WO2021198851A1

WO2021198851A1 - Headlamp assembly

Info

Publication number: WO2021198851A1
Application number: PCT/IB2021/052416
Authority: WO
Inventors: Sunil Kumar CHIPPA; Godwin George; Samraj Jabez Dhinagar
Original assignee: Tvs Motor Company Limited
Priority date: 2020-03-31
Filing date: 2021-03-24
Publication date: 2021-10-07
Also published as: CN115398143A; EP4127558A1

Abstract

The present subject matter relates to a headlamp assembly (104) that includes a circuit board assembly (202, 204) comprising a printed circuit board and a plurality of LEDs (206a-d) secured to the printed circuit board. A holder (208) may be used to secure the circuit board assembly (202, 204). A heat pipe (214a, 214b) may be coupled to the holder (208) and at least one heat sink (212) may be coupled to the heat pipe (214a, 214b) and the holder (208). The heat pipe (214a, 214b) may conduct heat generated by the plurality of LEDs (206a- d) to the holder (208) and to the heat sink (212) to dissipate the heat. The headlamp assembly may be retrofittable to a reflector (102).

Description

HEADLAMP ASSEMBLY

TECHNICAL FIELD

[0001] The subject matter described herein, in general, relates to a headlamp assembly, and in particular to a headlamp assembly for vehicles that uses light emitting diode (LED) lamps.

BACKGROUND

[0002] Lighting systems of motor vehicles comprise lighting and signalling devices that are mounted or integrated to the front, rear, sides and in some cases to the top of the motor vehicles. The lighting systems may include head lamps, turn signal lamps, fog lamps and tail lamps consuming most of the power either from vehicle battery or alternator in the motor vehicles.

[0003] Generally, halogen lamps and incandescent bulbs are used in the lighting systems by vehicle manufacturers due to low installation cost and ease of replacement and maintenance. In some implementations, LED lamps that include a plurality of LED units may be used in the lighting systems of motor vehicles, for example, in the headlamp assembly.

BRIEL DESCRIPTION OF DRAWINGS

[0004] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

[0005] Fig. la illustrates a perspective view of a LED headlight when viewed from front of a vehicle, in accordance with an example implementation of the present subject matter. [0006] Fig. lb illustrates a back view of a LED headlight when an LED headlamp assembly is retrofitted to a reflector, in accordance with an example implementation of the present subject matter.

[0007] Fig. 2 illustrates an exploded view of an LED headlamp assembly, in accordance with an example implementation of the present subject matter.

[0008] Fig. 3 illustrates an isometric view of an arrangement of a cover over a housing of an LED headlamp assembly, in accordance with an example implementation of the subject-matter.

[0009] Fig. 4a illustrates a top view of a housing on which a first circuit board assembly is fastened, in accordance with an example implementation of the present subject matter.

[0010] Fig. 4b illustrates a side view of a housing on which a second circuit board assembly is fastened, in accordance with an example implementation of the present subject matter. [0011] Fig. 5a illustrates a side view of a heat sink connected to a housing, in accordance with an example implementation of the present subject matter.

[0012] Fig. 5b illustrates an exploded view of a heat sink disconnected from a housing, in accordance with an example implementation of the present subject matter.

[0013] Fig. 6 illustrates a control circuit diagram for operating a LED headlight, in accordance with an example implementation of the subject-matter.

DETAILED DESCRIPTION

[0014] Conventional filament-based halogen bulbs used in headlights of motor vehicles are inefficient as they consume high power from the vehicle battery. The lifespan of halogen bulbs is also less owing to the likelihood of the filament-based bulbs being damaged due to vibrations and shocks in the vehicles, thus requiring frequent replacement of the halogen bulbs. In cases where the halogen bulbs are mounted within the reflector for illuminating the light beam, oftentimes, entire reflector has to be changed for replacing the bulb during bulb failure.

[0015] In contrast to halogen bulbs, light emitting diode (LED) bulbs have a longer lifespan. In addition, the response time of LED bulbs is also very less, and it achieves full brightness instantly. Performance of the LED bulbs, however, largely depends on the ambient temperature of the operating environment. Over-driving the LED bulbs in high ambient temperatures may result in overheating of LED electrical base and eventually leading to device failure. In such a case, heat dissipation from source of heat generation needs to be executed at a fast rate for regulating the temperature of the LED electrical base under its normal acceptable operating limits.

