Abstract:
A system and the method are provided for supplying power to a remote device. In one embodiment, the method involves regulating voltage for at least one device remote from a power source. The regulating includes monitoring a current response of the remote device and adjusting a voltage of the power source until the current response reaches an operating range of the remote device.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/952,070 filed on Jul. 26, 2007, the entire teachings of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     A robust market is emerging with preference towards powering low voltage (non AC mains) remote devices from a centralized infrastructure. This is as true for power systems, as it is for communication systems, surveillance systems, and control systems. For example, a need exists for efficient low voltage lighting for signage, power sources for cameras, and other devices that exhibit non-linear and piecewise linear loads. 
     When installing a new communication system, surveillance system, or control system, one of the first and most important considerations is power demand. Knowing the power demand allows for an efficient and cost-effective matching of a power source to the system requirements. A primary concern when installing lengths of wire between the power supply and remote device is voltage drop. In some instances, the amount of voltage lost between the originating power supply and the remote device can be significant and will vary with a changing load demand. Further, improper control of the power source to compensate for wire gauge, wire length and load current can lead to an unacceptable voltage presented at the remote device. 
     SUMMARY 
     Known methods and systems used for powering remote devices monitor voltage at the location of the remote device and feedback the monitored voltage on a pair of dedicated feedback wires (e.g., Kelvin leads). The dedicated feedback wires do not exhibit a significant voltage drop because the dedicated feedback wires only require an insignificant amount of power to transmit the monitored voltage to the controller that controls the voltage at the location of the power source. Monitoring the voltage at the location of the remote device has several disadvantages, for example, each remote device requires a pair of dedicated feedback wires which increases the system cost. Other disadvantages include electrical noise that can be induced on the feedback wire pair that leads to inaccuracies in the remote device&#39;s voltage regulation. Further, some remote devices are not designed to accommodate a four wire connection that is needed for two power connections and two feedback monitoring connections. 
     There is provided a method for providing regulated voltage for at least one device remote from a power source. The method involves monitoring a current response of the remote device and adjusting a voltage of the power source until the current response reaches an operating range of the remote device. 
     In some embodiments, the remote device can exhibit a non-linear or piecewise linear current-voltage characteristic. In some embodiments, the voltage can be adjusted in steps, wherein the steps can be discreet or continuous. In some embodiments, the operating range of the remote device can be determined by monitoring the current response until the step in the voltage results in a current response equal to a current response of a previous voltage step. In some embodiments, the operating range of the remote device can be determined by monitoring the current response for a specified current response. In some embodiments, the specified current response can be due to a specific voltage step. In some embodiments, the specified current response can be due to a specified sequence of voltage steps. In some embodiments, determining the operating range of the remote device can include adding a bias to the supply voltage step that results in a current response substantially equal to the current response of the previous voltage step. 
     In some embodiments, the current voltage relationship of the remote device can be processed at the power source to guide the voltage at the remote device to converge into the proper operating range. In some embodiments, the voltage can be adjusted to a level that compensates for the voltage drop in a paired wire pair due to at least one of device current draw, wire gauge, and wire length. In some embodiments, the voltage can be DC or AC. 
     There is also provided a system for providing regulated voltage for at least one device remote from a power source. The system includes a power source for supplying voltage to a remote device and a controller for monitoring a current response of the remote device and adjusting the voltage of the power source until a current response reaches an operating range of the remote device. 
     In some embodiments, the remote device can exhibit a non-linear or piecewise linear current-voltage characteristic. In some embodiments, the power source can be coupled to the remote device through a wire pair. In some embodiments, the controller can determine the operating range of the remote device by monitoring the current response. In some embodiments, the controller can monitor the current response over the wire pair. 
     In some embodiments, the supply voltage can be automatically adjusted to a level that compensates for the voltage drop in the wire pair due to at least to device current draw, wire gauge, and wire length. In some embodiments, the current voltage relationship of the remote device is processed at the power source to guide the voltage at the remote device to converge into the proper operating range. 
     In some embodiments, the voltage can be DC or AC. In some embodiments, the power source and controller can be integrated into a single device or comprise separate units. In some embodiments, the controller can have a sensor to monitor the current response. 
