Circuit and method of operation for an adaptive charge rate power
Contents
1. ae vi Selpi is HOIM 10 44 A 74 Attorney Agent or Firm Jones Day Krishna K We eseseesososeoesosoesoesoesessesoesoesosoesossessesoesoe Pathiyal Charles B Meyer 58 Field of Search 0 0 ccc 320 128 132 320 133 160 164 57 ABSTRACT 56 References Cited A convenient source of charging power for portable com munication devices is an integral power node of a computer U S PATENT DOCUMENTS data bus such as a USB universal serial bus port STERO r ee Unfortunately USB ports have limited power capacity 4433 251 S z oie 4 aE al making them generally incompatible with battery charge 4510431 A 4 1985 Winkler i controllers BCCs which are designed to receive a steady 5 173 855 A 12 1992 Nielsen et al high capacity input The invention provides a battery charg 5 229 649 A 7 1993 Nielsen et al ing circuit which adjusts to the parameters of an external 5 272 475 A 12 1993 Eaton et al power supply such as a USB port by adding a regulating 5 444 378 A 8 1995 Rogers circuit to a standard BCC design This regulating circuit 5 631 503 A 5 1997 Cioffi maximizes the current drawn by the BCC while keeping the 5 638 540 A 6 1997 Aldous voltage to the BCC above a preset minimum the low 5 651 057 A 7 1997 Blood et al voltage shut off level for the BCC If the voltage to the BCC rare x AA ou St begins to drop the regulating circuit reduces the current 5 850 113 A 12 1998 Weimer eal drawn so the voltage rises and stays within th2. am WE ae JON W DUDAS Director of the United States Patent and Trademark Office
3. LTC1734 controller 52 Resistors R1 and R2 are chosen such that Voyrg iS a suitable tolerance above 4 53 VDC when V 1 5 VDC In the intended and published usage of the LTC1734 controller 52 the voltage across resistor R3 is simply V proc since R3 is intended to be tied between PROG and ground In such a configuration determining and setting a fixed charge current IC 7 2 is straightforward In the system of the invention rather than adjusting R3 to control charge current as most alternative ideas suggest this circuit adjusts the voltage across a fixed R3 by changing the voltage across C1 that is V1 such that 1 5V V 51000 I CHG R3 Vo is controlled by the comparator 50 As the comparator 50 is an open drain comparator a MAX9120 comparator was used for testing purposes though similar parts such as the LMV7235 should work as well when V gt V gt the comparator 50 will sink current into its output pin otherwise the output pin will float The control loop operates as follows 1 as Icaro drops the voltage drop across the cable and connectors 16 also drops so Voypg rises per equation 1 above As V cyprg Tises the positive input to the compara tor 50 Vx will also rise For Vy rising when Vy gt V p 0 5 V zys V yrs being the input hysteresis for the comparator 50 the comparator 50 will turn on its output and pull charge out of Cl decreasing Vc and causing Icyrg to increase 2 as Icyrg Increases the voltag
4. Veura Vgus RCABLE XI caste 4 75 VDC 0 5 ohmsx0 5 A 4 5 VDC If the low voltage shutdown of the battery charge con troller is higher than Voyrg 4 5 VDC it will therefore US 6 833 686 B2 5 shutdown This is the case for the LTC1734 controller for example which shuts down at 4 53 VDC The above calculations did not even take into account component tolerances which cannot be ignored The LTC1734 application notes state that this device has a tolerance of 1 If the current regulator 34 incorporates a number of simple components then the circuit of FIG 3 may easily have a tolerance of 3 or so Thus Vegro may effectively be in the range of 4 37 VDC well below the 4 53 VDC cut off for the LTC1734 battery charge controller Equation 1 can also be used to determine a current level Icagze Which does not cause the battery charge controller 30 to shutdown 08 Vourc Vgus RCABLE X ICABLE Icasre Vgus Venra RCABLE 2 4 75 4 53 0 5 0 44A Thus reducing the current Icapgzg to 0 44 A is sufficient to avoid the low voltage shut off of the battery charge control ler 30 Allowing for 3 tolerance Icapte Vgus Venra X3 Reape 2 4 75 4 53 x 1 03 0 5 0 09 0 5 0 18 A That is the current Ic4gzz may have to be reduced to 0 18 A to avoid the low voltage shutdown Thus the use of the circuit in FIG 3 allows computer data buses and similar power supplies with limited c
