Abstract:
A charging circuit includes a fast transient input path to improve the transient response of the charging circuit and to avoid related problems such as inadvertent tripping of a power source. A charging circuit system and laptop computer including a charging circuit consistent with the invention is also provided. A method of allocating power from a power source configured to charge a battery includes sensing at least one predetermined supply parameter from a power source, providing a first control signal after a first time interval based on the sensing, providing a second control signal after a second time interval based on the sensing, wherein the second time interval is less than the first time interval, and regulating power to the battery based on at least one of the first and second control signals.

Description:
FIELD OF THE INVENTION 
     This invention relates to charging circuits for use in a variety of portable devices, and more particularly to a charging circuit with a fast transient input current path. 
     BACKGROUND OF THE INVENTION 
     Portable electronic devices such as laptop computers, cell phones, pagers, personal digital assistants, and the like are becoming a more common tool in today&#39;s society as the capabilities and uses of such devices continues to expand. Many portable electronic devices now include rechargeable batteries such as lithium, nickel-cadmium, or nickel-metal hydride batteries. 
     Some portable electronic devices may have integral charging circuits so that the battery may be recharged without removing the battery from the device. For instance, when the portable device is coupled to a power source, e.g., an AC/DC adapter providing a DC output voltage from a conventional 120 volt AC wall outlet, the charging circuit provides power to charge the battery. 
     The charging circuit may be further provided with a power allocation feature. In general, this power allocation feature serves to better utilize the power from a power source by varying the power provided to recharge the battery inversely with the power requirements for the rest of the portable device&#39;s system such that the sum of the two is within some maximum predetermined tolerance limits of the power source. For instance, with a constant voltage power source, the charging current level for the battery may be varied inversely with the current level required for the balance of the portable device&#39;s system to keep the sum within a predetermined maximum level of supply current from the power source. As such, unnecessary tripping of the power source should normally be prevented. 
     Such a power allocation feature typically has an input current path responsive to a sensed signal representative of the current provided by the power supply, a charging current path responsive to a sensed signal representative of the charging current provided to the portable device&#39;s battery, and a charging voltage path responsive to a sensed signal representative of the charging voltage provided to the portable device&#39;s battery. 
     However, the response time for the input current path and the charging current path is typically the same. Hence, the charging circuit is susceptible to transient conditions that may cause unintended tripping of the local power source. As fast load changes caused by high speed logic and microprocessors have increased, these transient conditions have also increased. For instance, the charging circuit may not be fast enough to decrease the charging current level to the battery in order to keep the local power source within a predetermined maximum parameter, e.g., current rating. Accordingly, there is a need in the art for a charging circuit with a power allocation feature having a fast transient input current loop. 
     BRIEF SUMMARY OF THE INVENTION 
     A charging circuit consistent with the invention includes: a first path configured to accept a signal representative of at least one supply parameter from an associated power source and provide a first control signal; a second path configured to accept the signal representative of the at least one supply parameter and provide a second control signal, wherein the second path has a faster transient response time than the first input path; a third path configured to accept a signal representative of at least one charging parameter from an associated battery and provide a third control signal; and a regulating circuit configured to accept the first, second, and third control signals and regulate the at least one charging parameter for the associated battery depending on at least one of the first, second, or third control signals. 
     A charging circuit system consistent with the invention includes: a power source having at least one predetermined supply parameter with a predetermined maximum rating; a battery; a sensor configured to sense the at least one predetermined supply parameter and provide a sense signal representative of the at least one parameter; and a charging circuit including: a first path configured to accept the sense signal and provide a first control signal; a second path configured to accept the sense signal and provide a second control signal, wherein the second path is configured to have a faster transient response time than the first path; and a third path configured to accept a signal representative of at least one charging parameter from the battery and provide a third control signal; and a regulating circuit configured to accept the first, second, and third control signals and regulate the at least one charging parameter for the battery depending on at least one of the first, second, or third control signals. 
     A laptop consistent with the invention includes: a CPU; a battery; and charging circuit including: a first path configured to accept a signal representative of at least one supply parameter from an associated power source and provide a first control signal; a second path configured to accept the signal representative of the at least one supply parameter and provide a second control signal, wherein the second path has a faster transient response time than the first input path; third path configured to accept a signal representative of at least one charging parameter from an associated battery and provide a third control signal; and a regulating circuit configured to accept the first, second, and third control signals and regulate the at least one charging parameter for the associated battery depending on at least one of the first, second, or third control signals. 
