Inductor component and DC/DC converter using the same

Disclosed herein is an inductor component that includes a magnetic core having magnetic thin ribbons laminated in a z-direction, a first coil conductor inserted into first and second through holes penetrating the magnetic core in the z-direction, and a second coil conductor inserted into third and fourth through holes penetrating the magnetic core in the z-direction. Each of the magnetic thin ribbons is divided into a plurality of small pieces by net-shaped cracks. A periphery of each of the first to fourth through holes is surrounded by the plurality of small pieces without being circumferentially divided by a slit having a size larger than the crack.

BACKGROUND

Field

The present disclosure relates to an inductor component and a DC/DC converter using the same and, more particularly, to an inductor component having two coil conductors inserted into through holes formed in a magnetic core and a DC/DC converter using such an inductor component.

Description of Related Art

As an inductor component having two coil conductors inserted into through holes formed in a magnetic core, an inductor component described in JP 2019-212806A is known. In the inductor component described in JP 2019-212806A, a slit is formed in the magnetic core so as to divide the periphery of the through hole in the circumferential direction to thereby reduce the coupling coefficient between the two coil conductors.

However, forming the slit in the magnetic core disadvantageously reduces the value of inductance. It is not easy to accurately control the width of the slit during processing, and the inductance value significantly depends on the slit width, so that the inductance value is apt to vary.

SUMMARY

It is therefore an object of the present disclosure to reduce a decrease and a variation in the inductance value in an inductor component having two coil conductors inserted into through holes formed in a magnetic core. Another object of the present disclosure is to provide a DC/DC converter using such an inductor component.

An inductor component according to the present disclosure includes: a magnetic core having a plurality of magnetic thin ribbons extending in first and second directions perpendicular to each other and laminated in a third direction perpendicular to the first and second directions; a first coil conductor inserted into first and second through holes penetrating the magnetic core in the third direction; and a second coil conductor inserted into third and fourth through holes penetrating the magnetic core in the third direction. The first and second through holes are disposed symmetric with respect to a first center line passing, in the first direction, the center position of the magnetic core in the second direction. The third and fourth through holes are disposed symmetric with respect to the first center line. The first and third through holes are disposed symmetric with respect to a second center line passing, in the second direction, the center position of the magnetic core in the first direction. The second and fourth through holes are disposed symmetric with respect to the second center line. Each of the plurality of magnetic thin ribbons is divided into a plurality of small pieces by net-shaped cracks, and the periphery of each of the first to fourth through holes is surrounded by the plurality of small pieces without being circumferentially divided by a slit having a size larger than the crack.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present disclosure will be explained below in detail with reference to the accompanying drawings.

FIG.1is a schematic perspective view illustrating the outer appearance of an inductor component1according to an embodiment of the present disclosure.FIG.2is a schematic exploded perspective view of the inductor component1.

As illustrated inFIGS.1and2, the inductor component1according to the present embodiment includes a magnetic core2having four through holes31to34, a coil conductor10inserted into the through holes31and32, and a coil conductor20inserted into the through holes33and34. The magnetic core2has a substantially rectangular parallelepiped outer shape. The width of the magnetic core2in the x- and that in the y-directions are Wx and Wy, respectively. The through holes31to34, each of which has a circular xy cross section, are formed to penetrate the magnetic core2in the z-direction. The magnetic core2has a configuration in which a plurality of magnetic thin ribbons extending in the xy direction are laminated in the z-direction with a non-magnetic material such as resin interposed therebetween. The coil conductors10and20are a good conductor such as copper (Cu).

The coil conductor10integrally includes an insertion part11inserted into the through hole31, an insertion part12inserted into the through hole32, and a connection part13positioned on the side of an upper surface2aof the magnetic core2and connecting the insertion parts11and12. Although the xy cross section of each of the insertion parts11and12is preferably a circular shape, it may be, for example, an elliptical shape. Further, although the xz cross section of the connection part13is preferably a substantially rectangular shape, it may be, for example, a rectangular shape. The cross-sectional area of each of the insertion parts11and12and that of the connection part13are preferably the same as each other. Leading ends11aand12aof the insertion parts11and12positioned on the side of a lower surface2bof the magnetic core2protrude from the lower surface2b. One of the protruding leading ends11aand12aserves as an input terminal, and the other thereof as an output terminal.

