WO2005057782A1

WO2005057782A1 - Connector with self identification circuit sensor

Info

Publication number: WO2005057782A1
Application number: PCT/US2003/036778
Authority: WO
Inventors: Richard Skowronski
Original assignee: Restech, Inc.
Priority date: 2003-11-14
Filing date: 2003-11-14
Publication date: 2005-06-23
Also published as: AU2003291029A1

Abstract

A cable connector including an integrated electromagnetic suppression choke within a single overmold provides a compact connector/choke combination. A changeable tip adapted to mate with the electromagnetic suppressing cable connector that is able to also include a self identification circuit. The changeable tip allows connection of an external power supply to a variety of electronic devices. The self identification circuit of exemplary embodiments has a series resettable fuse and zener diode placed across the two wires supplying power through the changeable tip. The zener voltage of the zener diode of the self identification circuit is used to identify the circuit. The output voltage, polarity and other power parameters of the power supply are set based upon the identification of the self identifying circuit. Alternatively, the self identification circuit can be incorporated into a power cable, into the electronic device itself, or elsewhere along the power supply output line.

Description

CONNECTOR WITH SELF IDENTIFICATION CIRCUIT SENSOR

Field of the Invention The present invention generally relates to the field of variable electronic power supply connectors and more particularly to power supply connectors that are electrically filtered or that operate with self-identifying circuits.

Background of the Invention Power supplies for electronic equipment, particularly portable or smaller electronic equipment, generally have a low voltage cord that terminates in an electrical connector that connects, in turn, to the electronic equipment. It is generally desirable to place electromagnetic suppression chokes, such as ferrite beads, onto the end of these cords. This electromagnetic suppression choke is generally placed around the cord at a location near the connector to the equipment in order to impede conduction along the cable of higher frequency electromagnetic energy and thereby reduce unintentional electromagnetic emissions to or from the connected electronic devices. The electrical connector on the cord connecting the power supply to the device is generally molded onto the cord to provide a physical connection that withstands the stresses of cable movement relative to the electronic device. An electromagnetic suppression choke, such as a ferrite bead, is also generally placed on the cable within a few inches of the connector and secured to the cable, typically with an "overmold." Overmolding in this application is a process whereby a cable that is routed through the center of a bead has plastic molded over the bead and a short portion of the cable on either side of the bead. This process securely positions the bead as well as provides a desirable aesthetic appearance. The connector and electromagnetic suppression choke in such arrangements, however, can consume four or five inches along the cord. Although this length is usually not a problem, consuming this length for the connector and filter can pose a significant problem for installations that place the cord and connector within a confined spaceSome arrangements for power supplies and associated cords use a cord reel or cord retractor that retracts the cord into a housing and/or onto a spool when the cable is not in use. In compact cord retractors, the electromagnetic suppression choke is too large to efficiently coil onto the spool with the cable. This generally requires storing the bead, connector, and the length of cable between them, in a housing outside the perimeter of the spool, or these cable end components are required to remain external to the spool or retractor housing. Using a spool or retractor housing that is also able to enclose the electromagnetic suppression choke, connector and intermediate cable results in a housing that is larger and therefore less convenient to • use. Some power supplies for electronic devices are generic in nature and have an output cable with a universal or generic connector to which specialized connectors can be connected. Such supplies often allow adjustment of the output voltage that is to be delivered to the electronic devices. These power supplies can be used with a wide variety of electronic devices and using the power supply with a new electronic device generally only requires the user to install an appropriate connector tip and to Docket No. 623-10001 2 properly adjust the power supply output voltage and mechanically fit the new device. This is particularly useful to travelers that carry a variety of electronic devices such as cell phones, Personal Digital Assistants (PDAs), portable computers, and the like. Manufacturers of such generic power supplies that support connection of specialized connectors are able to rapidly adapt their products for use with new electronic devices since only specialized connectors have to be developed for a new product, as opposed to entire new power supplies. Such power supplies also reduce the size and cost of inventories and retail store displays for an inventory of power supplies that are able to be used with a wide variety of devices since one or a few generic power supply models can be used with a large variety of small and inexpensive specialized connector tips that are adapted to the wide variety of devices. Such generic power supplies are also attractive to customers who are more comfortable in purchasing a third party power supply if that power supply can be adapted to a wide variety of current, and future, electronic devices. The ability to change connector tips further obviates obsolescence that is suffered as new devices are introduced and power supplies that are already owned by the customer are not compatible with the new electronic devices that the customer wishes to purchase. The most universal power supplies are those capable of automatically changing the output voltage as required to match the requirements of the electronic device to which power is to be supplied. Most generic power supplies only allow manual setting of output voltage. Incorrect voltage selection can result in a failure to charge the battery of the electronic device if the power supply output voltage is set too low, and can possibly result in damage to an expensive electronic device if the power supply output voltage is set too high. Some power supplies support changeable connector tips that provide feedback to the power supply to indicate the proper voltage to be supplied to the electronic device that is associated with that connector tip. Once a user attaches a connector tip that provides this feedback to the power supply, the power supply automatically adjusts its output voltage to properly supply power to the associated electronic device. Connector tips that provide feedback currently require at least one additional conductor on the cable over which to provide this feedback. The addition of this conductor increases the bulk, weight .complexity and cost of the cable. Therefore, what is needed is a power supply cable that includes an electromagnetic suppression choke and connector that consumes less space at the end of that cable. Also needed is a self-identification mechanism for devices connected to a power supply that does not require dedicated conductors on the power supply cable.

Summary of the Invention According to a preferred embodiment of the present invention, a two-wire self identification circuit has at least one current dependent resistor with a resistance characteristic comprising a low resistance when conducting less than a pre-defined current and a high resistance when conducting at least more than the pre-defined current. The two wire self identification circuit further has at least one voltage dependent conductor that exhibits a high impedance when a pre-defined voltage is across the voltage dependent conductor and wherein the voltage dependent conductor exhibits a low impedance Docket No. 623-10001 3 characteristic when the voltage across the voltage dependent conductor is above the pre-defined voltage, wherein the at least one current dependent resistor and the at least one voltage dependent conductor are electrically connected in series. In another aspect of the preferred embodiment of the present invention, an electromagnetic suppression cable connector has at least one contact and a cable that has at least one conductor. One or more of the at least one conductor is connected to one of the at least one contact. The electromagnetic suppression cable connector also has an electromagnetic suppression choke disposed about the cable and in proximity to the at least one contact. The electromagnetic suppression cable connector further preferably has an overmold formed around the electromagnetic suppression choke and the at least one contact. In another embodiment of the present invention, a method for identifying a self identifying circuit includes providing, in series across two conductors, at least one current dependent resistor and a voltage dependent conductor. The method also includes providing a time varying voltage across the two conductors and measuring the current flowing through the two conductors. The method also includes determining a voltage characteristic of the voltage dependent conductor based upon the time varying voltage and the current measurement and identifying a self identifying circuit based upon the voltage characteristic.

