EP3599796A1 - Led light band and lighting system - Google Patents

Abstract

The invention relates to an LED light strip (1) comprising a printed circuit board (2), at least one light-emitting diode (LED) (3) arranged on a first side (A) of the printed circuit board (2), two on the first one for each LED (3) Side (A) of the printed circuit board (2) arranged electrically conductive contact surfaces (4), and two printed conductors (5) arranged on a second side (B) of the printed circuit board (2). Two of the electrically conductive contact surfaces (4) are electrically connected with an LED (3). Of the contact areas (4) which are connected to the same LED (3), a contact area (4) with one of the two conductor tracks (5) each forms a coupling capacitor. The coupling capacitors are designed to generate a displacement current for energizing the LEDs (3) electrically connected to the contact surfaces (4) based on a high-frequency AC voltage applied to the conductor tracks (5) in the contact surfaces (4). The invention further relates to a lighting system (7).

Description

The present invention relates to a light-emitting diode light band (hereinafter “LED light band”) and a lighting system comprising such an LED light band.

Conventional LED light strips usually consist of segments, each typically having a length of approximately 50 mm. These segments are connected in parallel to each other and are usually operated with a constant DC voltage of 12 V or 24 V. Each of these segments usually has 6 or 7 LEDs.

In general, two variants for an electronic design of such LED light strips are known. According to a first variant, a light-emitting diode current of a segment is kept constant at a predetermined value by means of a current regulator. However, such LED light strips are relatively complex and accordingly expensive. According to a second variant, the light-emitting diode current of a segment is determined by means of an electrical resistance. Such LED light strips are simple and inexpensive to manufacture. However, a luminous flux of such an LED light band gradually drops over the length of the LED light band, since according to this variant no current regulator is provided. In both variants there are significant electrical losses that affect the efficiency of the LED light strips.

The object of the present invention is to describe an LED light strip and a lighting system which eliminate or reduce the above-mentioned disadvantages of conventional LED light strips.

This object is achieved by an LED light band and a lighting system in accordance with the independent claims. Advantageous refinements are specified in the subclaims. The disclosure content of the claims is hereby incorporated in full by reference into the present description.

In one embodiment of the LED light strip, this comprises a printed circuit board. At least one light-emitting diode, LED, is arranged on a first side of the circuit board. Furthermore, two electrically conductive contact surfaces are arranged on the first side of the circuit board for each LED. Two conductor tracks are arranged on a second side of the circuit board. Two of the electrically conductive contact areas are electrically connected with an LED. Of the contact areas that are electrically connected to the same LED, a contact area with one of the two conductor tracks forms a coupling capacitor. The coupling capacitors are set up to generate a displacement current for energizing the LED electrically connected to the contact surfaces, based on a high-frequency AC voltage applied to the conductor tracks in the contact surfaces.

In the present case, light-emitting diodes are understood to mean both light-emitting diode chips and LED components with such a light-emitting diode chip. For example, the LEDs can be surface-mounted. A light-emitting diode chip can comprise optoelectronic semiconductor bodies or an organic layer sequence. In other words, the light-emitting diode chips can be semiconductor chips or OLED chips. When used as intended, the light-emitting diodes preferably emit light in the visible spectral range or in the UV range or in the IR range.

One advantage of the LED light strip shown here is that the LEDs arranged on the first side of the circuit board are supplied with energy independently of one another in a contactless manner via the conductor tracks arranged on the second side of the circuit board. Contactless in this context describes the lack of electrical contact between the electrically conductive contact surfaces and the conductor tracks. There is physical contact between the electrically conductive contact surfaces and the conductor tracks via the circuit board.

Another advantage is that the individual LEDs are mounted on the circuit board in isolation from each other. The LEDs are not electrically interconnected. The lack of electrical interconnection between the LEDs, as is customary in conventional LED light strips, means that the LED light strip is simpler and more cost-effective to construct. This also enables the LED light strip to be separated between any LED. This is also not possible in conventional light strips due to the interconnection of the LEDs. Furthermore, no through-contacts through the printed circuit board are required for the LED light strip shown here, which likewise simplifies a manufacturing process for such a light strip and contributes to reducing the cost of the light strip.

