WO1995006994A1

WO1995006994A1 - Tracking external power supply

Info

Publication number: WO1995006994A1
Application number: PCT/US1994/008710
Authority: WO
Inventors: David Mark Demuro
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1993-09-02
Filing date: 1994-07-29
Publication date: 1995-03-09
Anticipated expiration: 1996-03-02
Also published as: ITRM940556A0; CN1060889C; CA2144966A1; FR2709886A1; BR9405568A; CA2144966C; AU683534B2; CN1114123A; AU1614295A; JPH08503599A; ITRM940556A1; GB2288292A; GB2288292B; GB9509136D0; IT1272798B

Abstract

An external power supply (22) powers an electronic device (20) having rechargeable cells (70). The external power supply (22) provides power (26) having a voltage which tracks the rechargeable cells. The voltage of the external power supply preferably tracks with an offset above the voltage (86) of the rechargeable cells. An external power supply type indicating device (130), such as a resistor, indicates to the electronic device the type of external power supply. The external power supply (22) can thus provide power for fast-charge or trickle-charge operations, and charge control circuitry within the electronic device is capable of accurately controlling charge of the rechargeable cells based upon the type of external power supply indicated by the resistor.

Description

TRACKING EXTERNAL POWER SUPPLY

The present application is a continuation in part application of U.S. patent application serial number 115,074 filed on September 2, 1993. entitled "Electronic Device Having Internal Charge Regulator and Temperature Sensor for Controlling Application of a Charging Current Thereto and Associated Method Therefor"; U.S. patent application serial number 083,571 filed on June 30, 1993 entitled "Electronic Device Having Internal Charge Regulator for Controlling Application of a Charging

Current Thereto and Associated Method Therefor"; and U.S. patent application serial number 149,686 filed on November 9, 1993 entitled "Method and Apparatus for Deterrrtining External Power Supply Type", all by David M. DeMuro.

Background of the Invention

The present invention relates generally to electronic devices which may be powered by rechargeable power supplies and, more particularly, to an electronic device having a rechargeable power supply, and an associated method, connectable to an external power source capable of providing operative power to recharge the rechargeable power supply of the electronic device.

Many electronic devices are constructed of designs which permit powering thereof by a battery power supply comprised of one or more battery cells. In some instances, use of a battery power supply to power the electronic device is necessitated when the electronic device is not, or cannot be, positioned proximate to a permanent, or other fixed, power supply. In other instances, a battery power supply is utilized to power the electronic device to increase the portability of the device as no power cable is required to interconnect the electronic device to the permanent, or other fixed, power supply. Typically, the one or more battery cells comprising the battery power supply utilized to power the electronic device are carried directly with, or housed within, the electronic device.

However, because a battery power supply is capable of storing only a finite amount of energy, powering of the electronic device with the battery power supply is limited by the energy storage capacity of the battery power supply. Powering of the electronic device by the battery power supply causes discharge of the stored energy of the battery power supply. Once the stored energy of the battery power supply is discharged beyond a certain level, replacement of the battery power supply is necessitated to permit continued operation of the electronic device. Increasing the energy storage capacity of a battery power supply, such as by increasing the number of battery cells comprising such power supply, increases the size (and weight) of the power supply. Such manner of increasing the energy storage capacity of a battery power supply reduces the portability of the electronic device when the battery power supply is carried with the electronic device.

Accordingly, when designing a battery power supply, a compromise is made between increased energy storage capacity and reduced portability of the electronic device which carries such a battery power supply.

A portable or transportable radiotelephone is one such electronic device which is typically powered by a battery power supply. The battery power supply is typically carried directly with the radiotelephone and is of a size and weight which does not unduly constrain the portability of the radiotelephone. A radiotelephone includes radio transceiver circuitry including transmitter circuitry and receiver circuitry which is operative to transmit and to receive, respectively, modulated signals. In typical operation of a radiotelephone, receiver circuitry portions thereof are powered continuously while awaiting reception of signals indicative of an incoming call to the radiotelephone. Thereafter, the transmitter circuitry portions of the radiotelephone are also powered to permit transmission of modulated signals therefrom.

