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VBUS CHARGE @D

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1. SO V prop is at a minimum As 444 drops over the course of this phase the power dissipated also continues to drop noting again that the power dissipated is the product of lazy gz and Clearly then the greatest power level is drawn during the constant current phase As noted above the charging of the battery 24 can be safely cycled during this phase so the restriction in current to the battery 24 during this phase is allowable This circuit also allows the user to boot his portable device 18 very quickly because it isolates the battery 24 from the portable device 18 If the battery 24 and portable device 18 were connected when the battery charge controller 20 attempted to condition a deep discharged battery 24 the volt age at the portable device 18 would be drawn down to the level ofthe deep discharged battery 24 Typically this would betoo low for proper operation ofthe portable device 18 With the circuit of the invention the battery 24 and portable device 18 are isolated by Q1 Even if the battery 24 is in a deep discharge state the portable device 18 will still see a voltage that is high enough for proper operation The time for the portable device 18 to boot up is therefore only limited by the enabling time of the battery charge con troller 20 itself A typical figure for this ramp up is 1 mS 4 mS though it could vary from one battery charge controller 201 to another Thus the use ofthe circuit in F
2. 26 Claims 8 Drawing Sheets 30 VOLTAGE SENSING CIRCUIT PORTABLE DEVICE 18 US 8 541 983 B2 Page2 56 References Cited 6 191 552 2 2001 Katesetal 320 112 6 211 649 4 2001 Matsuda 6 252 375 BI 6 2001 Richter et al U S PATENT DOCUMENTS 6 300744 Bl 10 2001 Shum 4 510 431 A 4 1985 Winkler 6 346 794 2 2002 Odaohhara 4 755 816 A 7 1988 DeLuca 6 362 610 3 2002 Yang 5 173 855 A 12 1992 Nielsen et al 6 373 229 Bl 4 2002 Slusky 5 179 335 A 1 1993 Nor 6 437 541 Bl 8 2002 Sakurai 5 229 649 A 7 1993 Nielsen et al 6 437 543 8 2002 Oler et al 5 272 475 12 1993 Eaton et al 6 498 458 12 2002 Chen 5 444 378 A 8 1995 Rogers 6 801 967 B2 10 2004 Nakamura et al 5 631 503 A 5 1997 Cioffi 6 936 936 8 2005 Fischer et al 307 151 5 638 540 A 6 1997 Aldous 2001 0004310 Al 6 2001 Kono 5 651 057 A 7 1997 Blood et al 2001 0015635 8 2001 Leppo et al 320 116 5 721 481 A 2 1998 Narita et al 2002 0079866 6 2002 320 150 5 734 254 A 3 1998 Stephens 2003 0052547 Al 3 2003 Fischer et al 5 769 877 A 6 1998 Barreras Sr 2003 0076138 Al 4 2003 Hwang 5 804 894 A 9 1998 Leeson et al 2003 0146736 8 2003 Kosuda et al 320 132 5 814 972 A 9 1998 Shimada et al 2003 0155892 Al 8 2003 Poletti 5 850 113 A 12 1998 Weimer et al 2003 0204708 Al 10 2003 Hulme et al 5 898 290
3. should read built around In column 7 lines 45 46 battery charge controller 201 should read battery charge controller 20 In column 7 line 61 serves as external driving element should read serves as an external driving element In column 8 lines 4 5 low power USB should read low power USB In column 8 line 32 should read Vgus In column 9 line 40 when battery is dead should read when the battery is dead In column 11 line 11 LMS33460 Whose should read LMS33460 whose Signed and Sealed this Eighteenth Day of February 2014 p Teh Michelle K Lee Deputy Director of the United States Patent and Trademark Office CERTIFICATE OF CORRECTION continued Page 2 of2 U S Pat No 8 541 983 B2 In column 11 line 15 5 8 should read 5 8V In column 11 lines 65 66 hardware the rest of the system should read hardware of the rest of the system In column 12 lines 23 24 accomplished by the keeping should read accomplished by keeping In column 12 line 25 and than 100 mS should read and then 100 mS In column 12 line 39 R920 is pull up resistor should read R920 is a pull up resistor In column 12 line 42 U907 produces battery presence indicator should read U907 produces a battery presence indicator In column 12 lines 57 58 C915 is input bypass capacitor and C922 is output filtering capacito
4. tery Comparator U907 provides the battery presence status indicator Battery connector short circuit protection is NAND ed U906 with the charger enable functionality thus automati cally disabling the battery charge controller U909 when a short is present The battery charge controller U909 automati cally re starts the charge if the battery voltage falls below an internal threshold and automatically enters sleep mode when VCC supply is removed Theory of Operation Note that the inputs and outputs of the circuit in FIGS 7A 7C can be summarized as follows Signal Connection Description VBUS To Power source USB or charger System Contro Signa Power input to the device used for battery charging or device operation CHRG EN enables disables charger and current delivery to the system Reset State HIZ pull down resistor makes RST LOW charger is OFF enables 450 mA current limit for the charger reset state LOW enables 750 mA current limit for the charger reset state LOW goes HIGH every time the VBUS is above 2 1 V charger status flag rese CHRG_A System Contro Signa System Contro Signa System Contro Signa System Contro Signa To rechargeable battery CHRG B USB CD CHRG FLG state LOW VBAT main power source for the rechargeable battery reset state battery voltage value US 8 541 983 B2 continued Signal Connection Description L BAT To portable provides system power
5. 775 659 A 11 1973 Carlsen II 4 433251 A 2 1984 Banks et al Continued FOREIGN PATENT DOCUMENTS DE 201 16 332 1 2002 WO PCT CA2004 000249 9 2004 OTHER PUBLICATIONS Notice Requesting Submission of Opinion issued in correspond ing Korean Patent Application No 10 2005 7015376 dated Oct 27 2010 pp 1 6 Charging Big Supercaps Portable Design p 26 Mar 1997 Continued Primary Examiner Edward Tso Assistant Examiner Alexis Boateng 74 Attorney Agent or Firm Finnegan Henderson Farabow Garrett amp Dunner LLP 57 ABSTRACT A battery charging circuit comprising a semiconductor switch having an output connected to a rechargeable battery a battery charge controller for receiving power from an exter nal source and supplying output power to a portable device and the input of the semiconductor switch the current output of the battery charge controller being controllable and a voltage sensing circuit for measuring the voltage drop across the battery charge controller and responding to the voltage drop across the battery charge controller by modulating the semiconductor switch to reduce the quantity of current sup plied to the rechargeable battery when the voltage drop is too great whereby the total power dissipated by the battery charge controller is controlled the portable device receiving the power it needs to operate and the rechargeable battery receiving any additional available power
6. DIA SWIL 84040 39849304330 4 3OV L10A 3SVHd 3SVHd 3SVHd 39V110A INVISNOO INVISNOO d33Q 434319 SOYVHOSIC x 39UVHD 9984 u3MOd US 8 541 983 B2 Sheet 4 of 8 Sep 24 2013 U S Patent ve 9 Old 0527 OUHO 7 90 yu 81 0 0 318v1uOd 9 gu aen Soy eS E 195 YSTIOWLNOO AH311V8 008 39 SNe US 8 541 983 B2 Sheet 5 of 8 Sep 24 2013 U S Patent aNd ONO QNO YVL A A A A y0 00 YOO e NOTIN ON 219 130 3d 8o vad OND ONO agar Pb ps m SSA i Ale ij jams 2138 310 T IVS x Ji 9 3 138 N9 A y 9969903 3 A A NE 00 860 7 3 N3 HO 4 v N 90 Nad X3 ano 512601541 00 Ak JIT OHO lt US 8 541 983 B2 Sheet 6 of 8 Sep 24 2013 U S Patent HZ DIA gt INGA 2709203 1V8A 3 20041 1004 A 25 DL d dial 1v8 NOI WAIHLIT OND A 3 0691 90691 86dl ALOE QNO 108 S QNO diyo bns H di 1X3 Oe US 8 541 983 B2 Sheet 7 of 8 Sep 24 2013 U S Patent
