Abstract:
A system for supplying AC power to a display via a CAT7 or similar low voltage cable comprises a transmitter connected to an AC power outlet and generating DC voltage transmitted by the CAT7 cable to a receiver. The receiver converts the DC voltage to AC voltage and supplies AC power to the display. A limiting circuit limits power transmitted by the CAT7 cable to a predetermined wattage, depending on the feedback from the receiver, which insures safe operation of the system. Power from the display is disconnected if a pre-programmed power consumed by the display is exceeded or falls below a predetermined threshold.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a system for supplying AC power to a display via a low voltage cable, such that a dedicated AC power outlet is no longer necessary. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is frequently desirable to install displays, such as flat screen TVs and the like, on concrete or masonry walls or in other locations lacking existing AC power outlets. Installing AC power outlets and running high voltage power cables to supply AC power to displays in such locations is often expensive and unsightly. In some cases, due to a historical nature of buildings, it is not possible to install electrical outlets and avoid damaging surrounding walls. In addition, installing AC power outlets requires a licensed high voltage contractor to do the installation. The same is true when a display is placed or installed temporarily with no power outlets within convenient reach. At the same time, low voltage cables, such as CAT5, CAT6 and CAT7 type cables, are frequently used to supply audio visual content, network and control signals to displays. These CAT type cables are small in diameter and are easy to route and feed through a wall, ceiling and floors. The CAT type cables can be installed by a low voltage contractor who is already on installation site and is involved in installation of audio visual equipment. 
         [0003]    Therefore, there is a need for a system for supplying AC power to a display via a low voltage cable, such that a dedicated AC power outlet connected by high voltage power cable is no longer necessary. 
       SUMMARY OF THE INVENTION 
       [0004]    The system for supplying AC power to a display via a low voltage cable according to this invention satisfies this need. It comprises a transmitter connected to an AC power outlet and generating DC voltage transmitted by a low voltage cable, comprising at least two wires, to a receiver. The receiver then converts the DC voltage, to AC voltage and supplies AC power to the display. A limiting circuit in the transmitter limits power transmitted by the low voltage cable to a predetermined wattage, depending on the feedback from the receiver, which insures safe operation of the system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  shows a schematic of a system according to this invention; 
           [0006]      FIG. 2  shows a schematic of a transmitter according to this invention; 
           [0007]      FIG. 3  shows a schematic of a receiver according to this invention; 
           [0008]      FIG. 4  shows a schematic of a transmitter with the limiting circuit in a disengaged position; 
           [0009]      FIG. 5  shows a schematic of a transmitter with the limiting circuit in an engaged position; 
           [0010]      FIG. 6  shows a schematic of a CAT5, CAT6 or CAT7 cable connecting the transmitter and receiver according to the preferred embodiment of this invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    This invention will be better understood with reference to the drawing  FIGS. 1 through 6 . The same numerals refer to the same elements on all drawing figures. 
         [0012]    Viewing  FIG. 1 , numeral  10  indicates a transmitter. Numeral  20  indicates a receiver. Numeral  30  indicates a low voltage cable. Numeral  40  indicates a display. Numeral  140  indicates a first voltage. Numeral  150  indicates a third voltage. Transmitter  10  is energized by first voltage  140 . Transmitter  10  generates a second voltage energizing receiver  20  by way of low voltage cable  30  connecting transmitter  10  and receiver  20 . Receiver  20  generates third voltage  150  and supplies same to display  40 . First voltage  140  is AC, the second voltage is DC and third voltage  150  is AC. 
         [0013]    Viewing now  FIG. 2 , numeral  50  indicates a first converter circuit. First converter circuit  50  converts first voltage  140  into a DC second voltage. Numeral  60  indicates a limiting circuit. Limiting circuit  60  has engaged and disengaged positions, such that the disengaged position limits power transmitted via low voltage cable  30  to a first wattage and the engaged position allowing up to a second wattage to be transmitted via low voltage cable  30 . 
         [0014]    Numeral  70  indicates an interrogating circuit interrogating circuit  70  controls limiting circuit  60  by way of interrogating receiver  20  with an interrogating signal at a predetermined frequency. Interrogating circuit  70  places limiting circuit  60  in the engaged position if receiver  20  is in communication with transmitter  10 . Interrogating circuit  70  places limiting circuit  60  in the disengaged position if receiver  20  is not in communication with transmitter  10 . Interrogating circuit  70  generates the interrogating signal. The interrogating signal is in a digital format and is transmitted as a data packet to receiver  20 . The data packet contains information that allows receiver  20  to know that a specific transmitter type is sending this data. Upon receipt of this signal, receiver  20  will acknowledge it and will send back confirmation identifying itself as capable of receiving the second wattage. Once interrogating circuit  70  receives the acknowledgment signal from receiver  20 , it will place limiting circuit  60  into the engaged position to increase power output. 
