LIGHT EMITTING DIODE BASED LIGHTING DEVICE

The present disclosure relates to the field of lighting, especially lighting with a light emitting diode, LED. Specifically, this disclosure is directed to a device.

This application claims priority of German Patent Application No. 102021118870.9, the disclosure content of which is incorporated herein by reference.

A light-emitting diode, LED, is used as light source in a variety of applications, for example, in lighting. Lighting is employed in different fields, one of which is automotive lighting. In this field LEDs are used for building headlights or headlamps or backlights. Usually, an LED is made from optical semiconductors like gallium nitride or InGaAlP and is comprised in a housing which typically contains silicone. In particular, this disclosure addresses an intelligent combination of a light emitting semiconductor and a silicon integrated circuit, IC, with some electronic functionality.

In some areas of applications such LED is exposed to radiation, for example, sun light traveling back through the optical system to the LED. Although absorbed power density of the sun light usually does not harm the silicon and the LED - semiconductor, its housing may be burnt. In order to encounter potential sunburn, the LED's housing is equipped with a shield, for example a metal sunshield. Such known solution is depicted in Fig. 1. Fig. 1 shows a sectional view of an LED package, in particular an intelligent LED package, of the state of the art. An LED 13 is mounted to a driver chip 31 both of which are contained in a housing frame 11. A cavity 12 extending within the housing frame 11 encloses or holds the driver chip 31 and the LED chip 13 and is filled with casting material 12a. A globe top 32 dam on top of the silicon driver chip 31 avoids casting material 12a on the LED 13 and allows the casting material 12a to cover the wire bonds 9. The LED package has a substrate 30 to allow routing in the package. The application printed circuit board is not shown in figure 1. Globe top 32 and casting material 12 a can basically contain silicones or epoxies. The driver chip 31 is made from silicon. The LED 13 usually is gallium nitride GaN, which may be covered with a partially light converting material. An epoxy and/or silicone-based mold-material or compound is used for the frame part 11 of the housing. The LED 13 and the driver chip 31 are not affected by sunlight. However, silicones and epoxies risk to be burnt, especially if they have a dark tint for optical reasons. The problem becomes even more prominent in case a projector lens 33 is assembled relative to the LED array. Such projector lens 33 is usually employed in automotive headlamps if the LED is part of a controllable LED array.

For protecting the housing frame 11, globe top 32 and the casting material 12a against potential sunburn, a sunshield 34 is provided. The sunshield 34 is made from metal and has an opening or aperture for light generated by the LED 13.

However, the sunshield 34 causes optical losses as it blocks up to 50 or even 60 percent of the light or photons emitted by the LED 13. Furthermore, the heat occurring at the sunshield 34 caused by absorption of the sunlight has to be dissipated .

One objective can therefore be seen in providing a device which overcomes the shortcomings of the known solutions.

The objective is achieved by the subject-matter of the independent claim. Embodiments and developments are defined in the dependent claims.

In one embodiment a device comprises a housing frame, a cavity, a light-emitting diode, LED, and a layered structure. The cavity is enclosed by the housing frame. The LED is mounted within the cavity. The layered structure is configured to cover the cavity and comprises an aperture for light emitted by the LED. Therein, the layered structure is configured to generate energy from the light emitted by the LED. The device further comprises a capacitor which is configured to store the energy generated by the layered structure. The capacitor is mechanically and electrically coupled to the layered structure.

The housing frame encompasses the cavity in which the LED is mounted. The layered structure covers the cavity except for the aperture which gives way for light emitted by the LED. Light emitted by the LED is reused by the layered structure to generate energy. This energy can be leveraged within the device. The harvested energy is stored on the capacitor, for example, in the form of a voltage induced on the capacitor.

On the one hand the layered structure realizes a shield against sunlight hitting the device. On top of that, the layered structure generates energy from the light emitted by the device's LED. By this, light emitted by the LED which is blocked from leaving the device by the layered structure is reused for generating energy for the device. The generation of energy, in particular electrical energy, achieves a reduced amount of thermal energy dissipation within the layered structure. Energy of the light emitted by the device's LED is reused for generating electrical energy within the layered structure, which is provided to the device.

