JP2015198566A - Dc/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC/DC converter capable of reducing a radiation electromagnetic field to the outside by canceling a magnetic flux generated in a loop circuit where a current is varied.SOLUTION: A DC/DC converter includes switching elements S3 and S4 and a choke coil L and boosts or drops an inputted DC voltage by turning on/turning off the switching elements S3 and S4. The DC/DC converter includes the two switching elements S3 and S4; a drive circuit 4 for simultaneously driving the two switching elements S3 and S4; and two loop-shaped circuit portions (S3, D3, C3) and (S4, C4, D4) in the substantially same shape including the switching elements S3 and S4 and varying currents by turning on/turning off the switching elements S3 and S4. The two circuit portions (S3, D3, C3) and (S4, C4, D4) are overlapped while being insulated so as to mutually cancel magnetic fluxes generated by currents circulating thereto.

Description

  The present invention relates to a DC / DC converter that includes a switching element and a choke coil, and that steps up or down an input DC voltage by turning on / off the switching element.

FIG. 5 is a circuit diagram showing a schematic configuration example of a conventional step-up DC / DC converter.
In this DC / DC converter, one terminal of the choke coil L is connected to the plus terminal of the DC power supply 3 with the minus terminal grounded, and the other terminal of the choke coil L is connected to an N-channel MOSFET (metal oxide semiconductor electric field). (Effect transistor) connected to the drain of S1 and the anode of diode D1.

The source of the FET S1 is grounded, the cathode of the diode D1 is connected to the plus terminal of the capacitor C1, and the minus terminal of the capacitor C1 is grounded. The gate of the FET S1 is ON / OFF controlled by the switching control circuit 4.
The output of the DC / DC converter is given to the load R as a voltage across the capacitor C1.

In the step-up DC / DC converter having such a configuration, when the FET S1 is turned on by PWM (Pulse Width Modulation) control, a large current that does not pass through the load R flows into the choke coil L to store energy.
Next, when the FET S1 is turned off, a current passing through the load R flows through the choke coil L and the diode D1, and the output voltage thereby is substantially equal to the output voltage of the DC power supply 3. On the other hand, a current due to the energy stored in the choke coil L also flows, and the resulting voltage is superimposed on the output voltage of the DC power supply 3 and output from the diode D1.

The output voltage when the FETS1 is off and the output voltage when the FETS1 is on are smoothed by the capacitor C1 and applied to the load R.
The output voltage applied to the load R is determined by the duty ratio of PWM control (ON time of FETS1 / (ON time + OFF time)).

FIG. 6 is a circuit diagram showing a schematic configuration example of a conventional step-down DC / DC converter.
In this DC / DC converter, the drain of the N-channel MOSFET S2 and the plus terminal of the filter capacitor C2 are connected to the plus terminal of the DC power source 3 whose minus terminal is grounded, and the minus terminal of the filter capacitor C2 is grounded. The source of the FET S2 is connected to the cathode of the diode D2 and one terminal of the choke coil L.

The gate of the FET S2 is ON / OFF controlled by the switching control circuit 5. The anode of the diode D2 is grounded, the other terminal of the choke coil L is connected to the plus terminal of the load R, and the minus terminal of the load R is grounded.
The output of the DC / DC converter is given to the load R from the other terminal of the choke coil L.

  In the step-down DC / DC converter having such a configuration, when FETS2 is turned on / off by PWM control, the output voltage corresponding to the duty ratio (ON time of FETS2 / (on time + off time)) is a choke coil. Smoothed at L and applied to load R.

  Patent Document 1 discloses an in-vehicle electronic control device in which radiated magnetic noise is reduced. A current loop is formed by the switching element, the choke coil, the output capacitor, and the filter capacitor. The current loop generates a magnetic flux having a magnetic flux direction opposite to the magnetic flux direction of the magnetic flux generated from the choke coil. Thereby, the magnetic flux generated from the choke coil and the magnetic flux generated from the current loop cancel each other, and the magnetic flux generated from the choke coil can be reduced.

JP 2009-177998 A

The conventional DC / DC converter described above has a problem that a loop circuit in which a current fluctuates is formed by turning on / off the FETs S1 and S2, and a radiated electromagnetic field is generated thereby.
In order to solve such a problem, an in-vehicle electronic control device as disclosed in Patent Document 1 has been proposed, but each magnetic flux generated by the current loop and the choke coil has a greatly different intensity distribution, It is impossible to completely cancel each other. In the first place, a choke coil is usually not included in a current loop through which a large fluctuation current flows, and the timing for generating a magnetic flux is different.