5. from said US 6 833 686 B2 11 power mode and said reference voltage signal is scaled down proportionally 9 The battery charging circuit of claim 4 wherein said regulating circuit further comprises a capacitor cou pling the output of said comparator to ground thereby smoothing out variances in the output of said compara tor 10 The battery charging circuit of claim 4 where said external power supply comprises a computer data bus hav ing a power node 11 The battery charging circuit of claim 10 wherein said computer data bus is a Universal Serial Bus USB 12 The battery charger of claim 4 wherein said com parator circuit has a hysteresis whereby said battery charge controller will not begin to deliver current again until said voltage level of said computer data bus is well above said reference voltage 13 The battery charger of claim 4 wherein said com parator is operable to lower the charge current when the voltage of the external power supply drops below a preset reference level 14 The battery charger of claim 4 wherein said battery charge controller includes a low voltage shut off circuit said battery charge controller shuts off if the incoming voltage falls below a preset limit and wherein said regulating circuit lowers the current output of said battery charge controller 10 15 20 25 12 when the voltage of the supply drops below a preset reference to avoid said preset limit 15 A batte
6. least one of the disadvantages of the prior art One aspect of the invention is broadly defined as a battery charging circuit which adjusts to the parameters of an external power supply to minimize charge time comprising a battery charge controller connected to the external power supply and electrifying a battery and a regulating circuit for maximizing the current drawn by the battery charge controller while keeping the voltage to the battery charge controller above a preset minimum limit the preset mini mum limit corresponding to a low voltage shut off level for the battery charge controller Another aspect of the invention is broadly defined as a method for charging a battery of a portable device via an external power supply which adjusts to the parameters of the external power supply to minimize charge time the method comprising the steps of connecting a battery charge controller to the external power supply and to a rechargeable battery in the portable device determining a low voltage shut off level for the battery charge controller monitoring the voltage that the external power supply provides to the battery charge controller and maximizing the current drawn by the battery charge controller while keeping the voltage to the battery charge controller above the low voltage shut off level for the battery charge controller BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the invention will become more apparent from
7. 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 exter nal 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 gen erally 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 portable device or operating one or more status LEDs light emitting diodes providing protection circuits such as overcurrent undervoltage and overtemperature protection and shutting themselves off when the charging source has been removed to minimize battery drain Unfortunately most of these battery charge controllers are designed to draw from a high capacity power supply with a steady 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 or when the power is delivered via unknown length and gauge of power wires the resistance of such power wires cause a voltage drop which aggravates the problem Some co
8. 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 a block diagram of the system presented in FIG 1 highlighting the problem of voltage drop between the personal computer and the portable electronic device FIG 3 presents a electrical schematic diagram of a battery charging circuit in a broad embodiment of the invention FIG 4 presents an electrical schematic diagram of a battery charging circuit using a comparator in an embodi ment of the invention FIG 5 presents an electrical schematic diagram of a battery charging circuit using an electronic potentiometer in an embodiment of the invention FIG 6 presents a timing diagram of charging current provided by the embodiment of FIG 5 and FIG 7 presents a flow diagram of an example method for charging a battery in a mobile device DESCRIPTION OF THE INVENTION The general problem addressed by the invention is that typical battery charge controllers are designed to received a 10 15 20 25 30 35 40 45 50 55 60 65 4 steady high capacity power supply while such a power supply is often unavailable or is simply inconvenient One of the most common battery charge controllers for example the LTC1734 from Linear Technology Corporation is designed to receive 5 VDC in a