7. across the battery charge controller 20 and knowing the maximum current that it may provide the total power is known Using this informa tion to modulate the power to the battery 24 the total power dissipated by the battery charge controller 20 may be con trolled Also because this circuit modulates the power available to the battery 24 this circuit can be designed to ensure that the portable device 18 receives the power it requires for opera tion while the rechargeable battery 24 only receives power when surplus capacity is available The total power consumed may therefore be modulated to stay within the limits of the power available from the USB port 12 and within the range of power that the battery charge controller 20 is able to dissipate This allows battery charge controllers 20 to be used off the shelf rather than having to design new and larger battery charge controllers 20 which can dissipate enough power to supply both the portable device 18 and battery 24 It also allows the battery charge controller 20 or external driving element to be kept physically small With this power modulation mechanism there is no longer power competition between the portable device 18 and the battery 24 The battery 24 receives power only if there is more power available than the portable device 18 requires This may seem inconsistent with the charging requirements of batteries such as lithium cells but the parameters of the circuit may eas
8. from a variety of power sources including limited capacity sources such as an integral power node of a computer data bus One such com puter data bus would be a USB universal serial bus port BACKGROUND OF THE INVENTION With the current computing and information revolution portable electronic devices such as cellular telephones per sonal digital assistants PDAs digital pagers and wireless email devices are becoming very common These portable devices are typically powered by internal batteries which must be recharged periodically by an external power source using a battery charger Battery chargers generally receive power from a standard AC electrical outlet and convert the AC power into a low DC voltage for recharging a battery The battery chargers of these portable devices also gener ally employ a battery charge controller to manage the charging of the battery Such battery charge controllers offer functionality such as regulating the voltage and current levels to the recharge able battery providing status signals to the main processor of the por table device or operating one or more status LEDs light emitting diodes providing protection circuits such as overcurrent under voltage reverse polarity and overtemperature protec tion and shutting themselves off when the charging source has been removed to minimize battery drain Lithium ion battery packs for example must be charged according to a relatively
9. strict algorithm so that they can be fully charged be charged and re charged many times and be safely operated This charging algorithm generally proceeds as follows 1 at the first stage any severe undervoltage or deep dis charge conditions are addressed During this pre charg ing stage the battery voltage is gently brought up from a very low or dead state usually at a rate of of the regular charge current 2 next the battery is charged at a constant current level until the voltage across the battery reaches its design level say 4 2 VDC At this point the battery will only be at 40 to 7096 of full capacity and then 3 charging of the battery continues at a constant voltage level again say 4 2 VDC until itis fully charged In this mode the current drawn by the battery will drop over time When the charge current has dropped to 10 of the initial charge rate or some other limit determined by the battery manufacturer charging is stopped Charging must stop at this point because trickle charging is not acceptable for lithium batteries an overcharge will dam age the cells possibly plating out lithium metal and becoming hazardous 20 35 40 45 50 65 2 Hence lithium batteries are almost invariably used with battery charge controllers designed to their particular charg ing parameters Unfortunately most battery charge controllers are designed to draw from a high capacity power supply with a stea
10. 4 1999 Beard et al 307 150 2004 0042138 Al 3 2004 Saito et al 5 898 293 4 1999 Tamaietal 320 136 2004 0100226 1 5 2004 Sakurai 320 136 5 926 006 A 7 1999 Burroughs et al 5 939 860 A 8 1999 William OTHER PUBLICATIONS 6 100 664 A 8 2000 Oglesbee et al 6 104 162 A 8 2000 Sainsbury et al Examiner s report on European Patent Application No 04712979 6 A oo et al mailed Dec 15 2010 from the EPO 4 pgs 118 au itor gt i 6130518 A 10 2000 Gabehart et al User s Manual vol 2 Japan Tokin Corp date 6 140 801 A 10 2000 Aoki etal 320 132 fe 6 157 169 12 2000 Lee China Office Action issued Nov 17 2011 in Application No 6 157 173 A 12 2000 Baranowski et al 320 152 2004800047271 and English Translation 4 pages 6 172 478 Bl 1 2001 et al 6 184 652 B1 2 2001 Yang cited by examiner US 8 541 983 B2 Sheet 1 of 8 Sep 24 2013 U S Patent Prior Art PORTABLE DEVICE CONTROLLER o 02 lt o gt ead E 5 USB CARD FIG 2 Prior Art U S Patent Sep 24 2013 Sheet 2 of 8 US 8 541 983 B2 FIG 3 18 PORTABLE DEVICE BATTERY USB CARD CHARGE CONTROLLER 12 Prior Art 20 FIG 4 30 VOLTAGE SENSING CIRCUIT BATTERY CHARGE CONTROLLER Vaus 24 18 US 8 541 983 B2 Sheet 3 of 8 Sep 24 2013 U S Patent
11. IG 4 allows computer data busses and similar power supplies with limited capacity to supply power to portable devices and discharged batteries simultaneously A number of different embodiments of the invention will now be described Each embodiment uses a very small num ber of simple reliable components Thus as a whole the invention provides an effective solution which is inexpensive reliable and consumes minimal board space in a portable device Basic Implementation FIG 6 presents an electrical schematic diagram of a charg ing circuit which employs four main components an NCP1800 battery charge controller 50 a semiconductor Q2 which serves as external driving element for the battery charge controller 50 an operational amplifier opamp 52 and a MOSFET metal oxide silicon field effect transistor Q3 which controls the current to the rechargeable battery 24 The NCP1800 battery charge controller 50 is a standard single cell Lithium ion battery charge controller as known in the art The maximum current that this device will provide is 5 20 25 30 35 40 45 50 55 60 65 8 regulated by the resistance between pin ISEL and ground In this case three resistors R2 R3 and R4 are used to set the maximum current levels for different operating conditions The default condition is that only 100 mA is available low power USB which establishes the value for resistor R2 is detected that the devic
12. OL DIA 7 MOE QNO OND QN9 QNO SSWdAg NS LAOA NIA dee ONS QNO OND OND SSYdA8 TOSEEELL DLL Jn SAUA U S Patent Sep 24 2013 Sheet 8 of 8 US 8 541 983 B2 90 CONNECTING BATTERY CHARGE CONTROLLER TO EXTERNAL POWER SUPPLY CONNECTING OUTPUT OF BATTERY CHARGE 92 CONTROLLER TO PORTABLE DEVICE AND A SEMICONDUCTOR IN PARALLEL 94 CONNECTING OUTPUT OF SEMICONDUCTOR TO RECHARGEABLE BATTERY 96 CONTROLLING CURRENT OUTPUT LEVEL OF BATTERY CHARGE CONTROLLER MEASURING VOLTAGE DROP ACROSS 98 BATTERY CHARGE CONTROLLER RESPONDING TO VOLTAGE DROP ACROSS BATTERY CHARGE CONTROLLER BY MODULATING SEMICONDUCTOR SWITCH TO REDUCE CURRENT TO RECHARGEABLE BATTERY WHEN VOLTAGE DROP S TOO GREAT FIG 8 100 US 8 541 983 B2 1 CIRCUIT AND METHOD OF OPERATION FOR AN ELECTRICAL POWER SUPPLY This is a continuation of U S application Ser No 13 028 361 filed Feb 16 2011 which is a continuation of U S application Ser No 12 860 591 filed Aug 20 2010 now U S Pat No 7 906 940 which is a continuation of U S application Ser No 10 372 180 filed Feb 21 2003 now U S Pat No 7 791 319 all of which are incorporated herein by reference This invention relates in general to battery chargers and more specifically to a method and apparatus for charging a battery in a portable communication device
