Abstract:
A multiple channel current regulator is configured to deliver a maximum current to a load associated with the channel in a lighting system. Different channels may have a different maximum current and the ratio among the maximum currents is fixed. In operation, the current of each channel can be individually modulated by a pulse stream that controls the current that flows to the load.

Description:
BACKGROUND 
       [0001]    Multi-channel current regulators are traditionally designed to source or sink identical or similar current at each channel at its maximum. This approach is reasonable for applications where loading is evenly distributed to the channels. 
         [0002]    There are, however, applications where the current requirement for each channel is different. In these occasions, this approach of designing current regulator is inadequate. For example, when the current regulator is used to drive multiple strings of LED of different colors, especially when each channel is subject to tuning by a dimmer, the traditional current regulator design is wasteful, costly, and difficult to incorporate into “smart-lighting” systems. 
         [0003]    The cause of this deficiency is that due to the difference in human sensation to lights of different colors, the lumens from different colored LEDs that are optimal in color mixes are different. For example, it takes fewer lumens for blue light to mix with green and red lights to generate a discernible white color light of various color temperatures. If the channel for driving the green light is designed for the same current capability, the blue channel is often over-designed and less energy efficient. 
         [0004]    A more serious deficiency is that when incorporated into a smart lighting system, such a current regulator makes the system performance inferior in another aspect. That is, in a system of correlated color temperature (CCT) tunable or color tunable, for example, it is desirable if each channel is separately tunable from maximum lumens to minimum lumens and with high resolution. With traditional multichannel power supplies in which all channels have identical or similar peak current capability, the channels that do not require to deliver up to their maximum capacity will have un-used current head room that is not subject to tuning in normal operation. The tuning circuit, on the other hand, is often designed for the whole current range to be compatible to the rest of the lighting system. The apparent dynamic range for the channels that are over-designed will be poor. As a result, the system dynamic range will be poor. This problem is not generally recognized and is not solved before this invention. 
       SUMMARY 
       [0005]    The Inventor recognized the shortcomings of the current smart-lighting system and endeavored to invent solutions, which are disclosed in this paper and are summarized below. 
         [0006]    One aspect of the invention relates to a multiple channel current regulator that is configured so each channel is capable to deliver a maximum current to a load but different channels may have a different maximum current and the ratio among the maximum currents is fixed. For example, in a four channel current regulator designed for a smart lighting system, the maximum currents of the four channels follow the ratio of 1:1:0.75:0.25. 
         [0007]    In this paper, the maximum current is to be understood as the current that a channel can source or sink with enough operational margins that the product and the system in which the product is incorporated can function safely. The current flowing in each channel may exceed the maximum value for a short time but for reliable and safe operation, this practice is not recommended. 
         [0008]    The multichannel current regulator may be realized in the form of an integrated circuit. Currently, silicon is the favored material for making integrated circuits but other semiconductor materials such as silicon carbide, gallium nitride, and gallium arsenide, etc. are also contemplated. 
         [0009]    Unless otherwise noted, all embodiments described in the paper are products with manufacturing limitations and therefore any number associated with the embodiments is to be treated as having the usual industry tolerances. For instance, a ratio of 1:1 in this paper is to be understood to mean a ratio that is close to be mathematical  1 : 1  as to be commercially acceptable for LED lighting systems. 
         [0010]    Another aspect of the invention is that the maximum current of each channel may be adjusted but the adjustment does not disturb the ratio among the channels, which remains fixed. 
         [0011]    Although it is contemplated that, for flexibility, the maximum current of each channel be adjustable individually, it is more economical to adjust the maximum currents of all channels with a common mechanism so the ratio among the maximum currents after the adjustment stays undisturbed. 
         [0012]    Another aspect of the invention is that while the ratio of the maximum currents is fixed, the actual current of each channel may be adjusted independently through modulation. 
