JPH0969766A - Opposite-conduction voltage clamp circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage clamping circuit which has the characteristic of a Zener diode used in a power converter or the like and has a high voltage and a large capacity. SOLUTION: A semiconductor switching element (for example, an IGBT insulated gate bipolar transistor TR) 1 and a diode 2 which has the cathode and the anode connected in antiparallel to the collector and the emitter of the semiconductor switching element 1 are provided, and a first resistance R1 (3) is connected between the collector and the gate of the semiconductor switching element 1, and a second resistance R2 (4) is connected between the sate and the emitter. First and second resistances R1 and R2 are so selected that VCE=VGES×[(R1+R2)/R2] is true with respect to relations between a clamp voltage VCE and a threshold VGES of the voltage between the gate and the emitter which switches the cut-off state between the collector and the emitter of the semiconductor switching element 1 to the conduction state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage clamp circuit having the function of a Zener diode and having a reverse conduction characteristic with a large current capacity.

[0002]

2. Description of the Related Art Conventionally, a Zener diode has been used for a small signal circuit for clamping a voltage, and a semiconductor element using zinc oxide such as a varistor has been used for clamping an instantaneous high voltage such as lightning surge. On the other hand, in a circuit having a Zener diode characteristic such as a snubber circuit in a power conversion circuit using a power semiconductor element, a voltage called a diode clipper using a diode 11 and a capacitor 12 shown in FIG. 7 [conventional diode clipper circuit] is used. Clamp circuits have been used. And as a result of clamping the voltage,
The electric charge stored in the capacitor 12 was discharged (consumed as Joule heat) by the resistor 13 connected as a discharge circuit [hereinafter, these are collectively referred to as "conventional example 1"]. Further, as a second conventional example, JP-A-3-250311
・ There is a positive / negative voltage output switching circuit. This is a direct current power source having positive and negative output terminals, a first Zener diode whose cathode is connected between the negative output terminal of the direct current power source and ground, and a positive output terminal of the direct current power source and the first Zener diode. A resistor connected between the anode of the first Zener diode, a regulator circuit, and a series circuit of a second Zener diode having a Zener voltage higher than the first Zener diode, an anode of the second Zener diode, and the regulator. A positive / negative voltage output switching circuit including an output terminal drawn from a connection point with the circuit, and a bias resistor connected between cathodes of the first and second Zener diodes.

[0003]

However, each of the voltage clamp circuits of Conventional Example 1 has the following drawbacks, and it has not satisfied the demands of the power conversion device. That is, as shown in FIG. 5 [a characteristic diagram of the anode current corresponding to the voltage between the anode and the cathode of the conventional Zener diode], the Zener diode has a good voltage clamp characteristic, but has a capacity of several W at the most, and a plurality of Zener diodes are used. Must be used in parallel. Moreover, in that case, those having the same Zener voltage must be combined. As shown in FIG. 6 [Characteristic diagram of varistor current corresponding to varistor voltage of conventional varistor], the varistor has a good voltage clamp characteristic at a high voltage of several hundreds of volts, but the amount of absorbed energy is small and it cannot be used continuously. In addition, since the operation characteristics are bidirectionally symmetric, an antiparallel connection diode is required in order to provide reverse conductivity like a Zener diode. Since the diode clipper circuit of FIG. 7 stores the electric power at the time of voltage clamping in the capacitor 12 through the diode 11, the clamp voltage fluctuates, which is not desirable in characteristics. Further, since the stored power is not instantly consumed but is stored as electric charge and is discharged by the resistor 13, in order to provide reverse conduction characteristics, the diode clipper circuit in which the circuit configuration of FIG. 7 is further provided with a reverse conduction function. ], Two diodes are required. Further, the conventional example 2 is a positive / negative voltage output switching circuit for supplying a predetermined DC voltage (medium voltage) to a developing device in an electrophotographic copying machine, a laser beam printer or the like, which is a circuit requiring an instantaneous high voltage. Is not appropriate, and is disadvantageous in cost for applications that do not require switching between positive and negative voltage outputs. In view of the above problems, it is an object of the present invention to provide a high voltage, large voltage clamp circuit having the characteristics of a Zener diode used in a power converter or the like.

