Abstract:
An LED lighting arrangement comprising at least one LED, for producing light is disclosed. A power supply provides power for the at least one LED. At least one control circuit is coupled to the at least one LED in a way that directly or indirectly uses, to power the at least one control circuit, one or more forward voltage drops across the at least one LED. Beneficially, one or more additional control circuits can be added without redesign of the power supply for the at least one LED.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an LED lighting arrangement. More particularly, the present invention relates to an LED lighting arrangement in which control circuitry is powered directly or indirectly from the forward voltage drop across one or more LEDs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Most LED power supply (or driver) circuits are commonly sold in modules that also include various control circuits to provide such features as timing functions, dimming capabilities, motion sensors, demand response features, color changing, etc. Accordingly, there are many basic functions in addition to electrical current control for LEDs that are typically incorporated into a driver module to control the LEDs. 
         [0003]    A drawback of the foregoing LED driver module is that all of the control circuits are typically included in the driver module. As a result, adding new control functionality to an LED lighting fixture can be expensive and time-consuming in that a new driver module design must be completed, built and tested if added control circuits are required. A need exists, therefore, for an LED lighting arrangement in which additional control circuits can be added without redesign of an LED driver module. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    In one form, the invention provides an LED lighting arrangement comprising at least one LED, for producing light. A power supply provides power for the at least one LED. At least one control circuit is coupled to the at least one LED in a way that directly or indirectly uses, to power the at least one control circuit, one or more forward voltage drops across the at least one LED. 
         [0005]    The foregoing LED lighting arrangement beneficially allows one or more additional control circuits to be added without redesign of an LED driver module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0006]    In the drawings, in which like reference numerals refer to like parts: 
           [0007]      FIG. 1  shows a simplified top plan view, including an electrical schematic, of printed-circuit (PC) boards with various circuits mounted on the PC boards, in accordance with the prior art. 
           [0008]      FIG. 2  shows a simplified top plan view, including an electrical schematic, of printed-circuit (PC) boards with various circuits mounted on the PC boards, in accordance with the present invention. 
           [0009]      FIGS. 3A and 3B  shows respective block diagram views of a circuit from  FIG. 2 . 
           [0010]      FIGS. 4 and 5  are views similar to  FIG. 2 , but with differing numbers of PC boards. 
           [0011]      FIGS. 6A and 6B  show simplified, cross-sectional views of an LED and a control circuit mounted on a PC board and sharing the same heat sink. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    After describing the general concept of powering control circuits from one or more LEDs, the present description considers examples of control circuits and details of LED power supplies, which are typically called driver modules. 
       Powering Control Circuits from LED(s) 
       [0013]      FIG. 1  shows a prior art LED lighting arrangement  10 , wherein a power supply  12  supplies power to three series-connected LEDs  14   a ,  14   b  and  14   c . Other numbers of LEDs could be used, depending on the application, from one to more than three. Control circuits  16  are mounted on a printed-circuit (PC) board  18 , together with the power supply  12 . LEDs  14   a - 14   c  are mounted on a separate PC board  20 . Power supply  12  and control circuits  16 , mounted on PC board  18 , are typically sold as an LED driver module. As mentioned above, it is desirable to avoid the need to redesign an LED driver module whenever a different control circuit is needed. 
         [0014]      FIG. 2  shows an inventive LED lighting arrangement  22   a , in which a circuit  24  is powered from one or more LEDs  14   a - 14   c . That is, the upper electrical lead  24   a  of circuit  24  could be replaced with either electrical lead  24   b  or  24   c , shown as phantom lines, so that one, two or all three LEDs could power the circuit  24 . Circuit  24  can be embodied as shown in  FIG. 3A  as a control circuit  26 , or as shown in  FIG. 3B  as voltage-conditioning circuit  28 , which in turn in connected to a control circuit  26 . Voltage-conditioning circuit is discussed below under a related heading. 
         [0015]    The LEDs  14   a - 14   c  in LED lighting arrangement  22   a  ( FIG. 2 ) act as coarse voltage regulators because the forward voltage drop across them (e.g., typically about 3.5 volts) remains relatively steady. Such voltage is about 3.5 volts for a single LED  14   c , about 7 volts for two serially connected LEDs  14   c  and  14   b  and about 10.5 volts for three serially connected LEDs  14   c ,  14   b  and  14   a . This is true regardless of the current supplied by power supply  12 , which typically ranges from 10 mAmps to 10 Amps and depends on the type of LEDs used. Owing to the foregoing inherent trait of LEDs, the voltage at their terminals can be used to power control integrated circuits (IC&#39;s) or other control circuits, such as control circuit  26  of  FIG. 3A  or  3 B, which cannot otherwise be powered from constant-current supplies. 
         [0016]    Most of the foregoing control IC&#39;s draw very little power in relation to the LEDs  14   a - 14   c , so any drop in light output due to their additional current usage would be minimal. If the amount of current required by a current-intensive control circuit  26  ( FIGS. 3A-3B ) would result in an unacceptable drop in light output, then the power supply (or driver)  12  for the LEDs is designed to supply sufficient current so as to power the LEDs as well as the current-intensive control circuit. This assures that the desired light output is achieved. 
         [0017]    Because LEDs act as coarse voltage regulators, a unique opportunity arises if control circuits, such as control circuit  26  ( FIGS. 3A-3B ), are mounted to the same PC board  20  to which the LEDs are interconnected and then connected electrically so the voltage drop across the LEDs directly or indirectly powers the control circuits. Because the control circuits are physically remote from the LED power supply  12 , more standard LED driver modules can be used for power supply  12 , which do not need to include added functionality of other control circuits, since such control circuits can be added to the lighting arrangement and powered by the voltage drop across the LEDs. This reduces LED driver module complexity and cost and improves reliability. 
