JP2006129145A - Active filter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active circuit which can reduce a noise occurrence upon switching by a more simple arrangement. <P>SOLUTION: An active filter circuit inputs the output voltage of an alternating-direct current supply, and outputs a voltage in which the noise component of the output voltage is reduced. The active filter circuit is provided with a switching circuit including a first inductor and a switching transistor, a second inductor provided in a place where voltage is induced according to the change of a current amount flowing through the first inductor, and a control circuit which outputs a gate driving signal switching the transistor ON when the voltage induced to the second inductor is equal to or less than 0 V. The outputted voltage of the switching circuit is set for the output voltage of the alternating-direct current supply, so that a voltage Vds between drain and source of the transistor becomes 0 V before the current amount flowing through the first inductor becomes higher than 0 A and after the transistor is switched to ON. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an active filter circuit that reduces and outputs not only noise components (harmonic components) included in the output voltage of an AC-DC power supply that rectifies and outputs an AC voltage, but also feedback and radiation noise.

Conventionally, various switching power supplies are known. For example, Non-Patent Document 1 shown below discloses a resonant switching power supply.
Transistor Technology Special Vol.57 “All about Switching Power Supply Technology”, published in 1997, CQ Publisher

  Conventionally, a power supply circuit including an AC-DC power supply, for example, a resonant switching power supply circuit, which uses a choke coil to reduce a noise component (harmonic component) included in a DC component after rectification. A power supply circuit employing a so-called choke input method is known.

  However, in the choke input method, since a choke coil having a large reactance component is used, there is a problem that the circuit scale becomes large and the weight of the entire circuit increases.

  In order to solve the above problem, there is a system that employs an active filter circuit using an active component such as a transistor instead of a choke coil.

  FIG. 9 is a circuit diagram of a known composite resonance type switching power supply C2 employing an active filter circuit. The switching power supply C2 has an active filter circuit 200 between the AC-DC power supply 100 and the current resonance circuit 300.

  The AC-DC power supply 100 rectifies the AC voltage supplied from the AC power supply 101 by the rectifier bridge circuit 102 provided in the final stage, and outputs the rectified voltage.

  The current resonance circuit 300 is a circuit that performs direct current direct conversion. More specifically, the current resonance circuit 300 oscillates the direct current voltage output from the active filter circuit 200 by the oscillation circuit 310 and converts the direct current voltage into an alternating current voltage, and then transforms the direct current voltage by the transformer 320. This is a circuit that rectifies the DC voltage again by the rectifier circuit 330 provided on the winding side, and outputs the rectified DC voltage to the load 400 connected to the subsequent stage of the current resonance circuit 300. Since the configuration of the current resonance circuit 300 is well known, further detailed description is omitted.

  The active filter circuit 200 is a non-resonant type (so-called hard switching type) active filter circuit. The active filter circuit 200 includes an input capacitor 201, an inductor 202, a diode 203, a switching transistor 204 having a parasitic capacitance 204c, an output capacitor 205, a snubber circuit 210, a resistor 220, and a control circuit 250. Consists of.

  The inductor 202, the diode 203, the transistor 204, and the capacitor 205 constitute a so-called step-up switching circuit.

The control circuit 250 switches the transistor 204 on / off based on the voltage V _{P1 at the} point P1 and the output voltage (voltage at the point P2) V _P2 applied to the output capacitor 205. Thereby, the noise component (harmonic component) contained in output voltage _VP2 can be reduced, and a power factor can be improved.

Hereinafter, each component constituting the control circuit 250 will be described. Operational amplifier 253, the two series the connected resistor 251 and 252, a voltage obtained by dividing the output voltage _{V P2,} amplifies a difference between the reference voltage Vref, during subsequent multiplexer (figure and MUL Output to 254. The reference voltage Vref is set to the voltage at the point P2 when the output is stable.

The multiplexer 254 multiplies the voltage obtained by dividing the voltage (full-wave rectified voltage) V _P1 at the point P1 by the two resistors 255 and 256 connected in series with the output from the operational amplifier 253, A sinusoidal voltage representing the multiplication result is output.

