JP2009284691A - Power conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that noise due to reverse recovery phenomenon may be superimposed on a ground line GL if a pair of diodes RD1 and RD2 are arranged for rectification when voltage polarity at a pair of terminals of a secondary side coil 20b of a transformer 20 is inverted. <P>SOLUTION: Capacitors 50 and 52, connected in series, are connected between cathode sides of respective diodes RD1 and RD2 and a node N1. A connection point (node N2) of the capacitors 50 and 52 is connected to a middle point tap mt of the secondary side coil 20b. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is a power conversion circuit comprising a transformer and a rectifying means for rectifying the voltage polarity of a pair of terminals of the secondary winding of the transformer when the voltage polarity is reversed. The present invention relates to a power conversion circuit including a diode connected to each of a pair of terminals of a secondary winding and having a cathode side of the pair of diodes connected to an output terminal.

  As a power conversion circuit, a power conversion circuit (inverter) including a series connection body of a pair of switching elements for selectively connecting a positive electrode and a negative electrode of a DC power supply to a terminal of an electric motor and insulated from a ground line Is well known. In general, the inverter includes a diode connected between the input and output terminals in addition to the switching element. As a result, when a current is flowing through one of the switching elements constituting the series connection body, when this is turned off, a forward current is applied to the diode connected between the input / output terminals of the other switching element. Flows.

  By the way, when one of the switching elements is turned on again in a situation where a forward current flows through the diode, a high-frequency common mode current is generated because a voltage near the switching element is fluctuated due to a reverse recovery phenomenon of the diode. It is known. The common mode current is generated when the parasitic capacitance between the originally insulated ground line and the inverter is charged and discharged by voltage fluctuation. When the common mode current flows through the ground line, the electronic device connected to the ground line may be damaged or electromagnetic radiation noise may be generated.

Therefore, conventionally, as seen in Patent Document 1 below, for example, it has been proposed to provide a pair of Y capacitors between a pair of power supply lines for supplying power to the motor. The Y capacitor is a series connection body of a pair of capacitors, and the connection point thereof is connected to the ground line. Thereby, it is possible to avoid the common mode current from flowing to another electronic device via the ground line.
JP 2000-315929 A

  By the way, as a power conversion circuit, a DCDC converter provided with a diode connected to each of a pair of terminals of a secondary winding to rectify the voltage polarity on the secondary side of the transformer when it is inverted. Is also well known. Even in this case, the common mode current may flow due to the reverse recovery phenomenon of the diode accompanying the reversal of the voltage polarity on the secondary side. However, the above technique cannot be directly applied to such devices.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a pair of diodes for rectifying a voltage polarity of a pair of terminals of a secondary winding of a transformer when the voltage polarity is inverted. Even if it is a case, it is providing the power converter circuit which can suppress suitably that the noise resulting from a reverse recovery phenomenon superimposes on a ground line.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  The invention according to claim 1 is a power conversion circuit comprising a transformer and a rectifying means for rectifying the voltage polarity of a pair of terminals of the secondary winding of the transformer when the voltage polarity is inverted, and the rectifying means In a power conversion circuit including a diode connected to each of a pair of terminals of the secondary winding and a cathode side of the pair of diodes connected to an output terminal, the secondary winding and the output A pair of capacitors interposed between terminals and connected in series between a pair of electrical paths including each of the pair of diodes, and a connection point of the pair of capacitors is connected to the secondary winding; It is characterized by that.

  In the above invention, when the forward current flows through one of the pair of diodes constituting the rectifying means, when the voltage polarity of the secondary winding is reversed, the forward current of the one diode rapidly decreases and then reverses. A recovery phenomenon occurs. Immediately after the end of the reverse recovery phenomenon, a resonance phenomenon occurs between the inductance component of the electric path near the diode and the parasitic capacitor of the diode, which may cause common mode noise. In this regard, in the above-described invention, the noise distribution path caused by the resonance phenomenon is a loop circuit including the secondary winding and one of the pair of capacitors, thereby making the noise distribution path into a short loop. As a result, it is possible to suitably suppress the noise caused by the reverse recovery phenomenon from being superimposed on the ground line.

  In the above invention, it is desirable that the diode and the capacitor are directly connected by wiring.

