Light emitting diode (LED)-based current separator for separating LED current between multiple LED channels and multi-channel light emitting diode (LED)-based lighting device

Abstract

A current separator based on a light-emitting diode (LED), for separating LED currents between a plurality of LED channels, wherein the current separator comprises at least two LED circuits connected in series, wherein each LED circuit comprises: a first branch (B1.1, B2.1), comprising at least one LED; a second branch (B1.2, B2.2), connected in parallel with the first branch (B1.1, B2.1) and comprising at least one LED; and a branch switch (W1, W3), connected in series with the at least one LED, wherein the forward voltage of the at least one LED in the second branch (B1.2, B2.2) is lower than the forward voltage of the at least one LED in the first branch (B1.1, B2.1); and a third branch (B1.3, B2.2), connected in parallel with the first and second branches (B1.2, B2.2) and comprising a shunt switch (W2, W4) for shunt current between the first branch (B1.1, B2.1) and the second branch (B1.2, B2.2).

Description

Technical Field

[0001] The present disclosure relates to a light emitting diode (LED) based current splitter for splitting LED current between a plurality of LED channels, wherein the current splitter comprises branches connected in parallel and in series, wherein at least some of the branches comprise at least one LED. Background Art

[0002] Lighting devices utilizing light-emitting diodes (LEDs) have been developed for a variety of lighting applications. Due to their long lifespan and high energy efficiency, LED lamps are now also being designed to replace traditional fluorescent lamps, known as retrofit applications. For such applications, the retrofit LED lamp is typically designed to fit into the socket of the corresponding fixture being retrofitted. Furthermore, since lamp maintenance is typically performed by the user, the retrofit LED lamp should ideally be easy to operate with any suitable fixture, without requiring rewiring of the fixture.

[0003] The present disclosure relates to multi-channel LED-based lighting devices. Each channel can include one or more LEDs capable of emitting light of a specific color. For example, the first channel can be directed to emit red light, the second channel can be directed to emit green light, and the third channel can be directed to emit blue light.

[0004] In this type of lighting fixture, a fixed voltage source can be used to power the LEDs in each channel. The current through each channel can be set at the factory by tuning a resistor placed in series with the LEDs in that particular channel. One drawback of this approach involves several interfering factors, such as power supply voltage variations, cable length (i.e., impedance), and interactions between channels, which can lead to errors in the target flux and color point.

[0005] Another option is to provide the lighting device with a current source, wherein the lighting device comprises a current separator for splitting the current on different channels.

[0006] More specifically, there are typically available controllers with multiple channels, wherein each channel is provided with a switch, wherein each switch is thus arranged to enable a specific corresponding channel. For example, the first switch may enable the red channel, the second switch may enable the green channel, the third switch may enable the blue channel, etc.

[0007] A pulse-width modulated (PWM) signal with a specific duty cycle can be supplied to the switch. The frequency of the PWM signal should be chosen so that it exceeds the refresh rate of the human eye. This prevents the user from seeing any flicker. By controlling the duty cycle, it is possible to control the contribution of each channel to the total amount of light emitted, and therefore also the color of the light emitted by the LED-based lighting device.

[0008] One disadvantage of the above structure is that the control resolution of the PWM signal is reduced by adding more channels. Summary of the Invention

[0009] The present disclosure aims to provide a current separator that reduces the effect of reduced control resolution of a PWM signal. Other objects of the present disclosure include a lighting device based on a multi-channel light emitting diode (LED), wherein the multi-channel LED-based lighting device includes the LED-based current separator according to the present disclosure.

[0010] In a first aspect, a current separator based on a light emitting diode (LED) is provided for separating LED current between a plurality of LED channels, wherein the current separator comprises at least two LED circuits connected in series.

[0011] Each LED circuit includes:

[0012] - a first branch (B1.1, B2.1), comprising at least one LED;

[0013] a second branch (B1.2, B2.2) connected in parallel with the first branch (B1.1, B2.1) and comprising at least one LED and a branch switch (W1, W3) connected in series with the at least one LED, wherein the forward voltage of the at least one LED in the second branch (B1.2, B2.2) is lower than the forward voltage of the at least one LED in the first branch (B1.1, B2.1);

[0014] - A third branch (B1.3, B2.3), connected in parallel with the first branch and the second branch (B1.2, B2.2), and comprising a shunt switch (W2, W4) for shunting the first branch (B1.1, B2.1) and the second branch (B1.2, B2.2).