     A method of allocating power from a power source configured to charge a battery consistent with the invention includes the steps of: sensing at least one predetermined supply parameter from the power source; providing a first control signal after a first time interval based on the sensing; providing a second control signal after a second time interval based on the sensing, wherein the second time interval is less than the first time interval; and regulating power to the battery based on at least one of the first and second control signals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, together with other objects, features and advantages, reference should be made to the following detailed description which should be read in conjunction with the following figures wherein like numerals represent like parts: 
     FIG. 1 is a block diagram of an exemplary portable electronic device having a charging circuit consistent with the present invention; and 
     FIG. 2 is a more detailed block diagram of the charging circuit of FIG. 1 consistent with the invention. 
    
    
     DETAILED DESCRIPTION 
     Turning to FIG. 1, a block diagram of a portable device system  100  including a portable electronic device  104  and power source  102  is illustrated. The portable electronic device  104  may be any variety of devices including laptop computers, cell phones, pagers, personal digital assistants, and the like that require a self contained power source such as a rechargeable battery  108  which facilitate the portable nature of such devices. The rechargeable battery  108  may include such batteries as lithium, nickel-cadmium, nickel-metal hydride batteries, or the like. 
     If the portable electronic device  104  is a laptop computer it would include a variety of components known to those skilled in the art which are not illustrated in FIG.  1 . For example, the laptop may include an input device for inputting data to the laptop, a central processing unit (CPU) or processor, for example a Pentium processor available from Intel Corporation, for executing instructions and controlling operation of the laptop, and an output device, e.g., a LCD or speakers, for outputting data from the laptop. 
     To recharge the battery  108 , a power source  102 , e.g., a power converter, may be coupled to the portable electronic device  104 . For instance, the power source  102  may be an AC/DC adapter which is configured to receive conventional  120  volts AC from a wall outlet and convert it to a DC output voltage for the portable electronic device  104 . Such an AC/DC adapter may be rated to provide an output DC voltage at a maximum current rating, e.g., 24 volts DC at 1.5 amps. The power converter  102  may also be a DC/DC adapter such as a “cigarette lighter” type adapter configured to plug into that type of socket. Such a power source  102  is illustrated in FIG. 1 as separate from the portable electronic device  104 , but it may be built into some portable devices. 
     The DC power from the power source  102  may be accepted by a charging circuit  106  consistent with the present invention. The charging circuit  106  generally senses the power level provided by the power source  102  and the power level provided to the battery  108  while the battery is being recharged. Because the power requirements for the system circuitry  110  of the device  104  may vary with time, a charging circuit  106  consistent with the invention is configured with a power allocation feature to vary the power provided to the battery during charging such that the sum of the power drawn by the battery  108  during charging and the system circuitry  110  does not exceed the power rating of the power source  102 . Because the power source  102  typically has a constant output DC voltage, the power allocation feature typically monitors the charging current provided to the battery  108  and the supply current from the power source  102  to ensure that a predetermined maximum shutoff threshold of the power source  102  is not exceeded. The shutoff threshold is typically some percentage, e.g. 50%, above a maximum rating. 
     Turing to FIG. 2, an exemplary embodiment of a charging circuit  206  consistent with the present invention having a power allocation feature with a fast transient input current path as detailed further herein is illustrated. Such a fast transient input current path enables the battery charging circuit  206  to more quickly respond to transients that may otherwise result in unintended tripping of the power source  202 . 
     A plurality of control paths are provided within the charging circuit  206  for monitoring power consumption data and providing associated control signals to a regulating circuit  218 . The regulating circuit  218  is responsive to the control signals from the plurality of control paths to control a charging rate for the battery  208 . For instance, a charging current level or voltage level to the battery  208  may be modified to keep the power source  202  within predetermined power limits. 
     In particular, an input control signal from terminals  217 ,  219  to an input terminal  227  of the regulating circuit  218  having a normal or slower transient response may include a current sense amplifier  209 , and an error amplifier  211  as illustrated in FIG.  2 . Such a normal or slower transient response time is more typical for providing a control signal to a regulating circuit  218  including a DC-DC converter since it has the advantage of being stable. 
     Such a normal transient response path may accept a signal from a sense resistor  205  representative of the current supplied from the power source  202 , e.g., an AC/DC adapter or a DC cigarette type adapter. Such a signal may be the voltage drop across the sense resistor  205 , which would be proportional to the current supplied from the power source  202 . The current sense amplifier  209  accepts the signal from the sense resistor  205  and provides an output proportional to the voltage drop across the first sense resistor  205 . The error amplifier  211  generates a control signal for the regulating circuit  218  representative of the error or difference between a reference voltage level provided by a reference source  220  and the output from the current sense amplifier  209 . The regulating circuit  218  may then be responsive to such control signal to make adjustments to the power provided to charge the battery  208 . 