The coil conductor20integrally includes an insertion part21inserted into the through hole33, an insertion part22inserted into the through hole34, and a connection part23positioned on the side of the upper surface2aof the magnetic core2and connecting the insertion parts21and22. The cross-sectional area of each of the insertion parts21and22and that of the connection part23are preferably the same as each other. Although the xy cross section of each of the insertion parts21and22is preferably a circular shape, it may be, for example, an elliptical shape. Further, although the xz cross section of the connection part23is preferably a substantially rectangular shape, it may be, for example, a rectangular shape. Leading ends21aand22aof the insertion parts21and22positioned on the side of the lower surface2bof the magnetic core2protrude from the lower surface2b. One of the protruding leading ends21aand22aserves as an input terminal, and the other thereof as an output terminal.

As illustrated inFIG.2, the through holes31and32are arranged in the y-direction and located at the same x-direction position. Similarly, the through holes33and34are arranged in the y-direction and located at the same x-direction position. The through holes31and33are arranged in the x-direction and located at the same y-direction position. Similarly, the through holes32and34are arranged in the x-direction and located at the same y-direction position.

When a center line XO passing the y-direction center position of the magnetic core2in the x-direction is assumed, the through holes31and32are disposed symmetric with respect to the center line XO, and the through holes33and34are disposed symmetric with respect to the center line XO. Further, when a center line YO passing the x-direction center position of the magnetic core2in the y-direction is assumed, the through holes31and33are disposed symmetric with respect to the center line YO, and the through holes32and34are disposed symmetric with respect to the center line YO. This makes coil conductors10and20substantially completely match each other in characteristics. The distance between the center of the through hole31and the center of the through hole32in the y-direction and that between the center of the through hole33and the center of the through hole34in the y-direction are each defined as a, and the distance between the center of the through hole31and the center of the through hole33in the x-direction and that between the center of the through hole32and the center of the through hole34in the x-direction are each defined as b.

FIG.3is a view for explaining the structure of a magnetic thin ribbon M constituting the magnetic core2.

The magnetic thin ribbon M constituting the magnetic core2is made of a high permeability metal material such as an amorphous alloy or a nanocrystalline alloy and divided into a plurality of small pieces P by net-shaped cracks CL, as illustrated inFIG.3. The cracks CL reduce the permeability of the magnetic thin ribbon M in the xy plane direction to prevent magnetic saturation of the inductor component1. When the inductor component1is used for a DC/DC converter, the average interval between the cracks CL is preferably set to 15 μm or more and 1 mm or less, whereby the permeability of the magnetic thin ribbon M can be adjusted to an optimum value.

FIG.4is a schematic view for explaining a manufacturing method for the magnetic core2.

In manufacturing the magnetic core2, first a plurality of (e.g., four) magnetic thin ribbons M are laminated with a non-magnetic material R such as resin interposed therebetween, followed by pressing for integration, whereby a magnetic sheet3A is obtained. The thickness of the magnetic thin ribbon M is, e.g., about 20 μm, and the permeability thereof is, e.g., about 20000. Then, the magnetic sheet3A is pressed with a roller6to form the cracks CL in the magnetic thin ribbons M constituting the magnetic sheet3A. The average interval between the cracks CL and the size of the small pieces P obtained by the cracks CL can be adjusted by the diameter, pressing force, and pressing speed of the roller6. As a result, a magnetic sheet3B in which the magnetic thin ribbons M have been divided into small pieces by the cracks CL is obtained. Dividing the magnetic thin ribbon M into small pieces by the cracks CL reduces the permeability of the magnetic thin ribbon M to about 100 to 200, which is a value optimally applied to use for a DC/DC converter.

Then, a cutter7is used to cut the magnetic sheet3B into the same planar size as that of the magnetic core2to obtain a plurality of unit magnetic cores3, followed by lamination of the plurality of unit magnetic cores3with a non-magnetic material4such as resin interposed therebetween, and pressing, whereby a block-shaped magnetic core2A is obtained. The upper and lower surfaces of the magnetic core2A may be covered with a cover film5made of, e.g., PET resin. After that, the through holes31to34are formed in the magnetic core2A through drilling, whereby the magnetic core2illustrated inFIGS.1and2is completed. Finally, the coil conductors10and20are inserted into the through holes31to34. Thus, the inductor component1according to the present embodiment is completed.

