EP4618115A1

EP4618115A1 - An inductor

Info

Publication number: EP4618115A1
Application number: EP24162729.8A
Authority: EP
Inventors: Mark Pavier; Kapila WARNAKULASURIYA
Original assignee: Infineon Technologies Austria AG
Current assignee: Infineon Technologies Austria AG
Priority date: 2024-03-11
Filing date: 2024-03-11
Publication date: 2025-09-17

Abstract

According to the invention there is provided an inductor comprising a flat wire having a width and a length, the length of the flat wire being wound around a virtual wire axis parallel to the width of the wire to form a coil and a magnetic core arranged at least at the virtual axis of the coil of flat wire. There may further be a power unit comprising a power module having a plane and an inductor as described, the inductor being electrically coupled to the power module and wherein the virtual wire axis is arranged perpendicularly to the plane of the power module.

Description

FIELD OF THE INVENTION

This invention relates to an inductor, in particular an inductor for use in power electronics such as a high current power unit.

BACKGROUND OF THE INVENTION

Electronics consume power which is converted to heat. Overheating of electronic components can result in several drawbacks such as reduced performance and shortened lifespan and in extreme circumstances it could become a safety hazard. Thus, preventing overheating of electronic components is important and a significant design consideration for manufacturers.
The problem of overheating can be particularly acute in power converters in which the voltage may be converted. A particular example of this is in buck converters which are used, for example, to step down a DC voltage to a lower level.
One solution is to include a cooling plate to dissipate the energy from the circuit.

SUMMARY OF THE INVENTION

To improve temperature regulation of electronic components, in particular power modules it is desirable to be able to improve the energy dissipation.
A power conversion module comprises an inductor, a capacitors, diodes and a transistor (usually a MOSFET). When the switch is closed current flows through the inductor, storing energy in its magnetic field. When the switch is opened the inductor resists change in current flow so the magnetic field is reduced and a voltage is induced across the inductor and current flows through the output load. By controlling the switch timing the average voltage at the output can be regulated. Adjusting the duty cycle controls the output voltage.
The arrangement of components may be important. For example, some components may generate a greater amount of heat and other components may conduct heat better. The inventor has identified a need to improve the heat dissipation from power modules and devices.
According to the invention there is provided an inductor comprising:

flat wire having a width and a length, the length of the flat wire being wound around a virtual wire axis parallel to the width of the wire to form a coil; and
a magnetic core arranged at least at the virtual axis of the coil of flat wire.

The magnetic core serves to intensify the magnetic field so that high inductance values can be achieved. The flat wire may be formed of, for example, copper and the magnetic core may be formed of, for example, ferrite. A flat wire is a wire which is substantially wider in a first direction perpendicular to the length of the wire than another direction perpendicular to the length of the wire and perpendicular to the first direction. A coil may have several complete turns or may alternatively only be a portion of a complete turn.
The magnetic core may be overmoulded and such an arrangement provides an easy and inexpensive manufacturing method. As an example, the coil can be manufactured and then the magnetic core simply overmoulded. The magnetic core may be overmoulded or alternatively surrounded using a similar manufacturing method.
The magnetic core may extend to the full width of the flat wire. Alternatively, the width of the flat wire may extend beyond the magnetic core.
The flat wire may form a spiral. The spiral may be formed of a single flat wire and has successive layers, each successive layer having a greater diameter and wherein the magnetic core extends between the layers of the spiral.
The magnetic core may form a magnetic block, the magnetic block extending beyond the coil in at least one direction perpendicular to the virtual wire axis. The magnetic block extends beyond the flat wire in all directions perpendicular to the virtual wire axis. In this way, the magnetic block completely encompasses the coil in all directions perpendicular to the virtual axis.
The coil may have an outer circumference and, along a first length along the virtual axis, the magnetic core fills all the space within the outer circumference of the coil along a cross section taken perpendicularly to the virtual axis. In this way all the space within the coil is filled with ferrite at a particular height. Preferably, the first length is at least half the width of the flat wire.
The flat wire preferably has a width of at least 2mm. The flat wire preferably has a thickness of less than 0.5mm.
The coil may be formed of copper or an alloy of copper. As an example, the coil conductor may be made from a material with conductivity > 150 W/m.K
The inductor may comprise a second inductor, the second inductor comprising:

a second flat wire having a width and a length, the length of the second flat wire being wound around a second virtual wire axis parallel to the wire axis and parallel to the width of the second wire to form a second coil; and
a second magnetic core,
wherein the magnetic core and the second magnetic core are formed in a single magnetic block.
Including two coils within a single block can simplify the manufacturing process.

