JP2011050160A - Isolated dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce noise in an isolated dc-dc converter in which an element for rectification is mounted over a substrate and the secondary winding of a transformer is connected to the substrate through a bus bar. <P>SOLUTION: In the transformer 30, a first connecting terminal 36 for one end of the secondary winding, a second connecting terminal 37 for the other end, and a third connecting terminal 38 for an intermediate tap are arranged at a certain height H1 from the bottom of an enclosure 35. These connecting terminals are so arranged that the connecting terminal 38 is sandwiched between the connecting terminal 36 and the connecting terminal 37 in the horizontal direction. A choke coil 40 is placed over a substrate 70 and a connecting terminal 42 extended toward the connecting terminal 38 from the enclosure 35 of the transformer 30 is connected with the connecting terminal 38. A conductive layer 73 for drain of the substrate 70 is extended in the direction of protrusion of the first connecting terminal 36 from the enclosure 35 of the transformer 30 as viewed in a plane. A conductive layer 74 for drain is extended in the direction of protrusion of the second connecting terminal 37 from the enclosure 35 of the transformer 30 as viewed in a plane. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an insulation type DC-DC converter.

  The DC-DC converter performs switching using a switching element such as a MOSFET to obtain a DC voltage. Switching noise and its harmonic components are generated at the time of switching, which causes the AM band (510 to 1710 kHz) radio noise level to deteriorate. In order not to adversely affect external equipment, it is necessary to reduce the radio noise level.

  In Patent Document 1, the wiring pattern in the secondary circuit, in particular, the secondary current is cut off by arranging the semiconductor rectifier element and the flywheel semiconductor element on the secondary side between two sets of transformers using printed coils. Accordingly, the flowing loop is shortened, and the parasitic inductance is reduced to reduce the switching loss and radiation noise of the switching semiconductor element.

JP 2007-274759 A

  When the synchronous rectification MOSFET is mounted on the substrate and the transformer is provided separately from the substrate, the synchronous rectification MOSFET 111 or the synchronous rectification MOSFET 112 is provided on the secondary side of the DC-DC converter 100 as shown in FIG. Current flows from the transformer T when is turned on, and does not flow when turned off. When this is repeated at a high frequency of several hundred kHz, the switching frequency (several hundred kHz) and its harmonic current are conducted to the output side. Further, when the loops R1 and R2 are formed by a path through which a current flows, a magnetic field is generated, which causes radiation noise and coupling. All of these cause the noise level to deteriorate, and particularly in the AM band (510 to 1710 kHz), the noise level deterioration has a bad influence on the radio when mounted on the vehicle. For this reason, it is necessary to reduce the noise level, and not only the addition of a filter circuit (smoothing filter F1) on the output side, but also a measure to reduce the noise itself in the converter is essential.

  The present invention has been made under such a background, and an object of the present invention is to provide an isolated DC in which a rectifying element is mounted on a substrate and a secondary winding of a transformer is connected to the substrate via a bus bar. -To reduce noise in a DC converter.

  According to the first aspect of the present invention, the secondary winding has an intermediate tap, and the first connection terminal for one end of the secondary winding and the second for the other end at a certain height from the bottom surface of the housing. A transformer arranged with a third connection terminal sandwiched between the first connection terminal and the second connection terminal in the horizontal direction, and the third connection terminal for the intermediate tap in the horizontal direction; Disposed separately from the transformer and below the first, second, and third connection terminals of the transformer, and electrically connected to the first connection terminal of the transformer via a first bus bar. The first conductive layer to be patterned, the second conductive layer electrically connected to the second connection terminal of the transformer via the second bus bar, and the third conductive layer having the ground potential are patterned. Electrically connecting the formed substrate and the first conductive layer and the third conductive layer of the substrate. A first rectifying element mounted on the substrate; a second rectifying element mounted on the substrate so as to electrically connect the second conductive layer and the third conductive layer of the substrate; A choke coil disposed above the substrate and extending in a plan view from the transformer housing toward the third connection terminal and electrically connected to the third connection terminal of the transformer; In the insulated DC-DC converter, the first conductive layer in the substrate extends in the protruding direction of the first connection terminal from the casing of the transformer in plan view, and the substrate The second conductive layer is extended in the protruding direction of the second connection terminal from the casing of the transformer in plan view.

