JP2012229974A - Reverse bias safe operation area measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reverse bias safe operation area measuring device capable of accurately measuring a reverse bias safe operation area.SOLUTION: A reverse bias safe operation area measuring device 1 is a device for measuring a reverse bias safe operation area of a measured IGBT 2. The reverse bias safe operation area measuring device 1 comprises: a power MOSFET 7; and a control voltage generation circuit 8 that generates a control voltage on the basis of a collector voltage of the measured IGBT 2 and applies the generated control voltage to a gate of the power MOSFET 7. When the collector voltage of the measured IGBT 2 exceeds a clamp voltage, the power MOSFET 7 is turned on and the collector voltage decreases. However, when the collector voltage of the measured IGBT 2 falls below the clamp voltage, the power MOSFET 7 is turned off and the collector voltage increases.

Description

  The present invention relates to a reverse bias safe operation region measuring apparatus for measuring a reverse bias safe operation region of a transistor element to be measured.

  Examples of power switching elements that perform power conversion and control include transistor elements such as IGBTs (Insulated Gate Bipolar Transistors), bipolar transistors, and power MOSFETs. Since these transistor elements handle a large amount of power and a large amount of current, their breakdown resistance must be sufficiently high. Therefore, in order to ensure reliability, a test is performed to determine whether a desired specification value (rated value) is satisfied for the transistor element after the manufacturing process is completed.

  One of the performance evaluation items measured during this test is RBSOA (Reverse Bias Safe Operation Area). The RBSOA is a region defined by the maximum value of the collector-emitter voltage (collector voltage) and the maximum value of the collector-emitter current (collector current) that do not destroy the measured transistor element when the measured transistor element is turned off. . As a reverse bias safe operation region measuring apparatus for measuring RBSOA, a device provided with a clamp circuit for clamping the collector voltage of a transistor element to be measured has been proposed (for example, see Patent Document 1).

JP 2010-175509 A

  When the current of the transistor element under measurement is small and the switching speed is slow, the parasitic reactance of the wiring can be ignored. However, since current IGBTs and the like are increased in speed and current, the parasitic reactance of the clamp circuit wiring cannot be ignored.

  Originally, the collector voltage is fixed at the clamp voltage when the transistor element is turned off. However, since there is a parasitic reactance in the clamp circuit, a voltage is generated in the direction opposite to the direction of current flow. Therefore, the current commutation to the clamp circuit cannot catch up, and the current that could not be commutated flows into the collector of the transistor element to be measured and causes an avalanche. For this reason, when the applied current is increased, the measured transistor element is destroyed by the heat generated by the avalanche before being destroyed beyond RBSOA. Therefore, RBSOA could not be measured accurately.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a reverse bias safe operation region measuring apparatus capable of accurately measuring a reverse bias safe operation region.

  A reverse bias safe operation region measuring apparatus according to the present invention is a device for measuring a reverse bias safe operation region of a transistor element under measurement having first and second main electrodes and a first control electrode, A voltage control transistor element having a third main electrode connected to the first main electrode, a grounded fourth main electrode, and a second control electrode; and a voltage of the first main electrode A control voltage generation circuit that generates a control voltage based on the second control electrode and applies the control voltage to the second control electrode, and the voltage control transistor element is turned on when the voltage of the first main electrode exceeds the clamp voltage When the voltage of the first main electrode is lower than the clamp voltage, the voltage control transistor element is turned off.

  According to the present invention, the reverse bias safe operation region can be accurately measured.

It is a figure which shows the reverse bias safe operation area | region measuring apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows the output characteristic of to-be-measured IGBT. It is a figure which shows the relationship between the collector current and collector voltage of measured IGBT at the time of turn-off. It is a figure which shows the reverse bias safe operation area | region measuring apparatus which concerns on a comparative example. It is a figure which shows the current waveform and voltage waveform of the measuring apparatus of a comparative example. It is a figure which shows the reverse bias safe operation area | region measuring apparatus which concerns on Embodiment 2 of this invention. It is a figure which shows the reverse bias safe operation area | region measuring apparatus which concerns on Embodiment 3 of this invention. It is a figure which shows the reverse bias safe operation area | region measuring apparatus which concerns on Embodiment 4 of this invention. It is a figure which shows the reverse bias safe operation area | region measuring apparatus which concerns on Embodiment 5 of this invention. It is a figure which shows the modification of the reverse bias safe operation area | region measuring apparatus which concerns on Embodiment 5 of this invention.