[0004]

In order to solve the above-mentioned problems, a voltage clamp circuit of the present invention comprises a semiconductor switching element and an anti-parallel connection in which a cathode and an anode are connected to a collector and an emitter of the semiconductor switching element, respectively. A first resistor R1 is connected between the diode and the collector and gate of the semiconductor switching element, a second resistor R2 is connected between the gate and emitter, and a first resistor R1 is connected.
The resistance values of the first and second resistors R2 are the required collector-emitter voltage VCE, which is a clamp voltage, and the threshold voltage VGES of the gate-emitter voltage that brings the collector-emitter of the semiconductor switching element from the cut-off state to the conductive state. From the relationship of VCE = VGES × {(R1 + R2) / R
2} is selected so that the required clamp voltage is obtained. Further, instead of the first resistor R1 between the collector and the gate of the semiconductor switching element, the Zener voltage VD≈VCE-VGES is obtained by the collector-emitter voltage VCE and the threshold value VGES of the gate-emitter voltage.
Or a variable resistor at least one of the first resistor R1 and the second resistor R2, or a variable resistor is inserted between the first resistor R1 and the second resistor R2. This is means for connecting the terminal of the sliding portion to the gate of the semiconductor switching element so that the required collector-emitter voltage VCE can be adjusted. That is, a semiconductor switching element and a diode in which a cathode and an anode are connected in antiparallel to a collector and an emitter of the semiconductor switching element are provided, and a first resistor R1 is connected between the collector and the gate of the semiconductor switching element, The second resistor R2 is connected between the gate and the emitter of the switching element, and the clamp voltage VCE of the semiconductor switching element and the gate-emitter voltage for turning the collector-emitter of the semiconductor switching element from the cutoff state to the conduction state It is a reverse conduction voltage clamp circuit in which the circuit is configured by selecting the first resistor R1 and the second resistor R2 so that the relation of the threshold value VGES becomes approximately VCE = VGES × {(R1 + R2) / R2}. Based on the voltage VCE and the threshold VGES, the approximate Zener voltage VD = VCE- The reverse conduction voltage clamp circuit according to the above paragraph, wherein the Zener diode serving as GES is replaced with the first resistor R1, and further, at least one of the first resistor R1 and the second resistor R2 is replaced with a variable resistor. The reverse conduction voltage clamp circuit according to the preceding two paragraphs, wherein the variable resistance is inserted between the first resistor R1 and the second resistor R2, and the sliding portion of the variable resistor is connected. Is a reverse conduction voltage clamp circuit according to the first paragraph in which the terminal is connected to the gate of the semiconductor switching element, and in the reverse conduction voltage clamp circuit according to the preceding paragraphs, the semiconductor switching element is I
It is a reverse conduction voltage clamp circuit which is a GBT.

[0005]

According to the present invention, the collector-emitter voltage VCE≈gate-emitter voltage threshold VGES × {(R1 + R2) /
R2} and Zener voltage VD≈VCE-VGES
A clamp voltage having the relationship of is obtained, and a Zener diode characteristic of high voltage and large capacity, which is a substitute for the Zener diode or varistor of Conventional Example 1, is obtained. Further, the resistor is replaced with a variable resistor to make it possible to adjust the required collector-emitter voltage VCE, so that a Zener diode characteristic of high voltage, large capacity and variable voltage, which is not present in Conventional Example 1, can be obtained.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. In each drawing, the same reference numerals represent the same or corresponding members. 1 is a block diagram showing a circuit configuration of a voltage clamp circuit according to a first embodiment of the present invention. This voltage clamp circuit is a semiconductor switching device [Insulated Gate Bipolar Transistor (in this embodiment, simply referred to as “IG
BT ”)] and 1 and its semiconductor switching element. The diode 2 of the anti-parallel connection in which the cathode and anode are connected to the collector and emitter of 1 respectively.
, The first resistor 3 is connected between the collector and the gate of the semiconductor switching element 1 and the second resistor 4 is connected between the gate and the emitter.

Here, the voltage / current characteristics of the semiconductor switching element 1 will be described. The gate-emitter voltage is raised, and the gate-emitter voltage is changed to the threshold voltage VG.
When it exceeds ES, a current starts to flow between the collector and the emitter, and the semiconductor switching element 1 changes from the cutoff state to the conduction state. Although there is a relationship with the impedance of the circuit, when it becomes conductive, the collector-emitter voltage of the semiconductor switching element-1 decreases. When the collector-emitter voltage of the semiconductor switching element-1 is increased in the circuit of FIG. 1, the gate-emitter voltage is also approximately VGES × R.
It rises in the relationship of 2 / {(R1 + R2)}. Where R
1 and R2 are the resistance values of the first resistor 3 and the second resistor 4, respectively.

Semiconductor switching element 1 collector
Due to the rise of the voltage between the emitters, the gate-emitter is switched from the cutoff state to the conduction state, and the semiconductor switching element
The collector-emitter voltage of 1 decreases. Along with this, the gate-emitter voltage also drops, so that the semiconductor switching element 1 tries to return from the conductive state to the cutoff state. However, in this region, the gain of the collector current with respect to the gate-emitter voltage is finite, and the gate-emitter voltage eventually becomes the threshold VGES.
It converges to the voltage between emitters. That is, the collector-emitter voltage VCE has a value that substantially satisfies VCE = VGES × {(R1 + R2) / R2}.