         [0015]    The interrogation occurs at least one time per second. This is done to assure that if low voltage cable  30  is disconnected from receiver  20  or accidently cut, the power available from transmitter  10  is reduced to the first wattage. If the interrogating signal is not received by receiver  20  within one second, receiver  20  automatically shuts down third voltage  150  to maintain safety interlock. 
         [0016]    Viewing now  FIG. 3 , numeral  90  indicates a second converter circuit. Second converter circuit  90  converts the second voltage to the fourth voltage. Numeral  100  indicates an inverter circuit. Inverter circuit  100  converts the fourth voltage to the third voltage. The fourth voltage is DC and is substantially double the second voltage. 
         [0017]    In the preferred embodiment described with the reference to the drawing  FIGS. 1 through 6 , the first voltage is substantially between 100V and 240V; the second voltage is substantially 60V; the third voltage is substantially between 95V and 120V. 
         [0018]    Viewing now  FIG. 4 , limiting circuit  60  is shown in the disengaged position, thus only the first wattage is available to low voltage cable  30 . In the preferred embodiment described with the reference to the drawing  FIGS. 1 through 6 , the first wattage is substantially 100 W. Further, in the preferred embodiment, limiting circuit  60  further comprises a first fuse indicated by numeral  60   a,  a second fuse indicated by numeral  60   b  and a relay indicated by numeral  60   c.  The fuse type is a polyfuse that disconnects current flow when current limit of the fuse is exceeded and reconnects current back when current flow is below the current rating of the fuse. 
         [0019]    First fuse  60   a  is connected serially to first converter circuit  50 . Second fuse  60   b  is connected serially to first fuse  60   a.  Relay  60   c  is connected in parallel with first fuse  60   a  between first converter circuit  50  and second fuse  60   b.    FIG. 4  shows relay  60   c  being open. Relay  60   c  is open in the disengaged position and closed in the engaged position. First fuse  60   a  has lower current limit rating than second fuse  60   b.  When relay  60   c  is open, current passes through both first fuse  60   a  and second fuse  60   b,  as indicated by a heavy dashed line in  FIG. 4 . Accordingly, power transmitted via low voltage cable  30  is limited to the first wattage, which is in this case 100 W. 
         [0020]    Viewing now  FIG. 5 , limiting circuit  60  is shown in the engaged position, thus allowing up to the second wattage to be transmitted via low voltage cable  30 . In the preferred embodiment described with the reference to the drawing  FIGS. 1 through 6 , the second wattage is substantially 172 W. 
         [0021]    National Electrical Code (NEC) dictates that the maximum power transmitted over a CAT type cable is 100 W. In the same Code, there is an exemption that if the receiver is known then the power can be increased to about 200 W. When using CAT type cables, special connectors are used to connect cables and equipment. The connectors are referred to as RJ-45. The RJ-45 connectors are rated to maximum 172 W and this is the limitation of the second wattage. 
         [0022]    When relay  60   c  is closed, current bypasses first fuse  60   a  and passes only through second fuse  60   b,  as indicated by a heavy dashed line in  FIG. 5 . Accordingly, power transmitted via low voltage cable  30  is allowed up to the second wattage, which in this case is 172 W. 
         [0023]    In the preferred embodiment, interrogating receiver  20  by interrogating circuit  70  further comprises receiving, by interrogating circuit  70 , a positive or negative authentication signal. The positive authentication signal is received when receiver  20  is capable of accepting the second wattage (i.e., 172 W). The negative authentication signal is received when receiver  20  is not capable of accepting the second wattage and can only accept first wattage. Interrogating circuit  70  places limiting circuit  60  in the engaged position in the event the positive authentication signal is received and places limiting circuit  60  in the disengaged position in the event the negative authentication signal is received. 
         [0024]    Interrogating circuit  70  generates interrogating signal. This signal is in digital format and is transmitted as a data packet to receiver  20 . The data packet contains information that allows receiver  20  to know that a specific transmitter type is sending this data. This information may contain model number, manufacturer name and serial number of transmitter  10 . Upon receipt of this signal, receiver  20  will acknowledge it and will send back confirmation identifying itself as capable of receiving the second wattage. Once interrogating circuit  70  receives the acknowledgment signal from receiver  20 , it will place limiting circuit  60  in the engaged position to increase power output. 
