GB2555873B

GB2555873B - Housing for mounting a transformer to a substrate

Info

Publication number: GB2555873B
Application number: GB1622117.8A
Authority: GB
Inventors: Francis Lee
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2016-11-11
Filing date: 2016-12-23
Publication date: 2019-09-11
Anticipated expiration: 2036-12-23
Also published as: GB201622117D0; GB2555873A; GB2555832A

Description

HOUSING FOR MOUNTING A TRANSFORMER TO A SUBSTRATE

This application relates to a housing for a transformer, in particular to a housing for a magnetic transformer to be mounted onto a substrate having components for input transformer circuitry and output transformer circuitry.

The components of the input circuitry must be electrically isolated from the components of the output circuitry, this is particularly important if the transformer is part of an Isolated DC-to-DC converter. Accordingly, the geometry of the transformer and the transformer circuitry (including the input circuitry and the output circuitry) is preferably designed to prevent electrical breakdown of the insulation area at the rated voltage of the transformer (including any safety margin) between the components of the input circuitry and the components of the output circuitry. A breakdown of the material of the insulator causing conduction through the insulator material is known as a puncture arc. In order to prevent a puncture arc, the shortest distance between two conductive paths on the transformer and the PCB, as measured along the surface of the insulation (also known as the creepage) must be maintained above a minimum value. A breakdown of the air around the surface of the insulator causing conduction through the air is known as a flashover arc. In order to prevent a flashover arc, the shortest distance between two conductive paths on the transformer and the PCB, as measured through air (also known as the clearance) must be maintained above a minimum value.

Such minimum creepage and clearance values may be required by safety approvals agencies such as UL and industry standards such as EN/UL 60950. The minimum creepage value is typically slightly larger than the minimum clearance value, which means that it is more likely that breakdown will cause a flashover arc rather than a puncture arc. This is the preferred configuration because puncture arcs typically cause irreparable damage to the insulator.

The minimum spacing between the components of the input circuitry and the components of the output circuitry creates an area within which no conductive components or other conductive material should be placed that may be known as the isolation area. However, the transformer will typically include a magnetic transformer core and it may be desirable to locate this magnetic core between the components of the input circuitry and the components of the output circuitry, rather than locating it on top of these components, in order to minimise the overall product height and/or to allow a greater area of the substrate in which to place components. The magnetic core may be made of a ferrite material, which itself is a conductor and accordingly it is desirable to provide additional isolation in order to insulate the magnetic transformer core from other components mounted on the substrate.

In one known embodiment, the magnetic core may be encapsulated in electrically insulating material prior to the input electrical winding and the output electrical winding of the transformer being wound around the magnetic core. For example, the magnetic core may be covered in electrical insulating tape or alternatively a magnetic core cover made of an electrically insulating material may be affixed around the magnetic core. However, this can increase the leakage inductance of the transformer and cause problems with the design of the transformer system.

Therefore, we have appreciated that it would be desirable to provide an improved means for electrically insulating the magnetic core of a transformer from the other components mounted on the substrate in order to aid the miniaturisation of the transformer and the design of the system including the substrate.

SUMMARY OF THE INVENTION

The invention is defined in the independent claims to which reference should now be directed. Advantageous features are set out in the dependent claims. A first aspect relates to a housing for a transformer, comprising: a substrate, a base having a first surface and a second surface, wherein the second surface is a mounting surface for mounting the housing to the substrate; a plurality of sidewalls extending from the first surface of the base to form a cavity having a closed boundary; at least one projection extending from the second surface of the base; and an auxiliary projection extending from one of the plurality of sidewalls; wherein the housing is formed monolithically from an electrically insulating material, wherein the substrate comprises a first substrate having input circuitry located thereon and a second substrate having output circuitry located thereon, wherein the first substrate and the second substrate are separate and wherein the at least one projection of the housing is configured to extend through a corresponding gap in the substrate between the first substrate and the second substrate; wherein the auxiliary projection is configured to: extend through a gap in a principle substrate; and extend between an input pin of the input circuitry located on the first substrate and an output pin of the output circuitry located on the second substrate; and wherein the cavity is arranged to receive a transformer comprising a magnetic core, an input electrical winding and an output electrical winding.

The housing provides additional electrical insulation in order to maintain desired creepage and clearance gaps between the respective components of the input circuitry and the output circuitry via the magnetic core of the transformer. Moreover, the invention advantageously provides an electrically insulating projection that is monolithically formed with the housing and arranged to extend through a substrate in order to also increase the creepage and clearance distances between the input and output circuitry components that are mounted on substrate, for example on the opposing side of the substrate to which the housing is arranged to be mounted. This means that the dimensions of the isolation area may be reduced and the components mounted on the substrate can be moved closer together by comparison, thus facilitating the miniaturisation of systems including the transformer, the substrate and the other components mounted on the substrate.

Optionally, the housing may comprise a plurality of electrically insulating projections extend monolithically from the second surface of the base. Advantageously, the plurality of projections may increase the creepage and clearance values of the printed circuit board transformer whilst minimising the length that the projections project from said opposing side of the substrate.

Optionally, the base of the housing may further comprise one or more recesses such that the second surface of the housing does not extend across the entire base of the housing. This enables the housing to extend over some of the components mounted to the substrate , which advantageously improves the ability for miniaturisation of the system whilst also facilitating larger magnetic cores that may in turn have a larger number of winds in the input and/or output electrical windings.

