Bridge magnetic devices and associated systems and methods

An electrical assembly includes a substrate, a bridge magnetic device disposed on an outer surface of the substrate, and at least one electrical component. The bridge magnetic device includes (1) a magnetic core disposed over and offset from a first portion of the outer surface of the substrate, (2) N windings wound around at least a portion of the magnetic core and electrically coupled to conductors of the substrate, where N is an integer greater than zero, and (3) a ground return conductor disposed on an outer surface of the magnetic core facing the first portion of the outer surface of the substrate. The at least one electrical component is disposed on the first portion of the outer surface of the substrate.

BACKGROUND

Magnetic devices, such as inductors and transformers, are used in a wide variety of applications. One common application of magnetic devices is in switching power converters. For instance, inductors are frequently used to filter switching power converter waveforms, and transformers are often used to transform voltage levels and/or to provide electrical isolation in switching power converters.

FIG. 1shows one application of an inductor in a switching power converter. Specifically,FIG. 1shows an elevational view of a prior art electrical assembly100including a buck switching power converter102and a load104disposed on a substrate106.FIG. 2shows an electrical schematic of assembly100. Switching power converter102includes input capacitors108, a switching circuit110, an inductor112including a winding114and a magnetic core116, output capacitors118, and a controller120. The outline of winding114is shown by dashed lines inFIG. 1where obscured by magnetic core116. Input capacitors108and switching circuit110are electrically coupled across an input power source122(not shown inFIG. 1). A first end124of winding114is electrically coupled to switching circuit110, and output capacitors118and load104are electrically coupled between second end126of winding114and a common node128.

Controller120controls operation of switching circuit110such that the switching circuit repeatedly switches winding first end124between two different voltage levels, corresponding to a voltage on a positive power node130and a voltage on common node128, to transfer power from input power source122to load104. Input capacitors108supply the bulk of the high frequency components of converter input current132. Thus, input capacitors108are located as close as possible to switching circuit110to minimize impedance between input capacitors108and switching circuit110. Impedance in the connection between capacitors108and switching circuit110causes undesired parasitic ringing, which may result in excessive losses, electromagnetic compatibility issues, and/or converter control difficulties.

Output capacitors118, on the other hand, filter output ripple current resulting from switching inductor112between voltage levels. Additionally, output capacitors118supply the high frequency components of converter output current134to load104. Such role of capacitors118is particularly critical in applications with large changes in output current134magnitude and/or in applications where load104has stringent voltage regulation requirements, such as in applications where load104includes an information technology device processor. Thus, output capacitors118should be located close to both winding second end126and load104, to minimize parasitic ringing and to maximize effectiveness of capacitors118. Minimizing separation distance between winding second end126, output capacitors118, and load104promotes low parasitic impedance in conductors electrically coupling these components, since parasitic impedance is typically proportional to conductor length. Low parasitic impedance, in turn, promotes low conduction loss and also promotes transient performance by minimizing conductor voltage drop during transient load steps. Accordingly, output capacitors118are located between inductor112and load104, so that the capacitors are close to both devices.

SUMMARY

In an embodiment, an electrical assembly includes a substrate, a bridge magnetic device disposed on an outer surface of the substrate, and at least one electrical component. The bridge magnetic device includes (1) a magnetic core disposed over and offset from a first portion of the outer surface of the substrate, (2) N windings wound around at least a portion of the magnetic core and electrically coupled to conductors of the substrate, where N is an integer greater than zero, and (3) a ground return conductor disposed on an outer surface of the magnetic core facing the first portion of the outer surface of the substrate. The at least one electrical component is disposed on the first portion of the outer surface of the substrate.

In an embodiment, an electrical assembly includes a substrate, at least one electrical component disposed on the substrate, and a bridge magnetic device disposed on the substrate. The bridge magnetic device includes a magnetic core and a ground return conductor arranged such that (1) the at least one electrical component is disposed between the substrate and the ground return conductor, and (2) the ground return conductor is disposed between the at least one electrical component and the magnetic core.

In an embodiment, an electrical assembly includes a substrate and a bridge inductor disposed on an outer surface of the substrate. The bridge inductor includes (1) a magnetic core offset from and disposed over a first portion of the outer surface of the substrate, and (2) a winding wound around at least a portion of the magnetic core. The winding has opposing first and second ends electrically coupled to conductors of the substrate. The electrical assembly further includes a switching circuit, a plurality of capacitors, and a load. The switching circuit is operable to repeatedly switch the first end of the winding between at least two different voltage levels. The plurality of capacitors is disposed on the first portion of the outer surface of the substrate, and the plurality of capacitors is electrically coupled to the second end of the winding. The load is disposed on the substrate proximate to the second end of the winding, and the load is electrically coupled to the second end of the winding. The bridge inductor, the switching circuit, and the plurality of capacitors collectively form at least part of a switching power converter operable to at least partially power the load.

In an embodiment, an electrical assembly includes a substrate, a bridge magnetic device disposed on an outer surface of the substrate, and at least one electrical component. The bridge magnetic device includes (1) a magnetic core disposed over a first portion of the outer surface of the substrate, and (2) N windings wound around at least a portion of the magnetic core. N is an integer greater than zero. The N windings form one or more flexible stand-offs offsetting the magnetic core from the first portion of the outer surface of the substrate, and the one or more flexible stand-offs allow the magnetic core to move with respect to the substrate. The at least one electrical component is disposed over the first portion of the outer surface of the substrate.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It has been discovered that bridge magnetic devices, such as bridge inductors or bridge transformers, can be used to promote small size, high efficiency, and/or high performance in an electrical assembly.

For example,FIG. 3shows an elevational view of an electrical assembly300including a buck switching power converter302and a load304disposed on an outer surface306of a substrate308. Substrate308is, for example, a printed circuit board. In some embodiments, load304is a component of an information technology device, such as a computer or a telecommunication device. For example, in certain embodiments, load304includes a processor310with an optional heat sink312disposed thereon, as shown inFIG. 3. However, load304could take other forms without departing from the scope hereof.FIG. 4is an electrical schematic of assembly300.

