CN220653203U - Active clamping circuit for switching tube and frequency converter - Google Patents

Abstract

The utility model relates to the technical field of frequency converters, in particular to an active clamping circuit for a switching tube and a frequency converter, and aims to solve the problem of peak voltage suppression. The TVS sub-circuit in the active clamp circuit comprises a bidirectional TVS, wherein the first end of the TVS sub-circuit is connected with a main electrode in the power input direction in a switching tube, and the second end of the TVS sub-circuit is connected with the first ends of the first sub-circuit and the second sub-circuit respectively; the two ends of the capacitor of the first sub-circuit are respectively connected with the first end and the second end; the second sub-circuit comprises a first unidirectional TVS unit, a second unidirectional TVS unit and an RC parallel unit which are connected in parallel, wherein the cathode and the anode of the first unidirectional TVS unit are respectively connected with the first end of the second sub-circuit and the cathode of the second unidirectional TVS unit, the anode of the second unidirectional TVS unit is connected with the second end of the second sub-circuit, and the second ends of the first sub-circuit and the second sub-circuit are also connected with the control electrode of the switching tube. With the above configuration, the spike voltage can be dynamically suppressed.

Description

Active clamping circuit for switching tube and frequency converter

Technical Field

The utility model relates to the technical field of frequency converters, in particular to an active clamping circuit for a switching tube and a frequency converter.

Background

The frequency converter generally adopts a full-control power electronic device (or a switching tube) such as IGBT (Insulate Gate Bipolar Transistor) and the like as a switching device to perform frequency conversion driving control on the high-speed motor. In order to realize reliable control of the high-speed motor, the switching frequency of switching tubes such as IGBTs in the frequency converter is often very high, so that the switching tubes need smaller control electrode resistance (such as gate electrode resistance or grid electrode resistance). However, taking an IGBT as an example, although the switching time is shortened due to the small gate resistance, a high collector current change rate di/dt is generated when the IGBT is turned off, particularly when the IGBT is turned off due to short-circuit protection, and stray inductances are distributed in a frequency conversion main loop of the frequency converter, and voltages generated between the collector and the emitter by the stray inductances under the action of the collector current change rate di/dt are superimposed on a bus of the frequency converter, so that peak voltages are generated. When the spike voltage is too large, the collector-emitter voltage of the IGBT exceeds the withstand blocking voltage, so that the IGBT is damaged.

For the problem of the spike voltage, an active clamp circuit is mainly provided for the IGBT in the frequency converter to suppress the spike voltage. As shown in fig. 1, an active clamp circuit composed of a unidirectional transient voltage suppression diode TVS, a fast recovery diode D1, and a resistor R2 is provided between the collector and the gate of the IGBT. However, such an active clamp circuit has only one clamped threshold voltage, and can only suppress a peak voltage exceeding the threshold voltage, which is relatively single, so that the suppression effect is poor.

Accordingly, there is a need in the art for a new solution to the above-mentioned problems.

Disclosure of Invention

In order to overcome the above-mentioned drawbacks, the present utility model is directed to an active clamp circuit for a switching tube and a frequency converter, which solve or at least partially solve the technical problem of how to effectively suppress a spike voltage generated on a bus of the frequency converter when the switching tube such as an IGBT in the frequency converter is turned off.

In a first aspect, an active clamp circuit for a switching tube is provided, the active clamp circuit comprising a TVS sub-circuit, a first sub-circuit, and a second sub-circuit;

the TVS sub-circuit comprises at least one bidirectional TVS diode, a first end of the TVS sub-circuit is connected with a main electrode in the power input direction in the switching tube, and a second end of the TVS sub-circuit is connected with first ends of the first sub-circuit and the second sub-circuit respectively;

the first sub-circuit comprises a first capacitor, two ends of the first capacitor are respectively connected with a first end and a second end of the first sub-circuit, and the second end is also connected with a control electrode of the switching tube;

the second sub-circuit comprises a first unidirectional TVS unit, a second unidirectional TVS unit and an RC parallel unit which are connected in parallel, wherein the first unidirectional TVS unit and the second unidirectional TVS unit comprise a unidirectional TVS diode or a plurality of unidirectional TVS diodes connected in series;

the cathode and the anode of the first unidirectional TVS unit are respectively connected with the first end of the second sub-circuit and the cathode of the second unidirectional TVS unit, the anode of the second unidirectional TVS unit is connected with the second end of the second sub-circuit, and the second end is also connected with the control electrode of the switching tube.