  The present invention has been made in view of the above-described circumstances, and provides a DC / DC converter capable of canceling out magnetic flux generated in a loop circuit in which current fluctuates and reducing an electromagnetic field radiated to the outside. The purpose is to do.

  A DC / DC converter according to a first aspect of the present invention includes a switching element and a choke coil. In the DC / DC converter that steps up or down an input DC voltage by turning on / off the switching element, An element, a drive circuit that drives the two switching elements simultaneously, and two circuit parts that include the switching element and have substantially the same loop shape in which the current varies when the switching element is turned on / off. And the two circuit parts are insulated and overlapped so that magnetic fluxes caused by currents flowing through each of the two circuit parts cancel each other.

  This DC / DC converter includes a switching element and a choke coil. When the switching element is turned on / off, the input DC voltage is boosted or lowered. The drive circuit drives the two switching elements simultaneously, and the current of the two circuit parts having substantially the same loop shape including the switching elements is changed by turning on / off the switching elements. The two circuit portions having substantially the same loop shape are insulated and overlapped so that magnetic fluxes caused by currents flowing through the circuit portions cancel each other.

  The DC / DC converter according to the second invention is characterized in that the two circuit portions are respectively mounted on the front and back surfaces of a substrate having a plurality of through holes, and are connected through the through holes as necessary. .

  In this DC / DC converter, two circuit parts having substantially the same loop shape are respectively mounted on the front and back surfaces of a substrate having a plurality of through holes, and the two circuit parts are connected through the through holes as necessary.

  According to the DC / DC converter according to the present invention, it is possible to realize a DC / DC converter capable of canceling the magnetic flux generated in the loop circuit in which the current fluctuates and reducing the radiated electromagnetic field to the outside. In addition, since the demand for reducing the loop area of the loop circuit is eased, it is possible to mount the elements apart from each other, and the heat radiation design is facilitated.

It is a circuit diagram which shows the principal part structure of embodiment of the DC / DC converter which concerns on this invention. FIG. 2 is a schematic view schematically showing a configuration example in which the inside of a broken line of the DC / DC converter shown in FIG. 1 is mounted on a substrate. It is a circuit diagram which shows the principal part structure of embodiment of the DC / DC converter which concerns on this invention. FIG. 4 is a schematic view schematically showing a configuration example in which the inside of a broken line of the DC / DC converter shown in FIG. 3 is mounted on a substrate. It is a circuit diagram which shows the structural example of the conventional DC / DC converter. It is a circuit diagram which shows the structural example of the conventional DC / DC converter.

Hereinafter, a DC / DC converter according to the present invention will be described with reference to the drawings showing embodiments thereof.
(Embodiment 1)
FIG. 1 is a circuit diagram showing a main configuration of a DC / DC converter according to Embodiment 1 of the present invention.
In this step-up DC / DC converter, one terminal of a choke coil L is connected to a plus terminal of a DC power supply 3 whose negative terminal is grounded, and the other terminal of the choke coil L is an N-channel MOSFET (switching element). ) It is connected to each drain of S3 and S4 and each anode of diodes D3 and D4.

The sources of the FETs S3 and S4 are grounded, the cathodes of the diodes D3 and D4 are connected to the plus terminals of the capacitors C3 and C4, and the minus terminals of the capacitors C3 and C4 are grounded. The gates of the FETs S3 and S4 are simultaneously ON / OFF controlled by a switching control circuit (drive circuit) 4.
The output of this DC / DC converter is given to the load R as the voltage across each of the capacitors C3 and C4.
A filter capacitor may be connected between the input terminal (one terminal of the choke coil L) and the ground terminal.

FIG. 2 is a schematic view schematically showing a configuration example in which the inside of a broken line of the DC / DC converter shown in FIG. 1 is mounted on a substrate having a front surface 1 and a back surface 2 and having through holes H1 to H5. It is. Here, for easy understanding, the thickness direction of the substrates 1 and 2 is shown enlarged.
In this DC / DC converter, a high-voltage side electric wire 9 and a grounding electric wire 10 are arranged in parallel on the front surface 1 of the substrate while being separated by an appropriate length, and a grounding wire 11 and a high-voltage side electric wire 12 are arranged on the back surface 2 of the substrate. They are arranged in parallel at an appropriate distance. The high-voltage side electric wire 9 and the grounding electric wire 11 and the grounding electric wire 10 and the high-voltage side electric wire 12 are arranged close to each other on the front surface 1 and the back surface 2 of the substrate.

