JP2009273244A - Switching circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching circuit, with the recovery surge voltage suppressed. <P>SOLUTION: The switching circuit, supplying electric power to a load, includes: a switching element 10 capable of controlling opening and closing states between terminals by a control signal; a flywheel diode 14 connected to the switching element 10 in series and feeding back a current from the load, when the switching element 10 is open; and an adjustment circuit 22 for adjusting a control signal (gate voltage) of the switching element 10, according to the temporal changes of a voltage between terminals (between collector and emitter) when the switching element 10 is closed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching circuit used for power supply to a load.

  Switching circuits are widely used in chopper circuits and DC-DC converters in power supplies. For example, a switching circuit is also used in an inverter circuit for driving a load such as a motor mounted on an electric vehicle, a hybrid vehicle, or the like.

  A chopper circuit is disclosed in which two switching circuits composed of an anti-parallel circuit of an insulated gate bipolar transistor (IGBT) and a diode are connected in series. In such a chopper circuit, when the IGBT is turned on, a reverse recovery current flows through the flywheel diode, and the recovery surge voltage applied to the flywheel diode increases as the collector current of the IGBT changes due to the influence of the wiring inductance. There is a problem.

  FIG. 7 shows the time variation of the collector-emitter voltage Vce of the switching element, the flywheel diode terminal voltage Vd, the output capacitor terminal voltage Vc, and the induced voltage VL caused by the parasitic inductance of the circuit when the switching element is turned on. Indicates. FIG. 7A shows a case where the collector current Ic of the switching element is relatively small, and FIG. 7B shows a case where the collector current Ic of the switching element is relatively large.

  The recovery surge voltage generated in the flywheel diode when the switching element is turned on is caused by a voltage induced by the parasitic inductance of the circuit due to dId / dt when the reverse recovery current of the flywheel diode returns to zero.

  As shown in FIG. 8, the equivalent circuit of the switching circuit includes parasitic inductors LU, LM, and LL included in each wiring. The recovery surge voltage (Vd) can be expressed by Equation (1) using an induced voltage VL = VLU + VLM + VLL expressed by the sum of voltages VLU, VLM, VLL generated by the respective parasitic inductors LU, LM, LL.

  Recovery surge voltage Vd = Vc−Vce−VL (1)

  When the collector current Ic of the switching element is relatively small, the collector current Ic of the switching element decreases rapidly when the switching element is turned on, and switching occurs when the recovery surge voltage (Vd) generated at both ends of the flywheel diode has a peak value. The collector-emitter voltage Vce of the element has already decreased, and the recovery surge voltage (Vd) increases as shown in FIG.

  On the other hand, when the collector current Ic of the switching element is relatively large, it takes time to lower the collector current Ic of the switching element when the switching element is turned on, and the recovery surge voltage (Vd) generated at both ends of the flywheel diode peaks. When the value is reached, the collector-emitter voltage Vce of the switching element is maintained relatively large, so that the recovery surge voltage (Vd) is relatively small as shown in FIG. 7B.

  In Patent Document 1, a current detector that flows through a diode is provided in the chopper circuit, thereby detecting a reverse recovery current of the flywheel diode, and an output thereof is input to the gate drive circuit of the IGBT via the insulation circuit. A circuit that suppresses the recovery surge voltage by controlling the turn-on time is disclosed.

Japanese Patent Laid-Open No. 10-127045

  However, when a current detector or an insulation circuit is provided to suppress the recovery surge voltage as in the above-described prior art, the configuration of the switching circuit becomes complicated, the circuit scale increases, and the manufacturing cost increases.

  The present invention is not limited to solving the above-described problems of the prior art, but an object of the present invention is to provide a switching circuit in which the influence of the recovery surge voltage is suppressed.

  One aspect of the present invention is a switching circuit for supplying power to a load, the switching element being capable of controlling an open / close state between terminals by a control signal, and connected in series to the switching element, wherein the switching element is opened. A flywheel diode that feeds back a current from the load when a state occurs, and an adjustment circuit that adjusts the control signal in accordance with a temporal change in the voltage between the terminals when the switching element is closed. It is characterized by providing.

  More specifically, it is preferable that the adjustment circuit slows down the switching element as the voltage drop rate between the terminals increases when the switching element is closed.