Switching power converter302includes input capacitors314, a switching circuit316, a bridge inductor318, output capacitors320, and a controller322. In some embodiments, one or more of input and output capacitors314,320are multi-layer ceramic capacitors. Bridge inductor318includes a magnetic core324having opposing sides325,327, and a staple-style winding326wound around at least a portion of core324. The outline of winding326is shown by dashed lines where obscured by core324inFIG. 3. Opposing first and second ends328,330of winding326terminate at core first and second sides325,327, respectively. Winding ends328,330also form respective solder tabs electrically coupled, such as surface mount soldered, to conductors (not shown) on substrate308. In certain alternate embodiments, however, winding ends328,330are electrically coupled to substrate308conductors in other ways, such as via thru-hole or socket pins.

Magnetic core324is disposed over and offset from a first portion332of substrate outer surface306. Bridge inductor318further includes a ground return conductor334disposed on an outer surface335of magnetic core324facing substrate outer surface first portion332, where outer surface335connects first and second core sides325,327. In some embodiments, ground return conductor334extends from core first side325to core second side327on outer surface335, as shown. As discussed below, opposing ends336,338of ground return conductor334form solder tabs (not shown) electrically coupled to conductors on substrate308, such that ground return conductor334is adapted to provide a path for current flowing from load304to switching circuit316. For example, in some embodiments, the ground return conductor solder tabs are surface mount soldered to conductors on substrate308. In certain alternate embodiments, however, ground return conductor ends336,338are electrically coupled to substrate308conductors in other ways, such as via thru-hole or socket pins. Portions340,342of winding326serve as standoffs adapted to offset magnetic core324from outer surface portion332. Additionally, portions344,346of ground return conductor334also serve as standoffs adapted to offset core324from outer surface first portion332.

Some of output capacitors320are disposed on substrate outer surface first portion332. Thus, certain of output capacitors320are disposed between substrate308and ground return conductor334, and ground return conductor334is disposed between capacitors320and magnetic core324. Accordingly, bridge inductor318“bridges” some of output capacitors320. For example, in a certain embodiment, bridge inductor318is adapted such that magnetic core324is offset by about 1.5 millimeters from substrate outer surface portion332, to allow bridging of capacitors320in embodiments where capacitors320are ceramic capacitors having a 1.2 millimeter height.

Input capacitors314and switching circuit316are electrically coupled across input and common power nodes348,350. Input and common power nodes348,350are, in turn, electrically coupled to an input power source352(not shown inFIG. 3), such as another power converter, a photovoltaic device, and/or a battery. Winding first end328is electrically coupled to switching circuit316at switching node354, and winding second end330is electrically coupled to an output power node356. Output capacitors320and load304are electrically coupled between output power node356and common power node350. Ground return conductor334forms part of common power node350, as shown inFIG. 4.

Controller322causes switching circuit316to repeatedly switch winding first end328between at least two different voltage levels, corresponding to voltage levels of input and common power nodes348,350, to transfer power from input power source352to load304. In certain embodiments, controller322is operable to regulate one or more operating characteristics of assembly300, such as input voltage Vin magnitude, input current Iin magnitude, input power magnitude, output voltage Vout magnitude, output current Io magnitude, and/or output power magnitude. Controller322is typically adapted to cause switching circuit316to switch at a frequency of 20 kilohertz or greater to promote low ripple current magnitude, fast converter transient response, and/or operation outside of a frequency range perceivable by humans.

Use of bridge inductor318in place of a conventional inductor, such as inductor112ofFIG. 1, helps assembly300potentially achieve one or more advantages over conventional electrical assemblies, such as assembly100ofFIG. 1. For example, use of bridge inductor318allows electrical components to be placed under the inductor's core324, thereby helping reduce the amount of surface area occupied by converter302. As can be observed fromFIGS. 1 and 3, width358of converter302ofFIG. 3is significantly smaller than width136of converter102ofFIG. 1, even though both converters have the same number of components.

As another example, use of bridge inductor318helps protect components under the inductor from mechanical damage. Bridge inductor318is typically larger and more mechanically robust than components located under its core. Accordingly, placement of bridge inductor318over components may insulate the components from mechanical stress that might otherwise damage the components and/or component connections.

Applicant has also discovered a synergistic arrangement of components in assembly300which helps minimize substrate conductor losses while promoting high performance. In particular, Applicant has discovered that disposing output capacitors320under bridge inductor318, and disposing load304at core second side327proximate to winding second end330, as shown inFIG. 3, promotes both high performance and low losses. In this component arrangement, capacitors320are close to both of winding second end330and load304, thereby promoting low parasitic ringing and high capacitor effectiveness. Additionally, relatively few of output capacitors320are disposed between winding second end330and load304. Thus, theFIG. 3component arrangement allows use of short substrate conductors electrically coupling winding second end330to load304, and coupling load304to switching circuit316. For example, a substrate conductor electrically coupling load304to winding second end330potentially needs to span only a relatively small linear separation distance360between these two components. Additionally, a substrate conductor electrically coupling load304to switching circuit316, to provide a path for return current (symbolically represented by arrow363inFIG. 4), need only span relatively small separation distance361between these components. A short substrate conductor, in turn, promotes low conductor impedance and associated conduction losses, since impedance is proportional to conductor length.

It should be appreciated that reducing substrate conductor length can significantly reduce conduction losses since substrate conductors are typically formed of thin metallic foil having a relatively large resistance. Applicant has conducted simulations showing that the component arrangement ofFIG. 3may improve efficiency from 2% to 4%, relative to an otherwise similar assembly where the load is significantly separated from the inductor.