         [0025]    Viewing now, simultaneously,  FIGS. 2 ,  4  and  5 , numeral  80  indicates a first combiner circuit. First combiner circuit  80  is connected serially to second fuse  60   b  and is in communication with interrogating circuit  70 . First combiner circuit  80  combines the second voltage and the interrogating signal and separates the second voltage from the positive or negative authentication signal. 
         [0026]    Combiner circuit  80  comprises a transformer that separately passes DC voltage for power and a high frequency digital signal for interrogation. These two signals simultaneously pass through the transformer and are available at receiver  20 . The interrogation signal can pass bidirectionaly between transmitter  10  and receiver  20 . 
         [0027]    Viewing again  FIG. 3 , numeral  110  indicates a responding circuit. Responding circuit  110  communicates either the positive or negative authentication signal to interrogating circuit  70  in response to the interrogating signal. Numeral  120  indicates a second combiner circuit. Second combiner circuit  120  is connected serially to second converter circuit  90  and is in communication with responding circuit  110 . Second combiner circuit  120  combines the second voltage with the positive or negative authentication signal and separates the second voltage from the interrogating signal. 
         [0028]    Combiner circuit  120  comprises a transformer that separately passes DC voltage for power and a high frequency digital signal for interrogation to responding circuit  110 . These two signals simultaneously pass through the transformer and are available at receiver  20 . The interrogation signal can pass bidirectional between transmitter  10  and receiver  20 . 
         [0029]    Numeral  130  indicates a current managing circuit. Current managing circuit  130  increases voltage to display  40  at a predetermined rate. In the preferred embodiment, the predetermined rate is substantially between 10 and 50 volts per second. 
         [0030]    All displays have capacitors on the power input. These capacitors are used to maintain steady voltage after AC power is received and rectified. Mere presence of these capacitors creates an in-rush current that can exceed 100 amps when AC power is applied to the monitor. This inrush current, if not managed, would exceed the current limit established for RJ-45 connectors and the current limit of the second voltage  50 . To reduce the inrush current, third voltage  150  on the input to display  40  needs to be slowly increased. This slow voltage rise allows display  40  input capacitors to charge at a slower rate and reduce inrush current to acceptable level. Depending on the display type and input capacitance, the rate of voltage increase can vary between 10 to 50 volts per second and still maintain acceptable inrush current. 
         [0031]    Further, current managing circuit  130  disconnects power from display  40  if a pre-programmed power consumed by display  40  is exceeded. In the preferred embodiment, the preprogrammed power is substantially 150 W. 
         [0032]    The total power transmitted over low voltage cable  30  is 172 W. The cable resistance loss, circuitry and efficiency of the voltage conversion in receiver  20  will use about 22 W, therefore the maximum power available for display  40  is substantially 150 W. If receiver  20  circuitry power consumption is decreased and conversion efficiency from the second voltage to the fourth voltage and to third voltage  150  is increased, then the output power can be increased above 150 W. 
         [0033]    Further, current managing circuit  130  disconnects power from display  40  if third voltage  150  falls below a predetermined threshold. In the preferred embodiment, the predetermined threshold is substantially 50 volts. 
         [0034]    As low voltage cable  30  length is increased, the power available to receiver  20  is decreased, since there is the power loss in low voltage cable  30 . Once voltage drops to about 50 volts, converter  90  is not capable of producing the voltage necessary fir display  40  to operate properly. Convertor  90  produces the third voltage that needs to be substantially 95 to 120 volts. If third voltage  150  is below 95 volts, it will not produce enough voltage for display  40  to operate. 
         [0035]    Viewing now  FIG. 6 , low voltage cable  30  is selected from the group consisting of a CAT5 cable, CAT6 cable and CAT7 cable. In the preferred embodiment shown in  FIG. 6 , a CAT7 cable comprising eight wires indicated by numerals  30   a,    30   b,    30   c,    30   d,    30   e,    30   f,    30   g  and  30   h  is used. 
         [0036]    Wires  30   a,    30   b,    30   c  and  30   d  transmit the positive side of the second voltage and wires  30   e,    30   f,    30   g  and  30   h  transmit the negative side of the second voltage. 
         [0037]    While the present invention has been described and defined by reference to the preferred embodiment of the invention, such reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled and knowledgeable in the pertinent arts. The depicted and described preferred embodiment of the invention is exemplary only, and is not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.