Brief Description of the Drawings The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. FIG. 1 illustrates a cut-away side view of an electrical connector with an overmolded adjacent ferrite bead choke according to an embodiment of the present invention. FIG. 2 illustrates a front view of the electrical connector with an overmolded adjacent ferrite bead choke as shown in FIG. 1 , according to an embodiment of the present invention. FIG. 3 illustrates a cut-away side view of an electrical connector that is integral to an overmolded ferrite bead choke according to an embodiment of the present invention. FIG. 4 illustrates a cut-away side view of a changeable tip electrical connector that is integral to an overmolded ferrite bead choke according to an embodiment of the present invention. FIG. 5 illustrates a cut-away side view of a keyed changeable tip electrical connector that is integral to an overmolded ferrite bead choke according to an embodiment of the present invention. FIG. 6 illustrates a front view of the keyed changeable tip electrical connector that is integral to an overmolded ferrite bead choke as shown in FIG. 5, according to an embodiment of the present invention. FIG. 7 illustrates an asymmetric base changeable tip for use with the changeable tip electrical connector as shown in FIG. 6, according to an embodiment of the present invention. FIG. 8 illustrates a rear view of the asymmetric base changeable tip shown in FIG. 7, according to an embodiment of the present invention. Docket No. 623-10001 4 FIG. 9 is a cut away view of a self identifying changeable tip according to an embodiment of the present invention. FIG. 10 is a mated cut-away side view of a keyed changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke that has an asymmetric base changeable tip mounted thereon according to an embodiment of the present invention. FIG. 11 is a voltage versus current chart for several exemplary series zener diodes and resettable fuse pairs according to an embodiment of the present invention. FIG. 12 is an electrical circuit schematic diagram for an identifiable connector tip sensing power supply that is connected to an appliance through a connector tip that contains a two wire self identification circuit according to an embodiment of the present invention. FIG. 13 is an electrical circuit schematic diagram for an identifiable connector tip sensing power supply that is connected to an appliance that contains a two wire self identification circuit according to an embodiment of the present invention. FIG. 14 illustrates a cut-away side view of an alternative changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke with a changeable tip in position for mating thereto, according to an embodiment of the present invention. FIG. 15 illustrates a cut-away side view of an alternative changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke with a changeable tip mated thereto, according to an embodiment of the present invention. FIG. 16 illustrates a power supply for a portable electronics device that includes a changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke with a changeable tip mated thereto, according to an embodiment of the present invention. FIG. 17 illustrates a retracting cord power supply for a portable electronics device that includes retractor for retracting input and output power cords, according to an embodiment of the present invention. FIG. 18 illustrates an electrical circuit schematic diagram for a dual zener voltage self identification circuit according to an embodiment of the present invention. FIG. 19 is a processing flow diagram for identification of a self identifying circuit according to an embodiment of the present invention. FIG. 20 is a cut-away side view of a second alternative changeable tip electrical connector with an asymmetric opening that has an adjacent overmolded ferrite bead choke, and a second alternative changeable tip, according to an exemplary embodiment of the present invention. FIG. 21 is a cut-away mated side view of a second alternative changeable tip electrical connector with an asymmetric opening that has an adjacent overmolded ferrite bead choke mated to a second alternative changeable tip, according to an exemplary embodiment of the present invention. FIG. 22 is a cut-away mated side view of a third alternative changeable tip electrical connector with an asymmetric opening that has no ferrite bead choke, according to an exemplary embodiment of the present invention. Docket No. 623-10001 5

Detailed Description As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The present invention, according to a preferred embodiment, overcomes problems with the prior art by providing a power supply cable with an integrated electromagnetic suppression choke and changeable tip as well as a self identification circuit incorporated into a changeable connector tip, electronic device powered by the power supply, or elsewhere along the power supply output line. A cut-away side view of an electrical connector 100 with an overmolded adjacent ferrite bead choke according to an embodiment of the present invention is illustrated in FIG. 1. The electrical connector 100 has a two-conductor cable 102 that is inserted through the center of a ferrite bead 106. Ferrite bead 106 of this embodiment is an electromagnetic suppression choke that is a thick walled ferrite cylinder with a central bore that is able to accept cable 102. The end of cable 102 of this embodiment is connected to a coaxial output connector 108. A center contact of coaxial connector 108 is connected to a first conductor of the two-conductor cable 102 by a first conductor or wire 110. A second conductor of the two-conductor cable 102 is connected to an outer contact of the coaxial connector 108 by a second conductor or wire 112. The coaxial connector 108 in this embodiment is placed just beyond the end of the cable 102 and the end of the ferrite bead 106. The ferrite bead 106, adjacent coaxial connector 108 and wire 102 in this embodiment are physically secured by a plastic overmold 104. The arrangement of the ferrite bead 106, coaxial connector 108, that is adjacent to the ferrite bead 106 and overmold 104 advantageously provides a compact connector with an integral electromagnetic suppression ferrite bead, thereby reducing the length of the output connector - ferrite bead structure of conventional power supply cords. Plastic overmold 104 of the exemplary embodiment provides a secure, compact and aesthetically pleasing structure for the cable end assembly that includes the connector 108, ferrite bead 106 and cable 102. An electrical connector front view 200 for an electrical connector with an overmolded adjacent ferrite bead choke, according to an embodiment of the present invention is illustrated in FIG. 2. The electrical connector front view 200 illustrates the coaxial output connector 108 and its center conductor 202. The plastic overmold 104 of this embodiment is further illustrated as completely surrounding the ferrite bead 106 and as seamlessly connecting to the coaxial connector 108. A cut-away side view of an alternative electrical connector 300 that has a coaxial output connector that is partially within an overmolded ferrite bead choke, according to an embodiment of the present invention is illustrated in FIG. 3. This alternative electrical connector 300 includes a two- conductor cable 302 that is similar to the two-conductor cable 102 of the electrical connector 100. This Docket No. 623-10001 6 alternative electrical connector similarly has a coaxial output connector 308 that is connected to the two conductors of the two-conductor cable 308 by a first wire 310 and a second wire 312. These components are similar to the coaxial connector 108 that is connected to the two conductors of the two- conductor cable 102 with a first wire 110 and a second wire 112 of electrical connector 100. The ferrite bead 306 of the alternative electrical connector 300, however, is positioned so as to enclose a portion of the coaxial connector 308. This positioning of the coaxial connector 308 relative to the ferrite bead 306 provides a smaller cable end assembly and more effective shielding. The overmold 304 similarly encases the ferrite bead 306 and part of the coaxial output connector 308 and provides a compact physical supporting structure for the end of the cable 302 and coaxial output connector 308. A cut-away side view of a changeable tip electrical connector 400 that is completely integral to an overmolded ferrite bead choke according to an embodiment of the present invention is illustrated in FIG. 4. The changeable tip electrical connector 400 accepts a changeable tip to allow the cable output to be adapted to a variety of electronic devices. The changeable tip electrical connector 400 of this embodiment includes a two-conductor cable 402 that has a first wire 412 and a second wire 410. First wire 412 is terminated at a first mating contact 416 and the second wire 410 is terminated at a second mating contact 414. The first mating contact 416 and second mating contact 414 allow mating contacts from a mating connector, such as is part of a changeable tip, to be inserted at the connector opening 408. Contacts 414 and 416 are retained in relative position by contact retainer 430. The changeable tip electrical connector 400 of this embodiment includes a ferrite bead 406 that encloses the contacts and the end of the cable 402. The ferrite bead 406 is secured to the cable 402 by an overmold 404. Overmold 404 extends around the ferrite bead 406 and forms the connector opening 408. Overmold 404 of the exemplary embodiment further extends into the cavity of the ferrite bead to secure contact retainer 430 in position. As an alternative, overmold 404 can extend into the cavity of ferrite bead 406 in order to secure the first mating contact 416 and the second mating contact 414 into position without the need for contact retainer 430. This exemplary changeable tip electrical connector 400 has a ferrite bead 406 that fully encloses the contacts, including first mating contact 414 and second mating contact 416, and allows a changeable tip to be mated thereto. The changeable tip in this embodiment is not enclosed by the ferrite bead 406. Further embodiments include a ferrite bead that is positioned so as to extend over at least a portion of the changeable tip that is mated to the contacts of those connectors. It is further clear that other embodiments of the present invention are able to provide more than two contacts and provide connections for more than two wires through the connection. A cut-away side view of a keyed changeable tip electrical connector 500 with an asymmetric opening that is integral to an overmolded ferrite bead choke according to an embodiment of the present invention is illustrated in FIG. 5. The keyed changeable tip electrical connector 500 of this exemplary embodiment includes a two-conductor cable 502 that has a first wire 512 and a second wire 510. First wire 512 is terminated at a first mating contact 516 and the second wire 510 is terminated at a second mating contact 514. The first mating contact 516 and second mating contact 514 allow mating contacts from a mating connector, such as on a changeable tip, to be inserted at the keyed connector opening 522 and the inner opening 508. Docket No. 623-10001 7 The keyed changeable tip electrical connector 500 of this embodiment includes a ferrite bead 506 that encloses the contacts and the end of the cable 502. The ferrite bead 506 of the keyed changeable tip electrical connector 500 extends beyond the end of the first mating contact 516 and second mating contact 514 in this embodiment and is part of the inner opening 508. Contacts 514 and 516 are held in relative position by contact retainer 530. The ferrite bead 506 is secured to the cable 502 by an overmold 504. Overmold 504 extends around the ferrite bead 506 and also forms the keyed connector opening 522 by means of the keyed receptacle 520. Overmold 504 of the exemplary embodiment further extends into the cavity of the ferrite bead 506 in order to secure contact retainer 530 into position. The keyed connector opening in this embodiment includes a keyed receptacle 520 that forms an asymmetric keyed connector opening 522. The asymmetric keyed connector opening 522 formed by keyed receptacle 520 in this embodiment ensures the proper orientation of the mating connector that is inserted into the keyed connector opening 508. The shape of the keyed asymmetric connector opening 522, and its configuration relative to the inner opening 508, the first mating contact 516 and the second mating contact 514 also serves to limit the type of mating connectors that can be inserted into the keyed changeable tip electrical connector 500. The ferrite bead 506 in this embodiment is shown to extend beyond the contacts of this connector to provide greater electromagnetic suppression. It is clear that various embodiments of the present invention are able to use electromagnetic suppression chokes, such as ferrite beads, that are placed adjacent to the contacts of a connector without enclosing them, placed so as to partially enclose, fully enclose or even extend beyond the end of contacts of the connector. A keyed changeable tip electrical connector front view 600 of a keyed changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke, according to an embodiment of the present invention is illustrated in FIG. 6. The keyed changeable tip electrical connector front view 600 illustrates the asymmetrical and offset configuration of the keyed receptacle 520, the asymmetric keyed connector opening 522, the inner opening 508, the first mating contact 516 and the second mating contact 514. This arrangement serves to ensure proper orientation and to restrict the changeable tips that can be attached to this keyed changeable tip electrical connector 500. Various shapes, sizes, offsets, keys, contact locations and other means can be used alone or combined in the tips, connector and/or bead to prevent improper installation of changeable tips. An asymmetric base changeable tip 700 for use with the keyed changeable tip electrical connector, according to an embodiment of the present invention, is illustrated in FIG. 7. The asymmetric base changeable tip 700 of this embodiment has a multiple terminal port with a first contact 704 and a second contact 702 that are configured to engage the first mating contact 516 and the second mating contact 514, respectively, of the keyed changeable tip electrical connector 500. The body of the asymmetric base changeable tip 700 includes the inner base 714, which engages the inner opening of a keyed changeable tip electrical connector 500, and a keyed base 706, which engages the keyed connector opening 522. The asymmetric base changeable tip 700 has an output port in the form of a coaxial connector 712 that is able to be inserted into an electronic device to which power is being supplied. The outer Docket No. 623-10001 8 contact of coaxial connector 712 is connected to the first contact 704 by a first conductor, first wire 708, and the inner contact of coaxial connector 712 is connected to the second contact 702 by a second conductor, second wire 710. The construction of the asymmetric base changeable tip 700 arranges the relative positions of the first contact 704, the second contact 702, the inner base 714 and the keyed base 706 so as to ensure proper connection to the keyed changeable tip electrical connector 500.