13. a2 United States Patent Veselic et al US008541983B2 US 8 541 983 B2 Sep 24 2013 10 Patent No 45 Date of Patent 54 75 73 n Q1 Q2 65 63 51 52 58 CIRCUIT AND METHOD OF OPERATION FOR AN ELECTRICAL POWER SUPPLY Inventors Dusan Veselic Oakville CA Martin George Albert Guthrie Moffat CA BlackBerry Limited Waterloo Ontario CA Assignee Notice Subject to any disclaimer the term of this patent is extended or adjusted under 35 U S C 154 b by 271 days Appl No 13 175 541 Filed Jul 1 2011 Prior Publication Data US 2011 0260680 A1 Oct 27 2011 Related U S Application Data Continuation of application No 13 028 361 filed on Feb 16 2011 now Pat No 7 999 514 which is a continuation of application No 12 860 591 filed on Aug 20 2010 now Pat No 7 906 940 which is a continuation of application No 10 372 180 filed on Feb 21 2003 now Pat No 7 791 319 Int Cl H02J 7 00 2006 01 H02J 7 16 2006 01 GOIR 19 12 2006 01 U S CI USPC 320 134 320 156 320 132 320 159 320 160 320 114 307 32 307 152 Field of Classification Search 320 112 113 114 115 152 157 320 155 134 132 156 165 158 159 160 307 32 34 38 39 152 159 See application file for complete search history BATTERY CHARGE CONTROLLER Vaus 56 References Cited U S PATENT DOCUMENTS 3
14. be selected by setting CHRG_A HIGH which sets Q905a in saturation ON and in turn puts 09045 in saturation ON as well presenting VBUS voltage at AC input of the battery charge controller U909 As an AC input to U909 provides override over the USB input if voltage on the AC input exceeds 1 5V charging input output path is defaulted to AC input charging current is now programmed by the value of R939 resistor Capacitor C925 is used to prevent Q9045 from conducting because of its gate to drain parasitic gate to drain capaci tance would charge the gate 1f pulled up to its source at RC time capacitance during the fast transient responses of VBUS voltage and allows the gate to rapidly charge at the VBUS level keeping the 09045 in saturation Resistor R935 is used to limit the discharge current of C925 so that Q905a does not exceed its specified limits R933 is a pull down resistor that prevents an AC input to the battery charge con troller U909 from floating C926 and C927 are input bypass capacitors It is important to keep the total input capacitance below 10 uF to comply with the USB inrush current specifi cation The total current that the system draws from VBUS should not exceed 500 uA when in suspend mode This is mainly accomplished by the very low operating current ofthe battery charge controller U909 typically 100 uA in the OFF mode of operation 09055 is used to disable the LBAT voltage booster when the battery charge contro
15. ctor switch Q1 to the battery 24 when the voltage drop is too great The voltage sensing circuit 30 allows the total power con sumption of the circuit to be inferred because the current output of the battery charge controller 20 is controllable and power is the product of voltage drop and current Most battery charge controllers 20 known in the art are provided with some sort of maximum current control In the exemplary embodi ments described hereinafter for example the maximum cur rent output of battery charge controller 20 is simply set via an external resistor R1 though of course the current output could also be controlled in many other ways for example being programmable application specific or set via some form of analogue or digital input signal Also in the embodiments described hereinafter the voltage sensing circuit 30 itself is provided via an operational ampli fier op amp Thus the voltage drop across the battery charge controller 20 could simply be measured by comparing the 20 25 30 35 40 45 50 55 60 65 6 voltage at the input and output ofthe battery charge controller 20 as shown in FIG 4 Alternatively one input to the op amp could betaken from the output ofthe battery charge controller 20 while the other could be some reference voltage V ggr either emulating the V ys input to the battery charge control ler 20 or being scaled in some manner Thus by monitoring the voltage drop
16. data or perform some other task In each case the power to the battery 24 is dynamically auto adjusted When limited power is available it is also desirable to cut off high power consuming components preserving power only for the processor This is easily done by connecting only the processor and memory ofthe portable device 18 to Q2 as shown in FIG 6 and connecting other high power consumers to the battery side of Q3 As a result if we are operating with a limited current source such as low powered USB of 100 mA and an excessive current component such as a vibrator typically 120 mA or a back light typically 150 mA is turned on the voltage output from Q2 would start to drop causing Q3 to increase its Rds resistance and preserve the current needed by the processor Comprehensive Implementation The design presented in FIGS 7A through 7C uses the same basic circuitry as in FIG 6 but adds several elements which provide further advantages These advantages include the following the battery can be charged with an input voltage being just above the battery level the start up of the portable device 18 when battery is dead or not present is different from that of FIG 6 the handling of input glitches from the external power supply is improved and contrary to the instructions of the manufacturer of the battery charge controller used in this implementation the VCC and IN pins are fed separately to avoid back voltage leaka
17. dy voltage that will not sag appreciably under its current demands This is a problem when one attempts to use a power supply with limited capacity Some computer data buses such as USB universal serial bus buses can be used to provide power to external devices but while such power supplies are very convenient they have limited capacity The majority of personal computers PCs and laptop com puters available today are provided with one or more USB ports as standard components USB ports are designed to support data communication at speeds of 12 megabits and 1 5 megabits per second support PnP Plug and Play installation software and support hot plugging i e devices can con nected and disconnected while the PC is running Thus USB ports are often used as interfaces to connect keyboards mouses game controllers printers and scanners to PCs As well USB ports are operable to supply limited power to connected external devices The standard USB specification requires that high power USB ports be operable to provide a supply voltage of 4 75 5 25 VDC and a supply current of at least 500 mA often referred to as five units The specifi cation for low power USB ports requires a supply voltage of 4 40 5 25 VDC and current of 100 mA referred to as one unit USB ports would seem to be a very logical choice as a power supply for portable devices for a number of reasons To being with USB ports supply alow DC voltage s
18. e battery 24 and thinking that the battery charge controller 0909 is delivering enough current The second functionality of U908 is the start up override on the U909 CE input pin which provides power to the system for a minimum of 100 mS to initiate and properly enumerate on the USB BUS This is accomplished by the keeping its RESET open drain output at GND before the VBUS reaches 2 5V and than 100 mS after This keeps the battery charge controller U909 enabled during that time U906a provides NAND ed functionality of EN and presence of the short on the battery connector A shorted battery disables the battery charge controller U909 in hard ware By having the voltageon the VBAT CHRG EN control line could enable or disable the battery charge controller U909 CHRG_EN HIGH would enable the battery charge controller U909 by pulling low the MR input pin of U908 R921 provides isolation from the battery and input of U906a so that the current drain is limited to maximum of 42 uA even though the U906 creates HIZ high impedance inputs and outputs when power is not present at its VCC R924 provides default LOW input level for U906a during the host processor reset R920 is pull up resistor for CHRG_FLG making it valid only during the time the battery charge controller U909 is enabled U907 produces battery presence indicator by monitoring BAT_ID input from the battery pack Its output would be at HIGH logic level any time the BAT_ID resisto
