JP4131352B2 - Step-down DC-DC converter device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a step-down DC-DC converter device.
[0002]
[Prior art]
In an electric vehicle, a dual power supply system in which power is supplied from a high-voltage main battery to a traveling motor and power is supplied from a low-voltage auxiliary battery to various auxiliary machines has been put into practical use because it is beneficial in various respects.
In this dual power supply type electric vehicle, instead of unnecessarily increasing the capacity of the auxiliary battery, the capacity is reduced, and if the power is insufficient, charging from the main battery through the step-down DC-DC converter device is various. This is a reasonable choice.
[0003]
This step-down DC-DC converter device includes an inverter circuit that forms a single-phase AC voltage from an input DC voltage, a transformer that transforms the single-phase AC voltage, a rectifier circuit that rectifies the output voltage of the transformer, and a rectified voltage. The transformer and the rectifier circuit are usually configured by a single-phase full-wave rectification method. In this single-phase full-wave rectification method, the transformer has a pair of secondary coils wound in the same direction and connected in series, and the rectifier circuit is composed of a single-phase full-wave rectifier circuit composed of a pair of rectifier elements. The midpoint of the pair of secondary coils connected to each other is grounded.
[0004]
[Problems to be solved by the invention]
However, the conventional step-down DC-DC converter device described above has a problem of radiating large electromagnetic noise.
The present invention has been made in view of the above problems, and an object thereof is to provide a step-down DC-DC converter device that realizes reduction of radiated electromagnetic noise.
[0005]
[Means for Solving the Problems]
According to the step-down DC-DC converter device according to claim 1, the pair of single-phase AC voltages (secondary voltages) output from the pair of secondary coils of the transformer are individually divided into half waves by the pair of rectifier elements. Rectified.
In the present invention, in particular, a grounding bus bar that connects the connection point (that is, the middle point) of both secondary coils to the low-order DC output terminal (so-called ground terminal) is located between the circuit board and the rectifying element, Further, the grounding bus bar is shaped so as to hide the rectifying element when viewed from the circuit board side .
[0006]
If it does in this way, electromagnetic wave noise of this step-down DC-DC converter device can be reduced, suppressing complication of a structure and extension of a manufacturing process.
More specifically, in the step-down DC-DC converter device, the main electromagnetic noise source is not an inverter circuit that performs high-speed switching, but a pair of rectifying elements and a pair of secondary coils of a step-down transformer to both rectifying elements. A pair of incoming lines (also referred to as half-wave rectification lines). This is because in the step-down DC-DC converter device, since the transformer secondary current is larger than the primary current, electromagnetic wave noise caused by a sudden change in the secondary current interrupted by the rectifier element becomes large. The line after a pair of lines are connected on the output side of both rectifier elements (the input side of the smoothing circuit) (also called a full-wave rectifier line) is the sum of the currents of both half-wave rectifier lines. The current change becomes much smaller and the electromagnetic noise becomes smaller. For the same reason, the electromagnetic noise of a line (referred to as a ground line) extending from the series connection point (middle point) of both secondary coils is also reduced.
[0007]
The present invention has been made by paying attention to the fact that the electromagnetic noise of the ground line is much smaller than that of both half-wave rectification lines. By covering the rectifier element from the circuit board with the ground line, both half-waves can be obtained. The adverse effect of electromagnetic noise radiated from the rectifying line and the rectifying element on the circuit elements of the circuit board is reduced.
Further, in this configuration, the grounding bus bar forming the grounding line has a wide flat plate shape to cover the rectifying element, so that the magnetic path length formed surrounding the grounding bus bar becomes long, and as a result, The inductance of the grounding bus bar is reduced, and the effect of reducing electromagnetic noise proportional to the inductance is also exhibited. Also, since the grounding bus bar has a large surface area, the cooling effect of the step-down transformer is also increased.
[0008]
According to the configuration of claim 2, in the step-down DC-DC converter device according to claim 1, the grounding bus bar connects one end of the secondary coil and the anode terminal of the rectifying element when viewed from the circuit board side. since having a size to hide the half-wave rectified line to an electromagnetic wave noise which acts on the circuit elements of the circuit board can be further reduced well.
According to a third aspect of the present invention, in the step-down DC-DC converter device according to the first or second aspect, the base portion forming the bottom plate portion of the case is a metal member, and the base portion and the grounding bus bar are used as a rectifying element. And the structure which sandwiches a half wave rectification line is employ | adopted.
[0009]
In this way, electromagnetic wave noise that reaches the circuit board through the grounding bus bar from the rectifying element or the rectifying line can be further reduced. Further, the base portion and the grounding bus bar facing each other have a large space capacitance and function as a so-called high frequency bypass capacitor, so that electromagnetic noise can be further reduced.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the step-down DC-DC converter device of the present invention will be described with reference to the following examples.