In conventional assembly100ofFIG. 1, in contrast, output capacitors118are necessarily disposed between inductor112and load104, as discussed above, thereby separating load104from inductor112. Therefore, a conductor electrically coupling winding second end126and load104in assembly100must span at least the relatively large separation distance138separating second winding end126and load104. Additionally, a conductor electrically coupling load104to switching circuit110, to provide a path for return current (symbolically represented by arrow163inFIG. 2), will need to span at least a relatively large separation distance161between these components. Accordingly, substrate100will typically experience significantly greater inductor-to-load and load-to-switching circuit conduction losses than assembly300, assuming both assemblies have similar substrate conductor thicknesses and widths.

Incorporation of ground return conductor334in bridge inductor318may also achieve significant advantages. To help appreciate some of these advantages, first consider a scenario without ground return conductor334.FIG. 5shows a side elevational view of an electrical assembly500, which is similar to assembly300ofFIG. 3, but includes a buck switching power converter502with bridge inductor318replaced by an alternate bridge inductor518. In contrast to bridge inductor318ofFIG. 3, bridge inductor518ofFIG. 5does not include a ground return conductor.FIG. 6shows an electrical schematic of assembly500.

As shown inFIG. 6, bridge inductor518is part of a current loop602. Current loop602includes input power source352, switching circuit316, inductor518, load304, and conductors in substrate308connecting these components.FIG. 7illustrates the approximate flow of current through loop602in the vicinity of inductor518. Arrow702represents current flowing through winding326from switching circuit316to load304. Arrow704represents current flowing through conductors of substrate308from load304back to switching circuit316. Loop602has a relatively large size in the vicinity of inductor518due to winding326being separated from substrate308by separation distance562. Additionally, components bridged by inductor518are within or near loop602, as illustrated inFIG. 7, since the components are between winding326and substrate conductors carrying current from load304to switching circuit316. Such characteristics of assembly500may result in one or more disadvantages.

For example, the fact that components under inductor518are within or near current loop602typically results in the components being within the magnetic flux path of loop602. Magnetic flux generated by current flowing through loop602may induce circulating currents in conductive portions of components within this magnetic flux path. For instance, magnetic flux generated by current flowing through loop602may induce circulating currents in the lead frames and connector pins of components disposed under inductor518. These circulating currents are generally undesirable because they cause losses and associated component heating. Additionally, circulating currents may cause improper component operation, particularly if the components contain logic circuitry or switching device drivers. Thus, locating components under bridge inductor518may result in undesired losses, heating, and/or improper assembly operation.

As another example, the fact that loop602is defined by winding326and conductors in substrate308causes inductance associated with inductor518to be a function of substrate308's configuration. For instance, inductance associated with inductor518may vary depending on the location and size of conductors in substrate308, particularly in embodiments where inductance associated with inductor518is intended to be small. Such dependence on substrate308configuration may make it difficult to achieve a desired inductance value.

Additionally, the relatively large size of current loop602in the vicinity of inductor518creates a relatively large magnetic flux path, thereby potentially enabling the flux to magnetically couple to components or circuitry external to inductor518. Such magnetic coupling may result in undesired losses, heating, and/or electromagnetic compatibility issues. For instance, stray magnetic flux from current loop602may cause electromagnetic interference with other circuitry on substrate308near converter502. Additionally, the stray magnetic flux may extend beyond assembly500, thereby potentially causing electromagnetic interference with external equipment and preventing compliance with electromagnetic compatibility regulations. Accordingly, electromagnetic filtering and/or shielding may be required to negate detrimental effects of stray magnetic flux in assembly500. Such filtering and shielding typically increases assembly cost and/or size.

Applicant has discovered, however, that these disadvantages associated with use of a bridge inductor can potentially be reduced, or even essentially eliminated, by addition of a ground return conductor to the bridge inductor. Returning toFIGS. 3 and 4, inductor318is part of a current loop402, as shown inFIG. 4. Current loop402includes input power source352, switching circuit316, inductor318, load304, and conductors in substrate308connecting these components.FIG. 8illustrates the approximate flow of current through loop402in the vicinity of inductor318. Arrow802represents current flowing through winding326from switching circuit316to load304. Arrow804represents current flowing from load304back to switching circuit316. In contrast to assembly500ofFIG. 5, current loop size in the vicinity of the bridge inductor is relatively small and well defined. In particular, current flowing from load304to switching circuit316flows through ground return conductor334as a path of least DC and AC impedance, instead of through substrate conductors, in the vicinity of inductor318. Thus, current loop402is defined by winding326and ground return conductor334is the vicinity of inductor300. As discussed above, ground return conductor334is disposed on a core outer surface335, such that linear separation distance362between winding326and ground return conductor334is relatively small. Accordingly, inductance associated with inductor318is typically not significantly dependent on substrate308's configuration. Additionally, the relatively small size of current loop402near inductor318promotes containment of magnetic flux resulting from current flowing in loop402, thereby reducing the likelihood of problematic coupling of the magnetic flux to external components and circuitry.

Furthermore, the fact that current loop402is defined by winding326and ground return conductor334means that components bridged by inductor318, such as capacitors320, are outside of current loop402, as illustrated inFIG. 8. Such fact helps minimize coupling of magnetic flux generated by current flowing through loop402to components under inductor318, thereby helping minimize associated losses, heating, and potential improper operation. Indeed, the inclusion of ground return conductor334may reduce magnetic flux levels under inductor318to the point where it is possible to locate components which are sensitive to magnetic flux, such as control logic or switching device drivers, under inductor318.

It is anticipated that ground return conductor334will typically be formed of a material, such as copper, that has a high thermal, as well as electrical, conductivity. Accordingly, incorporation of ground return conductor334in bridge inductor318may help cool inductor318and components in its vicinity. In some alternate embodiments, a heat transfer device, such as a heat pipe, thermally couples one or more components disposed on substrate outer surface first portion332to ground return conductor334, thereby helping cool the components.

