Abstract:
A redundant power supply method is provided. The method includes communicatively coupling a load to a first source via a plurality of first power supplies and to a second source via a plurality of second power supplies. The method further includes bi-directionally communicatively coupling a controller to the plurality of first power supplies and to the plurality of second power supplies. The method includes activating a first portion of the plurality of first power supplies to supply power to the load, wherein the controller determines the number (“N”) of first power supplies activated, and activating at least one of the plurality of second power supplies to supply power to the load. The method also includes monitoring for at least one fault condition in each of the active first power supplies and in each of the active second power supplies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to co-pending U.S. patent application Ser. No. 12/491,773 entitled “Multiple Power Supply Control,” filed on 25 Jun. 2009 by inventors Daniel Humphrey, Mohamed Amin Bemat, and Reynaldo P. Domingo, and owned by the same assignee now and at the time of invention. This application is a divisional of, and claims priority to commonly owned, co-pending, U.S. patent application Ser. No. 12/512,017, entitled “REDUNDANT POWER SUPPLY SYSTEMS AND METHODS,” filed on 29 Jul. 2009 now U.S. Pat. No. 8,067,857 by inventors Daniel Humphrey, Mohamed Amin Bemat, Reynaldo P. Domingo, and Xiqun Zhu. 
    
    
     BACKGROUND OF THE INVENTION 
     Description of the Related Art 
     This section is intended to introduce the reader to various aspects of art which may be related to one or more aspects of the present invention as described and claimed below. This discussion is believed helpful in providing the reader with background information, thereby facilitating a better understanding of various aspects of the present invention. Accordingly, it should be understood by the reader that the provided information should be read in this light and not as an admission of any prior art. 
     Redundant power supplies are often used where high reliability and nearly continuous availability of power is of primary importance. In such “mission critical” applications, it is not uncommon to have simultaneously online both a primary supply system and a redundant secondary supply system, with both systems capable of meeting the full demand presented by the load. While such a system provides significant protection from unexpected power supply interruption, the requirement to continuously maintain twice the required number of power supplies online significantly impacts the overall energy efficiency of each power supply, since the efficiency of a power supply is generally proportionate to the overall demand placed upon the supply. In other words, power supply efficiency, measured as a ratio of power supplied divided by power demand, tends to increase as the power demand increases. 
     Dynamic power savings can be used to improve the overall energy efficiency of systems using redundant power supplies. With dynamic power savings, rather than requiring all of the primary and secondary power supplies continuously online, only the power supplies necessary to support the load demand are placed continuously online. By way of an illustrative example, assume a system with a load having a maximum demand of 5,000 watts (5 kW), five (5) primary 1,000 watt (1 kW) power supplies, and five secondary 1 kW power supplies. Without dynamic power savings at a load demand of 3 kW, all ten supplies (five primary supplies+five secondary supplies) would continuously operate with each carrying approximately 10% (˜300 watts/each) of the load. With dynamic power savings, at a load demand of 3 kW, only six supplies (three primary supplies+three secondary supplies) would continuously operate, each carrying approximately 17% (˜500 watts/each) of the load. Thus, dynamic power savings generally increases overall system efficiency by increasing the load present on each of the independent power supplies comprising the system. 
     SUMMARY OF THE INVENTION 
     A redundant power supply method is provided. The method includes communicatively coupling a load to a first source via a plurality of first power supplies and to a second source via a plurality of second power supplies. The method further includes bi-directionally communicatively coupling a controller to the plurality of first power supplies and to the plurality of second power supplies. The method includes activating a first portion of the plurality of first power supplies to supply power to the load, wherein the controller determines the number (“N”) of first power supplies activated, and activating at least one of the plurality of second power supplies to supply power to the load. The method also includes monitoring for at least one fault condition in each of the active first power supplies and in each of the active second power supplies. 
     A redundant power supply system is also provided. The system can include a load suitable for providing a variable demand, at least one of a plurality of first power supplies communicatively coupling a first source to the load, at least one of a plurality of second power supplies communicatively coupling a second source to the load, and at least one controller bi-directionally communicatively coupled to at least a portion of said first and at least a portion of said second power supplies. The controller can be adapted to activate and deactivate at least a portion of the plurality of first power supplies in response to changes the variable demand presented by the load. The controller can also be adapted to monitor for at least one failure mode for at least a portion of the plurality of first power supplies and at least a portion of the second power supplies. 
