JPH1032476A - Overcurrent protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of element destruction without deviating from a safe operation area at the time of the overcurrent at the time of adding a sense IGBT(insulated gate bipolar transistor) to a main IGBT chip and equivalently detecting the collector current of the main IGBT from a sense current. SOLUTION: By connecting an MOSFETT1 between the emitter Es of the sense IGBT and the emitter E of the main IGBT and using it as a variable sense resistor, regardless of the size of the collector emitter voltage of the main IGBT, the collector current of the main IGBT is limitd to an almost fixed value. In such a manner, even for a normal IGBT without a built-in sense IGBT, overcurrent protection is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a semiconductor switching element, and more particularly, to a protection circuit for a voltage-driven element such as an insulated gate bipolar transistor (hereinafter simply abbreviated as IGBT) for preventing overcurrent breakdown. The present invention relates to an overcurrent protection circuit.

[0002]

2. Description of the Related Art FIG. 8 is a circuit diagram showing a conventional example of this kind. In this circuit, the output terminal 1 of the gate drive circuit 2 is connected to the gate terminal G of the IGBT 1 via a gate resistor Rg.
The emitter terminal E of the IGBT 1 is the output terminal 2 of the gate drive circuit 2, the sense resistor Rs is provided between the emitter terminal E and Es (also referred to as the sense terminal) of the IGBT 1, and the IGBT 1
1 has a diode D2 and an MO between the gate G and the emitter E.
A series circuit with SFET T2 is added to MOSFET T2
And the sense terminal Es of the IGBT 1 are connected to each other.

The IGBT 1 in FIG. 8 can be expressed as a parallel circuit of a main IGBT 11 and a sense IGBT 12 as shown in FIG. Note that Rs indicates a sense resistance. In this circuit, when the collector current of the main IGBT 11 increases, the current flowing through the sense resistor Rs also increases, and the sense voltage Vs increases. This Vs is MOS
When the gate threshold voltage Vth of the FET T2 is exceeded, M
OSFETT2 is turned on, lowering the gate-emitter voltage V _GE0 the IGBT 1. Since the IGBT generally has a characteristic that the saturation current value of the collector current decreases as the gate voltage decreases, the IGBT is limited to a collector current value that satisfies the relationship of Vs = Vth with a decrease in V _GE0 . As a result, the current of the IGBT 11 becomes excessively large, preventing the element from breaking out of the safe operation area (so-called ASO).

[0004]

As described above, FIG.
In the sense circuit shown in (a), the collector-emitter voltage V _CE of the main IGBT 11 is shared as the collector-emitter voltage V _CES of the sense IGBT 12 and the sense voltage Vs of the sense resistor Rs. That is, V _CE = V _CES + Vs. In a region where V _CE and V _CES are large and the Vs voltage can be ignored, the main IGBT 11 and the sense IGBT
The current ratio to 12 is determined by the IGBT characteristics, and the IGBT having the same characteristics has a value proportional to the area ratio of the chip. However, when V _CE and V _CES are small, Vs
The voltage cannot be ignored, and the current flowing through the sense IGBT 12 decreases and becomes smaller than the current proportional to the area ratio of the chip. As a result, the sense voltage characteristics are shown in FIG.
As shown in (b), even when the collector current Ic of the main IGBT 11 is kept constant, the sense voltage Vs becomes small when V _CE is small.

The current limitation is caused by the MOSFET T2
Since the gate threshold voltage Vth and the sense voltage Vs is when the equal of a large limiting current of the main IGBT11 when the V _CE is small voltage, limit current value when V _CE is large with characteristics such as reduced . Therefore, in the conventional circuit, when V _CE is small, the current limit value is large, which may deviate from the safe operation area of the IGBT, leading to element destruction. Further, when the current limiting operation is performed and V _CE changes from a small state to a large state, the current limit value decreases. However, the current reduction rate di / dt and the IGBT
A large voltage determined by the product of the IGBT and the wiring inductance between the snubbers is applied between the collector and the emitter of the IGBT. Generally, in the safe operation area of the IGBT, the allowable current value decreases as the voltage increases, so that the current limiting operation works. When V _CE changes from a small state to a large state, the safe operation area of the IGBT deviates from the safe operation area of the IGBT and element destruction occurs. There is a problem.