         [0018]    Separating the control circuits from the LED driver module allows for greater flexibility in circuit design in that the LED driver module does not need to be redesigned for each control scheme desired. Also, control circuits can be added at a later time if, for instance, PC board  20  ( FIG. 2 ) to which the LEDs are interconnected contains means (not shown) for mounting additional control circuits whenever desired. For example, a standard LED lighting arrangement can be made that provides a constant light output but has mounting means for additional control circuits. If, at a later time, the end-user decides to add dimming capabilities, or a motion sensor, or wireless controls, for instance, the user can simply plug the appropriate module(s) or component(s) into the PC board to which the LEDs are interconnected and the fixture will respond as desired. 
         [0019]    It is not required that all of the control circuits be located on the PC board  20  on which the LEDs  14   a - 14   c  are mounted. If desired, some control circuits (not shown in  FIG. 2 ) can be placed in the LED driver module, i.e., on PC board  18 , and others can be placed on the PC board  20  and powered by the LEDs  14   a - 14   c . Alternatively, as shown in the LED lighting arrangement  22   b  of  FIG. 4 , the LED power supply  12 , the LEDs  14   a - 14   c  and the circuit  24  which contains the control circuit  26  ( FIGS. 3A-3B ) can be mounted on a single PC board  30 . Further alternatively, as shown in the LED lighting arrangement  22   c  of  FIG. 5 , the LED power supply  12 , the LEDs  14   a - 14   c  and the circuit  24  which contains the control circuit  26  ( FIGS. 3A-3B ) can be mounted on respective PC boards  32   a ,  32   b  and  32   c.    
         [0020]    An additional benefit of LED lighting arrangements  22   a  ( FIG. 2) and 22   b  ( FIG. 4 ) is that, by mounting circuit  24 , which contains the control circuit  26  ( FIGS. 3A-3B ) on the same PC board to which the LEDs are interconnected, the control circuit(s) can be kept cool using the same heat sink arrangement used by the LEDs.  FIG. 6A  shows such an arrangement, in which LEDs  14   a - 14   c  and a control circuit  26  are mounted on a PC board  34 , to which is attached a heat sink  36 . The control circuit  26  advantageously also uses the same heat sink  36 . Similarly,  FIG. 6B  shows LEDs  14   a - 14   c  and a control circuit  26  mounted on a PC board  38  of metallic construction, to which optionally is attached a heat sink  36 . 
       Examples of Control Circuits 
       [0021]    Examples of LED lighting control systems, where the control circuits could be mounted on the PC board to which the LEDs are interconnected and not in the LED driver module, include:
       thermal sensors   RF communications   IR transceivers   LED protection circuits   time clocks   dimmer controls   failed LED bypassing or switching on of a spare LED   electric power utility-scale demand-response circuits to reduce power usage when demand for same is high   occupancy sensors   radio frequency identification (RFID) tag readers       
 
       Voltage-Conditioning Circuit 
       [0032]    Some control circuits  26  ( FIGS. 3A-3B ) require a tighter voltage range from a power source than an LED(s) can provide, and some control circuits require lesser voltage than an LED(s) can provide. Accordingly, a voltage-conditioning circuit is used. 
         [0033]    The voltage-conditioning circuit  28  of  FIG. 3B  which regulates voltage in a tighter range than an LED(s) provides may be used in the following circumstance. The coarse voltage regulation provided by an LED will typically be of the order of +/−20%. For a 3.5V LED forward drop, this may range between 2.9 and 4.2 volts. For many control circuits this regulation is adequate. Some circuits, however, require a much tighter range of voltages such as from 2.9 to 3.1 Volts. In these cases, a simple 3-terminal voltage regulator may take the input from the LED and provide the additional tighter regulation, referred to herein as “secondary” regulation, required by the control circuits. Such 3-terminal voltage regulators, such as the LM7805, are commonly available from multiple sources, such as from Fairchild Semiconductor of South Portland, Me. 
         [0034]    Incidentally, it is impractical to operate the foregoing “secondary” regulators directly from the current source which operates the LEDs for several reasons. First, the voltage of the LED power source is usually too high and would unnecessarily complicate the design of the secondary regulator, or second, the voltage of the LED power source would cause the secondary regulator to be much less efficient than when operated from the coarse regulation provided by an LED. 
         [0035]    An alternative voltage-conditioning circuit  28  ( FIG. 3B ), which provides voltage regulation, uses a resistor and a Zener diode, whose reverse-voltage characteristic provides voltage regulation. Variations of such a circuit will be apparent to a person of ordinary skill in the art based on the present specification. 
         [0036]    In cases where the voltage provided by an LED(s) is too high for a control circuit, but where the coarse voltage regulation of the LED(s) is adequate, a simpler voltage-conditioning circuit  28  ( FIG. 3B ), such as a voltage-divider circuit can be used to lower the voltage from the LED(s). 
       Additional Benefit for an LED Driver 
       [0037]    From the above description, it will be apparent that benefits extend to the LED driver module in that it can be off-the-shelf and/or generic version and therefore less expensive. Also, because some or all the control circuits are removed from the driver, the driver can be kept cooler than if the controls were incorporated into the driver, therefore making the driver more reliable and extending its the life. 
         [0038]    While the invention has been described with respect to specific embodiments by way of illustration, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true scope and spirit of the invention.