Abstract:
Apparatus and methods for boosting power supplied at a remote node in a distributed power system in response to a feedback signal derived from a measured voltage at a remote node include, in one embodiment, a power system with remote boost regulation employing a variable power supply and a remote active boost regulator working in coordination. The remote active boost regulator monitors the variable power supply output voltage; using an amplifier, compares the measured voltage with a reference voltage; and generates a feedback signal. The feedback signal is delivered to a variable power supply causing the power supply to increase, or boost, output voltage to compensate for distribution losses and remote loading.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to electrical power systems and specifically to varying nominal power supply output in response to a remote sense input.  
         BACKGROUND OF THE INVENTION  
         [0002]    In low voltage distributed power systems known to the prior art and shown in FIG. 1, a bulk power supply  10  provides one or more voltages to a number of distributed electronic loads  12 A through  12 N (generally  12 ). These loads  12  may be individual chassis within an equipment rack, or removable circuit cards connected to a computer motherboard or back-plane.  
           [0003]    The voltage levels at the individual loads  12  will be less than the rated output of the bulk power supply. This reduced power level at the loads results from power loss, or voltage “drop,” across current-carrying conductors of the power distribution system. This voltage drop results from the power supply current interacting with an equivalent impedance of the current-carrying conductors. FIG. 1 is a schematic representation of a distributed power system where the equivalent impedance of each segment of the power distribution system is shown in phantom view as resistors  14  and  16 A through  16 N (generally  16 ). Resistors ( 14  or  16 ) are shown in phantom because they represent the equivalent impedance due to the finite conductivity of the physical conductors and are not actual resistors. The magnitude of the voltage drop within any segment of the power distribution system is determined as the value of current flowing through that segment multiplied by the equivalent impedance value flowing within that segment.  
           [0004]    Thus, without compensation, a voltage “droop” occurring at the loads may impact performance by introducing errors, such as logical errors where logic levels of a particular circuit card are operating outside of their applicable specified input power values, or perhaps even in hardware faults for similar reasons.  
           [0005]    Although many techniques have been tried to solve this problem, the most sophisticated to date has been to use standard, commercially available variable bulk power supplies with remote sensing, where the voltage at a remote point can be increased above the supply&#39;s nominal rated output power by reporting a remote sense signal that is less than the actual sensed value. The variable bulk power supply increases its output to overcome the power distribution system loss and the artificial offset value. Current systems perform the artificial offset to the remote sense signal with resistive networks. The resistive networks are carefully designed to provide a fixed impedance value. The impedance value is selected to cause a controlled offset to the remote sense signal and induce the desired overall increase, “boost,” in supplied power.  
           [0006]    Although conceptually straightforward, implementation of a resistive network approach presents practical limitations. When selecting resistor values to fabricate the resistive network, the internal impedance of the bulk variable power supply must be included. Incorporation of the power supply impedance into the equation necessarily ties the design of the resistive network to the selected power supply. A power supply internal impedance typically varies between devices, for reasons related to the power supply&#39;s internal architecture and selected fabrication components. Substituting one power supply for another into a circuit including a resistive network designed to increase the remote voltage by a predetermined amount can result in a variation of the voltage supplied to the distributed loads that again could result in voltage droops, or conversely, could create excessive voltage resulting in damage to the loads. The present invention avoids this problem.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention relates to apparatus and methods for boosting power supplied at a remote node in a distributed power system. One embodiment of the invention boosts a regulated voltage at a remote point in a distributed power system to compensate for additional distribution losses beyond the point of regulation. The techniques disclosed are independent of the internal impedance characteristic of the variable power supply source.  
           [0008]    In one aspect, a power system with remote boost regulation employs a variable power supply and a remote active boost regulator working in coordination, where the remote active boost regulator monitors the variable power supply output voltage and generates a feedback signal. In this embodiment, the feedback signal is delivered to the variable power supply causing the power supply to increase, or boost, its output compensating for distribution losses and remote loading.  
           [0009]    One feature of the invention in one embodiment is the remote active boost regulator including a differential voltage amplifier which itself uses a reference voltage source. The reference voltage source is compared with the measured signal from the remote sensed voltage and the differential amplifier output is adjusted accordingly.  