In the above description, a device having a sense IGBT has been described. However, a normal IGBT also needs overcurrent protection. FIG. 10 shows a conventional example of this type. That is, the gate of the IGBT 1 is connected to the complementary (complementary symmetrically) connected transistor T via the gate resistor R10.
The output terminals of the transistors T8 and T9 are connected to each other. The input terminals of the complementary connection transistors T8 and T9 are connected to the gate driving DC power supply 20, a series circuit of the resistor R11 and the transistor T10, the resistor R12 and the output element of the photocoupler P1. (Eg, a phototransistor) are connected in parallel with each other. The base of the transistors T8 and T9 has a connection point between the resistor R11 and the transistor T10, the base of the transistor T10 has a connection point between the resistor R12 and the output element of the photocoupler P1, and the input element of the photocoupler P1. The control circuit 10 is connected to the light emitting diode (light emitting diode or the like), and the emitter of the IGBT 1 is connected to the negative terminal of the DC power supply 20 for gate drive. In such a circuit, when the photocoupler P1 is turned off by the control circuit 10, the current flowing through the resistor R12 to the base of the transistor T10 flows to the photocoupler P1, and the transistor T10 is turned off. When the transistor T10 is turned off, a base current flows through the base of the transistor T8 via the resistor R11, and the transistor T8 is turned on. When the transistor T8 is turned on, IG
A current flows through the gate of BT1 via the gate resistor R10, the gate voltage of IGBT1 rises, and IGBT1 turns on.

Next, a case where an overcurrent flows due to a short circuit accident or the like while the IGBT 1 is on will be described. Generally, the relationship between the collector current and the collector-emitter voltage of an IGBT is such that if a certain current or more is to flow, the collector-emitter voltage rises. Therefore, when the overcurrent due to a short circuit accident or the like reaches a certain current or more, the collector-emitter voltage sharply rises and has a characteristic of being saturated at a certain limit current. This limit current value depends on the gate voltage, and the larger the gate voltage, the larger the limit current. Also, since the IGBT has a parasitic capacitance C _CG as shown, if the collector-emitter voltage rises rapidly,
The gate-emitter capacitance C _GE is charged via the parasitic capacitance C _CG and the gate voltage rises, thereby further increasing the limit value of the collector current. Since the short-circuit withstand capability of the IGBT (the time until the element is destroyed in the short-circuit state) decreases as the limit current increases, the over-current state is detected at a higher speed when performing over-current protection.
It is necessary to turn off the IGBT in a short time. Therefore, conventionally, as shown in the figure, a DC current detector 30 is inserted in series with the IGBT 1, and when the collector current of the IGBT exceeds a certain set value, an off signal is output from the control circuit 10, and the IGBT 1 is turned off.
The BT is protected from short circuit breakdown. But,
Such a DC current detector is expensive and increases the cost. Further, in a device having a large current capacity, there is a problem that the DC current detector becomes large in size and the device becomes large in size.

Therefore, an object of the present invention is to provide a sense IG
In the IGBT with a built-in BT, the overcurrent protection and the current limiting operation are made to be constant irrespective of the voltage between the collector and the emitter to ensure the IGBT protection.
In a normal IGBT, the IGBT is protected without increasing the size and cost of the device.

[0009]

In order to solve such a problem, according to the first aspect of the present invention, a MOSFET is connected between an emitter of a sense IGBT and an emitter of a main IGBT, that is, a MOSFET is used instead of a resistor. And
The main IGB is connected to the gate of this MOSFET via a resistor.
By connecting the gate terminal of T and the collector terminal of the main IGBT via a diode, when the collector-emitter voltage of the main IGBT becomes larger than the gate voltage, the diode turns off and the MOSFET turns off.
Has the same value as the gate voltage of the main IGBT, and the on-resistance of the MOSFET has a small value. When the collector-emitter voltage of the main IGBT becomes lower than the gate voltage, the gate voltage of the MOSFET is discharged through the diode and decreases, and the on-resistance of the MOSFET becomes a large value. In other words, a variable resistor is formed that has a small sense resistance when the voltage between the collector and the emitter is large, and has a large sense resistance when the voltage between the collector and the emitter is small. Therefore, when the collector-emitter voltage of the main IGBT is small, the sense current is small, but the on-resistance of the MOSFET is large, so that the drain-source voltage is large and the main IGBT is detected.
The sense voltage can be the same as when the collector-emitter voltage of the BT is large. As a result, the characteristics of the sense voltage can be made independent of the collector-emitter voltage of the main IGBT.