Radiotelephones operative in many cellular communication systems are constructed to transmit modulated signals therefrom and also simultaneously to receive modulated signals transmitted thereto (the modulated signals transmitted by and to the radiotelephone are transmitted upon separate frequency channels). Radiotelephones operative in other cellular communication systems are constructed to transmit and to receive modulated signals during non-simultaneous time periods and, during two-way communication with the radiotelephone, the receiver and transmitter circuitry portions are powered during non- simultaneous time periods. Times during which the receiver circuitry portions of the radiotelephone are powered while awaiting transmission thereto of signals indicative of an incoming call shall hereinafter be referred to as times in which the radiotelephone is in the "standby" mode. (It should, of course, be noted that a user of a radiotelephone also oftentimes provides operative power to the radiotelephone only when the user desires to initiate and thereafter effectuate a telephone call; during other times no operative power is provided to the radiotelephone, and the radiotelephone is not powered to receive signals transmitted thereto. That is to say, the user of the radiotelephone may choose not operate the radiotelephone in the "standby" mode to receive an incoming call transmitted to the radiotelephone, but rather power the radiotelephone only during times in which the user initiates a telephone call.) Generally, the amounts of energy required to operate the transmitter circuitry portions of the radiotelephone are greater than the amounts of energy required to operate the receiver circuitry portions thereof. And, because practical devices are of less than ideal efficiencies, a certain portion of the energy applied to the radio ^lephone is converted into heat energy which results in heat build-up UA the radiotelephone. As more energy is required to operate the transmitter circuitry portions of the radiotelephone, there is a correspondingly greater amount of heat generation during operation of the transmitter circuitry portions of the radiotelephone than when only the receiver circuitry portions are operable.

Rechargeable battery power supplies comprised of one or more rechargeable battery cells have been developed and are commercially available. Some of such commercially-available, rechargeable battery power supplies are of constructions designed for use to power radiotelephones. The use of rechargeable battery power supplies is advantageous as the rechargeable battery cells thereof may be recharged by applying a charging current generated by a power supply. Once recharged, the rechargeable battery power supply may be reused. Some constructions of rechargeable battery power supplies may be recharged, and reused, up to, and even in excess of, five hundred times.

As mentioned previously, a rechargeable battery power supply is typically comprised of one or more battery cells. The cells are connected in a series (or other) connection, and are typically housed within a common housing. The housing, together with the battery cells, comprise the battery power supply which is also oftentimes referred to as a battery pack. For purposes of simplicity, such constructions are also generically referred to by the general term "battery". The present disclosure shall, at times, utilize such simplified terminology.

The battery cells of a rechargeable battery power supply are formed of various different materials of construction. For instance, a rechargeable battery cell may be comprised of a lithium (Li) material, a nickel-cadmium (Ni-Cd) material, or a nickel metal hydride (NiMHθ2) material. Battery cells constructed of these different materials exhibit different characteristics during charging thereof.

Battery charging apparatus is also commercially available to permit recharging of rechargeable battery power supplies. A battery charger comprising such battery charging apparatus is typically comprised of a power source for supplying operative power to recharge the rechargeable battery power supply when suitably connected to the charging apparatus to receive the operative power.

The energy of the operative power applied to the rechargeable battery power supply is converted into chemical energy which is stored by the rechargeable battery cells of the battery power supply. Application of the operative power to the battery cells over an elapsed period of time permits the rechargeable battery cells to become fully recharged. However, because practical devices are of less than ideal efficiencies, a certain portion of the energy applied to the battery cells is converted into heat energy which causes heat build-up of the battery cells.

