JP2015211568A - Gate drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To actualize a gate drive circuit of a simple configuration, having no lower limit of a switching speed in order to reduce a high frequency noise by gently changing the gate voltage of a power semiconductor device.SOLUTION: The gate drive circuit includes a constant current gate drive circuit 2 for driving a capacitor 6 connected in parallel to the gate of a power semiconductor device 1. One end of the gate drive circuit 2 is connected to the gate of the power semiconductor device 1, whereas the other end is connected to a power semiconductor device control circuit 4 which obtains the gate current of the power semiconductor device 1. The constant current gate drive circuit 2 charges the gate capacitance of the power semiconductor device 1 with a constant current, and also sets a drive current value of the capacitor 6 to be a value larger than a lower limit current value by which the current of the constant current gate drive circuit 2 intermittently continues.

Description

  The present invention relates to a gate drive circuit for driving a power semiconductor element.

  When a power semiconductor element (for example, an IGBT (Insulated Gate Bipolar Transistor)) is switched, switching loss and high-frequency noise are generated. In order to reduce these, a method of gradually changing the gate voltage using a constant current circuit has been proposed (see, for example, Patent Document 1).

Japanese Patent No. 5289565

  However, in the technique disclosed in Patent Document 1, since the constant current circuit controls the current to a constant value by applying negative feedback, a lower limit is set for the gate current at which the constant current circuit can operate stably. When the gate current is set below the lower limit value, the gate current is intermittently operated. Therefore, when used in intermittent operation, the loss increases compared to when it is not intermittent, and when it is not in intermittent operation, a semiconductor element capable of high-speed switching is required, which increases circuit cost and makes it difficult to adjust circuit constants. is there.

  The present invention has been made in order to solve the above-described problems. In order to reduce high-frequency noise by gently changing the gate voltage of a power semiconductor element, the gate has no lower limit of switching speed. The object is to realize a drive circuit with a simple configuration.

A gate drive circuit according to the present invention is a gate drive circuit for driving a power semiconductor element, wherein one end of the gate drive circuit is connected to the gate of the power semiconductor element and the other end obtains a gate current of the power semiconductor element. A constant current gate drive circuit for driving a load connected in parallel to the gate of the power semiconductor element,
The constant current gate drive circuit charges the gate capacitance of the power semiconductor element with a constant current, and the drive current value of the load is larger than a lower limit current value at which the current of the constant current gate drive circuit is intermittent. It is to make.

  According to the present invention, since the gate voltage of the power semiconductor element is gently changed to reduce high frequency noise, a gate drive circuit having no lower limit of the switching speed can be realized with a simple configuration.

1 is a configuration diagram illustrating a gate drive circuit according to a first embodiment of the present invention. It is a block diagram which shows the gate drive circuit by Embodiment 2 of this invention. It is a block diagram which shows the gate drive circuit by Embodiment 3 of this invention.

  Preferred embodiments of a gate driving circuit according to the present invention will be described below with reference to the drawings.

Embodiment 1 FIG.
1 is a diagram showing a configuration of a gate drive circuit according to a first embodiment of the present invention.
As shown in FIG. 1, the gate drive circuit according to the first embodiment is connected to the gate of IGBT1, which is a power semiconductor element made of Si semiconductor, and controls IGBT1 by limiting the gate current when IGBT1 is turned on. The gate drive circuit 2 is connected in parallel to the power semiconductor element control circuit 4 as a voltage source for outputting an ON command signal (ON command voltage) 3 to the constant current gate drive circuit 2, and the constant current gate drive circuit 2, The circuit includes a discharge circuit 5 that discharges a gate charge when the IGBT 1 is turned off, and a capacitor 6 as a load.

  As shown in the figure, the constant current gate drive circuit 2 includes resistors 20 and 21, transistors 22a and 23 formed of PNP bipolar transistors, and a diode 24 connected in series to the collector of the transistor 22a. The cathode of the diode 24 becomes an output terminal of the constant current gate drive circuit 2 and is connected to the gate of the IGBT 1 and the capacitor 6. The constant current gate drive circuit 2 has a function of limiting the drive circuit output current 7 to a predetermined upper limit value.

Next, the operation of the gate drive circuit according to the first embodiment will be described.
When the IGBT 1 is turned on, the constant current gate drive circuit 2 receives the on command signal 3 from the power semiconductor element control circuit 4. When the ON command signal 3 is input to the constant current gate drive circuit 2, the transistor 22 a is turned on, an emitter current flows through the resistor 20, and a base current flows through the resistor 21. Further, a collector current flows through the diode 24, and this collector current becomes the drive circuit output current 7 and flows to the capacitor 6, and also becomes the gate current 8 for the IGBT 1 to charge the gate capacitance of the IGBT 1.

