Abstract:
In embodiments of the present invention, there is provided a lighting control device connected in series with an AC supply line of a lighting driver at a control access point, wherein the lighting control device comprises an AC/DC converter configured to receive an input AC voltage from the AC supply line and to convert it to an output DC voltage. The lighting control device further comprises a lighting control circuit configured to use the output DC voltage as a power supply and to transmit control information to the driving unit.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to lighting systems, and particularly to methods and systems of controlled LED lighting. 
       BACKGROUND OF THE INVENTION 
       [0002]    Light Emitting Diodes (LED)s have become a prevailing technology in the industry of lighting. In a typical LED lighting system there is a LED driving unit, shortly denoted LED driver, closely attached to one or more LED arrays. The LED driver operation is typically based on a Pulse Width Modulation (PWM) technique, wherein a user can control the width and optionally the amplitude of power pulses, at the LED driver output, for achieving desired lighting characteristics. 
         [0003]    An advanced method and system for controlled driving of LEDs was suggested in our previous US patent application “Device and method for controlled LED lighting” the disclosure of which is incorporated herein by reference. In that publication, the LED driver receives control information from various control sources. An example control source is a dimmer, which imposes a variable dimming angle on the mains power that feeds the LED driver. Other control sources, such as various types of sensors or a remote controller, need dedicated power sources for their operation. Thus, in order to save system complexity, further wiring and power consumption, there is a need for an efficient remote controller for LED drivers, capable of operating without resorting to a dedicated power source. 
       SUMMARY OF THE INVENTION 
       [0004]    Accordingly, it is a principal object of the present invention to provide improved and efficient techniques of supplying power to a remote controller of a lighting driver, typically a LED driver. Such a remote controller is denoted herein as lighting control device for the sake of generality. In particular, the provided techniques save the need for a dedicated power supply for the lighting control device. 
         [0005]    Thus, in accordance with an embodiment of the present invention, there is provided a lighting control device that controls a lighting driver. The lighting control device comprises an input stage connected along an AC supply line of the lighting driver, an AC/DC converter configured to receive an input AC voltage from the AC supply line and to convert it to an output DC voltage, and a lighting control circuit configured to receive the output DC voltage as a power source and to transmit control information to the driving unit. 
         [0006]    In an embodiment, the input stage comprises a voltage limiter configured to determine the input AC voltage, and a limiter control circuit configured to reduce the input AC voltage when the AC/DC converter reaches an operating state, thereby saving power consumption of the voltage limiter. 
         [0007]    In some embodiments, the limiter control circuit comprises a switch capable to shortcut a part of the voltage limiter for reducing the input AC voltage. 
         [0008]    In some embodiments, the AC/DC converter comprises a voltage-raising stage, e.g. a transformer. 
         [0009]    In an embodiment, the lighting control circuit comprises a wireless transmitter for transmitting the control information to the lighting driver, while in other embodiments the lighting control circuit is configured to transmit the control information to the lighting driver through the AC supply line either by means of an RF transformer or by means of a coupling capacitor. 
         [0010]    In an embodiment, the lighting control device further comprises a user interface coupled to the lighting control circuit, whereas the lighting control circuit is further configured to receive one or more control commands from a user through the user interface and to produce the control information based on the control commands. An example of such a control command is a dimming command. 
         [0011]    In accordance with an embodiment of the present invention, there is also provided a method of controlling a lighting driver comprising the steps of: Connecting a lighting control device along an AC supply line of the lighting driver, wherein the lighting control device comprises an input stage, an AC/DC converter and a lighting control circuit; converting an input current of the lighting driver flowing through the AC supply line to an input voltage to the AC/DC converter; converting the input AC voltage to an output DC voltage by the AC/DC converter; supplying the output DC voltage to a lighting control circuit; and transmitting control information to the lighting driver from the lighting control circuit. 
         [0012]    These and other features and benefits of the invention disclosed herein will be more fully understood upon consideration of the following description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For a better understanding of the invention with regard to the embodiments thereof, reference is made to the accompanying drawings, in which like numerals designate corresponding elements or sections throughout, and in which: 
           [0014]      FIGS. 1A ,  1 B and  1 C are block diagrams that schematically illustrate lighting systems, in accordance with embodiments of the present invention; and 
           [0015]      FIG. 2  is a flowchart that schematically illustrates a method of controlled driving of LEDs, in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0016]    Embodiments of the present invention provide improved systems and methods for controlling a LED driver from a control access point, typically located on a wall, wherein an AC supply line of the LED driver, typically the live line, is accessible. 
         [0017]    Referring to  FIG. 1A , there is shown a block diagram that schematically illustrates a lighting system  100 , in accordance with an embodiment of the present invention. System  100  is powered from an AC supply  103 , typically a mains supply, through a branch point  104 , which feeds a LED driver  108 , to which a LED array  112  is connected. In branch point  104 , an AC supply line  116 , typically the mains live line, splits and drops to a control access point  120 . In applications wherein the present invention is not applied, there is typically a lighting switch installed in control access point  120 , sometimes attached to a dimmer. 
         [0018]    In an embodiment, a lighting switch  124  and an input stage  141  of a lighting control device  128  are connected in series along AC supply line  116  in control access point  120 . Control device  128  typically operates as a remote controller of LED driver  108 . Input stage  141  comprises a zener diode  136  connected in series with a diode pair  140 , together constituting a voltage limiter having a peak-to-peak voltage equal to the sum of the zener breakdown voltage and the knee voltages of the zener diode and each of diodes  140 . When switch  124  is in ON position, input stage  141  converts the input current of LED driver  108 , flowing through AC supply line  116 , to an input AC voltage  142  supplied to an AC/DC converter  144 . Input AC voltage  142  thus has the above peak-to-peak value, which is substantially smaller than AC supply  103 . AC/DC converter  144  converts input AC voltage  142  to an output DC voltage  143  supplied to a lighting control circuit  130 . Lighting control circuit  130  then controls LED driver  108 , as explained hereinafter. 
