JPH0257011A - Over-current protecting circuit for igbt - Google Patents

Abstract

PURPOSE:To cause a collector current to be <= a latch-up current when an IGBT is interrupted by forcibly conducting the IGBT regardless of an input signal for a constant period after the generation of an over current is detected and preventing the peak value of the over-current from being interrupted. CONSTITUTION:An over-current protecting circuit 4 is composed of a means to detect the over-current flows to an IGBT 3 with the coupling of a voltage monitoring circuit 9 and a rising detecting circuit 10 and a one-shoot circuit 11 to receive the output of this rising detecting circuit 10 and to output the pulse of prescribed width to a gate driving circuit 1. When the rising detecting circuit 10 sends an output signal, which expresses over-current detection, to the one-shoot circuit 11 and the one-shoot circuit 11 sends the pulse of the prescribed width of an output 'H' to the gate driving circuit 1, the gate driving circuit 1 conducts an IGBT3 regardless of the presence and absence of an input signal (a). Thus, even when the over-current is generated just before the rising of the input signal (a), the peak value of the over-current from being interrupted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applied to IGBT (Insulated Gate B) used in power conversion devices such as inverters.
The present invention relates to an overcurrent protection circuit that protects an ipolartransistor from overcurrent caused by a short circuit or the like.

[Conventional technology]

Conventionally, as this type of overcurrent protection circuit, a method has been adopted in which an overcurrent is detected by detecting an increase in the voltage between the collector and emitter of the IGBT, and the gate is cut off to protect the IGBT.

FIG. 5 shows an example of this. In the figure, 1 is a gate drive circuit for the IGBT 3, 2 is a resistor, and 4 is an overcurrent protection circuit. This overcurrent protection circuit 4 is connected to the collector of IGBT3.
A voltage monitoring circuit 5 that monitors the emitter voltage, a timer circuit 6 that receives the output from the voltage monitoring circuit 5 and outputs it with a certain time delay, and an IGBT 3 that uses the output of the timer circuit 6.
It is composed of a combination of a transistor 8 and a resistor 7, which performs gate cutoff. FIG. 6 shows operating waveforms of each part of the circuit shown in FIG. 5.

As shown in Figure 6, if an overcurrent occurs just before the input signal falls, the gate is turned off before the overcurrent protection circuit operates, and therefore, the overcurrent protection circuit is turned off while the overcurrent is flowing. It varies depending on the timing of occurrence.

[Problem to be solved by the invention]

By the way, in order to protect the IGBT 3 from a filtering current caused by a short circuit or the like, it is necessary to cut off the overcurrent within a range that the element can withstand. The withstand capability of the device is short-term, and the duration is determined by the allowable energy breakdown and the latch-up capability. The latter will eventually lead to thermal breakdown, but the latch-up that causes this occurs when the current exceeds the allowable value even momentarily (hereinafter, this allowable value will be referred to as the ``notch-up current (1)''). On the other hand, as shown in FIGS. 7 and 8, the current flowing through the ICBT 3 at the time of a short-circuit accident in the power conversion device shows a tendency to decrease as time passes after reaching a peak value. In FIG. 7, 14 is a DC power supply, and 15 is a wiring inductance.

The peak value (Icp) of this current is the latch amplifier current IL
There is no particular problem if it is smaller than ICI)>
In the case of IL, depending on the timing of overcurrent occurrence, Ic
There are cases where p is cut off, causing Lasocia whelk,
As a result, there is a problem that the element is destroyed.

An object of the present invention is to eliminate the disadvantages of the conventional example, and to
I prevent B T from cutting off the peak value of overcurrent.
An object of the present invention is to provide an overcurrent protection circuit for an IGBT that can prevent GBT launch-up and provide reliable protection.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an overcurrent detection means for detecting that an overcurrent has flowed into an IGBT, and a signal having a predetermined pulse width in response to the output of the detection means. The gist is that if an overcurrent occurs, the IGBT is forcibly turned on for a period corresponding to the predetermined pulse width, and then the overcurrent is cut off. It is something to do.

[Effect]

According to the present invention, after detecting the occurrence of an overcurrent, the IGBT is forced to conduct for a certain period of time regardless of the input signal, so that the peak value of the overcurrent is not cut off. The collector current when the lGBT is cut off can be made lower than the launch-up current.