The coupling capacitors form a coupling resonant circuit with the inductances of the conductor tracks. The high-frequency alternating voltage that is applied to the conductor tracks can, for example, have a frequency corresponding to a resonance frequency of this coupling resonant circuit or can deviate from this resonance frequency.

In one embodiment of the LED light strip, a rectifier circuit is arranged on the first side of the circuit board for each LED. By means of such a rectifier circuit, the displacement current generated in the contact areas is converted into a direct current for operating the respective LEDs. In an alternative embodiment, instead of a rectifier circuit, so-called AC LEDs, i.e. anti-parallel LEDs, used as LED. One of the anti-parallel LEDs is operated with one half-wave of the displacement current.

In one embodiment of the LED light strip, the printed circuit board is at least partially made of a plastic material. The circuit board forms a dielectric of the coupling capacitors. For example, polyimides or substances containing polyimide are suitable as the material for the printed circuit board. In an alternative embodiment, a material of the printed circuit board consists at least partially of polyethylene terephthalate, PET.

In one embodiment of the LED light strip, the circuit board is elastically deformable. In particular, the entire LED light band is also elastically deformable. this makes possible flexible and versatile use of the LED light strip in a wide variety of applications.

In one embodiment of the LED light strip, at least one further LED is arranged on the first side of the printed circuit board. The contact areas electrically connected to the at least one LED have a different area dimension than the contact areas electrically connected to the at least one further LED.

An extension parallel to a main plane of extent of the printed circuit board is considered here as a flat extension of the contact areas. One advantage of this embodiment is that the differently dimensioned contact areas result in differently dimensioned coupling capacitors comprising the contact area and the conductor strip. The coupling capacitors of different LEDs thus have different capacitances. This results in different resonance frequencies for the coupling resonant circuits of different LEDs. Depending on a frequency of the applied AC voltage, certain LEDs can thus be operated with a resonance frequency of their associated resonant circuit, while other LEDs are operated at this frequency outside the resonance frequency of their associated resonant circuits. This enables a selectively controllable lumen output of individual LEDs or individual groups of LEDs on the LED light band.

The selective controllability of the lumen output of different LEDs or LED groups enables, in particular, a so-called Human Centric Lighting, HCL, or a so-called horticultural lighting, in which daylight-like lighting for people or Plants and animals is produced. For this purpose, LEDs or LED groups with different color temperatures are provided with differently dimensioned coupling capacitors in the LED light band described here. For example, the coupling capacitors of LEDs with a higher color temperature are dimensioned larger than the coupling capacitors of LEDs with a lower color temperature. By correspondingly shifting the frequency of the applied AC voltage in accordance with a time of day or, for example, in accordance with a measured color temperature of a current daylight, daylight-like illuminations can be generated by dimming the LEDs or LED groups with different intensities with different color temperatures.

In one embodiment of the lighting system, the lighting system comprises an LED light strip described above. Furthermore, the lighting system comprises a feed device which is set up to apply a high-frequency AC voltage to the two conductor tracks of the LED light strip.

In one embodiment of the lighting system, the feed device is set up to apply a high-frequency AC voltage with a frequency in a range from 1 MHz to 10 MHz to the two conductor tracks. Of course, alternating voltages with other frequencies can also be used to operate the LED light strip.

In one embodiment of the lighting system, the feed device comprises a serial resonance converter, in particular a serial resonance converter with a full-bridge circuit. Such an infeed device is particularly advantageous since it approximates one sinusoidal output voltage can be generated, whereby an efficient capacitive coupling is generated in the coupling capacitors.

All of the configurations of an LED light strip or a lighting system described above can be combined with one another as required.

The LED light band and the lighting system are described below using exemplary embodiments in conjunction with Figures 1 to 3 explained in more detail. In the figures, the same reference numerals are used for elements with essentially the same function, but these elements need not be identical in every detail. The figures are generally not to scale. The proportions of the various components do not correspond to one another. For example, comparatively small elements may be exaggerated in size for better illustration and vice versa.