  The operational amplifier 257 shifts the voltage output from the multiplexer 254 to the plus side by an amount corresponding to the value of the drain voltage of the transistor 204 and outputs the result.

  An oscillator (referred to as OSC in the figure) 258 always outputs a sawtooth triangular wave signal having a constant frequency.

  The output of the oscillator 258 is applied to the set terminal (denoted as S in the figure) of the RS flip-flop 259, and the output of the operational amplifier 257 is applied to the reset terminal (denoted as R in the figure).

  FIG. 10 is a diagram illustrating the drain-source voltage Vds and the drain-source current Ids of the transistor 204 constituting the active filter circuit 200. Due to the fact that the oscillator 258 always outputs a triangular wave signal having a constant frequency, the set and the reset to the set are executed immediately after the flip-flop 259 is reset before the voltage Vds becomes 0 V or less. May be. In this case, as indicated by a circle, a large noise is generated in the current Ids when the voltage Vds falls in addition to when the voltage Vds rises.

FIG. 11 is a diagram illustrating the voltage V _c across the output capacitor 205 constituting the active filter circuit 200. The voltage V _c is affected by two noise components riding on the current Ids shown in FIG.

FIG. 12 is a diagram illustrating a ripple noise component included in the AC voltage V ₃₁₀ generated in the oscillation circuit 310 in the current resonance circuit 300. The maximum amplitude V _p-p of the ripple noise component is 20.9V.

  FIG. 13 is a diagram illustrating the noise terminal voltage of the active filter circuit 200. As shown in the figure, the gain of the noise terminal voltage is a 5 dB margin. The noise terminal voltage (also referred to as feedback noise) refers to the magnitude of high-frequency noise that returns (returns) to the point P1 of the active filter circuit 200, and the measured value is expressed as 1 μV = 0 dB.

Active filter circuit 200 in order to reduce ripple noise component contained in the output voltage V _P2, and a snubber circuit 210. This is to reduce a ripple noise component generated due to the configuration of the control circuit 250 described above.

  As described above, in the conventional active filter circuit 200, the snubber circuit 210 is further provided in order to reduce noise generated in the circuit in spite of the adoption of the choke coil in order to reduce the circuit scale. It is necessary to provide the circuit, and the circuit becomes complicated and the efficiency is lowered.

  An object of the present invention is to provide an active filter circuit having a novel configuration that can improve the power factor as compared with the conventional one without adding a noise reduction circuit in the circuit.

  The active filter circuit according to claim 1 is an active filter circuit that receives an output voltage of an AC-DC power supply that rectifies and outputs an AC voltage and outputs a voltage in which a noise component of the output voltage is reduced. A switching circuit including a first inductor and a switching transistor, and a control circuit for periodically switching the transistor to an on / off state, wherein a voltage is induced in accordance with a change in an amount of current flowing through the first inductor. And a control circuit that outputs a gate drive signal for turning on the transistor when the voltage induced in the second inductor is 0 V or less. Features.

  The active filter circuit according to claim 2 is the active filter circuit according to claim 1, wherein after the transistor is turned on, before the amount of current flowing through the first inductor becomes higher than 0 A, the drain and source of the transistor The output voltage of the switching circuit is set with respect to the output voltage of the AC-DC power supply so that the inter-voltage Vds is 0V.

  The active filter circuit according to claim 3 is the active filter circuit according to claim 2, wherein the control circuit has a gate drive signal having a frequency specified when a voltage induced in the second inductor becomes 0 V or less. Is output.

  The active filter circuit according to claim 1 outputs a gate drive signal for switching on the transistor when the voltage induced in the second inductor becomes 0 V or less. The voltage induced in the second inductor starts to decrease after the current flowing through the first inductor becomes 0 A or less. Therefore, the transistor is switched on after the current flowing through the transistor becomes 0 A or less. As a result, the loss due to switching can be reduced as much as possible, and there is no need to prepare another noise circuit to reduce the noise generated in the active circuit. Power factor improvement, efficiency improvement, and noise reduction can be performed.