Some battery charging apparatus are of construction- types which permit the electronic device and also the battery power supply both to receive operative power. Such battery charging apparatus provides operative power not only to recharge the rechargeable battery cells of the battery power supply but further provides operative power to permit operation of the electronic device. For instance, battery charging apparatus of construction-types permitting a radiotelephone together with a rechargeable battery pack to receive operative power to recharge the battery cells of the battery pack and also to permit operation of the circuitry of the radiotelephone is available. As mentioned previously, however, in practical devices, heat is generated as a byproduct of operation of the circuitry of the radiotelephone. And, heat is also generated as a byproduct of the process of recharging the battery cells of the battery power supply.

Various of the rechargeable battery constructions comprising the battery cells of a rechargeable battery power supply exhibit charging curves

(which are plots of voltage scaled as a function of time). Over time, during recharging of such constructions of battery cells, as the amount of energy stored therein increases, the voltage levels of the battery cells of the power supply increases. The voltage of the power ar ied to the rechargeable battery power supply must be greater than ti- voltage levels of the rechargeable battery power supply to cause e .rgy to be transferred to the battery power supply. However, when the voltage of the power applied to the battery power supply is significantly greater than the voltage levels of the battery power supply, a significant portion of the energy corresponding to the voltage differentials is converted into heat energy.

When the rechargeable battery power supply is embodied as a portion of an electronic device, such as a radiotelephone, the heat energy generated during application of the charging power to the rechargeable battery power supply results in heating of the electronic device. Such heating of the electronic device may cause discomfort to a user of the electronic device and also affect the performance thereof.

What is needed, therefore, is means by which charging power may be applied to a rechargeable battery embodied in an electronic device without generation of excessive amounts of heat energy. In a portable, battery-powered device such as a cellular telephone, an external power input is usually provided so that the user can operate the device from a primary source of power such as house current, or a vehicle's power source in order to conserve battery power. It is also desirable to have a battery charger internal to the device for recharging the unit's battery pack, which may be internal or external to the device. The device and its internal battery charger require a power supply or adapter external to the device to supply the proper voltage and current needed by the device to charge the internal battery or power the device.

Further, there are often a variety of external power supplies. For example, a high power version may be offered for fast-charging the battery, while a low cost, low power version may be offered for slow-charging the battery. Because the operation of the internal charger will differ depending on which external adapter is connected, the device must sense which type of external power adapter is present.

Accordingly, there is also a need to provide a means for detecting the type of external power adapter which is connected to a device, and modify the operation of the apparatus as a function of the type of power adapter and battery. The invention leads to greater system flexibility and improved performance with all types of external power supplies.

Brief Description of the Drawings

The present invention will be better understood when read in light of the accompanying drawings in which:

FIG. 1 is a graphical representation of a typical battery charging curve wherein voltage measured across output terminals of battery cells of a rechargeable battery pack during charging thereof is plotted as a function of time;

FIG. 2 is a block diagram of an external charger connected to an electrical device according to the present invention; FIG. 3 is a block diagram of another external charger connected to an electrical device according to the present invention; and

FIG. 4 is a view depicting an external charger connected to a cellular radiotelephone according to the present invention.

Description of the Preferred Embodiments

As mentioned hereinabove, a portable electronic device is oftentimes powered by a rechargeable power supply. When the rechargeable power supply is depleted of stored energy, battery charging apparatus is utilized to recharge rechargeable battery cells of the rechargeable power supply. Several constructions of battery charging apparatus are available which permit the portable electronic device to be positioned together with the rechargeable power supply carried therewith such that operative power is provided both to the rechargeable battery cells of the rechargeable power supply and also to the circuitry of the electronic device.

However, because power transfer between the battery charging apparatus and the electronic device is not wholly efficient, a certain portion of the energy of the operative power generated by the battery charging apparatus is converted into heat energy which elevates the temperature of the electronic device. And, when the voltage levels of the operative power generated oy the battery charging apparatus is significantly higher than the voltage levels of the battery cells of the rechargeable power supply, large portions of the operative power generated by the battery charging apparatus is significantly higher than the voltage levels of the battery cells of the rechargeable power supply, large portions of the operative power generated by the battery charging apparatus is converted into heat energy. As a result, the temperature of the electronic device powered by such rechargeable power supply exhibits a significant rise in temperature. In the particular instance in which the electronic device comprises a radiotelephone operative in a cellular communication system, conversion of operative power generated by the battery charging apparatus into heat energy causes an elevation of the temperature of the radiotelephone. Such elevation in the temperature of the radiotelephone can result in discomfort to the user of the radiotelephone, as well as affecting performance of the radiotelephone.