Figur 1

eine perspektivische Darstellung eines LED-Lichtbands gemäß einem Ausführungsbeispiel der Erfindung,

Figur 2

eine dreidimensionale Schnittzeichnung eines Ausschnitts des LED-Lichtbands gemäß Figur 1, und

Figur 3

ein Schaltbild eines Lichtsystems gemäß einem Ausführungsbeispiel der Erfindung.

The figures show:

Figure 1

2 shows a perspective illustration of an LED light strip according to an exemplary embodiment of the invention,

Figure 2

a three-dimensional sectional drawing of a section of the LED light strip according to Figure 1 , and

Figure 3

a circuit diagram of a lighting system according to an embodiment of the invention.

In the in the Figures 1 and 2 In the illustrated embodiment of an LED light strip 1, the LED light strip 1 comprises an elongated flexible strip-shaped printed circuit board 2. The printed circuit board has a width b1 of approximately 10 mm and a height h1 of approximately 100 μm, a base material of the printed circuit board being made of a polyimide There is a height of 50 microns. A plurality of LEDs 3 are mounted on a first side A of the printed circuit board 2. The LEDs 3 are arranged in a row along a main direction of extent of the LED light strip 1. Of course, the LEDs 3 can also be otherwise mounted on the printed circuit board 2. Furthermore, other shapes of the printed circuit board 2 than the elongated strip-shaped printed circuit board 2 shown here are of course also possible.

Figure 2 shows a section of the LED light strip 2 according to Figure 1 , in which an LED 3 according to the plurality of LEDs 3 Figure 1 you can see.

The LEDs 3 are each, for example, an LED chip provided with a leadframe-based plastic sheath, for example PLCC2 SMD LEDs, PLCC4 SMD LEDs or PLCC6 SMD LEDs, high-power SMD LEDs and / or LED chip arrays in SMD Housings (so-called CAS LEDs) which are mounted on the printed circuit board 2 using surface (SMD) mounting technology.

In an alternative embodiment (not shown), the LEDs 3 are LED chips which are mounted on the printed circuit board 2 using chip-onboard (COB) technology.

In this exemplary embodiment, the LEDs 3 are centered between two side edges of the printed circuit board 2 on the first side A. the circuit board 2 mounted. In addition to the LEDs 3, an electrically conductive contact surface 4 is arranged on the first side A of the circuit board 2 between each LED 3 and in each case one side edge of the circuit board 2. In this exemplary embodiment, the contact surfaces 4 are rectangular copper islands which extend parallel to a main extension plane of the printed circuit board 2. In this exemplary embodiment, the contact surfaces 4 have a height h2 of approximately 36 μm and a planar extent of approximately 32 mm ² , with a width b2 of approximately 4 mm and a length 12 of approximately 8 mm. However, the contact surfaces 4 of different LEDs 3 can also have different planar dimensions. This is related to below Figure 3 described in more detail. The contact surfaces 4 are produced, for example, by etching a copper-coated printed circuit board.

Two electrically conductive conductor tracks 5 are arranged on a second side B of the printed circuit board 2 opposite the first side A. Like the contact surfaces 4, the conductor tracks 5 are made of copper and extend parallel to one another along a longitudinal direction of the strip-shaped circuit board 2. The conductor tracks 5 each have a height h3 of approximately 36 μm and a width b3 of somewhat less than 5 mm. The conductor tracks 5, like the contact areas 4, are also etched out of a copper coating.

Each LED 3 has two contact areas 4, ie each LED 3 is electrically connected to two contact areas 4. The contact areas 4 and the conductor tracks 5 are arranged on the printed circuit board 2 such that one of the two contact areas 4 connected to the same LED 3 is opposite one of the two conductor tracks 5. In particular, as large a part as possible overlaps one Expansion surface of the contact surface 4 or in each case the entire expansion surface of the contact surface 4 with an expansion surface of the opposite conductor track 5. Each contact surface 4 forms a coupling capacitor with the conductor track 5 opposite it. The contact areas 4 each represent a first electrode, the conductor tracks 5 each represent a second electrode and the circuit board 2 located therebetween is a dielectric of these coupling capacitors.

