JPH0467720A - Igbt overcurrent protective circuit - Google Patents

Abstract

PURPOSE:To conduct the detection of overcurrents and the control of the decrease of the gate voltage of an IGBT at high speed, and to prevent the breaking of the IGBT by detecting overcurrents by the increase of voltage between the collector-emitter of the IGBT (an insulated gate bipolar transistor) to be driven, controlling the input side of a gate driver circuit by the detecting output and reducing the gate voltage of the IGBT. CONSTITUTION:When overcurrents are made to flow through an IGBT 11 and voltage between a collector and an emitter is increased, the voltage of a capacitor 36 is also elevated. When the voltage is made larger than reference voltage Vr, an output from a comparator 41 reaches a low level, a diode 43 is turned ON, each base of transistors(Tr) 28, 29 reaches approximately zero volt, the gate of the IGBT 11 is brought near to zero volt, and the IGBT 11 is turned OFF. A Tr 45 is turned ON, a node 37 is supplied with the positive voltage of a power supply 24 through the Tr 45, the voltage of the capacitor 36 is held under the state in which the voltage of the capacitor 36 is larger than reference voltage Vr, and the IGBT 11 is maintained at OFF.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" This invention is an I/O switching element used as a power switching element in a DC-AC inverter, a DC-DC converter, etc.
G B T (Insulated Gate Bip)
The present invention relates to an IGBT overcurrent protection circuit that protects an insulated bipolar transistor (olarTransistor) from overcurrent.

"Prior Art" IGBTs are sensitive to overcurrent, and when an overcurrent occurs, it is necessary to interrupt the current in a short period of time. Therefore, in the past, the third
The protection circuit shown in the figure was used.

That is, the collector of the driven IGBT II is connected to the positive power supply side through the terminal 12, the emitter is connected to the negative power supply side through the terminal 13, and the output side of the gate drive circuit I4 is connected between the base and emitter. In the case where an on/off control signal is manually inputted to the input side of the gate drive circuit 14 through the photocoupler 15, the on/off control signal is applied from the terminal 18 via the gate 17 to the base of the photodiode drive transistor 16 of the photocoupler 15. A direct current power transformer (DCCT) 19 is coupled between the emitter of the IGBTII and the terminal 13;
The output of the DCCT 19 is amplified by an amplifier 21 and supplied to an overcurrent detector 22.
When the current detected at 19 exceeds a predetermined value, this is detected and the gate 17 is closed. In this way, overcurrent of IGBTII was cut off.

"Problem to be Solved by the Invention" The current flowing through IGBTII is a direct current, and in the conventional overcurrent protection circuit shown in Fig. 3, a DCCT19 is used to directly detect this direct current. This has the disadvantage that the protection circuit is expensive. Also, when an overcurrent is detected, since the previous stage of the photocoupler 15 is controlled, the IGBTI
It took more than 20 IIS to turn off the gate voltage of I. [;Because BTII has a smaller semiconductor chip area than normal bipolar transistors or FETs, it detects overcurrent quickly and then detects IG within about 10 μs.
It is necessary to turn off the gate voltage of BTII.

According to the present invention, one end of a resistor is connected to the gate of a driven IGBT, one end of a capacitor is connected to the emitter, and the other ends of the resistor and capacitor are connected to each other. The connection point connects the driven IGBT through a diode.
The diode has a polarity opposite to the voltage applied to the collector of the IGBT. The voltage of this capacitor is the collector of the driven IGBT that is turned on.
approximately equal to the voltage between the emitters of the driven IGBT
When an overcurrent flows through the IGBT, the collector-emitter voltage of the driven IGBT increases accordingly. Therefore, the overcurrent of the driven IGBT can be detected by the voltage of this capacitor. Therefore, the voltage of the capacitor is compared with the reference voltage by a comparator, and if the driven IGBT becomes overcurrent,
The voltage of the capacitor becomes higher than the reference voltage, the output of the comparator becomes zero level, the input signal of the gate drive circuit of the driven IGBT is pulled to the output side of the comparator, and the output of the driven IGBT becomes higher than the reference voltage.
T is turned off. Along with this, pn is determined by the output of the comparator.
p) The i transistor is turned on, the positive power supply terminal is connected to the capacitor through this pnp transistor, and the overcurrent detection state is maintained.

Embodiment J FIG. 1 shows an embodiment of the present invention. Gate drive circuit 14
For example, the collector of the phototransistor 15a of the photocoupler 15 is connected to the positive side of the power source 24 through the resistor 23, the emitter is connected to the negative side of the power source 25, and the negative side of the power source 24 and the positive side of the power source 25 are connected to each other. and this connection point 2
6 is connected to the emitter of the driven ■GBTII, and the collector of the phototransistor 15a is npn)
The emitter of the transistor 27 is connected to the negative side of the power supply 25, and the collector is connected to the base of the npn transistor 28 and the base of the pnp transistor 29, respectively, and the positive side of the power supply 24 is connected to the base of the transistor 24 through the resistor 31. The collector of the transistor 28 is connected to the positive side of the power supply 24 through the resistor 32, the emitter is connected to the emitter of the transistor 29, and this connection point 33 is connected to the driven IC; BTII through the resistor 34. The collector of the transistor 29 is connected to the power supply 2.
Connected to the negative side of 5.