In one aspect of the above active clamp circuit, the TVS sub-circuit includes a bidirectional TVS diode;

alternatively, the TVS sub-circuit includes a bidirectional TVS diode and at least one unidirectional TVS diode connected in series with the bidirectional TVS diode, wherein in a series structure formed by the bidirectional TVS diode and the at least one unidirectional TVS diode, a cathode and an anode of each unidirectional TVS diode are respectively connected with a first end and a second end of the TVS sub-circuit;

alternatively, the TVS sub-circuit includes a plurality of bi-directional TVS diodes connected in series and at least one uni-directional TVS diode connected in series again with the plurality of bi-directional TVS diodes connected in series, wherein in a series structure formed by the plurality of bi-directional TVS diodes connected in series and the at least one uni-directional TVS diode, a cathode and an anode of each uni-directional TVS diode are connected to a first end and a second end of the TVS sub-circuit, respectively.

In one aspect of the above active clamp circuit, the first sub-circuit further includes a current limiting resistor, and the first capacitor is connected to the first end of the first sub-circuit through the current limiting resistor.

In one technical scheme of the active clamp circuit, the active clamp circuit further comprises an amplifying circuit, and the second end of the first sub-circuit is connected with the control electrode of the switching tube through the amplifying circuit.

In one technical scheme of the active clamp circuit, the first sub-circuit further includes a first diode, an anode of the first diode is connected with the first capacitor, and a cathode of the first diode is connected with the second end of the first sub-circuit.

In one technical scheme of the active clamp circuit, the second sub-circuit further comprises a second diode, an anode of the second diode is connected with an anode of the second unidirectional TVS unit, and a cathode of the second diode is connected with a second end of the second sub-circuit.

In one technical scheme of the active clamp circuit, the second end of the first sub-circuit is connected with the control electrode of the switching tube through the gate electrode resistor of the switching tube, and the second end of the second sub-circuit is also connected with the control electrode of the switching tube through the gate electrode resistor.

In one technical scheme of the active clamp circuit, the active clamp circuit further comprises a third diode, an anode of the third diode is connected between the gate resistor and the control electrode of the switching tube, and a cathode of the third diode is connected with a power supply.

In one technical scheme of the active clamp circuit, the first avalanche breakdown voltage value, the second avalanche breakdown voltage value and the third avalanche breakdown voltage value are sequentially increased and are all larger than the bus overvoltage value of the frequency converter to which the switching tube belongs;

the first avalanche breakdown voltage value is an avalanche breakdown voltage value of the TVS sub-circuit, the second avalanche breakdown voltage value is a sum of avalanche breakdown voltage values of the TVS sub-circuit and the first unidirectional TVS unit, and the third avalanche breakdown voltage value is a sum of avalanche breakdown voltage values of the TVS sub-circuit, the first unidirectional TVS unit and the second unidirectional TVS unit.

In a second aspect, a frequency converter is provided, which comprises an active clamp circuit according to any one of the above solutions for an active clamp circuit of a switching tube.

The technical scheme provided by the utility model has at least one or more of the following beneficial effects:

in the technical scheme for implementing the active clamp circuit for the switching tube, the active clamp circuit can comprise a TVS (Transient Voltage Suppressor) sub-circuit, a first sub-circuit and a second sub-circuit, wherein the TVS sub-circuit comprises at least one bidirectional TVS diode, the first end of the TVS sub-circuit is connected with a main electrode in the power input direction of the switching tube, and the second end of the TVS sub-circuit is connected with the first ends of the first sub-circuit and the second sub-circuit respectively; the first sub-circuit comprises a first capacitor, two ends of the first capacitor are respectively connected with a first end and a second end of the first sub-circuit, and the second end is also connected with a control electrode of the switching tube; the second sub-circuit comprises a first unidirectional TVS unit, a second unidirectional TVS unit and an RC parallel unit which are connected in parallel, wherein the first unidirectional TVS unit and the second unidirectional TVS unit comprise a unidirectional TVS diode or a plurality of unidirectional TVS diodes connected in series; the cathode and the anode of the first unidirectional TVS unit are respectively connected with the first end of the second sub-circuit and the cathode of the second unidirectional TVS unit, the anode of the second unidirectional TVS unit is connected with the second end of the second sub-circuit, and the second end is also connected with the control electrode of the switching tube. In the structure, three different clamping threshold voltages can be formed by utilizing the avalanche breakdown voltage values of the TVSs in the TVS sub-circuit, the first unidirectional TVS unit and the second unidirectional TVS unit, so that peak voltages generated under three conditions can be restrained, dynamic restraint of the peak voltages is realized, and the restraining effect of the peak voltages is remarkably improved.