When the voltage levels of the operative power generated by an external power supply track the voltage levels of the rechargeable battery cells of the rechargeable power supply, the amount of energy of the operative power generated by the battery charging apparatus which is converted into heat energy is minimized.

When the bat^tery charging apparatus comprises a variable-level power source, the tage levels of the operative power generated by such power source need not be of a constant voltage level. Instead, the voltage levels of the operative power may be varied, thereby to reduce the amount of energy which is converted into heat energy during recharging of the battery cells of the rechargeable power supply. By providing the variable-level power source comprising the battery charging apparatus with an indication of the voltage levels of the battery cells of the rechargeable power supply, the variable-level power source may be made operative to generate operative power of voltage levels which correspond to, but which are slightly greater than, the voltage levels of the battery cells of the rechargeable power supply, heat generation occurring during recharging of the battery cells may be reduced.

As also mentioned previously, the voltage levels of the battery cells of the rechargeable power supply increase as the amounts of energy stored by the battery cells increases during application of the operative power thereto.

FIG. 1 is a graphical representation of a typical battery charging curve of a nickel-cadmium rechargeable battery cell. The battery charging curve is formed of a plot of the voltage measured across output terminals of a nickel-cadmium rechargeable battery cell as a function of time.

In FIG. 1, voltage, scaled in terms of volts, is plotted along ordinate axis 10 and time, scaled in terms of seconds, is represented along abscissa axis 12. The resultant curve 14 generally increases over time responsive to the application of operative power thereto to recharge the battery cell. As illustrated, the general increase is, however, not linear. Points 16 and 17 on curve 14 are representative of voltage levels at which the current levels of the operative power applied to the battery cells of the rechargeable battery power supply are altered. Initially, and during the period of time identified in the figure by "rapid charge phase", the current levels of the operative power applied to the battery cell is of a relatively high value.

Then, during the period of time identified in the figure by "trickle charge phase" (corresponding to curve 14 portions between points 16 and 17), the current levels of the operative power applied to the battery is of a first reduced value. Thereafter, during the period of time identified in the figure by "maintenance charge phase," the current levels of the operative power applied to the battery cell is of a second reduced value.

Characteristic charging curves of other types of battery constructions may be similarly shown. While such other types of battery constructions have charging curves of other characteristic shapes, the general increase in voltage as increasing amounts of energy are stored by such batteries generally holds true. In any event, by causing the variable-level power source comprising the battery charging apparatus to track the voltage of the battery cells to which operative power is applied, generation of heat energy is reduced.

FIG. 2 illustrates an external power supply 22 in releasable connection with an electronic device 20 according to the present invention. The external power supply 22 includes a transformer 112, a rectifier 114, and a voltage regulator 120. The transformer 112 and rectifier 114 of FIG. 2 convert 120 volts of alternating current (AC) from a line current wall plug 140 to a direct current (DC) voltage. The rectifier 114 preferably is a full-wave rectifier. Conditioning circuitry for smoothing the rectified voltage are also preferably provided after the transformer 112. The electronic device 20 contains a battery made of a plurality of rechargeable cells 70. The rechargeable cells making up the battery can consist of any number of cells including one cell. Similarly, one rechargeable cell can easily be adapted to have two or more cells. The rechargeable cells 70 of the electronic device 20 are charged by power supplied from the external power supply 22.

