JP2009060709A - Gate drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce wasteful turn-off loss in steady state and suppress increase in the size of equipment. <P>SOLUTION: When in a gate drive circuit for a voltage-driven element, such as IGBT, a Zener diode 14 is connected between the collector and the gate of an element 4 in an attempt to reduce surge voltage when the element 4 is turned off, operation can be performed even in steady state depending on the Zener voltage characteristics. Therefore, when the direct-current voltage (measured value) of a main circuit and a turn-off current (measured value) are equal to or lower than a certain set value, a switch 20 comprised of FET or the like is turned off to prevent the Zener diode 14 from operating. Wasteful turn-off loss is thereby prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

    The present invention relates to a gate drive circuit for a voltage-driven power semiconductor element such as an IGBT (insulated gate bipolar transistor).

FIG. 2 shows a general inverter main circuit diagram using an IGBT.
1 is a DC power supply circuit (in the case of an AC input inverter, it becomes a rectifier + electrolytic capacitor, and the voltage value is Ed). , 3A and 3B are IGBT gate drive circuits (provided for each element), 6 is a control circuit for generating a gate drive signal GD, and 7 is a load such as a motor. Ls represents the wiring inductance between the DC power supply circuit 1 and the inverter circuit 2.

FIG. 3 shows a detailed circuit example of the gate drive circuit.
Reference numeral 8 is a positive power source for driving the circuit, 9 is a negative power source, 10 is a signal insulator such as a photocoupler, and receives a gate drive signal GD from the control circuit and outputs a signal S to the transistors 11 and 12. give. The transistors 11 and 12 are turned on in response to the signal S. When the transistor 11 is on, a current is supplied to the gate of the IGBT 4, and when the transistor 12 is on, the gate charge of the IGBT 4 is discharged. Reference numeral 13 denotes a current limiting resistor.

  The zener diode 14 breaks down when the IGBT collector-gate voltage exceeds the zener voltage (Vz) of the zener diode 14 when the IGBT is turned off, and the zener current is directed from the collector of the IGBT 4 to the gate. Flows in. As a result, the IGBT 4 is turned on, di / dt at turn-off is reduced, and the surge voltage between the collector and the emitter of the IGBT is clamped to the Zener voltage (Vz). The diode 15 blocks reverse current. This circuit has a function of suppressing the device breakdown voltage below the IGBT when the turn-off surge voltage is high.

FIG. 4 shows an example of an IGBT turn-off waveform (ic and V _CE ) when the Zener diode 14 and the diode 15 are not connected. (A) is when the current is small, and (b) is when the current is large. The surge voltage V _CE (peak) at that time is generally obtained as in the following equation (1). In general, Vce (peak) increases as Ed increases and ic increases.
Vce (peak) = Ed + ΔV = Ed + 2 ・ Ls ・ di / dt (1)

FIG. 5 shows an example of an IGBT turn-off waveform (ic and V _CE ) when the Zener diode 14 and the diode 15 are connected. (A) is for a small current, and (b) is for a large current. Since Vz> Ed + ΔV when the current is small, the waveform is the same as in FIG. 4, but Vce (peak) is clamped to Vz (Vce (peak) = Vz) when the current is large. Therefore, compared with FIG.
tf1 <tf2 (2)
ΔV1> ΔV2 (3)
It becomes. Further, the turn-off loss also increases as tf becomes longer in FIG.

For example, Patent Literature 1 and Patent Literature 2 describe a technique in which a voltage between the collector and gate of an IGBT connects a zener diode to reduce a surge voltage when the IGBT is turned off.
Japanese Patent No. 3598933 JP 2001-231247 A

When the Zener diode 14 is selected at the time of designing the gate drive circuit, the Zener voltage value (Vz) needs to be selected in consideration of the characteristic variation and temperature characteristics of the Zener diode to be applied. Usually, the variation is about ± 10% with respect to the typical value (representative value) of the Zener voltage Vz. For example, if the breakdown voltage of the IGBT is 1200 V, it is necessary to set Vz _(max) = 1100 V in consideration of the operation delay.

For this reason, it is necessary to select Vz _(typ) = 1000 V, and Vz _(min) = 900 V if the variation is taken into consideration.
Generally, the steady DC voltage Ed is set to 700 V to 800 V, and ΔV1 in Fig. 4 is 200 V to 300 V when the steady current is interrupted. When connected, a Zener operation is performed even in a steady state.

FIG. 6 shows a Zener diode operation region diagram with the collector current ic as the vertical axis and the DC voltage Ed as the horizontal axis. In steady operation, it operates in the region surrounded by ic _typ and Ed _typ in Fig. 6 (a). However, in actual equipment, it is necessary to assume a transient state or an abnormal state, so ic _typ and Ed _typ are assumed. It is necessary to consider even within the enclosed area. The region where the Zener operation is performed is the upper right region with respect to the characteristics of each Vz. That is, the area where the dotted square, which is the operation area of ic and Ed, overlaps the hatched area of the Vz line is the area where the Zener operation is actually performed.

In the example of FIG. 6A, if the applied Zener diode Vz is higher than the typ value, the Zener operation is not performed in the steady state. However, if Vz is the min value, both ic and Ed are stationary. A Zener operation is also performed at the operating value of the state (see region R), resulting in a waveform clamped at Vz _(min) as shown in FIG.
As described above, if a Zener diode with a low Zener voltage Vz is connected due to variations in the characteristics of the Zener diode, Zener operation is also performed in the current / voltage range that is generally applied, resulting in an increase in turn-off loss. Will occur. Therefore, it is necessary to consider this increase in the system design, and problems such as an increase in the size of the apparatus due to heat treatment of the generated loss occur.