     Another redundant power supply method is also provided. The method can include communicatively coupling a first source to a plurality of first power supplies, communicatively coupling a second source to a plurality of second power supplies, and communicatively coupling at least one controller to the plurality of first power supplies and the plurality of second power supplies. The communicative coupling between each of the first power supplies, each of the second power supplies, and the at least one controller can include: a power supply input failure signal; a power supply output failure signal; a power supply activation signal, adapted to transition the power supply from a deactivated state to an activated state; and a power supply deactivation signal, adapted to transition the power supply from an activated state to a deactivated state. The method can also include monitoring, via the controller, for a power supply input failure signal or a power supply output failure signal from each of the first power supplies and each of the second power supplies. The method includes having the controller respond to the receipt of a power supply input failure signal from at least one first power supply by transmitting a power supply activation signal to at least a portion of the plurality of second power supplies, and transmitting a power supply deactivation signal to the plurality of first power supplies. The method further includes having the controller respond to the receipt of a power supply output failure signal from at least one first power supply by transmitting a power supply activation signal to at least a portion of the plurality of second power supplies and transmitting a power supply deactivation signal to the at least one first power supply generating the power supply output failure signal. 
     As used herein, the term “power supply” and the plural “power supplies” can refer to any device, system, or combination of systems and/or devices suitable for the conversion of a power input to one or more desired power outputs. Such conversion process can include one or more of the following services on the power input, power output, or both power input and power output characteristics: AC-to-DC rectification, voltage regulation, current regulation, overcurrent protection, current filtering, frequency shifting, frequency filtering, frequency regulation, and voltage filtering. A non-limiting, exemplary, power supply can be found inside of a personal computer. Such a power supply can be used to convert 120 or 220 volt household alternating current to 12 volt direct current, 5 volt direct current, and 3.3 volt direct current for use by various components disposed within the computing device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features can be understood in detail, a more particular detailed description, briefly summarized above, may be had by reference to one or more exemplary embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments and therefore should not be considered or construed as limiting of its scope, for other equally effective embodiments as claimed herein may exist. 
       Advantages of one or more disclosed embodiments may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  depicts an illustrative redundant power supply system, according to one or more embodiments described herein; 
         FIG. 2  depicts an illustrative logic flow diagram for an exemplary redundant power supply system, according to one or more embodiments described herein; 
         FIG. 3  depicts an illustrative timing diagram for an exemplary redundant power supply system, according to one or more embodiments described herein; 
         FIG. 4  depicts an illustrative N+1 redundant power supply system with an illustrative output fault, according to one or more embodiments described herein; 
         FIG. 4A  depicts the illustrative N+1 redundant power supply system depicted in  FIG. 4  responding to a power supply output failure, according to one or more embodiments described herein; 
         FIG. 5  depicts an illustrative N+1 redundant power supply system with an illustrative source failure, according to one or more embodiments described herein; and 
         FIG. 5A  depicts the illustrative N+1 redundant power supply system depicted in  FIG. 5  responding to the source failure, according to one or more embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts an illustrative redundant power supply system  100 , according to one or more embodiments. The redundant power supply system  100  can include, but is not limited to, a load  110  communicatively coupled to a first source  120  via one or more first power supplies  130 , and communicatively coupled to a second source  140  via one or more second power supplies  150 . Although not depicted in  FIG. 1 , in one or more embodiments, the first source  120  can be the same as the second source  140 . The redundant power supply system  100  can also include a controller  160  having one or more signal outputs (two are depicted in  FIGS. 1 ,  170  and  180 ) and one or more signal inputs (three are depicted in  FIGS. 1 ,  165 ,  175 , and  185 ). 
     Although the redundant power supply system  100  will be discussed within the context of an electronic computing device, it should be noted that similar embodiments can also include virtually any electrically powered load  110  having power provided using one or more first power supplies  130  and one or more second power supplies  150 . 