[0015] One of the advantages of a current separator according to the present disclosure over current separators according to the prior art can be best understood using an example.

[0016] In the prior art, four switches are used to enable four channels. Each switch enables a specific channel. Each channel can be directed to a specific color of light. By providing a PWM signal as the control signal for each switch, a combination of channels can be used. This allows for different colors to be achieved. In other words, the four primary colors and a variety of other colors can be generated by mixing these four primary colors.

[0017] A current separator according to the present disclosure may also utilize four switches. In this case, the current separator may include two LED circuits connected in series, wherein each LED circuit includes three branches connected in parallel. The first branch includes at least one LED, the second branch includes at least one LED and a branch switch, and the third branch includes a shunt switch.

[0018] One of the three branches in the first LED circuit can be "enabled" at a time, and one of the three branches in the second LED circuit can be "enabled" at a time, resulting in a total of nine different layouts. One of the nine different layouts includes a situation where both branch switches of the LED circuit are activated, effectively creating a short circuit. Similarly, there are eight available layouts remaining, which can be considered as eight channels. Therefore, compared to the prior art situation where only four channels are obtained using four switches, the current separator according to the present disclosure can provide eight channels using only four switches. In other words, eight primary colors can be generated, as well as multiple other colors produced by mixing these eight primary colors.

[0019] The above reduces the undesirable effect of reduced PWM control resolution by adding more channels.

[0020] Note that, according to the present invention, the forward voltage of the at least one LED in the second branch (B1.2, B2.2) is lower than the forward voltage of the at least one LED in the first branch (B1.1, B2.1). The inventors have discovered that as long as the forward voltage of the at least one LED in the second branch is lower than the forward voltage of the at least one LED in the first branch, it is not necessary to include a branch switch in the first branch.

[0021] Without a switch in the first branch, it's impossible to actively and functionally disconnect the first branch so that current doesn't flow through it. The inventors have discovered that by ensuring that the forward voltage of at least one LED in the second branch is lower than the forward voltage of at least one LED in the first branch, current can still be directed to the second branch. Thus, by activating the branch switch in the second branch, the first branch is effectively deactivated.

[0022] It should also be noted that the current separator according to the present disclosure operates effectively when it is connected to or when it comprises a current source.A current source may be considered as an electronic circuit capable of providing a current independent of the voltage across it.

[0023] According to the present disclosure, any LED present in the current separator may relate to a cool white LED, a warm white LED, a cyan LED, a blue LED, or any similar LED.

[0024] In one example, at least one of the LED circuits further comprises:

[0025] - another branch (B1.4), connected in parallel with the first, second and third branches, and comprising at least one LED and another branch switch (W5) connected in series with the at least one LED, wherein the forward voltage of the at least one LED in the another branch (B1.4) is lower than the forward voltage of the at least one LED in the first branch (B1.1, B2.1).

[0026] The above examples describe a case where an additional branch is connected in parallel with other branches in the LED circuit. The additional branch may have a branch switch for enabling or disabling that particular branch. It should be noted that multiple additional branches may be utilized in accordance with the present disclosure.

[0027] Note: Preferably, the current separator has exactly two LED circuits connected in series. The inventors have realized that this particular layout may be beneficial for many lighting devices currently on the market.

[0028] In another example, the LED circuit according to the present disclosure may be a homogeneous LED circuit or a heterogeneous LED circuit.

[0029] In the context of this disclosure, a homogeneous circuit is a circuit with the same topology; for example, all LED circuits have three branches. A heterogeneous circuit is a circuit with different topologies; for example, a first LED circuit has three branches, while another LED circuit has four branches, etc.

[0030] In a further example, the LED-based current separator further comprises:

[0031] A controller is used to control any of the switches in the LED circuit.

[0032] Here, the controller may be arranged for activating a switch at most once for each of the LED circuits.

[0033] In another example, the controller is further arranged to cause dimming of the at least one LED by activating any of the branch switches.

[0034] A shunt switch can be used to provide dimming functionality. The current splitter according to the present disclosure is particularly suitable for use with a current source having a fixed current flow. By using a shunt switch, current can be diverted to a specific branch, thereby reducing the amount of light emitted by that branch. PWM signals are particularly well-suited for this purpose.