  Accordingly, an object of the present invention is to reduce the turn-off loss in a steady state and to suppress the enlargement of the apparatus.

In order to solve such a problem, the invention of claim 1 is a gate drive circuit for a voltage-driven power semiconductor device used in a power converter, wherein the semiconductor is used for the purpose of reducing a surge voltage at turn-off. In what connected the Zener diode which made the gate side an anode between the gate and collector of an element,
Both a switch element is connected in series with the Zener diode, and the DC voltage of the main circuit part of the power converter is less than a certain set value, or the cutoff current of the semiconductor element is less than a certain set value The switch element is turned off only when is established.

According to a second aspect of the present invention, there is provided a gate drive circuit for a voltage-driven power semiconductor element used in a power converter, wherein the gate drive circuit is connected between the gate and collector of the semiconductor element for the purpose of reducing a surge voltage at turn-off. In a connected zener diode with the gate side as the anode,
A switching element is connected in series with the Zener diode, and the DC voltage of the main circuit portion of the power converter is less than a certain set value, or at least the cutoff current of the semiconductor element is less than a certain set value The switch element is turned off when one of them is established.

  According to the present invention, even if the Zener voltage of the connected Zener diode is low, the Zener operation is difficult to occur, so that unnecessary turn-off loss can be suppressed and a small and low loss system can be constructed. It becomes possible.

  FIG. 1A is a circuit diagram showing an embodiment of the present invention. This is a circuit in which comparator circuits 16A and 16B, an AND circuit 19 and a switch circuit 20 such as an FET (field effect transistor) are added to the conventional example shown in FIG. A description thereof will be omitted. In addition, the DC voltage Ed and the collector current (or load current corresponding to the collector current) ic of the IGBT 4 are here measured values (detected values), and 17 and 18 are set values, respectively.

  The comparator circuit 16A compares the measured value Ed of the DC voltage with the set value 17 and outputs an H (high) level signal when the set value is high. Similarly, the comparator circuit 16 B compares the actually measured current value ic with the set value 18, and outputs an H (high) level signal when the set value is high. Therefore, only when the outputs of the circuits 16A and 16B both become H (high), the output of the AND circuit 19 becomes L (low) level and the switch circuit 20 is turned off. That is, the Zener diode 14 is not operated only when the actual measurement value Ed and the actual measurement value ic are both equal to or less than the set value, and the other operation is performed.

FIG. 1B shows a modification of FIG. 1A. In FIG. 1B, an insulator 21 such as a photocoupler and a pull-up resistor 22 are connected to the output of the circuit 19 in FIG. 1A to insulate the weak circuit 16A, 16B, 17, 18, 19 from the main circuit section. The basic circuit operation and functions are exactly the same except for the differences.
As shown in FIGS. 1A and 1B, the operation area diagram showing the relationship between ic, Ed, and Vz is as shown in FIG. 6B.

That is, in FIG. 6B, when the actual measurement values ic and Ed are equal to or less than the set values ic _ref and Ed _ref , an operation region in which the Zener operation is not performed is obtained regardless of the variation in the Zener voltage characteristics (see the shaded area). . However, in circuit design, when ic and Ed are turned off under the conditions of ic _ref and Ed _ref , Vce (peak) = needs to satisfy the relationship of the following equation.
Vce (peak) <Vz _(max) (4)

    In the above, the Zener operation is not performed only when both ic and Ed are below a certain set value. However, when at least one of them is less than a certain set value, the Zener operation is not performed. Also good.

Configuration diagram showing an embodiment of the present invention Configuration outline diagram showing a modification of FIG. General inverter main circuit diagram FIG. 2 is a general gate drive circuit example diagram. Operational explanation diagram without zener diode in FIG. Operation explanatory diagram with zener diode as shown in FIG. Zener diode characteristic variation and operating area explanatory diagram

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... DC power supply circuit, 2 ... Inverter, 3A, 3B ... Gate drive circuit, 4 ... IGBT, 5, 15 ... Diode, 6 ... Control circuit, 7 ... Load (motor), 8, 9 ... Power supply, 10, 21 ... Insulator (photocoupler), 11, 12 ... transistor buffer circuit, 13 ... resistor, 14 ... zener diode, 16A, 16B ... comparator circuit, 17,18 ... set value, 19 ... AND circuit, 20 ... switch circuit (FET) 22) Pull-up resistor.

Claims (2)

A gate drive circuit for a voltage-driven power semiconductor element used in a power converter, wherein the Zener diode has an anode on the gate side between the gate and collector of the semiconductor element for the purpose of reducing a surge voltage at turn-off. In what is connected,
Both a switch element is connected in series with the Zener diode, and the DC voltage of the main circuit part of the power converter is less than a certain set value, or the cutoff current of the semiconductor element is less than a certain set value The gate drive circuit is characterized in that the switch element is turned off only when is established. A gate drive circuit for a voltage-driven power semiconductor element used in a power converter, wherein the Zener diode has a gate side anode between the gate and collector of the semiconductor element for the purpose of reducing a surge voltage at turn-off. In what is connected,
A switching element is connected in series with the Zener diode, and the DC voltage of the main circuit portion of the power converter is less than a certain set value, or at least the cutoff current of the semiconductor element is less than a certain set value A gate drive circuit characterized in that the switch element is turned off when one of them is established.

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