  The active filter circuit according to claim 2 is the active filter circuit according to claim 1, and further, the drain-source voltage Vds of the transistor becomes 0 V before the current flowing through the first inductor becomes higher than 0 A. In addition, the output of the switching circuit is set. Thereby, after the voltage Vds becomes 0 V or less, so-called soft switching is realized in which the drain-source current Ids becomes 0 A or more, and the switching noise of the transistor (noise on the current Ids) is more effectively reduced. Can be reduced.

  The active filter circuit according to claim 3 outputs a gate drive signal having a frequency specified according to a voltage induced in the second inductor when the voltage induced in the second inductor is 0 V or less, thereby reducing the power factor of the input current of the active filter circuit. It can be further improved.

The configuration and operation of the active filter circuit 500 according to the embodiment will be described in the following order with reference to the accompanying drawings.
(1) Configuration of switching power supply (2) Configuration of active filter circuit
(2-1) Overall configuration
(2-2) Control circuit configuration
(2-3) Operation and effect of active filter circuit

(1) Configuration of Switching Power Supply FIG. 1 is a diagram illustrating a configuration of a switching power supply C1 that employs an active filter circuit 500 according to an embodiment. The switching power supply C1 has an active filter circuit 500 having a new configuration as a power factor correction circuit between the AC-DC power supply 100 and the current resonance circuit 300. In FIG. 1, the same components as those of the conventional switching power supply C2 described with reference to FIG. 9 are denoted by the same reference numerals.

  The AC-DC power supply 100 rectifies the AC voltage supplied from the AC power supply 101 by the rectifier bridge circuit 102 provided in the final stage, and outputs the rectified voltage.

  The active filter circuit 500 receives the rectified voltage output from the AC / DC power supply 100 and outputs a voltage obtained by reducing a noise component (harmonic component) from the voltage to the current resonance circuit 300.

  The current resonance circuit 300 is a circuit that performs direct current direct conversion. More specifically, the current resonance circuit 300 oscillates the direct current voltage output from the active filter circuit 500 by the oscillation circuit 310 and converts the direct current voltage into an alternating current voltage, and then transforms the direct current voltage by the transformer 320. The rectification circuit 330 provided on the winding side rectifies the DC voltage again, and outputs the rectified DC voltage to the load 400 connected to the subsequent stage. Since the configuration of the current resonance circuit 300 is well known, further detailed description is omitted.

(2) Configuration of active filter circuit
(2-1) Overall Configuration Hereinafter, each component of the active filter circuit 500 will be described in detail. The active filter circuit 500 includes an input capacitor 201, an inductor 202, a diode 203, an n-channel field effect transistor 204 having a parasitic capacitance 204c, an output capacitor 205, and a control circuit 550. Yes. The inductor 202, the diode 203, the transistor 204, and the capacitor 205 constitute a so-called step-up switching circuit. The output voltage output from the switching circuit is the output voltage V _P2 at the point P2 of the active filter circuit 500.

The active filter circuit 500 includes a control circuit 550 having a new configuration instead of the control circuit 250 used in the conventional active filter circuit 200. The control circuit 550 includes an inductor 206 provided at a position for inducing a voltage according to a change in the amount of current flowing through the inductor 202. When the voltage induced in the inductor 206 becomes 0 V or less, A gate drive signal having a frequency specified according to the time is output to turn on the transistor 204. In the active filter 500, after the transistor 204 is turned on, before the amount of current flowing through the inductor 202 becomes higher than 0A, the drain-source voltage Vds of the transistor 204 becomes 0V, so that the AC-DC power supply For an output voltage of 100, that is, a voltage V _{P1 at the} point P1, an output voltage V _P2 is set. By adopting this configuration, it is possible to realize so-called soft switching in which the current I _{202 of the} inductor 202 is made higher than 0 A after the voltage Vds becomes 0 V or less. By adopting control circuit 550, it is possible to reduce the noise component (harmonic component) included in output voltage _VP2 and improve the power factor.

  In the active filter circuit 500, by adopting the control circuit 550, the snubber circuit 210 and the resistor 220 are removed from the conventional active filter circuit 200 described with reference to FIG. In addition, the inconvenience of providing a noise reduction circuit for reducing noise generated in the active filter circuit in the active filter circuit can be eliminated.