In certain embodiments, stand-offs340,342,344,346are flexible, such that they allow magnetic core324to move with respect to substrate308. Such feature promotes assembly300reliability by allowing core324to move and thereby compensate for mechanical changes in substrate308. For example, substrate308may expand or contract due to temperature change, and substrate308may flex due to mechanical force. Flexibility in stand-offs340,342,344,346is achieved, for example, by forming winding326and ground return conductor334of flexible metallic foil that allows magnetic core324to move with respect to substrate308. If stand-offs340,342,344,346are not flexible, these mechanical changes to substrate308may cause one or more winding or ground return conductor ends to break or separate from substrate308, thereby damaging assembly300. Additionally, the fact that magnetic core324is offset from substrate308further promotes mechanically assembly flexibility by allowing room for substrate308to move with respect to magnetic core324, thereby promoting assembly robustness.

In assembly100ofFIG. 1, in contrast, magnetic core116is disposed essentially directly on substrate106outer surface107. Thus, winding ends124,126will have limited freedom to compensate for mechanical changes in assembly100, such as thermal expansion and contraction of substrate106. Furthermore, the fact that magnetic core116almost essentially touches substrate outer surface107allows little room for movement between the components. For example, if substrate106is flexed such that the substrate extends upward in the area of magnetic core116and downward at the substrate edges, such flexing will push the substrate into core116, thereby creating significant mechanical stress of winding ends124,126soldered to substrate106conductors. This stress may cause winding end solder joints to break. In assembly300ofFIG. 3, on the other hand, space between substrate outer surface306and core324potentially allows for substrate308to flex towards core324without damaging the assembly.

The number and type of components of assembly300may be varied without departing from the scope hereof. For example, the number of input or output capacitors may be changed, or additional control circuit may be added. Furthermore, the placement of components in assembly300may be varied without departing from the scope hereof. For example, one or more components could optionally be disposed on substrate bottom outer surface364, thereby potentially enabling converter width358to be reduced.

In some alternate embodiments, components in addition to output capacitors320, and/or in place of output capacitors320, are bridged by bridge inductor318. For example, in certain alternate embodiments, switching circuit316and/or controller322are disposed on substrate outer surface306under core324. As discussed above, inclusion of ground return conductor334in bridge inductor318may enable sensitive components, such as switching circuits and controllers, to be disposed under core324.

Although ground return conductor334offers a number of potential advantages, as discussed above, in some alternate embodiments, ground return conductor334is omitted to reduce cost and/or complexity, such as shown inFIG. 5. Additionally, in certain alternate embodiments, one or more substrate conductors are electrically coupled in parallel with ground return conductor334, such as to increase converter302's capacity, with the potential tradeoff of a reduction in advantages realized by use of the ground return conductor. Furthermore, in some alternate embodiments, winding326and/or ground return conductor334are electrically coupled to substrate conductors by additional solder tabs. Winding and ground return conductor solder tabs are interleaved, for example, in some of these alternate embodiments to further reduce current loop402size in the vicinity of inductor318.

Assembly300could be modified to use an alternative bridge inductor in place of bridge inductor318. For example,FIG. 9shows a perspective view of a bridge inductor900, which is one possible alternative to bridge inductor318. Bridge inductor900includes a magnetic core902having opposing first and second sides904,906, a staple-style winding908, and a ground return conductor910.FIG. 10shows a perspective view of inductor900with magnetic core902shown as transparent,FIG. 11shows a perspective view of winding908, andFIG. 12shows a perspective view of ground return conductor910.

Winding908is wound through magnetic core902from first side904to second side906. A first end912of winding908extends from core first side904and wraps under core904to form a first solder tab914facing, but offset from, a bottom outer surface916of the core. Similarly, a second end918of winding908extends from core second side906and wraps under core902to form a second solder tab920facing, but offset from, core bottom outer surface916. Magnetic core902is formed, for example, of a ferrite material.

Ground return conductor910is disposed on core bottom outer surface916, such that magnetic core902does not form a magnetic path loop around ground return conductor910. Ground return conductor910extends from core first side904to core second side906on core bottom outer surface916. Ground return conductor910forms two first solder tabs922at core first side904, and two second solder tabs923at core second side906. Solder tabs922,923face, but are offset from, core bottom outer surface916. In this document, specific instances of an item may be referred to by use of a numeral in parentheses (e.g., solder tab922(1)) while numerals without parentheses refer to any such item (e.g., solder tabs922). Only one of the two second solder tabs923are visible in the perspective views ofFIGS. 9,10, and12; the other second solder tab is disposed opposite of solder tab922(1) and mirrors solder tab922(1). First solder tab914of winding908is interleaved with first solder tabs922of ground return conductor910, and second solder tab920of winding908is interleaved with second solder tabs923of ground return conductor910. Such interleaving promotes small size of a current loop including bridge inductor900. Portions924,926of winding908and portions928of ground return conductor910are adapted to serve as stand-offs offsetting magnetic core902from a surface, such as a substrate, that the solder tabs are disposed on. In some embodiments, winding portions924,926and ground return conductor portions928are flexible. In certain alternate embodiments of assembly300including bridge inductor900in place of bridge inductor318, solder tabs922,923are electrically coupled to substrate conductors such that current flowing from load304back to switching circuit316flows through ground return conductor910from second solder tabs923to first solder tabs922.

The fact that winding908is a staple-style winding promotes inductor manufacturing simplicity, particularly in embodiments where magnetic core902is formed of a ferrite magnetic material. However, the configuration of winding908can be modified without departing from the scope hereof. For example, in some alternate embodiments, winding908is a multi-turn winding embedded in magnetic core902. Certain of these alternate embodiments are formed, for example, by placing winding908in a mold, disposing a magnetic material around the winding in the mold, and curing the material, such as by applying pressure, heat, and/or curing agents to the magnetic material, to form a molded magnetic core with winding908embedded therein. Ground return conductor910is optionally placed in the mold with winding908before disposing the magnetic material in the mold, such that both winding908and ground return conductor910are embedded in magnetic core902at the same time. Embedding winding908in magnetic core902concurrently with ground return conductor910promotes manufacturing simplicity and ease of aligning solder tabs914,920with solder tabs922,923. The magnetic material disposed in the mold is, for instance, powdered iron within a binder.

