JPH0286313A - Overcurrent protection circuit for semiconductor switch circuit - Google Patents

Abstract

PURPOSE:To protect overcurrent with simple circuit constitution by interrupting a signal given from a drive circuit to a gate-emitter inbetween at the detection of an overcurrent and using a short-circuit so as to short-circuit the gate and the emitter. CONSTITUTION:The overcurrent state is caused when an IGBT (Insulated Gate Bipolar Transistor) 11A is turned on, and when the collector-emitter voltage reaches a voltage of a power supply 5a or over, a transistor(TR) 8a with a current flowing at the normal conduction is turned off. This state is fed back to an ON/OFF signal circuit 13 by a logic gate circuit 20a. The circuit 13 receiving the signal turns off a switch 10c' and turns on a switch 10e. Thus, the gate and emitter of IGBTs 11a, 11b are short-circuited by a resistor 19f and the switch 10e. Thus, the stored charge between the gate and emitter of the IGBT 11a is discharged and the said IGBT 11a is turned off.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an I
G B T (Insulated Gate Bip)
The present invention relates to an overcurrent protection circuit for a complementary half-bridge circuit in which the emitter and gate of an IGBT are commonly connected.

[Conventional technology]

IGBT elements have the advantages of bipolar transistors, such as high breakdown voltage and easy increase in capacity, and power MO
It is attracting attention as a new device that combines the advantages of 3FET, such as being capable of high-speed switching and being easy to drive.

Figure 3 shows an equivalent circuit of an N-channel IGBT. N-channel MO3FETI, NPN) transistor 2. PNP
) transistor 3. and a short-circuit resistor 4 between the base and emitter of the transistor 2, and the drain and emitter of the MO3FETI.
The sources and the emitter and collector of transistor 2 are connected in parallel, and transistors 2 and 3 can be expressed as forming a thyristor circuit.

When turning on the N-channel IGBT, a forward bias voltage is applied between the gate and emitter. As a result, MO3
A channel is formed in the FETI, and the MOS FET
1 becomes conductive, and the emitter-base of the PNP transistor 3 is forward biased, thereby starting conduction.

Conversely, when turning off this element, a reverse bias voltage is applied between the gate and emitter. As a result, the MO3FETI is turned off, the base current of the PNP transistor 3 stops flowing, the transistor 3 is turned off, and as a result, the IG
BT turns off.

By the way, as described above, this element has a parasitic thyristor formed by the transistor 2.3. Therefore, when the collector current exceeds a predetermined value, a phenomenon called rough stub occurs (a phenomenon in which a parasitic thyristor turns on), and the collector current may not be cut off. Since this latch-up phenomenon is directly linked to element destruction of the IGET, it is necessary to provide overcurrent protection to prevent this from occurring.

When performing overcurrent protection of such an IGBT, the current level must be suppressed below the latch-up current.

In Fig. 3, when an off-gate signal is applied to the IGBT,
First, the N-channel MO3FETI is turned off. Since the collector current cannot suddenly decrease when the load is low, the FE
The current flowing between the drain and source of TI is now PNP
) Move to the collector of transistor 3. Therefore, the voltage drop across the resistor 4 becomes large, and the base-emitter of the transistor 2 is forward biased, making the transistor conductive and turning on the parasitic thyristor formed by the transistor 2.3. In this way, latch-up is more likely to occur during turn-off than in on-state, so turn-off at the time of overcurrent must be performed slowly.

The applicant had previously filed a patent application No. 2 as Japanese Patent Application No. 186948/1983.
An application has been filed for an overcurrent protection circuit for an IGBT drive circuit as shown in the figure.

In Figure 2, 12 is a photocoupler that insulates and transmits the control signal sent from the control circuit, and resistors 9d,
An ON10FF signal circuit 13 is formed by 9e, 9f, 9g, 9h, a diode 6c, a Zener diode 7b, and transistors 10c and 10d, and furthermore, transistors 10a and 10b form an ON circuit 14 and an OFF circuit 1.
It exists as 5 switches.

Forward bias power supply 5a and reverse bias power supply 5b connected in series
The midpoint of the connection with the IGBTII is connected to the emitter of the IGBTI II, and the transistors 10a and 10b as the switches are connected in series to the power supplies 5a and 5b with their emitters connected to each other, and the transistor LOa.

The midpoint of connection 10b is connected to the gate of IGBTII via resistor 9a.