Drawings

The present disclosure will become more readily understood with reference to the accompanying drawings. As will be readily appreciated by those skilled in the art: the drawings are for illustrative purposes only and are not intended to limit the scope of the present utility model. Wherein:

FIG. 1 is a schematic diagram of a prior art active clamp circuit for a switching tube;

FIG. 2 is a schematic diagram of an active clamp circuit for a switching tube according to one embodiment of the utility model;

fig. 3 is a schematic diagram of a TVS sub-circuit in accordance with one embodiment of the present utility model;

fig. 4 is a schematic diagram of a TVS sub-circuit in accordance with another embodiment of the present utility model;

fig. 5 is a schematic diagram of an active clamp circuit for a switching tube according to another embodiment of the utility model.

Detailed Description

Some embodiments of the utility model are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are merely for explaining the technical principles of the present utility model, and are not intended to limit the scope of the present utility model.

First, a switching tube according to the present utility model will be explained.

The switching transistor may be a fully controlled power semiconductor device, such as a Metal-Oxide-semiconductor field effect transistor (MOSFET), an insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, IGBT), or an integrated gate commutated thyristor (Integrated Gate Commutated Thyristor, IGCT), among others. Meanwhile, the switching transistors are all three-terminal devices, such as a MOSFET (metal oxide semiconductor field effect transistor) comprising a source electrode, a drain electrode and a gate electrode, and an IGBT comprising a collector electrode, an emitter electrode and a gate electrode. Wherein the source, drain, collector and emitter are main electrodes and the gate and gate are control electrodes. In the utility model, a main electrode in a power input direction in a switching tube is described as a first main electrode (such as a drain electrode of a MOSFET and a collector electrode of an IGBT), and a main electrode in a power output direction is described as a second main electrode (such as a source electrode of the MOSFET and an emitter electrode of the IGBT).

Embodiments of the active clamp circuit provided by the present utility model are described below.

Referring to fig. 2, fig. 2 is a schematic diagram of an active clamp circuit according to one embodiment of the utility model. As shown in fig. 2, the active clamp circuit in the embodiment of the present utility model mainly includes a TVS sub-circuit, a first sub-circuit, and a second sub-circuit, and is connected between a control electrode of a switching tube and a main electrode (i.e., a first main electrode) in a power input direction.

1. TVS sub-circuit

In this embodiment, the TVS sub-circuit may include at least one bidirectional TVS diode, where a first terminal of the TVS sub-circuit is connected to the first main electrode of the switching tube, and a second terminal of the TVS sub-circuit is connected to the first terminals of the first sub-circuit and the second sub-circuit, respectively. As shown in fig. 2, the TVS sub-circuit may include a bidirectional TVS diode TVS3, and two ends of the TVS3 are connected to the first and second ends of the TVS sub-circuit, respectively.

In some embodiments, the TVS sub-circuit may also include a bi-directional TVS diode and at least one uni-directional TVS diode in series with the bi-directional TVS diode. In a series structure formed by the bidirectional TVS diode and the at least one unidirectional TVS diode, the cathode and the anode of each unidirectional TVS diode are respectively connected with the first end and the second end of the TVS sub-circuit. As shown in fig. 3, the TVS sub-circuit may include one bidirectional TVS diode TVS1 and two unidirectional TVS diodes TVS2, TVS3 connected in series therewith. In the series structure formed by TVSs 1-3, the cathode and anode of TVS2 are respectively connected with the first and second ends of the TVS sub-circuit, and the cathode and anode of TVS3 are also respectively connected with the first and second ends of the TVS sub-circuit.