  From one end of the high-voltage side electric wire 9 (the other terminal of the choke coil L), a branch line passes through the through hole H1 and is routed on the back surface 2 side to connect to one end of the high-voltage side electric wire 12. After the branch line is routed from the other end of the high-voltage side electric wire 12 to the vicinity of the grounding electric wire 11, it passes through the through hole H3 and the other end of the high-voltage side electric wire 9 (plus the capacitor C3) Terminal).

From one end of the ground wire 10, the branch line passes through the through-hole H 2, is routed on the back surface 2 side, is connected to one end of the ground wire 11, and is connected to the other end of the ground wire 11. After the branch line is routed to the vicinity of the high-voltage side electric wire 12, it passes through the through hole H4 and is connected to the other end of the ground wire 10 (the negative terminal of the capacitor C3).
The control wire of the switching control circuit 4 is connected to the gate of the FET S3, and after the front surface 1 is routed to the vicinity of the high-voltage side wire 9, the gate of the FET S4 mounted on the back surface 2 passes through the through hole H5. It is connected to the.

The choke coil L, FETS3, diode D3, capacitor C3, and switching control circuit 4 are mounted on the surface 1 of the substrate in accordance with the wiring of the high-voltage side wire 9, the ground wire 11, the high-voltage side wire 12, and the ground wire 10. FETS4, diode D4, and capacitor C4 are mounted on the back surface 2 of the substrate.
As a result, the loop circuit formed by the FET S3, the diode D3, and the capacitor C3, and the loop circuit formed by the FET S4, the diode D4, and the capacitor C4 are mounted so as to overlap each other on the front surface 1 and the back surface 2 of the substrate. In addition, the currents flowing through the respective loop circuits can be reversed.

Hereinafter, an example of the operation of the step-up DC / DC converter having such a configuration will be described.
In the DC / DC converter, when FETs S3 and S4 are turned on by PWM control, a large current that does not pass through the load R flows into the choke coil L and energy is stored.
Next, when the FETs S3 and S4 are turned off, a current passing through the load R flows through the choke coil L and the diodes D3 and D4. The output voltage thereby is substantially equal to the output voltage of the DC power supply 3. On the other hand, a current due to the energy stored in the choke coil L also flows, and the resulting voltage is superimposed on the output voltage of the DC power supply 3 and output from the diodes D3 and D4.

The output voltage when the FETs S3 and S4 are off and the output voltage when the FETs S3 and S4 are on are smoothed by the capacitors C3 and C4 and applied to the load R.
The output voltage applied to the load R is determined by the duty ratio of PWM control (ON time of FETS3, S4 / (ON time + OFF time)).
When the FETs S3 and S4 are turned on / off, the currents flowing through the loop circuit of the FETS3, the diode D3, and the capacitor C3, and the loop circuit of the FETS4, the diode D4, and the capacitor C4 change, and electromagnetic waves due to the current change are radiated. .

  At this time, each loop circuit is mounted on the front surface 1 and the back surface 2 of the substrate so as to overlap each other in substantially the same shape, and the currents flowing in each loop circuit are opposite to each other. The electromagnetic waves to be applied are substantially the same in strength and opposite to each other, cancel each other, and reduce the electromagnetic waves radiated to the outside of the DC / DC converter.

(Embodiment 2)
FIG. 3 is a circuit diagram showing the main configuration of the second embodiment of the DC / DC converter according to the present invention.
In this step-down DC / DC converter, the drains of N-channel MOSFETs (switching elements) S5 and S6 and the plus terminals of filter capacitors C5 and C6 are connected to the plus terminal of the DC power source 3 whose minus terminal is grounded. The negative terminals of the filter capacitors C5 and C6 are grounded. Each source of the FETs S5 and S6 is connected to each cathode of the diodes D5 and D6 and one terminal of the choke coil L.

The gates of the FETs S5 and S6 are on / off controlled by a switching control circuit (drive circuit) 5. The anodes of the diodes D5 and D6 are grounded, the other terminal of the choke coil L is connected to the plus terminal of the load R, and the minus terminal of the load R is grounded.
The output of the DC / DC converter is given to the load R from the other terminal of the choke coil L.
A smoothing capacitor may be connected between the output terminal of the DC / DC converter (the other terminal of the choke coil L) and the ground terminal.