  According to the first aspect of the present invention, the choke coil is disposed above the substrate, and the connection terminal extending toward the third connection terminal from the transformer casing in plan view is the third connection terminal of the transformer. Electrically connected. The substrate and the transformer are separate from each other, and the substrate is patterned in the first conductive layer, the second conductive layer, and the third conductive layer that becomes the ground potential, and the first conductive layer is the first of the transformer. And the second conductive layer is electrically connected to the second connection terminal of the transformer via the second bus bar.

  Here, since the first conductive layer on the substrate is extended in the projecting direction of the first connection terminal from the casing of the transformer in plan view, the first connection terminal of the transformer, the first bus bar, The wiring by the first conductive layer of the substrate and the wiring by the third connection terminal of the transformer and the connection terminal of the choke coil can be brought close to each other, and magnetic fluxes generated when current flows in the opposite directions are connected to each other. The radiation noise can be reduced by acting so as to weaken each other.

  Similarly, since the second conductive layer on the substrate extends in the protruding direction of the second connection terminal from the casing of the transformer in plan view, the second connection terminal of the transformer, the second bus bar, The wiring by the second conductive layer of the substrate and the wiring by the third connection terminal of the transformer and the connection terminal of the choke coil can be brought close to each other, and magnetic fluxes generated when current flows in the opposite directions are connected to each other. The radiation noise can be reduced by acting so as to weaken each other.

  In the second aspect of the present invention, the secondary winding has an intermediate tap, and the first connection terminal for one end of the secondary winding and the second for the other end at a certain height from the bottom surface of the housing. A transformer arranged with a third connection terminal sandwiched between the first connection terminal and the second connection terminal in the horizontal direction, and the third connection terminal for the intermediate tap in the horizontal direction; Disposed separately from the transformer and below the first, second, and third connection terminals of the transformer, and electrically connected to the first connection terminal of the transformer via a first bus bar. The first conductive layer to be patterned, the second conductive layer electrically connected to the second connection terminal of the transformer via the second bus bar, and the third conductive layer having the ground potential are patterned. Electrically connecting the formed substrate and the first conductive layer and the third conductive layer of the substrate. A first rectifying element mounted on the substrate; a second rectifying element mounted on the substrate so as to electrically connect the second conductive layer and the third conductive layer of the substrate; A choke coil disposed above the substrate and extending in a plan view from the transformer housing toward the third connection terminal and electrically connected to the third connection terminal of the transformer; The first conductive layer on the substrate approaches the second conductive layer from the direction in which the first connection terminal protrudes from the transformer housing in plan view. A direction in which the second conductive layer in the substrate approaches the first conductive layer from the protruding direction of the second connection terminal from the housing of the transformer in plan view. Bent and extended To become Te and gist.

  According to the second aspect of the present invention, the choke coil is disposed above the substrate, and the connection terminal extending toward the third connection terminal from the transformer housing in plan view is the third connection terminal of the transformer. Electrically connected. The substrate and the transformer are separate from each other, and the substrate is patterned in the first conductive layer, the second conductive layer, and the third conductive layer that becomes the ground potential, and the first conductive layer is the first of the transformer. And the second conductive layer is electrically connected to the second connection terminal of the transformer via the second bus bar.

  Here, the first conductive layer on the substrate is bent and extended in a direction approaching the second conductive layer from the protruding direction of the first connection terminal from the casing of the transformer in plan view. The first connection terminal, the first bus bar, the wiring by the first conductive layer of the substrate, the third connection terminal of the transformer, and the wiring by the connection terminal of the choke coil can be brought close to each other. Radiation noise can be reduced by acting so that magnetic fluxes generated when current flows in the opposite direction are weakened.

  Similarly, since the second conductive layer on the substrate is bent and extended from the protruding direction of the second connection terminal from the transformer housing in a plan view to a direction approaching the first conductive layer, the transformer The second connection terminal, the second bus bar, the wiring by the second conductive layer of the substrate and the wiring by the third connection terminal of the transformer and the connection terminal of the choke coil can be brought close to each other. Radiation noise can be reduced by acting so that magnetic fluxes generated when current flows in the opposite direction are weakened.

  As described in claim 3, in the isolated DC-DC converter according to claim 1 or 2, the first rectifying element and the second rectifying element include a primary winding of the transformer. It may be a synchronous rectification MOSFET that is turned on / off in synchronization with a change in the direction of the flowing current.