           [0010]    In another aspect, a power system with remote boost regulation for connection with a variable power supply where the remote active boost regulator monitors the variable power supply output voltage and generates a feedback signal. In this embodiment, the feedback signal is delivered to the variable power supply causing the power supply to increase, or boost, its output compensating for distribution losses and remote loading.  
           [0011]    In yet another aspect, a method for reducing the effect of transmission losses in a distributed power system where a voltage is measured at a remote point in the distributed power system, the measured value is compared with a reference voltage value, and a changing feedback signal is generated in response to any differences between the measured and reference values. In this embodiment, the feedback signal is provided to a variable power source causing an increase, or a boost voltage, by an amount that is proportional to the feedback signal.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention is pointed out with particularity in the appended claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. Like reference characters in the respective drawing figures indicate corresponding parts. The advantages of the invention described above, as well as further advantages of the invention, may be better understood by reference to the description taken in conjunction with the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 is a block diagram of a distributed load power system known to the prior art;  
         [0014]    [0014]FIG. 2 is a block diagram of an embodiment of an electrical power system;  
         [0015]    [0015]FIG. 3 is a block diagram of an embodiment of a variable power source;  
         [0016]    [0016]FIG. 4 is a block diagram of an embodiment of a remote active regulator; and  
         [0017]    [0017]FIG. 5 is a flowchart of an embodiment of a variable power source with remote active regulation. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Referring now to FIG. 2, an embodiment of a power distribution system is shown in which the present invention can be used. The system includes a variable power supply  10 , a plurality of electrical loads  12 A through  12 N (generally  12 ) and a remote active boost regulator  20 . The variable power supply  10  has at least three terminals: a supply output terminal (V_OUT) providing a supply voltage; a supply input terminal sensing a feedback signal (REMOTE SENSE); and a supply sense return terminal (RETURN). The remote active boost regulator  20  also has at least three terminals: a regulator input terminal; a regulator sense return terminal; and a regulator output terminal.  
         [0019]    In one embodiment, the loads  12  represent electronic circuit cards; whereas, other embodiments, the loads may represent separate system components, modules, or any other element requiring electrical power. The configuration of the loads  12  can be lumped, where the loads are located in close proximity to each other, or distributed, where the loads are separated by conductors of the power distribution system. For either configuration of the loads  12 , some or all of the loads  12  may be located remotely from the variable power supply  10 . FIG. 2 is an electrical schematic representation of the power distribution system; therefore, the physical separation distances between the loads  12  and the variable power supply  10  are not depicted.  
         [0020]    The variable power supply  10  supply output terminal (V_OUT) is in electrical communication with a first side of each of the loads  12 , through a common electrical interconnect represented by a remote node  18 . In one embodiment, the remote node  18  represents a common interconnect at a distant location, as measured along the interconnecting electrical conductor, from the variable power supply  10 . Referring to FIG. 2, the remote node  18  is shown located between a load  12 B and a load  12 N. However, since FIG. 2 is a schematic circuit representation, the node  18  could equivalently be located at any point between the variable power supply  10  and the load  12  located at the most remote distance. Details reflecting the actual distances and locations of the loads  12  with respect to the variable power supply  10  are not apparent from a schematic diagram such as FIG. 2, but would be provided from a layout diagram.  
         [0021]    A second side of each of the loads  12  is in electrical communication with the variable power supply  10  supply sense return terminal (RETURN), with the remote active boost regulator  20  regulation sense return terminal and with a circuit reference potential. For the embodiment shown in FIG. 2, the sense return input is also in electrical communication with a ground potential representing, substantially, a relative zero circuit reference potential value. The remote active boost regulator  20  regulator input terminal is in electrical communication with the remote node  18 , and the remote active boost regulator  20  regulator output terminal is in electrical communication with the variable power supply  10  supply input terminal.  