[0016] Generally, heat sink plates, such as an aluminium heat sink plates or thermally conductive plastic heat sink plates, are used as heat sinks to dissipate the heat generated at the electrical base of the LED. However, heat often remains accumulated on the surface of heat sink plates and the LED electrical base, which over a time of continuous operation, experiences significantly high temperature that may lead to failure of the LED. Hence, typical LED headlamps have a completely different design from halogen or incandescent headlamps and the holders and reflectors for LED headlamps have to be customized for heat dissipation. As a result, LED headlamps are not usable with reflectors and holders that use incandescent bulbs or amongst themselves and because of which LED headlamps are not commonly used.

[0017] The present subject matter provides a LED headlamp assembly for facilitating heat dissipation that requires substantially low maintenance and helps solve the aforementioned and other problems and provides various advantages as will be understood from the following description.

[0018] According to an aspect of the present invention, the LED headlamp assembly includes a circuit board assembly comprising one or more printed circuit boards (PCBs) and a plurality of light emitting diodes (LEDs) secured to a PCBs. The LED headlamp assembly can be retrofitted into any existing reflectors of the vehicle. The LED headlamp assembly further includes a holder to secure the circuit board assembly. The holder is a thermally conductive plastic holder. In addition, the LED headlamp assembly comprises a heat pipe thermally coupled to the holder. At least one heat sink is coupled to the holder. The heat pipe conducts heat generated by the plurality of light emitting diodes (LEDs) away from the LEDS to the holder and to the heat sink to dissipate heat.

[0019] According to the present invention, the heat generated at the electrical base of the circuit board assembly by the plurality of LED lights, may be dissipated via the thermally conductive plastic holder. Also, a thermal conductive material such as a thermal conductive paste or liquid may be applied to a side of a metal core of the circuit board assembly facing the holder for better heat transfer from an electrical base of printed circuit boards. The thermal conductive material acts as a medium which fills air gaps between two surfaces between which heat needs to flow without any hot spot. The thermal conductive material may also be applied to provide a heat- conducting path to the heat sink such that a heat build-up does not occur. In an example implementation, a thermal interface material, which may be similar to the thermal conductive material or a non-adhesive thermal conductive paste, may also be applied between the circuit board assembly and the holder for enhancing the thermal coupling between them. An adhesive thermal conductive paste or liquid that acts as an adhesive may be applied between the heat pipe and the holder and between the heat pipe and the heat sink to dissipate heat from LEDs to heat sink via heat pipes.

[0020] The heat pipe of the retrofittable LED headlamp assembly may include a first section having a straight shape and a second section having a curved shape. This results in a J-shaped heat pipe where the stem of the J-shape corresponds to the first section and the curve of the J shape corresponds to the second section. In an example, heat transfer path through the heat pipe originates from the point where the heat pipe interfaces with the holder and terminates at the point where the heat pipe interfaces with the heatsink. This way the J-shaped heat pipe allows for dissipation of the heat from the circuit board assemblies to the heat sink. The J-shaped design of the heat pipe avoids heat from accumulating at the junctions of sections of the heat pipe to facilitate smooth transfer of heat. This shape of the heat pipe enables maximum thermal distribution and thus heat generated at the electrical base of the circuit board assembly by the plurality of LED lights is dissipated in an efficient manner through the heat pipes.

[0021] In an implementation of the present subject matter, the LED headlamp assembly is retrofittable on to the reflector of the vehicle. In one embodiment, a reflector is a plastic reflector coated with reflective material like silver or chrome such that light emitting from the LED falls on the reflector surface and gets reflected on to the road in an angle depending on the structure of the reflector surface. To allow the LED headlamp assembly to be retrofittable, the size of holder of the LED headlamp assembly and the size of the LED headlamp assembly are made as per the same standard specifications used for connecting incandescent lamps, such as S2 lamp. This is made possible by the heat dissipation arrangement provided in the LED headlamp assembly that is able to effectively dissipate heat from the small sized assembly also. The reflector may be detachably attached to the holder of the LED headlamp assembly via a clip, such that the holder is located in a recess provided in the reflector. In this manner, the LED headlamp assembly may be easily retrofitted without changing the reflector. Moreover, in case of LED failure, the entire assembly along with reflector need not be replaced and only individual malfunctioning LEDs may be replaced and thus huge investment in repair and maintenance may be avoided. [0022] The following description refers to the accompanying drawings.

Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar parts. While several examples are described in the description, modifications, adaptations, and other implementations are possible. Accordingly, the following detailed description does not limit the disclosed examples. Instead, the proper scope of the disclosed examples may be defined by the appended claims.

[0023] Fig. la illustrates a front view of the LED headlight 100 of a vehicle, in accordance with an example implementation of the present subject matter. The LED headlight 100 includes a reflector 102 comprising a recess. A LED headlamp assembly (not shown in figure) may easily be attached or detached via this recess, such that the LED headlamp assembly may be easily retrofitted without changing the reflector. In an example, the shape and size of the LED headlamp assembly and coupling mechanism provided in the LED headlamp assembly for coupling to the reflector may be made of the same specification as used for conventional halogen headlamps. Therefore, the LED headlight assembly can be easily retrofitted to the existing reflectors that use halogen headlamps without having to change the reflectors or the coupling mechanism. [0024] Fig. lb illustrates a back view of a LED headlight 100 when an LED headlamp assembly 104 is retrofitted to a reflector 102, in accordance with an example implementation of the present subject matter. The reflector 102 includes the recess where the LED headlight assemble may easily be attached or detached to a holder. [0025] Fig 2 illustrates an exploded view of an LED headlamp assembly, in accordance with an example implementation of the present subject matter. In an example, the LED headlamp assembly 104 may be retrofittable to conventional reflectors.

[0026] The LED headlamp assembly 104 may include circuit board assemblies 202, 204, each comprising a printed circuit board (PCB) and a plurality of light emitting diodes (LEDs) 206a-d arranged or secured on the printed circuit board. In one example, there may be two circuit boards assemblies, such as a first circuit board assembly 202 and a second circuit board assembly 204 as shown in the figure that are placed substantially perpendicular to each other, each circuit board assembly 202, 204 having one or more LEDs 206a-d arranged thereon to provide a particular pattern of light. The placement of the LEDs 206a-d may be selected based on the profile of the reflector 102 to which the LED headlamp assembly 104 is to be retrofitted. In one example, the LED placement may result in a pattern of light that mimics the light pattern of a conventional incandescent bulb source, thus making it possible to retrofit the LED headlamp assembly with a conventional reflector without having to change the reflector. [0027] In one example, a metal core printed circuit board (MCPCB) may be used as a printed circuit board. As may be understood, a metal core printed circuit board uses special substrate materials which are specifically formulated to improve the reliability of designs that run at higher than normal temperatures. The substrate actively draws heat from the locations of hot-running components through to the opposite layer of the board where it can dissipate heat efficiently and safety. Thus, a better thermal management with LED applications may be achieved using the metal core PCB to cool the PCB which uses a number of LEDs.

[0028] In one example, the LEDs 206a-d may be disposed on a first side, called a front side, of the circuit board assemblies 202, 204. A thermal conductive material such as a thermal conductive paste or liquid may be applied at a second side opposite to the first side, the second side being called a back side of the circuit board assembly 202,204, to enable heat transfer from the circuit board assembly to a holder 208. The circuit board assembly 202,204 may be mounted on the holder 208 via one or more screws or any other mounting means. This aids in better contact between the circuit board assembly 202, 204 and the holder 208, thereby preventing damage to the LED lights 206a-d during vibrations in the vehicles in which the LED headlamp assembly is fitted. In one example, the holder 208 may be a thermally conductive holder having a low thermal impedance for reducing the build-up of heat in the circuit board assembly 202, 204. The thermal impedance is defined as a measurement of temperature difference by which a material resists a heat flow, in this case the material being the thermally conductive holder. For example, the holder 208 may be made of a thermally conductive metal, such as Aluminium, or a thermally conductive plastic material.

