Abstract:
Apparatus defining a circuit module for receiving an operating voltage on an input and for generating a voltage of a lower magnitude that is applied to an intermediate bus. A holdover energy source, such as an ultra capacitor or the like, of the circuit module has a voltage lower than said input voltage and the voltage of said intermediate bus. The holdover energy source is connected under control of a voltage supervisor to a boost converter in response to the receipt of a transient on the input. The boost converter is responsive to the connection to generate a boost voltage that maintains a constant voltage on the intermediate bus.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to apparatus having power supply circuitry that employs an energy storage element to provide holdover power to a load. This invention further relates to power supply circuitry that employs a high-density low voltage energy storage device to provide holdover power to a load.  
         [0003]     2. Statement of the Problem  
         [0004]     In modern power system design for equipment such as computer servers or telecommunications network elements, a need exists for a certain amount of holdover energy storage on each field or replicable unit. This holdover energy storage is often referred to as “hold up capacitance” and permits the field or replicable unit to maintain normal operation even if there is a momentary interruption of its primary power source. Such interruptions are common when a fault in a particular unit causes its power fuse to blow. All other units connected to the same power source then experience a severe momentary voltage dip or transient. This can occur during rectifier switchovers, reconfiguration of universal power supplies, and power feeder reconfigurations. For high power units, the capacitance needed to store the required holdover energy can be large, physically big and expensive. A need therefore exists for apparatus that reduces the size and cost impact of the required holdover energy source while still providing the required holdover energy protection.  
         [0005]     A capacitor is the simplest and least expensive apparatus for providing holdover power. The magnitude of the capacitance and the magnitude of the load to which the capacitor is connected define the duration of the holdover time. The holdover time provided by low-density capacitors of a readily obtainable capacitance and physical size is in the order of microseconds. Longer holdover times are obtainable when larger capacitors are used. However, the duration of the obtainable holdover times is often limited by the space available to house the larger capacitors, and their affordability.  
         [0006]     It is known to use backup batteries to provide holdover power. But, batteries can be expensive and may require the use of banks of batteries having a capacity sufficient to power a load for minutes or hours when interruption of commercial power occurs. Power supplies having this holdover power capability are not economically feasible for many applications. The cost, weight, and size of such power supplies exceed the available space and cost of the circuitry to be protected.  
         [0007]     Electronic circuitry of the type used in computer servers and communication equipment is often modular or space limited and has a need for protection against power transients in the order of milliseconds. To be economically feasible, the holdover power apparatus should be proximate to the load to be protected. Also, it should be small in size and not occupy an inordinate amount of space on the circuit board or module containing the load circuitry to be protected.  
         [0008]     It is therefore a problem to equip electronic circuitry with holdover power protection that is economical in size and cost.  
       SUMMARY OF THE SOLUTION  
       [0009]     The present invention solves the above and other problems by the provision of a method and apparatus that provides holdover power circuitry that is economical in size and cost and that may be the integrated with the load circuitry to be protected. In circuit board or circuit module applications, the circuitry embodying the present invention is sized so that it may be economically mounted on the circuit board or circuit module containing load circuitry. It will be understood by those skilled in the art that the terms “circuit board” and “circuit module” are synonymous and interchangeable insofar as the present invention is concerned. It is immaterial to the present invention whether it is embodied on a “circuit board” or a “circuit module” since the present invention may be embodied using any known mounting technology. The drawing figures and the detailed description refer to both “circuit boards” and “circuit modules”.  
         [0010]     A circuit board is a collection of components such as chips and discrete components soldered to a printed wiring board. A module can be a circuit board, but can also be a more general element, like a fan unit, power supply or optical assembly.  
         [0011]     The holdover power apparatus embodying the present invention protects against voltage transients generated by load circuitry on a protected circuit module, as well as against voltage transients appearing on the power input to the protected circuit module. The holdover power apparatus of the present invention further protects against transients applied to the input of the protected circuit module by nearby circuit modules.  