9. 1 0 kQ R3 3 09 kQ R4 2000 R5 10 0 KQ Cl 1 uF C2 0 1 uF The R4 C1 time constant was chosen to be at least 10 times larger than the propagation delay of the MAX9120 for stability For testing purposes a 1Q resistor was used to simulate the resistance of the supply cable and connectors 16 With Vers 6 VDC loyeg 440 mA As Vays was gradually reduced Icaro remained at 440 mA until V 7 5 5 075 VDC at which point lozpreg started to drop By the time V 4 71 VDC the charge current Icure had dropped to 92 mA Using an HP54645D oscilloscope to probe the LTC1734 controller 52 s VCC pin showed the following for logrg 440 mA and Vgys 5 075 VDC VCC 4 63 VDC and for loyeg 92 mA and V gys 4 71 VDC VCC 4 63 VDC This is consistent with the chosen values of R1 and R2 using the PROG reference scheme With Vp775 4 63 VDC the LTC1734 controller 52 turned off and Vprog 4 625 VDC By returning Vsus to 6 VDC the LTC 3 controller 52 could be turned on again by momentarily pulling CHG_ CTRL to GND Similarly pulling CHG_CTRL above about 2 25 VDC turned the LTC1734 controller 52 back off Digital Potentiometer Embodiment The invention is not strictly limited to the case where the low voltage threshold is never exceeded In the embodiment of FIGS 5 and 6 for example the low voltage threshold could be exceeded with each periodic cycle of current ramping but the duty cycle still be sufficient to charge the battery The only di
10. United States Patent US006833686B2 12 10 Patent No US 6 833 686 B2 Veselic et al 45 Date of Patent Dec 21 2004 54 CIRCUIT AND METHOD OF OPERATION 6 362 610 B1 3 2002 Yang seseseseeeeeeeees 323 281 FOR AN ADAPTIVE CHARGE RATE POWER 6 507 172 B2 1 2003 Sherman eeeeee 320 134 SUPPLY 6 507 173 B1 1 2003 Spiridon et al 6 522 118 B1 2 2003 Barcelo et al 75 Inventors Dusan Veselic Oakville CA Michael 6 531 845 B2 3 2003 Kerai etal viet 320 107 F Habicher Waterloo CA Jacek S a ka a en 439 638 Idzik Kenilworth CA Jonathan T ee Malton Kitchener CA OTHER PUBLICATIONS 73 Assignee Research In Motion Limited Waterloo Electric Double Layer Capacitors vol 2 Oct 25 1996 CA Japan Tokin Corp Cat No EC 200E Supercapacitor User s Manual vol 2 Japan Tokin Corp Notice Subject to any disclaimer the term of this date unknown i patent is extended or adjusted under 35 Charging Big Supercaps Portable Design p 26 Mar U S C 154 b by 0 days 1997 Linear Technology LTC4056 4 2 Linear Li Ion Charger p with Termination in ThinSOT Apr 2003 pp 1 16 USA 21 Appl No 10 372 446 Linear Technology LTC4053 4 2 USB Compatible Lith 22 Filed Feb 21 2003 ium lon Battery Charger with Thermal Regulation 2001 1 16 USA 65 Prior Publication Data BR eu id on US 2004 0164707 A1 Aug 26 2004 cies 2 ERTE Primary Examiner Edward H Tso T
11. a physical components would be required at all In contrast an AC power supply would have to be provided as a separate physical component and a given AC power supply may require 120 VAC or 240 VAC as an input and may provide 3 4 5 6 7 5 or 9 VDC out with one of large number of different pos sible connectors and polarities A traveller who forgets an AC power supply at home may not be able to find a replacement In contrast the USB standard is widely accepted so that a traveller whose mobile device is equipped with a USB connector will have a much greater chance of finding a charging source Unfortunately USB ports can only provide limited power while typical battery charge controllers are designed to receive a steady high capacity power supply that is the input voltage at the battery charge controller is at or near its designed value and does not drop as charging current increases The problem becomes clear when considering the block diagram of FIG 2 The components of FIG 2 are the same as those of FIG 1 specifically a docking cradle 10 powered from a USB port 12 of a PC 14 via cable and connectors 16 and feeding a portable device 18 resting in the cradle 10 From this presentation it is clear that the voltage output from the USB port 12 V ysg will drop as it crosses the cable and connectors 16 due to its resistance Reapre lf either the cable resistance Roagze or the current drawn Icagzg is too great the volt
12. age arriving at the battery charge controller in the mobile device 18 may be too low This low voltage will cause many standard battery charge controllers to either shut down or to oscillate and fail to charge the battery in the portable device 18 efficiently True new dedicated battery charge controllers could be developed which are operable with the limited USB power supply and resistance of the cable and connector system but that would be an expensive and complicated solution Such a design would become even more complicated to be compatible with both computer data bus power supplies and other power sources such as AC power supplies US 6 833 686 B2 3 There is therefore a need for a method and apparatus which allows standard battery charge controllers to be supplied with power from standard computer data busses such as USB ports This design must be provided with consideration for the cost of electrical components the limited physical board area in portable devices the reliabil ity and the complexity of the design It is also desirable that this method and apparatus be operable with both computer data bus power supplies and other power sources such as AC power supplies 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