[0029] The holder 208 provides support to the circuit board assembly 202, 204 and helps in coupling the LED headlamp assembly 104 to the reflector 102, for example, when retrofitting the LED headlamp assembly. The circuit board assembly 202, 204 may further be secured to the holder 105 via fasteners 210a-d. For example, M 2.5 type of fasteners may be used for mounting the circuit board assembly 202, 204 on the holder 208. The components of the LED headlamp assembly 104 may be secured on the holder 208 by a combination of different coupling mechanisms. For example, high tolerance mounting holes may be used for mounting the circuit board assembly 202, 204 on the holder to make sure that the circuit board assembly 202, 204 is not mounted with an offset and therefore ensuring the beam pattern is as desired.

[0030] The position of the LED mounting Solder mask defined (SMD) pads on the circuit board assembly 202, 204 may be manufactured under controller CAD-CAM process with high tolerance. Further, the assembly of the LEDs on the circuit board assembly 202, 204 on the designated positions may be performed using automatic component pick and place technology. Further end of line automated vision-based inspection of the correct placement of the LED Chip on the circuit board assembly may help in ensuring that the LEDs are correctly mounted on the circuit board assembly.

[0031] According to an example implementation, the holder 208 may provide a medium for heat dissipation from the LEDs 206a-d to a heat sink 212 via one or more heat pipes 214 a-b. In one example, two heat pipes may be used such as 214a and 214b as shown in the figure. A thermal interface material may be used in between the holder 208 and the heat pipes 214a-b to conduct heat from holder to the heat pipes in an efficient manner. The thermal interface material may be, for example, such as a Dow Corning® TC-5629 Thermally Conductive Compound. In an example, grab fasteners 216a-b may be used for securing the heat pipes 214a-b to the holder 208. A heat sink 212 may be coupled to the holder 208 using grab screws 218a-d and to the heat pipe 214a-b wherein the heat pipe 214a-b can conduct heat generated by the plurality of LEDs 206a-d to the holder 208 and to the heat sink 212. The heat sink 212 acts as a heat exchanger to transfer the heat generated by LEDs to a fluid medium, such as, air or liquid coolant, where heat is dissipated away from the LED, thereby allowing regulation of the temperature of the LED at optimal levels. In an example, the heat sink 212 may have straight fin type arrangement that runs the entire length of the heat sink which will be discussed further with reference to Fig. 5.

[0032] In an example implementation, the heat pipes 214a-b may be made of a thermal conductive material, such as a metal or thermally conductive plastic, to provide heat dissipation from the LEDs 206a-d to the heat sink 212. Due to high thermal conductivity of the heat pipe 214a-b, i.e., the ability of heat pipe 214a-b to conduct heat, the heat dissipation from the LEDs 206 a-d to the heat sink 212 may be performed in an efficient manner. In one example, the heat pipe 214a-b may include a heat transfer fluid for efficient transfer of heat. In one implementation, the thermal interface material may also be applied between the circuit board assembly 202, 204 and the holder 208. As discussed above, the thermal interface material may be any material that is inserted between two components in order to enhance the thermal coupling between them. The thermal interface material may be applied between the circuit board assembly 202,204 and the holder 208 for better heat transfer for heat dissipation. [0033] A thermal conductive paste or liquid that also act as adhesive material may additionally be applied between the heat pipe 214a-b and the holder 208 and between the holder 208 and heat sink 212 to enable better heat transfer. In general, thermal conductive pastes or liquids create a mechanical attachment of components with thermal transfer properties without the need for additional fasteners or may further strengthen the attachment provided by fasteners. In this manner, a high structural/mechanical bond strength may be created between the holder 208 and the heat pipe 214a-b and between the holder 208 and the heat sink 212. With such strong mechanical attachment, the LED headlamp assembly of the present invention is less prone to damage during vibration of the vehicle.