  According to a second aspect of the present invention, in the first aspect of the invention, the secondary winding has a midpoint tap, and a connection point of the pair of capacitors is connected to the midpoint tap. It is characterized by.

  In the above invention, a loop circuit including one of the pair of diodes, one of the pair of capacitors and the secondary winding, and a loop circuit including the other of the pair of diodes, the other of the pair of capacitors and the secondary winding. Setting to make the impedances equal is easy. For this reason, the structure which avoids mode conversion becomes easy.

  According to the second aspect of the present invention, the electrical path including one of the pair of capacitors and the midpoint tap and the electrical path including the other of the pair of capacitors and the midpoint tap are connected to the pair of capacitors. It is desirable to have symmetry between the point and the midpoint tap.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the secondary winding is connected to a ground line.

  In the said invention, since a secondary side winding is connected to a ground line, there exists a possibility that the noise resulting from the said reverse recovery phenomenon may overlap with a ground line via a secondary side winding. For this reason, the utility value of the invention of claim 1 is particularly high.

  The invention according to claim 4 is the invention according to claim 3, wherein the secondary winding has a midpoint tap, and the ground line is connected to the midpoint tap. .

  In the above invention, since the ground line is connected to the midpoint tap, the voltage output alternately from each of the pair of diodes is the same as long as the absolute value of the voltage at both ends of the secondary winding is the same. It can be.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the pair of capacitors are connected between a cathode of the pair of diodes and a connection point of the pair of cathodes. It is characterized by that.

  In the above invention, the noise distribution path due to the resonance phenomenon caused by the secondary side winding and the diode, the inductance component between the diode and the capacitor, and the parasitic capacitor of the diode is shorted as a loop circuit including the secondary side winding, the diode and the capacitor. Can be looped.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the pair of capacitors are further connected between an anode side of the pair of diodes and a secondary winding of the transformer. And

  In the above invention, the loop circuit including the secondary winding, the diode, and the capacitor on the cathode side of the diode can be further divided. For this reason, the noise distribution path due to the resonance phenomenon can be further shortened.

  The invention according to claim 7 is the invention according to any one of claims 1 to 5, wherein the pair of capacitors are connected between an anode side of the pair of diodes and a secondary winding of the transformer. It is characterized by.

  In the above invention, the noise distribution path due to the LC resonance phenomenon caused by the inductance component between the secondary winding and the capacitor can be formed into a short loop as a loop circuit including the secondary winding and the capacitor.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the ground line is a ground line of a vehicle.

  Since a large number of in-vehicle electronic devices are connected to the ground line of the vehicle, if a high-frequency current flows through this, it is considered that these electronic devices are likely to be adversely affected. For this reason, this invention has especially high utility value of the invention of Claims 1-7.

(First embodiment)
Hereinafter, a first embodiment in which a power conversion circuit according to the present invention is applied to a power conversion circuit mounted on a hybrid vehicle will be described with reference to the drawings.

  FIG. 1 shows an overall configuration of a system according to the present embodiment.

  The illustrated high voltage battery 10 is a power source of an electric motor (not shown) as an in-vehicle power generation device, and outputs a predetermined high voltage (several hundred volts). The DCDC converter CV steps down the voltage of the high voltage battery 10 and outputs it. Specifically, the DCDC converter CV is an insulating converter including the transformer 20. One terminal of the primary side coil 20a of the transformer 20 can be electrically connected to the positive electrode side of the high-voltage battery 10 via the high-potential side switching element Sw1 and the high-potential side wiring Lp. It can be electrically connected to the negative electrode side of the high-voltage battery 10 via the element Sw2 and the low-potential side wiring Ln. Further, the other terminal of the primary side coil 20a of the transformer 20 can be electrically connected to the positive electrode side of the high voltage battery 10 via the high potential side switching element Sw3 and the high potential side wiring Lp. It can be electrically connected to the negative electrode side of the high voltage battery 10 via the element Sw4 and the low potential side wiring Ln. Here, in the present embodiment, N-channel MOS transistors are illustrated as the switching elements Sw1 to Sw4. Free wheel diodes D1 to D4 are connected between the input / output terminals of the switching elements Sw1 to Sw4, respectively.

