JP2012213255A - Voltage converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage converter capable of reducing noise generated by a current which flows through the wiring.SOLUTION: A power supply circuit 100 has a first wiring structure where a first current flows in the direction which generates a first magnetic field when a switch part SW11 is in a predetermined switch state and a second wiring structure where a second current flows in the direction which generates a second magnetic field which negates the first magnetic field when the switch part SW11 is in the predetermined switch state. Moreover, the first and second currents may be the currents of a harmonic component of the fundamental frequency of the current which flows in the voltage converter.

Description

  The present invention relates to a voltage converter.

  For example, Patent Document 1 discloses a converter circuit that reduces noise (magnetic field) generated by switching by reducing the switching loss of the switching element by the resonant action of the inductor L and the capacitor C during switching of the switching element. Yes.

JP-A-5-260729

  However, since the converter circuit described in Patent Document 1 does not have a structure for reducing noise generated by current flowing in the wiring, there is a case where a sufficient noise reduction effect cannot be obtained.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a voltage conversion device capable of reducing noise generated by current flowing through a wiring.

In order to achieve the above object, a voltage converter according to a first aspect of the present invention includes:
A voltage converter that changes the voltage of the input voltage and outputs the voltage by switching the switch unit,
A first wiring structure in which a first current flows in a direction to generate a first magnetic field when the switch unit is in a predetermined switch state;
A second wiring structure in which a second current flows in a direction to generate a second magnetic field that cancels the first magnetic field when the switch unit is in the predetermined switch state;
Have

  According to the present invention, it is possible to reduce noise generated by a current flowing through a wiring.

It is a figure for demonstrating the structure of the power supply circuit in the voltage converter circuit of Embodiment 1 of this invention. It is a figure showing the electric current or voltage in each part of the power supply circuit of FIG. It is a figure showing the electric current which flows into the power supply circuit of FIG. It is a figure showing the electric current which flows into the power supply circuit of FIG. It is a figure showing the electric current which flows into the power supply circuit of FIG. It is a figure of the noise spectrum of the magnetic field which generate | occur | produces in the conventional step-down circuit. It is a figure of the noise spectrum of the magnetic field which generate | occur | produces in the power supply circuit of FIG. It is a figure for demonstrating the structure of the power supply circuit in the voltage converter circuit of Embodiment 2 of this invention. It is a figure showing the electric current or voltage in each part of the power supply circuit of FIG. It is a figure showing the electric current which flows into the power supply circuit of FIG. It is a figure showing the electric current which flows into the power supply circuit of FIG. It is a figure showing the electric current which flows into the power supply circuit of FIG. FIG. 6 is a diagram for describing a configuration of a power supply circuit in a voltage conversion circuit according to a modification of the first embodiment.

  Embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
(Configuration of power supply circuit)
A power supply circuit 100 included in the voltage conversion apparatus according to the first embodiment is connected between a DC power supply 1 and a load 3 as shown in FIG. The DC voltage output from the DC power supply 1 is input to the power supply circuit 100, stepped down by the power supply circuit 100, and output to the load 3.

  The power supply circuit 100 includes a wiring LN11, a wiring LN12, a first capacitor C10 (for example, 100 μF), a second capacitor C11 (for example, 0.1 μF), and a third capacitor C12 (for example, 0.1 μF). ), An inductor L11, a switch unit SW11, a smoothing capacitor Cs, and a diode D11.

  The wiring LN11 is connected to the positive electrode of the DC power source 1 and the positive electrode of the load 3.

  The wiring LN12 is connected to the negative electrode of the DC power source 1 and the negative electrode of the load 3.

  The first capacitor C10, the second capacitor C11, and the third capacitor C12 are connected to the wiring LN11 and the wiring LN12. The second capacitor C11 and the third capacitor C12 are arranged at the subsequent stage of the first capacitor C10.

  The switch unit SW11 and the inductor L11 are arranged in the middle of the wiring LN11. The inductor L11 is disposed at the subsequent stage of the switch unit SW11.

  The switch unit SW11 is configured by a switching element such as an FET, and is switched on and off in accordance with a control signal from the control unit 150. The switch unit SW11 is in a conductive state when turned on and is in a nonconductive state when turned off.

  The diode D11 is connected between the wiring LN11 and the wiring LN12, its cathode is connected to the wiring LN11, and its anode is connected to the wiring LN12. In particular, the cathode is connected between the switch unit SW1 and the inductor L11 in the wiring LN11.

