JPH05161342A - Driving circuit for voltage driving semiconductor element - Google Patents

Abstract

PURPOSE:To lighten he stress of an element by equipping it with a means, which charges the capacitor of a variable voltage source quickly after an overcurrent detecting means detects normal ON condition at the time turning on a voltage driving semiconductor element. CONSTITUTION:In the case turning on operation of an IGBT element Q1, when a photocoupler PH1 is turned on, a transistor T1 is turned off, and an output transistor T2 is turned on, and T3 is turned off, and ON gate voltage V1 is applied between the gate and the emitter of an IGBTQ1, and Q1 starts to turn on. At this time, T11 and T20 are also turned off together with the transistor T1, so a Zener diode ZD1 becomes ON through a resistor R11 by the OFF of the transistor T11, and transistors T21 and T4 are turned on. And, when it detects that the collector voltage of the element Q1 has dropped to normal turn off voltage after start of the turn off, the gate voltage is established and turn off is ensured by immediately charging the capacitor C2 of an overcurrent soft breaking circuit quickly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to an IGBT and a power M.
The present invention relates to a drive circuit for a voltage-driven semiconductor element such as an OSFET, and more particularly to a drive circuit having a function of protecting an element from an overcurrent that occurs in a power converter such as an inverter when a short circuit accident occurs. In the following figures, the same reference numerals indicate the same or corresponding parts.

[0002]

2. Description of the Related Art Here, as a voltage drive type semiconductor device,
An IGBT will be described as an example. In the power converter,
Among overcurrent faults during operation, load short circuits and ground faults are faults that lead to element destruction. FIG. 5 is an explanatory diagram of the basic operation of the overcurrent protection circuit at the time of this short circuit accident. FIG. 5 (A) shows a circuit simulating this short circuit accident, and FIG. 5 (B) shows the IGBT element Q1 at that time. The voltage and current waveforms of As shown in this figure, the short-circuit period (that is, FIG.
During the period (between time points t0 to t1), the short circuit current Ic flows while the DC circuit voltage Ed is applied to the IGBT Q1. This short-circuit current Ic reaches the DC rating 4 to 5 times (about 10 times for a high breakdown voltage element) of the element Q1. Therefore, a very large electric power is applied to the device during the short circuit period. Therefore, in order to protect the short circuit without the occurrence of overvoltage, the period (10 μs) during which the device Q1 can withstand this short circuit state.
It is necessary to gently turn off the gate and softly cut off the current Ic as shown by the solid curve in FIG.

FIG. 6 shows a conventional example of a drive circuit having a built-in overcurrent protection function (that is, a soft shutoff function) for the element Q1.
A detailed description of this circuit is filed by the applicant of the present application.
No. 183209, it will be briefly described here. In this figure, Q1 is an IGBT of the main switching element, PH1 is a photo-isolating photocoupler, and V1 and V2 are an on-gate voltage applying voltage source and an off-gate voltage applying voltage source, respectively. Next, the normal operation of FIG. 6 will be described first. Drive signal VDR for turning on the element Q1
When the photocoupler PH1 is turned on based on, the transistor T1 is turned off, and as a result, the output transistor T2 is turned on and the output transistor T3 is turned off.
An on-gate voltage V1 is applied between the gate and emitter of TQ1 via a gate resistor RG. At this time, since the transistor T11 is turned off, the base current tends to flow to the transistor T4 via the resistor R11 and the Zener diode ZD1. However, the provision of the capacitor C1 delays the timing at which the transistor T4 operates.

When an on-gate voltage is applied between the gate and emitter of the IGBT Q1, Q1 turns on, the collector-emitter voltage of Q1 decreases to an on voltage (V _{CE (ON)),} and at the same time, the positive electrode of the capacitor C1. The terminal (that is, the cathode terminal of the Zener diode ZD1) is the diode D
1 is pulled to the collector potential side when the IGBT Q1 is turned on. In this case, in FIG. 6, V _ZD1 + V _{BE (T4)} > V2 + V _{CE (ON)} + V _{F (D1)} where V _ZD1 : Zener voltage of Zener diode ZD1 V _{BE (T4)} : V _BE V _{F (D1) of} transistor T4. : By selecting and placing the components so that the forward voltage of the diode D1 can be achieved, the IGBT
When Q1 is on, the zener diode ZD1 does not conduct and keeps the transistor T4 off.