An asymmetric base changeable tip rear view 800, according to an embodiment of the present invention, is illustrated in FIG. 8. The asymmetric base changeable tip rear view 800 illustrates the relative positions of the first mating contact 704, the second contact 702, the inner base 714 and the keyed base 706. These components are positioned so as to ensure proper mating to the keyed changeable tip electrical connector 500, as can be seen by comparison to the keyed changeable tip electrical connector front view 600. A cut away view of a self-identifying changeable tip 900 according to an embodiment of the present invention is illustrated in FIG. 9. The self-identifying changeable tip 900 of this embodiment is a keyed changeable tip similar to the asymmetric base changeable tip 700. The self-identifying changeable tip 900 includes a self-identification circuit that consists of a zener diode 904 and a series resettable fuse 902, that are connected in series between the first contact 704 and the second contact 702. One port of the zener diode 904 is connected to the first contact 704 through a first wire 906, and one port of the resettable fuse 902 is connected to the second contact 702 through a second wire 908. The operation of the self identifying circuit is described in detail below. A mated cut-away side view 1000 of a keyed changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke that is mated to an asymmetric base changeable tip 700 according to an embodiment of the present invention is illustrated in FIG. 10. The mated cut-away side view 1000 illustrates a mating asymmetric connector, i.e., the keyed changeable tip electrical connector 500, that has an inner opening 508 and an asymmetric connector opening 522. These asymmetric openings have a corresponding fit with an asymmetric connector, i.e., the asymmetric base changeable tip 700, in particular the inner body 714 and the keyed base 706, respectively. The first mating contact 516 and the second mating contact 514 are also shown as mating with the first contact 704 and the second contact 702, respectively. The mated connectors of this embodiment thereby provide a continuous circuit that connects the two conductors of the two- conductor cable 502 to the coaxial connector 712. The asymmetrical keying of the two connectors also restricts the connectors to those that are specifically intended to be mated. The asymmetrical keying further ensures that the proper orientation and polarity for the mated connector is maintained. The ferrite bead 506 is shown to extend over part of the mating contacts, i.e., the first contact 704 and the second contact 702, so as to provide for the electromagnetic suppression closer to the electronic device to which it is connected. Some embodiments of the present invention incorporate a self identifying circuit to allow a suitably equipped power supply to identify a device that is connected to the output of such a power supply. One type of self identifying circuit used by embodiments of the present invention incorporates a Docket No. 623-10001 9 zener diode that is in series with a resettable fuse. The series zener diode and resettable fuse are connected across two power supply output wires in order to identify the device attached to the power supply, as is illustrated for the self-identifying changeable tip 900. This self identifying circuit is able to be located within a changeable tip, such as the self-identifying changeable tip 900, that is attached to a connector that is part of a cable carrying the output of a power supply. The self identifying circuit in some embodiments is also able to be part of a cable assembly itself, a configuration that is particularly useful for a replaceable cable of a power supply or an extension power cable. The self identifying circuit in further embodiments is able to be located within the device that is being powered by the power supply. Examples of self identifying circuits used by embodiments of the present invention incorporate zener diodes such as the MAZS0510M, manufactured by the Panasonic Division of Matsushita Electronics Corporation of Japan, that are in series with a resettable fuse, such as the MICROSMD005 manufactured by the Raychem Division of Tyco Electronics of Menlo Park, CA. The resettable fuses used by exemplary embodiments of the present invention are current dependent resistors that have an electrical resistance that depends upon the current carried by the device. Exemplary resettable fuses exhibit a low resistance when they carry a current that is below a specified value. When the current through a resettable fuse increases to a point above that specified value, the resistance of the resettable fuse greatly increases. This increased resistance operates to limit the current that flows through the device. Unlike conventional fuses, however, the exemplary resettable fuses continue to conduct once the specified current is exceeded, but with a higher resistance. The exemplary resettable fuses are solid-state devices that, unlike conventional fuses or circuit breakers, are not damaged or reconfigured when the specified current exceeds the specified value. These exemplary resettable fuses return to their lower resistance state when the current through them is reduced, such as when the voltage across the device is removed. Zener diodes are well known in the electronic arts and are semiconductor devices that can be characterized as a voltage dependent conductor. A zener diode generally has a very high impedance when a voltage is applied in a reverse direction that is below a specified voltage. The specified voltage below which a zener diode exhibits this high impedance is referred to as its "zener voltage." As the voltage across a zener diode increases, the apparent impedance of the zener diode decreases and the zener diode generally passes any amount of current, below that which causes thermally induced damage, while maintaining the relatively constant zener voltage drop across the zener diode. Above the zener voltage, a zener diode can be characterized as exhibiting a low impedance characteristic. As an alternative to zener diodes, some embodiments of the present invention incorporate voltage dependent conductors that include one or more batteries and a series diode. These embodiments use a battery to reverse bias the diode so that current does not flow through the series diode-battery combination until the voltage across the combination exceeds the battery voltage plus the diode threshold voltage. Once this voltage is exceeded, this combination exhibits a low impedance characteristic. As yet another alternative to zener diodes, some embodiments of the present invention utilize a resistor in series with a resettable fuse. These embodiments supply a constant current through Docket No. 623-10001 10 the resistor/resettable fuse pair and measure the voltage across the pair. For example, self identification circuits are able to have a fifty milliamp (50 mA) resettable fuse with a series resistor of one kiloohm (1 K). A one milliamp (1 mA) constant current can be applied to this configuration during an identification phase for the self identification circuit, and a one volt (1V) voltage wili be measured. Another self identification tip can use a two kiloohm (2 K) resistor, and a one milliamp (1 mA) identification current would produce a two volt (2 V) voltage. The power supply of these embodiments measures the voltage while applying this constant current In order to identify the self identifying circuit. These embodiments supply a constant current that is below the current threshold for the resettable fuse, and thereby allow determination of the resistor value by measurement of the voltage across the resistor/resettable fuse pair when a constant current is being provided through that pair. In any of these alternative embodiments, the resettable fuse will "open" once the operating supply voltage is applied to the identification circuit. All of these self identifying circuits advantageously allow self identification while requiring only the two wires that supply the output of the power supply to the device and do not require any additional conductors to convey identification information. A voltage versus current chart 1100 for several exemplary series zener diodes and resettable fuse pairs, according to embodiments of the present invention, are illustrated in FIG. 11. The voltage versus current chart 1100 illustrates the voltage and current relationship for four self-identifying two-wire circuits that use the same resettable fuse but that use zener diodes that have different breakdown voltages. These four curves include a first curve 1102 that corresponds to a series zener diode- resettable fuse pair incorporating a zener diode with a zener voltage of 2.6 V. A second curve 1104 corresponds to a series zener diode-resettable fuse incorporating a zener diode with a zener voltage of 3.7 V. A third curve 1106 corresponds to a series zener diode-resettable fuse incorporating a zener diode with a zener voltage of 5.1 V. A fourth curve 1108 corresponds to a series zener diode-resettable fuse incorporating a zener diode with a zener voltage of 6.2 V. Geometric shapes disposed along each curve correspond to voltage-current points along those curves. The voltage versus current chart 1100 has a current axis 1112 and a voltage axis 1110. The current through a particular series zener diode - resettable fuse pair for a particular voltage across the pair, or the voltage for a particular current through the pair, is able to be determined by reference to these curves. These curves indicate that as the voltage across a pair increases from zero volts, the current remains essentially at zero and then increases rapidly as the zener voltage is approached. As the current initially increases from zero, the current is below the specified current for the series resettable fuse and the voltage - current relationship primarily reflects that of the zener diode. Once the current increases beyond the specified current for the resettable fuse, the resistance of the resettable fuse increases and serves to reduce the current through the series pair as the voltage across the series pair continues to increase. An electrical circuit schematic diagram 1200 for a circuit including