  The smoothing capacitor Cs is connected to the wiring LN11 and the wiring LN12. The smoothing capacitor Cs is disposed after the inductor L11.

  The control unit 150 includes a microcomputer or the like, and supplies a control signal to the switch unit SW11 to switch the switch unit SW11 on and off.

  In the power supply circuit 100 as described above, the closed circuit 110 including the second capacitor C11, the switch unit SW11, the diode D11, and the wiring connecting them is configured. In the power supply circuit 100, a closed circuit 120 including a third capacitor C13, a switch unit SW11, a diode D11, and a wiring connecting them is configured.

  The closed circuit 110 and the closed circuit 120 are formed so as to share a predetermined circuit element and are adjacent to each other, and in accordance with the switch state of the switch unit 11, currents in opposite directions are provided at least in part. Has a wiring structure through which the

(Power circuit operation)
The control unit 150 supplies a control signal for alternately switching on and off signals to the switch unit SW11 as shown in FIG. The switch unit SW11 is turned on when the supplied control signal is an on signal, and is turned off when the supplied control signal is an off signal.

  FIG. 3 shows a typical path of current flowing through the power supply circuit 100 when the switch unit SW11 is on. When the switch unit SW11 is on, the current charged when the first capacitor C10 is off is discharged, and the discharged current flows to the load 3 through the switch unit SW11 and the inductor L11. This current is smoothed by the smoothing capacitor Cs.

  FIG. 4 shows a typical path of current flowing through the power supply circuit 100 when the switch unit SW11 is off. When the switch unit SW11 is off, a current flows through the inductor L11, the load 3, and the diode D11. At this time, the first capacitor C10 is charged by the DC power supply 1.

  FIG. 2 shows currents that flow through the respective parts of the power supply circuit when the switch unit SW11 is switched on and off. The inductor L11 does not flow current or tries to flow current when the switch unit SW11 is switched on and off. As a result, as shown in FIG. 2, the current flowing through the switch unit SW12 gradually increases immediately after the switch unit SW11 is turned on, and the current flowing through the diode D11 gradually decreases after the switch unit SW11 is turned off. The current flowing through the load 3 (the current flowing through the inductor L11 and smoothed by the smoothing capacitor Cs) is the same as the sum of the current flowing through the diode D11 and the switch unit SW11. An input voltage (output voltage output from the DC power supply 1) input to the power supply circuit 100 is stepped down by the inductor L11 and applied to the load 3.

  Here, the second capacitor C11 and the third capacitor C12 are charged when the switch unit SW11 is turned off and discharged immediately after the switch unit SW11 is turned on (see FIG. 2). The main flow of current discharged by the second capacitor C11 and the third capacitor C12 is shown in FIG.

  The current that flows when the second capacitor C11 is discharged flows through the switch SW11, the inductor L11, and the load 3 and then flows into the first capacitor C10.

  The current that flows when the third capacitor C12 is discharged flows through the switch SW11, the inductor L11, and the load 3 and then flows into the second capacitor C12.

  Although not shown, it is conceivable that the current discharged by the second capacitor C11 flows in a pseudo manner from the switch part SW11 toward the diode D11 through the closed circuit 110. It is conceivable that the current discharged from the third capacitor C12 flows in a pseudo manner in the closed circuit 120 from the switch unit SW11 toward the diode D11.

  Due to the above-described current flow, a current that flows in the opposite direction flows through at least a part of the closed circuit 110 and the closed circuit 120 (see the dotted line arrow in FIG. 5). With such a current, the magnetic field generated by the current flowing through the wiring of the closed circuit 110 is canceled out by the magnetic field generated by the current flowing through the wiring of the closed circuit 120. Thereby, noise generated by the current flowing through the wiring in the power supply circuit 100 can be reduced.

  Further, the capacitance of the first capacitor C10 is larger than the capacitances of the second capacitor C11 and the third capacitor C12. The current discharged by the second capacitor C11 and the third capacitor C12 is a harmonic component current of the fundamental frequency of the current flowing through the switch unit SW11 (current flowing through the power supply circuit 100). For this reason, the magnetic field to be canceled corresponds to a magnetic field generated by the current of the harmonic component of the fundamental frequency of the current flowing through the switch unit SW11. Since such a magnetic field (noise) has a high frequency, it tends to adversely affect devices (especially radio etc.) around the power supply circuit 100. For this reason, the power supply circuit 100 can effectively reduce adverse effects on surrounding devices by reducing the generation of magnetic fields (particularly noise in a high frequency band such as a radio frequency band).