  A reverse bias safe operation area measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repeated description may be omitted.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a reverse bias safe operation region measurement apparatus according to Embodiment 1 of the present invention. The reverse bias safe operation area measuring apparatus 1 is an apparatus for measuring an RBSOA (Reverse Bias Safe Operation Area) of the IGBT 2 to be measured. The reverse bias safe operation area measuring apparatus 1 includes an inductive load 3 (L load), a main power supply 4, a capacitor 5, a clamp circuit 6, a power MOSFET 7, a control voltage generation circuit 8, and a current sensor 9. Prepare.

  The emitter of the IGBT 2 to be measured is grounded. One end of the inductive load 3 is connected to the collector of the IGBT 2 to be measured. The positive electrode of the main power supply 4 is connected to the other end of the inductive load 3. The negative electrode of the main power supply 4 is grounded. A capacitor 5 is connected between the positive electrode and the negative electrode of the main power supply 4. The capacitor 5 is an electrolytic capacitor, for example, has a large capacitance value, and stabilizes the power supply voltage of the main power supply 4.

  The inductive load 3 is constituted by a coil, for example. The inductive load 3 functions as a constant current source and plays a role of keeping the collector current constant before and after the IGBT 2 to be measured is turned off.

  The clamp circuit 6 includes a clamp diode 10, a clamp power supply 11, and a capacitor 12. The anode of the clamp diode 10 is connected to the collector of the IGBT 2 to be measured, and the cathode is connected to the positive electrode of the clamp power supply 11. The negative electrode of the clamp power supply 11 is grounded. A capacitor 12 is connected between the positive electrode and the negative electrode of the clamp power supply 11. This capacitor 12 stabilizes the voltage of the clamp power supply 11. The voltage of the clamp power supply 11 is set higher than the voltage of the main power supply 4 to prevent the current from always flowing from the main power supply 4 to the clamp circuit 6.

  The clamp circuit 6 clamps the upper limit value of the collector voltage of the IGBT 2 to be measured to the sum of the voltage of the clamp power supply 11 and the forward drop voltage of the clamp diode 10. Here, when the measured IGBT 2 causes an avalanche when the collector voltage of the measured IGBT 2 exceeds the avalanche voltage, the clamp voltage is set to a value lower than the avalanche voltage.

  The drain of the power MOSFET 7 is connected to the collector of the IGBT 2 to be measured, and the source is grounded. The control voltage generation circuit 8 includes a resistor 13 connected between the collector of the IGBT 2 to be measured and the gate of the power MOSFET 7, and a variable resistor 14 connected between the gate of the power MOSFET 7 and the ground point.

  The control voltage generation circuit 8 generates a control voltage based on the collector voltage of the IGBT 2 to be measured and applies it to the gate of the power MOSFET 7. Here, the resistance value of the variable resistor 14 is adjusted so that the power MOSFET 7 is turned on when the collector voltage of the IGBT 2 to be measured exceeds the clamp voltage.

  Next, an RBSOA measurement method using the measurement apparatus of the present embodiment will be described. First, a pulsed drive signal is input to the gate of the IGBT 2 to be measured from a gate driver (negative illustration). As a result, the IGBT 2 to be measured is turned ON, and the collector current starts to flow from the main power supply 4 to the IGBT 2 to be measured via the inductive load 3. Since the collector current is proportional to the pulse width of the drive signal, the drive signal is turned OFF when the pulse width is adjusted to reach a predetermined current value (for example, rated current).

  Thus, when the measured IGBT 2 changes from ON to OFF (turn-off time), the inductive load 3 tries to keep the collector current flowing in the main circuit of the measured IGBT 2 as it is. Therefore, the collector current does not instantaneously decrease to 0 A (ampere) but reaches 0 A while being attenuated.

  FIG. 2 is a diagram illustrating output characteristics of the IGBT to be measured. As shown in (1) of FIG. 2, if the collector current is constant, the collector voltage increases as the gate voltage decreases. Therefore, as shown in (1) of FIG. 3, at the time of turn-off, the collector current is constant and only the collector voltage increases. FIG. 3 is a diagram showing the relationship between the collector current and collector voltage of the IGBT to be measured at turn-off.