As described above, the magnetic core2can be manufactured by laminating the magnetic thin ribbons M which have been divided into small pieces by the cracks CL and then forming the through holes31to34. That is, the block-shaped magnetic core2A is machined only for formation of the through holes31to34and need not be machined for formation of the slit for dividing a magnetic path. Thus, the periphery of each of the through holes31to34is entirely surrounded by the plurality of small pieces P without being circumferentially divided by the slit having a size larger than the crack CL, thereby preventing a decrease and a variation in the value of inductance due to the presence of the slit. Further, the non-magnetic material R or 4 is interposed between the magnetic thin ribbons M adjacent in the z-direction, so that there occurs almost no magnetic flux that flows in the z-direction. That is, there occurs little eddy current due to z-direction magnetic flux.

The inductance value of the coil conductors10and20and coupling coefficient between the coil conductors10and20depend on the planar size of the magnetic core2and positions of the through holes31to34. It is generally believed that the coupling coefficient between the coil conductors10and20is preferably near zero; however, as will be described later, when the inductor component1is used as an inductor for a DC/DC converter, a variation in output voltage decreases in the presence of a certain level of coupling coefficient. Specifically, the coupling coefficient between the coil conductors10and20is preferably set to 0.03 to 0.2 and, more preferably, to 0.05 to 0.1.

FIG.5is a simulation result indicating the relation between the width Wy of the magnetic core2, a pitch b between the through holes31to34, and a coupling coefficient k. In the simulation, the positions of the through holes31to34are changed with the widths Wx and Wy of the magnetic core2set to 6 mm, the thickness of the magnetic core2in the z-direction to 2.8 mm, the diameter of the through holes31to34to 0.7 mm, and the diameter of the insertion parts11,12,21, and22to 0.6 mm. As illustrated inFIG.5, the coupling coefficient k between the coil conductors10and20decreases as the value of b/Wy increases. The value of b/Wy at which the coupling coefficient k is in the range of 0.03 to 0.2 is 26% to 65%, and the value of b/Wy at which the coupling coefficient k is in the range of 0.05 to 0.1 is 40% to 55%.

FIG.6is a simulation result indicating the relation between a width W, which is larger one of the widths Wx and Wy of the magnetic core2and an inductance value L. In the simulation, as a basic setting, the widths Wx and Wy of the magnetic core2is set to 6 mm, the thickness of the magnetic core2in the z-direction is set to 2.8 mm, the diameter of the through holes31to34is set to 0.7 mm, and the diameter of the insertion parts11,12,21, and22is set to 0.6 mm, and the values of Wx and Wy are changed while the sum or product of Wx and Wy is kept constant, or the positions of the through holes31to34are changed. As illustrated inFIG.6, the inductance value L reaches a peak value when the value of a/W is 50% and becomes 280 nH when the value of a/W is in the range of 35% to 70%.

FIG.7is a circuit diagram of a DC/DC converter41as a first example using the inductor component1.

The DC/DC converter41illustrated inFIG.7has a pair of input terminals51and52, a pair of output terminals53and54, a switching transistor SW1and an inductor L1connected in series in this order between the input terminal51and the output terminal53, a switching transistor SW2and an inductor L2connected in series in this order between the input terminal51and the output terminal53, and a capacitor C1connected between the output terminals53and54. A circuit composed of the switching transistor SW1and the inductor L1and a circuit composed of the switching transistor SW2and inductor L2are connected in parallel between the input terminal51and the output terminal53. The input terminal52and output terminal54constitute a ground line. A diode D1is connected in a backward direction between the connection point between the switching transistor SW1and the inductor L1and the ground line, and a diode D2is connected in a backward direction between the connection point between the switching transistor SW2and the inductor L2and the ground line.

The switching transistors SW1and SW2are alternately turned ON and OFF by a not-shown control circuit to generate an output voltage Vout which is obtained by lowering an input voltage Vin. The switching transistors SW1and SW2can be controlled such that the output voltage Vout is 20% or less of the input voltage Vin.