[0034] The heat pipe 214a-b of the LED headlamp assembly comprises a first section and a second section forming a substantial J-shape for dissipating the heat to the heat sink 212. The first section of the heat pipe 214a-b has a straight shape. The second section of the heat pipe 214a-b has a curved shape. The structure of the heat pipe 214a-b having a first straight section and a second curved section is designed to enable a continuous flow of fluid inside the heat pipe 214a-b. The J-shaped heat pipe avoids accumulation of heat at the junctions of the sections of the heat pipe and facilitates smooth transfer of heat. The J-shaped design of the heat pipe 214a-b thus aids in maximum thermal distribution and thus heat is dissipated in an efficient manner. The implementation of heat pipes 214a-b enables quick removal of heat from the LED electrical base to the heat sink 212 to regulate the temperature of the LED base and preventing the damage of the same.

[0035] In one example, the holder 208 may be formed in two sections- an elongated cuboidal section on whose sides the circuit board assemblies are fastened and a shortened cylindrical section. The elongated cuboidal section extends from the shortened cylindrical section. For discussion purposes, the elongated cuboidal section will be referred to as cuboidal section and the shortened cylindrical section will be referred to as cylindrical section. The cylindrical section can have a diameter that is greater than the width and height of the cuboidal section, but less than the length of the cuboidal section. The heat sink 212 may be disposed above the cylindrical section. [0036] Further, a part of the first section of the heat pipes 214a-b is inserted into the cuboidal section of the holder 208 to receive heat from the circuit board assembly 202, 204 through the surfaces of the cuboidal section. The remaining part of the first section of the heat pipes 214a-b is disposed in the cylindrical section of the holder 208. The second section of the heat pipes 214a-b extends out from the cylindrical section and curve backwards over the cylindrical section to be coupled to the heat sink 212 disposed above the cylindrical section. Hence, in operation, the heat pipes 214a-b can transfer heat from the circuit board assemblies 202, 204 to the heat sink 212 for increased heat dissipation. [0037] Typically, when incandescent bulbs are used, the heat generated is much less compared to heat generated when LED bulbs are used. Moreover, the heat generated by the incandescent bulbs is distributed over a surface of the bulb till the bulb holder. In order to dissipate the heat, the air surrounding the bulb and the material in contact with the bulb i.e., the reflector is sufficient in most cases to cool or maintain the surface temperature of the bulb. However, the incandescent bulbs have lower lifespan and may get damaged due to vibrations of vehicle. Whereas the heat generated by the LED headlamps is concentrated at the surface of the LED which has a much smaller area, for example, of 5 -6mm , as compared to the surface area of an incandescent bulb. Hence, conventionally, LED headlamps use large components for heat dissipation and therefore have a completely different size and design as compared to incandescent bulb-based headlamps and are not interchangeable or retrofittable.

[0038] In order to dissipate the huge amount of heat generated over the small area provided by an LED lamp, the present subject matter as discussed above discloses a LED headlamp assembly with various small sized heat dissipation mechanisms that work together. Due to the use of heat dissipation mechanisms that includes heat pipes, thermally conductive holder, metal PCB, thermal interface material, thermal conductive paste or liquid, and heat sink, the heat can be easily dissipated without having to increase the size of the components. Thus, a compact LED headlamp assembly of the same size as an incandescent lamp assembly can be obtained which can be retrofitted easily to any existing reflectors that otherwise use incandescent bulbs, without affecting the performance of the LED headlamp assembly. Further, the implementation of heat pipe helps in quick removal of heat from the LED base to the heat sink, which prevents an increase of the temperature of LED base and increases the life of the LED headlamp assembly.

[0039] In an implementation, a power supply assembly 220 including a DC power supply (not shown in figure) and a control circuit (not shown in figure) may supply power to the circuit board assembly 202, 204. The power supply assembly 220 may be connected to the LED headlamp assembly 104 through connectors 222a-b. A grommet 224 may provide path for wires 226 that connects the LEDs 206a-d to the connectors 222a-d. The grommet 224 prevents tugs or twists on the wire 226 from stressing electrical connections inside the LED headlamp assembly. [0040] Further, a cover 228 encloses the circuit board assembly 202, 204 coupled to the holder 208. The cover 228 may be fixed with fasteners to the holder 208. The cover 228 acts as a protection for the LED headlamp assembly 104 and prevents the LEDs, the circuit board assembly, and corresponding wires from tampering or damage. The cover 228 also provides an overall compact and aesthetic appearance to the LED headlamp assembly. The cover 228 also encloses the circuit board assembly and wires connecting them from environmental effects like dust and water