[0010] Further, according to the invention of claim 2, the MO
By connecting the resistor RS2 in parallel to the series circuit of the MOSFET and the resistor RS1 in place of the SFET, the MOSFE
A variable sense resistor is formed by the ON / OFF operation of T.
That is, when the collector-emitter voltage of the main IGBT is small, the MOSFET is turned off and the sense resistance becomes RS
2, when the collector-emitter voltage of the main IGBT is large, the MOSFET is turned on and the sense resistance becomes R
S1 · RS2 / (RS1 + RS2). Therefore, by adjusting the values of the resistors RS1 and RS2, it is possible to make the sense voltage have characteristics independent of the collector-emitter voltage of the main IGBT.

Further, according to the third aspect of the present invention, the main IG
A sense IGBT is formed in a BT chip,
A sense resistor is connected between the emitter of the GBT and the emitter of the main IGBT. When the sense voltage exceeds a certain set value, the gate voltage of the main IGBT is reduced, and the collector current is limited to protect the protection. A voltage setting circuit for changing a voltage setting value according to a collector-emitter voltage of the main IGBT;
A comparison circuit for comparing the voltage set value with the sense voltage; and a third switch circuit for reducing the gate voltage of the main IGBT according to the result.
When the collector-emitter voltage of the main IGBT is small, the sense current is also small, but the voltage setting value to be compared is also small. Therefore, the collector current limit value of the main IGBT is almost the same as when the collector-emitter voltage of the main IGBT is large. Value. Note that a voltage from another DC power supply can be used as a power supply for the voltage setting circuit instead of the gate voltage of the main IGBT (the invention of claim 4).

According to a fifth aspect of the present invention, there is provided an overcurrent protection circuit for preventing an IGBT from being destroyed by an overcurrent, wherein a gate-emitter voltage is provided between a gate of the IGBT and a positive terminal of a DC power supply for driving the gate. Is connected to the transistor via an input element of a photocoupler, and the collector of the transistor is connected to the emitter of the IGBT via a resistor so that the transistor is turned on when the voltage rises above the DC power supply voltage. I have to.

In addition, according to the invention of claim 6, in the overcurrent protection circuit for preventing the IGBT from being destroyed by overcurrent,
The IGBT is placed between the ON gate resistors of the IGBT.
When a current flows from the gate to the DC power supply for driving the gate, a comparator whose output voltage becomes high is connected, and the output of this comparator is connected to the output of the transistor through the input element of the photocoupler. A base is connected, and a collector and an emitter of the transistor are connected between a gate and an emitter of the IGBT via a resistor. According to the invention of claim 5 or 6, a voltage source lower in voltage than the gate driving DC power supply can be connected instead of the resistor (the invention of claim 7).

[0014]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. Note that the same components as those in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted. As is clear from FIG. 1, this circuit is different from that shown in FIG. 8 in that a MOSFET T1 is provided in place of the resistor Rs, and the gate and the IGB are provided.
A resistor R1 is connected between the gate G of T1 and a MOSF.
It is characterized in that diodes D1 are connected between the gate of ETT1 and the collector C of IGBT1. In this circuit, when the collector current of the IGBT 1 increases, the current flowing through the MOSFET T2 also increases,
The sense voltage Vs increases. Then, this voltage Vs becomes T
When the voltage exceeds the gate threshold voltage Vth of T2, T2 is turned on, and the gate-emitter voltage V _{GE0 of IGBT1} is turned on.
Lower. Since the IGBT has a characteristic that the saturation current value of the collector current decreases as the gate voltage decreases, the IGBT is limited to a collector current that satisfies the relationship of Vs = Vth with a decrease in V _GE0 .