a self identification circuit sensing power supply that is connected to an appliance through a changeable connector tip that contains a two wire self identification circuit, according to an embodiment of the present invention, is illustrated in FIG. 12. The schematic diagram 1200 includes a power supply 1202, a self identifying Docket No. 623-10001 11 changeable connector tip 1204 and an appliance 1206. The appliance 1206 of this exemplary embodiment is a conventional appliance or device that is supplied by an external power supply. Exemplary appliances include notebook computers, cell phones, personal digital assistants (PDAs), or any other such device. The appliance 1206 of this exemplary embodiment includes an appliance that includes a power input connector 1252. The self identifying changeable connector tip 1204 has an output connector 1254 that is adapted to mate to the power input connector 1252 of the appliance 1206. The self identifying changeable connector tip 1204 further has an input connector 1250 that is adapted to connect to output connector 1256 of the power supply 1202. This exemplary embodiment shows a two conductor power supply output that provides DC power to the appliance through a two conductor cable. The two conductors used to deliver power to the appliance are connected through two contacts in each of the input connector 1250 and output connector 1254. A first wire 1260 electrically connects a first set of contacts in these two connectors and a second wire 1262 electrically connects a second set of contacts in these two connectors. The first wire 1260 is similar to the first wire 708 of the asymmetric base changeable tip 700 and the second wire 1262 is similar to the second wire 710 of the asymmetric base changeable tip 700. The self identifying changeable connector tip 1204 has a self identifying circuit 1258 that consists of a zener diode 1232 and a resettable fuse 1234 that are placed in series across the first wire 1260 and the second wire 1262. This configuration places the series zener diode - resettable fuse pair across the two conductors supplying power to the appliance 1206, as well as across the output of the power supply 1202. This allows identification of the self identifying circuit 1258 by using only the same wires that as are used to supply power to the appliance. The power supply 1202 of this exemplary embodiment is a variable output voltage power supply that includes a current monitoring circuit. The power supply 1202 provides output power at a power supply output connector 1256. The power supply output connector is able to be mounted on the case of the power supply 1202 or to be located at the end of a cable connected to the power supply 1202. Such cables are able to be fixedly attached to the case of the power supply 1202, or the cable is able to be removed from the case of the power supply 1202. In addition, the output connector is able to include an electromagnetic suppression choke. The power supply 1202 of this exemplary embodiment includes a variable output voltage power generator 1220 that provides an output voltage based upon a selected reference voltage determined by reference voltage selector 1210. Reference voltage selector 1210 selects a reference voltage from a number of reference voltage inputs, including Reference A 1212, Reference B 1214 through Reference N 1216. Reference voltages in this exemplary embodiment are generated by conventional means, such as by zener voltage references within the power supply 1202. The power supply 1202 of the exemplary embodiment operates to identify the self identification circuit 1258 by identifying the threshold voltage of the zener diode 1232. In order to identify the threshold voltage of the zener diode 1232, the power supply 1202 is configured to use a default or programming voltage reference, such as REF. N, and configures the variable voltage generator 1220 to produce a voltage output through a resistance Rprogram 1224. Rprogram in this exemplary Docket No. 623-10001 12 embodiment is a 1 Kilo-ohm resistor. The voltage at the output of Rprogram 1224 is monitored by the voltage monitor buffer 1222 and provided to a controller 1218 for monitoring as described herein. Switch Spower 1226 is opened, under the control of controller 1218, to place Rprogram 1224 into the output circuit of the power supply 1202. Switch Spower 1226 is closed, under the control of controller 1218, to remove Rprogram 1224 from the output circuit and to deliver the programmed operating output voltage to appliance 1206. The operation of the power supply 1202 has a two stage operating profile. Power supply 1202 initially performs an identification phase during which the power supply 1202 identifies the self identifying circuit 1253 in order to determine the voltage requirement of the appliance 1206. Based upon the identification made during the initial identification phase, the power supply 1202 then transitions to an operational phase, wherein the power supply 1202 provides the correct operating voltage to the appliance 1206 that is determined based upon the identification made during the identification phase. The identification phase of this embodiments is performed with switch Spower 1226 in its open position and .the operational phase is performed with switch Spower 1226 in its closed position. The identification phase is performed with switch Spower 1226 in its open position, as is described below. The operation of this exemplary embodiment uses self identification circuits 1258, that are a part of self identifying connector tips 1204, that have threshold voltages that are well below the operating voltage of the appliance 1206 with which that self identifying connector tip is intended to work. This results in a negligible current being drawn by the appliance 1206, which is in parallel with the self identification circuit 1258, thereby allowing the voltage/current response of just the self identification circuit 1258 to be observed. Upon start-up, voltage selector 1210 of power supply 1202 is set to a default voltage higher than any anticipated voltage threshold of zener 1232. and Spower 1226 is set to its default open position. The high value of Rcurrent will limit current flow to be less than the threshold current of fuse 1234. This current is continuously monitored by current monitor 1230. The voltage across tip 1262 is monitored by voltage monitor 1222. If a tip 1204 in installed on the system, the voltage threshold of zener 1232 will be exceeded and will enter its low impedance state, resulting in small current to flow through tip 1204. The voltage sensed by voltage monitor 1222 will be effectively equal to the threshold voltage of zener 1232, thereby identifying the tip 1204. After identifying the self identification circuit's 1258 zener voltage, the controller 1218, which includes an analog to digital converter to convert the monitored output voltage to a digital format, performs a conversion from this analog voltage to a digital selection based on a predetermined database. Some embodiments of the present invention utilize an analog to digital converter within controller 1218 that produces digital control lines that directly correspond to reference voltages to select through reference voltage selector 1210. This is in accordance with an appliance voltage to smart tip definition. This selected voltage is the correct operational voltage for appliance 1206 based on the zener voltage identity of the tip 1204. Upon entering its operational mode, the exemplary power supply 1202 closes switch Spower 1226. When this output voltage is supplied by the power supply 1202 and applied to the self identification circuit 1258 the resulting current flow exceeds the limit of resettable Docket No. 623-10001 13 fuse 1234 causing it to enter its high resistance mode. Since, however, the resettable fuse continues to allow a small amount of current to flow through it while in its high impedance state, the operational voltage of power supply 1202 is still present across zener 1232, causing zener 1232 to remain in its low impedance state. The result is a stable self-identification circuit 1258 that appears essentially as an open circuit to appliance 1206 as the tiny current flow is too low to affect the powering of the appliance. However, this small current flow is detectable by power supply 1202 and indicate that tip 1204 is connected and therefore still in the operational mode, even if appliance 1206 is disconnected or otherwise not drawing any current. Power supply 1202 continues to monitor current flow and as long as current flow is detected, tip 1204 is known to be still connected and power supply 1202 remains in operational mode. If no current flow is detected, then tip 1204 has been disconnected or otherwise removed from the system, and power supply 1202 returns to the identification mode, waiting for another tip to be installed. Once another tip 1204 is installed, the identification process again starts and the process is repeated. The above operation of the power supply 1202 is illustrative of processing used to identify self identification circuits 1258. It is clear to those skilled in the relevant arts that alternative processing and techniques can be used to determine the zener voltage of the self identification circuit. For example, further embodiments of the present invention incorporate various power supply designs and operating techniques to identify the zener voltage of self identification circuits. For example, the processing of an alternative power supply 1202 of an alternative embodiment determines the voltage/current response of the self identification circuit 1258 by initially setting the output voltage of the voltage generator 1220 to a low voltage, by selection of an appropriate reference voltage via the reference voltage selector 1210, and increasing the output voltage of the voltage generator 1220 by selection of appropriate references voltages As the output voltage is increased, the current supplied to the self identifying changeable connector tip 1204 is monitored by the output current monitoring circuit of the power supply 1202. An electrical circuit schematic diagram 1300 for an identification circuit sensing power supply that is connected to an appliance that contains a two wire self