Optionally, the housing may further comprise a supporting member extending from the first surface of the base into the cavity, wherein the supporting member is configured to receive a magnetic core of a transformer. This supporting member advantageously fixes the positioning of the magnetic core of the transformer within the housing. The magnetic core may optionally be a toroidal magnetic core and the dimensions of the cavity of the housing and the supporting member may be configured accordingly.

Optionally, the supporting member may further comprise first and second wing sections extending from the supporting member towards the plurality of sidewalls in substantially opposing directions and wherein the first and second wing sections are configured to substantially engage the surface of the magnetic core of the transformer. These first and second wing portions advantageously position the magnetic core of the transformer with increased security within the housing. Furthermore, the engagement of the wing sections with the magnetic core preferably prevents the input or output electrical windings on one side of the wing section from coming into contact with the respective output or input electrical windings on the other side of the wing section. It will be appreciated that the wing sections could be included in the housing in the absence of the supporting member.

Optionally, at least one of the plurality of sidewalls comprises cutaway portions configured to receive the wires of the input electrical winding and/or the output electrical winding exiting from the cavity to connect to the substrate. This advantageously improves the routing of the wires from the electrical windings inside the housing to the respective substrate connections outside of the housing.

Optionally, the housing may further comprise an electrically insulating lid portion configured to abut against at least part of the plurality of sidewalls and to substantially enclose the housing cavity. This advantageously provides further electrical insulation and an additional barrier to conduction between the magnetic core of the transformer and any neighbouring components that may be mounted in the vicinity of the transformer. Optionally, the lid portion may be configured to extend around the plurality of sidewalls to fully cover the housing and fully enclose the housing cavity.

Optionally, the lid portion may comprise one or more holes for receiving encapsulation material being injected into the housing cavity. This advantageously enables encapsulation material to be injected into the housing cavity in order to provide additional mechanical support to the components within the housing as well as providing additional electrical insulation.

Optionally, the housing may further comprise one or more electrically insulating shelves protruding substantially horizontally from one or more side walls of the housing. Optionally, at least one of the one or more electrically insulating shelves may comprise cutaway portions configured to receive the wires of the input electrical winding and/or the output electrical winding exiting from the cavity to connect to the substrate. These electrically insulating shelves further extend the creepage and/or clearance paths and corresponding distances, and are particularly effective if some of the components are relatively tall.

The auxiliary projection acts to increase the creepage and clearance distances between input and output circuitry components that may be mounted on or to the principle substrate. This means that the dimensions of an isolation area of the principle substrate may be reduced and the components mounted on the principle substrate may be moved comparatively closer together, thus further facilitating the miniaturisation of systems including an electronic device comprising the transformer and mounted to the principle substrate.

Optionally, the at least one projection and the auxiliary projection may merge to form a single projection extending from both the second surface of the base and one of the plurality of sidewalls. This advantageously simplifies the formation of the at least one projection and the auxiliary projection. A second aspect relates to an electronic device comprising: the housing according to the first aspect, the second surface of the housing being mounted onto the substrate such that the at least one projection extends from the second surface of the base, through the gap in the substrate and between the respective conductive elements of the input circuitry and the output circuitry; a magnetic core located in the cavity of the housing; at least one input electrical winding wound around a portion of the magnetic transformer core and extending from the housing to electrically connect to the input circuitry; and at least one output electrical winding wound around a portion of the magnetic core and extending from the housing to electrically connect to the output circuitry, wherein the gap in the substrate is located in an isolation area defined by the space between the respective conductive elements of the input circuitry and the output circuitry.

The electronic device advantageously provides improved creepage and clearance distances between the input and output circuitry components on the opposing side of the substrate to which the housing is mounted. This means that the dimensions of the isolation area may be reduced and the transformer circuitry components mounted on the substrate can be moved closer together by comparison, thus facilitating the miniaturisation of the electronic device.

Optionally, the at least one input electrical winding and the at least one output electrical winding comprise electrically insulated wires wound directly around the magnetic core. This advantageously minimises inductance leakage in the transformer design.

Optionally, the creepage distance from the conductive elements of the input circuitry to the magnetic core as well as the creepage distance from the magnetic core to the conductive elements of the output circuitry are both at least half the value of the creepage distance required between the respective components of the input circuitry and output circuitry. This provides a minimum required total creepage and distance between the respective components of the input circuitry and output circuitry.

Optionally, the clearance distance from the conductive elements of the input circuitry to the magnetic core as well as the clearance distance from the magnetic core to the conductive elements of the output circuitry are both at least half the value of the clearance distance required between the respective components of the input circuitry and output circuitry. This provides a minimum required total clearance distance between the respective components of the input circuitry and output circuitry.

In a third aspect, a method for constructing a transformer comprises: winding at least one input electrical winding around a portion of a magnetic core; winding at least one output electrical winding around a portion of the magnetic core; inserting the magnetic core with the input electrical winding and the output electrical winding into a housing according to the first aspect described above; mounting the housing to a substrate such that the at least one projection extends from the second surface of the base, through a corresponding gap in the substrate, wherein the substrate has input and output circuitry mounted thereon and the gap is located in an isolation area defined by the space between the respective conductive elements of the input circuitry and the output circuitry; and electrically connecting the wires of the at least one input electrical winding and the at least one output electrical winding to corresponding conductive pads of the input circuitry and output circuitry of the substrate respectively.

The method of the third aspect provides an electronic device having improved electrical insulation maintaining the required creepage and clearance gaps between the respective components of the input circuitry and the output circuitry via the magnetic core of the transformer. Moreover, the method advantageously enables the dimensions of the isolation area to be reduced and the components of the transformer circuitry can be moved comparatively closer together on the substrate, thus facilitating the production of a miniaturised transformer device.