  For example, the adjustment circuit preferably includes a capacitor, a current limiting element connected in series to the capacitor, and a resistor connected in parallel with the current limiting element. Here, the current limiting element can be a diode. A series circuit of the current limiting element and the capacitor is connected to one end of the switching element, thereby adjusting the control signal of the switching element.

  The adjustment circuit may further include a resistor connected in series to the capacitor. By connecting a resistor in series with the capacitor, it is possible to adjust a control time constant of the control signal in accordance with a change in voltage between the terminals of the switching element. Thereby, for example, the occurrence of vibration in the control signal can be suppressed.

  More specifically, for example, the switching element is an IGBT, the current limiting element is an adjustment diode, and the adjustment circuit has a cathode of the adjustment diode connected to a collector of the IGBT, and the adjustment circuit It is preferable that the anode of the diode is connected to one end of the capacitor, and the other end of the capacitor is connected to the gate of the IGBT.

  Further, for example, the switching element is an FET, the current limiting element is an adjustment diode, and the adjustment circuit includes a cathode of the adjustment diode connected to a drain of the FET, and an anode of the adjustment diode It is preferable that the circuit is connected to one end of the capacitor and the other end of the capacitor is connected to the gate of the FET.

  ADVANTAGE OF THE INVENTION According to this invention, the switching circuit which suppressed the influence of the recovery surge voltage can be provided.

  As shown in FIG. 1, the switching circuit 100 according to the embodiment of the present invention includes a switching element 10, flywheel diodes 12 and 14, a capacitor 16, a control unit 18, a gate resistor 20, and an adjustment circuit 22. .

  A power source 200 is connected to the terminals T1 and T2 of the switching circuit 100. The power source 200 can be a DC power source. A load (for example, a motor) 300 is connected to the terminals T3 and T4 of the switching circuit 100. The switching circuit 100 receives power supplied from the power source 200, converts a voltage or the like, and supplies the power to the load 300.

  The switching element 10 is an element that can control opening and closing between terminals in response to a control signal. The switching element 10 can be, for example, an insulated gate bipolar transistor (IGBT), a field effect transistor (MOSFET), or the like. When the switching element 10 is an IGBT, the control signal is a gate voltage applied to the gate, and the collector-emitter is controlled to open and close. When the switching element 10 is a MOSFET, the control signal is a gate voltage applied to the gate, and the drain-source is controlled to open and close.

  Hereinafter, in the present embodiment, an IGBT will be described as an example, but the same applies to other switching elements such as MOSFETs.

  A flywheel diode 12 is connected in antiparallel between the collector and emitter of the switching element 10. The collector of the switching element 10 is connected to the terminal T4, and the emitter of the switching element 10 is connected to the terminal T2. The anode of the flywheel diode 14 is connected to the collector of the switching element 10, and the cathode is connected to the terminal T3. Terminal T3 and terminal T1 are short-circuited.

  Capacitor 16 is provided as a snubber for suppressing fluctuations in power supplied to load 300. Both ends of the capacitor are connected to terminals T2 and T3, whereby the capacitor 16 is connected in parallel to the series circuit of the switching element 10 and the flywheel diode 14.

  The control unit 18 generates a control signal for the switching element 10 and inputs the control signal to the gate of the switching element 10. The control signal from the control unit 18 opens and closes the collector-emitter of the switching element 10 and adjusts the output power supplied to the load 300 connected to the terminals T3 and T4. A control signal from the control unit 18 is input to the gate of the switching element 10 via the gate resistor 20.

  The switching circuit 100 according to the present embodiment further includes an adjustment circuit 22. The adjustment circuit 22 adjusts a control signal applied to the gate of the switching element 10 according to a temporal change in the collector-emitter voltage Vce when the switching element 10 is turned on. The basic adjustment is such that when the switching element 10 is turned on, the gate voltage is adjusted so that the rate at which the switching element 10 is turned on becomes slower as the rate of decrease in the collector-emitter voltage Vce increases.

  The adjustment circuit 22 includes a capacitor C, a diode D, and a resistor R1. The diode D is connected in parallel to the resistor R1, and the parallel connection circuit is connected in series to the capacitor C. The cathode of the diode D is connected to the collector side of the switching element 10, the anode of the diode D is connected to one end of the capacitor C, and the other end of the capacitor C is connected to the gate side of the switching element 10.

