JPH0756937B2 - Insulated gate element drive circuit - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention refers to an insulated gate element used for switching a main circuit in a power conversion device such as a motor control inverter device (that is, an element such as a power MOSFET that is turned on and off depending on the presence or absence of a gate applied voltage. An IGBT is a typical example of the insulated gate device of (1), and is therefore also referred to as an IGBT hereinafter).
The present invention relates to a drive circuit having a high noise margin function of limiting a short-circuit current (element current) when a main circuit is short-circuited. In the drawings below, the same reference numerals indicate the same or corresponding parts. Further, logic or levels High and Low are simply described as "H" and "L".

[Prior art]

FIG. 5 shows a conventional drive circuit of this type having a gate voltage cutoff function of an IGBT. In the figure, 1 is an IGBT inserted in the main circuit, 44 is a drive circuit that drives the gate of this IGBT1 to repeatedly interrupt the IGBT1, and 42 is the main circuit current of this IGBT.
It is a current tolerance for detecting iO. Reference numeral 43 denotes a comparison circuit, which has a role of turning on the IGBT 1 through the drive circuit 44 when the main circuit current iO detected through the current transformer 42 exceeds a predetermined value. Thus, in the conventional technology, the main circuit current iO
The main circuit short circuit protection was done by how quickly the gate voltage that drives the IGBT1 is turned off when the current flows as a short circuit current.

[Problems to be Solved by the Invention]

However, in the main circuit short circuit protection method as described above, the operation of the comparison circuit 43 and the drive circuit 44 must be speeded up,
On the other hand, such a circuit is apt to malfunction due to noise. Therefore, an object of the present invention is to suppress an excessive current flowing in the IGBT at the time of load short-circuiting by lowering the gate voltage of the insulated gate element, and thereby an IGBT drive circuit having a function of prolonging the time until the IGBT is destroyed. To provide a peripheral control circuit that is strong against noise and does not have to be so fast. Therefore, for example, when the load is short-circuited, the gate voltage of the IGBT may be turned off by the peripheral control circuit resistant to this noise. Furthermore, it also prevents erroneous turn-on when the IGBT is off.

[Means for Solving the Problems]

The means taken by the present invention to achieve the above-mentioned object are:
A control circuit (such as a gate G) and first and second main terminals (such as an emitter E and a collector C) are provided, and a drive circuit (auxiliary transistor 8) is provided between the control terminal and the first main terminal. , 9 etc.) (based on the gate drive power supply 10 etc.) when a drive voltage (gate voltage eg etc.) is applied, the first and second main terminals become conductive, and when the drive voltage is cut off, the main In a drive circuit for an insulated gate element (IGBT1, etc.) that has a blocking state between terminals, voltage detection means (voltage divider resistors 2, 3, etc.) that detects the voltage corresponding to the forward voltage (ecE, etc.) between the main terminals. Is provided in a current path parallel to the current path connecting the main terminals, is provided with a polarity that blocks a drive voltage from the drive circuit, and has a zener voltage lower than the drive voltage (6 or the like). And the drive voltage in the forward direction A circuit including a series circuit of the auxiliary transistor (such as 5) which is connected in parallel to the control terminal and the first main terminal,
Further, the detection voltage of the voltage detecting means is applied to a driving terminal (base B or the like) of the auxiliary transistor, and when the forward voltage between the first and second main terminals exceeds a predetermined value, the auxiliary transistor is turned on. And a reverse bias power supply for applying a reverse bias voltage between the control terminal and the first main terminal when the insulated gate element is turned off. (A reverse bias power supply 11 or the like) is provided between the first main terminal and the auxiliary transistor ”.

[Action]

An overcurrent flows through the insulated gate element when the main circuit is short-circuited, and an excessive forward voltage between the main terminals of the insulated gate element caused by this overcurrent is detected by the voltage detection means, and this detection voltage turns on the auxiliary transistor to insulate it. The drive voltage of the gate element is reduced to suppress overcurrent. At this time, the drive voltage of the insulated gate element is clamped to the Zener voltage of the Zener diode connected in series with the auxiliary transistor. For this reason, the main circuit current of the IGBT is limited and the time until the destruction of the IGBT becomes long, and the main circuit short circuit can be protected even if a gate voltage cutoff circuit that is not so fast, that is, strong against noise is used. Then, when the insulated gate element is turned off, a reverse bias voltage is applied between the gate G and the emitter E, so that erroneous turn-on can be prevented.