Optionally, the housing has the above first and second wing sections and the step of inserting the magnetic core further comprises separating the input electrical winding and the output electrical winding such that they are on opposing sides of the first and second wing sections extending from the supporting member towards the plurality of sidewalls of the housing. This advantageously positions the magnetic core of the transformer with increased security within the housing, whilst also preventing the input or output electrical windings on one side of the wing section from coming into contact with the respective output or input electrical windings on the other side of the wing section due to the engagement of the wing sections with the magnetic core.

Optionally, the method further comprises substantially enclosing the cavity using a lid portion, wherein the wires of the at least one input electrical winding and the at least one output electrical winding pass from the cavity to the respective conducting pads through one or more cutaway portions in the sidewalls and/or through one or more cutaway portions in the lid portion. This advantageously provides further electrical insulation and an additional barrier to conduction between the magnetic core of the transformer and any neighbouring components that may be mounted in the vicinity of the transformer.

Optionally, the method further comprises injecting encapsulation material through at least one hole in the lid portion. This advantageously enables encapsulation material to be injected into the housing cavity in order to provide additional mechanical support to the components within the housing as well as providing additional electrical insulation.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 illustrates a perspective view of a housing according to a first example;

Figure 2 illustrates a perspective view of the underside of the housing of Figure 1;

Figure 3 illustrates a top down view of the housing of Figure 1;

Figure 4 illustrates a perspective view of a housing according to the first example mounted onto a printed circuit board;

Figure 5 illustrates a perspective view of the underside of the housing mounted onto a printed circuit board of Figure 4;

Figure 6 illustrates a creepage distance of the transformer of Figures 4 and 5;

Figure 7 illustrates an electronic device formed from a printed circuit board mounted transformer, a magnetic core and input and output electrical windings;

Figure 8 is a cross-sectional view of an electronic device according to the first example;

Figure 9 illustrates a cross-sectional view of an electronic device according to a second example;

Figure 10 illustrates a housing according to the first example, further including a covering lid;

Figure 11 illustrates a first perspective view of an electronic device incorporating a housing according to a third example;

Figure 12 illustrates a second perspective view an electronic device incorporating a housing according to a third example;

Figure 13 illustrates a perspective view of an electronic device incorporating a housing according to a first embodiment of the invention;

Figure 14 illustrates a perspective view of an electronic device incorporating a housing according to the first embodiment of the invention; and

Figure 15 illustrates a perspective view of the underside of the electronic device incorporating a housing of Figure 14.

DETAILED DESCRIPTION

Figure 1 illustrates an insulating housing 10 for a transformer comprising a base 12. Four sidewalls 14 extend from the first or upper surface of the base 12 such that the housing 10 is substantially square or rectangular with the base 12 and the sidewalls 14 defining an internal cavity in the housing 10. The base 12 also has a second or mounting surface that is configured to mount the housing to a printed circuit board. Two projections or tabs 16 extend substantially perpendicularly from the second surface of the base 12 of the housing 10, as can be seen more clearly from Figure 2, which illustrates a perspective view of the underside of the housing 10.

However, it will be appreciated that any number of projections 16 may be provided, and that in some embodiments only a single projection may be provided. It is not essential for the projections 16 to extend perpendicularly from the mounting surface and alternative angles may be used within the scope of the present invention. Moreover, the base 12 and sidewalls 14 of the housing 10 may be configured to form another shape, e.g. a substantially circular or oval housing. In each of the Figures, like reference signs have been used to denote the same features.

The cavity of the housing 10 is configured to receive a magnetic core (not shown). A central pole 18 has been provided in the cavity to act as a supporting member for the magnetic core and to restrict the lateral movement of the magnetic core. Accordingly, the housing 10 may also be referred to as a transformer core tray or a transformer core cup. The central pole 18 has first 18a and second 18b wing sections extending in opposing directions. The housing 10 illustrated in the drawings has been configured to receive a substantially toroidal magnetic core in the cavity of the housing; however, it will be appreciated that other magnetic core geometries may be used in connection with the present invention and that the geometry of the housing 10 may be adapted to the geometry of the desired magnetic core. It will be appreciated that the invention may also be applied in conjunction with shell-type magnetic cores as well as single or multiphase cores and that the cores may have a solid construction or may alternatively be formed from laminated sheets. In one example, the magnetic core may be made of a ferrite material.

In the embodiment illustrated in Figure 1, there are two recesses 20 formed in the base 12 and a cutaway portion 22 is located at the top of three of the four sidewalls 14. The recesses 20 and cutaway portions 22 can also be seen from the view of the underside of the housing 10 in Figure 2. Figure 3 illustrates a top down view of the housing 10 of Figures 1 and 2 with the visible parts being labelled with the same reference numerals. The housing 10 is formed monolithically, i.e. formed in a single unit from a single piece of material with each of the features of the housing being integral to the housing 10 without joints or seams. In one embodiment, plastics of a suitable thickness to provide electrical insulation may be used as the material for forming the housing 10. However, it will be appreciated that alternative insulating materials may be used in order to form a housing according to the present invention.

Figure 4 illustrates the housing 10 of Figures 1 to 3 with the mounting surface of the base 12 mounted onto a substrate, in particular a printed circuit board (PCB) 24. The PCB 24 has a cut-out portion, slot or gap 25 that is shaped to receive the projection 16 of the housing 10 as can be seen more clearly in Figure 5, which illustrates the underside of the housing 10 and PCB 24.