     There is further provided a method for providing regulated voltage for at least one device remote from a power source. The method involves means for monitoring a current response of the remote device and means for adjusting a voltage of the power source until the current response reaches an operating range of the remote device. 
     Advantages of the above-mentioned embodiments over the prior art at least include eliminating a individual feedback loop for each remote device, eliminating the need for a licensed professional to install an AC mains connected power supply local to the device, allowing for a reduction in wire gauge to the full extent that is accommodated by the power source compensation, applicability to a broader range of devices that are not equipped for four wire hook ups, all of which reduces the systems overall cost. Additionally, the embodiments provide greater immunity to lengthy feedback wire pair nose pick up, which can cause inaccuracy in regulation control. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages will be apparent from the following more particular description of the embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments. 
         FIG. 1  is a diagram of a typical system for regulating voltage in a remote device, according to the prior art; 
         FIG. 2  is a diagram of a system for regulating voltage in a remote device, in accordance with one embodiment of the present invention; 
         FIG. 3  illustrates the relationships among voltage and current for an exemplary remote device and voltage and current for an exemplary power source; 
         FIG. 4A  is a flow diagram illustrating a method for regulating voltage in a remote device where a current threshold for the remote device is set prior to regulation; and 
         FIG. 4B  is a flow diagram illustrating a method for regulating voltage in a remote device where a current threshold for the remote device is determined; 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a typical power control system  100  according to the prior art. The system  100  includes a power source  110 , a remote device  120 , and a controller  130 . The power source  110  supplies an operating voltage to the remote device  120  over a wire pair or wire run  140 . Due to the finite resistance of the wire pair  140 , voltage drops are incurred as a function of the loading current of the remote device  120 , the wire pair&#39;s  140  gauge, and the wire pair&#39;s  140  length. Thus, it is necessary to raise the power source voltage  110  to compensate for this inherent loss. As such, the controller  130  includes a feedback loop  150  connected to the remote device  120  for monitoring a voltage level at the remote device  120 . If needed, the controller  130  adjusts the power source  110  via a control loop  160 . Although one remote device  120  is shown, multiple remote devices  120  can be connected to the power source  110  and the controller  130 . As such, each remote device  120  needs a separate feedback loop  150  to monitor its respective voltage level. 
       FIG. 2  shows a system  200  for regulating voltage in a remote device or remote system  220 . The system  200  includes a power source  210  which supplies an operating voltage to the remote device  220  over a wire pair or wire run  240 . Due to the finite resistance of the wire pair  240 , voltage drops are incurred as a function of the loading current of the remote device  220 , the wire pair&#39;s  240  gauge, and the wire pair&#39;s  240  length. Thus, it is necessary to raise the voltage of the power source  210  to compensate for the inherent voltage drop. The system  200  includes a controller  230  having a current sensor  250  for monitoring the current response of the wire pair  240  in close proximity to the power source  210 . The current sensor  250  can be part of or separate from the controller  230 . The controller  230  adjusts the power source  210  according to the current-voltage characteristic of the remote device  220 , as is explained further below. In one embodiment, the remote device  220  exhibits a nonlinear current-voltage characteristic. In another embodiment, the remote device  220  exhibits a piecewise linear current-voltage characteristic. Advantageously, the system  200  eliminates the need for the feedback loop  150  ( FIG. 1 ) between the controller  230  and the remote device  220 , as described with reference to  FIG. 1 . 
