JP3381491B2 - Semiconductor element protection circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power semiconductor element protection circuit, and more particularly to an apparatus for protecting a power semiconductor element from an overvoltage applied during switching.

[0002]

2. Description of the Related Art As an example of conventional technology, Japanese Patent Laid-Open No. 7-1
FIG. 13 shows a chopper circuit to which a gate drive circuit having an overvoltage detection circuit described in Japanese Patent No. 47726 is applied. In the figure, 1 is a DC power supply, 2 is a load device, 3 is a flywheel diode, 4 is wiring inductance, and 5 is a collector when a positive voltage or more is applied between the gate (G) and the emitter (E). (C) -Emitter (E) is turned on, and when the gate-emitter voltage becomes equal to or lower than a predetermined voltage, the collector-emitter is turned off. 5b is a capacitance between the gate and the emitter. 6 is a gate resistance connected in series to the gate of the IGBT 5, 7 is a drive circuit for turning on and off the IGBT 5,
Reference numeral 7a denotes a transistor which is turned on when the IGBT5 is turned on to apply a positive voltage between the gate and the emitter of the IGBT5, and 7b is turned on when the IGBT5 is turned off so that the voltage between the gate and the emitter of the IGBT5 becomes 0 voltage. Is a power supply for the drive circuit, 8 is a clamp element that conducts when a predetermined reference voltage is exceeded, and 9 is a diode.

Next, the operation will be described. When the switch element 7a is turned on and a positive voltage is applied between the gate and emitter of the IGBT 5 from the power supply 7c, the IGBT 5 is turned on, and a current flows from the DC power supply 1 through the load device 2 and the collector of the IGBT 5 through the emitter. At this time, IG
Although the collector-emitter voltage of BT5 becomes lower than the gate-emitter voltage, the diode 9 prevents the gate-emitter voltage from decreasing.

When the transistor 7a is turned off and the transistor 7b is turned on, the gate-emitter of the IGBT 5 is short-circuited via the gate resistor 6, the gate-emitter voltage drops, the IGBT 5 turns off, and the current flows to the load device 2. Current flows back through the diode 3. This I
FIG. 14 shows a voltage / current waveform when the GBT 5 is turned off. In FIG. 14, the voltage at the connection point between the transistors 7a and 7b is VS, the gate-emitter voltage of the IGBT 5 is VGE, and the collector-emitter voltage of the IGBT 5 is V.
CE, the current flowing through the collector-emitter of the IGBT 5 is IC, the gate resistor 6 is RG, and the voltage of the DC power supply 1 is E. At time T1, the capacitance becomes 5 when VS becomes 0V.
The charges accumulated in a and 5b are discharged through the gate resistor 6, and VGE decreases. When VGE drops to some extent and reaches time T2, due to the characteristics of the IGBT, VCE
Begins to rise. Due to the slope of this rise in VCE, IG
Since a current flows from the collector of BT5 to the gate resistance 6 via the electrostatic capacitance 5a, the decrease in VGE is suppressed until time T3. When VCE reaches the voltage E of the DC power supply, the IC
Decreases and commutates to the diode 3.

At this time, VCE is the reduction rate of IC, that is, d
The voltage of the product of ic / dt and the wiring inductance 4 is the voltage superimposed on the voltage E of the DC power supply. If this superimposed voltage is ΔVCE and the maximum voltage between the collector and emitter of the IGBT 5 at turn-off is VP, then VP = E + ΔVCE. Therefore, VC when the IGBT5 is turned off
E has the maximum VP when the clamp element 8 is not provided, and has a dotted line waveform in the drawing, and IC and VGE also have a dotted line waveform in the drawing.

If the clamp voltage, which is the reference voltage at which the clamp element 8 conducts, is VCL, the clamp element 8 conducts under the condition of VCE> VCL + VGE, and VCE is the sum of VCL and VGE as shown by the solid line in the figure. Clamped to the voltage of. At this time, a part of the current ICL of the IC flows through the clamp element 8, the gate resistor 6 (RG), and the transistor 7b, VGE becomes VGE = ICL × RG, and VGE rises as shown by the solid line in the figure, and IG
It acts to increase the current in BT5, and the current due to the energy in wiring inductance 4 flows through the collector-emitter. The current flowing in the IGBT 5 at this time is I
If C ′, then IC ′ = IC−ICL.

Normally, ICL has a very small value with respect to IC '. The relationship between this IC 'of IGBT and VGE is
This is a characteristic peculiar to the IGBT and is shown in FIG.
That is, the value of VGE is determined according to the size of IC 'to be flown. On the other hand, the IGBT has a characteristic that the switching loss increases as the gate resistance increases, and thus the smaller RG is better. Therefore, I
When RG is reduced to reduce the switching loss of the GBT 5, VGE has a value determined by IC 'as described above, and therefore ICL increases, and the load on the clamp element 8 and the gate resistor 6 increases.

FIG. 16 is a diagram showing a safe operation area when the IGBT is turned off, and the locus of the voltage / current waveform when the IGBT 5 is turned off must be suppressed within the area (A) in this figure. Therefore, in order to suppress the above-mentioned VP within this region (A), the value of the sum of the clamp voltage VCL of the clamp element 8 and the gate-emitter voltage VGE must be set at the line (B) in the figure. . This suppresses the jump-up voltage at turn-off of the IGBT 5 to VCL or less, and as a result, the IG within the safe operation area.
The BT can be switched.