In some embodiments, the TVS sub-circuit may further include a plurality of bi-directional TVS diodes connected in series and at least one uni-directional TVS diode connected in series again with the plurality of bi-directional TVS diodes, wherein the cathode and anode of each uni-directional TVS diode are connected to the first and second ends of the TVS sub-circuit, respectively, in a series configuration of the plurality of bi-directional TVS diodes connected in series with the at least one uni-directional TVS diode. As shown in fig. 4, the TVS sub-circuit may include two bi-directional TVS diodes TVS1, TVS2 connected in series, and two uni-directional TVS diodes TVS3, TVS4 connected in series again with TVS1, TVS2. In the series structure formed by TVSs 1-4, the cathode and anode of each TVS are connected with the first and second ends of the TVS sub-circuit respectively.

As shown in fig. 2, since the switching tube Q is connected in anti-parallel with the diode D, a forward recovery current is generated through the diode D when the switching tube Q is turned on, and the forward recovery current forms a loop with the switching tube Q through the active clamp circuit. In this loop, the capacitance between the second main electrode (e.g., the emitter of the IGBT) of the switching tube Q and the analog ground is charged, so that the voltage of the second main electrode increases, while the voltage of the power source (e.g., +15v power source) applied to the control electrode (e.g., the gate of the IGBT) of the switching tube Q is unchanged, which results in a decrease in the voltage between the control electrode and the second main electrode, that is, the turn-on voltage of the switching tube Q. If the on voltage drops to the threshold of the under-voltage protection, the switching tube Q is turned off. In contrast, the bidirectional TVS diode is arranged in the TVS sub-circuit, so that the occurrence of the situation can be avoided, and the switching tube Q can be normally turned on.

2. First sub-circuit

As shown in fig. 2, in this embodiment, the first sub-circuit may include a first capacitor C1, where two ends of the first capacitor C1 are connected to a first end and a second end of the first sub-circuit, respectively, and the second end of the first sub-circuit is further connected to the control electrode of the switching tube Q. In some embodiments, the second terminal of the first sub-circuit may be connected to the control electrode of the switching tube through the gate resistor of the switching tube. As shown in fig. 5, the second end of the first sub-circuit is connected to one end of the gate resistor Rg of the switching tube Q, and the other end of the gate resistor Rg is connected to the control electrode of the switching tube Q.

The process of voltage clamping the first sub-circuit is described below.

If the TVS sub-circuit breaks down while the switching tube Q is turned off, the first sub-circuit will act as a clamp. Under the action of the voltage change rate between the first and second main electrodes of the switching tube Q (e.g., the change rate dcpe/dt of the voltage Vce between the collector and the emitter of the IGBT), the first capacitor C1 generates a current I1 shown in fig. 2, and the voltage generated by the current I1 on the gate resistor of the switching tube Q increases the voltage of the control electrode of the switching tube Q (e.g., the gate voltage of the IGBT) and makes the voltage of the control electrode greater than the turn-on threshold voltage. In this way, the voltage of the control electrode can be gradually increased, and further, the voltage rise between the first main electrode and the second main electrode can be restrained, and the spike voltage can be restrained.

3. Second sub-circuit

The second sub-circuit may include a first unidirectional TVS unit and a second unidirectional TVS unit and an RC parallel unit connected in parallel in this embodiment. In some embodiments, the second terminal of the second sub-circuit may also be connected to the control electrode of the switching tube through the gate resistor of the switching tube. As shown in fig. 5, the second end of the second sub-circuit is connected to one end of the gate resistor Rg of the switching tube Q, and the other end of the gate resistor Rg is connected to the control electrode of the switching tube Q.

The first unidirectional TVS unit may include one unidirectional TVS diode or a plurality of unidirectional TVS diodes connected in series. As shown in fig. 2, the first unidirectional TVS unit may include one unidirectional TVS diode TVS2. When only one unidirectional TVS diode is included, the cathode and anode of the first unidirectional TVS unit are the cathode and anode of this unidirectional TVS diode; when a plurality of unidirectional TVS diodes are included in series, the cathode and anode of the first unidirectional TVS unit are the cathode and anode of the series structure formed by these unidirectional TVS diodes.

The second unidirectional TVS unit may also include one unidirectional TVS diode or a plurality of unidirectional TVS diodes connected in series. As shown in fig. 2, the second unidirectional TVS unit may include one unidirectional TVS diode TVS3. Meanwhile, the TVS3 is connected in parallel with an RC parallel unit formed by the resistor R and the capacitor C. The cathode and anode of the second unidirectional TVS unit are similar to those of the first unidirectional TVS unit and are not described herein. Further, the cathode of the first unidirectional TVS unit is connected with the first end of the second sub-circuit, the anode of the first unidirectional TVS unit is connected with the cathode of the second unidirectional TVS unit, the anode of the second unidirectional TVS unit is connected with the second end of the second sub-circuit, and the second end of the second sub-circuit is also connected with the control electrode of the switching tube.