The generated energy may be used for control signals, biasing and or reference signal generation.

The device may also comprise a driver chip configured to drive the LED as known to those skilled in the art. The driver chip realizes the functions of an analog driver and a digital control. The LED can sit on this intelligent silicon driver chip.

The device may comprise more than one LED. In this case the LEDs may be arranged in an array.

In a development the layered structure comprises layers implementing at least one photodiode.

The layers realize for instance a pn-junction. The photodiode comprised by the layered structure harvests at least part of the optical energy generated by the device's LED. This process may be referred to as photo-recycling.

In a further development a sensitivity of the photodiode is adapted to a spectral distribution of the light emitted by the LED. By this the amount of energy which can be generated from the light emitted by the LED is increased.

In a development the layered structure comprises layers implementing a pair of photodiodes or multiple pairs of photodiodes. Therein, for each pair, the photodiodes are arranged side by side along a plane parallel to a surface of the LED facing the aperture. Therein, the photodiodes are electrically connected amongst each other in a series connection.

By this the amount of energy which can be generated from the light emitted by the LED is increased.

In a development in each pair of photodiodes a sensitivity of one photodiode is adapted to a blue emission spectrum of the spectral distribution of the light emitted by the LED and a sensitivity of the other photodiode is adapted to a yellow emission spectrum of the spectral distribution of the light emitted by the LED.

By this the amount of energy which can be generated from the light emitted by the LED is further increased.

In a development a size of the aperture of the layered structure depends on a size of the LED, a distance between the LED and the layered structure, and a predefined emitting angle.

The layered structure is mounted to the housing frame. This results in a certain distance between the LED and the layered structure. The device's LED or LED array acts as a Lambertian emitter, sending out photons within +/- 90° towards the perpendicular of the LEDs plane. The emitting angle is formed between the surface normal of the LED surface and the aperture. As known to those skilled in the art, a Lambertian emitter radiates 50 % of its optical power in an emitting angle between 45° and 90° according to Lambert's cosine law. These emissions cause stray light and can hardly be used by a projection lens system. The light emitted by the LED in the higher angles, not optically imaged into the target application is reused for generating electrical energy in the device.

In a development the emitting angle may be predefined to angles between 30 and 70 degrees, specifically angles between 35 and 60 degrees, more specifically angles between 40 and 50 degrees .

In an example, angles of approximately 45° to 55° are employed, driven by the numerical aperture of typical projection lens systems.

As optical elements, like the photodiode realized by the layered structure, accept light hitting its surface in a range of emitting angles between 0° and even higher angles than 70°, energy generation by means of the layered structure can be optimized by designing the size and distance of the aperture according to the definitions described above.

In a development, the layered structure is further configured to shield the device, in particular the housing frame and/or a casting material and/or a substrate from light, in particular sunlight. In addition to its function as generator of energy from the light emitted by the LED, the layered structure also works as a shield against sunlight.

Sunlight hitting the device may have an intensity in the range of 1 to 10 W/mm^.

Due to the energy harvesting within the layered structure, which at the same time works as sunshield, the remaining heat in this sunshield is reduced.

In an exemplary implementation, the size of the aperture is designed to be slightly smaller than the size of the LED. Optical losses caused by the aperture are even larger the further away from the LED surface the layered structure is mounted. This energy is harvested by the layered structure.

The housing of the device may comprise mold material, for instance silicone or epoxy.

In a development the layered structure comprises silicon.

The silicon is not affected by incident sunlight and consequently very well realizes the double function of shielding the rest of the housing against incident sunlight towards and generating energy from light emitted by the LED and the sunlight by converting at least part of said light into energy, for example, electrical current.

In a development the aperture of the layered structure is achieved by means of etching the layered structure. In an implementation example, the aperture is provided by means of a MEMS process on wafer scale. It may be referred to as a silicon aperture or silicon opening.

In a development an angle between a plane parallel to the surface of the LED which is facing the aperture and a sidewall of the aperture of the layered structure is an acute angle or an elongate angle or amounts to approximately 90°.