         [0012]     The holdover power apparatus of the present invention detects the beginning of transients and generates a boost voltage that is applied to the load circuitry of the protected circuit module. The boost voltage maintains a constant voltage on the load circuitry of the protected circuit module. The protection time provided by the holdover power apparatus of the present invention is sufficient to provide protection against short duration transients generated anywhere in the system in embodying the present invention.  
         [0013]     In accordance with an embodiment of the invention, a plurality of circuit modules are provided each having a power input that receives an operating voltage (48 volts for example). Other voltages may be used if desired. The received operating voltage is applied to a power module comprising a voltage converter that reduces the received operating voltage to a lower voltage (12 volts for example). Other voltages may be used if desired. This lower voltage is applied to an intermediate bus, which is connected to a plurality of point of load (POL) voltage converters. Each POL voltage converter receives the lower voltage on the intermediate bus and outputs a reduced voltage that is applied to semiconductor chips and other devices comprising the load circuitry to be protected. Each POL voltage converter may supply the same or a different voltage to a different group of circuit elements defining a load. The number of POL voltage converters on a circuit module depends upon the number of different voltages and current levels required by the circuit elements on the circuit module.  
         [0014]     The input to a circuit module is also connected to a power supervisor which monitors the received operating voltage to detect the beginning of transients on the input. Upon the detection of a transient, the power supervisor activates a boost converter to maintain a constant voltage on the intermediate bus and, in turn, on input of the POL voltage converters.  
         [0015]     An input of the boost converter is connected to an energy storage element such as a conventional capacitor, an ultra capacitor, or a circuit module mounted rechargeable battery such of the AAA or D size. The energy storage element is maintained in a charged stage by a trickle charger connected to the input of the circuit module.  
         [0016]     The energy storage element is sized to have the energy required to power the boost converter to maintain a constant voltage on the intermediate bus for time duration greater than that of normally expected transients. The boost converter is controlled by the power supervisor, which maintains the boost converter in an off state during transient free conditions. Upon the detection of a low voltage transient, the power supervisor switches the boost converter to an on state in which the energy storage element supplies power to the boost converter to apply a boost voltage to the intermediate bus for the duration of normally encountered transients. This boost voltage counteracts the effect of the transient on the intermediate bus by maintaining a constant voltage on the intermediate bus.  
         [0017]     The energy storage element may comprise a low-density energy storage element, such as a conventional capacitor, for applications in which the required holdover time is in the order of microseconds. When greater holdover times are desired, the energy storage element may be a high-density, low voltage energy storage element such as an ultra capacitor or a small primary or rechargeable battery. High-density, low voltage energy storage elements provide holdover power for time durations is in the millisecond range.  
         [0018]     The embodiment described above is adapted to provide holdover power for transients detected on the power input to a circuit module. Such transients can propagate though the power module and destabilize the voltage on its intermediate bus. The present invention is also adapted to provide holdover protection from transients generated by circuit malfunctions on other circuit modules.  
         [0019]     Circuit malfunctions on another circuit module can cause other circuit modules to draw excessive current for a brief interval prior to the time the fuse or other overload protection device operates in the other circuit modules. Since the inputs of all circuit modules are connected to the same system supply bus, this brief excessive current in a malfunctioning circuit module can generate transients by a lowering of the operating voltage received by the input of all circuit modules. Such transients can disrupt normal functioning of circuitry of the other circuit modules. The holdover power apparatus of the present invention detects such transients and applies a boost voltage to the intermediate bus of a protected circuit module to maintain a substantially constant potential on the intermediate bus of the protected circuit module.  
         [0020]     The invention may include other exemplary embodiments described below. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0021]     The same reference number represents the same element on all drawings.  
         [0022]      FIGS. 1, 2  and  3  disclose prior art power systems; and  
         [0023]      FIG. 4  discloses a possible embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]      FIGS. 1-4  and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents.  
       DESCRIPTION OF FIG.  1   
       [0025]      FIG. 1  discloses prior art apparatus that provides holdover power for telephone offices and the like. The  FIG. 1  apparatus provides holdover power for an extended period of time such as minutes, hours or days. Battery plant  101  may be massive in size and is typically stored in a remote location such as a basement. The output of battery plant  101  extends to power distribution frame  102  which extends battery power over conductors  103  to power entry module  106  of shelf  104 . Shelf  104  houses circuit boards  108 - 1  through  108 -N. Circuit boards  108  are mounted in slots of shelf  104  in a manner well known in the art.  