  According to a fourth aspect of the present invention, in the isolated DC-DC converter according to the third aspect, the first synchronous rectification MOSFET and the second rectification element constituting the first rectification element are configured. The second synchronous rectification MOSFET has a drain terminal on the lower surface of the package and a source terminal on the side surface of the package, and the first synchronous rectification MOSFET and the second synchronous rectification MOSFET are formed on the substrate. The source terminals are preferably mounted so as to be on the back side.

  5. The insulation type DC-DC converter according to claim 1, wherein the first rectifying element and the second rectifying element include a primary winding of the transformer. The synchronous rectification IGBT may be turned on / off in synchronization with the change in the direction of the flowing current.

  6. The isolated DC-DC converter according to claim 5, wherein the first synchronous rectification IGBT and the second rectification element constituting the first rectification element are configured. The second synchronous rectification IGBT has a collector terminal on the lower surface of the package and an emitter terminal on the side surface of the package, and the first synchronous rectification IGBT and the second synchronous rectification IGBT are formed on the substrate. The emitter terminals are preferably mounted so that they are on the back side.

  According to the present invention, it is possible to reduce noise in an insulated DC-DC converter in which a rectifying element is mounted on a substrate and a secondary winding of a transformer is connected to the substrate via a bus bar.

The circuit block diagram of the insulation type DC-DC converter in embodiment. (A) is a top view of the insulation type DC-DC converter in 1st Embodiment, (b) is a front view of an insulation type DC-DC converter. The perspective view of the insulation type DC-DC converter in a 1st embodiment. The top view of the board | substrate in 1st Embodiment. (A) is a top view of an insulation type DC-DC converter for comparison, (b) is a front view of an insulation type DC-DC converter. The perspective view of the insulation type DC-DC converter for a comparison. The perspective view of the insulation type DC-DC converter in 2nd Embodiment. The top view of the board | substrate in 2nd Embodiment. The circuit block diagram of an insulation type DC-DC converter.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
As shown in the circuit configuration diagram of FIG. 1, the insulated DC-DC converter 1 includes a bridge circuit 10, a transformer 30, synchronous rectification MOSFETs 21, 22, 23, 24, a choke coil 40, and a capacitor 50.

  The insulated DC-DC converter 1 is mounted on, for example, an automobile and is used in a DC-DC converter that changes the voltage of a high-voltage battery for a traveling motor to a low voltage suitable for the power supply of an auxiliary machine.

  The bridge circuit 10 is composed of a plurality of arms, and converts the DC voltage of the DC power source into an AC voltage by controlling on / off of the switching elements constituting the arms. The switching operation of the switching element is performed at several hundred Hz.

  The transformer 30 has an insulating structure and includes a primary winding 31, a secondary winding 32, and a core 33. The primary winding 31 is connected to the bridge circuit 10. The transformer 30 has an intermediate tap 32 c in the secondary winding 32, and the intermediate tap 32 c is connected to the plus-side output terminal 61 through a smoothing filter including the choke coil 40 and the capacitor 50. Specifically, one end of the choke coil 40 is connected to the intermediate tap 32 c of the secondary winding 32, and the other end of the choke coil 40 is connected to the plus side output terminal 61. One end of the capacitor 50 is connected to the plus side output terminal 61, and the other end of the capacitor 50 is connected to the minus side (ground side) output terminal 62.

  One end 32a of both ends of the secondary winding 32 of the transformer 30 is connected to the minus side output terminal 62 via synchronously rectifying MOSFETs 21 and 22 connected in parallel. Specifically, the drains of the synchronous rectification MOSFETs 21 and 22 are connected to one end 32 a of the secondary winding 32, and the sources of the synchronous rectification MOSFETs 21 and 22 are connected to the negative output terminal 62.

  The other end 32b of the secondary winding 32 of the transformer 30 is connected to the negative output terminal 62 through synchronous rectification MOSFETs 23 and 24 connected in parallel. Specifically, the drains of the synchronous rectification MOSFETs 23 and 24 are connected to the other end 32 b of the secondary winding 32, and the sources of the synchronous rectification MOSFETs 23 and 24 are connected to the negative output terminal 62.

  The gates of the synchronous rectification MOSFETs 21 to 24 are connected to a control device (not shown). Each of the synchronous rectification MOSFETs 21 to 24 is turned on / off by a control command from the control device. At this time, the synchronous rectification MOSFETs 21 and 22 are turned on and off in synchronization. Similarly, the synchronous rectification MOSFETs 23 and 24 are turned on and off in synchronization. Further, the MOSFETs 21 and 22 and the MOSFETs 23 and 24 are complementarily turned on / off in synchronization with the change in the direction of the current flowing through the primary winding 31 of the transformer 30, that is, alternately turned on / off. Yes. The alternating current generated in the secondary winding 32 of the transformer 30 is rectified. Further, the smoothing filter constituted by the choke coil 40 and the capacitor 50 smoothes the alternating current component rectified by the respective synchronous rectification MOSFETs 21 to 24 and outputs it to the plus-side output terminal 61.