[0011]
[Example 1]
An embodiment of the step-down DC-DC converter device of the present invention will be described with reference to the circuit diagram shown in FIG.
(Circuit configuration)
This step-down DC-DC converter device is for voltage-converting power from a main battery 1 for running energy storage of an electric vehicle to an auxiliary battery 2 for feeding auxiliary equipment and a control device. Is a smoothing capacitor, 4 is an inverter circuit formed by bridge-connecting four MOS transistors 4a, 6 is a step-down transformer, 7 is a snubber circuit, 8 is two diodes (rectifier elements) for full-wave rectification, and 9 is a choke A smoothing circuit 12 composed of a coil 10 and a smoothing capacitor 11 is an integrated control circuit.
[0012]
The high end of the main battery 1 is connected to the bus bar 13 through the input terminal 14, and the low end of the main battery 1 is connected to the bus bar 15 through the input terminal 16.
The smoothing capacitor 3 is connected between the bus bars 13 and 15, and the bus bar 13 is connected to the drain electrode terminals of the pair of MOS transistors 4 a on the upper arm side forming the higher DC input terminal of the inverter circuit 4, and the bus bar 15 is connected to the inverter circuit 4. It is connected to the source electrode terminal of the pair of MOS transistors 4a on the lower arm side that forms the lower DC input terminal. The gate electrode of each MOS transistor 4a of the inverter circuit 4 receives the control voltage from the control circuit 12 through the buffer circuit 20 that amplifies the input voltage.
[0013]
A pair of AC output terminals of the inverter circuit 4 are connected to both ends of the primary coil of the step-down transformer 6.
The step-down transformer 6 has two secondary coils 61 and 62 wound in the same direction and connected in series with each other. One end of the secondary coil 61 is extended to the outside and a bus bar (half-wave rectification line) 17. One end of the secondary coil 62 is extended outside to form a bus bar (half-wave rectification line) 18. The bus bar 17 is connected to one anode electrode terminal of the pair of diodes 8, and the bus bar 18 is connected to the other anode electrode terminal of the pair of diodes 8.
[0014]
An intermediate terminal 6 a forming a series connection point (middle point) of the secondary coils 61 and 62 of the step-down transformer 6 is a low-order end of the auxiliary battery 6 through a bus bar (ground line) 19 and a ground terminal (low-order DC output end) 21. It is connected to the.
The cathode electrode terminals of both diodes 8 are connected to one end (higher DC output end) of the choke coil 10 through the full-wave rectification line 24, and the other end 25 of the choke coil 10 is connected to the auxiliary battery 2 through the bus bar 26 and the output terminal 27. Connected to the high end of the. In practice, both diodes 8 and 8 are mounted in the diode module 80 shown in FIG. 2, and a pair of anode electrode terminals (shown by screws in FIG. 2) and a pair of cathode electrode terminals (shown by screws in FIG. 2). Is provided on the upper surface of the diode module 80.
[0015]
The snubber circuit 7 is a CR high-pass filter equivalent to an equivalent circuit formed by connecting a resistance element and a capacitor in series, and is connected between the anode electrode terminals of a pair of diodes 8.
(Description of operation)
The control circuit 12 intermittently connects each MOS transistor 4a of the inverter circuit 4 until the voltage of the auxiliary battery 2 reaches a predetermined value by the input of a charging command to its input terminal (not shown), and a rectangular wave is applied to the primary coil of the step-down transformer 6. An alternating voltage is applied.
[0016]
The secondary voltage generated in the secondary coils 61 and 62 of the step-down transformer 6 is rectified by a pair of diodes 8 and 8 forming a single-phase full-wave rectifier circuit, whereby the full-wave rectification line 24 and the ground bus bar (ground line). The full-wave rectified voltage generated between the first and second terminals 19 is smoothed by the smoothing circuit 9 and applied to the auxiliary battery 2.
The smoothing capacitor 3 reduces the fluctuation of the discharge current of the main battery 1 due to the intermittent operation of the inverter circuit 4, and the snubber circuit 7 absorbs the high-frequency surge voltage as a CR high-pass filter.
(Arrangement of circuit parts)
2 and 3 are enlarged views of the main part arrangement of each DC-DC converter device described above. 2 is a longitudinal sectional view, and FIG. 3 is a plan view.
[0017]
Reference numeral 30 denotes a circuit board on which circuit elements 32 and 33 forming the control circuit 12 are mounted. The circuit board 30 extends above and parallel to the aluminum base plate (base part of the case) 31 with a predetermined distance from the main surface of the aluminum base plate 31. The circuit board 30 is fastened by screws to a pillar part (not shown) that is erected from the peripheral part (not shown) of the aluminum base plate 31 toward the circuit board 30.