         [0026]     Power entry module  106  receives battery power over conductors  103  and extends the received battery power over conductors  107 A and  107 B to the input of power converters  109 - 1  through  109 -N. Power converters  109  reduce the voltage received on their input to a lower voltage required by circuit loads  111 - 1  through  111 -N. Fuses F 1 , F 2  and FN protect their associated circuitry from damage caused by power overloads.  
         [0027]     The circuitry of  FIG. 1  is protected against transients such as lightning strikes and current surges by the massive energy inertia provided by a battery plant  101 . The circuitry of  FIG. 1  is protected against long-term power failure by the energy reserve of battery plant  101  as well as other facilities provided in the central office such as a reserve generating plant (not shown) that output emergency AC power to the entire central office including battery plant  101 .  
         [0028]     The apparatus of  FIG. 1  is satisfactory for use in telephone central offices in the like. However, short duration transients can still propagate through the power infrastructure, so some localized storage is needed to prevent circuit malfunction.  
       DESCRIPTION OF FIG.  2   
       [0029]      FIG. 2  discloses another prior art circuit that provides holdover energy backup. Circuit board  201  receives an input voltage that is extended through fuses F 1  and F 2  and diodes D 1  and D 2  to capacitor bank C. Capacitor bank C has sufficient reserve to provide holdover power for transients of a normally expected duration. The output of capacitor bank c is applied to power module  203  which reduces the received voltage to an intermediate level such as 12 volts. This intermediate voltage is applied to intermediate bus  204  and from there to the plurality of point of load POL voltage converters  206 - 1  through  206 -N. The POL voltage converters  206  are modular switching power supplies that convert the received intermediate voltage to an output voltage having a magnitude required by loads  207 - 1  through  207 -N.  
         [0030]     The ability of the circuit of  FIG. 2  to provide holdover power is limited by the power required by loads  207  and the capacity of capacitor bank C. A disadvantage of the circuit of  FIG. 2  is that the size of the space required to accommodate capacitor bank C is unacceptable for use with electronic apparatus where volumetric density or weight are important considerations. The holdover time provided by the apparatus of  FIG. 2  is in the order of microseconds when capacitors are used of a size that enables them to be accommodated in a reasonable fraction of the space available on circuit board  201 .  
       DESCRIPTION OF FIG.  3   
       [0031]      FIG. 3  discloses another prior art circuit that provides holdover power. The circuit of  FIG. 3  is similar to that of  FIG. 2  in that both have a power input, a pair of fuses, a pair of diodes, a power module, an intermediate bus, a plurality POL of voltage converters, and a plurality of loads. The above items of  FIG. 3  are identical in function to their counterparts on  FIG. 2 . On  FIG. 3 , the fuses are designated F 1  and F 2 , the diodes are designated D 1  and D 2 , the power module is designated  308 , the intermediate bus is designated  309 , the POL voltage converters are designated  311 - 1  through  311 -N and the loads are designated  312 - 1  through  312 -N. The circuit board is designated  301 . A further description of the above enumerated elements is not repeated herein since the function of these elements is identical to that of their priorly described counterparts on  FIG. 2 .  
         [0032]     The circuit of  FIG. 3  additionally has a power supervisor  302 , a charge circuit  303  and a capacitor bank C. Capacitor bank C of  FIG. 3  is connected by conductor  322  to the output of charge circuit  303 . Charge circuit  303  is connected to input conductors  331  and  306  to maintain a trickle charge on capacitor banks C. Charge circuit  303  boosts the voltage it receives on paths  306  and  331  to a higher voltage, such as 72 volts, which is applied over path  322  to capacitor bank C. The power available from a given sized capacitor increases as the square of the voltage on the capacitor.  