  When the gate voltage further decreases and the collector voltage increases to reach the clamp voltage, the current is commutated to the clamp circuit 6. When current flows through the clamp circuit 6, the collector of the IGBT 2 to be measured is in an electrical short circuit with the clamp power supply 11. For this reason, the collector voltage of the IGBT 2 to be measured is clamped to the clamp voltage by the clamp circuit 6.

  When the collector voltage exceeds the clamp voltage, the power MOSFET 7 is turned ON and the collector voltage of the IGBT 2 to be measured is lowered. On the other hand, when the collector voltage of the IGBT to be measured 2 falls below the clamp voltage, the power MOSFET 7 is turned OFF and the collector voltage of the IGBT to be measured 2 increases. By this negative feedback operation of the power MOSFET 7, the collector voltage becomes the same as the clamp voltage while the current from the inductive load 3 is commutated to the clamp circuit 6.

  Therefore, as shown in (2) of FIG. 2, only the collector current decreases as the collector voltage is constant and the gate voltage decreases. When the gate voltage further decreases, the IGBT 2 to be measured is turned OFF and the collector current becomes 0A.

  Thus, when the IGBT 2 to be measured changes from ON to OFF (turn-off), the current sensor 9 detects the current flowing through the collector of the IGBT 2 to be measured, so that the collector-emitter current (collector current) of the IGBT 2 to be measured is detected. ). Further, a probe of a voltmeter (negative illustration) is applied to the collector and emitter of the IGBT 2 to be measured, and the collector-emitter voltage (collector voltage) of the IGBT 2 to be measured is measured. From the IV waveform (Lissajous waveform) of FIG. 3 obtained by this measurement, RBSOA defined by the maximum value of the collector current (for example, rated current) and the maximum value of the collector voltage (for example, rated voltage) can be confirmed. it can.

  Subsequently, the effect of the measurement apparatus of the present embodiment will be described in comparison with a comparative example. FIG. 4 is a diagram illustrating a reverse bias safe operation region measuring apparatus according to a comparative example. In the comparative example, the power MOSFET 7 and the control voltage generation circuit 8 are not provided.

  Since the wiring of the clamp circuit 6 has a parasitic inductance S, a voltage is generated in the direction opposite to the direction of current flow at the time of turn-off. For this reason, the commutation of the current to the clamp circuit 6 cannot catch up, and the current that cannot be commutated flows into the IGBT 2 to be measured, causing an avalanche as shown in FIG. FIG. 5 is a diagram illustrating a current waveform and a voltage waveform of the measurement apparatus of the comparative example. CI represents a collector-emitter voltage, CII represents a collector current, and CIII represents a current flowing through the clamp diode 10.

The relational expression of current and voltage at this time is as follows from Kirchhoff's voltage law.
_{V AVA -L S · dI CL /} dt-V CL = 0
Here, V _AVA is an avalanche voltage of the IGBT 2 to be measured, L _S is a parasitic inductance, I _CL is a current flowing into the clamp circuit 6, and V _CL is a clamp voltage. The forward voltage of the clamp diode 10 was ignored.

When the above equation is expanded, the current I _CL becomes as follows.
_{I CL = (V AVA -V CL} ) / L S × t

Of the current flowing through the inductive load 3, the can only commutation current I _CL in the clamp circuit 6, the remaining current flows into the measured IGBT 2, the avalanche energy. Therefore, in the comparative example, when the applied current is increased, the IGBT 2 to be measured is destroyed by the heat generated by the avalanche before being destroyed exceeding RBSOA. Therefore, RBSOA could not be measured accurately.

On the other hand, in the present embodiment, the avalanche energy can be reduced by the power MOSFET 7 even when the wiring of the clamp circuit 6 and the power MOSFET 7 has a parasitic reactance S. When the collector voltage exceeds the withstand voltage and the IGBT 2 to be measured causes an avalanche, the relationship between the current flowing into the main circuit of the power MOSFET 7 and the voltage is as follows.
_{V AVA -L S · dI FET /} dt-V ON = 0
Here, I _FET is a current flowing into the power MOSFET 7, and V _ON is an ON voltage of the power MOSFET 7.