13. apacity to be used to charge mobile devices without causing the battery charge controller 30 to shut down The solution of this embodiment adapts to the capabilities of any external power source to minimize charge time If for example 5 VDC arrives at the input of the battery charge controller 30 with unlimited current and no voltage drop as the current draw increases then the regulating circuit 34 will not restrict the current drawn A number of different embodiments will now be described Each embodiment uses a very small number 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 Comparator Embodiment FIG 4 presents an electrical schematic diagram charging circuit which employs two main components a comparator 50 and a LTC1734 battery charge controller 52 having a current control pin PROG Varying the current drawn through the control pin PROG will vary the current supplied by the LT C1734 battery charge controller 52 to the battery 32 Drawing more current out of the PROG pin will increase the charge current while reducing the PROG current will reduce the charge current Many battery charge controllers have a similar current control system but this embodiment will be described with respect to the LTC1734 controller The LTC1734 controller can be operated in either constant current mode or constant vol
14. by adjusting the cur rent drawn by said battery charge controller to keep the voltage at the input to said battery charge controller above said preset minimum limit 4 The battery charging circuit of claim 3 where said regulating circuit comprises a comparator for receiving a voltage signal from the input to said battery charge controller and a reference voltage signal and responds to said voltage signal being less than said reference voltage by reducing the current supplied by said battery charge controller 5 The battery charging circuit of claim 3 where said regulating circuit comprises an electronic potentiometer operable to incrementally decrease its resistance in response to control pulses from a microprocessor thereby incrementally increas ing the current supplied by said battery charge control ler 6 The battery charging circuit of claim 3 wherein said regulating circuit comprises an electronic potentiometer operable to cyclically ramp though its range of resistance thereby cycling the current supplied by said battery charge controller through a range of 0 A to a current level that causes said battery charge controller low voltage shut off to trip 7 The battery charging circuit of claim 4 wherein said reference voltage is provided by said battery charge controller 8 The battery charging circuit of claim 4 wherein said comparator circuit further comprises a voltage divider for scaling down said voltage signal
15. e drop across the cable and connectors 16 rises causing Voy and consequently Vx to drop For Vy falling when Vy lt V 0 5 V prys the comparator 50 turns off its output allowing the LTC1734 controller 52 s PROG pin to pour charge into C1 causing VC to increase and decreasing Ioypg Resistor R4 smooths out the ripples on C1 and limits current transients through the comparator 50 s output US 6 833 686 B2 7 When the power supply is capable of supplying all the power the LTC1734 controller 52 can handle Vo will be at a minimum and I will be approximately determined by 1 5V R3 R4 Rour 4 Teng Rour is the resistance from the comparator 50 s output to GND when the output is active Because the LTC1734 controller 52 is susceptible to malfunction due to capacitive effects in the PROG circuit it is best to keep R4 0 1R3 but this will depend on the application and can easily be determined by one skilled in the art When power is first applied to this circuit through V gus V 1 0 and the charger will start and stay on A high on reset signal of 3 0V applied to CHG_ CTRL will keep the charger off once the off state has been established the CHG_ CTRL signal can be removed Conversely pulling CHG_ CTRL to GND for a period of time and then floating it will turn on the charger Testing of Comparator Embodiment The circuit of FIG 4 was tested with the following component values R1 10 0 KQ R2 2
16. e operating 5 939 860 A 8 1999 William range of the BCC 6 104 162 A 8 2000 Sainsbury et al 6 104 759 A 8 2000 Carkner et al 16 Claims 4 Drawing Sheets U S Patent Dec 21 2004 Sheet 1 of 4 US 6 833 686 B2 FIGURE 2 U S Patent Dec 21 2004 Sheet 2 of 4 US 6 833 686 B2 Veus Veus U S Patent Dec 21 2004 Sheet 3 of 4 US 6 833 686 B2 FIGURE 5 FIGURE 6 ICHRG U S Patent Dec 21 2004 Sheet 4 of 4 US 6 833 686 B2 FIGURE 7 START CONNECTING BATTERY CHARGE CONTROLLER TO EXTERNAL POWER SUPPLY AND TO RECHARGEABLE BATTERY DETERMINING LOW VOLTAGE 92 SHUT OFF LEVEL FOR BATTERY CHARGE CONTROLLER MONITORING VOLTAGE PROVIDED es TO BATTERY CHARGE CONTROLLER MAXIMIZING CURRENT PROVIDED BY BATTERY CHARGE CONTROLLER WHILE KEEPING VOLTAGE TO BATTERY CHARGE CONTROLLER ABOVE LOW VOLTAGE SHUTOFF LEVEL US 6 833 686 B2 1 CIRCUIT AND METHOD OF OPERATION FOR AN ADAPTIVE CHARGE RATE POWER SUPPLY 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 from a variety of power sources including limited capacity sources such as an integral power node of a computer data bus One such computer 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
