GB2544348A

GB2544348A - Low-profile LED drivers

Info

Publication number: GB2544348A
Application number: GB1520252.6A
Authority: GB
Inventors: Kelly Jamie
Original assignee: Tridonic GmbH and Co KG
Current assignee: Tridonic GmbH and Co KG
Priority date: 2015-11-10
Filing date: 2015-11-10
Publication date: 2017-05-17
Anticipated expiration: 2035-11-10
Also published as: GB2544348B; GB201520252D0

Abstract

An electronic device, such as an LED driver, comprises a casing 1 having an upper plate 1a and a lower plate 1b and an electronic component 3, such as an inductor or transformer, having a magnetic core 3a enclosed in the casing, wherein the magnetic core is in close contact with the casing. In this way, the magnetic core may function as a pillar to improve the stiffness of the casing and the casing may improve removal of heat from the magnetic core during operation.

Description

Low-profile LED drivers

The present invention relates to an electronic device according to the pre-characterizing part of claim 1.

For many purposes, an electronic device must be flat or slim. The outer dimensions of the electronic device depend on the electronic components and the case design, as the case has to provide protection against humidity and mechanical stress and to provide sufficient heat dissipation.

Electronic devices often contain electronic components having a magnetic core to confine and guide magnetic fields such as transformers and inductors. In particular, in power supplies or light emitting diode (LED) drivers using switching regulators or DC/DC converters, inductors are essential components. Even if the electronic device contains inductors, it is difficult to reduce the height because the ferrites of the inductors are one of the largest electronic components.

It is an object of the present invention to reduce the height of such electronic device.

Accordingly, the invention proposes an electronic device, which can be designed very flat.

This object is achieved by an electronic device according to the enclosed independent claim. Advantageous features of the present invention are defined in the corresponding subclaims .

According to the present invention, the electronic device comprises a casing having an upper plate and a lower plate and an electronic component having a magnetic core enclosed in the casing, wherein the magnetic core is in close contact with the upper plate and/or the lower plate.

Since there is no clearance or cap between the magnetic core and the upper plate and/or the lower plate, the height of the electronic device can be reduced and the electronic device can be designed very flat. Further, as the upper plate and/or the lower plate lies/acts on the magnetic core, the stiffness of the case structure can be improved.

The upper plate and/or the lower plate can be made from a thermally conductive material and the magnetic core can be connected to the upper plate and/or the lower plate in a heat-conducting manner. In this way, surface area over which the heat loss of the magnetic core can be dissipated is increased and the thermal resistance is reduced.

The upper plate and/or the lower plate can be made of metal and the magnetic core can be connected to the upper plate and/or the lower plate in a heat-conducting manner by an electrical insulator.

The upper plate and/or the lower plate can be made of aluminium and the electrical insulator can be an anodised layer of the aluminium.

The electrical insulator can be a layer of epoxy, a heat sink compound or a thermally conductive pad.

The upper plate and/or the lower plate can be supported by the magnetic core thus substituting pillars of a housing formed at least partially by the upper/lower plate.

The magnetic core can be a ferrite of an inductor.

The electronic component can be a component of a printed circuit board.

The electronic component can be mounted on the printed circuit board as floating component that pass through the printed circuit board and can be flexibly attached to the printed circuit board.

The printed circuit board can comprise a plurality of said electronic components, preferably having the same height.

Preferably, at least one semiconductor component mounted on the printed circuit board is in close contact with the upper plate and/or the lower plate.

The upper plate and the lower plate can be bent into U sections in cross section and can fit within each other in a heat-conducting manner.

The magnetic core can be clamped between the upper plate and the lower plate.

The invention is to be explained more detailed in the following with reference to the accompanying drawing, wherein: FIG. 1 shows, in schematic form, a first embodiment of the electronic device according to the present invention; FIG. 2 shows, in schematic form, a second embodiment of the electronic device according to the present invention; FIG. 3 shows, in schematic form, a third embodiment of the electronic device according to the present invention; FIG. 4 shows, in schematic form, a fourth embodiment of the electronic device according to the present invention; FIG. 5 shows, in schematic form, a fifth embodiment of the electronic device according to the present invention; FIG. 6 shows, in schematic form, a sixth embodiment of the electronic device according to the present invention; FIG. 7 shows, in schematic form, a seventh embodiment of the electronic device according to the present invention; and

Fig. 8 shows, in schematic form, an eighth embodiment of the electronic device according to the present invention.

The same features are denoted in the figures by the same reference signs. FIG. 1 shows a first embodiment of the electronic device according to the present invention, which is represented in a simplified manner in a sectional view. The electronic device can be a high frequency converter with a profile less than 8mm. Such converters are a particular area of interest in connection with LED lighting. Also associated with this are planar transformers and high frequency operation.

The electronic device shown in Fig. 1 comprises a casing 1 and a circuit board 2 that mechanically supports and electrically connects a transformer 3, a capacitor 4, diodes 5 and a power transistor 6.