[0041] The reflector 102 may be detachably attached to the holder 208 via a clip 230 for easy removal of the holder 208 for replacement. An O-ring 232 ensures sealing of the circuit board assembly 202, 204 and wires connecting them. [0042] Fig. 3 illustrates an isometric exploded view of an arrangement of a cover over a housing of an LED headlamp assembly, in accordance with an example implementation of the subject-matter. The arrangement further illustrates components that are explained with respect to Fig. 2. As can be seen from Fig. 3, LEDs 206a and 206b are mounted on the first circuit board assembly 202 and the LEDs 206c and 206d are mounted on the second circuit board assembly 204. The circuit board assembly 202, 204 may be mounted on the holder via one or more screws. [0043] The cover 228 further comprises glass covered slits 302 to allow passage of light from the plurality of LEDs 206a-d to a reflector surface 102, so that the light reflects on to the surface of the road. The glass covered slits 302 help in beam formation from the LEDs 206a-d. The cover 228 is secured to a proximal end of the holder 105 via at least one or more fasteners. In addition, the cover 228 is fixed to a distal end of the holder 208 via two or more fasteners. A proximal end of the holder 208 may be understood as the end that is in proximity to the reflector, while the distal end may be understood as the end that is away from the reflector. The cover 228 is used to enclose the circuit board assembly 202, 204 coupled to the holder 208. The cover 228 may be a plastic cover designed to enclose the LEDs 206a-d, circuit board assembly and the corresponding wires. Enclosing the circuit board assembly and the corresponding wires through the cover 228 prevents access to any of these parts that can lead to tampering or damage of the LED module.

[0044] Further, the cylindrical section 304 of the holder 208 includes a step 306 and a cuboidal section 308 extending from the step 306. The cover 228 may be fitted on the cuboidal section 308 of the holder 208 such that a rim of the cover 228 is in contact with the step 306. An O-ring 232 (shown in Fig. 2) may be disposed between the holder 208 and the cover 228 to prevent entry of dust or moist air into the cover 228. Further, at the step 306, a thermal conductive paste or liquid that acts as an adhesive may be applied between the holder 208 and the cover 228 adjacent to the O- ring 232 for sealing the circuit board assembly 202,204 including the LEDs 206a-d. In addition, the O-ring 232 may also ensure sealing of the circuit board assembly 202,204 and the wires connecting them. The cover 228 may be used as a protection assembly for the circuit board assembly to prevent tampering of LEDs during vibration of the vehicle. The holder 208 also includes a bracket 310 onto which the heat sink 212 (shown in figure 2) is fastened.

[0045] The entire LED headlamp assembly along with the protection cover may be attached or detached to the holder via the recess on the reflector, such that, the LED headlamp assembly may be easily retrofitted without changing the reflector. The constant current for the LEDs in the LED headlamp assembly to function may be provided by the DC power supply. The holder being thermally conductive creates path for heat dissipation from the LEDs to the heat sink via heat pipe. The shape of the heat pipe avoids build-up of heat at the junctions of the sections of the heat pipe and thus enable faster and efficient removal of heat to the heat sink to avoid the LED electrical base from getting damaged due to overheating. The heat sink is designed, such that the heat dissipation happens within a very small area of the circuit board assembly.

[0046] Fig. 4a illustrates a top view of a housing on which a first circuit board assembly is fastened, in accordance with an example implementation of the present subject matter. Fig. 4b illustrates a side view of a housing on which a second circuit board assembly is fastened, in accordance with an example implementation of the present subject matter. As has been discussed, the first circuit board assembly 202 and the second circuit board assembly 204 are fastened on to the cuboidal section 308 of the holder 208. The circuit board assemblies 202,204 are substantially perpendicular to each other, each circuit board assembly 202, 204 having one or more LEDs 206a-d arranged thereon to provide a particular pattern of light. In an example, the LED 206a may be for beam operation and the LED 206b is for the improvement of light pattern in front of the vehicle. In an example, the LED 206c is for the beam operation and the LED 206d is for the for the improvement of light pattern in front of the vehicle.