The collector of the NPN l-transistor 8 is connected via a resistor 9c to the midpoint between the resistor 9a and the gate of IGBTII, and the emitter of the transistor 8 is connected to the diode 6.
The transistor 8 and the diode 6b formed a discharge circuit 17 by connecting the positive electrode of the reverse bias power supply 5b and the emitter of the IGBT via the transistor 8b. This discharge circuit 17 receives an output from an overcurrent detector 16, which will be described later, and is connected to an IG.
The accumulated charge in the gate-emitter capacitance of BTII is discharged by the gate resistor 9c having a large resistance value.

Also, the base of the transistor 8 is the Zener diode 7.
transistors 10a and 1 through a and a diode 6e.
The diodes 6e, 6a and the Zener diode 7a forms an overcurrent detector 16 that monitors the collector-emitter voltage of the IGBTll and detects an overcurrent when the voltage increases.

In this way, the output from the overcurrent detection circuit 16 is introduced into the ON10 F F signal circuit 13, and the ON10 F F signal circuit 13 receives this output and is connected to the O
By turning off the N circuit 14, the IGBT gate
It has a function to cut off the path for applying forward bias voltage between the emitters.

Next, the operation will be explained. Normally, when forward bias is applied, the phototransistor of the photocoupler 12 is turned on, so the transistors 10c and 10d of the ON10FF signal/signal circuit 13 are turned off. Therefore, the transistor 10a of the ON circuit 14 is forward biased and turned on, and the transistor 10b of the OFF circuit 15 is reverse biased and turned off. As a result, the voltage of forward bias power supply 5a is applied between the gate and emitter of IGBTII via transistor 10a and resistor 9a, and IGBTII is turned on.

On the other hand, at the time of reverse bias, the phototransistor of the photocoupler 12 is turned off, so the transistor 10a is reverse biased and turned off, and the transistor 10b is forward biased and conductive. As a result, the voltage of the reverse bias power supply 5b changes to the resistance 9
a, is applied between the gate and emitter of IGBTII via transistor 10b, and IGBTII is turned off.

Next, the operation at the time of overcurrent will be explained. During forward bias, the collector-emitter voltage of ICBTII is determined by the Zener voltage of the Zener diode 7a of the overcurrent detection circuit 16, the forward bias voltage drop of the base-emitter diode of the NPN transistor 8 of the discharge circuit 17, and the diode 6b. When the voltage exceeds the sum of the forward voltage drop of and the transistor becomes conductive. At this time, the gate of IGBTII
The emitters are short-circuited by the resistor 9C1, the transistor 8 of the discharge circuit 17, and the diode 6b. This diode 6b protects the transistor 8 by applying the voltage of the power supply 5b between the cathode and anode during normal turn-off.

With the above steps, the gate and emitter are short-circuited, and the IGBTII
The collector current is cut off.

Also, at this time, the Zener voltage of the Zener diode 7b of the 0N10FF signal circuit 13 and the NPN transistor 1
The sum of the forward bias voltage drop of the diode between the base and emitter of 0c is the Zener voltage of the Zener diode 7a, the forward bias voltage drop of the base-emitter diode of the NPN transistor 8, and the forward voltage drop of the diode 6b. If the sum with the voltage of the reverse bias power supply 5b is made equal, the Zener diode 7b becomes conductive at the time of the overcurrent, and the NPN transistor 10c is forward biased and turned on. Therefore, transistor 10a is reverse biased and turned off. On the other hand, at this time the transistor 10
No forward bias voltage is applied between the base and emitter of d due to the diode 6C. Therefore, transistor 10d does not turn on, and therefore transistor 10b remains off.

As a result, it becomes possible to slowly discharge accumulated charges by using a gate resistor having a large resistance value.

Therefore, overcurrent can be interrupted without latch-up.

[Problem to be solved by the invention]

As described above, the overcurrent protection circuit for the IGBT shown in FIG. 2 can provide overcurrent protection without latch-up, and therefore has the advantage that the IGBT can be applied to a wider range of applications.

However, if both the element connected to the positive terminal of the main circuit power supply and the element connected to the negative terminal of the main circuit power supply are complementary half-bridge circuits using IGBTs, the above-mentioned overcurrent will occur when considering the configuration of these drive circuits. 2 protection circuits
A set is required. Therefore, the conventional overcurrent protection circuit shown in FIG. 2 has an extremely complicated circuit configuration.

SUMMARY OF THE INVENTION An object of the present invention is to provide an overcurrent protection circuit for a semiconductor switch circuit which eliminates the disadvantages of the conventional example and requires a simple circuit configuration even in the case of a complementary half-bridge circuit.