  When the emitter current of the transistor 22a increases, the voltage drop at the resistor 20 increases, and this voltage drop forward biases between the base and the emitter of the transistor 23, so that the transistor 23 becomes conductive. When the transistor 23 is turned on, the current (emitter current) flowing in the transistor 22a flows toward the transistor 23, and the voltage drop at the resistor 20 is reduced. On the other hand, when the voltage drop at the resistor 20 becomes small, the bias voltage between the base and the emitter of the transistor 23 becomes small, and the transistor 23 shifts from the conductive state to the cutoff state.

  By such a negative feedback operation, the forward voltage drop (for example, 0.6 V) between the base and emitter of the transistor 23 (PN junction) is ideally applied to the emitter of the transistor 22 a by the resistance value of the resistor 20. A constant current of the divided value flows. Since the collector current is substantially equal to the emitter current due to the nature of the transistor, the drive circuit output current 7 is also a constant current. In this way, the constant current gate drive circuit 2 drives the IGBT 1 that is a power semiconductor element at a constant current.

  Here, a case where there is no capacitor 6, that is, a case where the drive circuit output current 7 and the gate current 8 are equal is considered. When the operation of the constant current gate drive circuit 2 is transient, the drive circuit output current 7 oscillates due to circuit parasitic elements and transistor operation delays. When the drive circuit output current 7 is set to be small, there is a case where the gate current 8 is intermittently operated due to vibration during transition. For this reason, the capacitor 6 is used to flow the gate current 8 that can operate stably without being intermittent. As a result, a current sufficient for the drive circuit output current 7 to stably operate is passed through the capacitor 6, and a desired gate current 8 can be supplied to the IGBT 1 while stabilizing the drive circuit output current 7.

  As described above, according to the gate drive circuit of the first embodiment, when driving the IGBT 1 that is the power semiconductor element, the capacitor 6 is connected as the load of the constant current gate drive circuit 2, and the IGBT 1 and the capacitor are connected. 6, the constant current gate drive circuit 2 is configured to flow current, so that the IGBT 1 can be driven at a current lower than the lower limit value at which the constant current gate drive circuit 2 can stably operate.

Embodiment 2. FIG.
Next explained is a gate drive circuit according to the second embodiment of the invention. FIG. 2 is a configuration diagram of a gate drive circuit according to the second embodiment.
In the gate drive circuit according to the second embodiment, as shown in FIG. 2, the transistor 22b is configured by Darlington connection of PNP bipolar transistors. Further, the switch 9 is connected in series with the capacitor 6 as a load, and the power semiconductor element control circuit 4 is used as a control means for controlling the release and short-circuit state of the switch 9. The control means of the switch 9 is not limited to using the power semiconductor element control circuit 4 and may be other means. Other configurations are the same as those of the first embodiment shown in FIG.

  In the first embodiment, the transistor 22a is configured by only one PNP bipolar transistor. However, even if the transistor 22a is configured by Darlington connection as shown in FIG. 2, the effect obtained by using the capacitor 6 as the load is the same. is there. If high-frequency noise due to switching does not become a problem, the IGBT 1 can be switched at high speed by opening the switch 9 by controlling the power semiconductor element control circuit 4 and disconnecting the capacitor 6. As a result, the same effect as in the first embodiment can be obtained while minimizing the switching loss.

Embodiment 3 FIG.
Next explained is a gate drive circuit according to the third embodiment of the invention. FIG. 3 is a configuration diagram of a gate drive circuit according to the third embodiment.
In the third embodiment, as shown in FIG. 3, a capacitor 32 in the gate power supply 31 of the second IGBT 30 is used as a load of the constant current gate drive circuit 2. In FIG. 3, reference numeral 33 denotes a resistor, and reference numeral 34 denotes a diode connected in series to the resistor 33. Reference numeral 35 denotes a second gate drive circuit for driving the second IGBT 30. Other configurations are the same as those of the first embodiment shown in FIG.

  As described above, by connecting the series connection body of the resistor 33 and the diode 34 between the gate of the IGBT 1 and the gate power supply 31 of the second IGBT 30, the charge of the gate of the IGBT 1 is charged to the gate of the second IGBT 30. It can be diverted for charging and can save power required for gate drive. In addition, the gate power supply 31 requires an insulated power supply, but with the above configuration, the gate power supply 31 can be a non-insulated gate power supply 31 and does not use a transformer required for the insulated power supply. It is small and simple, and costs can be reduced.

  In the first embodiment, the energy charged in the capacitor 6 when the IGBT 1 is turned on is discharged by the gate drive circuit when the IGBT 1 is turned off, resulting in a loss. However, since the gate power supply 31 of the second IGBT 30 is used as a load in the third embodiment, the charging energy of the capacitor 32 can be used for the gate drive of the second IGBT 30. Thereby, the same effect as in the first embodiment can be obtained while suppressing the loss of the gate drive circuit.