         [0013]    One method with which the current may be modulated is with pulse width modulation (PWM). With this method, the current that flows into or from a LED light source in some embodiments is allowed to flow when a switching apparatus is open and is restricted when it is closed. The amount of current during a discernible time period, or the amount of light that is emitted from the light source during the time period is modulated by the varying duty cycles of a pulse stream that operates the switching apparatus. 
         [0014]    Other methods that may be employed to modulate the current flow at the channels include pulse frequency modulation, with which the pulse stream maintains a constant duty cycle but the frequency of the pulse stream varies. 
         [0015]    A voltage or a current pulse stream is made of consecutive pulses, each of which has a high level and a low level. The duty cycle of a pulse is the ratio of the duration when the pulse is at its high level to the duration when the pulse is at it low level. 
         [0016]    Another aspect of the invention is a current regulator, which may be constructed in one single integrated circuit. Although in most applications, a single chip multichannel current regulator may suffice, for capacity consideration, multiple chips may be incorporated into a system. 
         [0017]    Another aspect of the invention is that the current regulator is dimmable via either a digital diming signal or an analog diming signal. For economical consideration, it is more desirable to convert an analog dimming signal into a digital pulse stream, to modulate the current flow at each channel. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  depicts the block diagram of an example current regulator according to the invention. 
           [0019]      FIG. 2  depicts a typical smart lighting system that incorporates the example current regulator depicted in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
     Example 1 
       [0020]      FIG. 1  depicts the block diagram of an example current regulator  100  that embodies several aspects of this invention. The example current regulator  100  is a four-channel ratio-optimized constant-current regulator built for Tunable White and Tunable Color Smart Lighting applications. Other current regulators embodying this invention may have more or fewer than four channels. For example, a current regulator embodying this invention may have two or three channels. The current regulator  100  is designed for maximum current channel up to 500 mA with a total driving current up to 1.5 A. This particular driving current is picked for illustration because it serves a wide range of smart-lighting applications. The integrated low-side current sinks in this design allow for LED common-anode connections or different anode voltages. 
         [0021]    The current ratio among the channels is predetermined for Tunable Color or Tunable White applications. The maximum current can be adjusted via a resistor  60 , which may be external to the current regulator  100 , which may be constructed in a single integrated circuit (IC) chip. The resistor  60  may be coupled directly at terminal R SET    50  of the IC chip. The maximum currents at channel  1 , I 1   101 , channel  2 , I 2   102 , channel  3 , I 3   103 , and channel 4 , I 4   104  that flow to the output terminals Pin 1   10 , Pin 2   20 , Pin 3   30 , and Pin 4   40  respectively may be expressed according the following formulae: 
         [0000]        I   max1 =2000* V   REF   /R   SET    
         [0000]        I   max2 =2000* V   REF   /R   SET    
         [0000]        I   max3 =1500* V   REF   /R   SET    
         [0000]        I   MAX4 =500* V   REF   /R   SET    
         [0000]      where  V   REF =1.5 V 
         [0022]    For example, for a fixed V REF , with an R SET  resistor  60  set at 12 KΩ, channel  1 ,  2 ,  3 , and  4  can provide maximum current of 250 mA, 187.5 mA, 250 mA, and 62.5 mA respectively. With a different valued R SET  resistor  60 , one may adjust the maximum current for channel  1  through channel  4  to different values. The ratio among the maximum currents, however, will be maintained at the same predetermined. In applications, two or more channels may be tied together to drive one LED light source with the aggregated current. 
         [0023]    The current regulator  100  is designed to incorporate a dimming function through pulse width modulation. Other methods of modulating the currents for the dimming purpose such as pulse frequency modulation and analog dimming are also contemplated. Dimming signals are coupled to the PWM (PWM 1   55 , PWM 2   65 , PWM 3   75 , and PWM 4   85 ) pins of the IC chip. In this example, the current regulator  100  is configured, during startup, to operate in PWM dimming mode at a PWM frequency ranging, for example, from 500 Hz to 4 KHz. In this mode, high level of the PWM signals will turn on the current sink to allow current to flow through the LEDs and low level of the PWM signals will turn the current off to adjust the LED current and LED brightness of each corresponding channel. 