identifying circuit according to an embodiment of the present invention is illustrated in FIG. 13. The electrical circuit schematic diagram 1300 for the identification circuit sensing power supply that is connected to the appliance that contains a two wire identification circuit is similar to the electrical circuit schematic diagram 1200, except that the self identification circuit 1358 is contained within the appliance 1302 itself. A similar power supply 1202 is used in this configuration. This configuration advantageously allows the appliance 1302 to be used with a generic identification circuit sensing power supply 1202 but without a self identifying changeable connector tip 1204. The operation of these two configurations is also similar. Further embodiments of the present invention perform the identification phase of power supply operation by providing a constant current output from the power supply into the two wire self identifying circuit. These embodiments incorporate an identification circuit sensing power supply that provides a constant current that is sufficiently small to cause the resettable fuse or other current dependent resistor to have a low resistance. The operation of these embodiments allows the voltage of the zener diode or other voltage dependent conductor to be measured since it will conduct the current provided by the constant current source while maintaining its zener voltage. Selection of a current below the Docket No. 623-10001 14 value that causes the resettable fuse to increase resistance ensures that the voltage of the zener diode is accurately determined. A cut-away side view 1400 of an alternative changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke, and of an alternative changeable tip in position for mating thereto, according to an embodiment of the present invention, is illustrated in FIG. 14. The alternative changeable tip electrical connector 1432 has a two-conductor cable 1426 with two wires that are connected to two electrical contacts, a first electrical mating contact 1422 and a second electrical mating contact 1424. The alternative changeable tip electrical connector 1432 has a ferrite bead 1428 surrounding a portion of the two electrical contacts and the end of the two conductor cable 1426 in order to provide electromagnetic suppression for signals passing along the two conductor cable 1426. The alternative changeable tip electrical connector 1432 has a body formed by a plastic overmold 1420 that surrounds the ferrite bead 1428, the end of the two conductor cable 1426 and that forms a mating portion of the alternative changeable tip electrical connector 1432. The mating portion of the alternative changeable tip electrical connector 1432 includes an asymmetrical plug 1434 that has a keyed shape to engage properly formed changeable tips that are intended for use with this connector. The alternative changeable tip 1430 includes a coaxial output connector 1402 that is connected to an input connector having a first contact 1408 and a second contact 1406. The alternative changeable tip 1430 has a body 1404 that is formed by molded plastic in this exemplary embodiment. The body 1404 of this exemplary embodiment has a keyed recess 1436 that engages the asymmetrical plug 1434 to allow proper mating of the alternative changeable tip 1430 to the alternative changeable tip connector 1432. A cut-away mated side view 1500 of an alternative changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke with a changeable tip mated thereto, according to an embodiment of the present invention, is illustrated in FIG. 15. The cut away mated side view 1500 illustrates how the asymmetrical plug 1434 and the keyed recess 1436 of the alternative changeable tip 1430 have a corresponding fit and mate together. The first mating contact 1422 and the second mating contact 1424 are also shown as mating with the first contact 1408 and the second contact 1406, respectively. The mated connectors of this embodiment thereby provide a continuous circuit that connects the two conductors of the two-conductor cable 1426 to the coaxial connector 1402. The asymmetrical keying of the two connectors also restricts the connectors to those that are specifically intended to be mated. The asymmetrical keying further ensures that the proper orientation and polarity for the mated connector is maintained. A cut-away side view 2000 of a second alternative changeable tip electrical connector with an asymmetric opening that has an adjacent overmolded ferrite bead choke, and of a second alternative changeable tip in position for mating thereto, according to an embodiment of the present invention, is illustrated in FIG. 20. The second alternative changeable tip electrical connector 2004 has a two- conductor cable 2002 with two wires that are connected to two electrical contacts, a first electrical contact 2016 and a second electrical contact 2018. The alternative changeable tip electrical connector 2004 has a ferrite bead 2012 that is located adjacent to the electrical contacts and does not enclose Docket No. 623-10001 15 any part of the electrical contacts. Ferrite bead 2012 provides electromagnetic suppression for signals passing along the two conductor cable 2002. The alternative changeable tip electrical connector 2004 has a body formed by a plastic overmold 2010 that surrounds the ferrite bead 2012, the end of the two conductor cable 2002 and the electrical contacts. The overmold 2010 also forms a mating portion of the second alternative changeable tip electrical connector 2004. The mating portion of the second alternative changeable tip electrical connector 2004 includes an asymmetrical plug 2014 that has a keyed shape to engage properly formed changeable tips that are intended for use with this connector. The second alternative changeable tip 2006 includes a coaxial connector 2008 that is connected to a first mating contact 2020 and a second mating contact 2022. The second alternative changeable tip 2006 has a body 2026 that is formed by molded plastic in this exemplary embodiment. The body 2026 of this exemplary embodiment has a keyed recess 2024 that engages the asymmetrical plug 2014 to allow proper mating of the second alternative changeable tip 2006 to the second alternative changeable tip connector 2004. A cut-away mated side view 2100 of a second alternative changeable tip electrical connector with a second asymmetric opening that has an adjacent overmolded ferrite bead choke with a changeable tip mated thereto, according to an embodiment of the present invention, is illustrated in FIG. 21. The cut away mated side view 2100 illustrates how the asymmetrical plug 2014 and the keyed recess 2024 of the second alternative changeable tip 2006 have a corresponding fit and mate together. The first contact 2016 and the second contact 2018 are also shown as mating with the first mating contact 2020 and the second mating contact 2022, respectively. The mated connectors of this embodiment thereby provide a continuous circuit that connects the two conductors of the two-conductor cable 2002 to the coaxial connector 2008. The asymmetrical keying of the two connectors also restricts the connectors to those that are specifically intended to be mated. The asymmetrical keying further ensures that the proper orientation and polarity for the mated connector is maintained. A cut-away side iew 2200 of a third alternative changeable tip electrical connector with an asymmetric opening and of a second alternative changeable tip mated thereto, according to an embodiment of the present invention, is illustrated in FIG. 22. The third alternative changeable tip electrical connector 2204 has a two-conductor cable 2202 with two wires that are connected to two electrical contacts, a first electrical contact 2216 and a second electrical contact 2218. The alternative changeable tip electrical connector 2204 has a body formed by a plastic overmold 2210 that surrounds the end of the two conductor cable 2202 and the electrical contacts. The overmold 2210 also forms a mating portion of the third alternative changeable tip electrical connector 2204. The mating portion of the third alternative changeable tip electrical connector 2204 includes an asymmetrical plug 2214 that has a keyed shape to engage properly formed changeable tips that are intended for use with this connector. The third alternative changeable tip 2206 includes a coaxial connector 2208 that is connected to a first mating contact 2220 and a second mating contact 2222. The third alternative changeable tip 2206 has a body 2226 that is formed by molded plastic in this exemplary embodiment. The body 2226 of this exemplary embodiment has a keyed recess that engages the asymmetrical plug 2214 to allow proper mating of the third alternative changeable tip 2206 to the third alternative changeable tip Docket No. 623-10001 16 connector 2204. The third alternative changeable tip 2206 is further able to optionally include a self identification circuit. It is to be noted that neither the third alternative changeable tip connector 2204 or the third alternative changeable tip 2206 has a ferrite bead electromagnetic suppression choke. The cut away mated side view 2200 illustrates how the asymmetrical plug 2214 and the keyed recess of the third alternative changeable tip 2206 have a corresponding fit and mate together. The first contact 2216 and the second contact 2218 are also shown as mating with the first mating contact 2220 and the second mating contact 2222, respectively. The mated connectors of this embodiment thereby provide a continuous circuit that connects the two conductors of the two-conductor cable 2202 to the coaxial connector 2208. The asymmetrical keying of the two connectors also restricts the connectors to those that are specifically intended to be mated. The asymmetrical keying further ensures that the proper orientation and polarity for the mated connector is maintained. A power supply 1600 for a portable electronics device that includes a changeable tip electrical connector with an asymmetric opening that is integral to an overmolded ferrite bead choke with a changeable tip mated thereto, according to an embodiment of the present invention is illustrated in FIG. 16. Power supply 1600 of this embodiment has a power module 1504 