     The load  110  can include any system, device, or any combination of systems and/or devices requiring electrical power. In one or more embodiments, the load  110  can be a computing device requiring a high degree of reliability and near continuous up-time, for example a desktop computer, computer workstation, or rack mounted server. In one or more embodiments, the load  110  can have one or more power requirements, for example, the load  110  can have a first class of devices operating at a low voltage, a second class of devices operating at an intermediate voltage, and a third class of devices operating at a high voltage. In one or more specific embodiments, the load  110  can include one or more rack mounted servers having a first class of devices operating at a low voltage, for example a personal computer interface (“PCI”) card, an advanced graphics port (“ACP”) card, a central processing unit (“CPU”), or a dual in-line memory module (“DIMM”) operating at 3.3 volts DC; a second class of devices operating at an intermediate voltage, for example a personal computer interface (“PCI”) card, an advanced graphics port (“AGP”) card, a central processing unit (“CPU”), or a dual in-line memory module (“DIMM”) operating at 5 volts DC; and a third class of devices operating at a high voltage, for example a hard disk drive (“HOD”) or similar storage media operating at  12  volts DC. 
     The load  110  can be a fixed or variable demand load. A fixed demand load can provide a substantially constant power demand, whereas the power demand for a variable demand load can fluctuate over time as processes within the load are initiated or hafted. The load  110  can be an alternating current (“AC”) load, a direct current (“DC”) load; or any combination thereof. The load  110  can have any power demand, for example the load  110  can have a power demand of about 100 W or more; about 1,000 W or more; about 2,000 W or more; about 5,000 W or more; or about 10,000 W or more. The load can draw power from a plurality of power sources, for example a first source  120  and a second source  140 . 
     The first source  120  can include any system, device or combination of systems and/or devices suitable for providing electrical power. In most instances, the power provided by the first source  120  may not be of suitable voltage or waveform for use by the load  110 , therefore the power supplied by the first source  120  can be introduced to one or more first power supplies  130 , for conversion to a voltage and/or waveform suitable for consumption or use by the load  110 . In one or more embodiments, the first source  120  can be a commercial electrical distribution grid operating at one or more standard voltages, for example a 120 VAC (single phase) or 240 VAC (multi-phase) distribution system found in some residential, commercial, and industrial data centers. In one or more embodiments, all or a portion of the first source  120  can be provided using uninterruptible power supply, for example a power supply backed by a generator or other energy storage or energy producing device. 
     Similar to the first source  120 , the second source  140  can include one or more systems, devices or any combination of systems and/or devices suitable for providing electrical power. In most instances, the power provided by the second source  140  may not be of suitable voltage or waveform for direct use by the load  110 , therefore the power supplied by the second source  140  can be introduced to one or more second power supplies  150 , for conversion to a voltage and/or waveform suitable for consumption or use by the load  110 . In one or more embodiments, the second source  140  can be a commercial electrical distribution grid operating at one or more standard voltages, for example a 120 VAC (single phase) or 240 VAC (multi-phase) distribution system found in some residential, commercial, and industrial data centers. In one or more embodiments, all or a portion of the second source  140  can be provided using uninterruptible power supply, for example a power supply backed by a generator or other energy storage or energy producing device. 
     In one or more specific embodiments, the first source  120  and the second source  140  can share a common power source, for example the first source  120  can be a first tap and the second source  140  can be a second tap off a common feed bus. In one or more specific embodiments, the first source  120  can be a power source independent from the second source  140 , for example the first source  120  can be tapped off a first feed bus and the second source  140  can be tapped off an independent second feed bus. In one or more specific embodiments, either, or both, the first source  120  and/or the second source  140  can be at least partially backed with one or more standby power sources, for example an uninterruptible power supply or a generator. 
     The first source  120  can be coupled to one or more first power supplies  130  via one or more conduits  125 . The one or more first power supplies  130  can be coupled to the load via one or more conduits  135 . Each of the one or more first power supplies  130  can include, but is not limited to, a system that can perform one or more functions, for example adjusting the voltage of the power supplied by the first source  120 ; adjusting the waveform of the power supplied by the first source  120 , filtering one or more frequencies or frequency bands from the power supplied by the first source  120 ; and conditioning the power supplied by the first source  120 . 
     The second source  140  can likewise be coupled to one or more second power supplies  150  using one or more conduits  145 . The one or more second power supplies  140  can, in turn, be coupled to the load  110  using one or more conduits  155 . Each of the one or more second power supplies  150  can include, but is not limited to, a system that can perform one or more functions, for example adjusting the voltage of the power supplied by the second source  140 ; adjusting the waveform of the power supplied by the second source  140 , filtering one or more frequencies or frequency bands from the power supplied by the second source  140 ; and conditioning the power supplied by the second source  140 . 