[0035] The controller may be connected to a memory interface for controlling each switch to emit a specific color. According to the present disclosure, the memory may be a read-only memory ROM, a random access memory RAM, a cache memory or any similar memory.

[0036] According to the present disclosure, the controller may be, for example, a microcontroller or any other control device, such as a microprocessor, a field programmable gate array (FPGA), or any similar device. For example, the microcontroller may receive relevant input signals at some available input pins and may provide output control signals at other available output pins.

[0037] In another example, the branches are arranged to provide different colors of lighting by using different types of LEDs in each of said branches.

[0038] In a second aspect, a multi-channel light emitting diode (LED) based lighting device is provided, wherein the multi-channel LED based lighting device comprises an LED based current separator according to any one of the aforementioned examples, wherein a channel consists of: one of the branches in the first of the at least two LED circuits connected in series; and one of the branches in the subsequent of the at least two LED circuits connected in series.

[0039] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Disclosed is a current separator for separating LED current according to the prior art;

[0041] Figure 2 Disclosed is a current separator for separating LED current according to the present disclosure;

[0042] Figure 3 A current separator for separating LED current according to another example of the present disclosure is disclosed;

[0043] Figure 4 A table is shown indicating the channels that are enabled based on the switches that are activated. DETAILED DESCRIPTION

[0044] Figure 1 A current separator 1 according to the prior art for separating LED current is disclosed.

[0045] LED current separator 1 can be included in a multi-channel LED-based lighting device. Multi-channel means that the LED-based lighting device has multiple channels, where each channel is directed to emit an LED of a specific color. For example, the first channel can be directed to emit red light, the second channel can be directed to emit green light, and the third channel can be directed to emit blue light.

[0046] Figure 1 The LED current separator 1 has four channels, each of which includes switches 3, 4, 5, and 6 and correspondingly at least one LED 7, 8, 9, and 10. Each switch 3, 4, 5, and 6 can be controlled by a controller using a pulse-width modulated (PWM) signal. This allows the controller to emit four primary colors, such as red, green, blue, and white, and multiple secondary colors by mixing the channels.

[0047] The current source 2 is used to provide the LED current to the LED current separator 1. Note that the current source 2 can be implemented in many ways. For example, the current source 2 can be implemented as an LED driver.

[0048] Figure 2 A current separator 21 for separating LED current according to the present disclosure is disclosed. The current separator 21 includes two LED circuits connected in series, as shown by reference numerals 22 and 23 .

[0049] The first LED circuit 22 comprises a first branch B1.1, a second branch B1.2 and a third branch B1.3.

[0050] In this example, the first branch B1.1 includes at least one LED. Branch B1.1 can include a single LED, such as a power LED, or multiple LEDs. The LEDs can all be of the same type, or they can be of different types. The LEDs can emit the same color of light, or they can emit different colors of light. Note that the first branch B1.1 does not include a branch switch.

[0051] Second branch B1.2 is connected in parallel with first branch B1.1 and includes at least one LED and a branch switch W1. Branch switch W1 is used to activate or deactivate second branch B1.2. The inventors note that as long as the forward voltage of at least one LED in second branch B1.2 is lower than the forward voltage of at least one LED in first branch B1.1, the at least one LED in second branch B1.2 can be placed in parallel with at least one LED in first branch B1.1. This ensures that when branch switch W1 is activated, current flows through second branch B1.2 and not through first branch B1.1.

[0052] Typically, the forward voltage of an LED is between 1.8 volts and 3.3 volts. However, it can vary depending on the color of the LED. Red LEDs typically drop around 1.8 volts, but blue LEDs can drop from 3 volts to 3.3 volts due to the voltage drop and light frequency increasing with the band gap.

[0053] The third branch B1.3 is connected in parallel with the first branch B1.1 and the second branch B1.2, wherein the third branch B1.3 comprises a shunt switch W2 for shunting the first branch B1.1 and the second branch B1.2. The shunt switch W2 substantially short-circuits the first branch B1.1 and the second branch B1.2.

[0054] The topology described above for the first LED circuit 22 is repeated for the second LED circuit 23 .