  According to such a configuration, the high potential side switching element Sw1 and the low potential side switching element Sw4 are turned on, and the low potential side switching element Sw2 and the high potential side switching element Sw3 are turned on. The voltage polarity of the primary side coil 20a is inverted, and consequently the voltage polarity of the secondary side coil 20b is also inverted. Regardless of the reversal of the voltage polarity of the secondary coil 20b, a pair of terminals of the secondary coil 20b are connected to the anode sides of the diodes RD1 and RD2, respectively, in order to apply a constant voltage. The diodes RD1 and RD2 have the same specifications (the same on-voltage Vf, the same rated voltage, the rated current, etc., particularly the same impedance). The cathode sides of the diodes RD1 and RD2 are short-circuited at the node N1 and output to the smoothing circuit 22. In this embodiment, as the smoothing circuit 22, an LC filter including a coil 22a and a capacitor 22b is illustrated.

  The primary side of the high voltage battery 10 and the DCDC converter CV constitutes an in-vehicle high voltage system and is insulated from the ground line GL. On the other hand, the secondary side of the DCDC converter CV constitutes an in-vehicle low-pressure system that operates based on the ground line GL connected to the vehicle body. In order to achieve such a setting, in this embodiment, the midpoint tap mt of the secondary coil 20b of the transformer 20 is connected to the ground line GL. As a result, the diodes RD1 and RD2 have the high potential side switching element Sw1 and the low potential side switching element Sw4 turned on or the low potential side switching element Sw2 and the high potential side switching element Sw3 turned on. Accordingly, a voltage of “½” of the voltage across the secondary coil 20b is alternately output. The midpoint tap mt is a terminal connected to the center of the transformer coil (a midpoint that is equidistant from both terminals).

  The output voltage of the DCDC converter CV is applied to the low voltage battery 12. The low voltage battery 12 is a power supply means for an electric load in the in-vehicle low voltage system. FIG. 1 illustrates a load 24, an auxiliary power supply 26, and a control device 30 as such an electric load. Here, examples of the load 24 include an air conditioner and a headlight. Further, the auxiliary power source 26 is for stepping down the voltage (for example, “12V”) of the low-voltage battery 12 to generate a predetermined stable voltage.

  On the other hand, the control device 30 is control means that uses the low-voltage battery 12 as a control target and uses the auxiliary power supply 26 as a direct power supply. Specifically, the high potential side switching elements Sw1 and Sw3 and the low potential side switching elements Sw2 and Sw4 of the DCDC converter CV are operated in order to control the state of charge (SOC) of the low voltage battery 12 as desired. Specifically, the high potential side switching elements Sw1 and Sw3 and the low potential side switching elements Sw2 and Sw4 are operated via the drive circuit 32.

  The DCDC converter CV includes a capacitor 42 between the high potential side wiring Lp and the low potential side wiring Ln for suppressing fluctuations in the input voltage. Further, the DCDC converter CV includes the following as a countermeasure by superimposing the common mode current on the high potential side wiring Lp and the low potential side wiring Ln. First, Y capacitors CY1 and CY2 are provided between the high potential side wiring Lp and the low potential side wiring Ln. These Y capacitors CY1 and CY2 are a series connection body of a pair of capacitors, and the connection point thereof is connected to the ground line GL. A common mode choke coil 40 is provided between the Y capacitors CY1 and CY2.

  According to such a configuration, it is possible to avoid the common mode current superimposed on the high potential side wiring Lp and the low potential side wiring Ln from adversely affecting the control device 30, the load 24, and the like via the ground line GL.

  By the way, since the forward current flows in the diode RD1 by turning on the high potential side switching element Sw1 and the low potential side switching element Sw4, the low potential side switching element Sw2 and the high potential side switching element Sw3 are changed. When switching to a state in which a forward current flows through the diode RD2 by being turned on, a high-frequency current due to the reverse recovery phenomenon of the diode RD1 may flow. Similarly, the high potential side switching element Sw1 and the low potential side switching element are changed from the state in which the forward current flows through the diode RD2 because the low potential side switching element Sw2 and the high potential side switching element Sw3 are turned on. There is a possibility that a high-frequency current due to the reverse recovery phenomenon of the diode RD2 may flow even when switching to a state where the forward current flows in the diode RD1 by turning on the Sw4. In this case, the electric load connected to the ground line GL may be adversely affected.