Next, the component arrangement of the insulated DC-DC converter 1 will be described.
As shown in FIG. 2B, the insulated DC-DC converter 1 has components housed in a metal case 80. Specifically, the metal case 80 is an aluminum case. Here, FIG. 2 shows chips constituting the transformer 30, the choke coil 40, the substrate 70, the synchronous rectification MOSFETs 21 to 24, and the capacitor 50 of FIG. 1 among the components housed in the metal case 80. Capacitors 51 to 58 are shown. 3 constitutes the connection terminals 36, 37, 38 at the secondary winding 32 of the transformer 30, the choke coil 40, the substrate 70, the synchronous rectification MOSFETs 21 to 24, and the capacitor 50 of FIG. Chip capacitors 51 to 58 are shown. FIG. 4 shows a plan view of the substrate 70.

  The substrate 70 includes a rectangular metal plate 71, an electric insulating layer 72 formed on the upper surface of the metal plate 71, and conductive layers 73, 74, 75, 76, 77 patterned on the electric insulating layer 72. ing. The first conductive layer 73 and the second conductive layer 74 are for drain. The third conductive layer 75 is for a source and has a ground potential. Further, the conductive layer 76 is for connecting a chip capacitor. The conductive layer 77 has a DC output. As shown in FIG. 2B, the thickness H1 of the substrate 70 is, for example, several mm.

  The substrate 70 is disposed on the bottom surface of the metal case 80 inside the metal case 80, and the substrate 70 is fixed to the metal case 80 with screws (not shown). Since the substrate 70 is in contact with the metal case 80, the heat generated by the electronic components (MOSFETs 21 to 24, etc.) mounted on the substrate 70 can be released to the metal case 80 through the substrate 70, and the heat dissipation is excellent. Yes.

  The transformer 30 is fixed to the bottom surface of the metal case 80. The transformer 30 is disposed at a position adjacent to the substrate 70, and the substrate 70 and the transformer 30 are disposed separately. The transformer 30 has a first connection terminal for one end 32a of the secondary winding 32 on one side surface of the casing 35 at a certain height H2 (see FIG. 2B) from the bottom surface of the box-shaped casing 35. 36, a second connection terminal 37 for the other end 32b, and a third connection terminal 38 for the intermediate tap 32c extend in the horizontal direction. Each connection terminal 36, 37, 38 has a strip shape, and is arranged with the third connection terminal 38 sandwiched between the first connection terminal 36 and the second connection terminal 37 in the horizontal direction. (The connection terminal 38 for the intermediate tap 32c is located between the connection terminals 36 and 37). The height H2 of the connection terminals 36, 37, 38 is, for example, several centimeters.

  The first synchronous rectification MOSFETs 21 and 22 constituting the first rectification element and the second synchronous rectification MOSFETs 23 and 24 constituting the second rectification element are formed on the lower surface of the box-shaped resin package 90. It has a drain terminal D, and has a source terminal S and a gate terminal G on the side surface of the package 90. The source terminal S and the gate terminal G are in the shape of a strip and project from the side surface of the package 90 in a juxtaposed manner.

  The synchronous rectification MOSFETs 21 and 22 as the first rectification elements are mounted on the substrate 70 so as to electrically connect the first conductive layer 73 and the third conductive layer 75 of the substrate 70. That is, the synchronous rectification MOSFETs 21 and 22 are mounted on the first conductive layer 73 (for drain) of the substrate 70, and the drain terminal D and the first conductive layer 73 are joined. The source terminals S of the synchronous rectification MOSFETs 21 and 22 are joined to the third conductive layer 75 for the source.

  Similarly, the synchronous rectification MOSFETs 23 and 24 as the second rectification elements are mounted on the substrate 70 so as to electrically connect the second conductive layer 74 and the third conductive layer 75 of the substrate 70. . That is, the synchronous rectification MOSFETs 23 and 24 are mounted on the second conductive layer 74 (for drain) of the substrate 70, and the drain terminal D and the second conductive layer 74 are joined. The source terminals S of the synchronous rectification MOSFETs 23 and 24 are joined to the third conductive layer 75 for the source.