       FIG. 3  shows load and power supply characteristic graphs. Graph  1  and Graph  2  illustrate exemplary current-voltage relationships for a typical power source  210  ( FIG. 2 ) and a typical device  220  ( FIG. 2 ) (e.g., a Light Emitting Diode Panel, also known as a LED backlight device). Graph  1  illustrates the current-voltage relationship (I LED  (V LED )) for a system when the power source and a device are collocated. Graph  2  illustrates the current-voltage relationship (I PS (V PS )) for a system  200  ( FIG. 2 ) when the power source  210  ( FIG. 2 ) and the device  220  ( FIG. 2 ) are remotely located. As illustrated, Graph  2  shows that a higher voltage is required to operate the device in its optimal region. Thus, a voltage increase is necessary for the current at the remote device  220  ( FIG. 2 ) to equal the current at the collocated device (I PS =I LED ) because a voltage drop occurs over the wire pair  240  ( FIG. 2 ) supplying the remote device  220  ( FIG. 2 ) and a higher voltage compensates for that drop. For example, for a collocated system where the device is a LED backlight device, a voltage of approximately 9V must be supplied to operate in the optimal region, producing a current of 4.5 A. For a remote system  200  ( FIG. 2 ) where the remote device  220  ( FIG. 2 ) is a LED backlight device, a voltage of approximately 17.75V must be supplied to operate in the optimal region, producing a current of 4.5 A. The increase from the required voltage of 9V for a collocated system to 17.75V for a remote system  200  ( FIG. 2 ) results from a voltage drop of 8.75V over the wire pair  240  ( FIG. 2 ) supplying the remote device  220  ( FIG. 2 ). 
       FIG. 4A  shows one example of a flow diagram or algorithm  400  for varying the voltage at a remote device  220  ( FIG. 2 ). First, a current threshold that depends on the remote device&#39;s  220  type is set (Step  405 ). For example, the current threshold for a LED backlight device can be 4.5 A as shown above in connection with Graph  1  ( FIG. 3 ). Next, the power source  210  ( FIG. 2 ) is set to a minimum voltage (Step  410 ). For instance, a minimum voltage can be 3.00 volts. Next, the controller  230  ( FIG. 2 ) measures the current at the location of the power source  210  (Step  415 ). The controller  230  increments the power source  210  voltage (Step  420 ). For example, a power increment can be one volt or any range of voltages known in the art. The voltage increments can range from fractions of a volt to any number of volts and can be in discrete steps or continuous. A new current is measured based on the step increase in the power source  210  voltage (Step  425 ). 
     If the controller  230  determines that the current has reached the desired operating range of the remote device  220  (Step  430 ), then the controller  230  locks the power supply  210  at the current voltage (Step  450 ). The desired operating range varies with device and can be any range or combinations of ranges for the current voltage relationship of a given device. For example, the desired operating range can be a set current threshold. The system  200  ( FIG. 2 ) sets the power supply at the present voltage (Step  450 ) and continuously monitors the current (Step  460 ) with a change in current prompting a new convergence cycle (Step  410 ). 
     If the controller  230  determines that the current has not reached the desired operating range of the remote device  220 , then the controller  230  continues to increment the voltage by one step (Step  420 ) and measure the new current (Step  425 ) until the desired operating voltage has been reached (Step  430 ). In some embodiments, the system  200  may combine the power source  210  and the controller  230  as a single integral unit or as separate units. 
       FIG. 4B  shows another example of a flow diagram or algorithm  500  for the aforementioned system  200  ( FIG. 2 ), where the current threshold is determined by identifying the constant current region. First, the power source  210  ( FIG. 2 ) is set to a minimum voltage (Step  505 ). Next, the controller  230  ( FIG. 2 ) measures the current at the location of the power source  210  (Step  510 ). The controller  230  increments the power source  210  voltage by two steps (Step  515 ). A new current is measured based on the two step increase in the power source  210  voltage (Step  520 ). If the difference between the new current measurement and the measured current before the two step increase is not substantially equal to zero (Step  525 ), the controller  230  recognizes that the current is still climbing in the undesired linear region of the remote device  220  ( FIG. 2 ) and the controller  230  decreases the power source  210  voltage by one step (Step  530 ). From this new voltage, which is a single step voltage increase from the power source voltage before the two step increase, the controller  230  repeats the current difference measurement for a two step voltage increase (Step  510 ) until the current is no longer climbing in the linear region. If the controller  230  determines the current difference is substantially equal to zero, then the remote device  220  is operating in the constant current region and the controller  230  sets the current threshold (Step  535 ). The controller  230  decreases the power source  210  voltage by one step (Step  540 ). In some embodiments, the controller  230  can optionally increase the power source  210  voltage by a safety bias to ensure the remote device  220  is operating within the optimal operating region and not just on the edge of the constant current region. The system  200  ( FIG. 2 ) continuously monitors the current (Step  550 ) with a change in current prompting a new convergence cycle (Step  505 ). 