If a high-frequency AC voltage is applied to the conductor tracks 5, a displacement current is generated in the contact areas 4 by means of capacitive coupling. One of the conductor tracks 5 here represents an outgoing line, the other a ground return line for applying the high-frequency AC voltage. For example, at one end of the LED light strip 1 there are soldering points or other connection points for connecting the conductor tracks 5 with a feed device for applying the high-frequency AC voltage connect (not shown here).

In each area of each LED 3, a rectifier circuit 6 is also mounted on the first side A of the circuit board 2 in order to operate the LEDs 3 with a direct current. The rectifier circuits 6 have diodes and capacitors for rectifying and smoothing the displacement currents which are generated in the contact surfaces 4. The rectifier circuits 6 are described in more detail with reference to FIG Figure 3 described.

Figure 3 shows a circuit diagram of a lighting system 7 according to an embodiment of the invention. The circuit diagram of the lighting system 7 shows a circuit of an LED light strip 1, for example, the LED light strip 1 according to the Figures 1 and 2 , of which only the wiring of a single LED 3 is shown here for the sake of simplicity. In addition, the circuit diagram of the lighting system 7 according to FIG Figure 3 a circuit of a feed device 8 for applying a high-frequency AC voltage to the conductor tracks 5.

In the circuit of the LED light strip 1, two inductors 9 are shown, each with a capacitor 10 connected in series. The inductors 9 represent the self-inductors according to the Figures 1 and 2 Conductors 5 described. The capacitors 10 each represent the coupling capacitors belonging to an LED 3, each consisting of a contact area 4 and the opposite conductor track 5.

The feed device 8 has a serial resonance converter which, by means of a full bridge circuit, applies an almost sinusoidal, high-frequency AC voltage to the capacitors 10 via the inductors 9. To generate the high-frequency alternating voltage, a voltage of +5 V is present at a first terminal 13 of the feed device 8, a second terminal 14 of the feed device 8 is connected to a ground potential GND. The feed device 8 also has transistors 15 which are switched in such a way that a predetermined frequency of the high-frequency AC voltage is generated.

Between the capacitors 10 and the LED 3 there is a rectifier circuit 6, for example that with reference to FIG Figures 1 and 2 Rectifier circuit 6 mentioned. The rectifier circuit 6 has two diodes 11 to rectify the displacement currents generated in the contact surfaces 4. The diodes 11 are combined, for example, in one component as a so-called double diode. In one embodiment, a double diode with a periodic peak voltage of 100 V, a forward current of 125 mA and a switching time of at most 4 ns can be used.

The rectifier circuit also has two filter capacitors 12, which reduce residual ripple in the rectified voltage. A center between the two filter capacitors 12 forms a reference potential. In this way, a voltage that is as constant as possible for operating the LED 3 is generated. In an alternative embodiment, instead of the filter capacitors 12, inductive elements, such as coils, can also be used for smoothing.

In a first operating mode of the lighting system 7, the transistors 15 are switched in such a way that the predetermined frequency of the high-frequency AC voltage which is present on the conductor tracks 5 corresponds to a resonance frequency of the resonant circuit, comprising the inductors 9 and the capacitors 10. In a second operating mode of the lighting system 7, the transistors 15 are switched such that the predetermined frequency of the high-frequency AC voltage deviates from the resonance frequency of the resonant circuit. The greater this deviation, the weaker the resonant coupling across the capacitors 10 and, accordingly, the weaker the current that flows through the LED 3. Lumen output of the LED 3 is reduced in this way. A luminous flux of the LED 3 is thus greater in the first operating mode than in the second operating mode.

The resonance frequency of the resonant circuit is influenced, among other things, by the area of the coupling capacitors. It is thus possible to connect two LEDs with differently dimensioned contact areas, so that the resonance frequencies of the resonant circuits belonging to the LEDs vary. In this way, high-frequency AC voltages with different predetermined frequencies can be generated in the feed device 8, which for example correspond either to the resonant frequency of the resonant circuit of one LED or the other LED. One of the two LEDs is thus operated in the first operating mode, while the other LED is operated in the second operating mode.