[0018]
The step-down transformer 6 and the diode module 80 are fixed close to the aluminum base plate 31. Bus bars (half-wave rectification lines) 17 and 18 extending in parallel with the aluminum base plate 31 from the step-down transformer 6 are extended to a pair of anode electrode terminals of the diode module 80.
A pair of cathode electrode terminals of the aluminum base plate 31 are connected to one end of a bus bar (full wave rectification line) 24. The bus bars 17, 18, 24 are extended in parallel to the aluminum base plate 31 at a predetermined distance.
[0019]
One end of the grounding bus bar (grounding line) 19 is connected to the midpoint 6a of the step-down transformer 6 and extends directly above the busbars 17, 18, and 24 in parallel therewith. Further, as shown in FIG. 3, the ground bus bar 19 is widened at the diode module 80, so that the bus bars 17, 18, and 24 are almost covered with the ground bus bar 19 as viewed from the circuit board 30. ing. In FIG. 3, the grounding bus bar 19 is indicated by oblique lines for easy understanding. Therefore, the bus bar for grounding is extended between the bus bars 17, 18, 24 and the diode module 80 and the circuit board 30.
[0020]
(Example effect)
According to this embodiment configured as described above, the grounding bus bar 19 shields the bus bars 17 and 18 and the diode module 80 from the circuit board 30, so that the diodes 8 and 8 are intermittently connected and the switching element of the inverter circuit 4 is switched. It is possible to satisfactorily suppress the electromagnetic wave noise generated by the current change in the bus bars 17 and 18 and the diode module 80 accompanying the intermittent 4a from affecting the circuit elements on the circuit board 30. In addition, since the above-described effect can be obtained only by forming the grounding bus bar 19 in an irregular shape, the structure and the manufacturing process are not complicated.
[0021]
In addition, the ground bus bar 19 is favorably cooled by the cooling air blown in parallel with the circuit board 30, and the step-down transformer 6 is also favorably cooled by the ground bus bar 19.
The grounding bus bar 19 is flat in the direction perpendicular to the energizing direction, particularly in the vicinity of the diode module 80, so that the current flows in a distributed manner and the line inductance of the grounding bus bar 19 is reduced. There is also.
[0022]
Furthermore, the large parasitic capacitance between the bus bars 17, 18, 24 and the ground bus bar 19 reduces electromagnetic noise.
Note that the current fluctuation of the grounding bus bar 19 is the sum of the currents of both the diodes 8 and 8 as in the full-wave rectification line 24, and is much smaller than the bus bars 17 and 18.
[0023]
(Modification)
In the above embodiment, the circuit board 30 is provided independently of the ground bus bar 19, but may be provided on the main surface of the ground bus bar 19 on the side opposite to the diode module via an insulating layer.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of a step-down DC-DC converter device according to the present invention.
2 is a longitudinal sectional view of a main part of the step-down DC-DC converter device shown in FIG.
3 is a schematic plan view of an essential part of the step-down DC-DC converter device shown in FIG. 2. FIG.
[Explanation of symbols]
4 is an inverter circuit, 6 is a step-down transformer (transformer), 8 is a diode (rectifier element), 9 is a smoothing circuit, 19 is a bus bar for grounding, 30 is a circuit board, 31 is an aluminum base plate (base part of the case), 61, 62 is a secondary coil

Claims (3)

A transformer having a pair of secondary coils wound in the same direction and connected in series;
An inverter circuit that intermittently controls a DC voltage and applies a single-phase AC voltage to the primary coil of the transformer;
A pair of rectifying elements each having an anode terminal individually connected to each one end of the pair of secondary coils and a cathode terminal commonly connected to form a high-order DC output end;
A grounding bus bar for connecting the other end of the pair of secondary coils to a low DC output terminal;
A smoothing circuit for smoothing a rectified voltage between the high-level DC output terminal and the low-level DC output terminal;
A circuit board on which a control circuit for outputting a control voltage to the inverter circuit is mounted;
A case for accommodating the transformer, inverter circuit, rectifying element, grounding bus bar, and circuit board;
A step-down DC-DC converter device comprising:
The grounding bus bar is located between the circuit board and the rectifying element and extends substantially in parallel with the circuit board, and hides the pair of rectifying elements when viewed from the circuit board side. A step-down DC-DC converter device. The step-down DC-DC converter device according to claim 1,
The step-down DC-DC converter device, wherein the grounding bus bar hides a line extending from the one end of the secondary coil to the rectifying element when viewed from the circuit board side . The step-down DC-DC converter device according to claim 1 or 2,
The case is made of a metal to which the transformer is fixed and which is positioned on the opposite side of the grounding bus bar across the rectifying element and extends substantially parallel to the grounding bus bar and to which a ground potential is applied. A step-down DC-DC converter device characterized by having a base portion.

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