  Note that the diode D and the capacitor C do not need to be directly connected to the switching element 10, and for example, the capacitor C may be connected to the gate of the switching element 10 via the resistor R2. By connecting the resistor R2 in series with the capacitor C, it is possible to adjust the time constant when the control signal is controlled in accordance with the change in the collector-emitter voltage Vce of the switching element 10. Thereby, for example, the occurrence of vibration in the control signal can be suppressed.

  Hereinafter, the operation of the switching circuit 100 in the present embodiment will be described. FIG. 2 shows the collector-emitter voltage Vce of the switching element 10, the collector current Ic of the switching element 10, and the terminal voltage Vd of the flywheel diode 14 when the switching element 10 is turned on. In FIG. 2, a solid line indicates a change in the switching circuit 100 including the adjustment circuit 22, and a broken line indicates a change in the switching circuit 100 that does not include the adjustment circuit 22.

  As is apparent from FIG. 2, in the circuit provided with the adjustment circuit 22, the rate of decrease of the voltage Vce is slower than in the case where the adjustment circuit 22 is not provided, and the peak voltage value of the terminal voltage Vd of the flywheel diode 14 is also adjusted. The circuit is kept lower than the circuit without 22.

  That is, in the switching circuit 100 according to the embodiment of the present invention, since the adjustment circuit 22 including the capacitor C, the diode D, and the resistor R1 is connected between the gate and the collector, the collector current Ic of the switching element 10 is small, and the collector Even when the rate of decrease in the voltage Vce between the emitters is large, the adjustment circuit 22 suppresses an increase in the gate voltage of the switching element 10, and the switching speed of the switching element 10 becomes slow.

  On the other hand, when the collector current Ic of the switching element 10 is large and the decrease in the collector-emitter voltage Vce is slow, the influence of the adjustment circuit 22 on the gate voltage of the switching element 10 is small, and the switching speed of the switching element 10 is It does not decline.

  FIG. 3 is a diagram showing the relationship between the collector current Ic of the switching element 10 and the recovery surge voltage (Vd) of the flywheel diode 14 at the time of turn-on. FIG. 4 is a diagram showing the relationship between the collector current Ic of the switching element 10 and the switching loss of the switching element 10 at turn-on. 3 and 4, the solid lines indicate the characteristics of the switching circuit 100 including the adjustment circuit 22, and the broken lines indicate the characteristics of the switching circuit 100 that does not include the adjustment circuit 22.

  Even when the value of the gate resistance 20 is determined so as to suppress the switching loss of the switching element 10 to a desired value or less when the collector current Ic is large due to the operation of the adjustment circuit 22, The recovery surge voltage (Vd) of the flywheel diode 14 can be suppressed.

  Further, in the adjustment circuit 22 in the present embodiment, the diode D is connected in the forward direction from the gate to the collector, so that the collector-emitter voltage Vce becomes high when the switching element 10 is turned off. Thus, the influence of the collector-emitter voltage Vce is not transmitted to the gate because it passes through the resistor R1 and the capacitor C (and resistor R2). Therefore, the gate voltage of the switching element 10 is hardly affected by the collector-emitter voltage Vce.

  FIG. 5 shows the collector-emitter voltage Vce of the switching element 10, the collector current Ic of the switching element 10, and the terminal voltage Vd of the flywheel diode 14 when the switching element 10 is turned off. In FIG. 5, the solid line indicates a change in the switching circuit 100 when the adjustment circuit 22 is provided with the diode D, and the broken line is a case where the collector terminal of the switching element 10 and the capacitor are connected without providing the adjustment circuit 22 with the diode and R1. The change in the switching circuit 100 is shown.

  As is clear from FIG. 5, when the adjustment circuit 22 is provided with a diode, the switching element 10 is turned off when the adjustment circuit 22 is not provided with the diode and R1 and the collector terminal of the switching element 10 and the capacitor are connected. It can be shortened. This shows the same tendency even when the collector current Ic of the switching element 10 is small. Since the increase in the turn-off time of the switching element 10 merely increases the switching loss of the switching element 10, it can be said that the switching loss of the switching element 10 can be reduced by providing a diode in the adjustment circuit 22.

<Application example>
FIG. 6 shows an example in which the switching circuit 100 according to the embodiment of the present invention is applied to an inverter circuit for driving a three-phase motor.