19. e is plugged into a high powered USB source then the gate of MOSFET Q4 will be energized and the resistance between ISEL and ground will be set by the resistance of R2 and R3 in parallel Similarly if it is detected that the source of power for the circuit has even more power available an AC plug in or car adapter for example then MOSFET Q5 will be energized so that the resistance between ISEL and ground will be set by the resistance of R2 and R5 in parallel The circuit of FIG 6 will typically be included in the portable device 18 itself or in a docking cradle 10 thus it should also be operable with such larger capacity power supplies Application notes from the manufacturer of the NCP1800 battery charge controller 50 are available which will assist the designer in establishing the specific parameters and values for resistors R2 R3 and R4 and the driving transistor Q2 The voltage sensing portion ofthis circuit is provided by op amp 52 along with resistors R5 and R6 and capacitor C1 This circuit monitors the voltage on the collector side of Q2 via voltage divider R5 and R6 and compares it to a refer ence level in this case If the voltage on the collector side of Q2 drops then the voltage drop across Q2 rises and the power it must dissipate rises To reduce the power that must be dissipated the op amp 52 restricts the current through Q3 increasing its drain source resistance Note that Vz may simply be
20. e portable device 18 will be dragged down to the level of the deep discharged battery Typically portable devices 18 will not be operable at such a low voltage level and 5 the current that must be supplied to the battery 24 and the portable device 18 must be dissipated by the battery charge controller 20 or an external semiconductor in some way The more power that is dissipated the larger the battery charge controller 20 or the external semiconductor driven by the battery charge controller 20 must be Generally a semiconductor s ability to dissipate power varies with its surface area thus if the power dissipation is doubled the semiconductor must increase by four times the surface area New dedicated battery charge controllers could be devel oped which are designed to operate with a USB power supply and a portable device 18 but that would be an expensive and complicated solution Each battery charge controller would have to be designed to suit a particular pairing of a portable device 18 and battery 24 because it would have to take the power consumption requirements of both components into account 20 40 45 65 4 There is therefore a need for a method and apparatus which allows standard computer data busses such as USB ports to simultaneously power portable devices 18 and their associ ated battery charge circuits 20 without having to design new battery charge controllers with very specific applications This design m
21. er aspect of the invention is defined as a power supply circuit comprising means for measuring the voltage drop across a battery charge controller providing power to a portable device and the input of a semiconductor switch in parallel means for controlling the current output of the bat tery charge controller and means for responding to the volt age drop across the battery charge controller by modulating the semiconductor switch to reduce the quantity of current supplied to the rechargeable battery when the voltage drop is US 8 541 983 B2 5 too great whereby the total power dissipated by the battery charge controller is controlled the portable device receiving the power it needs to operate and the rechargeable battery receiving any additional available power BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings in which FIG 1 presents a physical layout of a personal computer connected to a portable electronic device in a manner known in the art FIG 2 presents an electrical block diagram of a battery charging circuit and portable device being powered in paral lel FIG 3 presents an electrical block diagram ofa battery and portable device both being powered by a battery charge con troller FIG 4 presents an electrical schematic diagram of a battery charging circuit in a broad embodiment of t
22. f the invention is defined as a battery charging circuit comprising a battery charge controller con nected to the external power supply and electrifying a battery and a portable device and having a maximum current setting anda regulating circuit for sensing the voltage drop across the battery charge controller and modulating the current to the battery to keep the power dissipated by the battery charge controller below a predetermined level An additional aspect ofthe invention is defined as a method for charging a battery of a portable device via an external power supply the method comprising the steps of connecting the input of a battery charge controller to the external power supply connecting the output ofthe battery charge controller in parallel to the portable device and the input of a semicon ductor switch connecting the output of the semiconductor switch to the battery controlling the current output of the battery charge controller measuring the voltage drop across the battery charge controller and responding to the voltage drop across the battery charge controller by modulating the semiconductor switch to reduce the quantity of current sup plied to the rechargeable battery when the voltage drop is too great whereby the total power dissipated by the battery charge controller is controlled the portable device receiving the power it needs to operate and the rechargeable battery receiving any additional available power A furth
23. flow through the switch 17 The portable electronic device of claim 9 wherein the voltage sensing circuit comprises an operational amplifier for comparing a voltage on an output of the controller to a refer ence value 18 A circuit for a portable electronic device comprising a switch configured to control a supply of power to a rechargeable battery a controller configured to receive USB power from an external source and supply power to the portable elec tronic device and asensing circuit configured to determine power supplied to the portable electronic device the controller responsive to the sensing circuit and config ured to control the switch to limit battery charging from theexternal source such that sufficient power is provided for operation of the portable electronic device 19 The circuit of claim 18 wherein the controller limits power consumption by the device and is configured to control the switch in response to the voltage drop to provide sufficient power for operation of the device 20 The circuit of claim 18 wherein the supply of power is limited by limiting current 21 The circuit of claim 18 wherein the supply of power is limited by limiting voltage 22 A method for controlling a USB power supply to a rechargeable battery comprising the steps of sensing a voltage drop across a controller and responsive to the voltage drop limiting battery charging from the USB power supply such that sufficient power