【Example】

FIG. 1 to FIG. 4 are circuit diagrams showing the configuration of essential parts as different embodiments of the present invention. 10 in FIG.
Is a DC power supply of, for example, 15V for driving the gate G of the IGBT 1 (hereinafter referred to as a gate drive power supply), 8 and 9 are auxiliary transistors for connecting and disconnecting the voltage of the gate drive power supply 10, eD
Is the drive signal voltage for IGBT1. Under normal conditions, when the drive signal voltage eD is “H”, the auxiliary transistors 8 and 9 are turned off and on, respectively, and the voltage of the gate drive power supply 10 passes through the auxiliary transistor 9 and the resistor 7 to the IGBT.
1 is applied between the gate G and the emitter E, the IGBT1 is turned on, and the main circuit current iO as the collector current is applied between the collector C and the emitter E through the main circuit power supply and the main circuit load (not shown). Flowing. Conversely, when the drive signal voltage eD is "L", the auxiliary transistors 8 and 9 are turned on and off, respectively, and the gate drive power source 10 is disconnected from the gate circuit of the IGBT1 and at the same time, the gate G and the emitter E of the IGBT1. The short circuit is short-circuited via the resistor 7 and the auxiliary transistor 8, and the IGBT 1 is turned off. In this way, the drive signal voltage eD causes the IGBT 1 to be repeatedly connected and disconnected so that the current iO required for the main circuit load flows. By the way, the voltage dividing resistors 2 and 3 inserted between the collector C and the emitter E of the IGBT1 and the gate G and the emitter E of the IGBT1.
The zener diode 6 and the auxiliary transistor 5 which are inserted between the zener diode 6 and the auxiliary transistor 5 are newly added in the present invention in order to protect the main circuit from a short circuit. That is, when the main circuit current iO has a normal value, the collector-emitter voltage ecE of the IGBT 1 is small, and this voltage ecE is divided by the voltage dividing resistors 2 and 3 to obtain a voltage across the resistor 3 and thus the auxiliary transistor. The voltage eBE between the base B and the emitter E of 5 is also sufficiently small, and the auxiliary transistor 5 remains off. As a result, the Zener diode 6 also remains non-conductive, and the IGBT1
The voltage between the gate G and the emitter E (hereinafter abbreviated as gate voltage) eg is not affected by the Zener diode 6 or the like, and the IGBT1 is large enough to be substantially equal to the voltage of the gate drive power supply 10 (about 15V in this example). It is driven by the gate voltage eg, and its collector-emitter voltage ecE can be a sufficiently small value. However, when the main circuit current iO becomes excessive due to the short circuit of the main circuit, the collector-emitter voltage ecE of the IGBT1 also becomes large, so that the base-emitter voltage eBE of the auxiliary transistor 5 also becomes large and this transistor 5 turns on. Switch to the state. As a result, the gate voltage eg of the IGBT 1 is limited to the Zener voltage of the Zener diode 6 (about 7V in this example). As a result, the excessive main circuit current iO of the main circuit is
The gate voltage eg is decreased in proportion to the decrease of the gate voltage eg, and the time until the breakdown of the IGBT1 can be lengthened. Therefore, with the structure shown in FIG. 1, main circuit short-circuit protection can be sufficiently performed even if a gate voltage off circuit that is not very high speed is used. In this way, the gate voltage eg is clamped to the Zener voltage of the Zener diode and the IGBT1 is not turned off completely, but the current limiting function of the IGBT1 itself is used to suppress the excessive main circuit current iO to a low value. Has the following effects. First, if the IGBT1 is turned off when the main circuit current iO becomes excessive due to the main circuit short circuit, the excessive current will be cut off, and a large di / dt will be generated during the cutoff. Due to this large di / dt, the voltage of the main circuit power supply oscillates, and in the case of an inverter circuit or the like, the vibration of the main circuit power supply voltage may cause other IGBTs to be destroyed. By suppressing the excessive main circuit current to a low value as in the present invention, a large di / dt does not occur, and thus the voltage of the main circuit power supply does not oscillate, and other IGBTs are not generated.
There is no risk of adversely affecting the. Next, considering the case where such an insulated gate element is configured as a power module, if the IGBT turns off when the main circuit current is excessive, that is, if the module side cuts off, the drive circuit (input from auxiliary transistors 8 and 9) Side circuit) side protection circuit cannot detect an abnormality and therefore cannot perform a protection operation. Then, since the IGBT is turned off, the drive circuit works to turn it on again despite the abnormal overcurrent, and the repetition causes oscillation. On the other hand, in the present invention, since the main circuit current is suppressed to a low value, the signal indicating that the output of the module is reduced can be obtained by the protection circuit on the drive circuit side. It is possible to perform a protection operation such as outputting. Although the cathode of the Zener diode 6 is connected between the output of the auxiliary transistors 8 and 9 and the gate G of the IGBT in the present invention, the cathode of the Zener diode 6 is connected to the input side of the auxiliary transistors 8 and 9. It is also possible. However, when connected to the input side of the auxiliary transistors 8 and 9,