However, this conventional method has the following problems. The safe operating area of the IGBT has a higher allowable voltage when the collector-emitter current is smaller than the rating of the IGBT. However, since the clamp voltage VCL is constant irrespective of the collector-emitter current, IG is maintained below the rated current.
When the BT5 is turned off and the peak voltage VP at the time of turn-off exceeds VCL, the clamp element 8 becomes conductive as described above even if the VP is within the safe operation region, and As described above, the current flows through the clamp element 8, and the load on the clamp element 8 increases. Also, in order to switch the IGBT 5 at high speed,
The switching loss must be small, which requires a small RG and, as a result, the IGBT
The current flowing through the clamp element 8 for each switching of No. 5 increases, and if the switching is handled at high speed, the loss of the clamp element 8 and the gate resistor 6 greatly increases. Therefore, the clamp element is required to have a large capacity with high energy resistance, and in order to achieve high reliability and long life, it is necessary to select a clamp element that is not easily deteriorated. In addition, a large gate resistance is required. This leads to an increase in size of the device and an increase in cost.

As another conventional technique for protecting power transistors, Japanese Patent Laid-Open No. 6-296362 discloses a protection circuit adapted to both low energy overvoltage and high energy overvoltage. This is because a Zener diode is provided as a clamp element between the drain and the gate of the VDMOS transistor, and the clamp value is limited to the clamp value determined by the Zener diode for the low energy overvoltage, and the clamp state is once set for the high energy overvoltage. After the shift to (4), the VDMOS transistor is brought into a completely conductive state to protect each. However, there is no description about a technique for reducing the power loss of the clamp element or the gate resistance.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is possible to reduce the loss of a clamp element and to protect a semiconductor element which is compact, highly reliable and low cost. The purpose is to provide a circuit.

[0012]

A semiconductor element protection circuit according to the present invention is provided with one of main electrodes of a semiconductor element.
Clamping means is provided between a collector electrode and a control electrode, and the clamp voltage, which is a reference voltage for conducting the clamping means, is changed according to the value of the current flowing between the main electrodes of the semiconductor element.

[0013] Claim 1, the semiconductor device turns on and off between the primary response electrode control signal input to the control electrode, the main
In a protection circuit for a semiconductor element, which is interposed between a collector electrode , which is one of the electrodes, and a control electrode, and which is conductive when a voltage exceeding a predetermined reference voltage is applied, it flows between the main electrodes. A clamp control circuit for changing the reference voltage of the clamp means according to the value of the current is provided.

According to a second aspect, in addition to the configuration of the first aspect, the semiconductor element has a current detection terminal, and this terminal is connected to the clamp control circuit.

According to a third aspect of the present invention, an insulated gate bipolar transistor is used as the semiconductor element in the first aspect.

According to a fourth aspect of the present invention, the clamp control circuit according to the first aspect reduces the reference voltage of the clamp means in response to an increase in the current between the main electrodes.

According to a fifth aspect of the present invention, the clamp means includes a plurality of clamp elements connected in series, and the clamp control circuit is provided between the switch element connected in parallel to the at least one clamp element and the main electrode of the semiconductor element. The protection circuit for a semiconductor device according to claim 1, further comprising a circuit that turns on the switch device when a current is a predetermined value or more.

A sixth aspect of the present invention is the protection circuit for a semiconductor element according to the fifth aspect, wherein a voltage dividing resistor is connected in parallel to each clamp element.

A seventh aspect of the present invention is the protection circuit for a semiconductor element according to the fifth aspect, wherein the switch element is a transistor.

[0020]

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1. Next, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, 10 is a clamp element composed of a Zener diode which is turned on when the voltage at both ends is equal to or higher than the clamp voltage VZ1, 11 is a clamp element which is composed of a Zener diode which is turned on when the voltage at both ends is equal to or higher than the clamp voltage VZ2, and 12 is A switch that short-circuits the clamp element 11, 13 is a current detector that detects the collector-emitter current of the IGBT 5, and sends a current detection signal S1, and 14 is a current detection signal S1 sent from the current detector 13,
A switch control device for opening and closing the switch 12 in accordance with the magnitude of the signal, 16 and 17 are clamp elements 1 respectively.
Resistors connected in parallel to 0 and 11 are provided for the purpose of evenly dividing the voltage applied to the clamp element.

FIG. 2 shows a safe operation area when the IGBT is turned off. Next, the operation will be described with reference to this figure. The switch controller 14 opens the switch 12 when the collector-emitter current IC of the IGBT 5 is within the range (C) of FIG. At this time, IGB
The clamp elements 10 and 11 are connected between the collector and gate of T5, and when the clamp voltage between the collector and emitter of the IGBT5 is VCL (C), VCL (C) = VZ1 + VZ2 + VGE.

In the region (D) of FIG. 2 where the IC is relatively large, the switch control device 14 closes the switch 12 and short-circuits the clamp element 11. At this time, IG
Only the clamp element 10 is connected between the collector and the gate of the BT5, and if the clamp voltage between the collector and the emitter of the IGBT5 is VCL (D), then VCL (D) = VZ1 + VGE.