Intermediate states are of course also possible, in which, for example, a predetermined frequency is selected which deviates, for example, by approximately 10% from the resonant frequency of the resonant circuit of the one LED and by approximately 5% from the resonant frequency of the resonant circuit of the other LED. Furthermore, entire groups of LEDs can be connected to differently dimensioned coupling capacitors, or any number of differently dimensioned coupling capacitors can be connected to corresponding LEDs, so that resonant circuits with any number of different resonance frequencies are present. In addition, the LEDs, which are connected to differently dimensioned coupling capacitors, can have different colors or color temperatures. In this way, a wide variety of dimming scenarios and color constellations can be generated with the lighting system 7.

Further details and design options of a lighting system 7 described here and a method for Operating such a lighting system 7 are in the application filed by the same applicant with the German Patent and Trademark Office at the same time, entitled "Lighting system and method for operating a lighting system" (file number: DE 10 2018 121 444.8 ), the disclosure content of which is hereby fully incorporated into this application by reference. A copy of the application "Lighting system and method for operating a lighting system" is also attached to this application.

The explanation of the invention with reference to the exemplary embodiments is not to be understood as restricting the invention to these. Rather, the elements generally described above and the elements described in the exemplary embodiments can be combined differently with one another depending on the requirement profile for an LED light band or lighting system, and each individual element alone contributes to the ideas described at the beginning of the invention.

LIST OF REFERENCE NUMBERS

1

LED light strip

2

circuit board

3

LED, LED

4

contact area

5

conductor path

6

Rectifier circuit

7

lighting system

8th

feed device

9

inductance

10

capacitor

11

diode

12

filter capacitor

13

first terminal

14

second terminal

15

transistor

GND

ground potential

A

first side of the circuit board

B

second side of the circuit board

b1

PCB width

h1

PCB height

b2

Width of the contact area

h2

Height of the contact area

12

Length of the contact area

b3

Width of the conductor track

h3

Height of the conductor track

Claims (9)

LED light strip (1), comprising: - a printed circuit board (2), - At least one light-emitting diode, LED, (3) arranged on a first side (A) of the printed circuit board (2), - For each LED (3) two on the first side (A) of the circuit board (2) arranged electrically conductive contact surfaces (4), and - Two conductor tracks (5) arranged on a second side (B) of the printed circuit board (2), wherein - Two of the electrically conductive contact surfaces (4) are electrically connected to an LED (3) and of the contact surfaces (4) which are connected to the same LED (3), one contact surface (4) each with one of the two conductor tracks ( 5) each forms a coupling capacitor, the coupling capacitors being set up to shift a displacement current for energizing the LED (3) electrically connected to the contact surfaces (4) based on a high-frequency AC voltage applied to the conductor tracks (5) in the contact surfaces (4) produce. LED light strip (1) according to claim 1, wherein a rectifier circuit (6) is arranged on the first side (A) of the printed circuit board (2) for each LED (3), the rectifier circuit (6) being set up to operate in the contact areas (4) rectify the generated displacement current and apply it to the respective LED (3). LED light strip (1) according to one of claims 1 or 2, wherein the circuit board (2) is at least partially made of a plastic material and wherein the circuit board (2) forms a dielectric of the coupling capacitors. LED light strip (1) according to one of claims 1 to 3, wherein the circuit board (2) is elastically deformable. LED light strip (1) according to one of claims 1 to 4, wherein the electrically conductive contact surfaces (4) have a planar extent parallel to the circuit board (2) in a range of 1 square millimeter to 100 square millimeters. LED light band (1) according to one of claims 1 to 5, wherein at least one further LED (3) is arranged on the first side (A) of the printed circuit board (2) and the contact surfaces () which are electrically connected to the at least one LED (3) 4) have a different planar extension than the contact surfaces (4) electrically connected to the at least one further LED (3). Lighting system (7) comprising an LED light strip (1) according to one of claims 1 to 6 and a feed device (8) which is set up to apply a high-frequency AC voltage to the two conductor tracks (5) of the LED light strip (1) , Lighting system (7) according to claim 7, wherein the feed device (8) is set up to apply a high-frequency AC voltage with a frequency in a range from 1 megahertz to 10 megahertz to the at least two conductor tracks (5). Lighting system (7) according to one of claims 7 or 8, wherein the feed device (8) comprises a serial resonance converter.

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