The semiconductor switching element 1 is a voltage driving element, and when a reverse voltage is applied between the collector and the emitter, the diode 2 has a diode characteristic. The semiconductor switching element 1 has elements of 1000 V or more, several hundred A or more, several hundred W or more, and the above circuit can realize a voltage clamp circuit having a high-voltage large-capacity Zener diode characteristic. Instead of the resistor 3 between the collector and the gate of the semiconductor switching device 1 in FIG. 1, the collector-emitter voltage VCE and the gate-emitter voltage are set by the threshold value VGES as shown in FIG. 2, and the Zener voltage VD≈VCE−
It is also possible to replace with the Zener diode 5 which becomes VGES. Further, the resistor 3 or the resistor 4 or both of FIG. 1 can be replaced with the variable resistor 6 and the variable resistor 7 as shown in FIG. Further, the variable resistor 8 is inserted between the resistor 3 and the resistor 4 of FIG. 1, and the terminal of the sliding portion thereof is connected to the gate of the semiconductor switching element 1 as shown in FIG. It is also possible to make the emitter-to-emitter voltage VCE adjustable.

[0010]

As described above, if the voltage clamp circuit of the present invention is used, a Zener diode characteristic of a high voltage and a large capacity can be obtained in place of the Zener diode or varistor of Conventional Example 1, and the resistor can be a variable resistor. If it is replaced with, the required collector-emitter voltage VCE can be adjusted, and a special effect that a high-voltage large-capacity and variable-voltage Zener diode characteristic that is not present in Conventional Example 1 can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a second embodiment [replacing one resistor with a zener diode] of the present invention.

FIG. 3 is a block diagram showing a circuit configuration in a third embodiment of the present invention [replacing one resistor or the other resistor or both with a variable resistor].

FIG. 4 is a circuit configuration of a fourth embodiment of the present invention [a variable resistor is inserted between one resistor and the other resistor, and a terminal of a sliding portion thereof is connected to a gate of a semiconductor switching element]. Block diagram showing

FIG. 5 is a characteristic diagram of the anode current corresponding to the voltage between the anode and the cathode of the Zener diode of Conventional Example 1.

FIG. 6 is a characteristic diagram of varistor current corresponding to the varistor voltage of the varistor of Conventional Example 1.

FIG. 7 is a diode clipper circuit of Conventional Example 1

8 is a diode clipper circuit in which the circuit configuration of FIG. 7 is further provided with a reverse conduction function.

[Explanation of symbols]

1 Semiconductor switching element [eg IGBT, insulated gate bipolar transistor, Insulated Gate Bipo
lar Transistor] 2,11,14 Diode 3,4,13 Resistor 5 Zener diode 6,7,8 Variable resistor 12 Capacitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Yamada, No. 2 Kurosaki Shiroishi, Yawatanishi-ku, Kitakyushu, Fukuoka Prefecture Yasukawa Electric Co., Ltd.

Claims (5)

[Claims] 1. A semiconductor switching element, and a diode in which a cathode and an anode are connected in antiparallel to a collector and an emitter of the semiconductor switching element, and a first resistor R1 is connected between the collector and the gate of the semiconductor switching element. , A second resistor R2 is connected between the gate and the emitter of the semiconductor switching element to make the clamp voltage VCE of the semiconductor switching element and the collector-emitter of the semiconductor switching element from a cutoff state to a conduction state The first resistor R1 and the second resistor R2 such that the relationship between the threshold voltages VGES of the inter-voltage is approximately VCE = VGES × {(R1 + R2) / R2}.
The reverse conduction voltage clamp circuit is characterized in that the circuit is selected. 2. The clamp voltage VCE and the threshold VG
2. The reverse conduction voltage clamp circuit according to claim 1, wherein a Zener diode having a substantially Zener voltage VD = VCE-VGES is replaced by the first resistor R1 by ES. 3. The first resistor R1 and the second resistor R
2. The reverse conduction voltage clamp circuit according to claim 1, wherein at least one of the two is replaced with a variable resistor to configure the circuit. 4. The first resistor R1 and the second resistor R
2. The reverse conduction voltage clamp circuit according to claim 1, wherein a variable resistor is inserted and connected between the two, and a terminal of a sliding portion of the variable resistor is connected to a gate of the semiconductor switching element. 5. The reverse conduction voltage clamp circuit according to claim 1, wherein the semiconductor switching element is an IGBT.