One of the coils may be wound in a first direction and the other coil may be wound in a second direction, opposite to the first direction. By winding the coils in opposite directions the magnetic flux is at least partially cancelled out.
The flat wire and the second flat wire may be formed of two separate wires or they may be formed of a single flat wire.
According to the invention there is provided a power unit comprising a power module having a plane and an inductor as described above, the inductor being electrically coupled to the power module and wherein the virtual wire axis is arranged perpendicularly to the plane of the power module.
The power unit may further comprise a cooling plate thermally coupled to the flat wire and wherein the power module is arranged on a first side of the flat wire and the cooling plate is arranged on the opposite side of the flat wire. The flat wire is thermally coupled to both the power module and also the cooling plate. The flat wire may have greater thermal conductivity than the magnetic core. For example, the flat wire may be formed of copper or a copper alloy with a thermal conductivity of over 300W/m. K whereas the magnetic core material will typically have a thermal conductivity of between 1 and 10W/m. K. Therefore the entire flat wire provides a conduit for heat from the power module to the cooling plate, thus effectively cooling the power module.
The power module may be, for example, a half bridge and the power unit as a whole may be a buck converter. The devices within the power module maybe arranged as a single phase in a synchronous buck converter, with each phase consisting of a high side and low side MOSFET device. Several phases maybe connected together to produce a circuit capable of supplying higher currents. Similar circuits may also be formed with transistors manufactured from GaN, SiC and other semiconductors.
The present invention is particularly useful in conjunction with high current applications, for example, applications involving currents in excess of 20A per phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 depicts a power module according to the prior art;
Figure 2a depicts an inductor according to the invention;
Figure 2b depicts just the copper coil without the ferrite block;
Figure 3 depicts an alternative inductor according to the invention;
Figure 4 depicts an alternative inductor according to the invention;;
Figure 5 depicts a circuit diagram representing an arrangement of inductors;
Figure 6 depicts an alternative inductor according to the invention;
Figure 7 depicts an alternative inductor according to the invention;
Figure 8 depicts a power unit according to the invention;
Figure 9 depicts a buck converter; and
Figure 10 depicts a multi-phase buck converter.

It should be noted that these figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings.