Next, a drive signal VDR for turning off the element Q1
When the photocoupler PH1 is turned off based on, the transistor T1 turns on, which causes the output transistor T2 to turn on.
Is off, T3 is on, and the gate of IGBT Q1
The off-gate voltage V2 is applied between the emitters via the resistor RG, and Q1 is turned off. At this time, the transistor T1
When turned on, the electric charge of the capacitor C1 is discharged to prepare for the next turn-on operation.

When a short circuit accident occurs during the ON period of the IGBT Q1, the collector-emitter voltage increases. V _ZD1 + V _{BE (T4)} <V2 + V _{CE (ON)} + VF _(D1) , the Zener diode ZD1, and therefore the transistor T4 becomes conductive, and the off-gate voltage V2 slowly established between the gate and emitter of the IGBT Q1 is applied to Q1. Is turned off to shut off the overcurrent. At this time, the gate-emitter voltage of the IGBT Q1 (hereinafter also abbreviated as gate voltage) V _GE
Unlike the normal turn-off operation, as shown by the solid waveform after time t1 in FIG. 5B, it gradually decreases with time depending on the voltage of the capacitor C2 as the variable voltage source. As a result, the rate of decrease of the collector current Ic also decreases, and the jumping voltage V _CEP of V _CE at the time of current interruption can be suppressed. The broken line in FIG. 5B shows the operation waveform when the off-gate voltage V2 is directly applied to the element Q1 to shut off the overcurrent.

In FIG. 6, for convenience, the Zener diode ZD1 is also referred to as an overcurrent detecting Zener diode, and a circuit composed of a capacitor C2 as a variable voltage source, a resistor R2, a resistor R3 and a transistor T4 is also called an overcurrent soft cutoff circuit. Call. Further, the delay circuit including the capacitor C1, the resistor R11 and the like, when the element Q1 is turned on, does not turn on the transistor T4 (that is, does not operate the soft shutoff circuit) until the turn-on is completed, and tries to ensure the turn-on of the element Q1. Therefore, the delay circuit is also called a turn-on confirmation timer.

[0008]

However, the overcurrent protection in the gate drive circuit of FIG. 6 has the following problems. (1) Since there is a turn-on confirmation timer (delay due to the capacitor C1), the protection operation does not work during the timer period (until t = t1 in FIG. 5), and after t = t1, V _GE begins to decrease and the cutoff operation starts. Therefore, excessive stress is applied to the element Q1.

That is, the time setting of the turn-on confirmation timer is determined by the turn-on operation of the inverter circuit shown in FIG. It should be noted that FIG. 1A is a configuration diagram of the main circuit of the inverter,
FIG. 3B shows operation waveforms when the IGBT is turned on. Further, in the same figure (A), C0 is a DC power source E
smoothing capacitor that constitutes d, Q1 (Q11 to Q16)
Is an IGBT, D0 that constitutes a three-phase bridge inverter
(D01 to D06) are freewheeling diodes connected in parallel with the respective IGBTs Q11 to Q16. As shown in FIG. 7B, when the IGBT Q1 is turned on, its collector-emitter voltage V _CE sharply decreases with reverse recovery of the freewheeling diode D0 of the series arm, and finally reaches a saturation voltage. At this time, as shown in the figure, the rate of voltage drop becomes slower as the voltage becomes lower, so the turn-on time from time t11 to time t12 becomes relatively long. Therefore, it is necessary to set the turn-on confirmation timer time described above to be relatively long. For this reason, in the conventional gate drive circuit, the IGBT element is stressed more than necessary during the overcurrent protection operation.

(2) There is a problem that the overcurrent protection operation does not work effectively in the event of a short circuit of the inverter. Next, this problem will be described with reference to FIG. Here, FIG. 8A shows the IG
The relationship between the basic configuration of the control circuit side of BTQ1 and each operation signal is shown. FIG. 1B shows I when the pulse width of the drive signal VDR given from the control circuit to the gate drive circuit is wide.
The operation waveform of GBT is shown in FIG.
The operation waveforms when the pulse width of R is narrow are shown respectively.

