Patent Application
20070127239
The present invention relates to driving arrangements for lighting sources including a plurality of light emitting diodes (LEDs).
The invention was developed with specific attention paid to its possible use in driving RGB LED sources used as variable brightness lighting sources and in general in driving a multichromatic lighting system, e.g. defining a tunable-white lighting system.
In addition to the use as display units, light emitting diodes (LEDs) are becoming increasingly popular as lighting sources. This applies primarily to so-called high-brightness (or High Flux—HF) LEDs. Typically, these LEDs are arranged in cells, with each cell comprised of one or more LEDs coupled in a parallel/series arrangement.
A combination of a plurality of cells each including one or more LEDs having a given emission wavelength (i.e. respective “colour”) produces combined light radiation whose characteristics (spectrum, intensity, and so on) can be selectively adjusted by properly controlling the contribution of each cell. For instance, three cells each including a set of diodes emitting at the wavelength of one of the fundamental colours of a trichromatic system (e.g. RGB) produce white light and/or a radiation of a selectively variable colour. Such arrangements may include cells each comprised of one or more LEDs of essentially the same colour and produce light systems whose intensities may be selectively adjusted to meet specific lighting requirements (for instance providing different lighting levels in different areas of a given space, a display area and so on).
Arrangements adapted for driving a plurality of such cells in association with a single constant current source are known in the art as witnessed, e.g. by WO-A-2004/100612.
Essentially, in these prior art arrangements each cell has an associated switch (typically, an electronic switch) adapted to act as a selectively activatable short-circuit path to the source. When the switch is activated (i.e. the switch is “closed”) the LED or LEDs in the associated cell are short-circuited and no radiation is generated by the cell. Conversely, when the switch is de-activated (i.e. the switch is “open”) the LED or LEDs in the associated cell are energized and radiation is generated by the cell. The arrangement includes a controller configured to control operation of the switches (typically according to a Pulse Width Modulation—PWM control law). Such an arrangement permits to selectively and automatically adjust the contribution of each cell to the overall light flux produced. Additionally, by resorting to such an arrangement, the current power source is never completely turned off, but only driven through different path.
Currently, the most common types of variable brightness lighting sources can be ascribed to two basic categories, i.e. so-called “passive” and “active” lighting sources.
A “passive” lighting source is e.g. a light emitting diode (LED) source having associated therewith simple and low-cost voltage-to-current converters able to supply the required constant current to the LEDs. As indicated, brightness variations are achieved in these sources by using a Pulse Width Modulation (PWM) technique.
Conversely, an “active” lighting source is e.g. a light emitting diode (LED) source having associated therewith at least one micro-controller able to manage a digital communication with the power supply, and able to control the LED brightness consequently.
Up to now, the two different categories of lighting sources (“passive” and “active”) have been typically driven with different and dedicated power supply arrangements.
In general terms, for proper operation of the lighting source, two main functions need be implemented in the arrangement, namely:
With reference to
Usually, an “active” lighting source 20 will be associated with a dedicated supply unit 25 equipped with a micro-processor 27. The micro-processor 27 in the supply unit is capable of operating as a digital communication interface and communicates with the micro-processor into the lighting source.
Insofar as power supply proper is concerned, the micro-processor 27 supplies the micro-processor 32 associated with the “active” RGB lighting source 20 via two wires, +Vcc and GND, in order to provide electrical power to the lighting source 30.
Additionally, the micro-processor 27 is configured for sending brightness information signals to the micro-processor 32, by way of serial data BUS lines 29. The corresponding output gates of the micro-processor 27 are thus connected to respective input gates of the micro-processor 32.
The micro-processor 27 thus communicates, via the two serial data BUS lines 29, the brightness information signals to the micro-processor 32. The micro-processor 32 is able to compute the brightness information signals received from the micro-processor 27 in order to properly control a supply block 34 to regulate the respective currents to be delivered to the RD, GD, BD loads.
Thanks to the on-board intelligence available with the light source 20, the arrangement of
A basic drawback of such an arrangement lies in extra-cost and extra-complexity added.
By way of direct comparison,
In the “active” arrangement of
In the “passive” arrangement of
As a consequence, while both the arrangements of
Essentially, the compatibility problem of the “Passive” and “Active” lighting sources cannot be solved with these prior art arrangements.
From the foregoing description of the current situation, it emerges that the need exists for arrangements capable of driving LED lighting source in a more satisfactory way as compared to the solutions according to the prior art described previously, especially insofar as the point of possible compatibility is concerned.
The object of the invention is thus to provide a fully satisfactory response to that need.
According to the present invention, that object is achieved by means of an arrangement having the features set forth in the claims that follow.
The claims are an integral part of the disclosure of the invention provided herein.
A preferred embodiment of the invention is thus a driving arrangement for lighting sources including a plurality of light emitting diodes (LEDs), the arrangement including a first power supply line and a set of signal lines for carrying brightness intensity information for said plurality of light emitting diodes, the arrangement including:
Such a driving arrangement is thus a flexible, compatible arrangement adapted for driving both “active” and “passive” as described in the foregoing.
In a first possible configuration of use, adopted for driving “active” sources, the first and second power supply line are jointly supply power to the processor included in the “active” lighting sources wherein the processor drives the light emitting diodes in the source as a function of the brightness intensity information provided to the processor via the set of signal lines (typically to the number of three in the diodes comprise an RGB arrangement).
In a second possible configuration of use, adopted for driving “passive” sources, the second power supply line is not used, and the brightness of the light emitting diodes in the source is controlled by switching signals applied thereto via the first power supply line and the set of signal lines.
The invention will now be described, by way of example only, with reference to the enclosed figures of drawing, wherein:
The arrangement described herein essentially uses the same supply unit topology for driving both “passive” and “active” LED lighting sources, such as e.g. RGB LED source.
Specifically, with reference to
In
The unit 52 is connected to the supply unit 45 via two power-lines +Vcc and GND and it is adapted to read the information available on signal bus 1a, 1b, 1c and to convert the level of the signal available on the two power lines +Vcc and GND for carrying brightness intensity and/or chromtic information for said light emitting diodes. In case of driving brightness intensity and chromatic information, the number of signal lines is increased in order to include a number of signal lines between four to six signal lines.
The supply unit 45 also includes a brightness control block 47 that causes the brightness variations of the source 50 using a PWM modulation technique on three switches namely a, b, and c: this is essentially the same arrangement described in the foregoing in connection with the “passive” source of
Essentially in line with the “active” arrangement of
The logic-power circuit elaborates the information of the signals 1a-1c in such a way that brightness intensity and/or chromatic information are converted into a suitable internal signal. This signal is then sent to a voltage-to-current conversion stage that, having Vcc as input, drives accordingly any of the LEDs RD-BD in the block 54.”
When connected to an “active” source 50, the arrangement illustrated in
Direct comparison of
The supply unit of
Without prejudice to the underlying principles of the invention, the details and the embodiments may vary, also appreciably, with reference to what has been described by way of example only, without departing from the scope of the invention as defined by the annexed claims.
Therefore, while a particular embodiment of the present invention has been shown and described with specific attention paid to its possible use in driving RGB LED sources, it should be understood that the present invention is not limited thereto since other embodiments may be made by those skilled in the art without departing from the scope thereof. It is thus contemplated that the present invention encompasses any such embodiments including the driving of a multichromatic lighting system, e.g. a tunable-whit lighting system.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP05425828 | Nov 2005 | EP | regional |