         [0019]    However, the power consumption of input stage  141  affects the efficiency of lighting system  100  and, in case of high power lighting system, might result in excess heating of control access point  120 . In order to mitigate this problem, a limiter control circuit is employed in an embodiment, comprising a control line  146 , a switch  148  and a detection circuit within AC/DC converter  144 , not shown in  FIG. 1A . The limiter control circuit operates as follows: 
         [0020]    During a few milliseconds after lighting control device  128  is turned on, e.g. by turning switch  124  to ON position, switch  148  is in OFF position, allowing voltage limiter  138  &amp;  140  to supply a sufficiently high initial input AC voltage to AC/DC converter  144 . This initial input AC voltage has a peak-to-peak value equal to the breakdown voltage of zener diode  136  plus three times diode knee voltage. When the detection circuit detects that the AC/DC converter has reached an operating state that allows it to continue operation without resorting to high input AC voltage, it causes control line  146  to turn switch  148  to ON position. Consequently, input AC voltage  142  reduces to about 1.4 volt peak-to-peak, determined by diode pair  140 . In an embodiment, switch  148  comprises a transistor, not shown in  FIG. 1A , for shortcutting zener diode  136 . In other embodiments, switch  148  is realized by a mechanical switch such as a reed relay. 
         [0021]    Referring again to lighting control circuit  130 , its main role is to produce and send control information to LED driver  108 . In an embodiment, such control information may be, for instance, lighting intensity adjustment, i.e. a dimming command initiated by a user of lighting system  100  through a user interface  149 . The user interface may be a dimming knob, a Man Machine Interface (MMI) comprising a touch screen or any other suitable interface. 
         [0022]    In an embodiment, lighting control circuit  130  transfers the control information to LED driver  108  through a Radio Frequency (RF) transformer  150 , whose secondary winding is connected in series with AC supply line  116  and whose primary winding is coupled to the lighting control circuit. 
         [0023]      FIG. 1B  shows a block diagram that schematically illustrates a lighting system  101 , in accordance with an alternative embodiment of the present invention. In this embodiment, intended for relatively low power lighting systems, limiter control circuit  146  &amp;  148  is omitted and the voltage limiter consists of zener diode  136  only. Consequently, input AC voltage  142  retains its initial value, of several volts, as long as lighting control device  128  is operating. 
         [0024]    In the embodiment illustrated in  FIG. 1B , also transformer  150  is missing and substituted by a choke  152  and a coupling capacitor  156  for transmitting the control information to LED driver  108  through AC supply line  116 . 
         [0025]      FIG. 1C  shows a block diagram that schematically illustrates a lighting system  102 , in accordance with yet an alternative embodiment of the present invention. In this embodiment, the voltage limiter consists of diode pair  140  only, thereby providing AC/DC converter  144  with a low peak-to-peak voltage of about  1 . 4  volt. Therefore, AC/DC converter  144  comprises a voltage-raising stage at its input, realized in the described embodiment by a voltage-raising transformer  160 , which saves the complexity of the above limiter control circuit at the expense of additional volume of lighting control device  128 . 
         [0026]    In lighting system  102 , the control information transfer is based on a wireless transmitter  164  and a wireless link  168  connecting lighting control circuit  160  with LED driver  108 . 
         [0027]    In yet alternative embodiments, any other suitable combination of the above techniques for producing input AC voltage  142  and for sending control information to LED driver  108  can be applied, as well as any other suitable techniques based on the above, that may be obvious to persons of ordinary skill in the art. 
         [0028]    The above description has focused on the specific elements of lighting systems  100 ,  101 ,  102  and particularly of lighting control device  128 , that are essential for understanding certain features of the disclosed techniques. Conventional elements that are not needed for this understanding have been omitted from  FIGS. 1A ,  1 B and  1 C for the sake of simplicity but will be apparent to persons of ordinary skill in the art. Furthermore, the configurations shown above are example configuration, which were chosen purely for the sake of conceptual clarity. In alternative embodiments, any other suitable configurations can also be used. 
         [0029]      FIG. 2  shows a flowchart  200  which schematically illustrates a method of controlling a LED driver from a control access point, in accordance with an embodiment of the present invention. The method begins with a connecting step  204 , wherein lighting control device  128  is connected along AC supply line  116  which leads AC power to LED driver  108 . Next, in a supplying step  208 , input stage  141  supplies input AC voltage  142  to AC/DC converter  144 . In step  210 , the detection circuit within AC/DC converter  144  checks whether the AC/DC converter has reached an operating state that allows it to continue its operation without resorting to high input AC voltage. This checking condition is illustrated in flowchart  200  by a return line from step  210  to step  208 . 
         [0030]    Upon a positive result in step  210 , the method proceeds to a reducing step  212 , in which limiter control circuit  146  &amp;  148  shortcuts zener diode  136  for reducing input AC voltage  142 . In a receiving step  216  lighting control device  128  receives user commands through user interface  149 . Finally, in a transmitting step  220 , lighting control circuit  130  converts the user commands to control information and transmits it in a predefined format to LED driver  108 . 
         [0031]    The flowchart shown in  FIG. 2  is an example flowchart, which was chosen purely for the sake of conceptual clarity. In alternative embodiments, any other suitable flowchart can also be used for illustrating the disclosed method. Method steps that are not mandatory for understanding the disclosed techniques were omitted from  FIG. 2  for the sake of simplicity. 
         [0032]    Although the embodiments described herein mainly address LED lighting, the methods and systems exemplified by these embodiments can also be used in other lighting applications. 
         [0033]    It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.