JPH08195664A - Snubber circuit of semiconductor device - Google Patents

Abstract

PURPOSE: To reduce generated loss and reduce the size by providing an insulation gate type bipolar transistor(TR), a capacitor, and a resistance. CONSTITUTION: A voltage driven type thyristor turns OFF, a main current I0 is ceased, and a main power source I0 shifts to the snubber circuit 6, thereby obtaining a snubber current IS. The snubber current IS flows to a main circuit through a capacitor 2, a resistance 3, and an insulation gate type bipolar TR IGBT4. A current IIGBT flowing to the IGBT4 is generated by generating a resistance voltage VR across a resistance 3 with a resistance current IR, applying this resistance voltage VR as a gate voltage to the IGBT 4, and placing the IGBT4 in an active area to make part of the snubber current IS flow. Consequently, the snubber current IS is shunt to the IGBT4 and capacitor 2 and the current IC which flows to the capacitor 2 is less than that in the absence of the IGBT4, and the voltage rise rate of the voltage of the capacitor 2, i.e., a voltage VT applied to the voltage-driven type thyristor 1 decreases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a snubber circuit for suppressing a spike voltage (voltage rise rate and peak value) applied to a semiconductor device in a power converter using the semiconductor device as a switching element. In particular, the present invention relates to a snubber circuit of a semiconductor device such as a voltage drive thyristor having a narrow safe operation area at turn-off.

[0002]

2. Description of the Related Art FIG. 4 shows a snubber circuit and a main circuit of a conventional voltage drive type thyristor (hereinafter simply referred to as thyristor). The main circuit is a step-down chopper circuit as an example. Next, this circuit will be described. The DC power supply Ed, the voltage drive type thyristor 1 and the diode 8 are connected in anti-series, and the diode 8
And a series circuit of the reactor 9 and the resistor 32 are respectively connected in parallel to form a main circuit. Further, the snubber circuit 6 in which the diode 81 and the capacitor 21 are connected in series and the diode 81 and the resistor 31 are connected in parallel is connected to the voltage drive type thyristor 1. This step-down chopper circuit is a circuit that adjusts the output power (power consumed by the reactor and the resistor) by turning on and off the voltage-driven thyristor 1. This snubber circuit 6 has the capacitor 21
The main current is commutated to suppress the rise rate and peak value of the voltage applied to the voltage-driven thyristor 1 at the time of turn-off (peak value of jump voltage).

[0003]

However, in the conventional snubber circuit 6 as described above, when the voltage drive type thyristor 1 is turned on, the electric charge stored in the capacitor 21 is discharged through the resistor 31. Joule loss occurs at the product of the current value and the resistance value. When the operating frequency of the voltage drive type thyristor 1 becomes as high as 10 kHz, the Joule loss becomes extremely large, and the snubber circuit becomes large due to the increase of the resistance capacity, and the efficiency of the device is deteriorated.

It is an object of the present invention to provide a snubber circuit of a semiconductor device which can eliminate the above problems.

[0005]

In order to achieve the above object, the present invention is a snubber circuit which absorbs a spike voltage applied to a semiconductor device as a switching device for opening and closing a circuit, and is a high potential side of the semiconductor device. An insulated gate bipolar transistor (IGBT) whose collector and emitter are connected to an anode and a cathode on the low potential side, a capacitor connected between the collector and gate of this IGBT, and a resistor connected between the gate and emitter And to have.

It is more effective to connect the cathode and anode of the constant voltage diode to the collector and gate of the IGBT, respectively. It is also effective to apply this snubber circuit to a voltage-driven switching element.

[0007]

[Operation] When the voltage drive type thyristor turns off,
The main current flowing through the voltage-driven thyristor flows into the snubber circuit, and this current causes electric charge to be stored in the capacitor, generating a voltage across the resistor. During the turn-off period, the inflowing current can be approximated to be constant, so that the voltage generated across the resistor is also constant. This constant voltage is applied to the gate of the IGBT, and by appropriately selecting this voltage value, the IGBT is brought into the operating state in the active region. By flowing a part of the main current through the IGBT in this active region, the amount of charge stored in the capacitor is reduced, the discharge current that flows through the resistor when the voltage-driven thyristor turns on is reduced, and the Joule loss that occurs in the resistor is reduced. To reduce. As a result, the circuit efficiency can be improved and the snubber circuit can be downsized.

Further, since the current flowing into the capacitor becomes small, the anode. The rise of the voltage applied between the cathodes (rate of voltage increase) becomes small, and the safe operation area (the locus of the voltage and current at turn-off is shown; if this is wide, a large current can flow at a high voltage) and a narrow voltage Even a drive type thyristor can be turned off without damage.

Further, by connecting a constant voltage diode in parallel with the capacitor, it is possible to prevent an overvoltage from being applied to the voltage drive type thyristor, and it is possible to reliably turn off the thyristor.

[0010]

1 shows a diagram in which the snubber circuit of the first embodiment of the present invention is connected to the main circuit of FIG. The snubber circuit 6 in which the series circuit of the capacitor 2 and the resistor 3 is connected in parallel between the collector 41 and the emitter 42 of the IGBT 4 and the connection point 5 of the capacitor 2 and the resistor 3 and the gate 43 of the IGBT 4 is connected is a voltage drive type. It is connected in parallel between the anode 11 and the cathode 12 of the thyristor 1 and connected to the main circuit. The main circuit is the same as that of the conventional example shown in FIG.