Depending on the pulse width of the drive signal VDR given to the gate drive circuit 1 from the PWM control circuit 2 of FIG. 8 (A) and the timing of a short circuit accident, the soft cutoff for slowly lowering the gate voltage V _GE may not function. ..
That is, as shown in FIG. 6B, the pulse width of the drive signal VDR is wide, and after the short circuit occurs, until the overcurrent is completely cut off (TW period), when the signal VDR does not disappear, the soft cutoff functions and the IGBT element Q1 Can be safely turned off. On the other hand, when the drive signal VDR disappears during the TW period as shown in FIG. 6C, the gate voltage V _GE rapidly changes like a normal turn-off, and the soft cutoff does not function. Thus, when 1) the pulse width of the drive signal VDR is narrow, and 2) when the OFF signal is input to the element immediately after the element is short-circuited, the soft cutoff does not work and the IGBT element Q1 cannot be safely turned off. was there. Therefore, it is an object of the present invention to provide a drive circuit for a voltage drive type semiconductor device that can solve the above problems.

[0012]

In order to solve the above-mentioned problems, a drive circuit for a voltage-driven semiconductor device according to claim 1 is
A signal isolating photocoupler (PH1 and the like) that is turned on and off by a drive signal from the control circuit and a base commonly driven through this photocoupler (and transistor T1 and the like) to reverse the on and off operations. Whether or not the forward voltage drop of the pair of output transistors (T2, T3, etc.) for driving the voltage-driven semiconductor element on and off and the voltage-driven semiconductor element in the on state exceeds a predetermined value. In accordance with the above, the overcurrent detection means (transistor T
11, overcurrent detection zener diode ZD1, diode D1, etc.), and the capacitor (C2, etc.) as a variable voltage source is gradually discharged based on the determination of the overcurrent abnormal state of the overcurrent detection means. A voltage-driven semiconductor device having overcurrent protection means (transistor T4, resistor R2, diode D2, etc.) for preferentially driving the bases of a pair of output transistors and gradually decreasing the gate voltage of the voltage-driven semiconductor device. In the driving circuit of (1), when the voltage-driven semiconductor element is turned on, a means for rapidly charging the capacitor of the variable voltage source after the overcurrent detection means determines the normal ON state (as the charging time shortening circuit 20). Transistors T21, T22, etc.).

According to a second aspect of the present invention, there is provided a drive circuit for a voltage-driven semiconductor element according to the first aspect, wherein at least the overcurrent detection means determines the abnormal state of the overcurrent. During the period, an ON signal fixing means (transistor T30 in the photocoupler output fixing circuit 30, capacitor C30, etc.) for fixing the output signal of the signal insulating photocoupler to a signal for turning on the semiconductor element is provided. To do.

According to a third aspect of the present invention, there is provided a drive circuit for a voltage-driven semiconductor element according to the second aspect, wherein in the drive circuit for a voltage-driven semiconductor element according to the second aspect, after the overcurrent detection means determines the overcurrent abnormal state, Means for canceling the signal fixing operation of the ON signal fixing means (transistor T31, C31 in the photocoupler output fixing circuit 30, etc.) at least after a lapse of a predetermined time that can be regarded as completion of the gate voltage drop of the voltage driven semiconductor ).

According to a fourth aspect of the present invention, there is provided a voltage driving type semiconductor element driving circuit according to any one of the first to third aspects, wherein the overcurrent abnormal state occurs in the semiconductor element. It is assumed that a means (a transistor T100 or the like) for bypassing the displacement current to be bypassed from the gate of the semiconductor element to the capacitor of the variable voltage source is provided.

[0016]

When the IGBT element Q1 is turned on, it is detected through the overcurrent detection zener diode ZD1 that the collector voltage of Q1 has dropped to a normal turn-on voltage, and the variable voltage source forming the overcurrent soft cutoff circuit is detected. A circuit (charging time shortening circuit) 20 for rapidly charging the capacitor C2 as described above is provided to eliminate the turn-on confirmation timer or shorten the timer time to such a degree that stress is not applied to the IGBT element at the time of short circuit. If there is no turn-on confirmation timer, the collector-emitter voltage V _CE when the element Q1 is turned on is V _ZD1 + V _{BE (T4)} > V2 + V _{CE (ON)} + V _{F (D1)} Zener diode ZD1, and hence transistor T4, is turned on during the period
Since the capacitor C2 as a variable voltage source is discharged through the resistor R2, the gate voltage V _GE of the element Q1 gradually decreases with the on-gate voltage V1 as an initial value, and V _CE becomes the relationship of the above expression. At that time, the resistor R3 is short-circuited to minimize the charging time. This ensures the normal turn-on of the element Q1, minimizes the delay of the soft shutoff operation during the overcurrent protection of the element Q1, and reduces the stress of the element Q1.

