Abstract:
A power supply system and corresponding methodology is provided for providing a self-protected power supply for use with electronic electricity meters. The self-protecting features are provided, in part, through the use of surface mounted resistive components corresponding to a resistor dropper portion of the power supply. The use of surface mount components also provides a general reduction in circuit board surface area requirements thereby providing a compact overall construction and provides economies with respect to reduction in manufacturing process steps. When the surface mount resistor divider is configured along with a half-wave rectifier, a low voltage DC supply is obtained from a direct connection to a much higher voltage AC mains source without requiring the use of coupling capacitors or transformers. Plural output voltages may be provided and capacitive filtering may be associated with the outputs. The use of a surface mount resistor divider in combination with surge protection elements helps to distribute any power surge over the power supply, which facilitates the use of less robust surge protection devices to achieve desired levels of protection.

Description:
PRIORITY CLAIM  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/604,207, entitled “RESISTOR DROPPER POWER SUPPLY WITH SURGE PROTECTION”, filed Aug. 25, 2004, which is incorporated herein by reference for all purposes. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present subject matter generally concerns a power supply system and methodology for supplying power to electronic metrology within an electric meter and the protection of such power supplies from the effects of power surges.  
       BACKGROUND OF THE INVENTION  
       [0003]     The successful integration of electronics based metrology into electric metering devices yields many practical advantages. Non-exhaustive, non-limiting examples of such advantages include the ability to perform complex calculations; collect, store and transmit data; and perform automatic self testing operations as well as make electrical measurements in the same manner as previous non-electronic electric meters. Such advances in electric meter metrology have come at a price, however in their implementation. For example, with the introduction of electronics to the metrology mix and especially with the introduction of solid state electronics and, in particular, integrated circuit technology, power supplies (or in some instances, power sources, such as batteries) have been required to furnish operating power for the electronic components.  
         [0004]     In addition to the power supply requirements for the electronic metrology components, it has been recognized that the electronic metrology components must operate in an often hostile environment. Therefore, various forms of protection from such hostile environment are desired. One common danger for such electronic metrology arises from the occurrence of surges on or along power lines to which the metrology electronics may be coupled.  
         [0005]     One example of the general state of the art is U.S. Pat. No. 6,229,295 B1 by Hemminger et al. entitled “Apparatus For Metering At Least One Type Of Electrical Power Over A Predetermined Range Of Service Voltages” that issued May 8, 2001. A surge protection element is represented as coupled to the input of a power supply  20 , and an additional element is provided as intended protection from lightning strike surges. Another example of the known art is found in Patent Application Publication U.S. 2002/0080545 A1 by Slater et al. entitled “Excessive Surge Protection Method And Apparatus,” published Jun. 27, 2002. Yet another example of the known art is found in U.S. Pat. No. 5,901,028 by Hamard entitled “Electricity Meter Provided With A System For Protection Against Surges,” issued May 4, 1999. Such &#39;028 patent discloses varistors connected between each phase and neutral configured to dump any surge on a phase to neutral. U.S. Pat. No. 5,023,747 to Lindsay issued Jun. 11, 1991 and entitled “Meter Based Surge Suppression System” discloses an electricity meter with a surge suppression system mountable on a meter mounting panel. U.S. Pat. No. 5,956,223 to Banting issued Sep. 21, 1999 entitled “Surge Protection System Including Proper Operation Indication” discloses a meter extender surge suppression system that is designed to fit between a utility meter and a meter box to protect downstream equipment from power surges on the power line. U.S. Pat. No. 5,994,892 to Turino et al. issued Nov. 30, 1999 entitled “Integrated Circuit Design Automatic Meter Apparatus and Method” discloses an electronic electricity meter that includes the placement of metal oxide (MOV) surge suppressors as a portion of the power supply circuitry.  