When the collector-emitter voltage V _{CE of} the IGBT becomes higher than the gate voltage V _GE0 , the diode D1 is turned off, and the gate of T1 has the same value as the gate voltage V _{GE0 of the} IGBT. Is a small value. On the other hand, the collector-emitter voltage V of the IGBT
_{When CE} falls _{below the} gate voltage V _GE0 , the gate voltage of T1 is discharged through the diode D1 and falls, and T1
1 has a large on-resistance. That is, when the collector-emitter voltage V _{CE of} the IGBT is large, a variable resistance having a small resistance value is formed, and when the collector-emitter voltage V _CE is small, a variable sense resistor having a large resistance value is formed. Note that when the collector-emitter voltage V _{CE of} the IGBT is small, the sense current is small. However, since the on-resistance of T2 is large, the drain-source voltage thereof is detected to be large, and when the collector-emitter voltage is large. The sense voltages can be substantially the same. As a result, it is possible to make the characteristic independent of the collector-emitter voltage of the IGBT as the sense voltage, and to make the collector current limiting operation of the IGBT independent of the collector-emitter voltage. .

FIG. 2 is a circuit diagram showing a second embodiment of the present invention, which is a modification of FIG. Note that the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. As is clear from FIG. 2, this circuit is different from T1 shown in FIG. 1 in that a series circuit of T3 and a resistor RS1 and a resistor R
It is characterized in that S2 is connected and a variable sense resistor is formed by turning on and off T3. That is, when the collector-emitter voltage is low, T3 is off, and the resistance value of the sense resistor is RS2. When the collector-emitter voltage is high, T3 is on and the resistance value of the sense resistor is:
RS1 · RS2 / (RS1 + RS2), and the resistance value R
By adjusting S1 and RS2, the sense voltage can be set to IGBT
Characteristics that do not depend on the collector-emitter voltage of the IGBT, and the characteristic that the collector current limiting operation of the IGBT does not depend on the collector-emitter voltage can be achieved.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention. Note that the same components as those in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted. As is clear from FIG.
This circuit is different from that shown in FIG. 8 in that a diode D1, a constant voltage diode ZD1, a voltage setting circuit including transistors T4 and T5 and resistors R1 to R6, a transistor T6 operating as a comparator (comparing circuit), and a transistor replacing the MOSFET T2 T7 and resistor R7
Is a feature of the present invention. In this circuit, the collector-emitter voltage V _CE of the IGBT is
When the voltage is lower than the voltage V1 of D1, the charge of the capacitor C1 is discharged through the diode D1 and the IGBT to turn off the transistor T4, and the transistor T5 is also turned off because no base current flows. As a result, the base voltage V2 of the transistor T6 is as follows: V2 = V _GE × (R5 + R6) / (R3 + R4 + R5 + R6)

When the sense voltage Vs becomes higher than the voltage V2, the transistor T6 turns on. Based on the sense voltage Vs, a base current is supplied to the transistor T7 via the transistor T6 and the resistor R7, and the transistor T7 turns on. . Then, the gate voltage V of the IGBT
_GE0 is reduced and limited to the collector current where Vs = V2. At this time, R5> R6, and the terminal voltage V of R6 when the transistor T6 is not turned on.
In 2 × R6 / (R5 + R6), the transistor T7 does not turn on, and R6 and R7 are selected so that the Vs voltage hardly changes even when the transistor T6 turns on.

On the other hand, when the collector-emitter voltage V _{CE of} the IGBT is higher than the voltage V 1 of the constant voltage diode ZD 1, the diode D 1 turns off and the transistor T 4
A base current flows through the resistor R1 and the constant voltage diode ZD1 to turn on the transistor T4. Then, the base current also flows through the transistor T5 and the transistor T5
Also turns on, and the resistor R3 is short-circuited. As a result, the base voltage V2 of the transistor T6 is as follows: V2 = V _GE × (R5 + R6) / (R4 + R5 + R6) When the sense voltage Vs becomes higher than the voltage V2, the transistor T6 is turned on. Based on the sense voltage Vs, a base current is supplied to the transistor T7 via the transistor T6 and the resistor R7, and the transistor T7 is turned on. Then, the gate voltage V _{GE0 of the} IGBT is reduced, and is limited to the collector current that satisfies Vs = V2.