DETAILED DESCRIPTION

Power modules are used to step down or step up a DC voltage or convert an AC to DC voltage or a DC voltage to an AC voltage. Such converters usually comprise at least a switch, a capacitor, a resistor and an inductor.
As an example, a buck converter is a DC to DC converter which increases current and decreases voltage. A buck converter comprises transistors, which generate significant heat and it is beneficial to dissipate the heat away from the transistor or power module as a whole.
Power modules will often include a cooling plate. However, the cooling plate is often arranged distal from the power module itself so heat conduction between the power module and cooling plate is less effective.
Figure 1 depicts a power unit comprising a power module 16 and an inductor formed of a coil 11, which may be formed from copper. The power module 16 may comprise elements such as one or more transistors, inductors and a capacitor. In some instances there may be one or more resistors and one or more diodes. The inductor 11 forms part of the power unit as a whole.
Figure 2a depicts an inductor according to the invention, the inductor comprising a flat wire formed into a copper coil 21 and a ferrite block 25 which forms a magnetic core. The invention comprises a conductive coil made from a flat wire. The flat wire has a width w_w and a length l_w and the flat wire is wound, along its length, around a virtual axis (not depicted) to form a coil, as depicted in Figure 2b. The virtual axis is parallel to the width w_w of the flat wire. The flat wire may have a width of at least 2mm and a thickness of less than 0.5mm.
According to the invention, the copper coil is within a ferrite block. Although ferrite is used in this example, any magnetic material may be used. The magnetic block is preferably formed by overmoulding and this provides a simple manufacturing technique as the ferrite material can simply be moulded once the copper coil has been formed.
The ferrite block has a height h_m, a width w_m and a length l_m. In the example of figure 2a, the ferrite block has the same, or substantially the same, height h_m as the width w_w of the flat wire. That is to say that the ferrite block extends to the full height of the copper coil.
The copper coil 21 has an outer circumference and the ferrite block extends at least as far as the outer circumference in directions perpendicular to the virtual axis. That is to say that there are no air spaces within the copper coil.
The use of the magnetic material in the coil make it possible to achieve high inductance values. In one example in an arrangement of figure 2 the ferrite block has dimensions of 3.5mm x 9mm x 5mm and has a copper coil formed from a flat wire of cross sectional diameter 3.5mm x 0.5mm and an inductance of 78nH is achieved at a 100A DC bias.
The coil formed from a flat wire preferably has a high thermal conductivity. As an example, the coil may be formed of copper which has a thermal conductivity of 385W/m.K. In contrast ferrite has a thermal conductivity of less than 10W/m.K. Alternatively, the coil could be formed of aluminium.
In some examples, a single ferrite block 35 may include two or more copper coils. In a preferred embodiment a single ferrite block includes two copper coils. Such an arrangement is depicted in Figure 3 in which there is a single ferrite block comprising a first coil 31 and a second coil 32. The coils each comprise a flat copper wire (as, for example, depicted in figure 2b) and are wound around two parallel virtual axes. The first coil copper coil is wound in a first direction and the second copper coil is wound in a second opposite direction. For example, the first copper coil may be would in an anti-clockwise direction and the second copper coil may be would in a clockwise direction. This means that the flux can be substantially cancelled out.
The ferrite block in figure 3 also does not extend to the full height of the width of the copper coil. Specifically, h_m < w_w. As an example, the height of the ferrite block could be 90% of the width of the coil. The saturation condition of the magnetic core (formed by the ferrite block) can be controlled by adjusting the height of the ferrite block. Consequently, there will be a slightly reduced level of inductance. As an example, for the same size of coils as depicted in figure 2 and the same 100A DC bias the inductance is 74.8nH.
In particular, it is desirable to avoid saturation of the ferrite block. Consequently, the height and overall volume of the ferrite block can be controlled and selected according to the specific technical requirements.
Figure 4 depicts an alternative arrangement in which the ferrite block 45 has a reduced cross sectional area and does not extend beyond the perimeter of the coil 41 in all directions perpendicular to the virtual axis. Due to the reduced ferrite volume this results in a reduced overall footprint area. However, it also results in a reduced inductance: using the variables described above of a 100A DC bias an inductance of 53 nH is achieved.
Figure 4 depicts an arrangement in which the ferrite block extends as far as the outer perimeter of the coils in each of two directions perpendicularly to the virtual axes.
The embodiments depicted in figures 3 and 4 have two coils and these can be used to supply a single load. The inductors can be arranged in parallel to supply a single load and figure 5 depicts a circuit diagram with the inductors in parallel. The inductors may be used simultaneously, or alternatively, using a switching unit. They may, for example, be used for different phases. For example, if the converter is a 2 phase synchronous buck converter, the input terminal of each inductor may be electrically connected to the output of one of the switch nodes of each output phase. In this case each phase output maybe connected to an independent separate inductor input. In this example the output terminal of each inductor may be connected to the same load. Similar approaches may be adopted for three our four converters, in this case three of 4 inductor coils, manufactured in a single or separate ferrite block will be required. By manufacturing the inductors in a single block, which can then be electrically connected to power modules manufacturing is simplified.
Figures 3 and 4 depict two separate coils within a single ferrite block. However, the coils could be formed from a single flat wire 61, as depicted in Figure 6. For simplicity, figure 6 does not depict the ferrite block although a ferrite block would be present.
Figure 7 depicts an arrangement in which the ferrite block 75, or magnetic core is only at the centre of the coil 71. The coil 71 forms a spiral with successive layer of greater diameter. The ferrite block (magnetic core) is only at the centre and does not extend between the successive layers of the coil.
Figure 8 depicts a power unit. There is a power module 86 which is electrically connected to an inductor 85 formed of a ferrite block and a copper coil. The power module may be a voltage regulator such as a half bridge such that the power unit forms a buck converter. The copper coil is arranged with the virtual axis perpendicular to the plane of the power module. On the other end of the inductor is a cooling plate 88 which serves to dissipate heat.
The copper coil within the inductor is electrically connected to the power module. The coil is also thermally coupled to both the power module and the cooling plate such that it forms a thermal conduit between the power module and the cooling plate. In particular, the high thermal conductivity of the copper makes this solution very effective.
The inductor 85 depicted in figure 8 could be any of the inductors depicted in figures 2, 3, 4, 6 or 7 and the ferrite blocks of all of the inductors depicted in figures 2-8 can be formed by overmoulding of the ferrite blocks.
The present invention is particularly useful in high current applications. An example of a buck converter, is depicted in figure 9 with the inductor L to which the present invention may be applied. For higher current requirements multiphase buck converters are used and an example is shown in figure 10. In this example the inductors to which the invention are applied are L1....L6.
The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The embodiments may be implemented by means of hardware comprising several distinct elements. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Furthermore, in the appended claims lists comprising "at least one of: A; B; and C" should be interpreted as (A and/or B) and/or C.