[Means to solve the problem]

In order to achieve the above object, the present invention connects the emitters and gates of an N-channel IGBT connected to the positive pole of the main circuit power supply and a P-channel IGBT connected to the negative pole of the main circuit power supply in common to form a complementary half bridge. In a semiconductor switch circuit forming a circuit, the IG of the circuit
IGBT by applying a signal between the gate and emitter of BT
A drive circuit that turns on and off the IGBT, a short circuit that shorts between the gate and emitter, and an overcurrent detection circuit that detects overcurrent by increasing the collector potential of each IGBT. The gist of the present invention is to cut off the signal applied between the gate and emitter from the drive circuit when detecting a current, and to short-circuit the gate and emitter using a short circuit.

[Effect]

According to the present invention, when an overcurrent detection circuit detects an overcurrent, this is fed back to the drive circuit, and the IG
The signal applied between the gate and emitter of BT is cut off. At the same time, the IGBT's gate and emitter were short-circuited due to the output from the drive circuit, resulting in an overcurrent.
The accumulated charge between the gate and emitter of T is discharged.

〔Example〕

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

FIG. 1 is a circuit diagram showing one embodiment of the semiconductor switch circuit of the present invention, and the same components as in FIG. 2 showing the conventional example are given the same reference numerals.

In the figure, 11a is an IGBT as a semiconductor switching element.
However, the N-channel IGBT11a is an element connected to the positive pole of the main circuit power supply (hereinafter referred to as the upper arm element), and the P-channel IGBT11b is an element connected to the negative pole of the main circuit power supply (hereinafter referred to as the lower arm element). (referred to as element),
These I G B Tl1a and Ilb form a complementary half bridge circuit in which the emitter and gate are commonly connected.

A forward bias power supply 5a connected in series to a semiconductor switch circuit including such IGBTs 11a and 11b
The connection midpoint between the and the reverse bias power supply 5b is IGBTlla,
1" connected to the commonly connected emitter of 1b, power supply 5
Switches 100' and 10d are connected to the series connection circuit of a and 5b.
' are connected in parallel, and the switch 10c'
and 10d' are connected to IGB through resistor 19c.
It is connected to the commonly connected gates of T11a and T11b.

In the figure, reference numeral 13 denotes an ON10FF signal circuit, which controls on/off of the switches 100' and 10d'. In this way, power supplies -5a, 5b, switch 1
0c'+10d' and the ON10FF signal circuit 13 form a drive circuit that applies a signal between the gates and emitters of IGBTl1a and Ilb to turn them on and off.

Further, a short circuit is formed between the gates and emitters of IGBTs 11a and 11b by a series connection circuit of a switch 10e and a resistor 19f, and this switch 10e is also 0N10.
It is turned on and off by a signal from the FF signal circuit 13.

Further, a series connection circuit of a transistor 8a and a resistor 19d and a series connection circuit of a resistor 19e and a transistor 8b are connected in parallel to the series connection circuit of the switch 10c'+lOd', and the base of the transistor 8a is connected to the resistor 19a and the diode 6a. via IGBTlla
The base of the transistor 8b is connected to the collector of the resistor 19b.
and is connected to the collector of IGB Tll b via the diode 6b, thereby forming an overcurrent detection circuit 16.

This overcurrent detection circuit 16 includes each IGBT11a,
An overcurrent is detected by an increase in the collector potential of 11b.

Transistors 8a and 8b are turned off, and logic gate circuit 20
A signal indicating that the potential at the connection point of transistors 8a and 20b to the collectors of transistors 8a and 8b has become L, and ON1
Switch 10c from 0FF signal circuit 13,
10d' on signal and the logic gate circuits 20a, 20
The outputs of the logic gate circuits 20a and 20b are introduced into the ON10FF signal circuit 13.

In the figure, 6f and 6g are IGBT11a and 1, respectively.
This is a diode connected between the collector and emitter of 1b.

Next, the operation will be explained.

Turn on upper arm element IGBT11a, lower arm element IG
When turning off B711b, 0N10FF signal circuit 13
An on signal is sent to the switch 100' and an off signal is sent to the switch 10d'. Then, both iGB T11a, 1
A voltage from a power source 5a is applied between the gate and emitter of 1b via a switch 10c and a resistor 19c. the result,
IGBTlla is turned on and IGBTlla is turned off. At this time, if IGBTlla is in normal conduction state (collector-emitter voltage is sufficiently low), the voltage of power supply 5a is applied between the emitter and base of PNP transistor 8a due to the path of resistor 19a and diode 6aS IGBTlla. is applied, and the transistor 8a becomes conductive. Therefore,
The voltage at the collector of the transistor 8a (point A in FIG. 1) becomes H. Conversely, turn off the upper arm element IGBT11a,
When turning on the lower arm element IGB711b, turn ON10.
The FF signal circuit 13 sends an off signal to the switch 100' and an on signal to the switch 10d'.