The casing 1 is formed of an upper plate la, a lower plate lb, left-hand and right-hand side plates lc, Id and front and back plates (not shown). The upper plate la, the lower plate lb and the left-hand and right-hand side plates lc, Id can be produced from one piece, for example, a thin rectangular aluminium, steel or plastic tube, in which the circuit board 2 assembled with the electronic components 3..6 is inserted.

The transformer 3 is the largest electronic component of the electronic device shown in Fig. 1. The magnetic core 3a of the transformer 3 has a cube shape and the upper surface of the magnetic core 3a is parallel to the upper plate la. Since the magnetic core 3a is in close contact (no clearance) with the upper plate la, the casing 1 of the electronic device can be designed very flat. In Fig. 1, the length of the electronic device depends on the length of the circuit board 2 and the thickness of the side plates lc, Id, the height of the electronic device depends on the thickness of the circuit board 2, the thickness of the upper plate la and the lower plate lb and the height of the magnetic core 3a, and the depth of the electronic device depends on the depth of the circuit board 2 and the thickness of the front and back plates (not shown). To use the magnetic core as a stiffening member for the casing it should be placed in the center of upper plate la and lower plate lb.

Fig. 2 shows a second embodiment of the electronic device according to the present invention, in which the height of the electronic device is further reduced by omitting the circuit board 2. In Fig. 2, the magnetic core 3a of the transformer 3 is in close contact with the upper plate la and the lower plate lb. The electronic components 3..6 can be fixed at the lower plate lb by means of adhesive bonding.

In Figs. 1 and 2, the transformer 3 is arranged in the left half of the casing 1. In the third embodiment of the electronic device represented in FIG. 3, the thickness of the upper plate la and the lower plate lb is reduced and the transformer 3 is located centrally to improve the stiffness of the thin structure. In FIG. 3, the magnetic core 3a is in close contact with the upper plate la and the lower plate lb, and the lower plate lb is further supported by a first circuit board 2a and a second circuit board 2b, on which the power transistor 6, the diodes 5 and the capacitor 4 are mounted, respectively.

With the present invention, even if a plurality of transformers and/or inductors are included in the electronic device, magnetic cores/ferrite of the inductors/transformers can be used as pillars to improve the stiffness of the casing. A large transformer or inductor can be split into a number of smaller elements in order to support the casing 1 at various locations.

Fig. 4 shows a fourth embodiment of the electronic device according to the present invention, in which the magnetic core 3a of the transformer 3, a magnetic core 7a of an inductor 7 and a magnetic core 8a of an inductor 8 are arranged to improve the stiffness of the casing by supporting the upper plate la and the lower plate lb at various locations. In Fig. 4, the magnetic cores 3a, 7a and 8a are in close contact with the upper plate la and the lower plate lb, wherein the transformer 3 is located centrally, the inductor 7 is located in the left half of the casing and the inductor 8 is located in the right half of the casing. Even if the depth of the electronic device is equal to or greater than the length of the electronic device, two or more transformers or inductors can be also arranged in the depth dimension. In this way, the magnetic cores 3a, 7a and 8a used as pillars can be evenly distributed within the casing 1. In Fig. 4, other electronic components can be arranged between the inductor 7, the transformer 3 and inductor 8.

Magnetic components will be responsible for a large proportion of the overall heat loss in a converter, especially at high frequency. Getting heat out of magnetic components that run hot could lead also to size reduction.

In Figs. 1 to 4, the casing can be made from a thermally conductive material, for example, aluminium and the magnetic cores 3a, 7a, 8a can be connected to the upper plate la and/or the lower plate lb in a heat-conducting manner. If the magnetic cores 3a, 7a, 8a have to be electrically isolated against the casing, an electroinsulation lacquer can be provided on the entire casing or the contact area, or an anodised layer can be provided on an aluminium casing. Further, a heat sink compound can be placed between the magnetic cores 3a, 7a, 8a and the upper plate la and/or the lower plate lb to improve the dissipation performance.

Fig. 5 shows a fifth embodiment of the electronic device according to the present invention, in which the magnetic cores 3a, 7a, 8a are connected to the upper plate la and the lower plate lb in a heat-conducting manner by an electrical insulator 9. In this way, the casing 1 provides a double sided cooling of the magnetic cores 3a, 7a, 8a.

The electrical insulator 9 can be a thermally conductive pad or a layer of epoxy (e.g. "Master Bond FLM 36" or "Berquist Bond-Ply 800"). Preferably, the electrical insulator 9 is flexible enough to compensate for different heights of the magnetic cores 3a, 7a, 8a that will exist due to tolerances.

In Fig. 5, the upper plate la and the lower plate lb are bent into U sections that fit within each other. A deformable/flexible filler 10 is injected into the gap, allowing heat to transfer from one half of the casing 1 to the other even if the heat loss from each half of the casing 1 will probably be different.