     The following is one example of the system  200  ( FIG. 2 ) using the algorithm  500  as described with reference to the preceding figures for remotely powered backlighting for LED signs having a current-voltage characteristic shown in Graph  1  ( FIG. 3 ) and is not intended to be a preferred embodiment. Assume the power source  210  ( FIG. 2 ) has a minimum voltage set to six volts (V PS =6.00V) (Step  505 ). Next, the controller  230  ( FIG. 2 ) measures the current at the location of the power source  210  and according to Graph  2  ( FIG. 3 ), the measured current is 1.5 A (Step  510 ), which means that the remote device&#39;s voltage is approximately four volts (V LED =4.00V). The controller  230  increments the power source  210  voltage by two steps (Step  515 ). 
     Assuming a step of 2.00V, the power source  210  voltage is increased from 6.00V to 10.00V. A new current is measured based on the power source  210  voltage increase to 10.00V, the new current being approximately 2.00 A (Step  520 ). Since the difference between the new current measurement and the measured current before the two step increase is 0.50 A (Step  525 ) the controller  230  recognizes that the current is still climbing in the undesired linear region of the LED sign and the controller  230  decreases the power source  210  voltage by one step from 10.00V to 8.00V (Step  530 ). 
     According to Graph  2  ( FIG. 3 ), the algorithm will continue looping through Step  510 , Step  515 , Step  520 , and Step  530  until the voltage at Step  510  has been increased to or above 17.00V (V PS =17.00) because 17.00V is the beginning of the constant current region, entering the optimal operating region. Continuing with the above example of algorithm  500  from a starting voltage of 17.00V, the controller  230  measures the current, the current being 4.50 A (Step  510 ). The controller  230  increments the power source  210  voltage by two steps (Step  515 ) increasing from 17.00V to 21.00V. A new current is measured based on the power source  210  voltage increase to 21.00V, the new current being 4.50 A. Since the difference between the new current measurement and the measured current before the two step increase is zero, the controller  230  determines the LED sign is operating within the constant current region and the controller  230  sets the current threshold (Step  535 ). The controller  230  decreases the power source  210  voltage by one step from 21.00V to 19.00V (Step  540 ). Optionally, the controller  230  then increases the power source  210  voltage by a safety bias to ensure the device is operating within the optimal operating region. Assuming a safety bias of 1.00V, the power source voltage is increased from 19.00V to 20.00V. The system  200  continuously monitors the current (Step  460 ) with a change in current prompting a new convergence cycle (Step  410 ). 
     The system  200  provides distinct economical advantages to distribute power from a remote or central location over wire pairs to devices that require low DC or AC voltages that must be regulated within a remote device dependant compliant range of operation. This is in contrast to installing a separate power supply at each device location. 
     One distinct economical advantage occurs for a device localized power supply scheme which requires a high voltage AC main outlet for each device location. The aforementioned system allows for a centralized approach that reduces the high voltage AC main hookup and the corresponding installation costs to a single outlet for the device. Further, most jurisdictions are governed by electrical codes which require a licensed professional to install the AC outlet, however in most instances for low voltage wiring a licensed professional is not required thereby reducing installation costs. 
     Another distinct economical advantage occurs when attempting to centralize power without the ability to compensate. Centralizing power without the ability to compensate demands that the wire gauge used is sufficiently sized to reduce the effect of its losses for a given wire pair. The cost of the wire increases with the increase in thickness of the wire gauge. The aforementioned system allows for the use of thinner wire gauge, since wire losses can be automatically compensated by voltage adjustment of the sourcing supply thereby reducing overall costs. 
     Another distinct economical advantage occurs because the aforementioned system allows for remote adjustment of the power being coupled to the remote device, eliminating the need for manual compensation. Manual compensation requires greater installer knowledge of the complex interaction of wire length, wire gauge, voltage drop and load current, as well parametric accuracy of these corresponding components. Manual adjustments are static and can not respond to dynamic load change or future renovations that could endanger device operation. The ability to provide remote or centralizing sourcing of power confers numerous advantages as, but not limited to, those shown above. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.