         [0033]     Power supervisor  302  monitors the input voltage applied to power module  308 . Power supervisor  302  maintains switch  304  in an open state as long as the voltage on the power input conductor  331  remains free of transients. When a transient is received, the transient is extended over path  331  to the input of power supervisor  302 . Power supervisor  302  responds to the receipt of the transient by extending a signal over conductor  323  to close the normally open contacts of switch  304 . The closure of these switch contacts extends the 72 volt output of capacitor bank C over path  322  and through the closed contacts of switch  304  and over the path  321  to the + input of power module  308 . This increases the input voltage to power module  308  and therefore increases the energy available on its output that is connected to intermediate bus  309 . This maintains a constant potential on intermediate bus  309  and the inputs of the POL voltage converters for the duration of the received transient. This, in turn, maintains a constant potential to loads  312  sufficient to maintain their operation. Power supervisor  302  continues to monitor the received input voltage and at the end of a transient, opens the contacts of switch  304  via conductor  323 . This disconnects the capacitor bank C from the + input of power module  308  and returns the operation of the circuit of  FIG. 3  to a transient free state. Charge circuit  303  then slowly recharges the capacitor, readying it for the next transient.  
         [0034]     The apparatus of  FIG. 3  is an improvement over that of  FIG. 2  in that its capacitor bank C is charged to a higher voltage. This is advantageous since the higher voltage of capacitor bank C of  FIG. 3  provides an increased holdover time compared to that of the circuit of  FIG. 2 . The holdover time is increased exponentially by the increased voltage of the capacitor bank C of  FIG. 3 . This is in accordance with Joules Law, which states that stored energy is related to the size of a capacitor and the square of the charge voltage.  
         [0035]     The circuit of  FIG. 3  provides increased holdover time because of the increased charge on the capacitor bank. However, the holdover time is still in a microseconds range if normally available, low-density capacitors are used having sizes commensurate with those used in circuit board or module applications. High voltage capacitors work, but are expensive and large per Joule stored.  
       DESCRIPTION OF FIG.  4   
       [0036]      FIG. 4  discloses a plurality of circuit modules  405 - 1  through  405 -N that uses holdover power using energy storage elements whose physical size, cost and weight is more compatible with circuit module technology. Circuit module  405 - 1  is shown in detail on  FIG. 4 . The details of the remaining circuit modules, such as  405 -N, are not shown since they are identical to the details of circuit module  405 - 1  in so far as the present invention is concerned.  
         [0037]     Circuit module  405 - 1  provides improved holdover power for loads  414 - 1  through  414 -N for the duration of transients received on conductors  436  and  437  of power input  435 . Circuit module  405 - 1  provides this improved holdover power capability by the use of an energy storage element  426  whose physical size is compatible with circuit board or module technology. Energy storage element  408  may advantageously comprise a high-density, low-voltage energy source  426  such as an ultra-capacitor or a battery. Such elements provide holdover power times in the millisecond range.  
         [0038]     Circuit module  405 - 1  is similar to that of  FIG. 3  in that it has a power module  407 , intermediate bus  412 , a plurality of POL voltage converters  413 - 1  through  413 -N and a plurality of loads  414 - 1  through  414 -N. Circuit module  405 - 1  is similar to that of  FIG. 3  in that it has conductors  436  and  437  of power input  435 , fuses F 1  and F 2  and a pair of diodes D 1  and D 2  that apply input power to power module  407 . No further description of the above-enumerated elements for  FIG. 4  is needed since these elements function in the same manner as do their counterpart elements on  FIG. 3 .  
         [0039]     Conductors  436  and  437  of power input  435  receive an operating voltage from a system power source (not shown). A typical input operating voltage may be 48 volts. However, the circuit of  FIG. 4  may operate with other voltages. The received input operating voltage is extended over conductors  436  and  437 , through fuses F 1  and F 2  and through diodes D 1  and D 2  to the input of power module  407 . Power module  407  is a switching power supply that reduces the received operating voltage to an intermediate voltage that is applied to intermediate bus  412 . This intermediate voltage may be 12 volts. However, the intermediate voltage may be of any level suitable for operation with electronic circuitry. Intermediate bus  412  extends the intermediate voltage to inputs of POL voltage converters  413 - 1  through  413 -N. Each POL voltage converter  413  reduces the received intermediate voltage to a reduced voltage that is applied to the one of loads  414 - 1  through  414 -N to which each POL voltage converter is connected.  