24. g current 4 The portable electronic device of claim 1 wherein the supply of power is limited by limiting voltage 5 The portable electronic device of claim 1 wherein total power consumed by the device is provided by the USB source 6 The portable electronic device of claim 1 wherein the controller comprises an external driving semiconductor for carrying supply current to the device and the switch whereby load current passes through the external driving semiconduc tor in lieu of the controller 7 The portable electronic device of claim 1 wherein the voltage sensing circuit comprises anoperational amplifier for receiving a voltage signal from an output of the controller and a reference signal and responds to the voltage signal being less than the refer ence voltage by reducing flow through the switch 8 The portable electronic device of claim 1 wherein the voltage sensing circuit comprises an operational amplifier for comparing a voltage on an output of the controller to a refer ence value 9 A portable electronic device including a graphical user interface and an interface for communicating with a commu nications network comprising a switch configured to control a supply of power to a rechargeable battery a controller configured to receive USB power from an external source and supply power to the portable elec tronic device and asensing circuit configured to determine power supplied to the portable electronic dev
25. gate of Q908 U907 provides the system with indication of battery pres ence R927 and R929 are used to set the reference and R928 is pull up resistor to open drain output of U907 BAT ID is than presented to its negative input and NO BAT N is set accordingly The preferred values for the components in this circuit are as shown in FIGS 7A 7C These values will of course vary with the application and design parameters Software Embodiments Rather than using only electronic hardware as shown above the invention may also be implemented using a com bination a hardware and software components including pro grammable devices such as digital signal processors DSPs micro controllers field programmable gate arrays FPGAs application specific integrated circuits ASICs and the like Such an embodiment could be implemented as shown in the flow chart of FIG 8 Like the embodiments described above this method could be used to charge any rechargeable battery in a portable or similar electronic device Any external power supply could be used though the invention is most useful with power supplies of limited capacity As shown in FIG 8 the method of the invention begins at step 90 by connecting the input of a battery charge controller 20 to the external power supply preferably via a USB cable and connectors 16 and a cradle 10 to hold the portable device 18 Theoutput ofthe battery charge controller 20 is connected in parallel to the por
26. ge and potential latch up problems in the battery charge controller The specific design parameters for this embodiment of the invention can be summarized as follows 1 constant current constant voltage charging capabilities as required for charging of Lithium Ion batteries 2 current selection for 100 mA 500 mA and 750 mA power supplies 3 operation of the portable device 18 when the rechargeable battery 24 is low dead or not present 4 start up and operation of the portable device 18 within less than 100 mS in the cases the battery 24 is not present or it is dead 5 compliance with USB suspend mode of operation system should draw less than 500 uA over voltage protection above 5 8V up to minimum of 10V protection against a short circuit on the battery connector 8 allow charging with the input voltage as low as the portable device 18 needs for its safe operation 9 voltage in the range of 3 3V 3 6V for pull up resistor on D line MO 20 25 30 35 40 45 50 55 60 65 10 10 provide means to connect and disconnect the voltage to pull up resistor on D line 11 battery presence indication and 12 providing status of the battery charge controller The general description of this comprehensive implemen tation of the invention follows The circuit of FIGS 7A 7C centres around a Texas Instru ments bq24020 Lithium Ion battery charge controller labelled as U909 in FIG 7C This bat
27. has limited capacity If one attempts to power the portable device 18 and battery charge controller 20 simultaneously from the USB card 12 it is quite likely that too great a load would be placed on the USB card 12 The excessive load on the USB card 12 may result in an undervoltage or low current condition that could result in a number of undesirable problems such as the bat tery 24 not becoming properly charged or becoming perma nently damaged or the portable device 18 operating errati cally or becoming damaged As an alternative the battery 24 and portable device 18 could be arranged as shown in FIG 3 so that they are both fed by the battery charge controller 20 While such a design would reduce the total power drawn by the portable device 18 and battery 24 in combination there are a number of other problems 1 most importantly there is still no control over the total power that is drawn from the USB port 12 2 the power drawn by the portable device 18 could disturb the carefully designed protection and charging mechanisms of the battery charge controller 26 3 the portable device 18 and battery 24 compete arbitrarily for the available power so they may adversely affect the operation of one another If the available voltage drops too low or insufficient current is available either device may operate erratically or fail all together 4 if the battery 24 is in a deep discharge state when power is turned on the voltage to th
28. he invention FIG 5 presents a timing diagram of voltage current and power curves for the charging of a lithium ion battery in an embodiment of the invention FIG 6 presents an electrical schematic diagram of a battery charging circuit in a simple embodiment of the invention FIGS 7A 7B and 7C present an electrical schematic dia gram of a battery charging circuit in a comprehensive embodiment of the invention FIG 8 presents a flow chart of a method of operating a battery charging circuit in an embodiment of the invention DESCRIPTION OF THE INVENTION As explained above there is currently no effective design which is capable of powering both a portable device 18 and a rechargeable battery 24 from a power supply with limited capacity A circuit which overcomes a number of the problems in the art is presented as a block diagram in FIG 4 This figure presents a battery charging circuit build around a standard battery charge controller 20 In this embodiment ofthe inven tion the battery charge controller 20 receives power from an external source V us and feeds a portable device 18 and rechargeable battery or batteries 24 in parallel but the feed to the battery 24 is made via a semiconductor switch Q1 Con trol ofthe current flow through the semiconductor switch Q1 is modulated by a voltage sensing circuit 30 which measures the voltage drop across the battery charge controller 20 and reduces the current flow through the semicondu
29. ice the controller responsive to the sensing circuit and config ured to control the switch to limit battery charging from the external source such that sufficient power is provided for operation of the portable electronic device 10 The portable electronic device of claim 9 wherein the controller is configured to control the switch in response to the voltage drop to provide sufficient power for operation of the device 11 The portable electronic device of claim 9 wherein the supply of power is limited by limiting current 12 The portable electric device of claim 9 wherein the supply of power is limited by limiting voltage 13 The portable electronic device of claim 9 wherein total power consumed by the device is provided by the USB source 40 45 16 14 The portable electronic device of claim 9 wherein the controller comprises an external driving semiconductor for carrying supply current to the device and the switch whereby load current passes through the external driving semiconduc tor in lieu of the controller 15 The portable electronic device of claim 9 wherein the voltage sensing circuit comprises an operational amplifier 16 The portable electronic device of claim 9 wherein the voltage sensing circuit comprises an operational amplifier for receiving a voltage signal from an output ofthe controller and a reference signal and responds to the voltage signal being less than the reference voltage by reducing the