The inductor component1according to the present embodiment is used in the thus configured DC/DC converter41as the inductors L1and L2. For example, the coil conductor10constitutes the inductor L1, and the coil conductor20constitutes the inductor L2. This allows a reduction in the number of components constituting the DC/DC converter41.

FIG.8is a graph illustrating the relation between parameters in the DC/DC converter41, specifically, the coupling coefficient k between the coil conductors10and20, a variation in the output voltage Vout, and ripple current flowing in the inductors L1and L2. Here, the output voltage Vout is set to 0.6 V, and the duty of the switching transistors SW1and SW2is set to 0.05. The variation in the output voltage Vout is a peak-to-peak value (mV). The value of the ripple current is an average value (Ap-p) between ripple current Δi (L1) flowing in the inductor L1and ripple current Δi (L2) flowing in the inductor L2.

The graph ofFIG.8reveals that the ripple current flowing in the inductors L1and L2becomes minimum when the coupling coefficient k is zero. However, the variation in the output voltage Vout decreases more when the coupling coefficient k increases in the positive direction than when the coupling coefficient k is zero. The ripple current increases when the coupling coefficient k increases in the positive direction, and an increase in the ripple current is sufficiently small when the coupling coefficient k is 0.2 or less and is substantially ignorable when the coupling coefficient k is 0.1 or less. On the other hand, in order to sufficiently reduce the variation in the output voltage Vout, the coupling coefficient k is preferably 0.03 or more and, more preferably, 0.05 or more.

Thus, when the inductor component1according to the present embodiment is used for the DC/DC converter41illustrated inFIG.7, it is necessary for the coil conductors10and20to have the same polarity. For example, the leading ends11aand21aof the insertion parts11and21are used as input terminals, and the leading ends12aand22aof the insertion parts12and22are used as output terminals.

FIG.9is a circuit diagram of a DC/DC converter42as a second example using the inductor component1.

The DC/DC converter42illustrated inFIG.9has a pair of input terminals51and52, a pair of output terminals53and54, a switching transistor SW1connected between the input terminal51and an intermediate terminal55, a capacitor C2and an inductor L1connected in series in this order between the intermediate terminal55and the output terminal53, a switching transistor SW2and an inductor L2connected in series in this order between the intermediate terminal55and the output terminal53, and a capacitor C1connected between the output terminals53and54. A circuit composed of the capacitor C2and inductor L1and a circuit composed of the switching transistor SW2and inductor L2are connected in parallel between the intermediate terminal55and the output terminal53. The input terminal52and output terminal54constitute a ground line. A diode D1is connected in a backward direction between the connection point between the capacitor C2and the inductor L1and the ground line, and a diode D2is connected in a backward direction between the connection point between the switching transistor SW2and the inductor L2and the ground line.

The switching transistors SW1and SW2are alternately turned ON and OFF by a not-shown control circuit to generate an output voltage Vout which is obtained by lowering an input voltage Vin. The switching transistors SW1and SW2can be controlled such that the output voltage Vout is 20% or less of the input voltage Vin.

The inductor component1according to the present embodiment is used in the thus configured DC/DC converter42as the inductors L1and L2. For example, the coil conductor10constitutes the inductor L1, and the coil conductor20constitutes the inductor L2. This allows a reduction in the number of components constituting the DC/DC converter42.

FIG.10is a graph illustrating the relation between parameters in the DC/DC converter42, specifically, the coupling coefficient k between the coil conductors10and20, a variation in the output voltage Vout, and ripple current flowing in the inductors L1and L2. Here, the output voltage Vout is set to 0.6 V, and the duty of the switching transistors SW1and SW2is set to 0.1. The variation in the output voltage Vout is a peak-to-peak value (mV). The value of the ripple current is an average value (Ap-p) between ripple current Δi (L1) flowing in the inductor L1and ripple current Δi (L2) flowing in the inductor L2.

The graph ofFIG.10reveals that the ripple current flowing in the inductors L1and L2becomes minimum when the coupling coefficient k is zero. However, the variation in the output voltage Vout decreases more when the coupling coefficient k increases in the positive direction than when the coupling coefficient k is zero. The ripple current increases when the coupling coefficient k increases in the positive direction, and an increase in the ripple current is sufficiently small when the coupling coefficient k is 0.2 or less and is substantially ignorable when the coupling coefficient k is 0.1 or less. On the other hand, in order to sufficiently reduce the variation in the output voltage Vout, the coupling coefficient k is preferably 0.03 or more and, more preferably, 0.05 or more.