As described above, in the circuit of FIG. 3, the collector-emitter voltage V _CE of the IGBT is
When the voltage V1 is smaller than the voltage V1 of the first voltage V1, the sense voltage V2 represented by the above equation and the voltage V1
_{When CE} is higher than the voltage V1 of the constant voltage diode ZD1, the current is limited by the sense voltage V2 shown in the above equation. The latter is larger (>) between the sense voltage V2 shown by the equation and the sense voltage V2 shown by the equation (>), and the collector current limiting operation of the IGBT is controlled by matching the sense voltage with the collector-emitter voltage characteristics of the IGBT. It is possible to obtain characteristics that do not depend on the inter-voltage.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention, which is a modification of FIG. Note that the same components as those in FIG. 3 are denoted by the same reference numerals, and description thereof is omitted. As is clear from FIG. 4, this circuit uses the output (V ₀ ) of the terminal 3 of the gate drive circuit 2 as the power supply of the voltage setting circuit and uses the comparator COM1 instead of the transistor T6 in comparison with the circuit shown in FIG. The feature is that the resistor 6 is omitted. Its operation is almost the same as that of FIG.
The collector-emitter voltage V _CE of the constant-voltage diode Z
When the voltage is lower than the voltage V1 of D1, the sense voltage V2 with current limitation is given by the following equation. _{V2 = V 0 × R5 / (} R3 + R4 + R5) ... Moreover, when the collector-emitter voltage V _CE of the IGBT is higher than the voltage V1 of the zener diode ZD1, the sense voltage V2 the current limit is applied, the following equation . V2 = V ₀ × R5 / (R4 + R5)

As described above, in the circuit of FIG. 4, the collector-emitter voltage V _CE of the IGBT is
When the voltage V1 is smaller than the voltage V1 of the first voltage V1, the sense voltage V2 represented by the above equation and the voltage V1
_{When CE} is higher than the voltage V1 of the constant voltage diode ZD1, the current is limited by the sense voltage V2 shown in the above equation. The latter is larger (>) between the sense voltage V2 shown by the equation and the sense voltage V2 shown by the equation (>), and the collector current limiting operation of the IGBT is controlled by matching the sense voltage with the collector-emitter voltage characteristics of the IGBT. It is possible to obtain characteristics that do not depend on the inter-voltage. Although the current limiting operation has been described above, even when the overcurrent is stopped using the sense voltage,
The same can be realized by using a circuit that operates as a gate stop signal instead of T2 and transistor T7 that reduce the gate voltage.

Next, an example of a normal IGBT overcurrent protection circuit without a built-in sense IGBT will be described below. FIG. 5 is a circuit diagram showing the first embodiment in such a case. The same parts as those in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted. The difference from FIG.
An emitter and a base of the transistor T11 are connected between a gate of the GBT1 and a positive terminal of the gate driving DC power supply 20 via a series circuit of an input element (such as a light emitting diode) of the photocoupler P2 and a resistor R13. The collector of T11 is connected to IGB via a resistor R14.
It is connected to the emitter of T1 and the DC current detector 30 as shown in FIG. 10 is omitted.

In such a circuit, the photocoupler P1 is turned on and off by the control circuit 10 so that the circuit shown in FIG.
The IGBT 1 can be turned on and off in the same manner as in the conventional example. Since the gate voltage of the IGBT 1 at this time is lower than the voltage of the DC power supply 20 for driving the gate, no base current flows through the emitter / base of the transistor T11, and the transistor T11 remains off. By the way, if an overcurrent flows due to a short circuit accident or the like when the IGBT 1 is on, the collector-emitter voltage of the IGBT 1 sharply rises, and the gate-emitter capacitance C _GE is charged via the parasitic capacitance C _CG , and the gate voltage Rises. When this gate voltage becomes higher than the voltage of the gate driving DC power supply 20, current flows through the emitter of the transistor T11, the same base, the input element of the photocoupler P2, and the resistor R13, and the transistor T11 is turned on. Further, when this current flows, an overcurrent signal is transmitted from the input element of the photocoupler P2 to the control circuit 10 via the output element (such as a phototransistor), and the IGBT 1 can be turned off by the overcurrent signal. further,
When the transistor T11 is turned on, the charge stored in the gate of the IGBT1 is changed from the transistor T11 to the resistor R1.
As a result, the gate voltage decreases and the limiting current decreases, so that the short-circuit withstand capability of the IGBT 1 can be increased. Therefore, even if the circuit is turned off more slowly than the conventional circuit, it is possible to protect the overcurrent without breaking the IGBT.