  The inverter circuit in this application example includes switching circuits 100a to 100f, a power source 200, a load (three-phase motor) 300, and a control unit 400. The switching circuits 100a and 100b, the switching circuits 100c and 100d, and the switching circuits 100e and 100f constitute an inverter circuit as an upper arm and a lower arm, respectively. In this application example, the capacitors 16 of the switching circuits 100a to 100f are provided in common as a whole.

  The control unit 400 is connected to the control units of the switching circuits 100a to 100f. In the control unit 400, (1) any one of the switching circuits 100a, 100c, and 100e that are upper arms is on, and any two of the switching circuits 100b, 100d, and 100f that are lower arms are on, 2) The switching circuit 100a repeats such a state that any two of the switching circuits 100a, 100c, and 100e that are the upper arms are on and one of the switching circuits 100b, 100d, and 100f that are the lower arms is on. Control of ~ 100f is performed. As a result, power is transferred between the power source 200 and the load (three-phase motor) 300.

  Since the basic operation as an inverter circuit in this application example is the same as that of a conventional inverter circuit, detailed description is omitted. In the inverter circuit, a diode connected in antiparallel to the switching element in the off state functions as a flywheel diode.

  Also in this application example, the recovery surge voltage (Vd) of the flywheel diode when the collector current Ic is small can be suppressed by the action of the adjustment circuit provided in each of the switching circuits 100a to 100f. Further, by setting the gate resistance to an appropriate value, the switching loss of the switching element 10 when the collector current Ic is large can be suppressed to a desired value or less. Moreover, the switching speed at the time of turn-off is not lowered, and this can also suppress the switching loss.

It is a figure which shows the basic composition of the switching circuit in embodiment of this invention. It is a figure which shows the time change of the voltage Vce at the time of turn-on in embodiment of this invention, the voltage Vd, and the electric current Ic. It is a figure which shows the relationship between IGBT electric current and recovery surge voltage in embodiment of this invention. It is a figure which shows the relationship between IGBT electric current and switching loss in embodiment of this invention. It is a figure which shows the time change of the voltage Vce, the voltage Vd, and the electric current Ic at the time of turn-off in embodiment of this invention. It is a figure which shows the example of application of the switching circuit in embodiment of this invention. It is a figure which shows the time change of the voltage Vce at the time of turn-on in the conventional switching circuit, the voltage Vd, the voltage Vc, and the voltage VL. It is a figure which shows the equivalent circuit of the conventional switching circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Switching element, 12, 14 Flywheel diode, 16 capacitor | condenser, 18 Control unit, 20 Gate resistance, 22 Adjustment circuit, 100 (100a-100f) Switching circuit, 200 Power supply, 300 Load, 400 Control unit, C capacitor, D diode , R1, R2 resistance.

Claims (6)

A switching circuit for supplying power to a load,
A switching element capable of controlling an open / close state between terminals by a control signal;
A flywheel diode connected in series to the switching element and for feeding back current from the load when the switching element is open;
An adjustment circuit that adjusts the control signal according to a temporal change in the voltage between the terminals when the switching element is closed;
A switching circuit comprising: The switching circuit according to claim 1,
The adjusting circuit is characterized in that, when the switching element is in a closed state, the speed at which the switching element is closed decreases as the voltage drop rate between the terminals increases. The switching circuit according to claim 1 or 2,
The adjustment circuit includes a capacitor, a current limiting element connected in series to the capacitor, and a resistor connected in parallel with the current limiting element. A switching circuit according to claim 3,
The adjustment circuit further includes a resistor connected in series to the capacitor. A switching circuit according to claim 3 or 4,
The switching element is an IGBT, and the current limiting element is an adjustment diode;
The adjustment circuit includes:
A cathode of the adjustment diode is connected to a collector of the IGBT;
An anode of the adjustment diode is connected to one end of the capacitor;
The other end of the capacitor is connected to the gate of the IGBT;
A switching circuit characterized by that. A switching circuit according to claim 3 or 4,
The switching element is an FET, and the current limiting element is an adjustment diode;
The adjustment circuit includes:
The cathode of the adjustment diode is connected to the drain of the FET;
An anode of the adjustment diode is connected to one end of the capacitor;
The other end of the capacitor is connected to the gate of the FET;
A switching circuit characterized by that.

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