Then, the emitters of both IGBT11a and 11b
The voltage of the power supply 5b is connected to the resistor 19c1 switch 1 between the gates.
0d'. As a result, IGBTlla
is turned off, and the same 11b is turned on. At this time IGBTIlb
If the NPN transistor 8b is in a normal conduction state, the NPN transistor 8b
The voltage of power supply 5b is applied between the base and emitter of IGB7.
11b, diode 6b, and resistor 19b, transistor 8b becomes conductive. Therefore, the potential of the collector of the transistor 8b (point B in FIG. 1) becomes L.

By the way, when the TGBT 11a is turned on, an overcurrent state occurs and the collector-emitter voltage of the ICBT 11a exceeds the voltage of the power supply 5a, the forward bias base current of the transistor 8a, which flows during normal conduction, is no longer able to flow. Therefore, the transistor 8a is turned off. Therefore, the potential at the aforementioned point A becomes L. Therefore, when an on signal is applied to switch 10c' and the potential at point A becomes L, I(:, B
This means that TIIa is in an overcurrent state, so the logic gate circuit 20a turns ON10 F F
It is fed back to the signal circuit 13.

Upon receiving this, the circuit 13 turns off the switch 100' and turns on the switch 10e. This allows I
The gates and emitters of G B T lla and llb are short-circuited by a resistor 19f and a switch 10e. Therefore, 1. The accumulated charge between the gate and emitter of G B Tl1a is discharged, and the IGBT11a is turned off (IGBT11a is turned off).
711b remains the same).

Conversely, when the IGB711b is turned on, an overcurrent state occurs, and the voltage between the collector and emitter of the IGET11b increases to the voltage of the power supply 5b.
When the voltage exceeds the voltage, the forward bias base current of the transistor 8b, which flows during normal conduction, cannot flow (and the transistor 8b is turned off. Therefore, the potential at the above-mentioned point B becomes H. Therefore, switch 10d'
When an on signal is applied to the switch and the potential at point B becomes H, it means that the IGB711b as the lower arm element is in an overcurrent state, so this state is turned ON10F by the logic gate circuit 20b. It is fed back to the F signal circuit 13. Upon receiving this, the circuit 13 turns off the switch 10d' and turns on the switch 10e. As a result, the accumulated charge of the IGB 711b is discharged through the path of the switch 10e and the resistor 19f, and the IC; BT11b is turned off (the IGBTlla remains unchanged).

〔Effect of the invention〕

As described above, the overcurrent protection circuit of the semiconductor switch circuit of the present invention has I (1, B
Even when forming a complementary half-bridge circuit by connecting T's emitters and gates together,
Since overcurrent protection can be performed with a simple circuit configuration, the drive circuit can be simplified, inexpensive, and highly reliable.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of an overcurrent protection circuit for a semiconductor switch circuit according to the present invention, FIG. 2 is a circuit diagram showing a conventional example, and FIG. 3 is an equivalent circuit diagram of an IGBT. 1...N-channel MO3FET 2...NPN) transistor 3...PNP) transistor 4...Resistor 5a...
・Forward bias power supply 5b...Reverse bias power supply 6a~
6g...Diode 7a, 7b...Zener diode 8...NPN Transistor 8a...PNP l
-Ransistor 8b...NPN I-Ransistor 9a~
9h...Resistors 10a to 10d...Transistors 10c, 10d', 10e-Switch 11...
IGBT 11a・"N channel I GET llb...P channel IGBT 12...Photocoupler 14...ON circuit 16...Overcurrent detection circuit 19a to 19f...Resistor 13...ON10 F F signal Circuit 15...OFF circuit 17...Discharge circuit 20a, 20b...Logic gate circuit

Claims (1)

[Claims] an N-channel IGBT connected to the positive terminal of the main circuit power supply;
In a semiconductor switch circuit in which the emitter and gate of a P-channel IGBT connected to the negative electrode of the circuit power supply are commonly connected to form a complementary half-bridge circuit, a signal is applied between the gate and emitter of the IGBT in the circuit. A drive circuit that turns the IGBT on and off, a short circuit that shorts the gate and emitter, and each IGBT
is provided with an overcurrent detection circuit that detects an overcurrent by an increase in the collector potential of the overcurrent detection circuit, and when the overcurrent detection circuit detects an overcurrent, the signal applied from the drive circuit between the gate and the emitter is cut off, and a short circuit is provided between the gate and the emitter. An overcurrent protection circuit for a semiconductor switch circuit characterized by short-circuiting between the two.