The PCB 24 has an input or primary side (the left hand side of Figures 4 and 5) comprising input (primary) pins or connectors 26a and input (primary) control circuitry 28a for controlling the input side of the transformer. The PCB 24 also has an output or secondary side (the right hand side of Figures 4 and 5) comprising output (secondary) pins or connectors 26b and output (secondary) control circuitry 28b for controlling the output side of the transformer. Whilst reference numerals 28a and 28b only point to a single component of the input and output control circuitry respectively in the figures, the reference numerals will be used to refer to the respective input control circuitry 28a and output control circuitry 28b as a whole.

As can be seen from the right hand pin of input pins 26a in Figure 4, the recesses 20 of the housing 10 may be configured to enable the housing to extend over some components mounted on the PCB 24. These components may be pins 26a, 26b (as shown in Figure 4) or components of the control circuitry 28a, 28b. Whilst it will be appreciated that a minimum creepage and clearance distance is preferably maintained between the components of the input and output sides of the PCB 24, such as the input pins 26a and the output pins 26b, such recesses 20 enable the housing 10 to be mounted on the PCB 24 but to also provide an internal cavity that is larger in diameter than the minimum creepage and clearance distances. This enables larger magnetic cores to be contained within the housing 10, which in turn means that the transformer windings wound around the magnetic core may be provided with a larger number of turns.

In the configuration of Figures 4 and 5, it can be seen that the slot or gap 25 is a cut-out portion in the PCB 24 that creates a void through which a suitably sized object may be passed through such that the object is interposed between the input circuitry 28a and the output circuitry 28b. In such a configuration, the gap 25 may be a hole in the PCB 24. In some other configurations, the cut-out portion may extend across the entire width of the PCB 24 such that the PCB 24 is separated into two PCB portions - i.e. a first PCB having input circuitry 28a located thereon and a second PCB having output circuitry 28b located thereon. This further improves the creepage distance between the input circuitry and the output circuitry. In this other configuration, the gap refers to the space between the two separate portions of the PCB. Accordingly, the phrase ‘gap’ will be used to refer to the cutout portion of both of the configurations described above and illustrated in Figures 4 to 6 and Figure 13.

The projections 16 act to provide a degree of mechanical support and stability to the fixing of the housing 10 to the PCB 24 or other substrate, although additional mounting connections (not shown) may be provided to mount the mounting surface of the housing base 12 to the PCB 24. Moreover, by extending through the complementary gap 25 in the printed circuit board between the input circuitry 28a and output circuitry 28b, the insulating projections 16 also provide an improved creepage and clearance distance between the components of the input control circuitry 28a and the components of the output control circuitry 28b that are mounted on the underside of the PCB 24. This will be explained further with reference to Figure 6, which illustrates a creepage distance of the underside of the printed circuit board mounted transformer of Figures 4 and 5.

In the illustration of Figure 6, the minimum creepage distance is A and the dashed lines represent an area of width A, between the components of the input control circuitry 28a and the components of the output control circuitry 28b, which may be referred to as an isolation area. In the illustration, all of the pins 26a, 26b and control circuitry components 28a, 28b are positioned outside of the isolation area such that the minimum creepage distance A will be observed even in the absence of the housing 10 having projections 16. However, the projections 16 extending through the gap 25 in the PCB 24 and beyond the underside of the PCB form a wall between the components of the input control circuitry 28a and the components of the output control circuitry 28b that are mounted on the underside of the PCB 24. This increases the creepage distance between these respective components as shown by the line B in Figure 6. A corresponding increase in the clearance distance will also be provided by the walls of the projections 16 as will be appreciated by the skilled person.

The distance that the projections 16 extend through the PCB 24 is preferably determined by how close the components of the transformer circuitry are to the projection and how tall the components of the transformer circuitry may be. The distance that the projections 16 extend through the PCB 24 is preferably controlled in order to maintain the desired creepage and/or clearance gaps. By providing a plurality of projections 16 as shown, the projections may act to counter any creepage path around the projections, for example if a component was to be positioned towards the ends of a straight wall projection running across the isolation barrier. This advantageously enables more of the isolation barrier to be utilised without compromising the required creepage and/or clearance gap in comparison to embodiments in which there are fewer projections 16, in addition to the other advantages described above. In particular, this means that the profile of an electronic device incorporating the housing 10 may be further reduced thus improving the miniaturisation of the electronic device.

Accordingly, the housing 10 may provide an improved safety margin for the creepage and clearance distances. Alternatively, the respective components of the input control circuitry 28a and the output control circuitry 28b that are mounted on the underside of the PCB 24 may be positioned closer together (not shown), i.e. within the isolation area marked by the dashed line in Figure 6, whilst still meeting the minimum creepage and clearance requirements since the actual isolation area between the respective components will have been reduced by the presence of the projections 16. Accordingly, the housing 10 may alternatively enable improved miniaturisation of a PCB mounted transformer.

Figure 7 illustrates an electronic device 29 according to a second aspect, wherein the electronic device 29 is formed from the housing 10 mounted onto a PCB 24, a toroidal magnetic core 30 and input (primary) 32a and output (secondary) 32b electrical windings. However, the advantageous features described below are derived from the configuration of the housing 10 of the first aspect of the invention and accordingly the following description also applies to the first aspect.