Thus, when the inductor component1according to the present embodiment is used for the DC/DC converter42illustrated inFIG.9, it is necessary for the coil conductors10and20to have the same polarity. For example, the leading ends11aand21aof the insertion parts11and21are used as input terminals, and the leading ends12aand22aof the insertion parts12and22are used as output terminals.

As described above, an inductor component according to the present disclosure includes: a magnetic core having a plurality of magnetic thin ribbons extending in first and second directions perpendicular to each other and laminated in a third direction perpendicular to the first and second directions; a first coil conductor inserted into first and second through holes penetrating the magnetic core in the third direction; and a second coil conductor inserted into third and fourth through holes penetrating the magnetic core in the third direction. The first and second through holes are disposed symmetric with respect to a first center line passing, in the first direction, the center position of the magnetic core in the second direction. The third and fourth through holes are disposed symmetric with respect to the first center line. The first and third through holes are disposed symmetric with respect to a second center line passing, in the second direction, the center position of the magnetic core in the first direction. The second and fourth through holes are disposed symmetric with respect to the second center line. Each of the plurality of magnetic thin ribbons is divided into a plurality of small pieces by net-shaped cracks, and the periphery of each of the first to fourth through holes is surrounded by the plurality of small pieces without being circumferentially divided by a slit having a size larger than the crack.

According to the present disclosure, the magnetic core is formed by the magnetic thin ribbons each having the net-shaped cracks, eliminating the need to form a slit at the periphery of the through hole. This can reduce a decrease and a variation in the value of inductance due to the presence of the slit.

In the present disclosure, when the distance between the centers of the first and third through holes in the first direction is assumed to be b, and the width of the magnetic core in the second direction is assumed to be Wy, the value of b/Wy may be the range of 26% to 65%. Thus, when the first and second coil conductors have the same polarity, the coupling coefficient therebetween can be controlled in the range of 0.03 to 0.2. Further, the value of b/Wy may be in the range of 40% to 55%. Thus, when the first and second coil conductors have the same polarity, the coupling coefficient therebetween can be controlled in the range of 0.05 to 0.1.

In the present disclosure, when the distance between the centers of the first and second through holes in the second direction is assumed to be a, and the larger one of the width of the magnetic core in the first direction and that in the second direction is assumed to be W, the value of a/W may be in the range of 35% to 70%. This can maximize an inductance value to be obtained.

In the present disclosure, the magnetic thin ribbon may be made of an amorphous alloy or a nanocrystalline alloy. This can further increase the inductance value.

In the present disclosure, the average interval between the cracks may be in the range of 15 μm to 1 mm. This can prevent magnetic saturation while achieving a high inductance value.

A DC/DC converter according to an embodiment of the present disclosure has first and second circuits connected in parallel between an input terminal and an output terminal. The first circuit includes a first switching transistor and a first inductor which are connected in series. The second circuit includes a second switching transistor and a second inductor which are connected in series. The first and second inductors are constituted respectively by the first and second coil conductors of the above inductor component.

A DC/DC converter according to another embodiment of the present disclosure has a first switching transistor connected between an input terminal and an intermediate terminal and first and second circuits connected in parallel between the intermediate terminal and an output terminal. The first circuit includes a capacitor and a first inductor which are connected in series. The second circuit includes a second switching transistor and a second inductor which are connected in series. The first and second inductors are constituted respectively by the first and second coil conductors of the above inductor component.

According to the present disclosure, the two inductors used for the DC/DC converter can be achieved by one inductor component.

In the present disclosure, the first and second inductors may have the same polarity. This can reduce a variation in output voltage while reducing ripple current flowing in the first and second inductors.

In the present disclosure, the first and second switching transistors may be controlled such that an output voltage appearing at the output terminal is 20% or less of an input voltage supplied to the input terminal. This achieves a large step-down ratio.

As described above, according to the present disclosure, it is possible to reduce a decrease and a variation in the inductance value in an inductor component having two coil conductors inserted into through holes formed in a magnetic core. Further, according to the present disclosure, there can be provided a DC/DC converter using such an inductor component.