The gate terminals G of the respective synchronous rectification MOSFETs 21 to 24 are electrically connected to the control device via connection members (not shown).
The first synchronous rectification MOSFETs 21 and 22 and the second synchronous rectification MOSFETs 23 and 24 are mounted on the substrate 70 such that the source terminals S are on the back side. That is, the source terminals S are arranged so as to face outward.

  Chip capacitors 51, 52, 53, and 54 are installed between the conductive layer 77 for DC output of the substrate 70 and the conductive layer 76, and the electrodes of the chip capacitors 51 to 54 and the conductive layers 76 and 77 are joined. . Further, chip capacitors 55, 56, 57, and 58 are installed between the conductive layer 76 and the third conductive layer 75 for source, and the electrodes of the chip capacitors 55 to 58 and the conductive layers 75 and 76 are joined. Yes.

  The choke coil 40 is disposed above the substrate 70. The choke coil 40 includes a casing (case) 41 having a box shape, and a strip-like connection terminal 42 extending in a horizontal direction from one of the opposing end faces and the other of the opposing end faces. A strip-like connection terminal 43 extends horizontally from the surface. The connection terminals 42 and 43 extend in the protruding direction C3 (see FIG. 4) of the third connection terminal 38 from the housing 35 of the transformer 30 in plan view. The connection terminals 42 of the choke coil 40 and the connection terminals 38 for the intermediate taps of the secondary winding 32 of the transformer 30 are overlapped with each other and fastened by a bolt B1 penetrating them. The connection terminal 43 of the choke coil 40 is electrically connected to the conductive layer 77 of the substrate 70 through the copper bus bar 102. Specifically, the connection terminal 43 of the choke coil 40 and one end of the bus bar 102 are fastened by a bolt B 2, and the other end of the bus bar 102 is joined to the conductive layer 77.

  Thus, in the choke coil 40, the connection terminal 42 extending in the protruding direction C <b> 3 of the third connection terminal 38 from the housing 35 of the transformer 30 in the plan view is electrically connected to the third connection terminal 38 of the transformer 30. Has been.

  The connection terminal 36 on the one end 32a side of the secondary winding 32 of the transformer 30 is fastened by the first bus bar 100 made of copper and the bolt B3, and the other end side of the first bus bar 100 is bent downwardly, so 1 conductive layer 73. Similarly, the connection terminal 37 on the other end 32b side of the secondary winding 32 of the transformer 30 is fastened to the second bus bar 101 made of copper and the bolt B4, and the other end side of the second bus bar 101 is bent downward. Bonded to the second conductive layer 74 of the substrate 70.

  As described above, the substrate 70 separate from the transformer 30 is disposed below the first, second, and third connection terminals 36, 37, and 38 of the transformer 30, and is connected to the first connection terminal 36 of the transformer 30. A first conductive layer 73 electrically connected via one bus bar 100 and a second conductive layer electrically connected to a second connection terminal 37 of the transformer 30 via a second bus bar 101. 74 and the third conductive layer 75 having the ground potential are patterned.

  Here, as shown in FIG. 4, the first conductive layer 73 on the substrate 70 extends in the protruding direction C <b> 1 of the first connection terminal 36 from the housing 35 of the transformer 30 in plan view, and the substrate 70. The second conductive layer 74 is extended in the protruding direction C2 of the second connection terminal 37 from the housing 35 of the transformer 30 in plan view.

  As described above, in the substrate 70, the first conductive layer 73 and the second conductive layer 74 for draining extend in parallel and linearly. The connection terminal 38 for the intermediate tap and the connection terminal 42 of the choke coil 40 extend between the first conductive layer 73 for drain and the second conductive layer 74. As a result, the magnetic fluxes generated when the current flows act so as to weaken each other. Details will be described later.

Next, the operation of the insulated DC-DC converter 1 will be described.
In FIG. 1, when AC power is supplied to the primary winding 31 of the transformer 30 and a current flows through the primary winding 31 in the direction of arrow A1 in FIG. Flows. At this time, the MOSFETs 23 and 24 are controlled to be on so that the current flowing through the secondary winding 32 is output from the positive output terminal 61 via the intermediate tap 32c and the smoothing filter (choke coil 40, capacitor 50). MOSFETs 21 and 22 are controlled to be in an off state.