FIG. 3 shows the voltage-current waveform at turn-off in this circuit. If the above IC is within the range (C), I
If GBT5 is turned off, wiring inductance 4
2 is less than VCL (C), that is, in FIG.
Clamping element 10 if voltage point (E) of
11 does not conduct. Further, when the IGBT 5 is turned off when the IC is in the range of the area (D), the jumping voltage is clamped at VCL (D), that is, the voltage point (F) in FIG. 2, and the clamp element 10 becomes conductive.
Therefore, the safe operation area at the time of turning off the IGBT 5 can be effectively used, the load on the clamp element can be reduced, and the power loss of the gate resistor 6 can be reduced. Further, even when the jump-up at turn-off is very large in the region (C) where the IC is relatively small and exceeds the voltage point (E), the clamp elements 10 and 11 become conductive, and the voltage of VCL (C) is applied. Since it is clamped, the IGBT 5 is reliably protected from overvoltage.

Embodiment 2. Another embodiment of the present invention will be described with reference to FIG. In the figure, 51 is an IGBT with a current-conditioning terminal, 12a is an NPN transistor that short-circuits the clamp element 11, and 14a is an IGBT 51.
It is a resistor that converts the current output from the current sense terminal of 1 to voltage. Next, the operation will be described. IGBT5
A current of a constant rate is output from the sense emitter (E2) with respect to the current flowing through the collector (C) -emitter (E1) of the No. 1 unit. The current output from this sense emitter is I
If S and RS are the resistances 14a, the voltage VRS across the resistance 14a is VRS = IS × RS.

The threshold of the base (B) -emitter (E) voltage for turning on the transistor 12a is VBE1, the forward voltage drop of the diode 9 is VF, and the transistor 7b.
If the forward voltage drop of V is VS, the current flows from the sense emitter (E2) through the base-emitter of the transistor 12a, the diode 9, the gate resistor 6, and the transistor 7b when the above VRS satisfies the condition of VRS> VBE1 + VF + VS. Flows, and the transistor 12a is turned on. Therefore, the collector
When the resistance value of the resistor 14a is selected such that VRS ≦ VBE1 + VF + VS when the emitter current is in the region (C) in FIG. 2 and VRS> VBE1 + VF + VS when the region (D) is in FIG.
Performs the same operation as.

That is, when the collector-emitter current is in the region (C) in FIG. 2, VRS≤VBE1 + VF
Since it is + VS, the base-emitter current does not flow and the transistor 12a remains off, and the clamp element 10, between the collector (C) and the gate (G) of the IGBT 51,
11 will be connected, and IGBT51 at this time
When the clamp voltage between the collector (C) and the emitter (E1) of is VCL (C), VCL (C) = VZ1 + VZ2 + VGE. When the collector-emitter current is in the region (D), VRS> VBE1 + VF + VS. Therefore, in the transistor 12a, a current flows between the base and the emitter, and the transistor 12a is turned on, and the clamp element is connected between the collector (C) and the gate (G) of the IGBT 51. Only 10 will be connected, and the collector (C) -emitter (E1) of the IGBT 51 at this time.
If the clamp voltage between them is VCL (D), then VCL (D) = VZ1 + VGE. Therefore, it is possible to effectively use the safe operation area at the time of turning off the IGBT, further reduce the load on the clamp element and reduce the power loss of the gate resistance.

Embodiment 3. Another embodiment of the present invention will be described with reference to FIG. In the figure, 12b is a PNP type transistor that short-circuits the clamp element 11, 14a is a resistor that converts the current output from the current sense terminal of the IGBT 51 into a voltage, 14c is an NPN type transistor, and 14b is the collector of the transistor 14c ( It is a resistor connected in series with C). Next, the operation will be described. IGBT51 collector (C) -emitter (E1)
A current with a constant magnification is output from the sense emitter (E2) with respect to the current flowing through. Assuming that the current output from the sense emitter is IS and the resistor 14a is RS, the voltage VRS across the resistor 14a is VRS = IS × RS.

Assuming that the threshold value of the base (B) -emitter (E) voltage for turning on the transistor 14c is VBE2, when the above VRS satisfies the condition of VRS> VBE2, the sense emitter (E2) changes the transistor 14c from the sense emitter (E2). A current flows through the base-emitter, turning on the transistor 14c. In this state, the IGBT 51 is turned off, the voltage of the collector (C) -emitter (E1) rises, and the voltage is clamped by the clamp element 10.
When the voltage becomes higher than the clamp voltage VZ1 of, the clamp element 10 becomes conductive through the emitter (E) -base (B) of the transistor 12b, the resistor 14b, and the transistor 14c.

At the same time, a current flows from the emitter (E) to the base (B) of the transistor 12b to turn on the transistor 12b, and the current of the clamp element 10 passes through the transistor 12b, the diode 9, the gate resistor 6 and the transistor 7b. Also flows. IGBT5 at this time
The gate-to-gate (G) -emitter (E1) voltage VGE of 1 is
The current IS flowing through the clamp element 10 and the resistor 14bRB
And the parallel connection value of the gate resistance 6RG, which is VGE = IS × {(RG × RB) / (RG + RB)}. Therefore, under the condition that VRS> VBE as described above, the clamp voltage of the collector (C) -emitter (E1) of the IGBT 51 becomes the value of VZ1 + VGE.