       Example 2 
       [0024]    In another embodiment of this invention, a smart LED lighting system can use either wired or wireless control to achieve energy efficient lighting management.  FIG. 2  depicts a block diagram of an example smart lighting system  200  embodying aspects of this invention. The lighting system  200  comprises an AC to DC power conversion unit  210 , a color management MCU  220 , a LED current regulator  230 , and light emitting diodes  240 . 
         [0025]    The AC to DC Power Conversion unit  210  provides constant voltages (CV) to power the MCU  220 , the LED current regulator  230 , and the light emitters  240 . This typical smart lighting system  200  requires 3.3 V supply for MCU  220  and 12 V/24 V for High-Power/Low-Power LED light source  240 . 
         [0026]    The interface between MCU  220  and the current regulator  230  includes an Enabling signal  2310 , pulse width modulation signals PWM 1   2355 , PWM 2   2365 , PWM 3   2375 , PWM 4   2385 , and FAULTB signal  2320 . The MCU  220  activates the EN signal  2310  to turn on the current regulator  230  to power the LED light sources  240 . When EN  2310  pin is low the current regulator  230  shuts down to conserve energy. MCU  220  implements light mixing algorithm and generates proper PWM signals through PWM pins  2355 - 2385 . In case of any general fault occurs in the current regulator  230 , a FAULTB signal  2310  goes low to interrupt MCU  220  for proper actions. 
         [0027]    The current regulator  230  is configured to a four-channel LED driver structure and can adopt either analog or PWM dimming control for each channel. The four parallel LED driver channel structure is configured for applications of either Tunable White (2-channel or 3-channel) or Tunable Color (3-channel, or 4-channel). The system depicted in  FIG. 2  supports a LED light source  240  of up to 8 LEDs of White, Blue, Green or 10 LEDs of Red in series and can deliver between 600 to 1,200 lumens of illumination. 
         [0028]    A reference current may be set by a resistor  260  that is external to the current regulator  230 . With a 12 KΩ resistor  260 , the reference current at the REF pin  2600  may be set at 0.125 mA. Because the Tunable White or Tunable Color applications use unequal amount of colored light lumens, the current regulator  230  adopts a current ratio of 1:0.75:1:0.25 among the four channels. This current ratio results in a more efficient use of the chip size of the current regulator  230 . Through internal current ratio circuitries such as current mirrors, the maximum current of channel  1 ,  2 ,  3  and  4  may be set at 250 mA, 250 mA, 187.5 mA and 62.5 mA, respectively. The actual current through each emitter string may be further modulated by a dimming mechanism. 
       Example 3 
       [0029]    In an embodiment of this invention, referring  FIG. 2 , a Tunable White light system for tuning the white color temperature based on two LED channels may be realized by using LED 1   201  and LED 2   202  to provide equal current through each channel and using PWM 1  and PWM 2  signals  2355 ,  2365  generated by MCU to emulate incandescent dimming effects. To further enhance the quality of CCT diming, one may use either I 3   203  (ratio 0.75) or I 4   204  (ratio 0.25) with proper modulation to provide finer CCT adjustments. 
       Example 4 
       [0030]    In another embodiment of this invention, as depicted in  FIG. 1 , a Tunable Color light system for tuning lighting color may be realized by using three LED channels to mix red, green, and blue colors to generate white light. The proper GRB color mixes ratio for white light is 8:6:2, which is the current ratio in the example current regulator  100 , among I 2   10 , I 3   20 , and I 4   30  as depicted in  FIG. 1 . With PWM signals generated by MCU  220  one may generate desired Tunable White and Color with three RGB LED light sources. To further improve Color Rendering Index (CRI), one may also use LED 1   10  (I max1  ratio 1) to provide additional White light intensity.