  FIG. 6 shows a noise spectrum of a magnetic field generated in a conventional step-down circuit (a power supply circuit in which the second capacitor C12 and wiring connected thereto are omitted in the power supply circuit 100 of FIG. 1), and FIG. 2 shows a noise spectrum of a magnetic field generated in the power supply circuit 100 according to the embodiment. As shown in FIGS. 6 and 7, it can be seen that the generated magnetic field is reduced by the configuration of the present embodiment as compared with the conventional case.

(Embodiment 2)
(Configuration of power supply circuit)
The power supply circuit 200 included in the voltage conversion device of the second embodiment is connected between the DC power supply 1 and the load 3 as shown in FIG. The DC voltage output from the DC power supply 1 is input to the power supply circuit 200, boosted by the power supply circuit 200, and output to the load 3.

  The power supply circuit 200 includes a wiring LN21, a wiring LN22, a first capacitor C20 (for example, 100 μF), a second capacitor C21 (for example, 0.1 μF), and a third capacitor C22 (for example, 0.1 μF). ), An inductor L21, a switch unit SW21, a smoothing capacitor Cs, and a diode D21.

  The wiring LN21 is connected to the positive electrode of the DC power source 1 and the positive electrode of the load 3.

  The wiring LN22 is connected to the negative electrode of the DC power source 1 and the negative electrode of the load 3.

  The first capacitor C20, the second capacitor C21, and the third capacitor C22 are connected to the wiring LN21 and the wiring LN22. The second capacitor C21 and the third capacitor C22 are arranged after the first capacitor C20 and the diode D21 and at the cathode of the diode D21.

  The diode D21 and the inductor L21 are arranged in the middle of the wiring LN21. The diode D21 is disposed at the subsequent stage of the inductor L21. The anode of the diode D <b> 21 is arranged facing the DC power supply 1.

  The switch unit SW21 is configured by a switching element such as an FET, and is switched on and off in accordance with a control signal from the control unit 150. The switch unit SW11 is in a conductive state when turned on and is in a nonconductive state when turned off. The switch unit SW21 is connected to the wiring LN21 and the wiring LN22. One end of the switch unit SW21 is connected to the wiring LN21 and between the inductor L21 and the diode D21.

  The smoothing capacitor Cs is connected to the wiring LN21 and the wiring LN22. The smoothing capacitor Cs is arranged at the subsequent stage of the diode D21.

  The control unit 250 is configured by a microcomputer or the like, and supplies a control signal to the switch unit SW21 to switch the switch unit SW21 on and off.

  In the power supply circuit 200 as described above, a closed circuit 210 including the second capacitor C21, the switch unit SW21, the diode D21, and a wiring connecting them is configured. In the power supply circuit 200, a closed circuit 220 including a third capacitor C23, a switch unit SW21, a diode D21, and a wiring connecting them is configured.

  The closed circuit 210 and the closed circuit 220 are formed so as to share a predetermined circuit element and are adjacent to each other, and in accordance with the switch state of the switch unit 21, currents in opposite directions are provided at least in part. Has a wiring structure through which the

(Power circuit operation)
The control unit 250 supplies a control signal for alternately switching on and off signals to the switch unit SW21 as shown in FIG. The switch unit SW21 is turned on when the supplied control signal is an on signal, and is turned off when the supplied control signal is an off signal.

  FIG. 10 shows a typical path of current flowing through the power supply circuit 200 when the switch unit SW21 is on. When the switch unit SW21 is on, the current flowing from the DC power source 1 is stabilized by the first capacitor 20, and returns to the DC power source 1 through the inductor L21 and the switch unit SW21. This current is stabilized by the first capacitor 20.

  FIG. 11 shows a typical path of current flowing through the power supply circuit 1 when the switch unit SW21 is off. When the switch unit SW21 is off, the current flowing from the DC power source 1 passes through the inductor L21 and the diode D21, is smoothed by the smoothing capacitor Cs, flows to the load 3, and returns to the DC power source 1. This current is stabilized by the first capacitor 20.