The housing 10 and the PCB 24, as well as their corresponding features, are as described with reference to Figures 1 to 6. However, in Figure 7 an input electrical winding 32a has been wound directly around one side of the magnetic core 30, an output electrical winding 32b has been wound directly around the opposing side of the magnetic core 30, and the magnetic core and electrical windings have been lowered into the internal cavity of the housing 10. The electrical windings 32a, 32b are insulated wires and thus there is an insulating layer between the electrical windings and the magnetic core 30, which may be a ferrite magnetic core; however, this arrangement does act to minimise the leakage inductance in the transformer in comparison to arrangements wherein the magnetic core itself is encapsulated within a cover for a magnetic core. There may be more than one input electrical winding 32a and/or more than one output electrical winding provided, for example a feedback winding may be provided on the primary side of the PCB 24 and associated with the input circuit.

The magnetic core 30 is laterally supported by the first 18a and second 18b wings of the central pole I support member 18, which abut against the internal diameter of the magnetic core 30. The first 18a and second 18b wing portions advantageously position the magnetic core 30 of the transformer with increased security within the housing 10, whilst still enabling the windings to be wound around the magnetic core 30 at the points where the wings do not engage with the magnetic core 30. These wings 18a, 18b also act to prevent the input electrical winding 32a and the output electrical winding 32b from touching each other or overlapping since the windings cannot be wound round the magnetic core at the points where the wings 18a, 18b abut the internal diameter of the magnetic core 30.

Whilst the central pole or support member 18 provides structural rigidity to the first wing 18a and the second wing 18b, it may be omitted so that the first wing 18a and the second wing 18b are provided without the central pole 18. Moreover, whilst the central pole 18 and wings 18a 18b are preferred features, they are optional and may be omitted from the housing 10 and the electronic device 29.

The ends of the wires forming the electrical windings exit the housing 10 through one or more cutaway portions 22 in the walls 14 of the housing 10. This advantageously improves the routing of the wires from the electrical windings inside the housing 10 to the respective PCB connections outside of the housing 10. The number, size and position of the cutaway portions 22 or opening(s) may vary from application to application; however, it will be appreciated that appropriate cutaway portions 22 will be configured to match the requirements of a given transformer lead-out arrangement.

The cutaway portions 22 may be made as big as possible to allow the maximum space for potting to flow freely into the transformer cup if the fully assembled device is injected with encapsulation material, which minimises the likelihood of cavities forming in the encapsulation material and makes it easier to fill the housing 10. This encapsulation material, for example epoxy resin, may be injected into the cavity of housing 10 in order to provide additional mechanical support to the components within the housing as well as to provide additional electrical insulation. However, the impact of the cutaway portions on the creepage distance from the magnetic core 30 to the other components that are located outside of the housing 10 is preferably taken into account when dimensioning the housing 10.

In Figure 7, the wires of the input electrical winding 32a and the output electrical winding 32b exit the housing 10 through opposing cutaway portions 22, although the skilled person would appreciate that insulated wires forming the electrical windings 32a, 32b may be configured to exit the housing 10 using a single cutaway portion 22. The ends of the wires of the electrical windings 32a, 32b terminate on respective conductive pads 34a, 34b that may be connected to the components that make up the respective input 28a and output 28b circuitry as well as the input pins 26a and the output pins 26b.

In a similar manner to the plurality of projections 16, the walls 14 of the housing 10 are configured to maintain the creepage and clearance distance of the respective components of the input side and the output side of the PCB 24 when a magnetic core 30, which may be formed of a conductive material, is placed in between the input control circuitry 28a and output control circuitry 28b of the PCB 24. In this configuration, the minimum isolation distance between the components of the input control circuitry 28a and output control circuitry 28b of the PCB 24 is represented more accurately as the sum of the isolation distance between the input control circuitry 28a and the magnetic core 30, and the isolation distance between the magnetic core 30 and the output control circuitry 28b.

Thus, if the minimum total isolation distance is 8mm for example, then the isolation distance between each of the components of the control circuitry 28a and 28b, and the magnetic core 30 preferably adds up to at least 8mm. In one embodiment, the respective distance between each of the components of the control circuitry 28a and 28b, and the magnetic core 30 may be set to be equal, i.e. each distance may be set to be at least 4mm for example, i.e. at least half of the minimum total isolation distance. Alternatively, the isolation or creepage distance may be 3mm on the primary side (between the input control circuitry 28a and the magnetic core 30) and 5mm on the secondary side (between the magnetic core 30 and the output control circuitry 28b).

The same principle applies to the clearance distance between the magnetic core 30 and each of the components of the input 28a and output 28b control circuitry. Accordingly, the height and thickness of the walls 14 of the housing 10 are preferably configured to provide a creepage and clearance distance between the magnetic core 30 and each of the components of the input 28a and output 28b control circuitry of at least half the respective total creepage and clearance distance desired.

Accordingly, the electronic device 29 advantageously provides an improved safety margin of creepage and clearance distances between the input and output circuitry components on the opposing side of the printed circuit board to which the housing 10 is mounted and/or an improved miniaturisation of the electronic device 29 by facilitating the moving of the components of the printed circuit board transformer circuitry closer together.

Figure 8 is a cross-section of the electronic device 29 shown in Figure 7, cut along a diagonal line extending from the corner of the housing 10 having the recess 20 positioned above the output pins 26b and the diametrically opposite corner of the housing 10. This figure further illustrates the geometry of the recess 20 of a first embodiment. The wires of the input electrical winding 32a and the output electrical winding 32b have not been shown in this figure for the sake of clarity. It is noted that the housing 10 shown in Figures 1 to 8 comprises two recesses 20 located on the corners adjacent the input pins 26a and the output pins 26b. However, the skilled person will appreciate that a single recess 20 may be provided or alternatively any number of recesses 20 may be provided around the base 12 of the housing 10. Moreover, the recesses 20 do not need to be located on a corner of the base 12 of the housing 10.