30. ily be designed to accommodate them As noted above battery charge controllers are usually designed to suit a particular battery or family of batteries For example lithium batteries are charged in three phases 1 resolving deep discharge conditions 2 constant current charging until the battery reaches a certain voltage level and then 3 constant voltage charging until the charging current drops to a certain point During the initial handling of deep discharge conditions comparatively little current is provided to the battery typi cally Yio of the charge current The circuit of the invention is therefore designed so that the battery will rarely be denied this very modest power demand The constant current charging phase draws the greatest amount of power but lithium cells do not suffer if the charg ing current is modulated or cycled during this phase Thus it is this phase that is altered the greatest by the circuit of the invention If the portable device 18 is used a great deal during this phase the only negative impact will be that the charging of the battery 24 takes much longer During the constant voltage charging phase the maximum current is less than that of the constant current phase and drops continuously as the battery 24 becomes fully charged More important the battery 24 voltage stays at a constant and maximum level during this phase so the total power dissi pated by the battery charge controller 20 will be lo
31. is provided for operation of a device by modulating a switch to control a quantity of power to the rechargeable battery 23 The method of claim 22 wherein the power 1s limited by limiting current 24 The method of claim 22 wherein the power 1s limited by limiting voltage 25 The method of claim 22 wherein total power consumed by the device is provided by the USB source 26 The method of claim 22 wherein the rechargeable battery is associated with a portable electronic device UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO 8 541 983 B2 Page 1 of 2 APPLICATION NO 13 175541 DATED September 24 2013 INVENTOR S Dusan Veselic et al It is certified that error appears in the above identified patent and that said Letters Patent is hereby corrected as shown below In the Specification In column lines 4 5 delete the line break between 13 028 and 361 should read 13 028 361 In column 2 lines 31 32 being with should read To begin with In column 2 line 65 of large number should read one of a large number In column 3 line 39 battery charge controller 26 should read battery charge controller 20 In column 3 line 44 fail all together should read fail altogether In column 4 line 4 battery charge circuits 20 should read battery charge controllers 20 In column 5 line 41 build around
32. ld then be populated to supply power to the USB transceiver chip U904 should only be required if the transceiver chip does not meet USB suspend current require ments and our device can wake up from suspend by looking at only D D line responses U905 and Q908 are mainly used to maintain L BAT VBAT when VBUS is not present and to keep to atleast 3 6V when is present while charger is delivering current to the system and battery voltage is less than 3 6V It is also used to split total power dissipation into two between the battery charge controller s main pass ele ment and Q908 to allow for higher charging currents at all battery voltage levels Another important functionality ofthis circuitry is to allow proper USB enumeration when battery is low dead or not present by allowing the system to the wake up within 15 mS when battery not present or dead Once the U909 delivers the whole programmed current U905 Q908 will maintain the minimum preprogrammed voltage at BAT 3 5V in our case by varying the drain to source resistance of Q908 U905 s positive input is used as a reference and is set by R934 and R913 C924 allows a slow ramp up of LBAT so that the battery charge controller U909 can deliver full pro grammed current until Q908 requests voltage increase on L_BAT if needed Resistor dividers R916 and R915 are used to set the minimum voltage at L_BAT while the R914 provides a pull down resistor for the
33. ller U909 is not deliv ering any current to the battery 24 and or portable device 18 It does this by shorting the positive input of the U905 which makes its output to drive Q908 into saturation ON U9065 is used as an inverter of CHRG_FLG flag simply to make it compatible with the software and hardware the rest of the system R931 is a pull up resistor for CHRG FLG open drain output 20 25 30 35 40 45 50 55 60 65 12 Processor supervisor U908 has dual functionality Its PFI power fail input input level is set by the resistor divider R937 R925 and R926 so it matches the U908 internal refer ence when VBUS drops down to 3 3V or the value of LBAT voltage set by the U905 and Q908 when operating with low dead or without battery causing its open drain output power fail output PFO to go to GND This would force the posi tive input node of U905 to go to GND and put Q908 in saturation ON This set of circuitry creates an Under Voltage Lock Out UVLO threshold for the L_BAT boost circuit This is important as the U909 can operate down to 2 5V causing its status flag to indicate current delivery to the sys tem even though it really does not the battery 24 internally disconnects below 2 5V Such a condition would cause the system to reset for battery voltage levels lower than the preset minimum LBAT value as the U905 Q908 would try to keep the LBAT voltage at the preset value by disconnecting th
34. n AC power supply would have to be provided as a separate physical component from a USB data cable and 4 there are no universal standards for AC power supplies a given AC power supply may require 120VAC or 240VAC as an input and may provide 3 4 5 6 7 5 or 9 VDC out with one of large number of different possible connectors and polarities traveller who forgets his AC power supply at home may not be able to find a suitable replacement US 8 541 983 B2 3 In contrast the USB standard is widely accepted so that a traveller whose mobile device is equipped with a USB con nector will have a much greater chance of finding a charging source Thus it would clearly be desirable to use USB power to charge portable devices Unfortunately though as noted above USB ports can only provide limited power The prob lem becomes clear when considering the block diagram of FIG 2 In this scenario the portable device 18 and the battery charge controller 20 are connected to the USB port 12 in parallel as under charging conditions the control switch 22 will be toggled so that the portable device 18 draws power from the USB port 12 When the battery 24 has become fully charged by the battery charge controller 20 and the USB port 12 power removed the control switch 22 is then toggled so that the portable device 18 draws power from the battery 24 This type of circuit may work in some circumstances but it is not acceptable where the power source
35. ntroller 20 is controlled the portable device 18 receiving the power it needs to operate and the rechargeable battery 24 receiving any additional available power The balance of the software code needed to perform this algorithm would be straightforward to one skilled in the art The method steps of the invention may be embodiment in sets of executable machine code stored in a variety of formats such as object code or source code integrated with the code of other programs implemented as subroutines by external pro gram calls or by other techniques as known in the art Even the hardware embodiments of the invention could be encoded ina software form such as the hardware development languages HDL code used to fabricate integrated circuits This HDL or similar code could be stored on any electronic memory means such computer diskettes CD Roms Random Access Memory RAM and Read Only Memory ROM As well electronic signals representing this software code may also be transmitted via a communication network Options and Alternatives While particular embodiments of the present invention have been shown and described it is clear that changes and modifications may be made to such embodiments without departing from the true scope and spirit of the invention For example 1 the circuit of the invention could be used with any manner of power source including conventional AC power sup plies often referred to as bricks computer data busse
