JP2010178461A - Semiconductor protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that generation loss is large, a special article permitted is necessary at a high frequency of operation and reliability deteriorates since a voltage equivalent to an element voltage is applied to a voltage clamping element and current is also made to flow at the time of a clamping operation in a circuit connecting the voltage clamping element between a collector and a gate as an overvoltage protection circuit of a voltage driving type semiconductor element. <P>SOLUTION: In a circuit system for suppressing an overvoltage due to surge when the voltage driving type semiconductor element is turned off, the semiconductor protection circuit connects a series circuit of a saturable reactor L<SB>1</SB>, a capacitor C<SB>1</SB>and a resistor R<SB>1</SB>between a collector terminal and a gate terminal of the voltage driving type semiconductor element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a protection circuit for suppressing overvoltage during transient operation of voltage-driven semiconductor elements such as IGBTs and MOSFETs.

  Currently, IGBTs and MOSFETs, which are voltage-driven semiconductor elements (hereinafter also referred to as elements), are applied to many power conversion circuits, and high performance is achieved. However, a transient operation at the time of switching is fast, and a large surge voltage is generated due to an inductance component floating in the power conversion circuit at the time of turn-off operation. Therefore, if this exceeds the rated voltage, there is a high possibility of causing element destruction. In order to prevent this, it is necessary to have a wiring structure that reduces the stray inductance to the limit. However, in consideration of fluctuations in the DC voltage of the power conversion circuit, measures with only the wiring structure are often insufficient. . Therefore, various methods for protecting the element from overvoltage have been proposed. A conventional technical example will be described below.

FIG. 5 shows a basic circuit configuration example of the prior art. In this figure, Q ₂ is an IGBT, D ₂ is a diode, and ZD is a voltage clamp element such as a Zener diode or an avalanche diode. In this way, a series circuit of D ₂ and ZD (hereinafter referred to as a clamp circuit) is connected between the collector and gate of the IGBT. Clamping voltage value ZD, the collector of IGBT - set to the upper limit value in the emitter voltage V _CE.

FIG. 6 shows an example of the waveform of each part. V _GE2 is the IGBT gate-emitter voltage, I _clamp2 is the current flowing through the voltage clamp element ZD and diode D ₂ , V _CE2 is the IGBT collector-emitter voltage, and I _C2 is the IGBT collector current waveform . The dotted line represents the waveform when there is no clamp circuit, and the solid line represents the waveform when there is a clamp circuit. When there is no clamp circuit, the IGBT starts to turn off and V _CE2 rises. When the power supply voltage is reached, the collector current I _C2 starts to decrease. A surge voltage as shown in FIG. 5 is generated by the current change rate and the floating inductance of the circuit.

Next, when there is a clamp circuit, when V _CE reaches the clamp voltage, a current flows through ZD of the clamp circuit, which flows into the gate of the IGBT. By this operation, V _GE2 rises, so the element operates in the direction to turn on, so V _CE2 starts to decrease, but if it falls below the clamp voltage, I _clamp2 does not flow, IGBT turns off again and V _CE2 rises. By repeating this operation at high speed, _VCE2 can be clamped to a constant value as shown in FIG. When I _C2 is shut off, it is in a steady-off state as usual. A system using such a voltage clamp element is disclosed in, for example, Patent Document 1 below.

JP 2000-245137 A

In the prior art, a voltage clamp element is used, and by selecting the voltage of this voltage clamp element appropriately, the element voltage can be clamped to an arbitrary set voltage, and all rated voltage-driven semiconductor elements are protected from overvoltage. it can. However, during the clamping operation, a voltage similar to the element voltage is applied to the voltage clamping element, and a current also flows. Therefore, the generated loss is large, and when operating at a high frequency, it is necessary to apply an acceptable special product, and the reliability is also lowered.
Accordingly, an object of the present invention is to enable overvoltage protection of an element without using a voltage clamp element.

  In order to solve the above-described problem, in the first invention, in a circuit system that suppresses overvoltage due to a surge at the time of turn-off of a voltage-driven semiconductor element, a series circuit of a saturable reactor, a capacitor, and a resistor is provided. The voltage driven semiconductor element is connected between a collector terminal and a gate terminal.

  According to a second aspect of the present invention, in a circuit system for suppressing overvoltage caused by a surge at the time of reverse diode recovery of a voltage-driven semiconductor element in which diodes are connected in antiparallel, a series circuit of a saturable reactor, a capacitor, and a resistor is provided. The voltage-driven semiconductor element is connected between the collector terminal and the gate terminal.

  In a third invention, the resistor is formed of a conductive member having a resistance value.

  In the present invention, a series circuit of a saturable reactor, a capacitor, and a resistor is connected between the collector terminal and the gate terminal of the voltage-driven semiconductor element so as to suppress overvoltage. As a result, only a current flows through this circuit for a short time during the voltage clamping operation period, and the loss during the clamping period of the voltage-driven semiconductor element can be greatly reduced. Further, even when operating at a high frequency, the loss is small and it is not necessary to use special parts, so that the reliability is increased.