     As used herein, the term “couple” or “coupled” can refer to any form of direct, indirect, optical or wireless electrical connection. The electrical connection can, in one or more embodiments, include, but is not limited to any electrically conductive or magnetically inductive connection linking two or more devices. The connection can be electrically conductive, for example using one or more conductors such as copper or aluminum wire, conductive strips on a printed circuit board, or the like to connect two or more components. The connection can be magnetically inductive, for example, stimulating the flow of current from a transformer secondary coil by passing a current through a primary coil inductively coupled to the secondary coil. The connection can be electro-magnetic, for example by controlling current flow through a relay contact via an independent relay coil such that passage of a current through the relay coil can magnetically open and close the relay contact. 
     As used herein, the terms “conduit” and the plural “conduits” can refer to any system or device suitable for sustaining the flow of electrical energy therethrough. In one or more embodiments, the term “conduit” can refer to any wired or wireless means for transmission of electrical energy at any voltage or current. In one or more specific embodiments, the term “conduit” can refer to one or more solid or hollow conductors formed using one or more conductive or superconductive materials, including, but not limited to copper, copper alloys, aluminum, aluminum alloys, nickel, nickel alloys, gold, gold alloys, silver, silver alloys, cuprate-perovskite ceramics (“high temperature superconductors”), or any combination thereof. In one or more embodiments, the term “conduit” can refer to conductors printed or otherwise deposited, layered, soldered, or disposed on single or multi-layer printed circuit boards. 
     In one or more embodiments, the capacity of each of the power supplies providing the one or more first power supplies  130  and one or more second power supplies  150  may be individually insufficient to meet the peak power demand of the load  110 , for example, each of the power supplies might be rated for a maximum power output of about 1,000 watts (1 kW), where the load may have a peak demand of 5,000 watts (5 kW). To accommodate the peak demand of the load  110 , multiple first power supplies  130  can be operatively coupled, for example, to accommodate a load having a peak demand of 5 kW, a total of five 1 kW power supplies  130  can be operatively coupled in parallel. Where multiple first power supplies  130  are connected in parallel to meet the peak demand of the load  110 , the total number of first power supplies can be referred to by the letter “N,” so for the preceding example, N=5. Similarly, multiple second power supplies  150  can be operatively coupled to meet the peak demand of the load  110 . Such an arrangement, where “N” first power supplies  130  and “N” second power supplies are coupled to the load  110  can be referred to as an “N+N” arrangement. 
     The controller  160  can be communicatively coupled to the load  110  via one or more conduits  185 , at least a portion of the one or more first power supplies  130  via one or more conduits  165 ,  170 , and at least a portion of the second power supplies  150  via one or more conduits  175 ,  180 . In one or more embodiments, the controller  160  can continuously or intermittently monitor one or more load  110  parameters. In one or more specific embodiments, the controller  160  can continuously or intermittently monitor the power demand of the load  110 . In response to the changing power demand of the load  110 , the controller  160  can variously activate or deactivate all or a portion of the one or more first power supplies  130 . For example, when the power demand exerted by the load  110  increases, the controller can sense the increase via one or more signals transmitted via the conduit  185 . In response, the controller  160  can activate one or more first power supplies  130  via one or more activation signals transmitted to the respective first power supplies  130  via the conduit  170 . 
     As used herein, the terms “activate,” “activation,” and “activated” refer to any process or method by which a power supply can commence or otherwise initiate power output. The power output of the power supply, when activated, can range from about 0% to about 100% of the rated power supply output capacity. 
     As used herein, the terms “deactivate,” “deactivation,” and “deactivated” refer to any process or method by which a power supply can halt the or otherwise terminate power output. The power output of the power supply, when deactivated, can be about 0% of the rated power supply output capacity. Deactivation can occur through interruption of the power input and/or power output using a mechanical, electrical, electro-mechanical, or semiconductor switching device. In one or more embodiments, deactivation can occur through interruption of one or more systems or controls within the power supply. 
     In one or more embodiments, one or more signals indicating the status of each of the one or more first power supplies  130  can be transmitted to the controller  160  via the conduit  165 . Similarly, one or more signals indicating the status of each of the one or more second power supplies  150  can be transmitted to the controller  160  via the conduit  175 . The one or more signals transmitted or otherwise communicated to the controller  160  via the conduits  165  and  175  can include, but are not limited to, one or more signals indicating the status of the input to each power supply, i.e. indicating a potential source failure; the status of the output from each power supply, i.e. indicating a potential power supply failure; and/or the performance of one or more internal devices, systems and/or controls within the power supply. 