  Therefore, in the present embodiment, a series connection body of a pair of capacitors 50 and 52 is provided between the cathode of the diode RD1 and the node N1, and between the cathode of the diode RD2 and the node N1, and these connection points (node N2). Is connected to the midpoint tap mt of the secondary side coil 20b of the transformer 20. Here, the capacitor 50 and the capacitor 52 have the same specifications (the same capacity, the same dimensions, etc., particularly the same impedance). Thereby, the flow path of the high-frequency current resulting from the reverse recovery phenomenon can be made into a short loop, so that the outflow to the ground line GL can be avoided. Hereinafter, since the forward current flows in the diode RD1 by turning on the high potential side switching element Sw1 and the low potential side switching element Sw4, the low potential side switching element Sw2 and the high potential side switching are switched. An example in which the element Sw3 is turned on to switch to a state in which a forward current flows in the diode RD2 will be described with reference to FIG.

  FIG. 2 is an equivalent circuit diagram of a portion including the diodes RD1 and RD2 and the secondary coil 20b immediately after the reverse recovery period and the reverse recovery period. In FIG. 2, parasitic capacitors cp1 and cp2 of the diodes RD1 and RD2 are shown. Specifically, FIG. 2A shows a current flow path due to the reverse recovery phenomenon of the diode RD1 due to the switching by a one-dot chain line. As illustrated, a reverse current flows through the diode RD1 by the closed loop circuit including the secondary coil 20b, the diode RD2, and the diode RD1. Thereafter, as shown in FIG. 2B, when the reverse recovery phenomenon ends, the diode RD1 stops flowing current. However, due to the parasitic inductance pL of the wiring between the diode RD1 and the secondary coil 20b and the LC resonance phenomenon between the parasitic capacitor cp1 of the diode RD1, as shown by the dotted line in the figure, the midpoint tap of the secondary coil 20b. A high-frequency current flows from mt to the loop circuit returning to the midpoint tap mt via the diode RD1 (parasitic capacitor cp1) and the capacitor 50. As described above, in the present embodiment, it is possible to avoid the high-frequency current flowing through the ground line GL by flowing the high-frequency current generated at the end of the reverse recovery period through the loop circuit.

  On the other hand, the case where the capacitors 50 and 52 are not provided is shown in FIG. Incidentally, FIG. 3 (a) and FIG. 3 (b) correspond to the previous FIG. 2 (a) and FIG. 2 (b). In this case, immediately after the end of the reverse recovery period, as shown by the dotted line in the figure, the high-frequency current due to the resonance phenomenon causes the midpoint tap mt, the ground line GL, and the diode RD1 (parasitic capacitor RD1) of the secondary coil 20b. flows into a closed loop circuit comprising cp1). Here, in the figure, for convenience, an electrical load is not connected between the connection point of the midpoint tap mt and the ground line GL and the connection point of the capacitor 22b and the ground line GL. An electric load may be connected between them. In this case, the common mode current flows through the electric load, which may adversely affect the electric load.

  As described above, in this embodiment, the midpoint tap mt of the secondary coil 20b is connected to the node N2 between the capacitors 50 and 52. This is a setting for making the impedance of the loop circuit including the midpoint tap mt, the diode RD1 and the capacitor 50 equal to the impedance of the loop circuit including the midpoint tap mt, the diode RD2 and the capacitor 52. This presupposes that the electrical path of the diode RD1 and the capacitor 50 and the electrical path of the diode RD2 and the capacitor 52 have geometric symmetry. That is, in this case, since the impedance of the pair of electric paths is considered to be equal, the impedance of the pair of loop circuits is equalized by connecting the node N2 between the capacitors 50 and 52 and the midpoint tap mt. Can do. Thus, by making the impedances of the pair of loop circuits equal, it is possible to avoid mode conversion in which common mode noise is converted into normal mode noise or normal mode noise is converted into common mode noise.

  The geometric symmetry is that the distance between the secondary coil 20b and the diode RD1 and the distance between the secondary coil 20b and the diode RD2 are set equal to each other, and the distance between the diode RD1 and the capacitor 50 is set. And the distance between the diode RD2 and the capacitor 52 is set equal. By the way, the wiring that connects them uses the same specification (same impedance).