The external power supply 22 has a voltage regulator 120 that tracks the voltage of the rechargeable cells 70 in response to a voltage signal received on line 86 from the electronic device 20. The voltage regulator

120 of the external power supply 22 provides a voltage to the electronic device 20 in relation to the voltage of the rechargeable cells 70. By providing a power supply external to the electronic device 20 that tracks the voltage of the rechargeable cells 70, heat dissipation inside the electronic device is reduced.

The external power supply 22 is operative to generate the operative power on line 26 of any of various voltage levels. The various voltage levels can be either a continuously variable voltage level or discrete incremental voltage increments. Line 26 of electronic device 20 is coupled to receive the operative power generated by the external power supply 22 when the external power supply is connected to the electronic device 20 at a connector 34. Line 26 can also be connected to provide operative power for components of the electronic device 20. For example, in the preferred embodiment, the electronic device 20 is a portable radiotelephone and, in such an embodiment, the external power supply 22, when connected, can power the components of the radiotelephone. Alternatively, the rechargeable cells 70 can be connected to power the components of the electronic device 20. Such .rechargeable cells 70 can be connected to power the internal components, even when the external power supply 22 is connected to the electronic device 20 at the connector 34. The power supplied by the external power supply 22 has a voltage controlled by the voltage regulator 120 of the external power supply 22. The external power supply 22 also contains a resistor 130 which indicates to the electronic device 20 the type of external power supply connected to the electronic device 20. A transistor 58 in the electronic device 20 controls power supplied from the external power supply 22 to the rechargeable cells

70, in part, in response to the type of external power supply indicated by the resistor 130. The transistor 58 regulates the current or charge supplied to the rechargeable cells 70. The voltage regulator 120 serves to regulate the voltage applied to the electronic device 20 from the external power supply 22.

The resistor 130 indicates to the electronic device 20 that the external power supply 22 is of a type that tracks the battery voltage. Older power supplies do not contain the necessary voltage tracking circuit. Further, the older power supplies, instead, contain current control circuits for charge control which, in the arrangement of the present invention, are placed within the electronic device 20. When an older power supply lacking the resistor 130 is detected by the electronic device 20, the electronic device 20 would know that the appropriate external voltage tracking function can not be provided by the older power supply. The resistor, known as a manual test resistor, can have a resistance of about 33,000 ohms for a fast-charger external power supply and about 10,000 ohms for a trickle-charger external power supply. The resistor 130 could, alternatively, be replaced by other indicating elements such as a reactive resistor-capacitor pair having a unique resonance characteristic, a diode, such as a Schottky diode or zener diode, having a unique reverse bias or breakdown voltage or other semiconductor such as a memory element. Further, an array of such elements, such as a resistor array, could be used. Thus, besides insuring that the electronic device 20 charges at the necessary charge rate for the external power supply 22, the resistor 130 also ensures that old power supplies will not be allowed use by the electronic device 20. Transistor 58 of the electronic device 20 controls the current or charge to the rechargeable cells 70, in part, based on a measurement across a resistor 61 and the type of external power supply indicated by a resistor 130. A controller 74 senses the type of external power supply 22 based on the resistance of the resistor 130. The controller may select a particular charging curve such as that illustrated in FIG. 1 based on the type of external charger indicated by the resistor 130.

An external power supply 22 typically is capable of providing one of two levels of current. One type of external power supply 22 supplies a high level of current to fast-charge the rechargeable cells 70. Another type of external power supply 22 provides a low current to trickle-charge the rechargeable cells 70. The controller 74 provides a control voltage to a comparator 63. The comparator 63 compares the control voltage with a voltage measured by a comparator 62 across the resistor 61. The output of the comparator 63 is used by the transistor 58 to control the current or charge to the rechargeable cells 70 from the external power supply 22. The controller 74 provides the control voltage to the comparator 63 based on the type of external power supply 22 indicated by the resistor 130. The controller 74 can also consider other parameters in addition to the type of external power supply 22 indicated by the resistor 130. These parameters considered by the controller 74 '"an include the voltage at the rechargeable cells 70, the current drain presently demanded by other components of the electronic device 20, or the temperature of the rechargeable cells 70, for example. As mentioned previously, recharging of rechargeable cells 70 is effectuated most efficiently when the voltage levels of the power applied to the rechargeable cells 70 is only slightly greater than the voltage of the rechargeable cells 70. When the voltage provided by the external power supply 22 significantly exceeds the voltage of the rechargeable cells 70, a significant portion of power is converted into heat energy. Such heat energy causes heat dissipation in the electronic device 20. However, by causing the voltage provided by the external power supply 22 to track to the voltage of the rechargeable cells 70, conversion of the power from the external power supply 22 into heat energy is reduced. Therefore, because the external power supply 22 has a voltage regulator 120 which responds to the voltage of the rechargeable cells 70 on the line 86, heating of the electronic device 20 is reduced.