Figure 9 is a simplified cross-section of an electronic device according to a second embodiment. In the second embodiment, the recess 20 is in the form of a lip or overhang that extends along the length of at least the sides of the housing 10 positioned above the input control circuitry 28a and the output control circuitry 28b. The overhanging recess 20 may optionally extend around the whole circumference of the housing 10. Although not all of the components of the first embodiment of the invention are depicted in the simplified schematic of Figure 9, the only intended difference between the first and second embodiments is the geometry of the recess as described above.

Figure 10 is another simplified illustration showing a lid 36 for the housing 10. In Figure 10, the lid 36 shown extends across the top of the housing 10 as well as extending down the sides of the housing 10. The lid 36 is configured to abut against at least part of the plurality of sidewalls 14 and to substantially enclose the cavity of the housing 10. Lid 36 acts to provide an insulation barrier between the magnetic core 30 and any other components that may be mounted to other surfaces above the transformer housing 10. It will be appreciated that the transformer may be mounted in a horizontal axis, a vertical axis or at some other angle and accordingly said other components need not necessarily be vertically above the magnetic core 30. This advantageously provides further electrical insulation and an additional barrier to conduction between the magnetic core 30 of the transformer and any neighbouring components that may be mounted in the vicinity of the transformer.

The shape of the lid 36 is configured to maintain the channel through which the wires of the input 34a and output 34b electrical windings exit the housing and extend to the PCB 24 as shown in Figure 10. However, it will be appreciated that the lid 36 may extend across the top of the housing 10 without extending down the sides of the housing 10.

In one embodiment, the lid 36 may comprise one or more holes for receiving encapsulation material that may be injected into the housing cavity. This advantageously enables an encapsulation material, such as epoxy resin, to be injected into the cavity of housing 10 in order to provide additional mechanical support to the components within the housing as well as providing additional electrical insulation.

The housing 10 and the electric device 29 described above may be used in any magnetic transformer component. In particular, the housing 10 and the electric device 29 may be used in a DC-to-DC converter.

Figures 11 and 12 illustrate two different perspective views of an electronic device incorporating a housing 10 according to a third embodiment. In this third embodiment, the housing 10 further comprises a first electrically insulating shelf 38a and a second electrically insulating shelf 38b. The first and second electrically insulating shelves 38a, 38b protrude from opposing sides of the top of the housing 10 in the vicinity of the cutaway portions 22. It will be appreciated that in this embodiment, only two cutaway portions 22 have been illustrated and that two corresponding electrically insulating shelves have been provided. However, a single, or any number of electrically insulating shelves may be provided as desired and the number of electrically insulating shelves need not be the same as the number of cutaway portions.

These electrically insulating shelves act as further isolation barriers, in particular with the aim of extending the creepage and clearance paths for any tall components that are placed alongside the housing 10, which might otherwise negate the creepage and clearance distances extending up the side of the housing 10. These electrically insulating shelves 38a, 38b may extend vertically as well as horizontally as shown by section 38a’ and 38b’; however, it is important to note that this vertical section is optional.

As shown in Figures 11 and 12, cutaway portions similar to the cutaway portions 22 have been included in the first and second electrically insulating shelves 38a, 38b. Moreover, whilst the vertical sections 38a’ and 38b’ have only been included at the rear faces of the first and second electrically insulating shelves 38a, 38b as seen from Figures 11 and 12, it will be appreciated that the vertical sections may instead, or in addition, be located at the front faces of the first and second electrically insulating shelves 38a, 38b. Furthermore, the electrically insulating shelves may be provided at any height part way up the total height of the sidewall 14 of the housing 10.

Figure 13 illustrates a perspective view of the underside of an electronic device according to a fourth embodiment. In this embodiment, the PCB 24 has been configured with a cut-out portion or gap 25 that extends across the entire width of the PCB 24 such that the PCB 24 is separated into two PCB portions - i.e. a first PCB 24a having input control circuitry 28a located thereon and a second PCB 24b having output control circuitry 28b located thereon. In this configuration, the first PCB 24a and the second PCB 24b may be positioned adjacent each other with the gap 25 between them as shown in Figure 13. This separation of the PCB 24 into a first PCB 24a and a second PCB 24b further improves the creepage distance between the input circuitry and the output circuitry.

In this configuration, the projection 16 of the housing 10 may extend through the gap 25 between the first PCB 24a and the second PCB 24b, i.e. the projection extends into and through the space or interval between the first PCB 24a and the second PCB 24b. As the skilled person will understand from the above, the gap 25 may be a hole or slot in an object (e.g. the PCB) or alternatively the gap 25 may be a space, interval, or hole between two separate objects (e.g the respective PCBs 24a and 24b). Accordingly, the phrase ‘gap’ will be understood by the skilled person to cover both of these variations.

Moreover, the housing of Figure 13 further comprises an auxiliary projection 17 extending out from a sidewall 14 of the housing. As shown in Figure 13, the sidewall 14 of the housing that the auxiliary projection 17 extends from is preferably the sidewall 14 that is adjacent to both the input pins 26a and the output pins 26b. The input pins 26a and the output pins 26b are provided for connection of the electronic device to another electronic component, that may be referred to as a principal component. The principle component may include a principle PCB or substrate that may be provided with pads or through holes for connection with the input pins 26a and output pins 26b.