  In each of the above embodiments, the gate driving circuit of the power semiconductor element made of Si semiconductor is shown. However, the power semiconductor element may be made of a non-Si semiconductor material having a wider band gap than that of the Si semiconductor. Examples of the wide band gap semiconductor that is a non-Si semiconductor material include silicon carbide, a gallium nitride-based material, and diamond.

  A power semiconductor element made of a wide band gap semiconductor can be used in a high voltage region where a unipolar operation is difficult with a Si semiconductor, can greatly reduce the switching loss generated during switching, and can greatly reduce the power loss. In addition, since power loss is small and heat resistance is high, when a power module is configured with a cooling unit, the heat sink fins can be downsized and the water cooling unit can be air-cooled. Miniaturization is possible.

  In addition, power semiconductor elements made of wide band gap semiconductors are suitable for high-frequency switching operations, and when applied to inverters and DC / DC converters that have a high demand for high-frequency operation, the switching frequency is increased to increase the frequency of inverters and DC / DC. Reactors and capacitors connected to the converter can be downsized. When the switching frequency is increased, the noise level becomes higher than that of a device using a conventional IGBT, and therefore, it is necessary to design in consideration of a trade-off between switching speed and loss (= cooling unit size). Therefore, the gate drive circuit of each of the embodiments described above works effectively even when a power semiconductor element made of a wide band gap semiconductor is used.

  As described above, the first to third embodiments of the present invention have been described. However, within the scope of the present invention, the embodiments can be freely combined, or each embodiment can be appropriately modified or omitted. Is possible.

1 IGBT, 2 constant current gate drive circuit, 3 ON command signal, 4 power semiconductor element control circuit, 5 discharge circuit, 6,32 capacitor, 7 drive circuit output current, 8 gate current, 20, 21, 33 resistance, 22a , 20b, 23 Transistor, 24, 34 Diode, 30 Second IGBT, 31 Gate power supply, 35 Second gate drive circuit.

The gate drive circuit according to the present invention, a first power semiconductor element, one end to the gate of the first power semiconductor element is connected, the other end of the gate current of the semiconductor device for the first power get connected to a voltage source, the first constant current gate drive circuit for driving the parallel connected load to the gate of the power semiconductor element, connected in series to said first power semiconductor device, the gate of the load A second power semiconductor element serving as a power source for the drive circuit ,
The constant current gate drive circuit charges the gate capacitance of the first power semiconductor element with a constant current, and the drive current value of the load is a lower limit current value at which the current of the constant current gate drive circuit is intermittent It will be a larger value.

Claims (8)

In a gate drive circuit for driving a power semiconductor element,
One end is connected to the gate of the power semiconductor element, and the other end is connected to a voltage source for obtaining a gate current of the power semiconductor element, and drives a load connected in parallel to the gate of the power semiconductor element. It has a constant current gate drive circuit,
The constant current gate drive circuit charges the gate capacitance of the power semiconductor element with a constant current, and the drive current value of the load is larger than a lower limit current value at which the current of the constant current gate drive circuit is intermittent. A gate drive circuit characterized by the above. The constant current gate drive circuit is
A first PNP bipolar transistor having the voltage source connected to the emitter;
A first resistor connected between the emitter and base of the first PNP bipolar transistor;
A second PNP bipolar transistor in which a connection point between the base of the first PNP bipolar transistor and the first resistor is connected to an emitter, and a collector of the first PNP bipolar transistor is connected to a base;
A diode having a cathode connected to the gate of the power semiconductor element and an anode connected to a collector of the second PNP bipolar transistor;
A second resistor having one end connected to a connection point between the collector of the first PNP bipolar transistor and the base of the second PNP bipolar transistor and the other end connected to a reference potential of the voltage source; The gate drive circuit according to claim 1, further comprising:   3. The gate drive circuit according to claim 2, wherein the second PNP bipolar transistor is constituted by Darlington connection of at least two PNP bipolar transistors. A switch connected between the load and the constant current gate drive circuit;
Control means for controlling the release and short-circuit state of the switch,
4. The gate drive circuit according to claim 1, wherein a switching speed of the power semiconductor element is variable. A second power semiconductor element connected in series to the power semiconductor element;
5. The gate drive circuit according to claim 1, wherein the load is a voltage source of a gate drive circuit of the second power semiconductor element. 6.   6. The gate drive circuit according to claim 5, wherein a series circuit of a diode and a resistor is connected between the gate and a voltage source of the gate drive circuit of the second power semiconductor element.   The gate drive circuit according to claim 1, wherein the power semiconductor element is an element formed of a wide band gap semiconductor.   8. The gate drive circuit according to claim 7, wherein the wide band gap semiconductor is a semiconductor using any one of silicon carbide, a gallium nitride material, and diamond.

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