Fig. 6 shows a sixth embodiment of the electronic device according to the present invention, in which the U-sections are hooked together by connecting ribs 11. In Figs. 5 and 6, at least one of the upper plate la and the lower plate lb is elastic and the magnetic cores 3a, 7a, 8a are clamped between the upper plate la and the lower plate lb fitted together. Spring force is used to pull the U-sections together.

Fig. 7 shows a seventh embodiment of the electronic device according to the present invention, in which the magnetic cores 3a and 7a are connected to the upper plate la and the lower plate lb in a heat-conducting manner by the electrical insulator 9 and the power transistor 6 is connected to the lower plate lb in a heat-conducting manner by the electrical insulator 9. The power transistor 6 is mounted to the underside of the circuit board 2, so that the height of the power transistor 6 must not be higher than the passive components of the circuit board 2.

Other semiconductors can be connected to the casing 1 in a heat-conducting manner. The casing 1 made from a thermally conductive material transports heat generated from the semiconductors outwards. Preferably, the semiconductors are designed to heatsink from the top face.

In Fig 7, the transformer 3 and the inductor 7 are mounted on the (printed) circuit board 2 as floating component that pass through the circuit board 2 and thus projects on both sides. It is therefore in contact with both plates la, lb but leaves also space on both sides of the printed circuit board 2 for semiconductor devices. Transformer 3 and inductor 7 are flexibly attached to the pcb 2 for example by elastic bonding. This elasticity could also be used to bias the semiconductor elements onto either the upper of the lower plate la, lb for improved heat transfer. To achieve this the position of the inductor 7/transformer 3 relative to the peb2 might be non-symmetric in the height direction. Fig. 8 shows an eighth embodiment of the electronic device according to the present invention, in which the circuit board 2 is fixed/positioned in the casing 1 by holding pieces 12 provided on the lower plate lb and holding pieces 13 provided on the upper plate la. In this way, the circuit board 2 and the magnetic cores 3a and 7a are hold by casing 1, wherein the power transistor 6 mounted to the underside of the circuit board 2 is pressed onto the lower plate lb.

The U-sections of the casing 1 can be assembled using glue to fill gaps and bond components to the anodised surfaces of the plates la, lb, lc, Id. Alternatively, a viscous or flexible heat transfer material can be used.

Claims

1. An electronic device comprising a casing (1) having an upper plate (la) and a lower plate (lb); and an electronic component (3, 7, 8) having a magnetic core (3a, 7a, 8a) enclosed in the casing (1), characterized in that the magnetic core (3a, 7a, 8a) is in close contact with the upper plate (la) and/or the lower plate (lb).

2. The electronic device according to claim 1, wherein the upper plate (la) and/or the lower plate (lb) is made from a thermally conductive material and the magnetic core (3a, 7a, 8a) is connected to the upper plate (la) and/or the lower plate (lb) in a heat-conducting manner.

3. The electronic device according to claim 2, wherein the upper plate (la) and/or the lower plate (lb) is made of metal and the magnetic core (3a, 7a, 8a) is connected to the upper plate (la) and/or the lower plate (lb) in a heat-conducting manner by an electrical insulator (9).

4. The electronic device according to claim 3, wherein the upper plate (la) and/or the lower plate (lb) is made of aluminium and the electrical insulator (9) is an anodised layer of the aluminium.

5. The electronic device according to claim 3, wherein the electrical insulator (9) is a layer of epoxy, a heat sink compound or a thermally conductive pad.

6. The electronic device according to anyone of claims 1 to 5, wherein the upper plate (la) and/or the lower plate (lb) is supported by the magnetic core (3a, 7a, 8a).

7. The electronic device according to anyone of claims 1 to 6, wherein the magnetic core (3a, 7a, 8a) is a ferrite of an inductor .

8. The electronic device according to anyone of claims 1 to 7, wherein the electronic component (3, 7, 8) is a component of a printed circuit board (2) .

9. The electronic device according to claim 8, wherein the electronic component (3, 7, 8) is mounted on the printed circuit board (2) as floating component that passes through the printed circuit board (2) and is flexibly attached the printed circuit board (2).

10. The electronic device according to claim 8 or 9, wherein the printed circuit board (2) comprises a plurality of said electronic components (3, 7, 8).

11. The electronic device according to anyone of claims 8 to 10, wherein at least one semiconductor component (5, 6) in addition to the electronic component(s) (3, 7, 8) is mounted on the printed circuit board (2) and in close contact with the upper plate (la) and/or the lower plate (lb) .

12. The electronic device according to anyone of claims 1 to 11, wherein the upper plate (la) and the lower plate (lb) are bent into U sections in cross section and are fit within each other in a heat-conducting manner.

13. The electronic device according to anyone of claims 1 to 12, wherein the magnetic core (3a, 7a, 8a) is clamped between the upper plate (la) and the lower plate (lb).