         [0006]     The disclosures of all of the foregoing United States patent documents are hereby fully incorporated into this application for all purposes by reference thereto. While various electronic metrology systems and power supply systems have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     In view of the recognized features encountered in the prior art and addressed by the present subject matter, an improved system and method for powering electronic systems integrated into and within electric meters has been developed. Surface mount technology is utilized to provide important aspects of a self-protected power supply while providing reduced circuit board real estate requirements as well as reducing certain previously required processing steps.  
         [0008]     In accordance with more particular aspects of the disclosed technology, one aspect of the present subject matter is to provide a power supply for an electric meter comprised principally of surface mount technology components. Such electronic components require significantly less circuit board real estate than more conventional components and may, therefore contribute to a more compact overall design.  
         [0009]     Another aspect of the related technology relates to a methodology for providing a self-protective feature to the power supply. By providing specialized configurations of components, surge energy applied to the power supply circuit can be dissipated, in major part, within the power supply circuit itself.  
         [0010]     Various features and aspects of the subject self-protecting power supply offer a plurality of advantages. For example, the disclosed technology provides for a self-protected power supply that may be associated with plural voltage level sources. Capacitive filtering may be associated with the outputs. Another advantage of the present subject matter is that the manufacturing methodology used allows certain previously used production techniques to be avoided, thus reducing the overall production cycle time and complexity. When an exemplary surface mount resistor divider is configured along with a half wave rectifier, a low voltage DC supply is obtained from a direct connection to a much higher voltage AC mains source without requiring the use of coupling capacitors or transformers. Still further, the use of a surface mount resistor divider in combination with surge protection elements helps to distribute any power surge over the power supply, which facilitates the use of less robust surge protection devices to achieve desired levels of protection.  
         [0011]     Additional aspects and advantages of the present subject matter are set forth in, or will be apparent to, those of ordinary skill in the art from the detailed description herein. Also, it should be further appreciated that modifications and variations to the specifically illustrated, referred and discussed features and steps hereof may be practiced in various embodiments and uses of the present subject matter without departing from the spirit and scope of the subject matter. Variations may include, but are not limited to, substitution of equivalent means, features, or steps for those illustrated, referenced, or discussed, and the functional, operational, or positional reversal of various parts, features, steps, or the like.  
         [0012]     Still further, it is to be understood that different embodiments, as well as different presently preferred embodiments, of the present subject matter may include various combinations or configurations of presently disclosed features, steps, or elements, or their equivalents (including combinations of features, parts, or steps or configurations thereof not expressly shown in the figures or stated in the detailed description of such figures).  
         [0013]     In one exemplary embodiment in accordance with present subject matter, a self-protected power supply may preferably include a resistor dropper portion, and a half-wave rectifier portion operatively associated with such resistor dropper portion, and may further includes a voltage clamp portion. In such an embodiment, the resistor dropper portion may further include n series connected groups of resistors, and n resistors connected in parallel within each of said groups of resistors, and with the number n≧2, all in accordance with present subject matter.  
         [0014]     In additional optional aspects of such exemplary embodiment of present subject matter, such a self-protected power supply may further include a capacitor portion, coupled in parallel with the voltage clamp portion, and still further, a voltage regulator portion, having an input portion and an output portion with such input portion coupled to the capacitor portion.  
         [0015]     In certain of the foregoing exemplary embodiments, an n number of resistors may be connected in parallel within each of the groups of resistors of the resistor dropper portion and may then be provided as surface mount resistors.  
         [0016]     In still further aspects of such exemplary embodiments, in some instances each of the n resistors within each of the n series connected group of resistors may be provided with substantially the same resistive value.  