In the configuration illustrated in Figures 14 and 15, a principle substrate 40 is shown facing a sidewall of the housing and having through holes 27a and 27b for the input pins 26a and output pins 26b respectively. These through holes facilitate electrical connection of the electronic device to the principle component. Moreover, the auxiliary projection 17 is shaped and configured to extend through a corresponding cut-away portion, slot or gap 42 in the principle substrate 40.

In this manner, the auxiliary projection may act to improve the creepage and clearance distances along the principle substrate 40 between the input pins 26a and output pins 26b. This means that the dimensions of an isolation area of the principle substrate 40 may be reduced and the components mounted on the principle substrate 40 may be moved comparatively closer together, thus further facilitating the miniaturisation of systems including an electronic device comprising the transformer and mounted to the principle substrate 40.

In Figures 13 to 15, the projection 16 and the auxiliary projection 17 are shown as merging together to form a single projection that extends from both the second surface of the base 12 and one of the plurality of sidewalls 14. This advantageously simplifies the formation of the projection 16 and the auxiliary projection 17. However, this is not necessary and the projection 16 and the auxiliary projection 17 may alternatively be formed as separate projections from the housing.

In Figures 14 and 15, a line box 44 is additionally shown surrounding the electronic device. This line box 44 corresponds to an encapsulation box that may be provided around the electronic device to be filled with encapsulation material. This encapsulation material advantageously increases the mechanical support, structural integrity and stability of the electronic device as well as improving the insulating characteristics between isolated elements of the electronic device. This is particularly advantageous in embodiments where the electronic device is formed using a separate first PCB 24a and second PCB24b. As an example, the encapsulation box may be made of plastic and the encapsulation material may be an epoxy resin.

Whist the additional features of Figures 13 to 15 have been described together, it will be appreciated that these additional features may be incorporated with the embodiments previously described above.

In a third aspect, a method for constructing a printed circuit board transformer is provided. The method comprises winding at least one input electrical winding 32a around a portion of a magnetic core 30 and winding at least one output electrical winding 32b around a portion of the magnetic core 30 with desired numbers of turns respectively to form a transformer. The windings may be hand wound or alternatively machine wound and appropriately insulated wire is preferably used. The method further comprises inserting the magnetic core 30, with the input electrical winding 32a and the output electrical winding 32b, into a housing 10 according to the first aspect. The method further comprises mounting the housing 10 to a substrate, such as a PCB 24 so that the at least one projection 16 extends from the mounting surface of the base 12, through a corresponding gap 25 in the PCB 24. The PCB 24 has input 28a and output 28b circuitry mounted thereon and the gap is located in an isolation area defined by the space between the respective conductive elements of the input circuitry 28a and the output circuitry 28b. The method further comprises electrically connecting the wires of the at least one input electrical winding 32a and the at least one output electrical winding 32b to corresponding conductive pads 34a, 34b of the input circuitry 28a and output circuitry 28b of the PCB 24 respectively.

The resulting electronic device 29 has improved electrical insulation and maintains the desired creepage and clearance gaps between the respective components of the input circuitry 28a and the output circuitry 28b via the magnetic core 30 of the transformer. Moreover, the method advantageously enables the dimensions of the isolation area to be reduced and the components of the transformer circuitry to be moved comparatively closer together on the printed circuit board or other substrate, thus facilitating the production of miniaturised printed circuit board mounted transformers. together on the printed circuit board or other substrate, thus facilitating the production of miniaturised printed circuit board mounted transformers.

In configurations where the PCB 24 is formed from a separate first PCB 24a having input circuitry located thereon and a separate second PCB 24b having output circuitry located thereon, the step of mounting the housing 10 to the PCB may comprise mounting the housing 10 to the first PCB 24a and the second PCB 24b.

The step of inserting the magnetic core 30 further comprises separating the input electrical winding 32a and the output electrical winding 32b such that they are on opposing sides of a first 18a and a second 18b wing section extending from the supporting member 18 towards the plurality of sidewalls 14 of the housing 10. This advantageously positions the magnetic core 30 of the transformer with increased security within the housing 10, whilst also preventing the input 32a or output 32b electrical windings on one side of the wing section 18a, 18b from coming into contact with the respective output 32b or input 32a electrical windings on the other side of the wing section 18a, 18b due to the engagement of the wing sections with the magnetic core 30. As described above, the wing sections 18a, 18b may be provided without the central pole 18.

The lid 36 may then be placed onto the housing 10 to substantially enclose the cavity with the lid 36, wherein the wires of the at least one input electrical winding 32a and the at least one output electrical winding 32b pass from the cavity to the respective conducting pads 34a, 34b through one or more cutaway portions 22 in the sidewalls 14 and/or through one or more cutaway portions in the lid 36. This advantageously provides further electrical insulation and an additional barrier to conduction between the magnetic core 30 of the transformer and any neighbouring components that may be mounted in the vicinity of the transformer.

The method may further comprise injecting encapsulation material through at least one hole in the lid 36. This advantageously enables the encapsulation material to be injected into the housing cavity in order to provide additional mechanical support to the components within the housing 10 as well as providing additional electrical insulation to the components in the housing 10.

Various modifications to the example embodiments described above are possible and will occur to those skilled in the art without departing from the scope of the invention which is defined by the following claims. In particular, it should be understood that features described in relation to a single embodiment can be present in other embodiments and that many of the features described are optional as set out in the summary of the invention and the following claims.