Further, a circuit for fixing the output signal of the photocoupler PH1 to a signal for turning on the voltage-driven semiconductor element Q1 is provided only for a predetermined period when a short-circuit fault is detected. That is, when the element Q1 has a short-circuit failure, the change in the drive signal VDR (the instruction to turn off the element Q1) is not accepted and the element Q1
The soft shutoff of is prevented from being interrupted rapidly, and the IGBT element is safely protected from overcurrent without generating overvoltage regardless of the pulse width of the drive signal VDR or the timing of occurrence of a short-circuit fault. To

[0018]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram as an embodiment of the invention according to claim 1 and corresponds to FIG. In the figure, the difference from FIG. 6 is that the capacitor C1 that gives a delay time for confirming the turn-on of the IGBT element Q1 is omitted, and instead the normal turn-on operation of Q1 is confirmed and then the capacitor C2 of the variable voltage source is confirmed. Transistors T20 and T2 as a circuit 20 for shortening the charging time of
1, T22 and resistor R20 are attached. The operation at the time of normal switching other than the added circuit 20 is performed by the transistor T1 that receives the signal of the photocoupler PH1 and the transistors T2 and T3 connected to it, as in the conventional example.

FIG. 2 is a time chart when the IGBT Q1 is turned on for explaining the operation of the charging time shortening circuit 20 of FIG.
IGBT-Q1 gate-emitter voltage (gate voltage)
V _GE is the collector-emitter voltage V _CE of Q1, respectively. First, the case of the turn-on operation of the IGBT Q1 will be described. When the photocoupler PH1 is turned on at t = 0, the transistor T1 is turned off, the output transistor T2 is turned on and the transistor T3 is turned off as described above, and the on-gate voltage V1 is applied between the gate and emitter of the IGBT Q1 and Q1 is Turn on starts.

At this time, the transistor T1 and T1
1 and T20 are also turned off. Therefore, depending on the turning off of the transistor T11, the Zener diode ZD1 may be connected via the resistor R11.
Is turned on, and the transistors T21 and T4 are turned on. When the transistor T20 is turned off, the transistor T22 tries to turn on via the resistor R20. On the other hand, since the transistor T21 is turned on, the transistor T22 remains off and the resistor R3 is not short-circuited. On the other hand, based on the turn-on of the transistor T4, the capacitor C2, which has been charged to the voltage (V1 + V2) until now, starts to gently discharge via the resistor R2, and thus the IGBT
The gate-emitter voltage V _GE of Q1 begins to fall.

In this way, the turn-on of the IGBT Q1 proceeds, and during the period until t = t20, the collector-emitter voltage V _CE of the IGBT Q1 is V _ZD1 + V _{BE (T4)} <V2 + V _{CE (ON)} + V _{F (D1 ) Due to} the relationship of (1), the transistor T21 turns on and the resistor R3
The transistor T22 which short-circuits is off. Next, after t = t20, V _CE becomes V _ZD1 + V _{BE (T4)} > V2 + V _{CE (ON)} + V _{F (D1)} (2), and T21 is turned off and T22 is turned on.
Is short-circuited at T22, and the capacitor C2 is charged suddenly. At the same time, the gate voltage V _GE changes to the on-gate voltage V1.
Then, the turn-on of the IGBT Q1 is secured.

At the time of failure, V _CE has the relation of equation (1), and T _CE
22 is turned off, the gate voltage continues to decrease as shown by the broken line portion of the gate voltage waveform V _{GE in} FIG.
Q1 is gently turned off.

When the IGBT Q1 is turned off, the photocoupler PH1 is off and T20 is on, so T22 is off. Therefore, the short circuit of the resistor R3 is released.

