JPS6395723A - Igbt latchup detection circuit - Google Patents

Abstract

PURPOSE:To facilitate the protection at overcurrent by providing a current supervisory means supervising a collector current of an IGBT (insulated gate bipolar mode transistor) and a voltage supervisory means supervising the collector-emitter voltage of the IGBT and discriminating it as the latchup state when the collector current is a prescribed value or over and the collector-emitter voltage is a prescribed value or below. CONSTITUTION:Current detectors 22a, 22b detect the collector current of IGBTs 21a, 21b and voltage detectors 23a, 23b detect its collector-emitter voltage. Thus, state discrimination circuits 24a, 24b discriminate it as latchup state when the collector current is higher than a prescribed value and a collector- emitter voltage is lower than a presribed value and output a signal A representing it. The output A is supplied a short-circuit thyristor 5, then the overcurrent flawing to the IGBT is branched into the short-circuit thyristor 5 to relieve the current dury of the IGBT. Moreover, since the current flowing through a fuse 3 keeps increasing, the fuse is blown in a short time, resulting that the destruction of the IGBT is protected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an I
G B T (In5lated Gate Bi)
The present invention relates to a latch-up detection circuit for a polar mode Transistor (Polar mode Transistor) device.

[Conventional technology]

IGBT elements have the advantages of bipolar transistors, such as high breakdown voltage and easy increase in capacity, and power MO8F.
It is a new device that has recently attracted attention as a new device that combines the advantages of ET, such as high-speed switching and easy drive.
They are commercialized under trade names such as EMFET or l1hFET.

Figure 3 shows such circuits. In other words, IGBT is M
OSFET (F), PNP transistor TR1, NP
It consists of an N transistor rR2 and a base-emitter shorting resistor R, and is characterized by having a built-in thyristor circuit made up of transistors TR1 and TR2.

It is said that the biggest drawback of such IGBTs is that a phenomenon called radiation (a phenomenon in which a parasitic thyristor is turned on) occurs when the collector current exceeds a predetermined value, and the current cannot be cut off. This is because a thyristor circuit is built in as shown in FIG. 3, so when the collector current exceeds a predetermined value, this thyristor circuit is turned on and the IGBT cannot be turned off. In other words, this thyristor circuit is unnecessary for the original operation of the IGBT, and in order to prevent this operation, the base and emitter of the 1CNPN transistor are short-circuited with a low resistance. If the base-emitter resistance could be reduced to OΩ, thyristor operation could be avoided, but in reality it cannot be reduced to 0Ω due to various constraints. As a result, IGBT is built-in (parasitic)
There is a possibility that the thyristor will operate, and if it turns on (latch up), the IGB'
r is no longer able to carry collector current, and such I
In an S-position using a GBT element, an excessive current flows and the circuit may burn out, which may lead to serious accidents.

Therefore, it is necessary to detect the latch-up condition. Therefore, it is possible to detect the current that flows during latch-up, that is, the latch-up current, but this is difficult to detect because it varies greatly depending on the element and the operating point temperature. Therefore, conventionally, rather than detecting latch-up, one method has been to avoid it.

FIG. 4 is a schematic diagram showing a conventional example for avoiding latch-up. This is an example in which an IGBT is used as a switching element in an inverter device (for one phase), and a DC reactor 6 is inserted between a DC smoothing capacitor 4 and an inverter circuit 2, which can occur in the event of an inverter output short-circuit accident, etc. Latch-up is prevented by slowing down the rate of change of overcurrent and turning off the IGBT when the collector current reaches the latch-up current.

(Problems to be Solved by the Invention) However, while this h method has the advantage of being able to eliminate the excessive M flow state before latch-up occurs and suppressing the 71 current in the circuit to a low value, on the other hand, The DC reactor inserted to avoid latch-up becomes large, which not only increases the size and cost of the device, but also causes loss due to the DC reactor, which reduces the conversion efficiency of the device. Furthermore, if a large DC reactor is used, latch-up current cannot be detected, and therefore the collector ff1F must be made smaller, making it impossible to use the element effectively.
There is also the problem of.

Therefore, it is an object of the present invention to make it possible to actively detect a latch-up condition without avoiding it, and to utilize the device effectively.

[Means for solving problems]

current monitoring means for monitoring the collector current of the IGBT;
A voltage monitoring means for monitoring the collector-emitter voltage of the GBT is provided, and a latch-up state is determined when the collector current is above a predetermined value and the collector-emitter voltage is below a predetermined value.

[Effect]

The output characteristics of the IGBT element are shown by the solid line in Figure 2,
This is generally called a saturated type, and when 1Tii is flowing, a high voltage is applied between the collector and emitter. Then, when latch-up occurs, IG
The output characteristics of BT deviate from the original characteristics and enter a low impedance state similar to a thyristor, as shown by the dotted line ■ in the figure. Therefore, it can be seen that IGBT latch-up can be detected by finding that an overcurrent is flowing and a low impedance state (low collector-emitter voltage) is established at the same time.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention.

This is each IGBT21a that constitutes one phase of the inverter.
, 21b have current detectors 22a and 22b, respectively.
, voltage detectors 23a, 23b, and state determination circuits 24a, 24b. , current detectors 22a, 22b detect collector currents of IGBTs 21a, 21b, and voltage detectors 23a, 23b.
detects its collector-emitter voltage. Therefore, the state determination circuit 24a.

24b determines that there is a latch-up state when the collector current is higher than a predetermined value and the collector-emitter voltage is lower than a predetermined value, and outputs a signal A indicating this. This output A is given to the short circuit thyristor 5, so the IGBT
The overcurrent flowing through the short-circuit thyristor 5 is shunted to the short-circuit thyristor 5, thereby reducing the current responsibility of the IGB'T. Further, since the current flowing through the fuse 3 continues to increase, it will blow out in a short time, and as a result, the IGBT can be saved from destruction and the circuit can be prevented from burning out. Therefore, the fuse 3 and the thyristor 5 form an overcurrent protection circuit. Note that this overcurrent protection circuit does not affect circuit operation at all under normal operating conditions, so it does not cause problems such as a reduction in conversion efficiency.

〔Effect of the invention〕

According to this invention, since the latch-up state can be accurately detected using the current monitoring means and the voltage monitoring means, the IGBT
There is no need to take precautions such as keeping the collector current of the element low, which not only makes it possible to effectively utilize the element, but also provides the advantage of facilitating protection against overcurrent.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of this invention, and FIG. 2 is an I
A characteristic diagram showing the output characteristics of the G B 'r element, Figure 3 is I
An equivalent circuit diagram showing a GBT element, and FIG. 4 is a schematic diagram showing a conventional example for avoiding latch-up. Description of symbols 1... DC power supply, 2... Inverter circuit, 21a. 21b... IGBT element, 22a, 22b-MR
Detector, 23a, 23b...Voltage detector, 24a
, 24b...Status determination circuit, 3...Fuse,
4... DC smoothing capacitor, 5... Short circuit thyristor, 6... DC reactor, F... FET, TR1.
...PNP transistor, TR2...NPN transistor, R...short circuit resistance.

Claims (1)

[Scope of Claims] Current monitoring means for monitoring a collector current of an IGBT used as a switching element; and voltage monitoring means for monitoring a collector-emitter voltage of the IGBT, wherein when the collector current is equal to or higher than a predetermined value, And collector/
A latch-up detection circuit for an IGBT, characterized in that a latch-up state is determined when an emitter voltage is below a predetermined value.