Bridge inductors can also be used in coupled inductor applications, where a coupled inductor is a magnetic device adapted to achieve both energy transfer and energy storage. For example,FIG. 13shows an end elevational view of an electrical assembly1300including a bridge coupled inductor1302disposed on an outer surface1303of a substrate1304. Bridge coupled inductor1302forms part of a switching power converter, as discussed below.

FIG. 14shows a perspective of bridge coupled inductor1302, which has a width1306, a depth1308, and a height1310. Bridge coupled inductor1302includes a magnetic core1312including a ladder structure1314and first and second leakage plates1316,1318.FIG. 15shows an exploded perspective view of magnetic core1312with first and second leakage plates1316,1318separated from ladder structure1314. Ladder structure1314includes first and second rails1320,1322, and N rungs1324, where N is an integer greater than one. Each rung1324is disposed between and connects first and second rails1320,1322. In some embodiments, first and second rails1320,1322are disposed parallel to each other, as shown. Ladder structure has1314opposing first and second sides1326,1328.

First leakage plate1316is disposed on first side1326of ladder structure1314under each of the N rungs1324, such that first leakage plate1316connects first and second rails1320,1322. First leakage plate1316also forms a first outer surface1330of magnetic core1312disposed over and facing a first portion1331of substrate outer surface1303. Second leakage plate1318is disposed on second side1328of ladder structure1314over each of the N rungs1324such that second leakage plate1318connects first and second rails1320,1322. First and second leakage plates1316,1318are each typically separated from ladder structure1314by material having a lower magnetic permeability than a one or more materials forming magnetic core1312. For example, in some embodiments, air, plastic, paper, and/or adhesive separates each of first and second leakage plates1316,1318from ladder structure1314.

Bridge coupled inductor1304further includes a respective winding1332wound around each of the N rungs1324, and a ground return conductor1334disposed on magnetic core first outer surface1330. In some embodiments, ground return conductor1334extends from a first side1335of magnetic core1312to a second side1337of magnetic core1312on first outer surface1330, as shown. Although windings1332have a common configuration in bridge inductor1302, in some alternate embodiments, two or more windings have different configurations, such as to create an embodiment with asymmetrical leakage inductance values.FIG. 16shows an exploded perspective view of bridge inductor1302with second leakage plate1318separated from the remainder of inductor1302to show the tops of windings1332.FIG. 17shows another exploded perspective view of inductor1302, but with both of ground return conductor1334and second leakage plate1318separated from the remainder of inductor1302. Second rail1322and the N rungs1324are shown as transparent inFIG. 17to better show the N windings1332.FIGS. 18-20respectively show a perspective view, a top plan view, and a side elevational view, of one instance of windings1332.

Opposing ends1336,1338of each winding1332form a respective solder tab1340,1342surface mount soldered to conductors of substrate1304. Solder tabs1340,1342face, but are offset from, magnetic core outer surface1330. In some alternate embodiments, though, one or more of solder tabs1340,1342are supplemented with or replaced by an alternative connector, such as a through-hole pin or a socket pin. Each winding1332also forms two stand-offs1344,1346adapted to offset magnetic core1312from first portion1331of substrate outer surface1303. In some embodiments, stand-offs1344,1346are formed of flexible metallic foil such that the stand-offs are flexible.

Magnetic core1312does not form a magnetic path loop around ground return conductor1334. Ground return conductor1334has opposing first and second sides1348,1350, as shown inFIG. 17. Ground return conductors1334forms N first solder tabs1352on first side1348, and N second solder tabs1354on second side1350, although only one instance of solder tab1354is visible in the shown views. First and second solder tabs1352,1354are surface mount soldered to conductors of substrate1304. In some alternate embodiments, however, one or more of solder tabs1352,1354are supplemented with or replaced by an alternative connector, such as a through-hole pin or a socket pin. Additionally, the number of first and/or second solder tabs1352,1354may be varied without departing from the scope hereof. Ground return conductor1334also forms a stand-off1356with each first solder tab1352and a stand-off1358with each second solder tab1354. Stand-offs1356,1358are adapted to offset magnetic core1312from substrate1304. In some embodiments, stand-offs1356,1358are formed of flexible metallic foil such that the stand-offs are flexible.

First solder tabs1340of windings1332are interleaved with first solder tabs1352of ground return conductor1334. Similarly, second solder tabs1342of windings1332are interleaved with second solder tabs1354of ground return conductor1334. Such interleaving reduces the size of a current loop including bridge coupled inductor1302, as discussed further below.

Ladder structure1314magnetically couples the N windings1332, while first and second leakage plates1316,1318provide leakage magnetic flux paths for windings1332, such that each winding1332has an associated leakage inductance. Leakage inductance values are adjusted during the design of inductor1302, for example, by varying a separation distance between first leakage plate1316and ladder structure1314, and/or by varying a separation distance between second leakage plate1318and ladder structure1314. Magnetic coupling of windings1332is associated with transfer of energy between windings, while leakage inductance of windings1332is associated with energy storage in inductor1302.

FIG. 21shows an electrical schematic of assembly1300. Assembly1300further includes input capacitors1360, N switching circuits1362, output capacitors1364, and a controller1366. These components, along with bridge inductor1302, form part of a buck converter1368including multiple parallel power stages1370adapted to transfer power from an input power source1372to a load1374. In certain embodiments, one or more of input capacitors1360and output capacitors1364are multi-layer ceramic capacitors. In some embodiments, load1374is a processor of an information technology device. Controller1366, input power source1372, and load1374are not shown inFIG. 13, and these components may be integrated with assembly1300or external to assembly1300. At least some of switching circuits1362, input capacitors1360, and output capacitors1364are disposed on substrate outer surface portion1331, between substrate1304and ground return conductor1334, such that inductor1302bridges these components. Thus, ground return conductor1334is disposed between at least some of these components and magnetic core1312.