The angle between the plane parallel to the surface of the LED and the sidewall of the aperture influences the amount of photons emitted by the LED which enter the photodiode of the layered structure by one of the surfaces of said photodiode, e.g. by the sidewall. By adjusting said angle, the amount of harvested energy can be increased. The elongate angle may also be referred to as an obtuse angle.

In a further development the device comprises a transparent layer which is mounted to the layered structure such that the transparent layer covers the layered structure and the aperture .

By means of the transparent layer the LED of the device is protected against mechanical damage and particles. The transparent layer realizes a lid.

The transparent layer may comprise glass.

The transparent layer is bonded or directly bonded to the layered structure, for example by means of anodic bonding. Alternatively the transparent layer is directly fixed to the layered structure by means of metal contacts or adhesives.

The transparent layer may further have an anti-reflection coating on one side or both sides. This further increases the quota of photons incoupling into the layered structure's photodiode in case of the unwanted light and it increases the amount of wanted light traveling through the transparent lid.

In a development at least one surface of the layered structure is roughened.

The roughening of the surface of the layered structure increases the optical incoupling into the structured layer and therefore the absorption of photons. Furthermore, stray light reflected back to the LED and its driver chip is reduced. The amount of photon induced noise in the driver chip is thereby reduced.

In an exemplary implementation, micro roughening is used for roughening the layered structure's surface. In case silicon is used for implementing the layered structure, after the roughening the silicon looks black.

In a development at least one surface of the layered structure has a dielectric antireflection coating.

The electrical connection between the capacitor and the layered structure may optionally comprise a diode.

In a further development the device comprises a circuit which is connected to the capacitor. Therein, the circuit is configured to provide a direct voltage using the energy stored on the capacitor and/or a supply voltage provided by a voltage source that can be connected to the circuit. The circuit provides the direct voltage from the energy stored on the capacitor, i.e. the capacitor voltage. Alternatively, the direct voltage is provided by the circuit by additionally using the supply voltage from the voltage source which can be connected to the circuit, for example an external battery.

The direct voltage comprises a direct current voltage, DC- voltage .

In a further development the circuit is configured to operate in a first mode, in a second mode and in a third mode. In the first mode the direct voltage is supplied by converting the supply voltage only. In the second mode the direct voltage is supplied by converting the energy stored on the capacitor and converting the supply voltage. In the third mode the direct voltage is supplied by converting the energy stored on the capacitor only.

Depending on the amount of energy stored on the capacitor, for instance depending on the amount of voltage stored on the capacitor, the circuit operates either in the first or in the second mode or in the third mode. In the first mode the capacitor has no energy for contributing in provision of the direct voltage, such that the supply voltage is used instead. In the second mode the amount of energy stored on the capacitor is above zero, but is not sufficient for providing the direct voltage, such that the circuit additionally uses the supply voltage. In the first mode the capacitor has enough energy for furnishing the direct voltage.

The direct voltage supplied by the circuit may be used for an analog power supply or a digital power supply of the device. The circuit thereby achieves so called current balancing.

Said current balancing leads to a reduced current load on the voltage source which provides the supply voltage.

Furthermore, the difference in voltages between the direct voltage supplied by the circuit and the energy or voltage used for generation of said direct voltage, thereby increasing the energetic efficiency.

In an exemplary implementation the device is used in an automotive headlamp. The supply voltage is supplied by the car battery which provides about 12 V when the car is running. The device requires a digital power supply of approximately 1.8 V and an analog power supply of approximately 4 to 5 V. The voltage induced on the capacitor may amount to about 0.7 or 1.8 V. Consequently, the voltage stored on the capacitor is closer to the voltages needed within the device, which increases the efficiency of the device.

In a development the circuit comprises a first voltage converter and a second voltage converter, a first input, a second input and an output. The first input is configured to receive the energy stored on the capacitor, the second input is configured to receive the supply voltage. The output is configured to provide the direct voltage. The first voltage converter is connected between the first input and the output. The second voltage converter is connected between a second input and the output.