[0047] In an example, the placement of the LEDs 206a-d may be selected based on the profile of the reflector (not shown in figure) to which the headlamp assembly is to be retrofitted. In one example, the LED placement may result in a pattern of light that mimics the light pattern of a conventional incandescent bulb source, thus making it possible to retrofit the headlamp assembly with a conventional reflector without having to change the reflector. [0048] Fig. 5a illustrates a side view of a heat sink connected to a housing, in accordance with an example implementation of the present subject matter. As shown in the figure, the heat sink 212 has a straight fin type arrangement that runs the entire length of the heat sink. The fin type arrangement allows the heat sink 212 to dissipate the heat generated from the LEDs to a fluid medium, such as, air or liquid coolant, thereby allowing regulation of the temperature of the LED at optimal levels. The heat sink is mounted on a bracket 310 of the holder 208 using grab screws 218a-d.

[0049] Fig. 5b illustrates an exploded view of a heat sink disconnected from a housing, in accordance with an example implementation of the present subject matter. As shown in Fig 5b, the heat sink 212 is disconnected from the bracket 310 of the holder 208. One or more grab screws 218 may be used for fastening the heat sink 212 on the holder 208.

[0050] Fig. 6 illustrates a control circuit 600 diagram for operating a LED headlight, in accordance with an example implementation of the subject-matter. The control circuit 600 as illustrated in Fig. 6 of the present invention may be built based on buck topology. Further, a buck converter (not shown in the figure) may be connected to a DC power supply 602 to transform the output voltage to a level less than an input voltage into an input circuit 604. The output voltage may be further provided to an LED module 606 which includes a high beam LED circuit and a low beam LED circuit via a switch unit 608. The input circuit 604 includes components such as a LED driver IC 610, a metal oxide semiconductor field effect transistor (MOSFET) 612, and an Inductor 614. In an example, the inductor 614 in the input circuit 604 may resist sudden variations in the input current. The ED driver IC 610 and [0051] The switch unit 608 may be used to control the two modes of operation of the headlamp. The two modes of operation may be a low beam condition and a high beam condition. A high beam (HB) and a low beam (LB) test point may be provided from where the supply may be given to the HB LED circuit and LB LED circuit respectively. The high beam point may be connected to a constant current (Ic) circuit via a first unidirectional circuit in series. The output of the first unidirectional circuit may be connected to the high beam LED. Similarly, a low beam point may be connected to a constant current (Ic) circuit, via a second unidirectional circuit in series, wherein the output of the second unidirectional circuit may be connected to the low beam LED. A third unidirectional circuit may also be connected between the high beam point and the low beam point. The high beam and low beam points may be connected via the third unidirectional circuit to isolate the high beam circuit during low beam condition.

[0052] When the switch may be at the high beam condition, the power from the supply may be connected to both high beam and low beam points via the unidirectional circuits. In another implementation, when the switch may be at a low beam condition, the power from the supply may be connected to only low beam point and the power to the high beam point may be blocked via the third unidirectional circuit. Thus, during the low beam condition, only the LB LED may glow while in high beam condition, both the LB and the HB LEDs may glow.

[0053] The control circuit of the present invention may also provide temperature protection for the LEDs via a thermal shutdown protection circuitry (not shown in the figure). As the temperature of the LEDs crosses a threshold value, the current in the circuit declines linearly with respect to the temperature, which means that the current reduces as the junction temperature crosses a threshold value, to prevent overheating.

[0054] The present invention thus provides various advantages, such as the heat dissipation from the LED source happens within a very small area of the metal core printed circuit board. Lurther, the placement of LEDs on the holder does not compromise with the light pattern with similar types of reflectors. The retrofittable LED headlamp module may be easily replaced without changing the reflector, thus huge investment in the reflector module may be avoided and overall adoption and use of LED headlamps may increase thereby reducing power consumed. [0055] Although the subject matter has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the subject matter, will become apparent to persons skilled in the art upon reference to the description of the subject matter. It is therefore contemplated that such modifications can be made without departing from the scope of the present subject matter as defined.