         [0017]     In yet further present embodiments, a power supply system may be provided as a self-protected power supply for use with electronic electricity meters. In exemplary such present systems, a resistor dropper portion may comprise a plurality of surface mounted resistive components, with the resistor dropper portion having an input thereto associated with an AC mains which in turn is associated with an electronic electricity meter with which the power supply is used. Still further in such exemplary embodiments, additional aspects of such a combination may preferably include a half-wave rectifier portion operatively associated with the resistor dropper portion for providing a DC voltage output having a relatively lower voltage than the voltage of the associated AC mains. Also, a surge protection portion may be operatively interposed between the associated AC mains and the resistor dropper portion. With the foregoing various combinations, advantageously, any power surge is relatively distributed over the power supply system to achieve desired levels of protection for the associated electronic electricity meter while a relatively lower voltage DC supply is obtained from a direct connection to a much higher voltage AC mains source. All of such advantages are thereby provided without requiring the use of coupling capacitors or transformers. At the same time, the present subject matter also provides a general reduction in circuit board surface area requirements, thereby resulting in a relatively compact overall construction.  
         [0018]     Exemplary embodiments and aspects of the present subject equally relate to and include corresponding methodology. For example, one present exemplary method relates to providing a self-protected power supply for use with electronic electricity meters. Such exemplary method may advantageously include steps of connecting a first predetermined number of surface mount resistors in parallel with a common input thereto, such method further associated with connecting a second predetermined number of surface mount resistors in parallel to a common output thereto, and connecting a half-wave rectifier in series between the first predetermined number of surface mount resistors and the second predetermined number of surface mount resistors. In accordance with such present methodology, a relatively higher AC voltage source associated with the common input to the first predetermined number of surface mount resistors may be reduced to a relatively lower voltage DC voltage for supplying the electronics of an electronic electricity meter associated with the self-directed power supply. In some of the foregoing embodiments, a further step may be practiced for selecting the number of the first predetermined number of surface mount resistors to be equal to the number of the second predetermined number of surface mount resistors. In other of the foregoing embodiments, a further step may be practiced of selecting the resistive value of the first predetermined number of surface mount resistors to be substantially the same resistive value as that of the second predetermined number of surface mount resistors.  
         [0019]     Additional present exemplary methodology involves a method for providing a self-protected power supply for an electronic metrology device, involving the steps of providing a surge protective device configured for connection to a power mains supply with which the electronic metrology device is associated, connecting a self-protected power supply to such a surge protective device, and connecting a voltage regulator configured for connection to an associated electronic metrology device, the electronics of which is to be powered by the self-protected power supply while the electronic metrology device determines measurements based on the power mains supply. Further in accordance with certain embodiments of such methodology, the resistive values of the surface mount resistors may be selected in dependence on selected characteristics of the power mains supply and the electronic metrology device.  
         [0020]     Additional embodiments of the present subject matter, not necessarily expressed in this summarized section, may include and incorporate various combinations of aspects of features, components, or steps referenced in the summarized objectives above, and/or other features, components, or steps as otherwise discussed in this application. Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the remainder of the specification.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     A full and enabling disclosure of the present subject matter, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:  
         [0022]      FIG. 1  is a schematic diagram illustration of an exemplary embodiment of a resistor dropper portion of a power supply in accordance with the present subject matter;  
         [0023]      FIG. 2  is a schematic diagram illustration of an exemplary voltage regulator in accordance with the present subject matter for use, for example, with the  FIG. 1  exemplary resistor dropper portion of the present power supply; and  
         [0024]      FIG. 3  is a block diagram illustrating an exemplary configuration of a self-protective power supply in accordance with the present subject matter. 
     