Furthermore, according to a preferred embodiment of the present invention, the voltage regulator 120 of the external power supply 22 provides a voltage to the electronic device offset higher than the voltage of the rechargeable cells 70 on the line 86. Preferably, the voltage provided by the external power supply 22 to the electronic device 20 is offset approximately 1.4 volts above the voltage of the rechargeable cells 70 indicated by the line 86. Thus, the voltage regulator 120 of the external power supply 22 is preprogrammed to provide this approximately 1.4 volt offset from the external power supply 22. This approximately 1.4 volt offset is preferred for a nickel metal hydride (NiMHθ2) or a nickel- cadmium (Ni-Cd) battery of a nominal 6 volts. The approximately 1.4 volt offset provides a drop of about 0.9 volts across the transistor 58, the resistor

61 and the diode 65 and a drop of about 0.5 volts across the rechargeable cells 70. However, for such a battery, the offset can range from approximately 0.5 volts to approximately 3.0 volts, being from approximately one-thirtieth to approximately one-half of the battery voltage, when also taking into consideration the above-listed voltage drop across charge control components of the electronic device 20. Furthermore, when using a lithium battery having a nominal voltage of 8.4 volts or a lithium solid-state battery having a nominal voltage of 9.0 volts, the offset provided by a voltage regulator 120 of the external power supply 22 would be higher. For example, a 12 volt battery would preferably have an offset of approximately 1.9 to approximately 5.0 volts.

The offset helps reduce heating of the electronic device 20 by shifting power consumption away from the components internal to the electronic device 20, such as transistor 58, resistor 61, or diode 65, for example. The offset voltage also provides for an adequate voltage drop across the transistor 58, the resistor 61 and the diode 65 for current or charge control by the controller 74 with minimal heat inside the electronic device 20.

FIG. 3 illustrates a block diagram of an external power supply 23 connected via a connector 35 to an electronic device 20 according to an alternative embodiment of the present invention. The external power supply 23 receives a control voltage on line 86 indicative of the voltage of the rechargeable cells 70. The external power supply 23 provides a charge voltage to the rechargeable cells 70 via the transistor 58 based upon the voltage of the rechargeable cells 70 on the line 86. The external power supply 23 also contains an external charger type indicating device such as a diode 135 which indicates the type of external power supply connected to the electronic device 20.

The external power supply 23 contains a pulse-width modulator 160 in place of the voltage regulator 120 of the embodiment of FIG. 2. In the illustrated embodiment of FIG. 3, the pulse-width modulator 160 converts a direct current input from, for example, a cigarette lighter adapter 150 of an automobile to a desired direct current output voltage. Based upon the voltage of the rechargeable cells 70 input on the line 86, the pulse-width modulator 160 modulates pulse widths of an input from a cigarette adapter connector 150 of an automobile. Smoothing circuitry such as a capacitor 170 is used on the output of the pulse-width modulator 160 to provide a smooth direct current output to the electronic device 20. Although the embodiment of FIG. 3 illustrates the pulse-width modulator 160 connected to a connector 150 of, for example, a cigarette adapter, the pulse-width moduiator 160 can also operate on other input voltages. For example, a 120 volt alternating current line voltage can be provided to the pulse-width modulator 160 when at least one rectification diode is used.