When the VRS is lower than VBE2 of the transistor 14c, the transistor 14c cannot be turned on and the transistor 12b cannot be turned on. Therefore, at this time, the collector (C) -of the IGBT 51
The clamp elements 10 and 11 are connected between the gates (G), and under the condition that VRS ≦ VBE2, the IGB
The clamp voltage between the collector (C) and the emitter (E1) of T51 is VZ1 + VZ2 + VGE. Therefore,
If the resistance value of the resistor 14a is selected so that VRS ≦ VBE2 when the collector-emitter current is in the region (C) in FIG. 2 and VRS> VBE2 when the region (D) is in FIG.
Performs the same operation as. That is, as described above,
When the emitter current is in the region (C) in FIG. 2, V
Since RS ≦ VBE, the clamp voltage between the collector (C) and the emitter (E1) of the IGBT 51 is VCL.
Assuming (C), VCL (C) = VZ1 + VZ2 + VGE. When the collector-emitter current is in the region (D), VRS> VBE, so the clamp voltage between the collector (C) and the emitter (E1) of the IGBT 51 is VC.
If L (D), then VCL (D) = VZ1 + VGE. Therefore, the safe operation area at the time of turning off the IGBT can be effectively used, the load of the clamp element can be reduced, and the power loss of the gate resistance can be reduced.

Fourth Embodiment Another embodiment of the present invention will be described with reference to FIG. In the figure, 12c is a thyristor which short-circuits the anode of the clamp element 10 and the gate (G) of the IGBT 51, and 14d is a zener diode which conducts when the voltage VRS of the resistor 14a exceeds a predetermined voltage. Next, the operation will be described. In the figure, the IGBT
The sense emitter (E2) outputs a current having a constant magnification with respect to the current flowing through the collector (C) -emitter (E1) of 51. Assuming that the current output from the sense emitter is IS and the resistor 14a is RS, the voltage VRS across the resistor 14a is VRS = IS × RS.

The Zener voltage of the Zener diode is VDZ,
When the threshold voltage of the gate (G) -cathode (K) that turns on the thyristor 12c is VGK and the forward voltage drop of the transistor 7b is VS, when the above VRS satisfies the condition of VRS> VDZ + VGK + VS, the sense emitter (E2) to Zener diode 14d and thyristor 12c gate (G)
-A current flows through the cathode (K), the gate resistor 6, and the transistor 7b, and the thyristor 12c is turned on. Therefore, when the resistance value of the resistor 14a is selected such that VRS ≦ VDZ + VGK + VS when the collector-emitter current is in the region (C) in FIG. 2 and VRS> VDZ + VGK + VS when the region (D) is shown in FIG.
Performs the same operation as.

That is, when the collector-emitter current is in the region (C) in FIG. 2, VRS≤VDZ + VGK
Since it is + VS, the thyristor 12c has a gate (G)-
The cathode (K) current does not flow and remains off.
The clamp elements 10 and 11 are connected between the collector (C) and the gate (G) of the BT51, and at this time, I
When the clamp voltage between the collector (C) and the emitter (E1) of the GBT 51 is VCL (C), VCL (C) = VZ1 + VZ2 + VGE. Further, when the collector-emitter current is in the region (D), VRS> VDZ + VGK + VS, so that the gate (G) -cathode (K) current flows in the thyristor 12c to turn on, and the collector (C) -gate (G) of the IGBT 51 is turned on. ), Only the clamp element 10 is connected, and when the clamp voltage between the collector (C) and the emitter (E1) of the IGBT 51 at this time is VCL (D), VCL (D) = VZ1 + VGE. Therefore, the safe operation area at the time of turning off the IGBT can be effectively used, and the load on the clamp element and the power loss of the gate resistance can be reduced.

Embodiment 5. Next, another embodiment of the present invention is shown in FIG. In FIG. 7, 11a is a clamp element having a clamp voltage VZ2, 11b is a clamp element having a clamp voltage VZ3, 12d is a switch for short-circuiting the clamp element 11a, and 12e is a clamp element 11.
The switch for short-circuiting b, 15 receives the detection signal S1 of the current detector 13, and the switch 1 is switched depending on the magnitude of the signal.
Switch control device for opening and closing 2d, 12e, 16, 17
a and 17b are clamp elements 10, 11a and 11 respectively.
It is a resistor connected in parallel with b and is provided for the purpose of evenly dividing the voltage applied to the clamp element.

FIG. 8 shows a safe operation area when the IGBT is turned off. Next, the operation will be described with reference to this figure. When the collector-emitter current IC of the IGBT 5 is in the range of the region (C) of FIG. 8 which is relatively small, the switch controller 15 opens both the switches 12d and 12e.
At this time, the clamp elements 10, 11a and 11b are connected between the collector and the gate of the IGBT 5, and I
Clamp voltage between the collector and the emitter of GBT5 is VC
If L (C), then VCL (C) = VZ1 + VZ2 + VZ3 + VGE.

When the IC is in the area (D1) shown in FIG. 8 where the IC is relatively medium, the switch control device 15 operates the switch 1
2e is closed and the clamp element 11b is short-circuited. At this time, the clamp elements 10 and 11a are connected between the collector and gate of the IGBT 5, and if the clamp voltage between the collector and emitter of the IGBT 5 is VCL (D1), then VCL (D1) = VZ1 + VZ2 + VGE. In addition, the area (D
In the case of 2), the switch controller 15 closes the switches 12d and 12e, and the clamp elements 11a and 11e.
Short b. At this time, only the clamp element 10 is connected between the collector and the gate of the IGBT 5, and if the clamp voltage between the collector and the emitter of the IGBT 5 is VCL (D2), then VCL (D2) = VZ1 + VGE.