[0055] The first branch of the second LED circuit 23 is denoted by reference numeral B2.1, the second branch of the second LED circuit 23 is denoted by reference numeral B2.2, and the third branch of the second LED circuit 23 is denoted by reference numeral B2.3. The branch switch in the second branch B2.2 of the second LED circuit 23 is denoted by reference numeral W3, and the branch switch in the third branch B2.3 of the second LED circuit 23 is denoted by reference numeral W4.

[0056] Figure 3 A current separator 31 for separating LED current according to another example of the present disclosure is disclosed.

[0057] Here, with Figure 2 1, 2, and 3. The same reference numerals are used for the same or similar aspects as compared to the reference numerals of FIG. 1. Note that the three LED circuits are placed in series, as shown by reference numerals 22, 23, and 24. The third LED circuit 24 also includes three branches, as shown by reference numerals B.31, B3.2, and B3.3.

[0058] The current splitter 31 may be connected to a current source 2 having a fixed amount of current as output. To create a dimming effect, each of the shunt switches W2, W4 and W6 may be periodically activated to shunt the LEDs in any branch.

[0059] Figure 4 A table is shown indicating the channels that are enabled based on the switches that are activated.

[0060] The first four columns of the table relate to Figure 2 The current separator is shown with switches W1, W2, W3, and W4. The fifth column indicates the specific color, or channel, selected based on which of the four switches is activated. Here, "WW" represents warm white light, "CW" represents cool white light, "Cyan" represents cyan light, and "Blue" represents blue light.

[0061] The table shows that, for example, if branch switch W1 is deactivated, shunt switch W2 is deactivated and shunt switch W4 is activated, warm white is selected, which means that current will only flow through the at least one LED of the first branch of the first LED circuit 22 .

[0062] Note that in the case where both branch switches W2 and W4 are activated, neither LED will illuminate since in this case the current will simply return to the current source.

[0063] Other variations of the disclosed embodiments may be understood and implemented by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may perform the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium provided with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any reference signs in the claims should not be construed as limiting their scope.

Claims

1. A current separator based on a light emitting diode (LED), for separating LED current between a plurality of LED channels, wherein the current separator comprises at least two LED circuits connected in series, wherein each LED circuit comprises: - a first branch (B1.1, B2.1), comprising at least one LED; a second branch (B1.2, B2.2) connected in parallel with the first branch (B1.1, B2.1) and comprising at least one LED and a branch switch (W1, W3) connected in series with the at least one LED, wherein the forward voltage of the at least one LED in the second branch (B1.2, B2.2) is lower than the forward voltage of the at least one LED in the first branch (B1.1, B2.1); - A third branch (B1.3, B2.3), connected in parallel with the first branch and the second branch (B1.2, B2.2), and comprising a shunt switch (W2, W4) for shunting the first branch (B1.1, B2.1) and the second branch (B1.2, B2.2).

2. The LED-based current separator of claim 1 , wherein at least one of the LED circuits further comprises: - another branch (B1.4), connected in parallel with the first branch, the second branch and the third branch, and comprising at least one LED and another branch switch (W5) connected in series with the at least one LED, wherein the forward voltage of the at least one LED in the another branch (B1.4) is lower than the forward voltage of the at least one LED in the first branch (B1.1, B2.1).

3. The LED-based current separator according to any one of the preceding claims, wherein the current separator has two LED circuits connected in series.

4. The LED-based current separator according to any one of claims 1 and 2, wherein the LED circuit is a homogeneous LED circuit.

5. The LED-based current separator according to any one of claims 1 and 2, wherein the LED circuit is a heterogeneous LED circuit.

6. The LED-based current separator according to any one of claims 1 and 2, wherein the LED-based current separator further comprises: - a controller for controlling any of said switches in said LED circuit.

7. An LED-based current separator according to claim 6, wherein the controller is arranged to activate at most one switch for each of the LED circuits at a time.

8. The LED-based current separator according to claim 6, wherein the controller is further arranged to dim the at least one LED by activating any one of the shunt switches (W2, W4).

9. An LED based current separator according to any one of claims 1, 2, 7 and 8, wherein the branches are arranged to provide different coloured illumination by using different types of LEDs in each of the branches.

10. A multi-channel light emitting diode (LED) based lighting device, wherein the multi-channel LED based lighting device comprises the LED based current separator according to any one of the preceding claims, wherein the channels are composed of: one of the branches in a first LED circuit in the at least two serially connected LED circuits; and One of the branches in a subsequent LED circuit of the at least two serially connected LED circuits.

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