Turning now to the schematic view of FIG. 4, a radiotelephone, referred to generally by reference numeral 620 is shown. The electronic device 20 of the embodiments of FIGS. 2 or 3 can be the radiotelephone 620 with the elements of the electronic device 20 disposed within the housing of the radiotelephone 620 of FIG. 5 except for the rechargeable cells 70 which here are shown to comprise a battery pack 624.

The radiotelephone 620 is connected to the external power supply 622 by way of lines 626 and 628 which connect the external power supply

622 to connecting elements of radiotelephone 620 through a plug connector 630. A line current wall plug 642 is also shown in FIG. 4 permitting connection of the external power supply to a conventional household power supply. While the line current wall plug 642 comprises a plug connector permitting connection to a conventional household power supply, other plug connectors permitting connection to other types of power supply are, of course, similarly possible.

Because the external power supply 622 is positioned remote from radiotelephone 620, but connected thereto by way of lines 626 and 628, radiotelephone 620 may be conveniently operated by a user in spite of the connection between radiotelephone 620 and the external power supply 622. Because the voltage levels of the operative power generated by the external power supply 622 track the voltage levels of the battery pack, recharging of the rechargeable cells of the battery pack is efficiently accomplished without conversion of excessive amounts of energy into heat energy.

In summary, the present invention provides a tracking external power supply for providing a power to charge rechargeable cells. The external power supply provides power having a voltage which tracks the voltage of the rechargeable cells. The voltage of the rechargeable cells is delivered to the external power supply, and the external power supply provides a tracking voltage in response thereto. The voltage of the power supplied by the external power supply preferably is offset from the voltage of the rechargeable cells by a predetermined amount. The voltage is offset to further reduce heat dissipation within the electronic device and provide a voltage offset for operation of internal charge control components and provide for efficient charging of the rechargeable cells. The external power supply may be of a high current, high power type capable of fast-charging the rechargeable cells, or alternatively, it may be of a low current type which is only capable of slow-charging the rechargeable cells. The type of external power supply is indicated by a resistor, and the electronic device identifies the type of external power adapter in response to this resistor by detecting the value of the resistor in the external power supply to identify the type of external power supply.

Claims

ClaimsWhat is claimed is:

1. An external power supply for connection to an electronic device, the electronic device having charge control circuitry capable of charging one or more rechargeable cells using power from said external power supply, wherein said external power supply comprises:

a connector capable of connection to the electronic device to provide external power to said electronic device and to receive a signal from the electronic device; and

a power converter operatively coupled to said connector to provide the external power to the electronic device at a voltage based on the signal received from the electronic device.

2. An external power supply according to claim 1, wherein said power converter comprises a voltage control circuit operatively coupled to said connector that tracks a voltage of the rechargeable cells in response to the signal from the electronic device.

3. An external power supply according to claim 2, wherein said voltage control circuit has a voltage control characteristic that tracks with a voltage offset above the voltage of the rechargeable cells in response to the signal from the electronic device.

4. An external power supply according to claim 3, wherein said voltage control circuit has a voltage control characteristic that tracks with a voltage offset of approximately one-thirtieth to approximately one-half of a voltage of the rechargeable cells.

5. An external power supply according to claim 4, wherein said voltage control circuit has a voltage control characteristic that tracks with a voltage offset of approximately 0.2 volt to approximately 3.0 volts.

6. An external power supply according to claim 1, further comprising an external charger type indicating device operatively coupled to said connector to indicate to the electronic device the type of external power supply used.

7. An external power supply according to claim 6, wherein said external charger type indicating device further comprises a resistor operatively coupled to said connector to indicate to the electronic device the type of external power supply used.

8. An external power supply according to claim 1, further comprising another connector operatively coupled to provide power to said power converter from a source.

9. An external power supply according to claim 8, wherein said another connector comprises a cigarette adapter.

10. An external power supply according to claim 8, wherein said another connector comprises a line current wall plug.