Although only a single input capacitor1360is visible in the elevational view ofFIG. 13, it is anticipated that assembly1300will typically include a number of input capacitors electrically coupled in parallel, which are symbolically shown as a single capacitor in theFIG. 21schematic. Additionally, althoughFIG. 13shows five output capacitors1364, the number of output capacitors may be varied without departing from the scope hereof. Output capacitors1364are electrically coupled in parallel and are symbolically shown as a single capacitor in theFIG. 21schematic.

Each power stage1370includes a respective one of the N switching circuits1362electrically coupled across input and common power nodes1376,1378. Input capacitors1360and input power source1372are also electrically coupled across nodes1376,1378. Each power stage1370further includes a respective one of the N windings1332of bridge coupled inductor1302electrically coupled between a switching node1380of the power stage and an output power node1382. Output capacitors1364are electrically coupled between output and common power nodes1382,1378. Controller1366controls each switching circuit1362to repeatedly switch its respective winding first end1336between at least two voltage levels corresponding to the voltages on input and common power nodes1376,1378, to transfer power from input power source1372to load1374. In some embodiments, controller1366is adapted to control switching circuits1362so that they switch out of phase with respect to each other, such that each power stage1370may considered a “phase,” and buck converter1368may be considered a “multi-phase” buck converter. Additionally, in certain embodiments, controller1366is adapted to control switching of switching circuits1362to regulate input voltage Vi, input current Ii, input power, output voltage Vo, output current Io, and/or output power. Controller1366typically is adapted to cause switching circuits1362to switch at a frequency of 20 kilohertz or greater to promote low ripple current magnitude, fast converter transient response, and/or operation outside of a frequency range perceivable by humans.

Certain embodiments of electrical assembly1300will potentially achieve some or all of the advantages discussed above with respect to electrical assembly300ofFIG. 3. For example, use of bridge coupled inductor1302in place of a conventional coupled inductor promotes small assembly size by allowing components to be placed between substrate1304and magnetic core1312, as shown inFIG. 13. Additionally, bridge inductor1302advantageously protects the components it bridges from mechanical stress. Inclusion of ground return conductor1334in bridge coupled inductor1302also promotes low losses, electromagnetic compatibility, and the ability to dispose sensitive components under bridge inductor1302, in a manner similar to that discussed above with respect to assembly300. While inclusion of ground return conductor1334potentially offers significant benefits, it is omitted in some alternate embodiments to reduce cost and/or complexity.

The configuration of bridge coupled inductor1302also offers a number of potential advantages. For example, leakage inductance values can be readily adjusted during the design of inductor1302by varying spacing between leakage plates1316,1318and ladder structure1314, as discussed above. Additionally, leakage plates1316,1318help shield other electrical circuitry from magnetic and electric fields generated by current flowing through windings1332. Specifically, a respective portion1384of each winding1332is disposed between first rail1320and first leakage plate1316, and a respective portion1386of each winding1332is disposed between second rail1322and first leakage plate1316, such that winding portions1384,1386are shielded by first leakage plate1316. Second leakage plate1318also shields tops of windings1332. However, in some alternate embodiments, one of first and second leakage plates1316,1318is omitted to reduce cost and complexity. Additionally, in some other alternate embodiments, first and second leakage plates1316,1318are replaced with other means to achieve leakage magnetic flux paths, such as gapped outer legs, as taught, for example, in U.S. Patent Application Publication Number 2009/0237197 to Ikriannikov et al., which is incorporated herein by reference.

AlthoughFIGS. 13-21show N being four, assembly1300may be modified so that N is any integer greater than one. For example, the value of N may be selected during the design of assembly1300at least partially based on the expected magnitude of current required by load1374, since current capacity of buck converter1368is somewhat proportional to number of power stages1370. Additionally, in some alternate embodiments, ground return conductor1334is supplemented by one or more conductors on substrate1304, such as to increase converter capacity, with a possible diminishment of advantages associated with using ground return conductor1334. Furthermore, the number, type, and placement of components in assembly1300may be varied without departing from the scope hereof. For example, in some alternate embodiments, controller1366is replaced with a number of discrete controllers disposed at different locations on assembly1300, such as one controller for each power stage1370. As another example,FIG. 22shows an end elevational view of an electrical assembly2200, which is similar to assembly1300ofFIG. 13, but with switching circuits1362and input capacitors1360disposed next to bridge inductor1302, instead of under bridge inductor1302. This alternate location of switching circuits1362allows an optional heat sink2202to be attached to each switching circuit1362, as shown.

Moreover, assembly1300could be modified to replace bridge coupled inductor1302with one or more alternate inductors. For example, in some alternate embodiments where N is equal to four, bridge inductor1302is replaced with two separate bridge coupled inductors, where each bridge coupled inductor includes two windings and supports a respective pair of the four power stages1370. As another example, in some other alternate embodiments, bridge inductor1302is replaced with N discrete (non-coupled) inductors, such as N instances of bridge inductor900ofFIG. 9, where each inductor900bridges a respective one of the N switching circuits1362.

Although bridge inductors are discussed above with respect to buck converter applications, bridge inductors can also be used with other switching converter topologies. For example, assembly300ofFIG. 3could be modified such that buck converter302is instead a boost or a buck-boost converter. Similarly, assembly1300ofFIG. 13could be modified such that multi-power stage buck converter1368is instead a multi-power stage boost converter or buck-boost converter.