(2-2) Configuration of Control Circuit The configuration of the control circuit 550 will be described below. Operational amplifier 553 by two resistors 551 and 552 are connected in series, a voltage obtained by dividing the output voltage _{V P2,} amplifies a difference between the reference voltage Vref1, the value after amplification, subsequent PWM Output to the comparator 554.

The comparator 555 compares the voltage V ₂₀₆ induced in the inductor 206 connected to the point P3 with the reference voltage Vref (= 0V). When the voltage V ₂₀₆ is equal to or lower than the reference voltage Vref, the comparator 555 outputs a high level signal. Output. The one-shot pulse generation circuit 556 outputs a short wavelength pulse signal as a timing signal only once in response to a high level signal input. The output circuit 557 is a charging circuit, and in response to an input of a timing signal, a signal having a potential level (voltage) corresponding to the amount of charge that has been charged is a subsequent voltage control oscillator (represented as VCO in the figure) 558 outputs (discharges). The output circuit 557 starts charging again after outputting (discharging) the signal. The voltage control oscillator 558 outputs a triangular wave signal having a frequency specified by the potential level (voltage) of the input signal for one cycle. By adopting the voltage control transmitter 558, it is possible to flexibly cope with a change in the output voltage V _P2 and further improve the power factor of the input current.

  The PWM comparator 554 outputs a PWM signal from the output of the operational amplifier 553 and the output of the voltage controlled oscillator 558. When the value of the triangular wave signal output from the voltage controlled oscillator 558 is greater than or equal to the output of the operational amplifier 553, the PWM comparator 554 outputs a high level gate drive signal for switching the transistor 204 on to the gate of the transistor 204.

The control circuit 550 switches on the transistor 204 when the voltage V ₂₀₆ induced in the inductor 206 becomes 0 V or less. The voltage induced in the inductor 206 starts to decrease after the current flowing through the inductor 202, that is, the current I ₂₀₂ flowing into the transistor 204 becomes 0 A or less. Therefore, the transistor 204 is always switched on after the current I ₂₀₂ becomes 0 A or less.

Further, in the active filter circuit 500, the voltage Vds is set to 0 V before the amount of current flowing through the first inductor becomes higher than 0 A after the transistor 204 is turned on in accordance with the conditions described below. An output voltage V _P2 is set for V _P1 . As a result, after the voltage Vds reaches 0 V, so-called soft switching is performed in which the current I ₂₀₂ becomes 0 A or more, and noise on the drain-source current Ids of the transistor 204 can be effectively reduced. .

The condition that the voltage Vds becomes 0 V before the current I ₂₀₂ becomes higher than 0 A is a voltage E (so-called maximum value) of the AC voltage output from the AC power supply 101 provided in the AC-DC power supply 100. is a value obtained by multiplying the ^{2 1/2} the effective value), i.e., AC - the maximum amplitude of the voltage _{V P1} rectified output from the DC power supply 100, the value of the output voltage _{V P2} of the active filter circuit 500 Is more than twice as large. When the voltage E of the AC power supply 101 is 100V, for example, by setting the output voltage _VP2 to 380V, the above condition is satisfied and soft switching can be performed.

Here, for example, the set value of the output voltage _{V P2} while the state of 380V, consider the case where the voltage E of the AC power supply 101 was changed from 100V to 230V. In this case, the above condition cannot be satisfied, and the value of the voltage Vds cannot be set to 0 V before the current I ₂₀₂ exceeds 0 A. However, in this case, the voltage Vds does not drop to 0V, and moves to the next cycle at a point as close to 0 as possible (meaning that the PWM signal of the next frequency is output to the gate of the transistor 204). )) Is executed, and switching loss can be reduced as much as possible. Therefore, even when the voltage E is 230 V, the active filter circuit 500 does not provide another noise reduction circuit that reduces noise generated in the circuit, unlike the conventional active filter circuit 200, and performs switching. It is possible to greatly reduce the loss and reduce the generation of noise. Even in this case, soft switching can be realized by preparing a detecting means for detecting that the drain-source voltage Vds is 0 V and using this.