In this circuit, the IC is the area (C).
When the IGBT 5 is turned off within the range of, if the jump voltage is VCL (C) or less, that is, the voltage point (E) in FIG. 8 or less, the clamp elements 10, 11a, 1
1b does not conduct. Further, when the IGBT 5 is turned off when the IC is in the range of the area (D1), the jumping voltage is clamped at VCL (D1), that is, the voltage point (G) in FIG. 8, and the clamp elements 10 and 11a are turned on. Further, when the IGBT 5 is turned off when the IC is in the range of the area (D2), the jump voltage is VCL (D2), that is, the voltage point (FG) of FIG.
And the clamp element 10 becomes conductive. Therefore, the safe operation area at the time of turning off the IGBT 5 can be effectively used, and the load on the clamp element can be reduced. Further, even when the jump-up at turn-off is very large in the region (C) where the IC is relatively small and exceeds the voltage point (E), the clamp elements 10 and 11 become conductive, and the voltage of VCL (C) is applied. Since it is clamped, the IGBT 5 is reliably protected from overvoltage. Since the clamp voltage of the clamp means can be switched in three steps, the safe operation area at the time of turning off the IGBT can be effectively used, and the load on the clamp element and the power loss in the gate resistance can be reduced.

Sixth Embodiment Another embodiment related to the fifth embodiment will be described with reference to FIG. In the figure, 51
Is an IGBT with a current sensing terminal, 12f is an NPN type transistor that short-circuits the clamp element 11a, 12g
Is an NPN type transistor that short-circuits the clamp element 11b, and 14e and 14f are resistors that exchange the current output from the current sense terminal of the IGBT 51 with a voltage.

Next, the operation will be described. IGBT51
A current with a constant magnification is output from the sense emitter (E2) with respect to the current flowing through the collector (C) -emitter (E1) of the. The current output from this sense emitter is I
S is S, the resistance 14f is RS1, and the resistance value of the sum of the resistances 14e and 14f is RS2.
Is VRS1 = IS × RS1 and VRS2 = IS × RS2. The threshold value of the base (B) -emitter (E) voltage for turning on the transistor 12g is VBE1, the threshold value of the base (B) -emitter (E) voltage for turning on the transistor 12f is VBE2, and the transistor 12
g collector (C) -emitter (E) ON voltage to V
If the forward voltage drop of CE1 and the diode 9 is VF and the forward voltage drop of the transistor 7b is VS, the above-mentioned V
When RS1 and VRS2 satisfy the condition of VRS1 ≦ VBE2 + VCE1 + VF + VS VRS2> VBE1 + VF + VS, current flows from the sense emitter (E2) through the base-emitter of the transistor 12g, the diode 9, the gate resistor 6, and the transistor 7b, and the transistor 12g is turned on. To do.

At this time, since the voltage VRS1 of the resistor 14f is lower than VBE2 + VCE1 + VF + VS from the above equation, the transistor 12f cannot be turned on and only the clamp element 11b is short-circuited. When the condition of VRS1> VBE2 + VCE1 + VF + VS VRS2> VBE1 + VF + VS is satisfied, the sense emitter (E2) to the base-emitter of the transistor 12g, the diode 9,
A current flows through the gate resistor 6 and the transistor 7b,
The transistor 12g is turned on, and then the sense emitter (E2) to the base-emitter of the transistor 12f,
A current flows through the collector-emitter of the transistor 12g, the diode 9, the gate resistor 6, and the transistor 7b, and the transistor 12f is also turned on. At this time, both the clamp elements 11a and 11b are short-circuited. Therefore, the collector-emitter current is in the region (C) in FIG.
In the case of VRS2 ≦ VBE1 + VF + VS region (D1), in the case of VRS1 ≦ VBE2 + VCE1 + VF + VS VRS2> VBE1 + VF + VS region (D2), when the resistance of VRS1> VBE2 + V + 2 + V + 2 + V + 2 + VCE2 + VCE2 + VCE2 + VCE2 + VCE2 + VCE2 + VCE2 + VCE2 + VCE2 + VCE2 + VCE2 + VCE2 + 14. Performs the same operation as.

That is, when the collector-emitter current is in the region (C) in FIG. 8, VRS2 <VBE1 + V
Since it is F + VS, the base-emitter current does not flow in the transistors 12g and 12f and remains off.
The clamp elements 10, 11a, 11b are connected between the collector (C) and the gate (G) of the BT51, and the collector (C) -emitter (E of the IGBT 51 at this time is connected thereto.
If the clamp voltage between 1) is VCL (C), then VCL (C) = VZ1 + VZ2 + VZ3 + VGE.

In addition, the collector-emitter current is in the region (D
When 1), VRS2> VBE1 + VF + VS, VRS1
Since ≦ VBE2 + VCE1 + VF + VS, the transistor 12g is turned on, the transistor 12f is turned off, and only the clamp elements 10 and 11a are connected between the collector (C) and the gate (G) of the IGBT 51, and the collector of the IGBT 51 at this time. If the clamp voltage between (C) and the emitter (E1) is VCL (D1), then VCL (D1) = VZ1 + VZ2 + VGE. In addition, the collector-emitter current is in the region (D2)
, VRS2> VBE1 + VF + VS, VRS1>
Since VBE2 + VCE1 + VF + VS, both the transistors 12g and 12f are turned on, and the IGBT51
Clamp element 1 between collector (C) and gate (G) of
Only 0 will be connected, and the IGBT at this time
If the clamp voltage between the collector (C) and the emitter (E1) of 51 is VCL (D2), then VCL (D2) = VZ1 + VGE. Therefore, the same effect as that of the fifth embodiment shown in FIG. 7 can be obtained.