FIG. 4 is a schematic view schematically showing a configuration example in which the inside of the broken line of the DC / DC converter shown in FIG. 3 is mounted on a substrate having a front surface 7 and a back surface 8 and having through holes H6 to H10. It is. Here, in order to facilitate understanding, the thickness direction of the substrates 7 and 8 is shown enlarged.
In the DC / DC converter, a high-voltage side electric wire 13 and a grounding electric wire 14 are arranged in parallel with an appropriate distance from each other on the surface 7 of the substrate, and a grounding wire 15 and a high-voltage side electric wire 16 are arranged on the back surface 8 of the substrate. They are arranged in parallel at an appropriate distance. The high-voltage side electric wire 13 and the grounding electric wire 15 and the grounding electric wire 14 and the high-voltage side electric wire 16 are arranged close to each other on the front surface 7 and the rear surface 8 of the substrate.

  From one end of the high-voltage side electric wire 13 (plus terminal of the filter capacitor C5), the branch line passes through the through hole H6 and is routed to the back surface 8 side, and is connected to one end of the high-voltage side electric wire 16. After the branch line is routed from the other end of the high-voltage side electric wire 16 to the vicinity of the grounding electric wire 15, the other end of the high-voltage side electric wire 13 (one of the choke coils L) passes through the through hole H8. Terminal).

From one end of the ground wire 14, the branch line passes through the through hole H 7, is routed on the back surface 8 side, is connected to one end of the ground wire 15, and is connected to the other end of the ground wire 15. After the branch line is routed to the vicinity of the high-voltage side electric wire 16, it passes through the through hole H <b> 9 and is connected to the other end of the ground wire 14.
The control electric wire of the switching control circuit 5 is connected to the gate of the FET S5 and is connected to the gate of the FET S6 mounted on the back surface 8 through the through hole H10.

The choke coil L, FETS5, diode D5, filter capacitor C5, and switching control circuit 5 are provided on the surface 7 of the substrate in accordance with the wiring of the high-voltage side wire 13, the ground wire 14, the high-voltage side wire 16, and the ground wire 15. The FET S6, the diode D6, and the filter capacitor C6 are mounted on the back surface 8 of the substrate.
As a result, the loop circuit formed by the FET S5, the diode D5 and the filter capacitor C5, and the loop circuit formed by the FET S6, the diode D6 and the filter capacitor C6 are overlapped in substantially the same shape on the front surface 7 and the back surface 8 of the substrate, respectively. The current flowing through each loop circuit can be reversed to each other.

Hereinafter, an example of the operation of the step-down DC / DC converter having such a configuration will be described.
In this DC / DC converter, when the FETs S5 and S6 are turned on / off by PWM control, the output voltage corresponding to the duty ratio (ON time of the FETS5 and S6 / (on time + off time)) is generated by the choke coil L. Smoothed and applied to the load R.
When the FETs S5 and S6 are turned on / off, the currents flowing in the loop circuit of the FETS5, the diode D5, and the filter capacitor C5, and the loop circuit of the FETS6, the diode D6, and the filter capacitor C6 fluctuate. Is done.

  At this time, each loop circuit is mounted on the front surface 7 and the back surface 8 of the substrate so as to overlap with each other in substantially the same shape, and the currents flowing in each loop circuit are opposite to each other. The electromagnetic waves to be applied are substantially the same in strength and opposite to each other, cancel each other, and reduce the electromagnetic waves radiated to the outside of the DC / DC converter.

1,7 Surface (substrate)
2,8 Back side (substrate)
3 DC power supply 4, 5 Switching control circuit (drive circuit)
9, 12, 13, 16 High-voltage side wire 10, 11, 14, 15 Ground wire C3, C4 capacitor C5, C6 Filter capacitor D3-D6 Diode H1-H10 Through-hole L Choke coil R Load S3-S6 FET (switching element) )

Claims (2)

In a DC / DC converter comprising a switching element and a choke coil, and stepping up or down an input DC voltage by turning on / off the switching element.
The two switching elements, a drive circuit that drives the two switching elements simultaneously, and the switching elements, and the switching elements are turned on / off to change two currents in a substantially isomorphous loop shape. A DC / DC converter comprising: a circuit portion, wherein the two circuit portions are insulated and overlapped so that magnetic fluxes caused by currents flowing through the circuit portions cancel each other.   2. The DC / DC converter according to claim 1, wherein the two circuit portions are respectively mounted on front and back surfaces of a substrate having a plurality of through holes, and are connected through the through holes as necessary.

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