〔Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the ICBT overcurrent protection circuit of the present invention, and like FIG. 5 showing the conventional example,
In the figure, 3 is an IGBT, 1 is its gate drive circuit, 2 is a resistor, and 4 is an overcurrent protection circuit.

In this embodiment, the overcurrent protection circuit 4 is an IC;
3, and a circuit 11 that receives the output of the rise detection circuit 10 and outputs a pulse of a predetermined width to the gate drive circuit 1. Of these, the input signal is
The rising edge of the voltage monitoring circuit 9 (
This means that VCE exceeds a predetermined value), thereby detecting an overcurrent and sending a signal to its output.

The one-shot circuit 11 receives the output of the rising edge detection circuit 10 and outputs a pulse of a predetermined width to the gate drive circuit 1.

FIG. 2 shows the operating waveforms of each part of the circuit shown in FIG. In response to this, when sending out a pulse with a predetermined width of the output "tobi" to the gate drive circuit 1 as shown in d, the gate drive circuit 1 outputs the output of the one-shot circuit 11 regardless of the presence or absence of the input signal a. During the "H'" period, the IGBT3 is made conductive. By doing so, even if an overcurrent occurs just before the fall of the input signal, the ICBT 3 can be made conductive for a predetermined period, and the peak value of the overcurrent can be prevented from being cut off.

FIG. 3 shows a second embodiment of the present invention, in which the overcurrent protection circuit 4 uses a current detector 12 provided on the collector side of the IGBT 3 and an It consists of a current detection circuit 13,
A current detector 12 detects the current flowing through the GBT 3, and an overcurrent detection circuit 13 determines whether there is an overcurrent.

As in the first embodiment, the one-shot circuit 11 receives the overcurrent detection signal and generates a drive signal with a predetermined time width, and outputs the IG signal through the gate drive circuit 1 regardless of the state of the human power signal.
Make BT3 conductive.

FIG. 4 shows the operating waveforms of each part of the circuit shown in FIG. 3. When the current Ic flowing through the IGBT 3 exceeds a predetermined level (Ioc shown in the figure), a detection signal S is sent from the overcurrent detection circuit 13. Ru. Using this as a trigger, a pulse with a predetermined pulse width T1 is applied from the one-shot circuit 11 to the drive circuit, and as a result, the gate-emitter voltage VGE of the IGBT 3 becomes as shown in the figure, and after passing through the T3 period after overcurrent detection. IGBT3 turns off. Therefore, the peak value (Icp) of overcurrent is not cut off, and latch-up can be prevented.

Note that in the figure, when the IGBT 3 is in the off state, ■ and E are negative voltages, but ■6E may be Ov depending on the case.

(Effects of the Invention) As described above, the IGBT overcurrent protection circuit of the present invention forcibly interrupts the IGBT for a certain period of time regardless of the input signal.
By making T conductive, the collector current can be kept below the latch-up current when the IGBT is cut off, and reliable protection can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing a first embodiment of the IGBT overcurrent protection circuit of the present invention, and FIG. 2 is an operation waveform diagram of the same as above.
FIG. 3 is a block circuit diagram showing the second embodiment, FIG. 4 is an operation waveform diagram of the same as above, and FIG. 5 is a block circuit diagram showing a conventional example.
FIG. 6 is an operating waveform diagram similar to the above, FIG. 7 is a simulated circuit diagram at the time of a short circuit accident, and FIG. 8 is a diagram of voltage and current waveforms of the element at that time. 1... Gate drive circuit 2... Resistor 3...
T GBT 4...Overcurrent protection circuit 5.
...Voltage monitoring circuit 6...Timer circuit 7...
・Resistor 8...Transistor 9...
Voltage monitoring circuit 10...rise detection circuit 11
... One-shot circuit 12 ... Current detector 13
...Overcurrent detection circuit 14...DC power supply 15.
・Wiring inductance N soku ■9: O −〇

Claims (1)

[Claims] An overcurrent detection means for detecting that an overcurrent has flowed through the IGBT, and a one-shot circuit for receiving the output of the detection means and sending out a signal with a predetermined pulse width are provided. Forced IG for a period corresponding to the pulse width
An overcurrent protection circuit for an IGBT, which is characterized by cutting off an overcurrent after making a BT conductive.