FIG. 6 is a circuit diagram showing a second embodiment for a normal IGBT. This is a modification of FIG. 5, and instead of omitting the resistor R14 from the one shown in FIG. 5, a series circuit of a constant voltage diode ZD2 and a capacitor C2 is connected in parallel with the gate driving DC power supply 20. , The constant voltage diode ZD2 and the capacitor C2.
Is connected to the collector of the transistor T11 at the connection point with. The operation is almost the same as that of FIG. 5, but when the transistor T11 is turned on in an overcurrent state, the gate voltage is instantly clamped to the voltage of the capacitor C2, and the reduction of the limiting current is fast, so that the short-circuit withstand capability is further increased. Benefits are obtained.

FIG. 7 is a circuit diagram showing a third embodiment for a normal IGBT. The difference from FIG.
10, R13, R14 and the transistor T11 are omitted, a resistor R15 is connected in series with the transistor T8, a resistor R16 is connected in series with the transistor T9, a diode D3 is connected in parallel with the transistor T8, and an input terminal of the comparator COM2 is provided at both ends of the resistor R15. And the output of the comparator COM2 is connected to the input element of the photocoupler P2 and the base of the transistor T12 via the resistor R18, and a series circuit of the transistor T12 and the resistor R17 is connected between the gate and the emitter of the IGBT1. It is composed. In such a circuit, by turning on and off the photocoupler P1 by the control circuit 10, the IGBT1 can be turned on and off as in the conventional case. In FIG. 5, the gate is charged / discharged via the resistor R10. Here, charging is performed via the resistor R15 and discharging is performed via the resistor R16.
And is divided into a resistance for ON and a resistance for OFF.

Here, when an overcurrent flows due to a short circuit accident or the like while the IGBT 1 is on, the collector-emitter voltage rises sharply, the gate-emitter capacitance _CGE is charged via the parasitic capacitance _CCG , and the gate voltage rises. Rises. And
When this gate voltage becomes larger than the voltage of the gate driving DC power supply 20, a current flows through the diode D3 → the resistor R15. In addition, when this current flows, the resistance R1
The potential of the gate 5 becomes higher on the gate side, and the comparator COM2
Is set to a high level. When the output voltage of the comparator COM2 becomes high, a current flows from the photocoupler P2 to the resistor R18 to the base of the transistor T12, and the transistor T12 is turned on. In addition, when this current flows, an overcurrent state is detected by the photocoupler P2.
The IGBT 1 can be turned off by the overcurrent signal. Further, when the transistor T12 is turned on, the charge stored in the gate of the IGBT1 is changed from the resistance R17 to the transistor T12.
As a result, the gate voltage decreases and the limiting current also decreases, so that the short-circuit withstand capability of the IGBT 1 can be increased. Therefore, also in this circuit, overcurrent protection can be achieved without breaking the IGBT even if the circuit is turned off more slowly than the conventional circuit. The transistor T1
By connecting a capacitor (voltage source) between the emitter of the IGBT 1 and the emitter of the IGBT 1, the gate voltage can be instantaneously clamped to the capacitor voltage as in the case of FIG. It is possible to further increase the withstand amount.

[0028]

【The invention's effect】

 1) Forming a sense IGBT in the main IGBT chip
In the conventional circuit, the collector / emitter of the main IGBT is used.
Voltage V_CEThe current limit varies with the _CEIs small
The IGBT has a large current limit,
The problem is that there is a risk of deviating
However, according to the present invention, the collector of the sense voltage
To eliminate the dependence on the emitter voltage
The following effects can be expected. (B) V_CECurrent limit does not increase even when
Therefore, always operate within the safe operation area of IGBT
And the reliability of the conversion device is improved. (B) Current limit is applied V_CEFrom small to large
The current limit does not change even when the power supply enters
No wiring is required between the IGBT and snubber as in the conventional circuit.
There is no phenomenon that large voltage is applied by the conductance
Become. In general, the safe operation area of an IGBT has a large voltage.
The allowable current value decreases when the voltage increases, but a large voltage is applied.
IGBT operation in the safe operating area
You can enter. Therefore, the reliability of the converter
improves.