         [0022]    In a realization of an embodiment of the invention, a portion of the variable power supply  10  output power will be dissipated, or lost, before the power is delivered to the loads  12 . This loss is attributable to an equivalent impedance of the current carrying conductors of the power distribution system and is related to their finite conductivity. Referring to FIG. 2, the characteristic impedance is shown in as phantom resistive elements indicating that the resistance is due to the conductor, and not an actual resistor element. A resistive element  14  represents the equivalent impedance attributed to the segment of the power distribution system located between the variable power supply  10  and the remote node  18 . Equivalent impedances  16 A through  16 N (generally  16 ) of each segment of the circuit are shown in phantom and represent the equivalent impedance between the remote node  18  and each individual load  12 . Summation of the variable power supply  10  output voltage, the voltage drop across the resistive element  14  yields the equivalent voltage at the node  18 . Summation of the voltage at the node  18  and each of the resistive elements  16 , yields the voltage value supplied to each of the respective loads  12 .  
         [0023]    Generally, the remote active boost regulator  20  measures the voltage value at the remote node  18 , compares that value to a reference voltage, and generates a feedback signal being a function of the difference between the two values. The feedback signal is provided as an output signal on the remote active boost regulator  20  regulator output terminal. The feedback signal is provided as an input to the variable power supply  10  and causes the variable power supply  10  to adjust its output voltage, when necessary. The regulating action allows the variable power supply  10  output to be maintained at a substantially fixed value, even under conditions of changing loads, such as when the loads  12 , representing circuit cards, are removed or replaced from a back-plane while power is applied.  
         [0024]    In one embodiment, a nominal supply voltage value is provided at the loads  12 , by providing a requested voltage value at the remote node  18  that is an amount greater than the nominal supply voltage. The amount by which the nominal variable power supply  10  output is boosted is predetermined to be a value sufficient to compensate for the additional voltage drop across each resistive element  16  between the remote node  18  and each respective load  12 . In another embodiment, the remote active boost regulator  20  provides a feedback signal to the variable power supply  10  providing a supply output voltage of sufficient magnitude to result in a voltage value at the remote node  18  that is between approximately 2% and approximately 4% above the nominal supply voltage, compensating for additional voltage drops due to the electrical conductors interconnecting the remote node  18  to the individual loads  12 , represented by an equivalent resistive elements  16 . In one embodiment, the variable power supply  10  nominal output voltage is between approximately 0.5 volts and approximately 15 volts. In another embodiment, the variable power supply  10  nominal output voltage is more than approximately 3.3 volts. In yet another embodiment, the variable power supply  10  nominal output voltage is more than approximately 5 volts. In yet other embodiments, the variable power supply  10  nominal output voltage operates at 12 volts, or 24 volts, or 48 volts, for such applications as powering Direct Current (DC)/DC converters, disk drive motors, and cooling fans.  
         [0025]    A preferred embodiment includes a variable power supply  10  that is a low-voltage DC power supply. Other embodiments are possible where the variable power supply  10  is a regulating high-voltage DC power supply.  
         [0026]    Referring to FIG. 3, in one embodiment, the variable power supply  10  includes a non-inverting power amplifier  42 , and a reference source  44 . A first (non-inverting) input to the amplifier  42  is connected to a first side of a the reference source  44 . A second side of the reference source  44  is connected to a ground potential. The output of the amplifier  42  is connected to the variable power supply  10  output terminal (V_OUT) and to a second (inverting) input to the amplifier  42 , through at least two resistive elements  46  and  48 . The inverting input of the amplifier  42  is also connected to the variable power supply  10  return terminal (RETURN) through a resistive element  50 . The variable power supply  10  remote sense input (REMOTE SENSE) is connected to a second input of the amplifier  42 , through a resistive element  48 .  
         [0027]    The variable power supply  10  provides a primary voltage delivered to the distributed loads shown in FIG. 2. The regulated output voltage is supplied across the variable power supply  10  output terminals: V_OUT; and RETURN. Referring again to FIG. 3, the amplifier  42  provides a gain control mechanism for the output voltage. The amplifier  42  includes a feedback path, where control through the feedback path can be used to increase or decrease the variable power supply  10  output voltage signal as a function of the signal present at the inputs to amplifier  42  and the particular selected values of the resistive components ( 46 ,  48 , and  50 ). In one embodiment, the variable power supply  10  remote sense input accepts a current signal from the remote active boost regulator  20 . This current input signal is also input into the inverting terminal of the amplifier  42  providing a remote sense feedback signal that controls the output of the amplifier  42  and can be used to further regulate the output by increasing or decreasing the output voltage.  