         [0040]     Power supervisor  404  detects transients on input conductors  436  and  437  and operates boosts converter  406  to maintain a constant voltage on intermediate bus  412  for the duration of the transient. Power supervisor  404  controls the operation of switch  427  as well as the operation of boost converter  406 . Conductor  446  extends the potential on the output of diode D 2  to input  453  of power supervisor  404 . This enables power supervisor  404  to monitor transients appearing on conductor  437 . Conductor  429  of power supervisor  404  controls power switch  427 , causing it to connect the output of boost converter  406  over conductors  434  and  432  to intermediate bus  412  whenever a power transient is detected.  
         [0041]     Conductor  429  receives signals from power supervisor  404  to maintain the switch contacts  427  in an open state so long as transients are not applied to input conductor  437 . Conductor  425  extends the output of energy storage element  426  to boost converter  406 . This activates boosts converter  406  which applies a boost voltage to conductor  434 . Upon the detection of a transient, power supervisor  404  extends a signal over conductor  429  to close the contacts of switch  427 . This applies the boost voltage on conductor  434  trough switch contacts and via conductor  432  to intermediate bus  412  for the duration of the received transient. Conductor  431  interconnects boost converter  406  and power supervisor  404 .  
         [0042]     Circuit module  405 - 1  also detects transients on intermediate bus  412  and operates boosts converter  406  to maintain a constant voltage on intermediate bus  412 . Conductor  447  extends from intermediate bus  412  to a second input  452  of power supervisor  404 . This connection enables power supervisor  404  to detect a transient on intermediate bus  412  and operate switch  427  and boost converter  406  and the same manner as priorly described to maintain a constant voltage on intermediate bus  412  for the duration of a received transient.  
         [0043]     As priorly mentioned, circuit module  405 - 1  is protected from transients applied to its input by malfunctioning circuitry of other circuit modules. Such transients are detected as above described. In response to the detection of such transients, the boost circuitry of the present invention is activated to maintain a substantially constant voltage on intermediate bus  412 .  
         [0044]     Energy storage element  408  is advantageously a high-density, low-voltage storage device that is maintained in a charged date by charge circuit  403 . A typical voltage for energy storage device  408  is 3.5 volts. Other voltages may be used if desired.  
         [0045]     The boost circuitry of circuit module  405 - 1  is effective to provide holdover power in the millisecond range when energy storage element  426  comprises an ultra capacitor or a battery of similar energy density.  
         [0046]     Ultra capacitors are well-known devices in the art. An ultra capacitor is constructed using a metal foil bonded to an activated carbon mat. The activated carbon is separated by a glass paper and layered or rolled into a container. The properties of an ultra capacitor are dependent upon how porous the activated carbon mat is and how small the electrolyte ions are. Activated carbon electrodes used in ultra capacitors have a large surface area and small charge separation distances on the order of 10 Angstrom&#39;s or less. This combination of large surface area and small charge separation distance allows ultra capacitors to store large amounts of energy. Because the charging and discharging of an ultra capacitor is not a chemical process, ultra capacitors can be cycled almost indefinitely with no deterioration. Ultra capacitors have 10 times the energy density of conventional electrolytic capacitors and 10 times the power density of battery storage systems. Power density is the ratio of power delivery capability to the weight of the device. Advantageously, the high power density of ultra capacitors permits them to store adequate holdup energy for a module consuming several hundred watts, while still having small size, weight, and cost properties.  
         [0047]     The above description discloses a possible exemplary embodiment of this invention. It is expected that those skilled in the art can and will design alternative embodiments that infringe on this invention as set forth in the claims below literally or through the Doctrine of Equivalents. As priorly described, the apparatus of the present invention may be embodied using any mounting technology and is not limited to circuit boards or circuit modules. Also, each circuit module may serve one or more loads. Some circuit modules may not require holdover power protection. It will be understood by those skilled in the art that a circuit module is any element or combination of elements adapted to serve as a mounting for electrical components.