As described above, the turn-on gate voltage waveform V _GE shown in FIG. 2 temporarily decreases from this value with the on-gate voltage V1 as the initial value. But during this time,
As the turn-on of the IGBT element Q1 progresses, the charging time shortening circuit 20 of the present invention will soon operate and the IGBT
Since the on-gate voltage V1 is applied between the gate and the emitter of Q1, the charging time shortening circuit 20 does not interfere with the normal turn-on operation of Q1. However, when Q1 is turned on, the on-gate voltage V1 is more surely set to the initial value Q1.
In order to supply the voltage to the transistor T3, a transistor T3 having a switching speed faster than those of T4 and T21 is selected.
A capacitor may be attached to the cathode terminal of the Zener diode ZD1 as a timer that does not cause stress on the GBT element Q1.

FIG. 3 shows an embodiment of the invention according to claims 2 and 3, which is the same as the circuit shown in FIG.
A photocoupler output fixing circuit 30 including T31 and capacitors C30 and C31 is added. This circuit 3
When 0 causes a short-circuit accident in the IGBT Q1 and the protection function is operating as in the case of FIG. 1, the output of the photocoupler PH1 is fixed (to a signal that turns on Q1) without accepting changes in the drive signal VDR. It is a circuit for doing.

Next, the operation of the photo coupler output fixing circuit 30 will be described. At the start of turn-on of the IGBT Q1, the photo coupler PH1 is turned on and the transistor T11 is turned on.
When turned off, the Zener diode ZD1 from the resistor R11
Although the base current tries to flow through the transistors T30 and T31 via the capacitor, capacitors C30 and C31 are provided to delay the turn-on timing of the transistors T30 and T31. The capacitor C30 is set by the IGBT element Q
Transistor T30 until time 1 is fully turned on
Make sure that the on-time is delayed. If the transistor T30 is turned on in such a circuit, it means that a short-circuit accident has occurred in the IGBT element Q1. Then, when the transistor T30 is turned on, the output of the photocoupler PH1 becomes the same as when the photocoupler PH1 is turned on. Therefore, the drive signal VDR changes in this state, and the photocoupler PH1
The output does not change even when is turned off. That is, element Q1
It is prevented that the soft shutoff operation is interrupted by the OFF command of the drive signal VDR to perform the quick shutoff.

Next, the capacitor C31 is set so that the turning on of the transistor T31 is delayed until the overcurrent protection operation is completed. Therefore, when the transistor T31 is turned on, the base and emitter of the transistor T30 are short-circuited, and the transistor T30 is turned off. When the transistor T30 is turned off in this way, the output of the photocoupler PH1 depends on the drive signal VDR. That is, the circuit 30 that fixes the output of the photocoupler PH1 is reset. As a result, the element Q1 can immediately resume normal operation after the end of the overcurrent protection operation.

FIG. 4 shows an embodiment of the invention according to claim 4, which is the same as the circuit shown in FIG.
And a transistor T100 as a displacement current bypass means for connecting the gate G of the IGBT Q1 and the IGBT Q1. Although the transistor T100 is used in FIG. 4, a diode can also be used. This transistor T100 is used when the IGBT element Q1 is short-circuited.
Element Q1 as the collector-emitter voltage V _CE rises
Of the gate voltage V _GE of the element Q1 due to the current (displacement current) flowing through the junction capacitance of the element Q1 (in other words, the element Q1
Of the gate G of the capacitor C2 above the potential on the positive electrode side of the capacitor C2) and has an effect of accelerating the turn-off of the element Q1.

[0029]

According to the invention of claim 1, the delay timer for confirming the turn-on, which is conventionally provided to prevent the overcurrent soft cutoff circuit from working at the turn-on of the IGBT Q1, is eliminated or its delay time is eliminated. Is set to an extremely small value, and instead of this, when it is detected that the collector potential of the element Q1 has dropped to a normal turn-on potential after the turn-on is started by the zener diode ZD1 for overcurrent detection, the variable voltage source of the overcurrent soft cutoff circuit is immediately detected. Since the capacitor C2 as a component is rapidly charged to establish the gate voltage of Q1 and the turn-on of the element Q1 is ensured, an overcurrent based on the existence of the conventional turn-on confirmation timer can be achieved without adding a large circuit. Reliable element Q1 while reducing the excessive stress of element Q1 during current protection.
Can be protected from overcurrent.