36. provided from Vg and a voltage regulator V is used as an input to the op amp 52 rather than V because the regulator will provide a constant output voltage whereas V has a wide range making the design more difficult The values of resistors R5 and R6 are established simply by the need to scale the V lt value to the gr Value Also note that capacitor C1 is included in the circuit to smooth out fluctuations and to prevent oscillation As described above this circuit allows the portable device 18 to draw power via Q2 without causing the combined draws of the portable device 18 and the battery 24 to exceed the power capacity of Q2 As the portable device 18 draws power the voltage on the collector side of Q2 drops and the current via Q3 is throttled in a linear mode Power dissipation must be designed for the worst case scenario For example ifthe maximum design parameters are as follows up to 0 85 A is available an input voltage could be as high as 6V and pre charging of the battery 24 is complete at 3 0V that is where the highest charge current is delivered to battery as shown in FIG 5 then 6V 3V 0 85 A 2 55 W of power that would be dissi pated by the external drive element Q2 note that in circuits which do not use such an element all of this power would be dissipated by the battery charge controller 50 This external drive element Q2 must dissipate heat gener ated by the current that flows thro
37. r should read C915 is an input bypass capacitor and C922 is an output filtering capacitor In column 12 line 59 C912 is bypass capacitor should read C912 is a bypass capacitor In column 12 line 66 voltage for USB transceiver chip should read voltage for a USB transceiver chip In column 13 line 18 when battery is low dead should read when the battery is low dead In column 13 lines 19 20 by allowing the system to the wake up within 15 mS when battery not present or dead should read by allowing the system to wake up within 15 mS when the battery is not present or dead In column 13 line 31 with indication should read with an indication In column 13 lines 32 33 R928 is pull up resistor should read R928 is a pull up resistor In column 13 lines 41 42 combination a hardware should read combination of hardware In column 14 lines 4 5 converters which could be used should read converters could be used In column 14 line 22 invention may be embodiment should read invention may be embodied In column 14 line 31 such computer diskettes should read such as computer diskettes
38. r is present and its pull up is provided by signal Low drop out voltage regulator U901 TOKO TK71733SCL provides a regulated 3 3V supply for the USB data line pull up resistors as well as a3 3V supply for various components in the charger circuit and as an indicator that an external source is attached EXT_PWR_CD U901 has reverse bias and overcurrent protection built in thermal shut down and short circuit protection U901 provides power for U906 U908 and U905 as well as the 3 3V voltage for pull up resistor It is also used to provide the indication of VBUS presence to the system EXT_P WR CD R904 is used to limit the current to the input pin of the system C915 is input bypass capacitor and C922 is output filtering capacitor C910 is used to filter RF noise coming from the RF circuitry and C912 is bypass capacitor for inter nal reference Q907 is used to switch USB_VPU voltage and allow soft enumeration on the USB bus R909 provides default OFF condition for P FET and R905 provides fast discharge of the USB_SFTCN control line during the RST or suspend initia tion without battery presence U904 provides supply voltage for USB transceiver chip it is a standard voltage regulator as known in the art It is US 8 541 983 B2 13 enabled when VBUS is present and automatically shuts down the power when VBUS goes OFF C921 and C913 are output filter capacitors U904 can optionally be removed to save cost R942 shou
39. reset state device battery voltage level VBUS the input voltage is presented via Q904a to the USB input pin ofthe battery charge controller U909 0904 is used for OVP and is controlled by U912 3 0V under voltage detector National Semiconductor LMS33460 Whose input voltage is provided via resistor divider R937 and R925 R926 Its open drain output keeps Q904 in saturation while VBUS R937 R925 R926 R925 R926 lt 3 0V which provides OVP above 5 8 While USB input to the battery charge controller U909 is present 100 mA and 500 mA current limit could be selected B CHRG_B LOW provides 100 mA and CHRG B HIGH provides 500 mA Resistor R941 sets default LOW logic level to the ISET2 input of U909 thus allowing a 100 mA default current limit This is important as it makes the system compliant with the USB specification when operating with low dead or without battery A USB device is limited to 100 mA operation until the device enu merates to 500 mA if the host USB supports this Resistor R940 provides a default LOW input level to the gate of Q905a which keeps it out of saturation OFF while in reset mode and therefore sets the gate voltage of 09045 at its source level at the level of VBUS voltage which disal lows the VBUS presence at AC input of the battery charge controller U909 controller Resistors R932 and R936 are pull up resistors for Q904 Charging current of 750 mA used for non USB power sources could
40. s such as USB ports external battery packs laptop power supplies and DC outlets in automobiles and on aircraft 2 any manner of electrical appliance could be charged with such a circuit including portable laptop computers per sonal digital assistants PDAs cellular telephones wire less email and paging devices and 3 any manner ofrechargeable battery could be used including single or multiple lithium ion nickel cadmium or other types of cells Again such implementations would be clear to one skilled in the art from the teachings herein and do not take away from the invention What is claimed is 1 A portable electronic device comprising a switch configured to control a supply of power to a rechargeable battery a controller configured to receive USB power from an external source and supply power to the portable elec tronic device and a sensing circuit configured to determine power supplied to the portable electronic device the controller responsive to the sensing circuit and con figured to control the switch to limit battery charging US 8 541 983 B2 15 from the external source such that sufficient power is provided for operation of the portable electronic device 2 The portable electronic device of claim 1 wherein suf ficient power is power required to meet the dynamic needs of the portable electronic device 3 The portable electronic device of claim 1 wherein the supply of power is limited by limitin