In the active filter circuit 500, a step-up switching circuit is used as a switching circuit including the inductor 202 and the switching transistor 204. However, the present invention is not limited to this, and a step-down or step-up / step-down switching circuit is used. However, soft switching can be realized. In this case, even when soft switching cannot be realized due to input / output conditions, the loss due to switching is reduced as in the case where the set value of the output voltage V _P2 is set to 380 V, and the conventional active filter circuit 200 Thus, without preparing another noise reduction circuit in order to reduce the noise generated in the circuit, it is possible to significantly reduce the loss due to switching and reduce the generation of noise.

(2-3) Operation and Effect of Active Filter Circuit FIG. 2 is a time chart showing the voltage Vgs, the voltage Vds, the current I _202, and the voltage V ₂₀₆ . Hereinafter, the signals in the circuit in the state I, the state II, the state III,..., The state V,.

The state I starts when the voltage Vgs switches to the high level. When the voltage Vgs applied to the gate is switched to the high level, the n-channel transistor 204 is turned on. The diode 203 is in an off state. In this case, energy (charge) is linearly accumulated in the inductor 202 and the flowing current I ₂₀₂ also increases. State I ends when the value of current I ₂₀₂ exceeds 0A.

During state II, the value of current I ₂₀₂ increases linearly. State II ends when the voltage Vgs is switched to a low level and the transistor 204 is switched off.

State III begins with transistor 204 switching off. As transistor 204 switches off, current I ₂₀₂ is bypassed to parasitic capacitance 204c. As a result, the voltage Vds rises from 0V. State III ends when the value of the voltage Vds becomes V _0.

State IV begins when the value of the voltage Vds becomes V _0. When the voltage Vds becomes V ₀ , the diode 203 is turned on, and the energy (charge amount) accumulated in the inductor 202 passes through the diode 203. As a result, the energy stored in the inductor 202 decreases, and the current I ₂₀₂ also decreases. State IV ends when current I ₂₀₂ reaches 0A.

The state V starts when the current I ₂₀₂ becomes 0 A or less. In this case, the diode 203 is switched off. The energy of the output capacitor 205 is discharged to the input capacitor 201 through a resonance circuit with the inductor 202. State V ends when voltage V ₂₀₆ falls below 0V. In the state V, partial voltage resonance is performed by the inductor 206 and the parasitic capacitance 204 c of the transistor 204. Phase compensation is performed by partial voltage resonance using the parasitic capacitance 204c, and the power factor of the output voltage _VP2 can be improved without preparing a capacitor and increasing the circuit scale.

At the same time as the voltage V ₂₀₆ becomes 0 V or less, the voltage Vgs switches to the high level. Accordingly, the same state VI as the state I described above starts. Thereafter, the state VI to the state I to the state V are repeatedly generated.

FIG. 3 is a time chart showing the voltage Vds, the current I _202, and the voltage V ₂₀₆ when the AC voltage E output from the AC power supply 101 is 100V. When the voltage E is 100 V, so-called soft switching is performed in which the current I ₂₀₂ becomes 0 V or more after the voltage Vds becomes 0 V or less as shown by encircled. As a result, no noise is generated when the voltage Vds falls.

FIG. 4 is a time chart showing the voltage Vds, the current I _202, and the voltage V ₂₀₆ when the voltage E output from the AC power supply 101 is 230V. When the voltage E is 230V, the above-described conditions for performing soft switching are not satisfied. Even in this case, the control circuit 550 moves to the next cycle at a point where the voltage Vds is as close to 0V as possible (as shown by encircled) (output of the PWM signal of the next frequency is performed). Resonant switching is performed, and loss due to switching can be reduced as much as possible, and generation of switching noise can be reduced.

  FIG. 5 is a diagram illustrating waveforms of the voltage Vds of the transistor 204 and the current Ids when the AC voltage E output from the AC power supply 101 is 100V. Since soft switching is performed, no noise is generated when the voltage Vds falls. As shown in FIG. 10, when the conventional control circuit 250 using a flip-flop is used, noise is generated when the voltage Vds rises and falls, whereas the active filter circuit In 500, the number of places where noise is generated can be reduced to one.