  Incidentally, the fact that the high-frequency current flows in the electric circuit shown by the dotted line in FIG. 3 and the high-frequency current flows in the loop circuit shown by the dotted line in FIG. 2 is shown by the dotted line in FIG. This is because the impedance of the loop circuit indicated by the dotted line in FIG. 2 is smaller than that of the electrical path. This is realized because of the short loop. That is, since the electrical resistance of the wiring is proportional to the wiring length, the impedance is reduced by a short loop compared to the path passing through the ground line GL.

  The reason why the midpoint tap mt of the secondary coil 20b is connected to the ground line GL via the capacitor 21 is to prevent the potential of the midpoint tap mt from fluctuating due to potential fluctuation of the ground line GL. belongs to. That is, when a current flows through the ground line GL, the potential of the ground line GL varies depending on the location. When the ground line GL and the midpoint tap mt are connected without passing through the capacitor 21, the influence of the change in potential at the connection point of the ground line GL with the midpoint tap mt is the midpoint tap. It occurs directly at mt. On the other hand, when the connection is made via the capacitor 50, it is possible to avoid the influence of the low frequency fluctuation such as the fluctuation of the current flowing through the ground line GL from occurring in the midpoint tap mt.

  According to the embodiment described above, the following effects can be obtained.

  (1) A pair of capacitors 50, 52 connected in series between the respective cathode sides of the pair of diodes RD1, RD2 is provided, and a node N2 between the capacitors 50, 52 is connected to the secondary coil 20b. As a result, the noise distribution path caused by the resonance phenomenon at the end of the reverse recovery phenomenon of the diodes RD1 and RD2 can be formed into a short loop, so that the noise due to the reverse recovery phenomenon is superimposed on the ground line GL. It can suppress suitably.

  (2) The connection point of the pair of capacitors 50 and 52 is connected to the midpoint tap mt of the secondary coil 20b. This facilitates the setting of equal impedance between the loop circuit including the midpoint tap mt, the diode RD1, and the capacitor 50 and the loop circuit including the midpoint tap mt, the diode RD2, and the capacitor 52. For this reason, the structure which avoids mode conversion becomes easy.

  (3) The secondary coil 20b is connected to the ground line GL. In this case, noise due to the reverse recovery phenomenon may be superimposed on the ground line GL via the secondary coil 20b. For this reason, the utility value of the method of connecting the node N2 between the capacitors 50 and 52 to the midpoint tap mt is particularly high.

  (4) The ground line GL is connected to the midpoint tap mt of the secondary coil 20b. Thereby, as long as the absolute value of the voltage of the both ends of the secondary side coil 20b is the same, the voltage output alternately from each of a pair of diode RD1, RD2 can be made the same.

  (5) A pair of capacitors 50 and 52 are connected between the cathodes of the pair of diodes RD1 and RD2 and the node N1. For this reason, a loop circuit for allowing a high-frequency current to flow due to the reverse recovery phenomenon can be made into a short loop without interposing other members than the wiring between the diodes RD1, RD2 and the capacitors 50, 52. In addition, the impedance of the loop circuit can be suppressed as much as possible.

  (6) The ground line GL was used as a vehicle ground line. In this case, since many in-vehicle electronic devices are connected to the ground line GL, it is considered that when a high-frequency current flows through the ground line GL, these electronic devices are likely to be adversely affected. For this reason, the utility value of the method of connecting the connection point of the capacitors 50 and 52 to the midpoint tap mt is particularly high.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 4 shows a system configuration diagram of the present embodiment. In FIG. 4, members corresponding to those shown in FIG. 1 are given the same reference numerals for convenience.

  As shown in the drawing, in this embodiment, capacitors 54 and 56 are connected in series between the anodes of the diodes RD1 and RD2 and the secondary coil 20b of the transformer 20. A connection point (node N3) between the capacitors 54 and 56 is connected to the secondary coil 20b. As a result, the loop circuit for flowing a high-frequency current caused by the reverse recovery phenomenon of the diodes RD1 and RD2 can be further shortened.