The process of voltage clamping the second sub-circuit is described below.

1. First case

If the TVS sub-circuit and the first unidirectional TVS unit are broken down while the switching tube Q is turned off, but the second unidirectional TVS unit is not broken down, the first sub-circuit may be bypassed, and the second sub-circuit may play a role of clamping. At this time, the capacitor of the RC parallel unit in the second sub-circuit is equivalent to being parallel connected with the miller capacitor of the switching tube Q, and this capacitor will start to charge, slow down the rise of the voltage between the first and second main electrodes, and play a role in suppressing the spike voltage. In this embodiment, the capacitance of the RC parallel unit is much larger than that of the miller capacitance, so the capacitance of the miller capacitance is negligible.

2. Second case

If the TVS sub-circuit, the first unidirectional TVS unit, and the second unidirectional TVS unit are broken down while the switching tube Q is turned off, the second sub-circuit still functions as a clamp. At this time, the breakdown current (I2 in fig. 2) will increase the voltage of the control electrode (e.g. the gate voltage of the IGBT) of the switching transistor Q by the voltage generated by the second sub-circuit on the gate resistor of the switching transistor Q, and make the voltage of the control electrode greater than the turn-on threshold voltage. In this way, the voltage of the control electrode can be gradually increased, and further, the voltage rise between the first main electrode and the second main electrode can be restrained, and the spike voltage can be restrained.

In the embodiment of the utility model, three clamping threshold voltages can be formed by the TVS sub-circuit, the first unidirectional TVS unit and the second unidirectional TVS unit, so that dynamic suppression of peak voltage is realized. Specifically, the avalanche breakdown voltage value Vtvs1 of the TVS sub-circuit forms a first avalanche breakdown voltage value, the sum of the avalanche breakdown voltage values (vtvs1+vtvs2) of the TVS sub-circuit and the first unidirectional TVS unit forms a second avalanche breakdown voltage value, and the sum of the avalanche breakdown voltage values (vtvs1+vtvs2+vtvs3) of the TVS sub-circuit, the first unidirectional TVS unit and the second unidirectional TVS unit forms a third avalanche breakdown voltage value. The first avalanche breakdown voltage value, the second avalanche breakdown voltage value and the third avalanche breakdown voltage value are sequentially increased and are all larger than the busbar overvoltage value udc_max of the frequency converter to which the switching tube belongs.

When the peak voltage is larger than the first avalanche breakdown voltage value but smaller than the second avalanche breakdown voltage value and the third avalanche breakdown voltage value, the TVS sub-circuit is broken down, and the first sub-circuit plays a role in clamping; when the peak voltage is larger than the second avalanche breakdown voltage value but smaller than the third avalanche breakdown voltage value, the TVS sub-circuit and the first unidirectional TVS unit are broken down, and the second sub-circuit plays a role in clamping; when the peak voltage is larger than the third avalanche breakdown voltage value, the TVS sub-circuit and the first and second unidirectional TVS units are broken down, and the second sub-circuit still plays a role of clamping. The specific process of the first and second sub-circuits for clamping is referred to in the foregoing description, and will not be described herein.

The first, second and third avalanche breakdown voltage values can be flexibly set by those skilled in the art according to actual requirements, which is not particularly limited in the embodiment of the present utility model. For example, in some preferred embodiments, the first, second, third avalanche breakdown voltage values satisfy the following conditions:

Udc_max＜Vtvs1＜Vces*70％；

Udc_max＜(Vtvs2+Vtvs1)＜Vces*75％；

Udc_max＜(Vtvs1+Vtvs2+Vtvs3)＜Vces*80％。

vces is the voltage between the first and second main electrodes when the switching transistor is operating in saturation (e.g., the voltage between the collector and emitter when the IGBT is operating in saturation).

The first sub-circuit and the second sub-circuit are further described below.

1. A first sub-circuit is described.

In some embodiments, the first sub-circuit may further include a current limiting resistor through which the first capacitor is connected to the first end of the first sub-circuit. As shown in fig. 5, the first sub-circuit may include a current limiting resistor R1, and one end of the first capacitor C1 is connected to this current limiting resistor R1, and the other end is connected to the first end of the first sub-circuit.