17. ed by the ADJUST input it is used to increment or decrement the electronic potentiometer R9 Also a separate reset circuit is provided using resistors R10 R11 R12 capacitor C3 and transistor Q3 This circuit could be powered using any reliable voltage V2 in the preferred embodiment V2 3 3 VDC which is provided from V_ and a voltage regulator The preferred values for the components in this circuit are R6 2 2 kohms R7 12 8 kohms R8 1 0 kohms R9 10 kohms R10 200 0 kohms R11 10 0 kohms R12 200 kohms C3 22 pF US 6 833 686 B2 9 Software Embodiments Rather than using only electronic hardware as shown above the invention may also be implemented using a combination a hardware and software components includ ing programmable devices such as digital signal processors DSPs microcontrollers 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 7 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 The method of the invention adjusts to the parameters of external power supplies to minimize charge time As shown in FIG 7 the method of the invention begins at step 90 by connecting a batt
18. ery charge controller 30 Icagze the voltage drop across Resse Will decrease thus avoiding the low voltage shut off of the battery charge controller 30 and allowing the battery 32 to be charged A number of current regulators 34 are described herein but in general it desirable that the current regulator maximize the current being fed to the battery 32 and therefore maximizing the current drawn from the power supply Icasze while keeping the Vizr voltage greater than the low voltage shut off level of the battery charge controller 30 In some embodiments of the invention the current regu lator 34 uses Voeyrg as an input via connection 36 while in other embodiments the current regulator 34 uses an output of the battery charge controller 30 via connector 38 Still other embodiments use no feedback to the current regulator 34 Say for example that the voltage provided from the computer data bus is 4 75 5 25 VDC that is Vgys 4 75 5 25 VDC the circuit must therefore be designed to operate at V gys 4 75 VDC Suppose also that the resistance of the cable and connectors 16 is 0 5 ohms Reasze 0 5 ohms and that the low voltage shut off of the battery charge controller 30 is 4 53 VDC The battery charge controller will endeavour to draw as much current as needed to charge the battery 32 which in the case of a USB bus will be limited to about 0 5 A Thus the voltage arriving at the battery charge controller Voyp Will be d
19. ery charge controller 30 to the external power supply and to the rechargeable battery in the portable device 18 As described herein above the connec tion to the external power supply is preferably made via a USB cable and connectors 16 and a cradle 10 to hold the portable device 18 A low voltage shut off level for the battery charge controller in the portable device 18 is then determined at step 92 This low voltage shut off level is generally predeter mined as the software algorithm is executed by the portable device 18 and the parameters of the battery charge control ler 30 being used in the portable device 18 can be pro grammed into it The voltage provided by the external power supply to the battery charge controller 30 is then monitored at step 94 This step could be provided periodically continuously or in response to an event such as a change in the charge current Various devices such as microcontrollers are often pro vided with integral ADCs analogue to digital converters which could be used to perform this monitoring function The current drawn by the battery charge controller 30 is then maximized at step 96 with the limitation that the voltage being supplied to the battery charge controller 30 must be kept above the low voltage shut off level The current drawn by the battery charge controller 30 could be controlled in a number of manners For example most microcontrollers have DAC digital to analogue converter out
20. f reasons To begin with USB ports supply a low DC voltage supply 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 diagram of FIG 1 This is quite a straightfor ward system as the docking cradle 10 is connected to a USB port 12 of a personal computer PC 14 via a simple USB cable and connectors 16 The mobile device 18 need only be placed into the docking cradle 10 and an electronic connec tion 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 mobile device 18 rather than using a separate AC charger For example a USB power supply will have less electrical noise than an AC charger unless the AC charger incorporates large DC capacitors or inductors an AC charger requires either a heavy transformer or an expensive switching power supply current neither of which would be required if USB power is used 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 extr