    
       [0025]     Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features, elements, or steps of the present subject matter.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     As discussed in the Brief Summary of the Invention section, the present subject matter is particularly concerned with a self-protecting power supply system and methodology for powering electronic metrology systems associated with electric meters. In accordance with such present subject matter, the power supply may be implemented principally from surface mount components mounted on a printed circuit board. The power supply itself for example may include a plurality of resistors configured in series—parallel combinations coupled, along with a pair of rectifier diodes, to a Zener diode and parallel connected storage capacitor.  
         [0027]     With specific reference to exemplary  FIG. 1 , the power supply, which may be denoted as a resistor dropper configuration, may in accordance with the present subject matter be directly connected to an AC mains  50 . In an exemplary embodiment, AC mains  50  may correspond such as to a 240 Volts (V) alternating current (AC) source; however, such is not a limitation to the present subject matter as the various components of the power supply (as will be well understood by those of ordinary skill from the disclosure herewith) may be configured to allow operation at other alternative voltage source levels. Such alternative levels may be lower, e.g. at 110V AC, or higher as required by the source availability and the associate load and/or the metrology for which the power supply is to supply operating voltage.  
         [0028]     As may be seen more particularly from exemplary  FIG. 1 , the resistor dropper power supply may make use of a plurality of respective resistors  10  through  34 , configured in series—parallel combinations. Within the series—parallel combinations may exist for example three groups of three parallel connected resistors. In the exemplary embodiment illustrated, those groups would comprise resistors  10 ,  20 , and  30 , resistors  12 ,  22 , and  32 , and resistors  18 ,  24 , and  34 . Furthermore, in such exemplary configuration, each resistor would correspond to identically valued resistors.  
         [0029]     In an exemplary configuration designed for use with a mains source  50  providing 240V AC, the individual resistors of the three groups of parallel-connected resistors may each correspond to 20 Kohm resistors. As should be apparent to those of ordinary skill in the art from the totality of the present disclosure, the series—parallel combination as illustrated in  FIG. 1  of identically valued groups of resistors will collectively so configured provide an effective (i.e., equivalent) series resistance value equal to the common individual component value, i.e. an effective series resistance, in this exemplary case, of 20 Kohms.  
         [0030]     It should also be readily apparent to those of ordinary skill in the art that other series—parallel combinations of resistors may be used in accordance with the present subject matter to effect similar resistive combinations. As non-limiting examples, two groups of two resistors, four groups of four resistors, or five groups of five resistors, as well as other configurations generally represented as “N”×“N” groups may be employed. A significant aspect to the selection of combinations is the amount of energy that can be dissipated from an energy surge coupled to the power supply, as will be discussed more fully below.  
         [0031]     With further reference to  FIG. 1 , it will be seen that the resistor dropper power supply further includes a pair of diodes  40 ,  42  connected in series within the series—parallel configuration of the resistors. Connected in parallel with diodes  40 ,  42  are resistors  14 ,  16  that may be high value resistors and function as equalization resistors within the resistor dropper supply. In an exemplary configuration, resistors  14 ,  16  may each correspond to 1 Mohm resistors.  
         [0032]     Finally, the resistor dropper portion of a power supply in accordance with the present subject matter includes a Zener diode  52  and parallel connected storage capacitor  54 . Together, Zener diode  52  and capacitor  54  establish (i.e., set) and provide at terminal  60  an interim operating voltage value to be applied to the input of a voltage regulator portion of the power supply (discussed more fully with reference to  FIG. 2 ). In the exemplary configuration illustrated in  FIG. 1 , Zener diode  52  may be selected for example to provide an interim power supply voltage of 22 volts.  
         [0033]     As previously noted, the resistor dropper power supply of the present technology may be configured to operate at any of a number of input voltage levels (and at various output voltages, too). The above specific example illustrated an input voltage level of 240V AC that resulted in the selection of a 20 Kohm resistor value for use in the series—parallel combination circuit.  
         [0034]     More generally in accordance with the present subject matter, the value chosen for the resistor element depends on the voltage value of the input voltage source and the current level required to operate the electronic metrology with which the supply is to be associated. In the case for example where the input source may be 110 V AC, the resistor value may be selected to be 10 Kohms. A general formula for determining the current that should be available in accordance with the present subject matter to operate the electric meter metrology when used in an exemplary 240V AC mains voltage system is given by:  
         I   average     =       AVERAGE   ⁢           ⁢     (       V   AC240Vrms     -     (       V   z     +     2   *     V   diode         )       )         R   dropper           
 