Furthermore, the principles discussed above with respect to bridge inductors could also be applied to bridge transformers, which include a magnetic core adapted to be offset from a substrate that the transformer is disposed on. For example,FIG. 23shows a perspective view of a bridge transformer2300. Bridge transformer includes a magnetic core2302having a ladder structure similar to ladder structure1314ofFIG. 15. Specifically, magnetic core2302includes first and second rails2304,2306and N rungs (not visible inFIG. 22) disposed between and connecting rails2304,2306, where N is an integer greater than one. A respective winding2308is wound around each rung. Windings2308are similar to windings1332of assembly1300. For example, opposing ends of each winding2308form a respective solder tab adapted for surface mount soldering to a substrate conductor. A ground return conductor, such as one similar to ground return conductor1334of assembly1300, is optionally disposed on an outer surface2310of magnetic core2302. Magnetic core2302does not, however, include leakage plates, since leakage inductance is typically undesirable in transformers.

Bridge transformer2300is, for example, disposed on an outer surface of a substrate in a manner similar to that discussed above with respect to bridge inductors. In such applications, windings2308form stand-offs2312adapted to offset magnetic core2302from a portion of the substrate outer surface that transformer2300is disposed on. Electrical components are, for instance, disposed on the substrate outer surface between the substrate and the magnetic core, such that bridge transformer2300bridges the components.

Combinations of Features

Features described above as well as those claimed below may be combined in various ways without departing from the scope hereof. The following examples illustrate some possible combinations:

(A1) An electrical assembly may include a substrate and a bridge magnetic device disposed on an outer surface of the substrate. The bridge magnetic device may include (1) a magnetic core disposed over and offset from a first portion of the outer surface of the substrate, (2) N windings wound around at least a portion of the magnetic core and electrically coupled to conductors of the substrate, where N is an integer greater than zero, and (3) a ground return conductor disposed on an outer surface of the magnetic core facing the first portion of the outer surface of the substrate. The electrical assembly may further include at least one electrical component disposed on the first portion of the outer surface of the substrate.

(A2) In the electrical assembly denoted as (A1), at least one of the N windings may form one or more stand-offs adapted to offset the magnetic core from the outer surface of the substrate.

(A3) In either of the electrical assemblies denoted as (A1) or (A2), opposing ends of at least one of the N windings may form solder tabs surface mount soldered to conductors of the substrate.

(A4) In any of the electrical assemblies denoted as (A1) through (A3), the ground return conductor may form at least one additional stand-off adapted to offset the magnetic core from the outer surface of the substrate.

(A5) In any of the electrical assemblies denoted as (A1) through (A4), the ground return conductor may be electrically coupled to electrical conductors of the substrate.

(A6) In any of the electrical assemblies denoted as (A1) through (A5), the magnetic core optionally does not form a magnetic path loop around the ground return conductor.

(A7) In any of the electrical assemblies denoted as (A1) through (A6), the bridge magnetic device may be selected from the group consisting of a bridge inductor and a bridge transformer.

(A8) In any of the electrical assemblies denoted as (A1) through (A6), the bridge magnetic device may be an inductor, and the inductor and the at least one electrical component may collectively form at least part of a switching power converter.

(A9) In the electrical assembly denoted as (A8), the switching power converter may be a buck-type converter, and the at least one electrical component may include at least one output capacitor.

(A10) In the electrical assembly denoted as (A9), the at least one output capacitor may include at least one multi-layer ceramic capacitor.

(A11) In either of the electrical assemblies denoted as (A9) or (A10), the at least one electrical component may further include at least one input capacitor.

(A12) In any of the electrical assemblies denoted as (A8) through (A11), the at least one electrical component may further include a switching circuit.

(A13) The electrical assembly denoted as (A12) may further include a heat transfer device adapted to transfer heat from the switching circuit to the ground return conductor.

(A14) In any of the electrical assemblies denoted as (A8) through (A13), N may be an integer greater than one, and the switching power converter may be a multi-phase switching power converter.

(A15) In the electrical assembly denoted as (A14), the ground return connector may include a plurality of solder tabs electrically coupled to conductors of the substrate, opposing ends of each of the N windings may form a respective solder tab electrically coupled to conductors of the substrate, and the plurality of solder tabs of the ground return conductor may be interleaved with the solder tabs of the N windings.

(A16) Any of the electrical assemblies denoted as (A8) through (A15) may further include a controller adapted to at least partially control operation of the switching power converter, and the controller may be disposed on the first portion of the outer surface of the substrate.

(A17) In any of the electrical assemblies denoted as (A8) through (A16): (1) N may be an integer greater than one; (2) the magnetic core may include (a) a ladder structure including first and second rail and N rungs, each of the N rungs connecting the first and second rails, (b) a first leakage plate disposed on a first side of the ladder structure under each of the N rungs, the first leakage plate connecting the first and second rails and forming the outer surface of the magnetic core facing the first portion of the outer surface of the substrate, and (c) a second leakage plate disposed on a second side of the ladder structure over each of the N rungs, the second side of the ladder structure being opposite to the first side of the ladder structure, the second leakage plate connecting the first and second rails; and (3) each of the N windings may be wound around a respective one of the N rungs.

(A18) In the electrical assembly denoted as (A17), a respective first portion of each of the N windings may be disposed between the first rail and the first leakage plate, and a respective second portion of each of the N windings may be disposed between the second rail and the first leakage plate.

(A19) Any of the electrical assemblies denoted as (A8) through (A18) may further include N switching circuits, each of the N switching circuits may be adapted to repeatedly switch a first end of a respective one of the N windings between at least two different voltage levels, and the ground return conductor may be electrically coupled between the N switching circuits and a load powered by the switching power converter to provide a path for current flowing from the load to the N switching circuits.

(A20) In any of the electrical assemblies denoted as (A8) through (A19), the magnetic core may have opposing first and second sides, and the ground return conductor may extend from the first side to the second side of the magnetic core, on the outer surface of the magnetic core.

(A21) In the electrical assembly denoted as (A20), the outer surface of the magnetic core may connect the first and second sides of the magnetic core.

(B1) An electrical assembly may include a substrate, at least one electrical component disposed on the substrate, and a bridge magnetic device disposed on the substrate. The bridge magnetic device may include a magnetic core and a ground return conductor arranged such that: (1) the at least one electrical component is disposed between the substrate and the ground return conductor, and (2) the ground return conductor is disposed between the at least one electrical component and the magnetic core.