Claims

An inductor comprising:
a flat wire having a width and a length, the length of the flat wire being wound around a virtual wire axis parallel to the width of the wire to form a coil; and

a magnetic core arranged at least at the virtual axis of the coil of flat wire.
The inductor according to any one of the preceding claims wherein the magnetic core is overmoulded.
The inductor according to any one of the preceding claims wherein the magnetic core extends to the full width of the flat wire.
The inductor according to any one of claims 1 to 2 wherein the width of the flat wire extends beyond the magnetic core.
The inductor according to any one of the preceding claims wherein the coil forms a spiral.
The inductor according to claim 5 wherein the spiral, formed of a single flat wire has successive layers, each successive layer having a greater diameter, and wherein the magnetic core extends between layers of the spiral.
The inductor according to any one of the preceding claims wherein the magnetic core forms a magnetic block, the magnetic block extending beyond the coil in at least one direction perpendicular to the virtual wire axis.
The inductor according to claim 7 wherein the magnetic block extends beyond the coil in all directions perpendicular to the virtual wire axis.
The inductor according to any one of claims 6 to 8 wherein the coil has an outer circumference and, along a first length along the virtual axis, the magnetic core fills all the space within the outer circumference of the coil along a cross section taken perpendicularly to the virtual axis.
The inductor according to claim 9 wherein the first length is at least half the width of the flat wire.
The inductor according to any one of the preceding claims further comprising a second inductor, wherein the second inductor comprises:
a second flat wire having a width and a length, the length of the second flat wire being wound around a second virtual wire axis parallel to the virtual wire axis and parallel to the width of the second wire to form a second coil; and

a second magnetic core,

wherein the first magnetic core and the second magnetic core are formed in a single magnetic block.
The inductor according to claim 11 wherein the coil is wound in a first direction and the second coil is would in a second direction, opposite to the first direction.
The power module according to either claim 11 or claim 12 wherein the flat wire and the second flat wire are formed of a single flat wire.
A power unit comprising a power module having a plane and an inductor according to any one of the preceding claims and electrically coupled to the power module and wherein the virtual wire axis is arranged perpendicularly to the plane of the power module.
The power unit according to claim 14 further comprising a cooling plate thermally coupled to the flat wire and wherein the power module is arranged on a first side of the flat wire and the cooling plate is arranged on the opposite side of the flat wire.