  On the other hand, when a current flows through the primary winding 31 of the transformer 30 in the reverse direction of the arrow A1, a current flows through the secondary winding 32 in the reverse direction of the arrow A2. At this time, the MOSFETs 21 and 22 are controlled to be in an ON state so that the current flowing through the secondary winding 32 is output from the positive output terminal 61 via the intermediate tap 32c and the smoothing filter (choke coil 40 and capacitor 50). The MOSFETs 23 and 24 are controlled to be turned off. That is, when alternating current is continuously supplied to the primary winding 31, the current generated in the secondary winding 32 is controlled by alternately turning on and off the MOSFET in synchronization with the change in the direction of the alternating current. The current generated in the secondary winding 32 is output from the plus side output terminal 61 as a direct current.

  In the substrate 70, a first conductive layer 73 for drain and a second conductive layer 74 are arranged side by side in the center, and a third conductive layer 75 for source is formed on both sides of the first conductive layer 73 and the second conductive layer 74. The first and second connection terminals 36 and 37 of the transformer 30 are connected to one end of the two conductive layers 73 and 74 via the bus bars 100 and 101.

  Therefore, the first conductive layer 73 on the substrate 70 extends in the protruding direction C1 of the first connection terminal 36 from the housing 35 of the transformer 30 in a plan view, so the first connection terminal of the transformer 30 36, the wiring by the first bus bar 100 and the first conductive layer 73 of the substrate 70 and the wiring by the third connection terminal 38 of the transformer 30 and the connection terminal 42 of the choke coil 40 can be brought close to each other. Radiation noise can be reduced by acting so that the magnetic fluxes generated when the currents A10 and A11 (see FIG. 2) flow through these wirings in opposite directions are weakened.

  Similarly, since the second conductive layer 74 in the substrate 70 extends in the protruding direction C2 of the second connection terminal 37 from the housing 35 of the transformer 30 in plan view, the second connection of the transformer 30 is performed. The wiring by the terminal 37, the second bus bar 101, and the second conductive layer 74 of the substrate 70 can be brought close to the wiring by the third connection terminal 38 of the transformer 30 and the connection terminal 42 of the choke coil 40. Radiation noise can be reduced by acting so that the magnetic fluxes generated when current flows in the opposite directions are mutually weakened.

5 and 6 show an insulation type DC-DC converter for comparison.
5 and 6, the conductive layer 120 and the conductive layer 121 in the substrate 70 are for the drain, and the conductive layer 122 is for the source (ground). The conductive layer 122 is located in the center of the substrate 70, and the conductive layer 120 and the conductive layer 121 are extended on both sides of the conductive layer 122. The conductive layer 120 and the conductive layer 121 are bent in an “L” shape in plan view. Synchronous rectification MOSFETs 21 and 22 are erected and joined between the conductive layer 120 and the conductive layer 122, and synchronous rectification MOSFETs 23 and 24 are erected and joined between the conductive layer 121 and the conductive layer 122. The connection terminal 36 of the secondary winding 32 of the transformer is electrically connected to one end of the conductive layer 120 by the first bus bar 100. The connection terminal 37 of the secondary winding 32 of the transformer is electrically connected to one end of the conductive layer 121 by the second bus bar 101.

  In this way, the source conductive layer 122 is formed in the center, the drain conductive layers 120 and 121 are extended on both sides thereof, and one end side of the drain conductive layers 120 and 121 is bent to form the transformer 30. It is approaching. The synchronous rectification MOSFETs 21 and 22 and the synchronous rectification MOSFETs 23 and 24 are arranged so that the source terminals S face each other. A loop passing through the bus bars 100 and 101 is formed by the path through which the current flows (see FIG. 1), and when the source (ground) conductive layer 122 is arranged at the center, the area of the inner portion of the loop becomes large.

  On the other hand, in the embodiment shown in FIGS. 2 to 4, the distance between the synchronous rectification MOSFETs 21 to 24 and the secondary winding 32 of the transformer 30 is shortened, and the secondary winding 32 of the transformer 30 and the synchronous rectification are reduced. The area of the inner portion of the loop due to the current path between the MOSFETs 21, 22, 23, and 24 can be reduced. This also reduces the effects of magnetic field radiation and coupling generated by the loop.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The first conductive layer 73 on the substrate 70 extends in the projecting direction C1 of the first connection terminal 36 from the housing 35 of the transformer 30 in plan view, and the second conductive layer 74 on the substrate 70 is planar. As viewed, the second connection terminal 37 extends from the casing 35 of the transformer 30 in the protruding direction C2. Thereby, the noise accompanying switching can be reduced, and therefore the AM band noise level superimposed on the output line can be reduced. Therefore, the AM band conduction radio noise level can be reduced. Moreover, it is only necessary to change the component arrangement, and there is no cost increase.