         [0028]    Referring to FIG. 4, in one embodiment, the remote active boost regulator  20  includes a two-stage amplifier including a first-stage amplifier  22  and a second-stage transistor amplifier  24 . The base terminal of the transistor  24  is connected to the emitter terminal of the transistor  24  through a resistive element  26 . The base terminal of the transistor  24  is also connected to the amplifier  22  output through a resistive element  28 . The emitter terminal of the transistor  24  is connected to the remote active boost regulator  20  voltage sensing input terminal (V_NODE) and a first input terminal of the amplifier  22  through a resistive element  32 . The collector terminal of the transistor  24  is connected to the remote active boost regulator  20  output terminal (REMOTE SENSE) and to the remote active boost regulator  20  return terminal through a resistive element  30 . The output of the amplifier  22  is also connected to a first input of the amplifier  22  through a capacitive element  36 .  
         [0029]    The first-stage amplifier  22  amplifies the voltage difference measured at the input of the amplifier  38  between the measured voltage at remote node  18  of FIG. 2, and a reference source  40 . The amplifier  38  amplifies the difference and provides it as an output voltage signal. The first-stage amplifier  22  voltage signal is input to the second-stage amplifier where it is applied to the base of the transistor  24 . The transistor  24  acts as a current amplifier, amplifying the current related to the output of the first-stage amplifier  22 . The amplified current resides on the collector of transistor  24  and is provided as an output representing the remote active boost regulator  20  feedback signal. The capacitive element  36 , and resistive elements act in combination with the amplifier  22  and the transistor  24 , to provide a loop response time. The loop response time is an indication of how fast the remote active boost regulator  20  can respond to a change in the measured voltage. The loop response time can be varied depending upon the selection of the components. The remote active boost regulator  20  loop response time is selected to be compatible with the loop response time of the variable power supply  10 , so that the combined circuit does not adversely impact the original stability, or response time, of the variable power supply  10  alone.  
         [0030]    Other embodiments are possible where feedback signals provided by the remote active regulator  20  consist of modulated signals, such as pulse-width modulated signals, frequency modulated signals, or phase shift keyed modulated signals. Other embodiments are also possible where the feedback signal is converted from an analog to digital signal and transmitted to the variable power supply  10  as a digital number, where it is subsequently transformed back into an analog feedback signal at the input to the variable power supply  10 . Yet other embodiments are possible where the feedback signals provided by the remote active regulator  20  are provided over fiber-optic cables, perhaps to overcome electromagnetic interference with the feedback signal in electrically “noisy” environments.  
         [0031]    An embodiment of the distributed load power distribution system with remote active boost regulation is shown in FIG. 5. After system power-up, the variable power supply  10  provides input power to the power distribution system, shown in FIG. 2 as loads  12  (step  10 ). The current flows throughout the power distribution system to each load  12 , experiencing voltage drops resulting from the equivalent impedance of the interconnecting leads ( 14  or  16 ). The remote active boost regulator  20  measures the voltage at a the remote node  18  (step  20 ). This voltage for the embodiment shown in FIG. 2, is the variable power supply  10  output voltage level at the supply terminal less the value of the resistive drop attributable to the segments of the power distribution system between the variable power supply  10  and the remote node  18 , and are calculated as the supply output current multiplied by the resistive value  14 . The remote active boost regulator  20  compares the voltage measured at the remote node  18  with a reference voltage to determine any difference between the two values (step  30 ). Where a difference exists between the voltage measured a the remote node  18  and the reference voltage, the remote active regulator  20  alters a feedback signal and delivers it to the remote sense terminal of the variable power supply  10  (step  40 ). The variable power supply  10  accepts the feedback signal input from the remote active regulator  20  and adjusts its output level in response, providing a boost voltage where the voltage measured at the remote node  18  is below the reference voltage (step  50 ).  
         [0032]    Having shown the preferred embodiments, one skilled in the art will realize that many variations are possible within the scope and spirit of the claimed invention. It is therefor the intention to limit the invention only by the scope of the claims.