Circuit configuration diagram showing the first embodiment of the present invention BH characteristic curve example of a saturable reactor Operation waveform diagram of each part in Figure 1 Circuit configuration diagram showing a second embodiment of the present invention Circuit configuration diagram showing conventional technology Operation waveform diagram of each part in Fig. 5

  The main point of the present invention is that a series circuit of a saturable reactor, a capacitor, and a resistor is connected between a collector terminal and a gate terminal in order to suppress an overvoltage due to a surge at the time of turn-off of the voltage-driven semiconductor element. It is.

FIG. 1 shows an example of the circuit configuration of the first embodiment of the present invention. In this configuration, L ₁ is a saturable reactor, R ₁ is a resistor, C ₁ is a capacitor, and these series circuits are connected between the collector terminal and the gate terminal of IGBTQ ₁ . The saturable reactor L ₁ has, for example, a BH characteristic (magnetic flux density-magnetic field strength characteristic) as shown in FIG. 2. When the magnetic field strength is increased from zero to the positive direction, the period a In this case, the magnetic flux density also increases, but in the period b, the increase rate is greatly reduced and eventually becomes saturated to a constant magnetic flux density.

The slope of this characteristic is proportional to the self-inductance of L _1, tend to maintain the self-inductance of the period in a L _1, be self-inductance in the period b is in the very low tendency I understand.

FIG. 3 shows a waveform example of each part in the circuit configuration of FIG. 1 having such a saturable reactor. In this figure, the turn-off starts, the gate voltage V _GE1 decreases, and when the gate threshold value is reached, V _CE1 starts to rise. Then, since the same voltage V _CE1 is also applied between the collector and the gate of _{IGBTQ 1,} I clamp1 current starts to flow. As described in FIG. 2, due to the BH characteristic, I _clamp1 has a large self-inductance in period a and increases slowly, but gradually shifts to period b and the self-inductance decreases, so I _clamp1 Suddenly increases.

Since this current flows into the gate portion of IGBTQ ₁ , the gate voltage V _GE1 tends to increase. Therefore, the voltage rise of the V _CE1 becomes direction IGBTQ ₁ is turned on is prevented. In the turn-off waveform, by setting the saturation characteristic and the inductance value of the saturable reactor L ₁ so that a current flows through the I _CLAMP1 at the desired timing to clamp the voltage, it is possible to obtain a desired operation.

Here, the capacitor C ₁ is connected to prevent a DC component from flowing through this circuit. As a design method, for example, the impedance of the capacitor C ₁ by setting sufficiently smaller than the impedance of L _1, constant or current values when the I _CLAMP1 is set by the value of resistor R ₁ and the value of the saturable reactor L ₁ be able to.

FIG. 4 shows a circuit configuration example of the second embodiment of the present invention. The difference from the first embodiment is that a free-wheeling diode is connected in antiparallel with IGBTQ ₁ and the other points are the same as in the first embodiment. In such a configuration, the IGBT is turned off from the mode in which the current I _D1 flows through the diode D ₁ while the gate of the IGBT Q ₁ is turned on, and the diode is reversely recovered under an external condition. in mode, the voltage across the diode D _1, i.e. the voltage across the IGBTQ _1, like the first embodiment, the operation shown in FIG.

That is, when the voltage across the diode rises, the current I _clamp1 flows into the gate of IGBTQ ₁ through the series circuit of the resistor R ₁ , the saturable reactor L ₁ , and the capacitor C ₁ according to this rise, and the gate voltage V _GE1 is raised, becomes the direction to turn on the IGBTQ _1, voltage increase V _CE1 is suppressed.

  In addition, although the example of the electrical component was shown as resistance in the said Example, it is not restricted to an electrical component, The wiring material and conductive material which have resistance value can be applied. In addition, it is possible to apply a conductive material having a resistance value to the winding material of the saturable reactor and a capacitor component having a large equivalent series resistance.

Q ₁ , Q ₂ ... IGBT D ₁ , D ₂ .. Diode R ₁ ... Resistance
L ₁ ... Saturable reactor C ₁ ... Capacitor ZD ... Voltage clamp element

Claims (3)

  In a circuit system that suppresses an overvoltage due to a surge during turn-off of a voltage-driven semiconductor element, a series circuit of a saturable reactor, a capacitor, and a resistor is provided between a collector terminal and a gate terminal of the voltage-driven semiconductor element. A semiconductor protection circuit characterized by being connected.   In a circuit system for suppressing overvoltage caused by a surge during reverse recovery of a diode in a voltage-driven semiconductor element in which diodes are connected in antiparallel, a series circuit of a saturable reactor, a capacitor, and a resistor is connected to the collector of the voltage-driven semiconductor element. A semiconductor protection circuit characterized by being connected between a terminal and a gate terminal. The semiconductor protection circuit according to claim 1, wherein the resistor is formed of a conductive member having a resistance value.