Claims

I/We Claim:

1. A headlamp assembly (104) comprising: a circuit board assembly (202, 204), comprising a printed circuit board and a plurality of light emitting diodes (LEDs) (206a-d) secured to the circuit board assembly (202, 204); a holder (208) to secure the circuit board assembly (202, 204), wherein the holder (208) is thermally conductive; a heat pipe (214a, 214b) thermally coupled to the holder (208), the heat pipe (214a, 214b) having a first section and a second section, the first section having a straight shape and the second section having a curved shape; and at least one heat sink (212) coupled to the holder (208) and to the heat pipe (214a, 214b), wherein the heat pipe (214a, 214b) is to conduct heat generated by the plurality of LEDs (206a-d) to the holder (208) and to the heat sink (212) to dissipate the heat.

2. The headlamp assembly (104) as claimed in claim 1 comprising: a cover (228) enclosing the circuit board assembly (202,204), the cover (228) being coupled to the holder (208), and wherein the cover (228) comprises glass covered slits (302) to allow passage of light from the plurality of LEDs (206a-d) to a reflector (102).

3. The headlamp assembly (104) as claimed in claim 2, comprising an O-ring

232 secured to the cover (228) to seal the headlamp assembly to the reflector (102).

4. The headlamp assembly (104) as claimed in claim 2, wherein the placement of the LEDs (206a-d) on the circuit board assembly (202,204) is fixed with respect to the holder (208) to provide a light pattern based on a reflector profile to which the headlamp assembly is to be coupled.

5. The headlamp assembly (104) as claimed in claim 1, wherein the holder (208) comprises a cylindrical section (304) and a cuboidal section (308) extending from the cylindrical section (304), wherein a first section of the heat pipe (214a, 214b) is inserted into the cylindrical section (304) and the cuboidal section 308, and a second section of heat pipe (214a, 214b) curves above the holder (208) and is coupled to the heat sink (212).

6. The headlamp assembly (104) as claimed in claim 1, comprising a clip (230) to detachably attach the holder (208) to a reflector (102).

7. The headlamp assembly (104) as claimed in claim 1, wherein the circuit board assembly (202,204) is coupled to the holder (208) by one or more fasteners (210a-d).

8. The headlamp assembly (104) as claimed in claim 1, wherein the heat pipe (214a, 214b) is coupled to the holder (208) by one or more grab fasteners (216a, 216b).

9. The headlamp assembly (104) as claimed in claim 1, wherein a thermal conductive material is provided on a side of the printed circuit board facing the holder.

10. The headlamp assembly (104) as claimed in claim 1, wherein the thermal conductive material is applied in between the holder (105) and the heat sink (212).

11. The headlamp assembly (104) as claimed in claim 1, wherein a thermal interface material is applied between the circuit board assembly (202, 204) and the holder (208).

12. The headlamp assembly (104) as claimed in claim 1, wherein a thermal conductive material is applied between the heat pipe (214a,214b) and the holder (208) and between the heat pipe (214a, 214b) and the heat sink (212).

13. The headlamp assembly as claimed in claim 1, wherein the headlamp assembly (104) is retrofittable to the reflector (102).

14. A control circuit (600) to operate a headlamp of a headlamp assembly as claimed in any one of claims 1-13, wherein the control circuit (600) comprises: a DC power supply (602) connected to a buck convertor to transform output voltage to a level lesser than an input voltage; an input circuit (604) connected to the DC power supply, wherein the input circuit is to receive the output voltage; and an LED module (606) to receive output voltage from the input circuit through a switch unit (608), wherein the LED module (606) comprises a high beam LED circuit and a low beam LED circuit for operation of a headlamp.

15. The control circuit (600) as claimed in claim 14, wherein, when the LED module (606) is operated in high beam, the switch unit (608) is to supply output voltage to low beam LED circuit and high beam LED circuit.

16. The control circuit (600) as claimed in claim 14, wherein when the LED module (606) is operated in low beam, the switch unit (608) is to supply output voltage to low beam LED circuit and cut off power to high beam LED circuit.