FIG. 2 is an operation waveform diagram for explaining the operation of the voltage drive thyristor to which the snubber circuit of FIG. 1 is connected. The voltage-driven thyristor turns off and the main current I _O
Becomes zero and the main current I _O moves to the snubber circuit 1 and becomes the snubber current I _S. Since the actual turn-off is performed in an extremely short time, the phenomenon during the turn-off period is omitted here and the main current I _O is instantly zero. The snubber current I _S flows out to the main circuit through the capacitor 2, the resistor 3 and the IGBT 4. Current flowing in IGBT (IGBT current I _IGBT )
The resistance voltage V _R is generated in the resistor 3 by the resistance current I _R , the resistance voltage V _R is applied as a gate voltage to the IGBT 4, the IGBT 4 enters the active region, and a part of the snubber current I _S flows. Occurs. Therefore, the snubber current I _S is I
The current (capacitor current I _C ) that splits between the GBT 4 and the capacitor 2 and flows in the capacitor 2 is reduced compared to the case where the IGBT 4 is not provided (conventional snubber circuit), and the voltage of the capacitor 2, that is, the voltage-driven thyristor 1 is applied. Voltage V
The voltage increase rate of _T (dV / dt = I _C / C, C: capacitor capacity) decreases. Further, since the charge Q accumulated in the capacitor 2 decreases, the capacitor voltage (V _C = Q / C), that is, the voltage VT applied to the voltage-driven thyristor 1 also decreases. Further, the resistance current I _R also decreases, and the Joule loss (E = RI _R / 2, I _R : resistance current) generated in the resistor 3 is generated.
Decreases. The capacitor voltage V _C is several hundreds to several thousand and several hundreds V, the resistance voltage V _R is several V to several tens, and since the capacitor voltage V _C is large by about two digits, the voltage VT applied to the voltage drive thyristor is the capacitor voltage V _It is almost equal to _C.

When the voltage V _T applied to the voltage drive thyristor becomes the power supply voltage Ed, the voltage increase rate dV / dt.
Rapidly decreases and becomes the power supply voltage Ed when the snubber current I _S (I _C + I _IGBT ) becomes zero. FIG. 3 shows the second aspect of the present invention.
3 shows a snubber circuit of an embodiment. The difference from the snubber circuit of FIG. 1 is that a constant voltage diode is connected in parallel with the capacitor. By connecting the constant voltage diode, it is possible to prevent the capacitor 2 of the snubber circuit 6 from being overvoltage when the voltage driving thyristor is turned off, and to prevent the overvoltage from being applied to the voltage driving thyristor.

From the above, by driving a current of half or more of the main current in the IGBT 4 during the turn-off period (several μs), the safe operation area is narrow, in other words, the voltage drive with a small allowable voltage increase rate. In the thyristor 1,
By connecting this snubber circuit 4, the allowable voltage rise rate dV
/ Dt can be reduced to 1/2 or less of the conventional value, and the turn-off can be reliably performed. Further, by reducing the Joule loss generated in the snubber circuit 6 at the time of turn-off to 1/4 or less, the size of the snubber circuit 4 can be reduced to 1/2 or less of the conventional size.

By connecting a constant voltage diode in parallel with the capacitor, the voltage jumping from the power supply voltage at the time of turn-off can be cut and the voltage-driven thyristor can be turned off more reliably.

[0015]

By using a snubber circuit having an IGBT, a capacitor and a resistor, the rate of increase in voltage (dV / dt) generated when the semiconductor device is switched off can be suppressed,
Even a voltage-driven thyristor with a narrow safe operation area can be reliably turned off. Further, since the generated loss of the snubber circuit can be reduced, the snubber circuit can be downsized. Furthermore, by connecting a constant voltage diode in parallel with the capacitor, it is possible to prevent an overvoltage applied to the voltage drive type thyristor and turn off more reliably.

[Brief description of drawings]

FIG. 1 is a snubber circuit diagram of a first embodiment of the present invention.

FIG. 2 is an operation waveform diagram of a voltage drive thyristor.

FIG. 3 is a snubber circuit diagram of a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional snubber circuit and a main circuit.

[Explanation of symbols]

1 voltage-driven thyristor 11 anode 12 cathode 2 capacitor 21 capacitor 3 resistor 31 resistor 32 resistor 4 IGBT 41 collector 42 emitter 43 gate 5 connection point 6 snubber circuit 7 a constant voltage diode 8 diode 9 reactor I _T voltage drive thyristor current V _T the voltage drive thyristor voltage I _S snubber current I _C capacitor current V _C capacitor voltage I _IGBT IGBT current I _R resistor current V _R resistor voltage

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H03K 17/567

Claims (3)

[Claims] 1. A snubber circuit for absorbing a spike voltage applied to a semiconductor device as switching means for opening and closing the circuit, wherein a collector and an emitter are respectively provided on an anode on a high potential side and a cathode on a low potential side of the semiconductor device. An insulated gate bipolar transistor (IGBT) connected to each other, a capacitor connected between the collector and the gate of the IGBT, and a resistor connected between the gate and the emitter of the snubber circuit of a semiconductor device. . 2. A snubber circuit for a semiconductor device according to claim 1, wherein a cathode and an anode of a constant voltage diode are connected to an emitter and a gate of the IGBT, respectively. 3. The snubber circuit for a semiconductor device according to claim 1, wherein the semiconductor device is a voltage-driven switching element.