that includes circuits to convert an input voltage, such as 115 Volts AC or 12 Volts DC, into a DC output voltage. The input power is received through an input power cord 1502 that has a power plug 1508. The input power cord 1502 is detachably connected to the power module 1504 by a connector 1510. The output power of the power module 1504 is provided through a two conductor DC power cable 1506, that includes a changeable tip connector 500 and a self identifying changeable tip 700 mated thereto. A retracting cord power supply 1700 for a portable electronics device that includes a retractor for retracting input and output power cords, according to an embodiment of the present invention is illustrated in FIG. 17. The retracting cord power supply 1700 is similar to the power supply 1600 and includes an integral power module and cord retractors in order to greatly increase the portability of the device. The retracting cord power supply 1700 incorporates a cord and retractor assembly that is similar to that taught in U.S. Patent Application Number 10/181 ,665, filed July 19, 2002 and in International Patent Applications PCT/US01/03368, PCT/US01/14869, and PCT/US01/42394. The entire contents and teachings of U.S. Patent Application Number 10/181 ,665 and International Patent Applications PCT/US01/03368, PCT/US01/14869, and PCT/US01/42394 are hereby explicitly incorporated herein by reference. The retracting cord power supply 1700 includes a housing 1702 that has a power module 1708 adapted to mount onto the housing 1702. A retracting cord power supply side view 1720, that corresponds to a side view of power supply 1700, indicates that the retracting cord power supply 1700 includes an input power cord 1502 with an attached plug 1508 as described above. The retracting cord power supply 1700 further includes a two conductor DC power cord 1506 with the attached changeable tip connector 500 and a self identifying changeable tip 700 mated thereto, as were described above. These cords are retracted into the housing 1702 by retractor 1704 that has a spool to co-wind and carry both cords as they are retracted, which results in the cords being wound as shown. All or some of these cords are able to be extracted from the housing 1702 for use to connect to a power outlet and a device. Docket No. 623-10001 17 An electrical circuit schematic diagram for a dual zener voltage self identification circuit 1800 according to an embodiment of the present invention is illustrated in FIG. 18. The dual zener voltage self identification circuit 1800 is similar to the self identification circuit 1258 described above. The dual zener voltage self identification circuit 1800 has a two contact input connector and a two contact output connector. The two contact input connector has a first input contact 1802 and a second input contact 1804. The contacts of the two contact input connector are connected to the two contacts of the output connector, by two wires. The first input contact 1802 is connected to a first output contact 1806 via a first wire 1820. The second input contact 1804 is connected to the second output contact 1808 by a second wire 1822. The dual zener voltage self identification circuit 1800 has a first zener diode 1810 and a first resettable fuse 1812 are connected in series between the first wire 1820 and the second wire 1822. This operates as described above. Additionally, the dual zener voltage self identification circuit 1800 has a second zener diode 1814 and a second resettable fuse 1816 that are also connected in series between the first wire 1820 and the second wire 1822. The zener voltage of the second zener diode 1814 is selected to be higher than the zener voltage of the first zener diode 1810. This results in a two- step voltage/current response for the dual zener voltage self identification circuit 1800 and allows a greater number of unique self-identifying circuits to be defined. The operation of an identifying power supply that operates with a dual zener voltage self identification circuit 1800 includes increasing a voltage across the two conductors connected to the input port of the circuit, monitoring the current conducted by the circuit until the current increases and then stabilizes, as is described above for a one zener diode self identification circuit. As the voltage is further increased, the current conducted by the first zener diode 1810 and resettable fuse 1812 remains low or constant, as described above. As the zener voltage of the second zener diode 1814 is approached, the current supplied to the circuit further increases as the second zener diode begins to conduct. As the voltage supplied to the dual zener voltage self identification circuit 1800 is increased further, the second resettable fuse 1816 increases resistance and the current remains at a low level even as voltage increases. The two current "steps" relative to voltage are detected by a power supply connected to the dual zener voltage self identification circuit 1800 and a mapping for the two identified zener voltages is able to be made.An identification processing flow diagram 1900 for identifying a self identifying circuit according to an embodiment of the present invention is illustrated in FIG. 19. The identification processing flow diagram 1900 begins by turning on, at step 1902, the power to an identifying power supply, such as power supply 1202 in this example. The processing next applies, at step 1914, the programming voltage at the output of the power supply 1202 with the switch Spower 1228 open. This causes current to flow through Rprogram 1224. The operation of Rprogram 1224 limits the current at the output of the power supply 1202, as delivered at connector 1256, so that the voltage at the output of the power supply will correspond to the zener voltage of zener diode 1232. The processing then determines, at step 1904, if current is flowing from the power supply 1202.. If no current flow is detected, the processing assumes that a device or changeable tip is not connected to the Docket No. 623-10001 18 power supply. If no current draw is detected, the processing returns to applying, at step 1914, programming voltage with Spower 1226 open, as described above. If a current flow is detected at the output of the power supply, a device, changeable tip or other component with a self identifying circuit is assumed to be connected to the output of the power supply. If a current draw is detected at the output of the power supply, the processing of this embodiment then measures, at step 1906, the output voltage of the power supply. The measured voltage is then presented, at step 1908, to controller 1218, which includes an analog to digital converter, which selects an operating voltage based upon that measured voltage. The operating output voltage is able to be determined by a look-up table that correlates measured voltage to an output voltage, or an arithmetic relationship can be used by various embodiments of the present invention. An analog to digital converter can also be incorporated into the controller 1218 that produces a digital output that can be used to directly provided to reference voltage selector 1210 in order to select the reference voltage that corresponds to the operating voltage. Once the operational voltage is selected, the processing sets, at step 1910, the output voltage of the power supply 1202 to this operating voltage and closes switch Spower 1226. Once the output voltage is set to the operating voltage , the processing enters the operational phase and monitors, at step 1912, to determine if current is flowing from the output of the power supply. As long as current is flowing out of the power supply, the self identifying circuit is assumed to be connected to the power supply and the operational voltage is maintained. If current flow is detected, the processing remains in this step and continues to monitor for current flow. If current flow is not detected, the self identifying circuit is assumed to have been disconnected. The processing provides an ability for the user to connect any arbitrary self identifying circuit to the output of the power supply by returning to the identification phase and applying, at step 1914, a programming voltage at the output of the power supply and opening switch Spower 1226 in order to identify the self identification circuit 1258. Some embodiments of the present invention, as are described above, allow a self identifying circuit to be installed into a two wire circuit that allows a power supply to identify that self identifying circuit. These embodiments require only the two wires used to deliver power to a device and do not require any additional conductors to communicate identification data to the power supply. These self identifying circuits can be incorporated, for example, into changeable tips that are placed on the output cable of the power supply, within the output cable itself, and within devices to which the power supply can connect. This advantageously allows self identification circuits to be used with thinner cables since additional conductors are not used. These thinner cables are especially advantageous when used with cord retractors or in portable applications where product bulk is a disadvantage. It is to be further understood that the power supplies that are used by or in conjunction with embodiments of the present invention are able to include power supplies that accept either or both of AC or DC input power at any voltage and that are able to then produce either or both of AC or DC power, according to the desires and requirements of the particular embodiment. The power supplies of the various embodiments are further able to produce output voltages that are higher or lower than the voltage of the input power received by the power supply, as is required or desired by the various embodiments. Docket No. 623-10001 19 The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). Although specific embodiments of the invention have been disclosed, those having ordinary skill in the art will understand that changes can be made to the specific embodiments without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted, therefore, to the specific embodiments, and it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention. What is claimed is:

Claims

Docket No. 623-10001 20 CLAIMS

1. A two-wire self identification circuit, comprising: at least one current dependent resistor with a resistance characteristic comprising a low resistance when conducting less than a pre-defined current and a high resistance when conducting at least the pre-defined current; and at least one voltage dependent conductor that exhibits a high impedance when a voltage that is below a pre-defined voltage is across the voltage dependent conductor and that exhibits a low impedance characteristic when the voltage across the voltage dependent conductor is above the predefined voltage, wherein the at least one current dependent resistor and the at least one voltage dependent conductor are electrically coupled in series.

2. The two-wire self identification circuit according to claim 1 , wherein the at least one current dependent resistor includes at least one resettable fuse.

3. The two-wire self identification circuit according to claim 1 , wherein the at least one voltage dependent conductor includes at least one zener diode.

4l The two-wire self identification circuit according to claim 1 , wherein the at least one voltage dependent conductor comprises at least one battery and at least one diode.

5. The two-wire self identification circuit according to claim 1 , wherein the at least one voltage dependent conductor comprises at least one resistor.

6. The two-wire self identification circuit according to claim 1 , wherein the at least one current dependent resistor and the at least one voltage dependent conductor are connected in series across at least two terminals of a multiple terminal port.

7. The two-wire self identification circuit according to claim 6, further comprising a connector tip, the connector tip comprising at least two conductors, wherein at least a first conductor of the at least two conductors is connected to a first terminal of the at least two terminals and at least a second conductor of the at least two conductors is connected to a second terminal of the at least two terminals.

8. The two-wire self identification circuit according to claim 6, further comprising an asymmetric connector for the multiple terminal port.

9. The two-wire self identification circuit according to claim 8, wherein the asymmetric connector is mechanically keyed to a mating asymmetric connector with which the connector tip is associated. Docket No. 623-10001 21

10. The two-wire self identification circuit according to claim 1 , wherein at least one of the at least one current dependent resistor and the at least one voltage dependent conductor is part of a connector tip.

11. The two-wire self identification circuit according to claim 10, wherein the connector tip comprises a mechanically keyed connector for connecting to a power port of an electronic device.

12. The two-wire self identification circuit according to claim 10, wherein the connector tip is associated with an electronic device and an operating output voltage of the electronic device is associated with the pre-defined voltage.

13. The two-wire self identification circuit according to claim 10, wherein the connector tip is adapted for one of a portable computer, a personal digital assistant, a kitchen appliance, a construction appliance and a portable phone.

14. The two-wire self identification circuit according to claim 10, wherein the connector tip comprises: a first contact and a second contact; a first conductor and a second conductor, the first conductor connected to the first contact at a junction and the second conductor connected to the second contact at the junction; an electromagnetic suppression choke located in proximity to the junction; and an overmold positioned so as to enclose the junction and the electromagnetic suppression choke.