The first sub-circuit is not provided with unidirectional TVS diodes as compared to the second sub-circuit. The more unidirectional TVS diodes in general, the greater the peak current that the second sub-circuit will experience. The current limiting resistor R1 is arranged in the first sub-circuit, so that the peak current (or breakdown current) can be limited, and the peak current born by the second sub-circuit is reduced, thereby playing a role in protecting the unidirectional TVS diode in the second sub-circuit.

Further, in some embodiments, the active clamp circuit may further include an amplifying circuit, and the second end of the first sub-circuit may be connected to a control electrode of the switching transistor through the amplifying circuit. As shown in fig. 5, the active clamp circuit may include a gate push-pull amplifying circuit composed of two triodes (PNP and NPN), and the second end of the first sub-circuit is connected to one end of the gate push-pull amplifying circuit, and the other end of the gate push-pull amplifying circuit is connected to the control electrode of the switching transistor Q.

As shown in fig. 5, the current I1 is smaller after being limited by the current limiting resistor, and if the current I1 is directly applied to the gate resistor Rg to generate a voltage, the voltage of the control electrode of the switching tube Q is not effectively increased, so that the suppression effect of the spike voltage is affected. In this regard, the current after current limiting may be amplified by amplifying the current, and then a voltage is generated on the gate resistor Rg by the amplified current, thereby improving the suppression effect of the spike voltage.

In some embodiments, the first sub-circuit may further include a first diode, an anode of the first diode being connected to the first capacitor, and a cathode of the first diode being connected to the second terminal of the first sub-circuit. As shown in fig. 5, the first sub-circuit may include a first diode D1, an anode of the D1 is connected to one end of the first capacitor C1, and a cathode of the D1 is connected to a second end of the first sub-circuit. In fig. 5, a current limiting resistor R1 is provided, where the cathode of D1 may be connected to one end of the current limiting resistor R1, and the other end of the current limiting resistor R1 is connected to the second end of the first sub-circuit. Based on the arrangement of the first diode, the control electrode current of the switching tube can be prevented from flowing back to the first main electrode through the first sub-circuit, for example, the gate electrode current of the IGBT can be prevented from flowing back to the collector through the first sub-circuit.

2. The second sub-circuit is described.

In some embodiments, the second sub-circuit may further include a second diode, an anode of the second diode being connected to an anode of the second unidirectional TVS unit, and a cathode of the second diode being connected to a second terminal of the second sub-circuit. As shown in fig. 5, the second sub-circuit may include a second diode D2, the anode of D2 being connected to the anode of the second unidirectional TVS unit, and the cathode of D2 being connected to the second terminal of the second sub-circuit. In fig. 5, the second unidirectional TVS unit includes only one unidirectional TVS diode TVS2, where the anode of D2 is connected to the anode of TVS2. Based on the arrangement of the second diode, the control electrode current of the switching tube can be prevented from flowing back to the first main electrode through the second sub-circuit, for example, the gate electrode current of the IGBT can be prevented from flowing back to the collector through the second sub-circuit.

In an embodiment of the active clamp circuit provided by the utility model, the active clamp circuit may further include a third diode, an anode of the third diode is connected between the gate resistor and the control electrode of the switching tube, and a cathode of the third diode is connected to a power supply. As shown in fig. 5, the active clamp circuit may include a third diode D3, the anode of D3 is connected between the gate resistor Rg and the control electrode of the switching tube Q, and the cathode of D3 is connected to the +15v power supply. Based on the setting of the third triode, the voltage of the control electrode can be clamped into positive voltage, so that the switching tube can be driven normally.

The utility model further provides a frequency converter.

In an embodiment of a frequency converter according to the utility model, the frequency converter may comprise an active clamp as described in the active clamp embodiment above. The frequency converter in the embodiment is a frequency converter constructed based on a switching tube. In some embodiments the frequency converter may be used as a frequency converter for frequency converting drives of high power, high speed motors. It should be noted that, the frequency converter further includes some conventional devices that enable the frequency converter to operate normally, and the embodiments of the present utility model do not specifically limit and describe these conventional devices.

Thus far, the technical solution of the present utility model has been described in connection with one embodiment shown in the drawings, but it is easily understood by those skilled in the art that the scope of protection of the present utility model is not limited to these specific embodiments. Equivalent modifications and substitutions for related technical features may be made by those skilled in the art without departing from the principles of the present utility model, and such modifications and substitutions will fall within the scope of the present utility model.