The first voltage converter converts the energy stored on the capacitor, e.g. the voltage stored on the capacitor, to the direct voltage provided at the output of the circuit. The second voltage converter converts the supply voltage to the direct voltage provided at the output of the circuit. By this, the direct voltage at the output of the circuit is maintained stable, i.e. its level is kept basically constant. Furthermore, the level of the direct voltage is independent of the amount of energy generated within the layered structure.

The circuit may be implemented within the driver chip, for example. Space consumption is thereby reduced.

In a development the first voltage converter comprises a DC/DC converter, in particular a step-up converter or a charge pump. The second voltage converter comprises a linear dropout converter, LDO.

The text below explains the proposed device in detail using exemplary embodiments with reference to the drawings. Components and circuit elements that are functionally identical or have the identical effect bear identical reference numbers. In so far as circuit parts or components correspond to one another in function, a description of them will not be repeated in each of the following figures. Therein,

Figure 1 shows a sectional view of an LED package of the state of the art,

Figure 2 shows an exemplary embodiment of the proposed device in a sectional view,

Figures 3A, B and C each show an exemplary realization of the proposed layered structure, Figure 4 shows another exemplary embodiment of the proposed device with the circuit, and

Figure 5 shows an exemplary embodiment of the proposed circuit.

Figure 2 shows an exemplary embodiment of the proposed device in a sectional view. The device 10 comprises a housing frame 11, a cavity 12, an LED 13 and a layered structure 14. The cavity 12 is enclosed by the housing frame 11, the substrate 30, the layered structure 14 and an optional transparent layer 17. The LED 13 is mounted within the cavity 12, in particular the LED 13 sits on a driver chip 31, in particular a silicon IC 31, which is mounted onto the substrate 30. The layered structure 14 is configured to cover the cavity 12.

The structure 14 comprises an aperture for light emitted by the LED 13. The layered structure 14 is configured to generate energy from the light emitted by the LED 13, in particular light emitted at higher angles of an emitting angle 15.

The housing frame 11, the substrate 30, casting material 12a, globe top 32 and wire bonds 9 make up a housing 8 of the device 10.

The layered structure 14 comprises layers, for instance at least one pn-junction, which implement at least one photodiode. For this the layered structure 14 may comprise photovoltaic material. The layered structure 14 may comprise silicon.

The layered structure 14 is used to harvest the energy of unusable photons emitted by the LED 13. Also, the layered structure 14 is configured to harvest photons from sunlight hitting the surface of the layered structure 14 which does not face the LED 13. At the same time the layered structure 14 shields the device 10, specifically heat sensitive material of the housing frame 11 and/or casting material 12a filling up the cavity 12 and/or the substrate 30 from incident sunlight. Energy from unusable photons emitted by the LED 13 which is wasted in state-of-the-art implementations like those shown in Figure 1 is harvested by the device 10. It is subsequently reused as an energy source within the device 10.

The photovoltaic material of the layered structure 14 may be optimized for the wavelength emitted by the LED 13. In an exemplary implementation the LED's 13 emission spectral distribution may have a strong or narrow peak in blue at approximately 450 nm and a wide peak in yellow at approximately 500 nm to 700 nm. The layered structure 14 realizes a photodiode. The sensitivity of this photodiode is adapted to the spectral distribution of the light emitted by the LED 13, such that it converts with high efficiency the range of the spectral distribution of the light emitted by the LED 13.

In a development the layered structure 14 may comprise layers which implement more the one photodiode as detailed above. Thereby, a higher amount of energy may be harvested within the device. For example, by connecting the photodiodes in a series connection a higher voltage can be achieved. Therein each of the photodiodes may be optimized for just one of the spectral peaks of the LEDs 13 emission. Optionally, the device 10 may further comprise the driver chip 31. As shown in Figure 2, the driver chip is also mounted within the cavity 12 in mechanical and electrical contact with the LED 13.