21. ferred to as bricks com puter data busses such as USB ports external battery packs laptop power supplies DC outlets on aircraft 2 any manner of electrical appliance could be charged with such a circuit including portable laptop computers personal digital assistants PDAs cellular telephones wireless email and paging devices and 3 any manner of rechargeable 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 battery charging circuit which adjusts to the param eters of an external power supply to minimize charge time comprising a battery charge controller connected to said external power supply and electrifying a battery and a regulating circuit for maximizing the current drawn by said battery charge controller while keeping the volt age to said battery charge controller above a preset minimum limit said preset minimum limit correspond ing to a low voltage shut off level for said battery charge controller 2 The battery charging circuit of claim 1 where said battery charge controller to includes a current control input 3 The battery charging circuit of claim 2 where said regulating circuit comprises a regulating circuit responsive to the voltage at the input to said battery charge controller
22. fficulty with such a circuit is that it would be necessary to reset the battery charge controller with each cycle The circuit of FIGS 5 and 6 ramps through a range 10 15 20 25 30 35 40 45 50 55 60 65 8 of current supply but uses a reset circuit to stop the ramping before the low voltage threshold is exceeded Like the embodiment of FIG 4 this circuit uses the LTC1734 battery charge controller 52 though other battery charge controllers having a current control pin PROG could also be used However rather than having a comparator circuit as in FIG 4 which modulates the current draw to avoid the low voltage shut off this circuit ramps from a low current level through to a high current level Before the low voltage threshold is reached the LTC1734 controller 52 shuts down and the cycle is repeated The circuit also includes provisions for setting the current draw to a number of predetermined and fixed levels Looking first at the simplest case with the inputs FAST CH HI LO CH and ADJUST all at 0 VDC then there will be no current flow through either of the semiconductors Q2 or Q3 The resistance between PROG and ground will therefore be equal to the sum of resistors R6 and R7 and this will determine the current flow through the LTC1734 con troller 52 If these resistors are set to 2 2 kohms and 12 8 kohms respectively then the circuit will provide 100 mA If the FAST CH is held high then current w
23. ill flow through R6 and the resistance from PROG to ground will only be 2 2 kohms Thus the current flow through the LTC1734 controller 52 will be approximately 750 mA This setting would not be useful with a low capacity supply such as a USB port but could be used with a high capacity supply such as an AC transformer Finally with the HI LO CH input high current will flow through resistor R8 electronic potentiometer R9 and Q2 Resistor R8 preferably has a value of 1 kohm and R9 is preferably a MAX5467 potentiometer which has a range of 0 10 kohms in 32 discrete steps Thus this circuit will step through a resistance of 11 kohms down to 1 kohm in 32 discrete steps note that this circuit is in parallel to R7 so R7 must be considered in determined the current drawn from PROG This would result in the current output similar to that shown in FIG 6 the number of steps that would actually be made prior to reaching the low voltage shut off varies with the particular application due to component values and tolerances and other factors The ADJUST and HI LO CH inputs could be controlled using a microcontroller or similar device As well hardware components such as an oscillator could also be used to control the rate through which the steps of potentiometer are stepped In the preferred embodiment of the invention the HI LO CH input also feeds the CS pin on the MAX5467 This is a chip select input in combination with U D input f
24. mputer 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 and are deliv ered via standard USB cables whose power wires could vary in length and gauge anywhere from 20 AWG 28 AWG for example The majority of personal computers PCs and laptop computers 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 USB 2 0 provides for up to 480 megabits per second support PnP Plug and Play instal lation software and support hot plugging i e devices can be connected 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 able to supply limited power to a connected device The standard USB specification requires that high power USB ports be operable to provide a supply voltage of 4 75 5 25 VDC and supply a maximum current of at least 500 mA five units The specification for low power USB ports requires a supply voltage of 4 40 5 25 VDC and current of 100 mA one unit 10 15 20 25 30 35 40 45 50 55 60 65 2 USB ports would seem to be a very logical choice as a power supply for portable devices for a number o