2) Normal IG without sense IGBT
In the case of overcurrent protection of a BT, an expensive and large-sized DC current detector was conventionally required, but according to the present invention, the following effects can be expected. (A) Since it can be composed of a transistor, a resistor, a photocoupler, and the like, which are small enough to allow the gate current of the IGBT to flow, the device can be reduced in size and cost. (B) In the event of an overcurrent, the gate voltage is automatically reduced and the current limit is kept small, thereby increasing the short-circuit withstand capability.
The element is less likely to be broken, and the reliability of the device is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a first embodiment of overcurrent protection using a normal IGBT.

FIG. 6 is a circuit diagram showing a first modification of FIG.

FIG. 7 is a circuit diagram showing a second modification of FIG. 5;

FIG. 8 is a circuit diagram showing a conventional example.

9 is an explanatory diagram of the sense circuit and the sense voltage characteristics of FIG.

FIG. 10 is a circuit diagram showing a conventional example of overcurrent protection in a normal IGBT.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... IGBT, 2 ... Gate drive circuit, 10 ... Control circuit,
11: Main IGBT, 12: Sense IGBT, 20 ...
DC power supply, 30 DC current detector, T1 to T3 MOS
FET, T4 to T12: transistor, D1 to D3: diode, R1 to R18, Rg, Rs, Rs1, Rs2
... Resistors, C1, C2, capacitors, ZD1, 2, constant voltage diodes, COM1, 2, comparators, P1, 2, photocouplers.

Claims (7)

[Claims] 1. A sense IGB in a main IGBT chip.
T, an overcurrent protection circuit for equivalently detecting the current of the main IGBT from the current flowing through the sense IGBT and limiting and protecting the collector current of the main IGBT. A MOSFET between the emitter, a gate of the main IGBT via a resistor at a gate of the MOSFET, and
A collector terminal of the main IGBT is connected to a gate of the MOSFET via a diode, and a drain-source voltage of the MOSFET is connected to the main IGBT.
An overcurrent protection circuit characterized by detecting as an equivalent current of 2. A MOSF in place of said MOSFET.
2. The overcurrent protection circuit according to claim 1, wherein a series circuit including an ET and a resistor and a circuit in which the resistor is connected in parallel to the series circuit are connected. 3. A sense IGBT in a main IGBT chip.
T, a sense resistor is connected between the emitter of the sense IGBT and the emitter of the main IGBT, and when the sense voltage exceeds a certain set value, the main I
An overcurrent protection circuit for lowering a gate voltage of a GBT and limiting a collector current thereof for protection, comprising: a series circuit in which a plurality of resistors are connected in series; and a first switch for short-circuiting one of the resistors when operated. The circuit and the input side are connected to the gate terminal of the main IGBT via a resistor and connected to the collector terminal of the main IGBT via a diode, and when a voltage of a certain fixed value or more is applied to the input, A voltage setting circuit including a second switch circuit that operates the first switch circuit, a comparison circuit that compares the voltage setting value with the sense voltage, and a second circuit that reduces the gate voltage of the main IGBT according to the result. An overcurrent protection circuit, comprising: a switching circuit according to claim 3. 4. The overcurrent protection circuit according to claim 3, wherein a voltage from another DC power supply is used as a power supply of the voltage setting circuit instead of a gate voltage of the main IGBT. 5. An overcurrent protection circuit for preventing an IGBT from being destroyed by overcurrent, wherein a voltage between a gate and an emitter of the IGBT is lower than the DC power supply voltage between a gate of the IGBT and a positive terminal of a DC power supply for gate drive. An overcurrent protection, wherein an emitter and a base of a transistor are connected via an input element of a photocoupler and a collector of the transistor is connected to an emitter of the IGBT via a resistor so that the transistor is turned on when it rises. circuit. 6. An overcurrent protection circuit for preventing an IGBT from being destroyed by an overcurrent, wherein the IGBT is connected between an ON gate resistor of the IGBT.
When a current flows from the gate to the DC power supply for driving the gate, a comparator whose output voltage becomes high is connected, and the output of this comparator is connected to the output of the transistor through the input element of the photocoupler. An overcurrent protection circuit, wherein a base is connected, and a collector and an emitter of the transistor are connected between a gate and an emitter of the IGBT via a resistor. 7. The overcurrent protection circuit according to claim 5, wherein a voltage source lower in voltage than the gate drive DC power supply is connected instead of the resistor.