Embodiment 7. Another embodiment related to the fifth embodiment will be described with reference to FIG. In the figure, 1
4g is a Zener diode for driving the transistor 12g, and 14h is a Zener diode for driving the transistor 12f. Next, the operation will be described.
The sense emitter (E2) outputs a current of a constant magnification with respect to the current flowing through the collector (C) -emitter (E1) of the IGBT 51. If the current output from the sense emitter is IS and the resistor 14a is RS, the resistor 1
The voltage VRS across 4a is VRS = IS × RS. Set the Zener voltage of Zener diode 14g to VDZ
1. If the Zener voltage of the Zener diode 14h is VDZ2, when VDZ1> VRS, VDZ2> VRS, current does not flow from the Zener diodes 14g, 14h to the bases (B) of the transistors 12g, 12f. 12g and 12f remain off. Therefore, the collector (C) -of the IGBT 51
The clamp voltage between the emitter (E1) is VZ1 + VZ2 +
It becomes VZ3 + VGE.

When VDZ1 <VRS, VDZ2> VRS, from the sense emitter (E2) of the IGBT 51, the Zener diode 14g, the base (B) -emitter (E) of the transistor 12g, the diode 9, the gate resistor 6, the transistor A current flows through 7b, turning on the transistor 12g. On the other hand, since VDZ2> VRS, no current flows from the Zener diode 14h to the base (B) of the transistor 12f, and the transistor 12f remains off. Therefore, the IGBT 51 at this time
The clamp voltage between the collector (C) and the emitter (E1) of the above is VZ1 + VZ2 + VGE.

When VDZ1 <VRS and VDZ2 <VRS, from the sense emitter (E2) of the IGBT 51, the Zener diode 14g, the base (B) -emitter (E) of the transistor 12g, the diode 9, the gate resistor 6, the transistor 9 are formed. A current flows through 7b, turning on the transistor 12g. Further, from the sense emitter (E2) of the IGBT 51, the Zener diode 14h, the base (B) -emitter (E) of the transistor 12f, the collector (C) -emitter (E) of the transistor 12g, the diode 9, the gate resistor 6, the transistor A current flows through 7b, turning on the transistor 12f. Therefore, the clamp voltage between the collector (C) and the emitter (E1) of the IGBT 51 at this time is VZ1 + VGE.
The other operations and their effects are the same as those described with reference to FIG.

Embodiment 8. Another embodiment related to the fifth embodiment will be described with reference to FIG. In the figure, 1
2h is a PNP-type transistor that short-circuits the clamp element 11b, and 12k is a PNP that short-circuits the clamp element 11a.
Type transistor, 14e and 14f are resistors for converting the current output from the current sense terminal of the IGBT 51 into a voltage, 14k is an NPN type transistor for driving the transistor 12h, 14m is an NPN type transistor for driving the transistor 12k, 14n is a transistor 12h
And a resistor 14p is a resistor that allows a drive current of the transistor 14p to flow.

Next, the operation will be described. IGBT51
A current with a constant magnification is output from the sense emitter (E2) with respect to the current flowing through the collector (C) -emitter (E1) of the. The current output from this sense emitter is I
S, the resistance 14f is RS1, the resistance value of the sum of the resistance 14e and the resistance 14f is RS2, the voltage across RS1 and RS2 is VRS1 = IS × RS1, VRS2 = IS × RS2. The base that turns on the transistor 14k (B) -Emitter (E) voltage threshold is VBE3, transistor 14
Assuming that the threshold value of the base (B) -emitter (E) voltage for turning on m is VBE4, the above VRS1 and VRS2
When VRS1 ≦ VBE4 VRS2> VBE3, a current flows from the sense emitter (E2) through the base (B) -emitter (E) of the transistor 14k, and the transistor 14k is turned on. Also,
Since VRS1 ≦ VBE4, the transistor 14m cannot be turned on.

In this state, the IGBT 51 is turned off, the voltage of the collector (C) -emitter (E1) rises, and the voltage is clamped by the clamp element 10 and the clamp element 11a.
When it becomes higher than the clamp voltage VZ1 + VZ2, the clamp elements 10 and 11a become conductive via the emitter (E) -base (B) of the transistor 12h, the resistor 14n, and the transistor 14k. At the same time, transistor 12h
The current flows from the emitter (E) to the base (B) of the transistor 12h, so that the transistor 12h is turned on and the clamp element 1
The currents 0 and 11a also flow through the transistor 12h, the diode 9, the gate resistor 6, and the transistor 7b. On the other hand, since the transistor 14m is off, the transistor 12k cannot be turned on. The gate (G) -emitter (E1) voltage VGE of the IGBT 51 at this time is the current IS flowing through the clamp elements 10 and 11a and the resistance 14n.
It becomes the value of the product of RB1 and the parallel connection value of the gate resistance 6RG, and VGE = IS × {(RG × RB1) / (RG + RB
1)}.

Therefore, as described above, VRS> VBE
Under these conditions, the clamp voltage of the collector (C) -emitter (E1) of the IGBT 51 is VZ1 + VZ2 + VG
It becomes the value of E. When the condition of VRS1> VBE4 VRS2> VBE3 is satisfied, current flows from the sense emitter (E2) through the base (B) -emitter (E) of the transistor 14k, and the transistor 14k is turned on. Since VRS1> VBE4, the sense emitter (E) is added to the base (B) -emitter (E) of the transistor 14m.
A current flows from 2) and the transistor 14m is turned on.