Claims

1. A housing for a transformer, comprising: a substrate; a base having a first surface and a second surface, wherein the second surface is a mounting surface for mounting the housing to the substrate; a plurality of sidewalls extending from the first surface of the base to form a cavity having a closed boundary; at least one projection extending from the second surface of the base; and an auxiliary projection extending from one of the plurality of sidewalls; wherein the housing is formed monolithically from an electrically insulating material; wherein the substrate comprises a first substrate having input circuitry located thereon and a second substrate having output circuitry located thereon, wherein the first substrate and the second substrate are separate and the at least one projection of the housing is configured to extend through a corresponding gap in the substrate between the first substrate and the second substrate; wherein the auxiliary projection is configured to: extend through a gap in a principle substrate; and extend between an input pin of the input circuitry located on the first substrate and an output pin of the output circuitry located on the second substrate; and wherein the cavity is arranged to receive a transformer comprising a magnetic core, an input electrical winding and an output electrical winding.

2. The housing of claim 1, wherein a plurality of electrically insulating projections extend monolithically from the second surface of the base.

3. The housing of claim 1 or 2, wherein the base further comprises one or more recesses such that the second surface of the housing does not extend across the entire base of the housing.

4. The housing of any preceding claim, further comprising a supporting member extending from the first surface of the base into the cavity, wherein the supporting member is configured to receive a magnetic core of a transformer.

5. The housing of claim 4, wherein the cavity of the housing and the supporting member are configured to receive a toroidal magnetic core of a transformer.

6. The housing of claim 4 or 5, wherein the supporting member further comprises first and second wing sections extending from the supporting member towards the plurality of sidewalls in substantially opposing directions and wherein the first and second wing sections are configured to substantially engage the surface of the magnetic core of the transformer.

7. The housing of any preceding claim, wherein at least one of the plurality of sidewalls comprises cutaway portions configured to receive the wires of the input electrical winding and/or the output electrical winding exiting from the cavity to connect to the substrate.

8. The housing of any preceding claim, further comprising a lid portion configured to abut against at least part of the plurality of sidewalls and to substantially enclose the housing cavity.

9. The housing of claim 8, wherein the lid portion is further configured to extend around the plurality of sidewalls.

10. The housing of claim 8 or 9, wherein the lid portion further comprises one or more holes for receiving encapsulation material being injected into the housing cavity.

11. The housing of any preceding claim, further comprising one or more electrically insulating shelves protruding substantially horizontally from one or more side walls of the housing.

12. The housing of claim 11, wherein at least one of the one or more electrically insulating shelves comprises cutaway portions configured to receive the wires of the input electrical winding and/or the output electrical winding exiting from the cavity to connect to the substrate.

13. The housing of any preceding claim, wherein the at least one projection and the auxiliary projection merge to form a single projection extending from both the second surface of the base and one of the plurality of sidewalls.

14. An electronic device comprising: a housing according to any of claims 1 to 13, the second surface of the housing being mounted onto the substrate such that the at least one projection extends from the second surface of the base, through the gap in the substrate and between the respective conductive elements of the input circuitry and the output circuitry; and a transformer comprising: a magnetic core located in the cavity of the housing; at least one input electrical winding wound around a portion of the magnetic core and extending from the housing to electrically connect to the input circuitry; and at least one output electrical winding wound around a portion of the magnetic core and extending from the housing to electrically connect to the output circuitry; wherein the gap in the substrate is located in an isolation area defined by the space between the respective conductive elements of the input circuitry and the output circuitry.

15. The electrical device of claim 14, wherein the at least one input electrical winding and the at least one output electrical winding comprise electrically insulated wires wound directly around the magnetic core.

16. The electrical device of claim 14 or 15, wherein the creepage distance from the conductive elements of the input circuitry to the magnetic core as well as the creepage distance from the magnetic core to the conductive elements of the output circuitry are both at least half the value of the creepage distance required between the respective components of the input circuitry and output circuitry.

17. The electrical device of any of claims 14 to 16, wherein the clearance distance from the conductive elements of the input circuitry to the magnetic core as well as the clearance distance from the magnetic core to the conductive elements of the output circuitry are both at least half the value of the clearance distance required between the respective components of the input circuitry and output circuitry.

18. A method for constructing a transformer, comprising: winding at least one input electrical winding around a portion of a magnetic core; winding at least one output electrical winding around a portion of the magnetic core; inserting the magnetic core with the input electrical winding and the output electrical winding into a housing according to any of claims 1 to 13; mounting the housing to the substrate of claim 1 such that the at least one projection extends, from the second surface of the base, through a corresponding gap in the substrate, wherein the substrate has input and output circuitry mounted thereon and the gap is located in an isolation area defined by the space between the respective conductive elements of the input circuitry and the output circuitry; and electrically connecting the wires of the at least one input electrical winding and the at least one output electrical winding to corresponding conductive pads of the input circuitry and output circuitry of the substrate respectively.

19. The method of claim 18, wherein the substrate comprises a first substrate having input circuitry located thereon and a second substrate having output circuitry located thereon, wherein the first substrate and the second substrate are separate and wherein mounting the housing to the substrate comprises mounting the housing to the first substrate and the second substrate.

20. The method of claim 18, wherein the housing is a housing according to claim 6 and the step of inserting the magnetic core further comprises separating the input electrical winding and the output electrical winding such that they are on opposing sides of the first and second wing sections extending from the supporting member towards the plurality of sidewalls of the housing.

21. The method of any of claims 18 to 20, wherein the method further comprises substantially enclosing the cavity using a lid portion, wherein the wires of the at least one input electrical winding and the at least one output electrical winding pass from the cavity to the respective conducting pads through one or more cutaway portions in the sidewalls and/or through one or more cutaway portions in the lid portion.

22. The method of claim 21, wherein the method further comprises injecting encapsulation material through at least one hole in the lid portion.