  In the present embodiment, the node N3 between the capacitors 54 and 56 is connected to the midpoint tap mt of the secondary coil 20b, so that the impedance of the loop circuit including the midpoint tap mt and the capacitor 54 and the midpoint tap are increased. The impedance of the loop circuit including mt and the capacitor 56 is set equal. Furthermore, the impedance of the loop circuit including the capacitor 54, the diode RD1, and the capacitor 50 is set equal to the impedance of the loop circuit including the capacitor 56, the diode RD2, and the capacitor 52. This is a setting for avoiding mode conversion.

  In such a setting, the distance between the secondary coil 20b and the capacitor 54 is the same as the distance between the secondary coil 20b and the capacitor 56, and the distance between the capacitor 54 and the anode of the diode RD1 is equal to that of the capacitor 56 and the diode RD2. This is realized by making the distance between the anodes the same. Further, it is realized by setting the capacitors 54 and 56 to the same specification (same capacitance, same dimensions, etc., particularly the same impedance).

  In the present embodiment described above, the following effects can be obtained in addition to the effects according to the respective effects of the first embodiment.

  (7) A series connection body of capacitors 54 and 56 is also connected between the anode side of the diodes RD1 and RD2 and the secondary side coil 20b of the transformer 20. As a result, the noise distribution path caused by the LC resonance phenomenon immediately after the end of the reverse recovery phenomenon can be further shortened.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 5 shows a system configuration diagram of the present embodiment. In FIG. 5, members corresponding to those shown in FIG. 1 are given the same reference numerals for convenience.

  In the present embodiment, a series connection body of capacitors 54 and 56 is provided between the anode of the diode RD1 and the secondary coil 20b and between the anode of the diode RD2 and the secondary coil 20b. A connection point (node N3) between the capacitors 54 and 56 is connected to the secondary coil 20b. As a result, the high-frequency current distribution path resulting from the reverse recovery phenomenon of the diodes RD1 and RD2 is short-looped into a loop circuit including the secondary coil 20b and the capacitor 54 and a loop circuit including the secondary coil 20b and the capacitor 56. can do. Also by this, it is possible to suitably suppress or avoid the high-frequency current caused by the reverse recovery phenomenon from flowing through the ground line GL.

  Here, the inductance component contributing to the LC resonance that causes the high-frequency current flowing in the loop circuit is due to the parasitic inductance between the capacitor 54 and the secondary coil 20b, or between the capacitor 56 and the secondary coil 20b. This is due to parasitic inductance. Therefore, in order to increase the high-frequency current taken into these loop circuits, it is desirable to place the capacitors 54 and 56 as close as possible to the anode sides of the diodes RD1 and RD2. Specifically, for example, the distance between the secondary coil 20b and the capacitor 54 is preferably longer than the distance between the capacitor 54 and the anode of the diode RD1. It is desirable that the distance between the secondary coil 20b and the capacitor 56 be longer than the distance between the capacitor 56 and the anode of the diode RD2.

  In this embodiment as well, by connecting the node N3 between the capacitors 54 and 56 to the midpoint tap mt of the secondary coil 20b, the impedance of the loop circuit including the midpoint tap mt and the capacitor 54, and the midpoint tap The impedance of the loop circuit including mt and the capacitor 56 is set equal. This is a setting for avoiding mode conversion. In this setting, the distance between the secondary coil 20b and the capacitor 54 is the same as the distance between the secondary coil 20b and the capacitor 56, and the capacitors 54 and 56 have the same specifications (same capacitance, same dimensions, etc.). (In particular, the same impedance).

  In the present embodiment described above, in addition to the effects according to the effects (2) to (4) and (6) of the first embodiment, the following effects can be obtained.

  (8) A series connection body of capacitors 54 and 56 was connected between the anode side of the diodes RD1 and RD2 and the secondary side coil 20b of the transformer 20, and these connection points were connected to the secondary side coil 20b. As a result, the high-frequency current flow path caused by the reverse recovery phenomenon of the diodes RD1 and RD2 can be short-circuited as a loop circuit including the secondary coil 20b and the capacitors 54 and 56.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  In the first embodiment, the impedance of the loop circuit including the capacitor 50, the secondary side coil 20b, and the diode RD1 is made equal to that of the loop circuit including the capacitor 52, the secondary side coil 20b, and the diode RD2. Is not limited to a configuration in which these loop circuits are geometrically symmetric. For example, even in a geometrically asymmetric configuration, the impedance of both loop circuits can be made equal by connecting a resistor to one of the loop circuits. Further, for example, when the impedances of the pair of loop circuits other than the secondary side coil 20b are different from each other, the connection point of the capacitors 50 and 52 is shifted from the midpoint tap mt of the secondary side coil 20b. It is also possible to make the impedance of the pair of loop circuits equal by connecting to the positions.