When the main circuit current iO becomes excessive due to the main circuit short circuit, the auxiliary transistor 5 is turned on, and the drive signal voltage eD is clamped to the Zener voltage, the auxiliary transistor 9 that was on is inverted to off due to the decrease in the potential, and The auxiliary transistor 8 which has been turned off is turned on. This inversion of the auxiliary transistors 8 and 9 turns off the IGBT1. Then, since the IGBT1 is turned off, the IGBT1 is turned on again in spite of the abnormality of the main circuit short circuit, and there is a problem that the IGBT1 eventually becomes the oscillation state. Therefore, it is not preferable to connect the cathode of the Zener diode 6 to the input side of the auxiliary transistors 8 and 9.
It is desirable to connect to the output side of the auxiliary transistors 8 and 9 as in the present invention. Next, FIGS. 2 and 3 show the circuit of FIG. 1 in addition to preventing erroneous turn-on (where v corresponds to the collector-emitter voltage ecE in this example) due to so-called dv / dt when the IGBT1 is off. To prevent this, when the IGBT1 is off (that is, when the auxiliary transistor 8 is on and the auxiliary transistor 9 is off), the IGBT1
Is a circuit example in which a reverse bias power supply 11 is inserted so that a reverse bias voltage (3 to 4 V in this example) is applied between the gate G and the emitter E of the above. In FIG. 2, a reverse bias power source 11 is connected between the collector of the auxiliary transistor 8 and the emitter of the auxiliary transistor 5, and in FIG. 3, the reverse bias power source 11 is connected between the emitter E of the IGBT 1 and the voltage dividing resistor 3. Are connected. The configuration shown in FIG. 3 has the following advantages. That is, in the case of the IGBT 1 having a low threshold voltage, the Zener diode 6 must be made to have a low Zener voltage in accordance with it, but such a Zener diode is a special product and is difficult to obtain. However, when the reverse bias power supply 11 is provided between the emitter E of the IGBT 1 and the auxiliary transistor 8, the Zener voltage of the Zener diode 6 does not need to be lowered because it is reverse biased by the reverse bias power supply 11. That is, even if the IGBT1 has a low threshold voltage, it is not necessary to use a special Zener diode having a low Zener voltage in accordance with it. However, the diode 4 in FIG. 2 is a diode for preventing sneak-in from the reverse bias power source 11 via the auxiliary transistor 5 and the Zener diode 6. Next, FIG. 4 shows an embodiment in which an overcurrent flowing through the IGBT1 is detected by means different from the voltage detecting means shown in FIGS. 1 to 3, and a current corresponding to the current flowing through the IGBT1 is detected by the auxiliary IGBT. Then, using the current detection means, the current flowing through this auxiliary IGBT is taken out via the current detection resistor.
It is intended to protect the IGBT1. Reference numeral 21 is an auxiliary IGBT as an auxiliary insulated gate element having a small current capacity, and 31 is a current detection resistor. And this auxiliary IGBT 21 and current detection resistor 31
The series circuit with is connected in parallel to the IGBT1 with the terminal on the side of the resistor 31 being connected to the emitter E of the IGBT1, and the IGBT
The gates G of T1 and T21 are coupled to each other and driven together. Further, in FIG. 4, the Zener diode 6 is inserted on the emitter E side of the auxiliary transistor 5. In this circuit, when the IGBT1 is on, the auxiliary IGBT21 is also in the on state, and when the main circuit current iO1 flows, the current corresponding to the current iO of the IGBT1 flows to the current detection resistor 31 via the auxiliary IGBT, and both ends of this resistor 31 A voltage corresponding to the main circuit current iO1 will appear. When the main circuit current iO1 increases and the voltage generated across the resistor 31 becomes higher than the sum of the Zener voltage of the Zener diode 6 and the base B-emitter E voltage eBE of the auxiliary transistor 5, the auxiliary transistor 5 is turned on, and the gate voltage eg of the IGBT1 is almost equal to the Zener diode 6
It drops to the Zener voltage of. By this action, the current iO flowing between the main terminals of the IGBT1 can be suppressed, and the power breakdown of the IGBT1 can be prevented. The circuit of FIG. 4 has an advantage that the Joule heat generated by the current detecting resistor 31 can be made smaller than that of the voltage dividing resistor 2 of FIGS. In each of the above embodiments, the auxiliary transistor 5 is a FET.
, IGBT1,21 are MOSFET, Bi-M
It may be the OS. Further, in FIG. 4, the IGBT 1 and the auxiliary IGBT 21 may be formed on one chip or may be separate chips.