  (2) The first rectifying element and the second rectifying element are synchronously rectifying MOSFETs 21, 22, 23, 24 that are turned on / off in synchronization with a change in the direction of the current flowing through the primary winding of the transformer 30. Therefore, the voltage drop in the conductive state can be reduced as compared with the case where the diode is used, and the conversion efficiency of the DC-DC converter can be improved.

(3) The first synchronous rectification MOSFETs 21 and 22 constituting the first rectification element and the second synchronous rectification MOSFETs 23 and 24 constituting the second rectification element are connected to the drain terminal D on the lower surface of the package 90. And the source terminal S on the side surface of the package 90, the first synchronous rectification MOSFETs 21 and 22 and the second synchronous rectification MOSFETs 23 and 24 are on the substrate 70, and the source terminals S are on the back side. Has been implemented. Thereby, the area of the inner part of a loop can be made small.
(Second Embodiment)
Next, the second embodiment will be described focusing on the differences from the first embodiment.

FIG. 7 shows a perspective view of an insulation type DC-DC converter in the present embodiment instead of FIG. FIG. 8 shows a plan view of a substrate 70 in the present embodiment that replaces FIG.
As shown in FIGS. 7 and 8, the first conductive layer 83 in the substrate 70 approaches the second conductive layer 84 from the protruding direction C1 of the first connection terminal 36 from the housing 35 of the transformer 30 in plan view. It is bent and extended in the direction. In addition, the second conductive layer 84 on the substrate 70 is bent and extended in a direction approaching the first conductive layer 83 from the protruding direction C2 of the second connection terminal 37 from the housing 35 of the transformer 30 in plan view. Has been.

  Therefore, the first conductive layer 83 on the substrate 70 is bent and extended in a direction approaching the second conductive layer 84 from the protruding direction C1 of the first connection terminal 36 from the housing 35 of the transformer 30 in plan view. Therefore, the first connection terminal 36 of the transformer 30, the first bus bar 100, the wiring by the first conductive layer 83 of the substrate 70, the third connection terminal 38 of the transformer 30, and the connection terminal of the choke coil 40 The wiring by 42 can be made to approach. As a result, radiation noise can be reduced by acting so that magnetic fluxes generated when currents flow in the opposite directions are weakened to each other.

  Similarly, the second conductive layer 84 on the substrate 70 is bent and extended in a direction approaching the first conductive layer 83 from the protruding direction C2 of the second connection terminal 37 from the casing 35 of the transformer 30 in plan view. Since the second connection terminal 37 of the transformer 30, the second bus bar 101, the wiring by the second conductive layer 84 of the substrate 70, the connection of the third connection terminal 38 of the transformer 30 and the choke coil 40 are provided. The wiring by the terminal 42 can be made to approach. As a result, radiation noise can be reduced by acting so that magnetic fluxes generated when currents flow in the opposite directions are weakened to each other.

The embodiment is not limited to the above, and may be embodied as follows, for example.
-Although connection terminals were connected with volt | bolt B1, B2, B3, B4, you may connect by welding instead.

  Although the synchronous rectification MOSFETs 21, 22, 23, and 24 are used, the present invention is not limited to this. For example, an IGBT may be used instead of the MOSFET. That is, the first rectifying element and the second rectifying element are synchronous rectifying IGBTs that are turned on / off in synchronization with a change in the direction of the current flowing through the primary winding 31 of the transformer 30. In addition, the first synchronous rectification IGBT constituting the first rectification element and the second synchronous rectification IGBT constituting the second rectification element have a collector terminal on the lower surface of the package and are provided on the side surface of the package. It has an emitter terminal. The first synchronous rectification IGBT and the second synchronous rectification IGBT are mounted on the substrate 70 such that the emitter terminals are on the back side.

  A diode may be used as the rectifying element instead of the transistor.