Claims (10)

1. An active clamp circuit for a switching tube, wherein the active clamp circuit comprises a TVS sub-circuit, a first sub-circuit and a second sub-circuit;

the TVS sub-circuit comprises at least one bidirectional TVS diode, a first end of the TVS sub-circuit is connected with a main electrode in the power input direction in the switching tube, and a second end of the TVS sub-circuit is connected with first ends of the first sub-circuit and the second sub-circuit respectively;

the first sub-circuit comprises a first capacitor, two ends of the first capacitor are respectively connected with a first end and a second end of the first sub-circuit, and the second end is also connected with a control electrode of the switching tube;

the second sub-circuit comprises a first unidirectional TVS unit, a second unidirectional TVS unit and an RC parallel unit which are connected in parallel, wherein the first unidirectional TVS unit and the second unidirectional TVS unit comprise a unidirectional TVS diode or a plurality of unidirectional TVS diodes connected in series;

the cathode and the anode of the first unidirectional TVS unit are respectively connected with the first end of the second sub-circuit and the cathode of the second unidirectional TVS unit, the anode of the second unidirectional TVS unit is connected with the second end of the second sub-circuit, and the second end is also connected with the control electrode of the switching tube.

2. The active clamp circuit of claim 1, wherein,

the TVS sub-circuit comprises a bidirectional TVS diode;

or,

the TVS sub-circuit comprises a bidirectional TVS diode and at least one unidirectional TVS diode connected in series with the bidirectional TVS diode, wherein in a serial structure formed by the bidirectional TVS diode and the at least one unidirectional TVS diode, the cathode and the anode of each unidirectional TVS diode are respectively connected with a first end and a second end of the TVS sub-circuit;

or,

the TVS sub-circuit comprises a plurality of series-connected bidirectional TVS diodes and at least one unidirectional TVS diode which is connected with the plurality of series-connected bidirectional TVS diodes in series again, wherein in a series structure formed by the plurality of series-connected bidirectional TVS diodes and the at least one unidirectional TVS diode, the cathode and the anode of each unidirectional TVS diode are respectively connected with the first end and the second end of the TVS sub-circuit.

3. The active clamp circuit of claim 1, wherein the first sub-circuit further comprises a current limiting resistor, the first capacitor being coupled to the first end of the first sub-circuit through the current limiting resistor.

4. The active clamp circuit of claim 3, further comprising an amplifier circuit, wherein the second terminal of the first sub-circuit is coupled to the control electrode of the switching tube through the amplifier circuit.

5. The active clamp circuit of claim 1, wherein the first sub-circuit further comprises a first diode, an anode of the first diode being coupled to the first capacitor, and a cathode of the first diode being coupled to the second terminal of the first sub-circuit.

6. The active clamp circuit of claim 1, wherein the second sub-circuit further comprises a second diode, an anode of the second diode being connected to an anode of the second uni-directional TVS unit, and a cathode of the second diode being connected to a second terminal of the second sub-circuit.

7. The active clamp circuit of claim 1, wherein the second terminal of the first sub-circuit is connected to the control electrode of the switching tube through a gate resistor of the switching tube, and the second terminal of the second sub-circuit is also connected to the control electrode of the switching tube through the gate resistor.

8. The active clamp circuit of claim 7, further comprising a third diode, an anode of the third diode connected between the gate resistor and a control electrode of the switching tube, and a cathode of the third diode connected to a power supply.

9. The active clamp circuit of any one of claims 1 to 8,

the first avalanche breakdown voltage value, the second avalanche breakdown voltage value and the third avalanche breakdown voltage value are sequentially increased and are all larger than the bus overvoltage value of the frequency converter to which the switching tube belongs;

the first avalanche breakdown voltage value is an avalanche breakdown voltage value of the TVS sub-circuit, the second avalanche breakdown voltage value is a sum of avalanche breakdown voltage values of the TVS sub-circuit and the first unidirectional TVS unit, and the third avalanche breakdown voltage value is a sum of avalanche breakdown voltage values of the TVS sub-circuit, the first unidirectional TVS unit and the second unidirectional TVS unit.

10. A frequency converter, characterized in that it comprises an active clamp circuit for a switching tube according to any of claims 1 to 9.