supply (first power supply)
Vb power supply

Claims (9)

A first switching element connected to a first power supply;
A second switching element having one terminal connected to the first switching element and the other terminal grounded,
In a drive circuit for a voltage driving element, a connection midpoint between the first switching element and the second switching element is connected to a gate terminal of the voltage driving element.
A first resistance element connected between the first power supply and the first switching element, and one terminal connected to a second power supply having a voltage equal to the voltage of the first power supply, and A terminal is connected to a gate terminal of the voltage driving element and a connection midpoint between the first switching element and the second switching element, and a voltage of the first resistance element side terminal of the first switching element is connected to the terminal. And a third switching element for performing a switching operation based on the driving circuit. 2. The driving circuit according to claim 1, wherein the second power supply is the same power supply as the first power supply. A second resistance element and a third resistance element connected in series between a connection midpoint between the first switching element and the second switching element and a gate terminal of the voltage driving element; The other terminal of the third switching element is connected to a connection point between the second resistance element and the third resistance element, and the resistance value of the third resistance element on the voltage driving element side is the second resistance element. 3. The driving circuit for a voltage driving element according to claim 1, wherein the resistance is set lower than the resistance value of the resistance element. The third switching element has an emitter terminal connected to the second power supply, a collector terminal connected to a connection point between the second resistance element and the third resistance element, and a base terminal connected to the first power supply. 4. The driving circuit according to claim 3, wherein the driving circuit is a PNP transistor connected between the switching element and the first resistance element. The third switching element has a source terminal connected to the second power supply, a drain terminal connected to a connection point between the second resistance element and the third resistance element, and a gate terminal connected to the first power supply. 4. The driving circuit for a voltage driving element according to claim 3, wherein the driving circuit is a P-channel MOSFET connected between the switching element and the first resistance element side. A first switching element connected to a power supply, and a second switching element having one terminal connected to the first switching element and the other terminal grounded;
In a drive circuit for a voltage driving element, a connection midpoint between the first switching element and the second switching element is connected to a gate terminal of the voltage driving element.
A first resistance element connected between the second switching element and ground;
One terminal is connected to the gate terminal of the voltage driving element and the midpoint of connection between the first switching element and the second switching element, the other terminal is grounded, and the first terminal of the second switching element is And a third switching element for performing a switching operation based on the voltage of the resistor element side terminal. A second resistance element and a third resistance element connected in series between a connection midpoint between the first switching element and the second switching element and a gate terminal of the voltage driving element; And one terminal of the third switching element is connected to a connection point between the second resistance element and the third resistance element, and the resistance value of the third resistance element on the voltage driving element side is the second resistance element. 7. The driving circuit for a voltage driving element according to claim 6, wherein the resistance value is set lower than the resistance value of the resistance element. The third switching element has a collector terminal connected to a connection point between the second resistance element and the third resistance element, an emitter terminal grounded, and a base terminal connected to the second switching element and the third switching element. 8. The driving circuit for a voltage driving element according to claim 7, wherein the driving circuit is an NPN transistor connected between the first resistance element and the first resistance element. The third switching element has a drain terminal connected to a connection point between the second resistance element and the third resistance element, a source terminal grounded, and a gate terminal connected to the second switching element and the third switching element. 8. The driving circuit for a voltage driving element according to claim 7, wherein the driving circuit is an N-channel MOSFET connected between the first resistance element and the first resistance element.

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