(B2) In the electrical assembly denoted as (B1), the bridge magnetic device may further include N windings wound around at least a portion of the magnetic core, and at least one of the N windings may form one or more stand-offs adapted to offset the magnetic core from the substrate, where N is an integer greater than zero.

(B3) In the electrical assembly denoted as (B2), the ground return conductor may form at least one additional stand-off adapted to offset the magnetic core from the outer surface of the substrate.

(B4) In either of the electrical assemblies denoted as (B2) or (B3), N may be an integer greater than one, the ground return connector may include a plurality of solder tabs electrically coupled to conductors of the substrate, opposing ends of each of the N windings may form a respective solder tab electrically coupled to conductors of the substrate, and the plurality of solder tabs of the ground return conductor may be interleaved with the solder tabs of the N windings.

(B5) Any of the electrical assemblies denoted as (B2) through (B4) may further include N switching circuits, where each of the N switching circuits is adapted to repeatedly switch a first end of a respective one of the N windings between two different voltage levels.

(B6) In the electrical assembly denoted as (B5), the bridge magnetic device and the N switching circuits may form at least part of a switching power converter.

(B7) In the electrical assembly denoted as (B6), the ground return conductor may be electrically coupled between the N switching circuits and a load powered by the switching power converter, to provide a path for current flowing from the load to the N switching circuits.

(B8) In any of the electrical assemblies denoted as (B2) through (B7), opposing ends of at least one of the N windings may form solder tabs surface mount soldered to conductors of the substrate.

(B9) In any of the electrical assemblies denoted as (B1) through (B8), the magnetic core optionally does not form a magnetic path loop around the ground return conductor.

(B10) In any of the electrical assemblies denoted as (B1) through (B9), the bridge magnetic device may be selected from the group consisting of a bridge inductor and a bridge transformer.

(B11) In any of the electrical assemblies denoted as (B1) through (B10), the magnetic core may have opposing first and second sides, and the ground return conductor may extend from the first side to the second side of the magnetic core.

(C1) An electrical assembly may include a substrate and a bridge inductor disposed on an outer surface of the substrate. The bridge inductor may include (1) a magnetic core offset from and disposed over a first portion of the outer surface of the substrate, and (2) a winding wound around at least a portion of the magnetic core, where the winding has opposing first and second ends electrically coupled to conductors of the substrate. The electrical assembly may further include a switching circuit, a plurality of capacitors, and a load. The switching circuit may be operable to repeatedly switch the first end of the winding between at least two different voltage levels. The plurality of capacitors may be disposed on the first portion of the outer surface of the substrate, and the plurality of capacitors may be electrically coupled to the second end of the winding. The load may be disposed on the substrate proximate to the second end of the winding, and the load may be electrically coupled to the second end of the winding. The bridge inductor, the switching circuit, and the plurality of capacitors may collectively form at least part of a switching power converter operable to at least partially power the load.

(C2) In the electrical assembly denoted as (C1), the magnetic core may have opposing first and second sides, the first end of the winding may terminate at the first side of the magnetic core, the second end of the winding may terminate at the second side of the magnetic core, and the load may be disposed at the second side of the magnetic core.

(C3) In either of the electrical assemblies denoted as (C1) or (C2), the load may include a processor of an information technology device.

(C4) In any of the electrical assemblies denoted as (C1) through (C3), the first and second ends of the winding may form respective first and second solder tabs surface mount soldered to conductors of the substrate.

(C5) In any of the electrical assemblies denoted as (C1) through (C4), the switching circuit may be disposed on the first portion of the outer surface of the substrate.

(C6) In any of the electrical assemblies denoted as (C1) through (C5), the bridge inductor may further include a ground return conductor disposed on an outer surface of the magnetic core facing the first portion of the outer surface of the substrate, and the ground return conductor may be electrically coupled to conductors of the substrate.

(C7) In the electrical assembly denoted as (C6), the magnetic core optionally does not form a magnetic path loop around the ground return conductor.

(C8) In either of the electrical assemblies denoted as (C6) or (C7), the ground return conductor may be adapted to carry current flowing from the load to the switching circuit.

(D1) An electrical assembly may include a substrate and a bridge magnetic device disposed on an outer surface of the substrate. The bridge magnetic device may include (1) a magnetic core disposed over a first portion of the outer surface of the substrate, and (2) N windings wound around at least a portion of the magnetic core, where N is an integer greater than zero. The N windings may form one or more flexible stand-offs offsetting the magnetic core from the first portion of the outer surface of the substrate, where the one or more flexible stand-offs allow the magnetic core to move with respect to the substrate. The electrical assembly may further include at least one electrical component disposed over the first portion of the outer surface of the substrate.

(D2) In the electrical assembly denoted as (D1), the bridge magnetic device may further include a ground return conductor disposed on an outer surface of the magnetic core facing the first portion of the outer surface of the substrate, and the ground return conductor may be electrically coupled to conductors of the substrate.

(D3) In the electrical assembly denoted as (D2), the ground return conductor may form one or more additional flexible stand-offs offsetting the magnetic core from the first portion of the outer surface of the substrate, where the one or more additional flexible stand-offs allow the magnetic core to move with respect to the substrate.

(D4) In either of the electrical assemblies denoted as (D2) or (D3), the magnetic core optionally does not form a magnetic path loop around the ground return conductor.

(D5) In any of the electrical assemblies denoted as (D1) through (D4), the bridge magnetic device may be selected from the group consisting of a bridge inductor and a bridge transformer.

Changes may be made in the above methods and systems without departing from the scope hereof. For example, single-turn windings may be replaced with multiple-turn windings in many embodiments. As another example, magnetic cores formed of discrete magnetic elements may be replaced with monolithic magnetic cores, such as cores formed of molded powder magnetic material. Therefore, the matter contained in the above description and shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.