In this state, the IGBT 51 is turned off, the voltage of the collector (C) -emitter (E1) rises, and that voltage is the clamp voltage VZ1 of the clamp element 10.
When it becomes higher, the clamp element 10 becomes the emitter (E) -base (B) of the transistor 12k and the resistor 14k.
p, the transistor 14m, or the emitter-collector of the transistor 12k, the emitter (E) -base (B) of the transistor 12h, the resistor 14n, and the transistor 14k. At the same time, transistor 1
The current flows through the emitter (E) -base (B) of 2h to turn on the transistor 12h, and the current flow through the emitter (E) -base (B) of the transistor 12k causes the transistor 12k to turn on and clamp. The current of the element 10 flows through the collector (C) -emitter (E) of the transistors 12k and 12h, the diode 9, the gate resistor 6, and the transistor 7b.

At this time, the gate (G) -of the IGBT 51-
The voltage VGE between the emitters (E1) is equal to the current IS flowing through the clamp element 10, the resistor 14nRB1 and the resistor 14pRB.
2 becomes the product value of the parallel connection value of the gate resistance 6RG, and VGE = IS × {(RG × RB1 × RB2) / (RG ×
RB1 + RG × RB2 + RB1 × RB2)}. Therefore, as described above, VRS2> VBE
3. Under the condition of VRS1> VBE4, the clamp voltage of the 1 collector (C) -emitter (E1) of the IGBT 5 is VZ1 + VGE. Therefore, when the collector-emitter current is in the region (C) in FIG. 8, when VRS1 ≦ VBE4 VRS2 ≦ VBE3 region (D1), when VRS1 ≦ VBE4 VRS2> VBE3 region (D2), VRS1> VBE4 VRS2> VBE3 When the resistance values of the resistors 14e and 14f are selected so that the above, the same operation as in FIG. 7 is performed.

That is, when the collector-emitter current is in the region (C) in FIG. 8, VRS1≤VBE4, V
Since RS2 ≦ VBE3, transistors 14k, 1
4m remains off because the base-emitter current does not flow, and the clamp elements 10, 11a, and 11b are connected between the collector (C) and the gate (G) of the IGBT 51, and the collector of the IGBT 51 at this time. When the clamp voltage between (C) -emitter (E1) is VCL (C), VCL (C) = VZ1 + VZ2 + VZ3 + VGE.

The collector-emitter current is in the region (D
When 1), VRS1 ≦ VBE4, VRS2> VBE3
Therefore, the transistor 14k is turned on, the transistor 14m is turned off, and from the above, only the transistor 12h can be turned on, and only the clamp elements 10 and 11a are connected between the collector (C) and the gate (G) of the IGBT 51. If the clamp voltage between the collector (C) and the emitter (E1) of the IGBT 51 at this time is VCL (D1), then VCL (D1) = VZ1 + VZ2 + VGE.

The collector-emitter current is in the region (D
When 2), VRS1> VBE4, VRS2> VBE3
Therefore, both the transistors 14k and 14m are turned on, and as described above, the transistors 12h and 12k can be turned on, and the collector (C) -of the IGBT 51-
Only the clamp element 10 is connected between the gates (G), and the collector (C) of the IGBT 51 at this time is connected.
-Clamp voltage between emitter (E1) is VCL (D2)
Then, VCL (D2) = VZ1 + VGE. Therefore, the same effect as that of the fifth embodiment shown in FIG. 7 can be obtained.

Ninth Embodiment Another embodiment related to the fifth embodiment will be described with reference to FIG. In the figure, 1
2m is a thyristor that short-circuits the anode of the clamp element 11a and the gate (G) of the IGBT 51, 12n is a thyristor that short-circuits the anode of the clamp element 10 and the gate (G) of the IGBT 51, and 14r is a voltage VRS of the resistor 14a which is equal to or higher than a predetermined voltage. Zener diode that conducts when it becomes 1
Reference numeral 4s is a Zener diode which conducts when the voltage VRS of the resistor 14a exceeds a predetermined voltage.

Next, the operation will be described. In the figure,
The sense emitter (E2) outputs a current of a constant magnification with respect to the current flowing through the collector (C) -emitter (E1) of the IGBT 51. If the current output from the sense emitter is IS and the resistor 14a is RS, the resistor 1
The voltage VRS across 4a is VRS = IS × RS. Set the Zener voltage of Zener diode 14r to VDZ
3, the Zener voltage of Zener diode 14s is VDZ4,
The threshold voltage of the gate (G) -cathode (K) for turning on the thyristor 12m is VGK1, and the thyristor 12n is
When the threshold value of the voltage of the gate (G) -cathode (K) that turns on the transistor is VGK2 and the forward voltage drop of the transistor 7b is VS, the sense is performed when the above VRS is VRS> VDZ3 + VGK1 + VS VRS ≦ VDZ4 + VGK2 + VS. From the emitter (E2) to the Zener diode 14r and the gate of the thyristor 12m (G)
-A current flows through the cathode (K), the gate resistor 6, and the transistor 7b, and the thyristor 12m is turned on. Further, since VRS ≦ VDZ4 + VGK2 + VS, the thyristor 12n cannot be turned on.