25. nd has a low voltage lockout at 4 53V that is if the LTC1734 receives a supply voltage of less than 4 53 VDC it simply shuts down When the voltage drop across the supply cable and connectors 16 are considered the voltage supplied by the power node of a data bus such as a USB port may be lower than this low voltage lockout Therefore though the LTC1734 is widely available inexpensive and reliable it cannot be used effectively in this environment A circuit which overcomes this problem is presented as a block diagram in FIG 3 This figure presents a battery charging circuit which uses a standard battery charge con troller 30 known in the art coupled to a rechargeable battery or batteries 32 The battery charge controller 30 is provided with power from some manner of external power such as a computer data bus This power connection is presented in FIG 3 in the form of input voltage V gus This Vgus voltage will be reduced due to the resistance of the electrical cable and connectors 16 Reagzg Thus the battery charge con troller 30 only receives a voltage of Voyrg Veus ReasreXlcasze As will be explained in greater detail hereinafter the voltage drop across Reagzg May result in the Voyrg voltage being lower than the low voltage threshold for the battery charge controller 30 The invention therefore adds a current regulator 34 to the circuit The resistance Rogge is of course fixed but by reducing the current drawn by the batt
26. puts which could be used to control the current provided by a device such as the LTC1734 controller 52 described herein above 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 program calls or by other techniques as known in the art Even the hardware embodiments of the invention could be encoded in a software form such as the hardware develop ment 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 communi cation network Options and Alternatives While particular embodiments of the present invention have been shown and described it is clear that changes and 10 15 20 30 35 40 45 50 55 60 65 10 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 supplies often re
27. ry charger comprising a battery charge controller whose current output varies with the voltage applied to a control signal input and a comparator for lowering the charge current when the voltage of the supply drops below a preset reference level 16 A method for charging a battery of a portable device via an external power supply which adjusts to the param eters of said external power supply to minimize charge time said method comprising the steps of connecting a battery charge controller to said external power supply and to a rechargeable battery in said portable device determining a low voltage shut off level for said battery charge controller monitoring the voltage that said external power supply provides to said battery charge controller and maximizing the current drawn by said battery charge controller while keeping the voltage to said battery charge controller above said low voltage shut off level for said battery charge controller a a a E UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO 6 833 686 B2 Page of 1 APPLICATION NO 10 372446 DATED December 21 2004 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 Cover Page Col 2 Under 74 Attorney Agent or Firm remove Charles B Meyer Signed and Sealed this Thirty first Day of October 2006
28. tage mode 10 15 20 25 30 35 40 45 50 55 60 65 6 In the constant voltage mode entered when the charge voltage of the battery 32 reaches 4 2 VDC externally the LTC1734 controller 52 servos its DRIVE pin to maintain its BAT pin at 4 2 VDC In this mode the current provided by the LTC1734 controller 52 will necessarily drop and the current flowing out of the PROG pin will drop accordingly As this latter mode of operation is not affected by the system described herein it will not be discussed in any further detail As noted above the minimum required voltage at VCC for proper operation of the LT C1734 controller 52 is 4 53 VDC and the USB specification states that for standard USB equipment under a high load i e 500 mA Veyre may be pulled as low as 4 35 V too low for the LTC1734 controller 52 to operate To prevent this the comparator 50 monitors Vorrg scaled down to a more useful voltage Vy by the voltage divider R1 and R2 fed to the inverting input of the comparator 50 and compares it to a reference voltage Vp which is fed to the comparator 50 s non inverting input Vp is derived by low pass filtering the LTC1734 control ler 52 s PROG pin output through resistor R5 and capacitor C2 as Veprog 1 5 VDC when the LTC1734 controller 52 is operating in the constant current mode R5 also serves to isolate other components from the LTC1734 controller 52 ensuring proper operation of the
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