  In the second embodiment, the loop circuit including the capacitors 50 and 54 and the secondary coil 20b and the loop circuit including the capacitors 52 and 56 and the secondary coil 20b have the same impedance. The configuration of the loop circuit is not limited to a geometrically symmetric structure. For example, even in a geometrically asymmetric configuration, the impedance of both loop circuits can be made equal by connecting a resistor to one of the loop circuits.

  In the third embodiment, the impedance of the electrical path including the capacitor 54 and the secondary side coil 20b and the loop circuit including the capacitor 56 and the secondary side coil 20b are equalized. The configuration is not limited to a substantially symmetrical structure. For example, even in a geometrically asymmetric configuration, the impedance of both loop circuits can be made equal by connecting a resistor to one of the loop circuits. Further, for example, when the impedances of portions other than the secondary coil 20b in the pair of loop circuits are different from each other, the connection point of the capacitors 54 and 56 is shifted from the midpoint tap mt of the secondary coil 20b. It is also possible to make the impedances of the pair of loop circuits equal by connecting to each other.

  In each of the above embodiments, the midpoint tap mt of the secondary coil 20b is connected to the ground line GL via the capacitor 21, but the present invention is not limited to this, and the capacitor 21 may be omitted.

  In each of the above embodiments, the midpoint tap mt of the secondary coil 20b is connected to the ground line GL, but the present invention is not limited to this. For example, even when the secondary coil 20b is not connected to the ground line GL, a high-frequency current flows to the high-voltage system side via the parasitic capacitance between the primary coil 20a and the secondary coil 20b of the transformer 20, In view of the possibility of flowing to the ground line via the connection point of the Y capacitor CY2, the application of the present invention is effective.

  The DCDC converter is not limited to a step-down converter, and may be a step-up converter.

  -As a power converter circuit, not only what is mounted in a hybrid vehicle, For example, you may mount in an electric vehicle.

The system configuration figure of a 1st embodiment. The circuit diagram which shows the effect concerning the embodiment. The circuit diagram which shows the distribution | circulation aspect of the high frequency current in the conventional circuit. The system block diagram of 2nd Embodiment. The system block diagram of 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... High voltage battery, 12 ... Low voltage battery, 20 ... Transformer, 24 ... Load, 30 ... Control device, 50, 52, 54, 56 ... Capacitor, CV ... DCDC converter (one embodiment of power conversion circuit), mt ... Medium Point tap, RD1, RD2 ... diode, GL ... ground line.

Claims (8)

A power conversion circuit comprising a transformer and a rectifying means for rectifying the voltage polarity of a pair of terminals of the secondary winding of the transformer when the voltage polarity is inverted, and the secondary winding as the rectifying means A power conversion circuit including a diode connected to each of the pair of terminals and a cathode side of the pair of diodes connected to an output terminal;
A pair of capacitors that are interposed between the secondary winding and the output terminal and connected in series between a pair of electrical paths including each of the pair of diodes;
A power conversion circuit, wherein a connection point of the pair of capacitors is connected to the secondary winding.   The power conversion circuit according to claim 1, wherein the secondary winding has a midpoint tap, and the connection point of the pair of capacitors is connected to the midpoint tap.   The power conversion circuit according to claim 1, wherein the secondary winding is connected to a ground line.   The power conversion circuit according to claim 3, wherein the secondary winding has a midpoint tap, and the ground line is connected to the midpoint tap.   5. The power conversion circuit according to claim 1, wherein the pair of capacitors are connected between a cathode of the pair of diodes and a connection point of the pair of cathodes. 6.   6. The power conversion circuit according to claim 5, wherein the pair of capacitors are further connected between an anode side of the pair of diodes and a secondary winding of the transformer.   6. The power conversion circuit according to claim 1, wherein the pair of capacitors are connected between an anode side of the pair of diodes and a secondary winding of the transformer.   The power conversion circuit according to claim 1, wherein the ground line is a ground line of a vehicle.

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