Therefore, at this time, the clamp elements 10 and 1 are provided between the collector (C) and the gate (G) of the IGBT 51.
Therefore, the clamp voltage between the collector (C) and the emitter (E1) of the IGBT 51 is VZ1 +.
It becomes VZ2 + VGE. When the above VRS becomes the condition of VRS> VDZ3 + VGK1 + VS VRS> VDZ4 + VGK2 + VS, the sense emitter (E2) to the Zener diode 14r and the gate (G) of the thyristor 12m.
-A current flows through the cathode (K), the gate resistor 6, and the transistor 7b, and the thyristor 12m is turned on. In addition, from the sense emitter (E2) to the Zener diode 14
s, a current flows through the gate (G) -cathode (K) of the thyristor 12n, the gate resistor 6, and the transistor 7b, and the thyristor 12n is turned on. Therefore, at this time, the collector (C) -gate (G) of the IGBT 51
The clamp element 10 is connected between them, and the IG
The clamp voltage between the collector (C) and the emitter (E1) of BT51 is VZ1 + VGE. Other operations and effects are similar to those in FIG. 7.

Although a transistor is used as the switch 12 in FIGS. 4, 5, 9, and 10, other self-arc-extinguishing semiconductor elements may be used. Although the transistor is used as the switch element of the switch control device 14, other self-arc-extinguishing type semiconductor element may be used. Further, in FIGS. 7, 9, 10, 11, and 12, the case where the clamp elements are connected in series is described, but a plurality of more than that may be connected in series.
In each of the embodiments, the example in which the IGBT is used as the semiconductor element is shown, but other types of power transistors can be used.

[0059]

According to the present invention, when the current flowing between the main electrodes of the semiconductor element is small, the reference voltage at which the clamp element is turned on is increased, the current between the main electrodes is increased, and the allowable voltage in the safe operation area is low. In this area, the reference voltage at which the clamp element turns on is lowered so that the safe operation area when the semiconductor element is turned off is used effectively and the clamp element conducts only when necessary. Also, the current duty of the gate resistance can be reduced, a small size, high reliability and low cost can be obtained, and the semiconductor element can be protected safely and reliably.

[Brief description of drawings]

FIG. 1 is a diagram showing a semiconductor element protection circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the first embodiment of the present invention.

FIG. 4 is a diagram showing a semiconductor element protection circuit according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a semiconductor element protection circuit according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a semiconductor element protection circuit according to a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a semiconductor element protection circuit according to a fifth embodiment of the present invention.

FIG. 8 is a diagram for explaining the operation of the fifth embodiment of the present invention.

FIG. 9 is a diagram showing a semiconductor element protection circuit according to a sixth embodiment of the present invention.

FIG. 10 is a diagram showing a semiconductor element protection circuit according to a seventh embodiment of the present invention.

FIG. 11 is a diagram showing a semiconductor element protection circuit according to an eighth embodiment of the present invention.

FIG. 12 is a diagram showing a semiconductor element protection circuit according to a ninth embodiment of the present invention.

FIG. 13 is a diagram showing an embodiment of a conventional semiconductor element protection circuit.

FIG. 14 is a diagram explaining an operation of a conventional semiconductor element protection circuit.

FIG. 15 is a diagram illustrating characteristics of an IGBT.

FIG. 16 is a diagram illustrating the operation of a conventional semiconductor element protection circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Load 4 Wiring inductance 5 IGBT 6 Gate resistance 7 Driving circuit 9 Diode 10 Clamp element 11 Clamp element 11a, 11b
Clamp element 12 Switch 12a, 12g, 12f NPN transistor 12b, 12k, 12h PNP transistor 12c, 12m, 12n Thyristor 12d, 12e Switch 13 Current detection circuit 14, 15 Switch control device 14a, 14b, 14e, 14f, 14n, 14p Resistance 14c, 14k, 14m NPN transistors 14d, 14g, 14h, 14r, 14s Zener diodes 16, 17 Resistors 17a, 17b
Resistor 51 IGBT with current sense terminal

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02H 3/08-3/253 H02H ⁷ /12-7/127

Claims (7)

(57) [Claims] 1. A semiconductor element for turning on / off between main electrodes in response to a control signal input to the control electrode,
In a protection circuit for a semiconductor device, which is interposed between one of the collector electrode and the control electrode and which is conductive when a voltage exceeding a predetermined reference voltage is applied, a current flowing between main electrodes A protection circuit for a semiconductor device, comprising a clamp control circuit for changing the reference voltage of the clamp means according to the value of. 2. The protection circuit for a semiconductor device according to claim 1, wherein the semiconductor device has a current detection terminal, and this terminal is connected to the clamp control circuit. 3. The protection circuit for a semiconductor device according to claim 1, wherein the semiconductor device is an insulated gate bipolar transistor. 4. The protection circuit for a semiconductor device according to claim 1, wherein the clamp control circuit decreases the reference voltage of the clamp means in response to an increase in current between the main electrodes. 5. The clamp means includes one in which a plurality of clamp elements are connected in series, and the clamp control circuit includes a switch element connected in parallel to at least one clamp element and a current between a main electrode of the semiconductor element. The semiconductor element protection circuit according to claim 1, further comprising a circuit that turns on the switch element when the value is equal to or more than a predetermined value. 6. The protection circuit for a semiconductor device according to claim 5, wherein a voltage dividing resistor is connected in parallel to each clamp device. 7. The protection circuit for a semiconductor device according to claim 5, wherein the switch device is a transistor.