 where V AC240VrmS  corresponds to the input source voltage, V diode  is the voltage drop across the rectifier diodes  40 ,  42  and R dropper  is the value of the individual resistor elements of the exemplary three groups of three resistors. 
 
         [0035]     More generally, this later “value” (as taken from the individual resistor elements), may be as drawn from some other “N”×“N” combination as may be used in certain embodiments in accordance with the present subject matter. In the specific case illustrated above, an available current of 4.82 mA may be provided (as shown by the exemplary calculation hereinbelow).  
               I   average     =           V   rms     *     2       -         (       V   z     +     2   *     V   diode         )     *   π     2         π   *     R   dopper                     =         240   *     2       -         (     22   +   1.2     )     *   π     2         π   *   20   *     10   3                     =     4.82   ⁢           ⁢   mA               
 
         [0036]     With respect now to  FIG. 2 , a schematic diagram of an exemplary voltage regulator for use with the present technology will be discussed. As previously discussed, the resistor dropper portion of the power supply in accordance with the present technology is configured to provide an interim output voltage that may in an exemplary configuration be set at about 22V DC to be applied to an input of an electronic voltage regulator. In an exemplary configuration the electronic voltage regulator may correspond to a low dropout voltage regulator (LDO) provided in the form of an integrated circuit device  70 . In such an exemplary configuration, i.e., where the input to the voltage regulator  70  at terminal  60  is 22V DC, such voltage regulator  70 , in conjunction with a mid power level output transistor  80 , is configured to provide a continuous low level load that may correspond in such an exemplary embodiment to approximately 2 mA and, for short periods of time, a significantly higher load on the order of 350 mA for about 25 mS every few minutes.  
         [0037]     With specific regard to the exemplary voltage regulator illustrated in  FIG. 2 , LDO  70  is supplied with an interim input voltage by way of terminal  60  from the resistor dropper portion of the power supply, and then in turn supplies a regulated output voltage at terminal  82  that may correspond to approximately 3.4V DC (based on the exemplary specific embodiment disclosed hereinabove). Such regulated output voltage is regulated to the desired level via the interrelationship of a pair of feedback resistors  66  and  68 . At the same time, a pair of capacitors  62  and  64  provides transient voltage control for such regulated output voltage  82 .  
         [0038]     With reference now to  FIG. 3 , the overall operation of the power supply of the present technology as well as yet another feature thereof (the self-protecting capabilities), will be discussed. As illustrated in exemplary  FIG. 3 , the power supply of the present technology may be viewed as a self-protecting supply in that the component portions of the supply are designed to safely endure (i.e., survive) surges that may typically be expected to occur in the operating environment of an electric meter with which the power supply may be associated.  
         [0039]     In an exemplary embodiment of the power supply in accordance with the present technology, an electric meter metrology module and such associated power supply may be designed to withstand both fast transients and high voltage surges. In an exemplary configuration voltage surges up to about 6 KV may be accommodated. As illustrated in  FIG. 3 , the full protection is provided per the present subject matter through use of a board mounted power supply and an exemplary external metal oxide (MOV) transient suppressor  90  connected across the input voltage supply  50 .  
         [0040]     In an exemplary embodiment, the external MOV  90  may divert surges with surge levels above 1.5 KV up to about 6 KV. The exemplary on board power supply  100  is designed to sustain surges up to 1.5 KV for approximately 100 uS while always providing a DC regulated voltage of, in an exemplary configuration, about 3.4V DC. All the components mounted on the circuit board are surface mount components that reduces board space and removes the otherwise used through-hole process during manufacturing, thereby reducing cycle time.  
         [0041]     The components that control the surge voltage are the dropper resistor portion (i.e., ladder)  110  corresponding to the three resistor groups  10 ,  20 ,  30 ;  12 ,  22 ,  32 ; and  18 ,  24 ,  34  ( FIG. 1 ), the half wave rectifying diodes  40 ,  42  and the Zener diode  52 .  
         [0042]     During a positive portion of the output waveform from input source  50 , both the diodes  40  and  42  of the half wave rectifier  120  are in conduction mode and a surge pulse may be absorbed by the resistor dropper portion  110  and the Zener diode within representative element  130  (which Zener diode is element  52  of  FIG. 1 ), and as a result the rest of the circuit is protected. During a negative portion of the output waveform from input source  50 , both diodes  40  and  42  of the half wave rectifier  120  are blocked and the surge pulse may be completely absorbed by the diodes  40 ,  42 , and again the rest of the circuit is protected. During the positive portion of the surge, the maximum surge current that the resistor dropper portion (or ladder)  110  and the Zener  52  (part of element  130 ) have to withstand is calculated with the formula given below:  
           I   surge_max     ≈       V   surge       R   ladder         =         1500   +   340       20   *     10   3         =     92   ⁢           ⁢   mA           
 
         [0043]     In an exemplary embodiment in accordance with the present technology, the power dissipated in the resistor ladder  110  during a 1.5 KV, 100 uS surge is 170 W for the whole resistor network as represented and explained by the equation just below, and is about 19 W for each resistor.  
         P     surge_disapated   ⁢   _max       =           (       V   surge     +     V   max_grid       )     2       R   dropper       =           (     1500   +   340     )     2       20   *     10   3         =     170   ⁢           ⁢   W             
 
         [0044]     The Zener diode  52  has to dissipate approximately 2 W for 100 uS as represented and explained by the equation just below. 
 
 P   zener     —     diode     —     dissipation   =V   zener   *I   surge     —     max =22*92*10 −3 =2 W 
 
 During the negative sinusoidal wave, the diodes  40  and  42 , each rated at 1 kV, block the surge voltage. The resistors  14  and  16  divide the surge equally between diodes  40  and  42 . Thus, the power supply alone is able to withstand surges up to 1.5 kV during 100 uS. As will be understood by those of ordinary skill in the art from the disclosure herewith, including the illustrations, representative features  140  as shown in  FIG. 3  correspond with the voltage regulator portion of the present power supply subject matter more fully illustrated and discussed in conjunction with  FIG. 2  herein. Also, as will be understood, the representative output node  200  of  FIG. 3  has the same characteristics as achieved at the output node  82 , illustrated in  FIG. 2 . 
 
         [0045]     While the present subject matter has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would in such fashion be readily apparent to one of ordinary skill in the art.