6, when the AC voltage E output from the AC power source 101 is 100 V, shows a so-called spike noise waveform generated voltage V _c applied to the output capacitor 205. As shown in FIG. 2, in the active filter circuit 500, noise does not occur when the voltage of the transistor 204 falls, and therefore spike noise generated corresponding to this does not occur.

FIG. 7 is a diagram illustrating a ripple noise component included in the AC voltage V ₃₁₀ generated in the oscillation circuit 310 in the current resonance circuit 300 when the AC voltage E output from the AC power supply 101 is 100V. The maximum amplitude V _p-p of the ripple noise component is 17.4V. As shown in FIG. 12, the maximum amplitude V _p-p of the ripple noise component in the case of using the conventional control circuit 250 using the flip-flop is 20.9 V, and by using the active filter circuit 500, about 17 % Can also reduce the noise generation rate.

  FIG. 8 is a diagram illustrating the noise terminal voltage of the active filter circuit 500. The gain of the noise terminal voltage is a 15 dB margin. The noise terminal voltage (also referred to as feedback noise) refers to the magnitude of high-frequency noise that returns (returns) to the point P1 of the active filter circuit 200, and the measured value is expressed as 1 μV = 0 dB. As shown in FIG. 13, the noise terminal voltage when using the conventional control circuit 250 using flip-flops has a gain of 5 dB, whereas the active filter circuit 500 has a gain of 15 dB. Can be improved.

It is a circuit diagram of the switching power supply provided with the active filter circuit which concerns on embodiment. It is a time chart which shows the state of each signal in an active filter circuit. It is a time chart which shows the state of each signal in an active filter circuit in case the output of the alternating current power supply used with alternating current-direct current power supply is 100V. It is a time chart which shows the state of each signal in an active filter circuit in case the output of the alternating current power supply used with alternating current-direct current power supply is 230V. It is a time chart which shows the voltage and electric current between the drain-source of the transistor in an active filter circuit. It is a figure which shows the spike noise component which appears in the output capacitor of an active filter circuit. It is a figure which shows the ripple noise component which the alternating voltage produced | generated within a current resonance circuit contains. It is a figure which shows the margin of the noise terminal voltage of an active filter circuit. It is a circuit diagram of a switching power supply provided with the conventional active filter circuit. It is a time chart which shows the voltage and electric current between the drain-source of the transistor in the conventional active filter circuit. It is a figure which shows the spike noise component which appears in the output capacitor of the conventional active filter circuit. It is a figure which shows the ripple noise component which the alternating voltage produced | generated within a current resonance circuit contains. It is a figure which shows the margin of the noise terminal voltage of an active filter circuit.

Explanation of symbols

100 AC-DC power supply, 200,500 active filter circuit, 250,550 control circuit, 202,206 inductor, 204 transistor, 300 current resonance circuit, 400 load, 554 PWM comparator, 558 voltage controlled oscillator.

Claims (3)

An active filter circuit that receives an output voltage of an AC-DC power supply that rectifies and outputs an AC voltage and outputs a voltage in which a noise component of the output voltage is reduced,
A switching circuit including a first inductor and a switching transistor;
A control circuit that periodically switches a transistor to an on / off state, and includes a second inductor provided at a position where a voltage is induced according to a change in an amount of current flowing through the first inductor. A control circuit for outputting a gate drive signal for switching on the transistor when the voltage induced in the inductor becomes 0 V or less;
An active filter circuit comprising:   After the transistor is switched on, before the amount of current flowing through the first inductor becomes higher than 0 A, the drain-source voltage Vds of the transistor becomes 0 V with respect to the output voltage of the AC-DC power supply. 2. The active filter circuit according to claim 1, wherein a voltage output from the switching circuit is set. 3. The active filter circuit according to claim 2, wherein the control circuit outputs a gate drive signal having a frequency specified when a voltage induced in the second inductor becomes 0V or less.

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