     Advantageously, another control signal path from terminals  217 ,  219  to an input terminal  227  of the regulating circuit  218  having a fast transient response is also provided in a charging circuit  206  consistent with the invention. This control signal path may include the current sense amplifier  209 , and an error amplifier  214 . As with the other normal transient response control signal path, the current sense resistor  205  and current sense amplifier  209  provide an amplified signal representative of the current supplied by the power source  202 . The error amplifier  214  then generates a fast transient control signal for the regulating circuit  218  representative of the error or difference between a reference voltage level, which may be provided by a fast reference source  222 , and the output from the current sense amplifier  209 . The reference voltage level provided by the fast reference source  222  should be about 25% greater than the value of the reference voltage provided by the normal reference source  220  in order not to be triggered by a normal system over-current. 
     In addition to the normal and fast transient control signal paths, additional control signal paths providing control signals representative of various operating conditions of the battery  208  may also be provided. For instance, a battery current path may provide a control signal representative of the charging or discharging current flow to and from the battery  208 , while a battery voltage path may provide another control signal representative of a voltage level of the battery  208 . The battery current path from terminals  248 ,  250  to an input terminal  227  of the regulating circuit  218  may include a current sense amplifier  226 , and an error amplifier  228  as illustrated in FIG.  2 . The sense resistor  207  provides a signal to the current sense amplifier  226  through terminals  248 ,  250  representative of the charging or discharging current provided to the battery  208 . This signal is equivalent to the voltage drop across the sense resistor  207 . 
     The current sense amplifier  226  accepts the signal from the sense resistor  207  and provides an output proportional to the voltage drop across the sense resistor  207 . The error amplifier  228  generates a control signal for the regulating circuit  218  representative of the error or difference between a reference voltage level provided by a reference source  220  and the output from the current sense amplifier  226 . The regulating circuit  218  may then be responsive to such control signal, e.g., to make any necessary adjustments to the charging current provided to the battery  208 . 
     In addition, the battery voltage path from terminal  252  to an input terminal  227  of the regulating circuit  218  may include a pair of resistors  216 ,  218  together with an error amplifier  244  configured to monitor the battery charging voltage. The pair of resistors  216 ,  218  form a voltage divider for scaling the voltage of the battery  208  to a voltage near that provided by the voltage reference source  220 . The error amplifier  244  may then provide a control signal to the regulating circuit  218  dependent on the difference between the voltage at node  233  and the voltage provided by the voltage reference source  220 . The regulating circuit  218  may then be responsive to this control signal to maintain battery voltage at desired levels. 
     The control signals from the various paths, including the fast transient input path, are all provided to the regulating circuit  218 . Such regulating circuit may be any variety of circuits known to those skilled in the art for controlling power levels provided to the battery  208 . One exemplary regulating circuit  218  may include a pulse width modulated (PWM) switching transistor circuit functioning as a DC-DC converter. The PWM signal may be generated by a comparator comparing the output signal from a respective error amplifier  211 ,  214 ,  228 , or  244  with an input ramp signal. The resulting PWM signal may then control a switching circuit to boost, e.g., with the switching transistor in parallel with the load, or buck, e.g., with a switching transistor in series with the load, the input DC voltage to the desired output DC voltage level. 
     For instance, when the charging circuit  206  is charging the battery  208 , switches  233  and  235  external to the charging circuit  206  may be closed. The various paths of the charging circuit  206  provide control signals to the regulating circuit  218  representative of the power conditions of the power source  202  and the charging power conditions for the battery  208 . The fast transient input control signal path may provide a control signal indicative of a supply current level greater than a predetermined maximum supply rating from the power source  202 . 
     Advantageously, the regulating circuit  218  is responsive to this control signal to quickly decrease the charging current provided to the battery  208 . In this way, the power source  202  may avoid an unintended trip that may otherwise occur if the charging current was not so quickly reduced. This occurs when the regulating circuit  218  is able to decrease charging current to the battery  208  quick enough so the total current from the system circuitry  210  and the battery charging current remains less than a predetermined maximum shutoff threshold for the power source  202 . For some power sources such as an AC/DC adapter, such a predetermined maximum shutoff threshold level may be about 50% higher than a normal maximum rating for the AC/DC adapter. 
     The embodiments that have been described herein, however, are but some of the several which utilize this invention and are set forth here by way of illustration but not of limitation. It is obvious that many other embodiments, which will be readily apparent to those skilled in the art, may be made without departing materially from the spirit and scope of the invention.