When the above equation is expanded, the current I _FET is as follows.
I _FET = (V _AVA −V _ON ) / L _S × t

When the withstand voltage of the IGBT 2 to be measured is 600V, V _CL = 600V. Assuming V _AVA = 610 V and V _ON = 5 V, the current I _FET is as follows:
I _FET = (V _AVA −V _ON ) / L _S × t = 605 V / L _S × t

On the other hand, the current I _CL flowing into the clamp circuit 6 is as follows.
I _CL = a _{(V AVA -V CL) / L} S × t = 10V / L S × t.

_Thus, the ratio of _{I FET} and _{I CL} is as follows.
I _FET / I _CL = 60
However, it is assumed that the parasitic inductance S of the wiring of the clamp circuit 6 and the power MOSFET 7 is the same. Compared with the clamp circuit 6, the power MOSFET 7 can commutate the current flowing through the inductive load 3 60 times.

  Therefore, the measuring apparatus according to the present embodiment can significantly reduce the avalanche energy as compared with the comparative example. As a result, destruction due to avalanche is less likely to occur, so that RBSOA can be accurately measured.

Embodiment 2. FIG.
FIG. 6 is a diagram showing a reverse bias safe operation region measuring apparatus according to Embodiment 2 of the present invention. The configuration of the control voltage generation circuit 8 is different from that of the first embodiment. The control voltage generation circuit 8 according to the second embodiment includes a Zener diode 15 having a cathode connected to the collector of the IGBT 2 to be measured, an anode connected to the gate of the power MOSFET 7, and a gate and a ground point of the power MOSFET 7. And a resistor 16 connected therebetween. The withstand voltage of the Zener diode 15 is the same as the clamp voltage. As a result, adjustment of the variable resistor 14 becomes unnecessary, so that the working efficiency is improved as compared with the first embodiment.

Embodiment 3 FIG.
FIG. 7 is a diagram showing a reverse bias safe operation region measurement apparatus according to Embodiment 3 of the present invention. In this apparatus, the clamp circuit 6 is omitted from the apparatus of the first embodiment. Thereby, the apparatus can be simplified as compared with the first embodiment. Further, the backflow of current due to the recovery current of the clamp diode 10 can be eliminated.

Embodiment 4 FIG.
FIG. 8 is a diagram showing a reverse bias safe operation region measuring apparatus according to Embodiment 4 of the present invention. In this apparatus, the clamp circuit 6 is omitted from the apparatus of the second embodiment. Thereby, the apparatus can be simplified as compared with the second embodiment. Further, the backflow of current due to the recovery current of the clamp diode 10 can be eliminated.

Embodiment 5 FIG.
FIG. 9 is a diagram showing a reverse bias safe operation region measuring apparatus according to Embodiment 5 of the present invention. Compared with the first and second embodiments, an operational amplifier 17 and resistors 18 and 19 are added. The control voltage generation circuit 8 of the fifth embodiment has resistors 20 and 21.

  The resistors 20 and 21 are connected in series between the collector of the IGBT 2 to be measured and the ground point, and constitute a voltage attenuation circuit. The resistors 18 and 19 are connected in series between the positive side of the clamp power source and the ground point, and constitute a voltage attenuation circuit.

  A connection point between the resistors 20 and 21 is connected to the + input terminal of the operational amplifier 17, and a connection point between the resistors 18 and 19 is connected to the −input terminal of the operational amplifier 17. The output terminal of the operational amplifier 17 is connected to the gate of the power MOSFET 7.

  Next, the operation will be described. A control voltage is generated at the connection point between the resistors 20 and 21, and a reference voltage is generated at the connection point between the resistors 18 and 19. The operational amplifier 17 infinitely amplifies the difference voltage between the control voltage and the reference voltage input from the + input terminal and the − input terminal and applies the amplified voltage to the gate of the power MOSFET 7.

  When the collector voltage of the IGBT 2 to be measured exceeds the clamp voltage, the control voltage at the + input terminal becomes larger than the reference voltage at the −input terminal. Accordingly, the power MOSFET 7 is turned ON, and the collector voltage of the IGBT 2 to be measured is lowered. On the other hand, when the collector voltage of the IGBT 2 to be measured falls below the clamp voltage, the control voltage at the + input terminal becomes smaller than the reference voltage at the −input terminal, so that the operational amplifier 17 amplifies this differential voltage and outputs a − voltage. To do. Accordingly, the power MOSFET 7 is turned OFF, and the collector voltage of the IGBT 2 to be measured is increased. Thereby, the collector voltage of the IGBT 2 to be measured can be adjusted to the clamp voltage with high accuracy.