When the photodiode 15b of the photocoupler 15 emits light according to the manual on/off control signal, the phototransistor 1
5a is turned on, the transistor 27 is turned off, and the transistor 28 is turned on.The positive voltage of the power supply 24, for example, +15V, is applied to the gate of the driven IGBTII, and the driven IGBTII is turned on. When the photodiode 15b is turned off by the on-off control signal, the transistor 27 is turned on, the transistor 29 is turned on, and the power supply 25 is turned on.
A negative voltage of, for example -15V, is applied to the gate of driven IGBTI 1, and driven IGBTI II is turned off. The connection point 26 is zero volts in this example, and in this invention, one end of the resistor 35 is connected to the gate of the driven IGBTII through a resistor 34, one end of the capacitor 36 is connected to the emitter of the driven IGBTII, and the resistor 35 is connected to the gate of the driven IGBTII. The other ends of the capacitor 36 and the capacitor 36 are connected to each other, and the connection point 37 is connected to the collector of the driven IGBTII through a diode 38. The cathode of diode 38 is I
It is considered to be the collector side of GBTII. The connection point 37 is connected through a resistor 39 to the inverting input of a comparator 41, and a reference power supply 42 is connected between the non-inverting input of the comparator 41 and the emitter of IGBTII, in this example a positive reference voltage V.
r is applied to the non-inverting input of comparator 41.

The output end of the comparator 41 is connected through a diode 43 to the input side of the gate drive circuit 14, in this example a transistor 28.
Connected to the base of 29. The cathode of the diode 43 is the output end of the comparator 41. The output terminal of the comparator 41 is connected to the base of a pnp transistor 45 through a resistor 44, the emitter of the transistor 45 is connected to the positive side of the power supply 24, and the collector of the transistor 45 is connected to the connection point 37 through a resistor 46. be done. A diode 47 is connected in parallel with the capacitor 36, and the cathode of the diode 47 is on the connection point 37 side.

In this configuration, the input on/off control signal causes the photodiode 15b to emit light, and the voltage at the connection point 33 increases to +15
When the voltage reaches V, this voltage charges the capacitor 36 and turns on IGBTII. I turned on
C; Since the voltage between the collector and emitter of BTII is about 2 to 3 cm, the charge on the capacitor 36 is transferred to the diode 38.
The voltage of the capacitor 36 becomes approximately equal to the collector-emitter voltage of IGBTII. When the current of IGBTl,1 is below a predetermined value, the voltage of the capacitor 36 is smaller than the reference voltage Vr,
The output of comparator 41 is at a high level, and diode 43 and transistor 45 are both off.

When an overcurrent flows through IGBTII, the voltage between the collector and emitter of IGBTII increases, and the voltage across capacitor 36 also increases.This voltage becomes higher than reference voltage Vr, and the output of comparator 41 becomes a low level. (approximately zero volts), the diode 43 is turned on, the bases of transistors 28 and 29 are almost zero volts, the gate of IGBTII is close to zero volts, and IC and BTII are turned off. Also transistor 4
5 is turned on, and the power supply 2 is connected through this transistor 45.
A positive voltage of 4 is supplied to the connection point 37, and the voltage of the capacitor 36 is maintained higher than the reference voltage Vr, and the IG
BTII is held off. Since the accumulated charge in the input capacitance of IGBTII is gradually discharged to about 2cm through the resistor 34, an excessive surge voltage is less likely to occur when IGBTII is turned off.

When the photodiode 15b is turned off by the input on/off control signal, the transistors 27 and 29 are both turned on, and the connection point 33 becomes approximately -15V, and the gate-emitter of IGBTII is reverse biased, and the charge on the capacitor 36 is reduced. The voltage is approximately equal to the on-voltage of the diode 47. As a result, the output of comparator 41 becomes high level, and transistor 45 is turned off. At this time, the diode 43 prevents the 15 V from the bases of the transistors 28 and 29 from being applied to the output side of the comparator 41 and the base of the transistor 45.

In FIG. 2, the comparator 41 and reference voltage source 42 in FIG.
Ant regulator 48 consisting of several semiconductor integrated circuits
In this case, the shunt regulator 48 is a TL manufactured by Texas Instruments.
431 can be used. The voltage across the capacitor 36 is divided by resistors 49, 51 and supplied to the shunt regulator 48, and this voltage dividing point is connected to the collector of the transistor 45 via the resistor 46. Other details are the same as in Figure 1.

"Effects of the Invention" As described above, according to this invention, the driven IGBT II
An overcurrent is detected by an increase in the collector-emitter voltage of the IGBTI II, and the detected output controls the input side of the gate drive circuit 14 to reduce the gate voltage of the IGBTI II. Control can be performed at high speed, and there is no risk of destroying the IGBTll. When an overcurrent is detected, the transistor 45 is turned on and a holding current is supplied to the capacitor 36, so that the overcurrent detection state is maintained and chattering of the gate voltage of IGBTII being repeatedly turned on and off is prevented. Furthermore, since an expensive direct current power transformer is not used, an inexpensive structure can be achieved. Since the gate voltage of IGBTII is cut off without applying a reverse bias and is gradually lowered to about 2V through the resistor 34, it is difficult to generate a surge voltage when IGBTII is turned off.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a connection diagram showing the other side, and FIG. 3 is a block diagram showing a conventional IGBT overcurrent protection circuit.

Claims (1)

[Claims] (1) Driven IGBT (insulated bipolar transistor)
One end of the resistor is connected to the gate of the driven IGB.
One end of the capacitor is connected to the emitter of T, the other end of the resistor and the other end of the capacitor are connected to each other, and between the connection point and the collector of the driven IGBT,
A diode is connected in the opposite direction to the voltage applied to the collector, and a comparator is provided to compare the voltage of the capacitor with a reference voltage, and the output side of the comparator is the input of the gate drive circuit of the driven IGBT. an IGBT overcurrent protection circuit, which is connected to the side and connected to the base of a pnp transistor, the emitter of which is connected to the positive power supply terminal, and the collector is connected to the connection point of the resistor and capacitor.