     Where an “N+N” redundancy is being used, the controller  160  can also activate a similar number of second power supplies  150  via one or more activation signals transmitted to all or a portion of the second power supplies  150  via the conduit  180 . In one or more embodiments, the controller can deactivate one or more first power supplies  130  and one or more second power supplies  150  via one or more deactivation signals transmitted to all or a portion of the second power supplies  150  via the conduit  180 . Transmission of one or more deactivation signals can be, for example, in response to a decrease in the power demand of the load  110  as measured by the controller  160 . 
     Using an “N+N” redundant power supply arrangement, where a sufficient number of first power supplies  130 , i.e. “N” first power supplies  130 , and a like number of second power supplies  150 , i.e. “N” second power supplies  150 , are required to be active to provide redundancy. Such an arrangement effectively halves the load carried by each active first and second power supply. For example, assuming a 10 kW maximum load  110  and 2 kW power supplies, five first power supplies  130  and five second power supplies  150  would be required to achieve N+N redundancy. At a power demand of 8 kW, four first power supplies and all four second power supplies would be active, each power supply operating at approximately 50% load. 
     In one or more specific embodiments, an “N+1” redundancy scheme can provide a reliable power supply to the load  110 . Using an “N+1” redundancy scheme the controller  160  can activate the number of first power supplies  130  necessary to support the load  110 , i.e. “N” first power supplies  130 , and only one second power supply  150 . At a power demand of 8 kW, the controller can activate four 2 kW first power supplies  130  and one 2 kW second power supply  150 . With only five power supplies activated, each power supply will now operate at approximately 80% load (8 kW (load)/10 kW (5×2 kW active power supplies). Thus, an N+1 arrangement can significantly increase the load of each active power supply coupled to the load  110 . Since overall efficiency increase of each power supply can be proportionate to the load placed upon the power supply, five power supplies operating at 80% load will generally operate more efficiently than eight power supplies operating at 50% load, even though the total power delivered to the load  110  remains the same. 
       FIG. 2  depicts an illustrative logic flow diagram  200  for an exemplary redundant power supply system, according to one or more embodiments. The logic flow diagram  200  illustrates an exemplary method for providing redundancy using an N+1 power supply arrangement. In such an arrangement, the required number of first power supplies  130  and the required number of second power supplies  150  can be determined by the peak demand of the attached load  110 . The controller  160  can be communicatively coupled to the load  110  and to each of the first power supplies  130  and the second power supplies  150 . The controller  160  can monitor one or more load parameters via signals transmitted via conduit  185 , one or more first power supply  130  parameters via signals transmitted via conduit  165 , and one or more second power supply  150  parameters via signals transmitted via conduit  175 . The controller  160  can activate and deactivate each of the first power supplies  130  via one or more activation or deactivation signals transmitted via conduit  170 , and each of the second power supplies  150  via one or more activation or deactivation signals transmitted via conduit  180 . 
     The method  200  can begin at  203  with the controller  160  determining the load  110  power demand. Based on the power demand of the load  110 , at  206 , the controller  160  can transmit or otherwise communicate one or more activation signals to an appropriate number of first power supplies  130  via conduit  170 . For example, if the load  110  communicates or otherwise transmits a power demand of 6 kW to the controller  160 , the controller  160  would activate a total of three 2 kW rated first power supplies  130  to supply sufficient power to the load. 
     At  209  the controller  160  can communicate or otherwise transmit one or more deactivation signals to any first power supplies  130  not activated at  206 . At  212  the controller  160  can communicate or otherwise transmit one or more activation signals to a single second power supply  150 . At  215  the controller  160  can communicate or otherwise transmit one or more deactivation signals to any second power supplies  150  not activated at  212 . After the controller  160  activates the appropriate number of first power supplies  130  and one second power supply  150 , an “N+1” power supply arrangement can be established. After establishing the “N+1” power supply arrangement, the controller  160  can monitor for one or more system failures, for example a failure of the first or second sources  120 ,  140  or a failure of one or more first or second power supplies  130 ,  150 . 