Further, according to the invention of claim 2, the output of the photocoupler PH1 is fixed to a state where the element Q1 should be turned on at least during the overcurrent protection operation.
It is possible to prevent the soft cutoff circuit from being reset during the overcurrent protection operation period to generate an overvoltage due to the rapid cutoff of the element Q1.

According to the invention of claim 3, after the overcurrent protection operation, the fixed output of the photocoupler PH1 in the invention of claim 2 is released, so that the normal operation of the element Q1 is promptly performed. It can be restarted.

According to the fourth aspect of the invention, during the overcurrent protection operation, the displacement current generated in the element Q1 is bypassed to the capacitor C2 side of the variable voltage source to prevent the gate voltage of the element Q1 from rising. Therefore, the turn-off of Q1 can be accelerated.

[Brief description of drawings]

FIG. 1 is a circuit diagram as an embodiment of the invention according to claim 1.

FIG. 2 is a time chart for explaining an operation of main parts of FIG.

FIG. 3 is a circuit diagram as an embodiment of the invention relating to claims 2 and 3.

FIG. 4 is a circuit diagram as an embodiment of the invention according to claim 4;

FIG. 5 is an explanatory diagram of a basic operation of an overcurrent protection circuit.

6 is a conventional circuit diagram corresponding to FIG.

FIG. 7 is a diagram showing a main circuit configuration of an inverter and an operation waveform when the IGBT is turned on.

FIG. 8 is an explanatory diagram of an overcurrent protection operation at the time of a short circuit accident in the IGBT inverter.

[Explanation of symbols]

 Q1 IGBT VDR drive signal PH1 photo coupler T1 transistor T2 output transistor T3 output transistor T4 transistor T11 transistor T20 transistor T21 transistor T22 transistor T30 transistor T31 transistor T100 displacement current bypass means (transistor) ZD1 overcurrent detection Zener diode D R1 diode D1 Gate resistance R1 resistance R2 resistance R3 resistance R5 resistance R11 resistance R20 resistance C2 capacitor C30 capacitor C31 capacitor V1 on-gate voltage (source) V2 off-gate voltage (source) 20 charging time reduction circuit 30 photocoupler output fixed circuit

Claims (4)

[Claims] 1. A photocoupler for signal insulation which is turned on and off by a drive signal from a control circuit, and a base which is commonly driven via the photocoupler to perform reverse on and off operations, and voltage drive. Pair of output transistors for driving the ON-OFF type semiconductor element and the forward voltage drop of the voltage-driven type semiconductor element in the ON state,
Overcurrent detection means for determining whether the semiconductor element is in an overcurrent abnormal state or a normal ON state according to whether or not the predetermined value is exceeded, and based on the determination of the overcurrent abnormal state of the overcurrent detection means. And gradually discharge the capacitor as the variable voltage source to preferentially drive the bases of the pair of output transistors,
In a drive circuit for a voltage-driven semiconductor device, which comprises an overcurrent protection unit for gradually lowering the gate voltage of the voltage-driven semiconductor device, the overcurrent detection unit is configured to operate normally when the voltage-driven semiconductor device is turned on. A drive circuit for a voltage-driven semiconductor element, comprising means for rapidly charging a capacitor of the variable voltage source after determining a different ON state. 2. The drive circuit for a voltage-driven semiconductor element according to claim 1, wherein the output signal of the signal-insulating photocoupler is output at least during a period when the overcurrent detection means determines the abnormal state of the overcurrent. A drive circuit for a voltage-driven semiconductor element, comprising an ON signal fixing means for fixing the semiconductor element to a signal to be turned ON. 3. The drive circuit for a voltage-driven semiconductor element according to claim 2, wherein at least the gate voltage of the voltage-driven semiconductor element is completed after the overcurrent detection means determines the abnormal state of the overcurrent. A drive circuit for a voltage-driven semiconductor device, comprising means for releasing the signal fixing operation of the ON signal fixing means after a lapse of a predetermined time which can be regarded as 4. The drive circuit for a voltage-driven semiconductor element according to claim 1, wherein a displacement current generated in the semiconductor element in the abnormal overcurrent state is supplied to the variable voltage from a gate of the semiconductor element. A drive circuit for a voltage-driven semiconductor device, characterized in that it comprises means for bypassing to a source capacitor.