  DESCRIPTION OF SYMBOLS 1 ... Isolated DC-DC converter, 21 ... Synchronous rectification MOSFET, 22 ... Synchronous rectification MOSFET, 23 ... Synchronous rectification MOSFET, 24 ... Synchronous rectification MOSFET, 30 ... Transformer, 31 ... Primary winding, 32 ... Secondary winding, 32a ... one end, 32b ... other end, 32c ... intermediate tap, 35 ... housing, 36 ... first connection terminal, 37 ... second connection terminal, 38 ... third connection terminal, 40 ... Choke coil, 42 ... connection terminal, 70 ... substrate, 73 ... first conductive layer, 74 ... second conductive layer, 75 ... third conductive layer, 83 ... first conductive layer, 84 ... second conductive Layer ... 90 ... Package, 100 ... First bus bar, 101 ... Second bus bar, D ... Drain terminal, G ... Gate terminal, S ... Source terminal.

Claims (6)

The secondary winding has an intermediate tap, and at a certain height from the bottom surface of the housing, the first connection terminal for one end of the secondary winding, the second connection terminal for the other end, and the second tap for the intermediate tap A transformer arranged with a third connection terminal sandwiched between the first connection terminal and the second connection terminal in the horizontal direction;
Disposed separately from the transformer and below the first, second, and third connection terminals of the transformer, and electrically connected to the first connection terminal of the transformer via a first bus bar. The first conductive layer to be patterned, the second conductive layer electrically connected to the second connection terminal of the transformer via the second bus bar, and the third conductive layer having the ground potential are patterned. A substrate,
A first rectifying element mounted on the substrate so as to electrically connect the first conductive layer and the third conductive layer of the substrate;
A second rectifying element mounted on the substrate so as to electrically connect the second conductive layer and the third conductive layer of the substrate;
A choke coil disposed above the substrate and extending in a plan view from the transformer housing toward the third connection terminal, the choke coil being electrically connected to the third connection terminal of the transformer;
In an isolated DC-DC converter comprising:
The first conductive layer on the substrate extends in a protruding direction of the first connection terminal from the casing of the transformer in plan view, and the second conductive layer on the substrate is in the plan view An insulated DC-DC converter, wherein the second connecting terminal extends from a transformer casing in a protruding direction. The secondary winding has an intermediate tap, and at a certain height from the bottom surface of the housing, the first connection terminal for one end of the secondary winding, the second connection terminal for the other end, and the second tap for the intermediate tap A transformer arranged with a third connection terminal sandwiched between the first connection terminal and the second connection terminal in the horizontal direction;
Disposed separately from the transformer and below the first, second, and third connection terminals of the transformer, and electrically connected to the first connection terminal of the transformer via a first bus bar. The first conductive layer to be patterned, the second conductive layer electrically connected to the second connection terminal of the transformer via the second bus bar, and the third conductive layer having the ground potential are patterned. A substrate,
A first rectifying element mounted on the substrate so as to electrically connect the first conductive layer and the third conductive layer of the substrate;
A second rectifying element mounted on the substrate so as to electrically connect the second conductive layer and the third conductive layer of the substrate;
A choke coil disposed above the substrate and extending in a plan view from the transformer housing toward the third connection terminal and electrically connected to the third connection terminal of the transformer;
In an isolated DC-DC converter comprising:
The first conductive layer on the substrate is bent and extended in a direction approaching the second conductive layer from the protruding direction of the first connection terminal from the casing of the transformer in plan view, and The second conductive layer on the substrate is extended and bent in a direction approaching the first conductive layer from a protruding direction of the second connection terminal from the casing of the transformer in a plan view. Isolated DC-DC converter.   The first rectifying element and the second rectifying element are synchronous rectifying MOSFETs that are turned on / off in synchronization with a change in direction of a current flowing through the primary winding of the transformer. The insulated DC-DC converter according to claim 1 or 2.   The first synchronous rectification MOSFET constituting the first rectification element and the second synchronous rectification MOSFET constituting the second rectification element have a drain terminal on the lower surface of the package and on the side surface of the package. 4. A source terminal, wherein the first synchronous rectification MOSFET and the second synchronous rectification MOSFET are mounted on the substrate such that the source terminals are on the back side. An insulated DC-DC converter as described in 1.   The first rectifying element and the second rectifying element are synchronous rectifying IGBTs that are turned on / off in synchronization with a change in direction of a current flowing through the primary winding of the transformer. The insulated DC-DC converter according to claim 1 or 2.   The first synchronous rectification IGBT constituting the first rectification element and the second synchronous rectification IGBT constituting the second rectification element have a collector terminal on the lower surface of the package and are provided on the side surface of the package. 6. An emitter terminal is provided, and the first synchronous rectification IGBT and the second synchronous rectification IGBT are mounted on the substrate such that the emitter terminals are on the back side. An insulated DC-DC converter as described in 1.

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