     At  218  the controller  160  can determine whether a first source  120  failure has occurred. The failure of the first source  120  can include any number of failure modes, for example: a complete loss of voltage, current, and/or frequency, or a deviation any parameter outside of pre-established limits exceeding a pre-determined temporal threshold. For example, a first source  120  failure can include, but is not limited to, voltage sag, voltage spike, frequency shift, or a complete failure of the first source  120 . In one or more embodiments, if a first source  120  failure has occurred, the controller  160  can communicate or otherwise transmit one or more activation signals to transition N−1 deactivated second power supplies  150  to an active state. 
     In the event of a first source  120  failure, the controller  160  can transmit one or more activation signals to the second power supply at  221 . Upon receipt of the one or more activation signals by the second power supply  150 , the output voltage of the second power supply  150  can begin to increase or “ramp-up.” In one or more embodiments, the transition from the first source  120  to the second source  140  can be transparent to the load  110  when the “ramp-up” time of the second power supply  150  is less than or equal to the “run-down” or “wind-down” time of the failed first power supply  130 . The concepts of “run-down” and “ramp-up” are discussed in greater detail in  FIG. 3  which depicts an illustrative timing diagram  300  for an exemplary redundant power supply system, according to one or more embodiments. The timing diagram  300  depicts an exemplary temporal relationship between the “run-down” time  310  of an illustrative first power supply  130  and the “ramp-up” time  320  of an illustrative second power supply  150 . 
     In one or more embodiments, the input voltage  340  supplied to the first power supply  130  by the first source  120  can drop to an unacceptable level at time t 1 , for example the input voltage  340  can drop to about zero (0) volts. When the first source  120  voltage is removed, the output voltage  350  of the first power supply  130  can begin to decay at time t 1 . The output voltage  350  of the first power supply  130  can drop to an unacceptable level, i.e. a level insufficient to support the operation of the load  110 , at or alter time t 2 . 
     Upon receiving one or more signals indicating the failure of the first source  120 , the controller  160  can provide one or more activation signals  360  to the second power supply  150  at time t 1 . The input voltage  370  supplied to the second power supply  150  can be maintained at an acceptable operating level, for example 120 VAC or 240 VAC at all times. The output voltage  380  of the second power supply  150  can begin to increase upon receipt of the activation signal from the controller  160  at time t 1 . The output voltage  380  of the second power supply  150  can reach an acceptable level, i.e. a level sufficient to support the operation of the load  110 , at or before time t 2 . The input voltage  390  to the load  110  remains at an acceptable level throughout the transition from the first power supply  130  to the second power supply  150  when the “ramp-up” time  320  of the second power supply  150  is less than or equal to the “run-down” time  310  of the first power supply  130 . 
     Referring back to  FIG. 2 , if a first source  120  failure is not detected at  218 , the controller can determine whether an output failure has occurred on the first power supply  130  at  230 . Upon detecting a first power supply  130  output failure at  230 , the controller can determine whether one or more deactivated first power supplies  130  are available at  233 . If at least one deactivated first power supply  130  is available, the controller  160  can transmit or otherwise communicate one or more activation signals to at least one deactivated first power supply  130  at  236 . At  239 , the deactivated first power supply can transition to the active state. In this instance, the load  110  continues to receive adequate power at all times since the single active second power supply  150  (ref. at  212 ) can temporarily replace the failed first power supply  130  while the controller  160  transitions one or more deactivated first power supplies  130  to an active state at  233  and  236 . 
     If at least one deactivated first power supply  130  is not available at  233 , the controller  160  can transmit or otherwise communicate one or more activation signals to at least one deactivated second power supply  150  at  245 . At  248 , the deactivated second power supply  150  can transition to the active state. In this instance, the load  110  continues to receive adequate power at all times since the single active second power supply  150  (ref. at  212 ) can temporarily replace the failed first power supply  130  while the controller  160  transitions one or more deactivated second power supplies  150  to an active state at  245  and  248 . 
     If a first source  120  failure is not detected at  218 , the controller can determine whether an output failure has occurred on the second power supply  130  at  260 . If a second power supply  150  output failure is detected by the controller at  260 , the controller can determine whether one or more deactivated second power supplies  150  are available at  263 . If at least one deactivated second power supply  150  is available, the controller  160  can transmit or otherwise communicate one or more activation signals to at least one deactivated second power supply  150  at  263 . At  266 , the deactivated second power supply  150  can transition to the active state. In this instance, the load  110  continues to receive adequate power at all times since the first power supply  130  (ref.  206 ) can temporarily provide adequate power to the load while the controller  160  transitions one or more deactivated second power supplies  150  to an active state at  263  and  266 . 