15. The two-wire self identification circuit according to claim 14, wherein the electromagnetic suppression choke is positioned immediately to the junction.

16. The two-wire self identification circuit according to claim 14, wherein the electromagnetic suppression choke is positioned over the junction and encloses at least part of the first contact and the second contact.

17. The two-wire self identification circuit according to claim 1 , further comprising: a second current dependent resistor with a resistance characteristic comprising a second low resistance when conducting less than a second pre-defined current and a second high resistance when conducting more than the second pre-defined current; and a second voltage dependent conductor that exhibits high impedance when a second voltage that is below a second pre-defined voltage is across the second voltage dependent conductor and that exhibits a second low impedance characteristic when the second voltage across the second voltage dependent conductor is above the second pre-defined voltage, Docket No. 623-10001 22 wherein the second current dependent resistor and the second voltage dependent conductor are electrically coupled in series with each other and in parallel with the at least one current dependent resistor and the at least one voltage dependent conductor.

18. A self identifying circuit sensor for use with a self identifying circuit comprising at least one current dependent resistor coupled in series with at least one voltage dependent conductor, the self identifying circuit sensor comprising: an output port with at least two conductors; an adjustable voltage generator for supplying an adjustable voltage across two conductors of the output port; a current monitor for determining a current measurement of current flowing through the two conductors of the output port; and an identification determination circuit, communicatively coupled to the adjustable voltage generator and the current monitor, for controlling the adjustable voltage and monitoring the current flow so as to identify a self identifying circuit connected across the two conductors by determining a voltage/current relationship of the self identifying circuit.

19. The self identifying circuit sensor according to claim 18, wherein the adjustable voltage generator has an operating output voltage set based upon the identified self identifying circuit.

20. The self identifying circuit sensor according to claim 18, wherein the output port comprises a keying shape for mating with a connector.

21. The self identifying circuit sensor according to claim 18, wherein the output port further comprises a cable, the cable comprising the at least two conductors.

22. The self identifying circuit sensor according to claim 21 , further comprising: an electromagnetic suppression choke disposed about the cable and in proximity to the output port; and an overmold formed around the electromagnetic suppression choke and the output port.

23. The self identifying circuit sensor according to claim 21 , further comprising a retractor for retracting the cable.

24. The self identifying circuit sensor according to claim 23, wherein the retractor encloses at least one of the adjustable voltage generator, the current monitor, and the identification determination circuit.

25. The self identifying circuit sensor according to claim 23, wherein the retractor comprises: a housing; a spool rotatably mounted in the housing; Docket No. 623-10001 23 a first cable at least partially carried by the spool; and a second cable, separate from the first cable, at least partly carried by the spool, wherein the first cable and the second cable are co-wound together onto and off of the spool.

26. A self identifying circuit sensor for use with a self identifying circuit, the self identifying circuit comprising at least one current dependent resistor coupled in series with at least one voltage dependent conductor, the self identifying circuit sensor comprising: an output port with at least two conductors; an adjustable current generator for supplying an adjustable current across two conductors of the output port; a voltage monitor for producing a voltage measurement of a voltage across the two conductors of the output port; and an identification determination circuit, communicatively coupled to the adjustable current generator and the voltage monitor, for controlling the adjustable current and monitoring the voltage measurement so as to identify a self identifying circuit connected across the two conductors by determining a voltage/current relationship of the self identifying circuit.

27. The self identifying circuit sensor according to claim 26, further comprising an adjustable voltage generator, wherein the adjustable voltage generator has an operating output voltage set based upon the identified self identifying circuit.

28. A self-identifying power supply connector tip, comprising: an input port comprising at least two conductors; an output port connected to the at least two conductors; at least one current dependent resistor with a resistance characteristic comprising a low resistance when conducting less than a pre-defined current and a high resistance when conducting more than the pre-defined current; and at least one voltage dependent conductor that exhibits a high impedance when a voltage that is below a pre-defined voltage is across the voltage dependent conductor and that exhibits a low impedance when the voltage across the voltage dependent conductor is above the pre-defined voltage, wherein the current dependent resistor and the voltage dependent conductor are electrically coupled in series between two of the at least two conductors.

29. The self-identifying power supply connector tip according to claim 28, further comprising: a first contact and a second contact, the first contact and the second contact contained within the output port; a first conductor and a second conductor, the first conductor connected to the first contact at a junction and the second conductor connected to the second contact at the junction; an electromagnetic suppression choke located in proximity to the junction; and Docket No. 623-10001 24 an overmold positioned so as to enclose the junction and the electromagnetic suppression choke.

30. The self-identifying power supply connector tip according to claim 28, wherein the pre-defined voltage is associated with an operating voltage for an electronic device to be connected to the output port.

31. The self-identifying power supply connector tip according to claim 30, wherein the operating output voltage is higher than the pre-defined voltage.

32. An electromagnetic suppression cable connector, comprising: at least one contact; a cable comprising at least one conductor, wherein the at least one conductor is connected to the at least one contact; an electromagnetic suppression choke disposed about the cable and in proximity to the at least one contact; and an overmold formed around the electromagnetic suppression choke and the at least one contact.

33. The electromagnetic suppression cable connector according to claim 32, wherein the at least one conductor supplies power to a device through the at least one contact.

34. The electromagnetic suppression cable connector according to claim 32, wherein the overmold comprises a keying shape for mating with a second connector.

35. The electromagnetic suppression cable connector according to claim 32, further comprising a retractor for retracting at least a portion of the cable.

36. The electromagnetic suppression cable connector according to claim 35, where in the retractor comprises: a housing; a spool rotatably mounted in the housing; a first cable at least partially carried by the spool; and a second cable, separate from the first cable, at least partly carried by the spool, wherein the first cable and the second cable are co-wound together onto and off of the spool.

37. The electromagnetic suppression cable connector according to claim 32, further comprising a second mating connector, the second mating connector comprising. at least one mating contact; and Docket No. 623-10001 25 a second cable comprising at least one mating conductor, the at least one mating conductor connected to the at least one mating contact and adapted for electrical contact with the at least one contact.

38. The electromagnetic suppression cable connector according to claim 37, wherein the second connector further comprises: a second electromagnetic suppression choke disposed about the second cable and the at least one mating contact; and a second overmold formed around the second electromagnetic suppression choke and the at least one contact.

39. The electromagnetic suppression cable connector according to claim 38, wherein the overmold comprises a keying shape for mating with the second connector.

40. A method for identifying a self identifying circuit, the method comprising: providing, coupled in series across two conductors, at least one current dependent resistor and a voltage dependent conductor; applying a voltage through the two conductors and a resistor coupled in series therewith; measuring the voltage across the two conductors; and determining a voltage characteristic of the voltage dependent conductor based upon the time varying voltage and the current measurement, i

41. The method according to claim 40, further comprising: applying an output voltage without a series resistor, the output voltage based upon the identifying

42. A method for identifying a self identifying circuit, the method comprising: providing, coupled in series across two conductors, at least one current dependent resistor and a voltage dependent conductor; providing a time varying voltage across the two conductors; measuring the current measurement of current flowing through the two conductors; determining a voltage characteristic of the voltage dependent conductor based upon the time varying voltage and the current measurement; and identifying a self identifying circuit based upon the voltage characteristic.

43. A method for identifying a self identifying circuit, the method comprising: providing, across two conductors, a self identifying circuit comprising at least one current dependent resistor electrically coupled in series with at least one voltage dependent conductor; providing a known current through the two conductors; measuring a voltage across the two conductors; and Docket No. 623-10001 26 identifying a self identifying circuit based upon the voltage.