41. table device 18 and the input of the semiconductor switch Q1 per step 92 and the output of said semiconductor switch Q1 is connected to the rechargeable battery 24 per step 94 Next the current output ofthe battery charge controller 20 is controlled in some manner at step 96 As noted above this may be done in many ways for example a DAC digital to analogue converter output of a micro controller could be used to send an appropriate signal to the current control input of the battery charge controller 20 20 25 30 35 40 45 50 55 60 65 14 The voltage drop across the battery charge controller 20 is then measured at step 98 This task could also be performed in many ways For example many micro controllers provided with integral ADCs analogue to digital converters which could be used to perform this function Because the current is controlled at step 96 and the voltage drop across the battery charge controller 20 is measured at step 98 this methodology can deduce what the power dissi pation is for the battery charge controller 20 The method of the invention is therefore able to control the power dissipation by modulating the semiconductor switch Q1 in response to the voltage drop across the battery charge controller 20 at step 100 reducing the quantity of current supplied to the recharge able battery 24 when the voltage drop is too great In this way the total power dissipated by the battery charge co
42. tery charge controller provides the constant current and constant voltage modes required to charge Lithium Ion cells and supports externally programmable current limits Its UVLO under voltage lock out threshold is provided by the PFI PFO U908 comparator Texas Instruments TPS3103E15 with reference and its threshold is set by the resistor dividers of the VBUS input U908 is also used to guarantee initial start up operation of U909 with minimum of 100 mS This provides means to enumerate when operating with low dead or without battery Overvoltage protection OVP is provided by the U912 which is set to 5 8V Charging status is provided by the battery charge controller U909 which indicates whether or not the controller is delivering current to the system Voltage for the D pull up resistor is provided U901 a low voltage drop out regulator Toko TK71733SCL and its switching capabil ity via Q907 The same voltage is also used to power up the components that are used only when the external power is available via VBUS U906 U905 etc A comparator U905 LMC7111A and a MOSFET Q908 are used to boost the system voltage when operating with low dead battery or without the battery This closed loop also throttles current to the system under no battery and low battery conditions This occurs because when the BAT voltage drops due to the system load U905 acts to turn off Q908 directing more current to the system away from bat
43. ugh it The more power that is dissipated the larger physical size this pass element must be generally the surface area that a device requires rises with the square of the power to be dissipated That is if the power is doubled a transistor with four times the surface area is required The sizes of transistors are standardized so the preferred embodiment of this circuit is designed to employ SOT 23 or superSOT 6 packages which are capable of dis US 8 541 983 B2 9 sipating up to 1 6 W The next size is SOT 223 which is considerably larger with twice the power dissipation As noted above throttling of power to the battery 24 is done so that the current always satisfies the needs of the portable device 18 and any current left over difference between the input current and the current to the portable device 18 is delivered to the battery 24 For example sup pose that the circuit is connected to a high power USB port 500 mA is available and a portable device 18 such as por table Blackberry handheld device When the Blackberry goes to sleep it may only require 0 3 mA 0 7 mA so the balance of the available current 499 3 mA 499 7 mA may be provided to battery 24 Once the Blackberry wakes up which it does periodically to perform house keeping jobs it draws say 30 mA 70 mA depending on what it does At this point the battery 24 receives 430 mA 470 mA The analysis occurs when the Blackberry is to receive or transmit some
44. upply which is often very close to or just above the voltage of the battery being charged many portable devices having battery voltages in the range of 2 5 4 5 VDC As well many portable devices may be operable to upload and download data or software to and from a personal computer or a laptop computer often referred to as syncing Thus many portable devices are supplied with docking cradles as shown in the system dia gram of FIG 1 This is quite a straightforward system as the docking cradle 10 is connected to a USB port 12 ofa personal computer PC 14 viaa simple USB cable and connectors 16 The portable device 18 need only be set down in the docking cradle 10 and an electronic connection to the PC 14 is made If the USB port 12 has sufficient power it makes much more sense to use the USB port 12 to supply charging power to the portable device 18 rather than using a separate AC charger For example 1 a USB power supply will have less electrical noise than an AC charger unless the AC charger incorporates large DC capacitors or inductors 2 an AC charger requires either a heavy transformer or an expensive switching power supply neither of which would be required if USB power is used 3 in the USB power supply implementation the cable and connectors 16 used to connect the docking cradle 10 to the PC 14 could be used to carry both power and data so no extra physical components would be required at all In contrast a
45. ust be provided with consideration for the tight operating parameters of battery charging circuits the limited physical board area in portable devices and the reliability and complexity of the design SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a novel method and apparatus which allows standard battery charge controllers to be supplied from standard computer data ports and other power sources which obviates or mitigates at least one of the disadvantages of the prior art One aspect of the invention is broadly defined as a battery charging circuit comprising a semiconductor switch having an output connected to a rechargeable battery a battery charge controller for receiving power from an external source and supplying output power to a portable device and the input of the semiconductor switch the current output of the battery charge controller being controllable and a voltage sensing circuit for measuring the voltage drop across the battery charge controller and responding to the voltage drop across the battery charge controller by modulating the semi conductor switch to reduce the quantity of current supplied to the rechargeable battery when the voltage drop is too great whereby the total power dissipated by the battery charge controller is controlled the portable device receiving the power it needs to operate and the rechargeable battery receiv ing any additional available power Another aspect o
46. wer during the constant voltage phase than it was during the constant current phase As will be described in greater detail hereinafter the volt age sensing circuit 30 is designed to saturate the semiconduc tor switch Q1 when the full charge voltage level is reached i e the semiconductor switch Q1 does not restrict current flow at all at this point US 8 541 983 B2 7 The change in power dissipation overtime is shownin FIG 5 Four curves are shown in this figure the voltage of the battery 24 labelled V the charge current labelled legancz the voltage drop across the battery charge controller 20 labelled V prop and the total power dissipated labelled PBCC Note that V prop varies inversely with Vg and that the power dissipated by the battery charge controller 20 is the product of Ii 454 and V prop Clearly during the conditioning phase the battery voltage 15 low so V prop will be high However 4441s also low during this phase about of Lj maxi mum charging current so the total power dissipated is mod est During the constant current phase the charge current rises to but the voltage of the battery drops as the battery becomes charged so the power dissipated by the battery charge controller 20 drops over the course of this phase As the constant voltage phase begins the battery voltage has reached its fully charged level

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