       FIG. 4  depicts an illustrative “N+1” redundant power supply system  400 , according to one or more embodiments.  FIG. 4A  depicts the illustrative “N+1” redundant power supply system  400  depicted in  FIG. 4  responding to first power supply  130 B output failure, according to one or more embodiments.  FIGS. 4 and 4A  depict three first power supplies  130 A,  130 B, and  130 C, each having a capacity of “C” and three second power supplies  150 A,  150 B, and  150 C, each also having a capacity of “C” coupled to a load  110  having a maximum power demand of “3 C.” Using an “N+1” redundancy arrangement, and assuming dynamic power savings are employed, when the load  110  is operating at a power demand of “2 C,” two first power supplies  130 A and  130 B and one second power supply  150 A can be activated. Under the “N+1” redundancy arrangement depicted in  FIG. 4 , one first power supply  130 C and two second power supplies  150 B and  150 C can be maintained in a deactivated state by the controller  160  (not shown). 
     The controller  160  can detect the failure of first power supply  130 B via one or more signals transmitted or otherwise communicated via the conduit  165 . In response to the failure, the controller  160  can transmit or otherwise communicate one or more activation signals to the deactivated first power supply  130 C via the conduit  170 . As depicted in  FIG. 4A , the power supplied to the load  110  remains sufficient at all times, supplied by the first power supply  130 A and the second power supply  150 A. After the output voltage of the first power supply  130 C reaches a level sufficient to power the load  110  (i.e. completes “ramping-up”), the system  400  again can operate under an “N+1” redundancy arrangement. 
       FIG. 5  depicts an illustrative “N+1” redundant power supply system  500  with an illustrative first source  120  failure, according to one or more embodiments.  FIG. 5A  depicts the illustrative “N+1” redundant power supply system  500  depicted in  FIG. 5  responding to the first source  120  failure, according to one or more embodiments.  FIGS. 5 and 5A  depict three first power supplies  130 A,  130 B, and  130 C, each having a capacity of “C” and three second power supplies  150 A,  150 B, and  150 C, each also having a capacity of “C” coupled to a load  110  having a maximum power demand of “3 C.” Using an “N+1” redundancy arrangement, and assuming dynamic power savings are employed, when the load  110  is operating at a power demand of “2 C,” two first power supplies  130 A and  136 E and one second power supply  150 A can be activated by the controller  160 . Under the “N+1” redundancy arrangement depicted in  FIG. 5 , one first power supply  130 C and two second power supplies  150 B and  150 C can be deactivated by the controller  160  (not shown). 
     Upon an unacceptable fluctuation in one or more parameters in the first source  120 , e.g. unacceptable voltage, current, or frequency deviations, one or more signals will be transmitted or otherwise communicated from the first power supplies  130 A and  130 B to the controller  160 . Referring to  FIG. 5A , upon loss of the first source  120 , the first power supplies  130 A and  130 B will begin to ramp down. The controller  160  can transmit or otherwise communicate one or more activation signals to the deactivated second power supplies  150 B and  150 C. The second power supplies  150 B and  150 C can “ramp up” while the first power supplies  130 A and  130 B are “ramping down” due to the failure of the first source  120 . 
     As previously discussed in detail with regards to  FIGS. 2 and 3 , as depicted in  FIG. 5A , the power supplied to the load  110  remains sufficient at all times, supplied by the first power supplies  130 A and  130 B and second power supplies  150 B and  150 C as the first power supplies  130 A,  130 B are “running-down” and the second power supplies  150 B,  1500  are “ramping-up.” After the first power supplies  130 A and  130 B complete their run-down, the power supplied to the load  110  can be completely supplied by the second power supplies  150 A,  150 B, and  150 C. 
     Certain embodiments and features have been described above using one or more sets of numerical limits. It should be appreciated that ranges from any lower limit to any upper limit are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below. All numerical values are “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art. 
     Various terms have been defined above. To the extent a term used in a claim is not defined above, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. All patents, patent applications, articles, books, specifications, other publications, documents and things referenced herein are hereby incorporated herein by this reference in their entirety for all purposes. To the extent of any inconsistency or conflict in the definition or use of a term between any of the incorporated publications, documents or things and the text of the present document, the definition or use of the term in the present document shall prevail. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.