The size of the aperture of the structure 14 is dimensioned depending on the size of the LED 13, the distance between the LED 13 and the layered structure 14 and the predefined emitting angle 15. The emitting angle 15 extends between the normal 19 of the surface of the LED 13 and an edge 18 of a sidewall 16 of the aperture. The edge 18 represents the limitation of the opening of the aperture. In case the sidewall 16 has rectangular shape, i.e. is parallel to the normal 19 of the surface of the LED 13, the edge 18 coincides with the sidewall 16 of the aperture.

In an example implementation, the emitting angle 15 is predefined at approximately 45° as indicated in Figure 2.

The aperture may be etched by means of a MEMS process.

According to Lambert's cosine law, the LED 13 representing a Lambertian emitter emits 50 % of its optical power between 45 and 90°. In an example implementation the LED 13 has a total light emission of 8 W. 50 % of this light-emission occurs in the angle between 45 and 90°. Efficiency of the layered structure 14 photodiode amounts to about 25 %. Consequently roughly 1 W is generated as energy by the device 10. Said energy is available for the device 10, for instance for the driver chip 31.

Optionally, the device 10 may further comprise the transparent layer 17 which is mounted to the layered structure 14 such that the transparent layer 17 covers the layered structure 14 and the aperture. The transparent layer 17 may be made up of glass.

Figure 3A shows an exemplary realization of the proposed layered structure 14 in a sectional view. Here an angle 35 between a plane 36 parallel to a surface of the LED 13 which is facing the aperture and the sidewall 16 of the aperture of the layered structure 14 is an elongate angle. The angle 35 in this example amounts to approximately 135°. In an exemplary case of MEMS processing of silicon crystal planes the emitting angle becomes 180° - 54,7° = 125.3°.

Figure 3B shows another exemplary realization of the proposed layered structure 14 in a sectional view. In this case, the angle 35 formed between the plane 36 parallel to the surface of the LED 13 and the sidewall 16 of the aperture of the layered structure 14 is an acute angle. The angle 35 in this example amounts to approximately 54.7°.

Figure 3C shows another exemplary realization of the proposed layered structure 14 in a sectional view. In this case the sidewall 16 of the layered structure 14 is perpendicular to the surface of the LED 13, such that the angle 35 amounts to approximately 90°.

As indicated in Figures 3A to 3C, micro roughening may be optionally applied to one or more of the surfaces of the layered structure 14 in the exemplary implementations. An exemplary view of the resulting surface is depicted on the side of Figures 3A to 3C. The micro roughening increases incoupling of photons and by that the absorption of light in the layered structures 14. Furthermore, stray light reflected backwards to the LED and its driver chip 31 or other parts of the device is reduced. Consequently, less photon induced noise occurs in the driver chip 31.

Figure 4 shows an exemplary embodiment of the proposed device with the circuit. The embodiment coincides with the embodiment of Figure 2 and shows more details of the electrical configuration and components of the device 10. The device 10 further comprises a capacitor 20 which is mechanically and electrically connected to the layered structure 14. Optionally, a diode 23 is additionally provided between the layered structure 14 and capacitor 20. The capacitor 20 is configured to store energy Vhrv provided by the layered structure 14, for instance in the form of a voltage Vhrv. The device 10 further comprises at least one circuit 21 which is connected to the capacitor 20. The circuit 21 is configured to provide a direct voltage Vddx using the energy Vhrv stored on the capacitor 20 and/or a supply voltage Vbat provided by a voltage source that can be connected to the circuit 21.

Optionally, device 10 as depicted in Figure 4 comprises another circuit 22 which is connected in parallel to the circuit 21 and is configured to provide another direct voltage Vddy using the energy Vhrv stored on the capacitor 20 and/or the supply voltage Vbat.

The circuit 21 is configured to operate in a first mode, in a second mode and in a third mode. In the first mode the direct voltage Vddx is supplied by converting the supply voltage Vbat. The first mode is active at start-up of the device, for example. In the second mode the direct voltage Vddx is supplied by converting the energy Vhrv stored on the capacitor 20 and converting the supply voltage Vbat. The second mode is entered as soon as the harvested energy Vhrv starts to increase. In the third mode the direct voltage Vddx is supplied by converting the energy Vhrv stored on the capacitor 20 only. The third mode is entered as soon as the energy Vhrv is high enough.