【The invention's effect】

According to the present invention, a series circuit of a Zener diode and an auxiliary transistor is provided in parallel with the gate-emitter circuit of the insulated gate element, and the voltage between the main terminals of the insulated gate element is detected via voltage detection means for detecting the voltage between the main terminals of the insulated gate element. When the voltage exceeds a predetermined value, the auxiliary transistor is turned on, and the gate voltage of the insulated gate element is limited to a smaller value by the Zener diode. It is possible to lengthen the time to reach (by using the current limiting function of the insulated gate element itself and suppressing the excess current to a low value), so it is not necessary to increase the response speed of the peripheral control circuit. A gate voltage cutoff circuit resistant to noise can be obtained. Further, no large di / dt is generated due to the interruption of the insulated gate element at the time of excessive current, and the other insulated gate elements are not affected. Then, by setting the excessive current to a low value, it is easy to detect an abnormality, and the protection operation in the drive circuit is surely facilitated. Furthermore, by inserting a reverse bias power supply so that a reverse bias voltage is applied between the gate and emitter when the insulated gate element is turned off, erroneous turn-on when the insulated gate element is turned off is prevented, and it is resistant to noise in various situations. A circuit that can provide reliable protection is obtained.

[Brief description of drawings]

1 to 4 are drive circuit diagrams showing the essential parts of different embodiments of the present invention, and FIG. 5 is a conventional drive circuit diagram. 1,21: Smoke saving gate device, (1: IGBT, 21: Auxiliary IGBT), 2,3:
Voltage dividing resistance, 31: current detection resistance, 4: sneak prevention diode, 5, 8, 9: auxiliary transistor, 6: Zener diode, 7:
Resistor, 10: Gate drive power supply, 11: Reverse bias power supply.

Claims (1)

[Claims] 1. A control terminal and first and second main terminals are provided, and when a drive voltage from a drive circuit is applied between the control terminal and the first main terminal, the first and second main terminals are provided. In a drive circuit of an insulated gate element in which the two main terminals are in a conductive state and the main terminals are in a blocking state when the drive voltage is cut off, voltage detection for detecting a voltage corresponding to a forward voltage between the main terminals A means provided in a current path parallel to the current path connecting between the main terminals, provided in a polarity that blocks a drive voltage from the drive circuit, and a zener diode having a zener voltage lower than the drive voltage; A circuit including a series circuit with an auxiliary transistor having a drive voltage in the forward direction is connected in parallel to the control terminal and the first main terminal, and the detection voltage of the voltage detection means is used for driving the auxiliary transistor. In addition to terminals The auxiliary transistor is turned on when the forward voltage between the first and second main terminals exceeds a predetermined value, and the drive voltage is limited to a Zener voltage. An insulated gate element, characterized in that a reverse bias power supply for applying a reverse bias voltage between the control terminal and the first main terminal when off is provided between the first main terminal and the auxiliary transistor. Drive circuit.