  FIG. 9 shows the current flowing through each part of the power supply circuit when the switch part SW21 is switched on and off. The inductor L21 does not flow current or tries to flow current when the switch unit SW21 is switched on and off. As a result, as shown in FIG. 9, the current flowing through the switch unit SW21 gradually increases immediately after the switch unit SW21 is turned on, and the current flowing through the diode D21 gradually decreases after the switch unit SW21 is turned off. The sum of the current flowing through the diode D21 and the switch unit SW21 is the current flowing through the inductor L21. The current flowing through the load 3 is a current obtained by smoothing the current flowing through the inductor L21 by the smoothing capacitor Cs. An input voltage (output voltage output from the DC power supply 1) input to the power supply circuit 200 is boosted by the inductor L21 and applied to the load 3.

  Here, the second capacitor C21 and the third capacitor C22 are charged when the switch unit SW21 is off, and discharged immediately after the switch unit SW21 is turned on (see FIG. 9). The main flow of current discharged by the second capacitor C21 and the third capacitor C22 is shown in FIG.

  The current that flows when the second capacitor C21 is charged flows from the DC power source 1 to the inductor L21, the diode D21, the second capacitor C21, and the DC power source 1.

  The current that flows when the third capacitor C22 is charged flows from the DC power source 1 to the inductor L21, the diode D21, the third capacitor C22, and the DC power source 1.

  Due to the above-described current flow, a current that flows in the opposite direction flows through the closed circuit 210 and the closed circuit 220 at least partially (see the dotted arrows in FIG. 10). With such a current, the magnetic field generated by the current flowing through the wiring of the closed circuit 110 is canceled out by the magnetic field generated by the current flowing through the wiring of the closed circuit 120. Thereby, noise generated by the current flowing through the wiring in the power supply circuit 100 can be reduced.

  Further, the capacitance of the first capacitor C20 is larger than the capacitances of the second capacitor C21 and the third capacitor C22. The current discharged by the second capacitor C21 and the third capacitor C22 is a harmonic component current of the fundamental frequency of the current flowing in the diode D21 (current flowing in the power supply circuit 200). For this reason, the canceled magnetic field corresponds to a magnetic field generated by the current of the harmonic component of the fundamental frequency of the current flowing through the diode D21. Since such a magnetic field (noise) has a high frequency, it tends to adversely affect devices (especially a radio) around the power supply circuit 200. For this reason, the power supply circuit 200 can effectively reduce adverse effects on surrounding devices by reducing the generation of magnetic fields (particularly noise in a high frequency band such as a radio frequency band).

(Modification)
The configuration of the power supply circuit having two closed circuits with opposite current directions as described above can be changed as appropriate. For example, even a circuit as shown in FIG. 13 has an effect of canceling out a magnetic field generated by the flow of current. The power supply circuit in FIG. 13 is a modification of the power supply circuit 100 in FIG. 1, and corresponding elements are denoted by the same reference numerals. This power supply circuit has a configuration in which a diode D12 is added to the power supply circuit 100 of FIG. 1, and a closed circuit 110 and a closed circuit 120 are formed so as to be contrasted vertically. Since current flows in the closed circuit 110 and the closed circuit 120 in the directions indicated by the dotted arrows, the magnetic fields generated in both directions are canceled out, so that the same effect as in the first embodiment can be obtained. The switch unit may be disposed in each closed circuit. In this case, a switch unit for changing the input voltage is configured by the plurality of switch units.

  It should be noted that the present invention can be variously modified and modified without departing from the broad spirit and scope of the present invention. Further, the above-described embodiments and modifications are for explaining examples of the present invention and do not limit the scope of the present invention.

1 DC power supply 3 Load 100, 200 Power supply circuit 150, 250 Control unit 110, 120 Closed circuit 210, 220 Closed circuit

Claims (2)

A voltage converter that changes the voltage of the input voltage and outputs the voltage by switching the switch unit,
A first wiring structure in which a first current flows in a direction to generate a first magnetic field when the switch unit is in a predetermined switch state;
A second wiring structure in which a second current flows in a direction to generate a second magnetic field that cancels the first magnetic field when the switch unit is in the predetermined switch state;
The voltage converter characterized by having. The first current and the second current are currents of harmonic components of the fundamental frequency of the current flowing in the voltage converter,
The voltage converter according to claim 1.

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