  FIG. 10 is a diagram showing a modification of the reverse bias safe operation region measurement apparatus according to Embodiment 5 of the present invention. In this device, instead of attenuating the clamp voltage with resistors 18 and 19 to a reference voltage, the reference voltage is taken directly from the power supply 22. Thereby, since the clamp circuit 6 and the resistors 18 and 19 can be omitted, the apparatus can be simplified.

  In the first to fifth embodiments, the IGBT 2 to be measured is an IGBT in a bare chip state, but is not limited thereto, and may be a bipolar transistor as long as it is an element capable of measuring RBSOA in a bare chip state. The power MOSFET 7 may be replaced with an IGBT.

  The resistance values of the resistors 13, 16, 20, 21 and the variable resistor 14 are large. Accordingly, when a voltage is applied to the IGBT 2 to be measured, the current flowing through the resistors 13, 16, 20, 21 and the variable resistor 14 is negligibly smaller than the current flowing through the IGBT 2 to be measured and the clamp circuit 6.

  The IGBT 2 to be measured and the power MOSFET 7 are not limited to those formed of silicon, but may be formed of a wide band gap semiconductor having a band gap larger than that of silicon. The wide band gap semiconductor is, for example, silicon carbide, a gallium nitride-based material, or diamond. A power semiconductor element formed of such a wide band gap semiconductor can be miniaturized because of its high voltage resistance and allowable current density. By using this miniaturized element, a semiconductor module incorporating this element can also be miniaturized. Further, since the heat resistance of the element is high, the heat dissipating fins of the heat sink can be miniaturized and the water cooling part can be air cooled, so that the semiconductor module can be further miniaturized. In addition, since the power loss of the element is low and the efficiency is high, the efficiency of the semiconductor module can be increased. Note that it is desirable that both the switching element and the diode element be formed of a wide band gap semiconductor, but either one of the elements may be formed of a wide band gap semiconductor, and the effects described in this embodiment Can be obtained.

1 Reverse Bias Safe Operating Area Measuring Device 2 IGBT to be measured (Transistor element to be measured)
6 Clamp circuit 7 Power MOSFET (Transistor element for voltage control)
8 Control Voltage Generating Circuit 13 Resistor 14 Variable Resistor 15 Zener Diode 16 Resistor 17 Operational Amplifier

Claims (6)

An apparatus for measuring a reverse bias safe operating region of a transistor element under measurement having first and second main electrodes and a first control electrode,
A voltage control transistor element having a third main electrode connected to the first main electrode, a grounded fourth main electrode, and a second control electrode;
A control voltage generation circuit that generates a control voltage based on the voltage of the first main electrode and applies the control voltage to the second control electrode;
When the voltage of the first main electrode exceeds the clamp voltage, the voltage control transistor element is turned on,
The reverse bias safe operation region measuring apparatus according to claim 1, wherein when the voltage of the first main electrode falls below the clamp voltage, the voltage control transistor element is turned off. When the voltage of the first main electrode exceeds the avalanche voltage, the measured transistor element causes an avalanche,
The reverse bias safe operation region measuring apparatus according to claim 1, wherein the clamp voltage is lower than the avalanche voltage. The control voltage generation circuit includes:
A resistor connected between the first main electrode and the second control electrode;
The reverse bias safe operation region measuring apparatus according to claim 1, further comprising: a variable resistor connected between the second control electrode and a grounding point. The control voltage generation circuit includes:
A Zener diode having a cathode connected to the first main electrode and an anode connected to the second control electrode;
The reverse bias safe operation region measuring apparatus according to claim 1, further comprising a resistor connected between the second control electrode and a grounding point.   The reverse bias safe operation region measuring apparatus according to any one of claims 1 to 4, further comprising a clamp circuit that clamps a voltage of the first main electrode.   The reverse bias safe operation region measurement according to any one of claims 1 to 5, further comprising an operational amplifier that amplifies a difference voltage between the control voltage and a reference voltage and applies the amplified voltage to the second control electrode. apparatus.

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