The other circuit 22 coincides with the circuit 21 and is configured to operate in the first mode, in the second mode, and in the third mode, as well. In the first mode the other direct voltage Vddy is provided by converting the supply voltage Vbat only, in the second mode the other direct voltage Vddy is generated by converting the energy Vhrv stored on the capacitor 20 and additionally converting the supply voltage Vbat, while in the third mode the other direct voltage Vddy is supplied by converting the energy Vhrv stored on the capacitor 20 only.

Each of the circuits 21 and 22 works as a current balancing circuit in that it - depending on the amount of energy Vhrv available on the capacitor 20 - generates the direct voltage Vddx or Vddy by using only the energy Vhrv stored on the capacitor 20 or additionally using the supply voltage Vbat or using only the energy of the supply voltage Vbat. The difference between the direct voltages Vddx or Vddy and the voltage Vhrv stored on the capacitor 20 is small, which enables high efficiency in the voltage conversion and provision of the direct voltages Vddx and/or Vddy. The direct voltages Vddx and/or Vddy may be used within the device 10 for driving the analog and/or digital components of the driver chip 31, for instance. Figure 5 shows an exemplary embodiment of the proposed circuit. Each of circuits 21, 22 as of Figure 4, comprises a first voltage converter 213 and a second voltage converter

214, a first input 211, a second input 212 and an output 215. The first input 211 is configured to receive the energy Vhrv from the capacitor 20. The second input 212 is configured to receive the supply voltage Vbat. At the output 215 the direct voltage Vddx or the other direct voltage Vddy is supplied.

The first voltage converter 213 comprises a DC/DC converter, in particular a step-up converter. The second voltage converter 214 comprises a linear dropout converter, LDO. The DC/DC converter 213 is connected between the first input 211 and the output 215. The LDO 214 is connected between the second input 212 and the output 215.

In the first mode, i.e. at start-up, only the second voltage converter 214 is active and converts the supply voltage Vbat into the direct voltage Vddx, Vddy which is provided at the output 215. This is indicated by the lower arrow 2 in Figure

5.

In the second mode i.e. when the energy or the voltage Vhrv stored on the capacitor 20 is above zero but lower than necessary, the first and the second voltage converter 213,

214 are active which enables conversion of the energy Vhrv and an additional conversion of the supply voltage Vbat in order to provide the direct voltage Vddx, Vddy at the output

215. This is indicated in the higher arrow 1 and lower arrow 2 in Figure 5.

In the third mode, i.e. when enough energy Vhrv is stored on the capacitor 20, only the first voltage converter 213 is active and converts the voltage Vhrv into the direct voltage Vddx, Vddy which is provided at the output 215. This is indicated by the upper arrow 1 in Figure 5.

In case of usage of the device 10 as an automotive headlamp, at least in the second and third mode the car battery's energy is saved.

It will be appreciated that the invention is not limited to the disclosed embodiments and to what has been particularly shown and described hereinabove. Rather, features recited in separate dependent claims or in the description may advantageously be combined. Furthermore, the scope of the invention includes those variations and modifications, which will be apparent to those skilled in the art and fall within the scope of the appended claims. The term "comprising" used in the claims or in the description does not exclude other elements or steps of a corresponding feature or procedure. In case that the terms "a" or "an" are used in conjunction with features, they do not exclude a plurality of such features. Moreover, any reference signs in the claims should not be construed as limiting the scope.

References

1, 2 arrow 8 housing

9 bonding wires

10 device 11 housing frame 12, cavity

12a casting material

13 LED

14 layered structure

15 emitting angle

16 side wall

17 transparent layer

18 edge

19 normal

20 capacitor

21, 22 circuit 211, 212 input 213, 214 voltage converter 215 output 23 diode

30 substrate

31 driver chip

32 globe top

33 projector lens

34 sunshield

35 angle

36 plane

Vddx, Vbat voltage

Vhrv energy, voltage