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Method and apparatus for maximizing the sustainable flash of a handheld portable electronic device

  • US 7,777,809 B2
  • Filed: 09/28/2007
  • Issued: 08/17/2010
  • Est. Priority Date: 09/28/2007
  • Status: Active Grant
First Claim
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1. A method for maintaining a maximum sustainable flash current over a whole length of a flash using a programmable current drive in a handheld portable device powered by a battery of a given type, that places other variable loads on the battery, in addition to the flash, comprising:

  • (a) measuring a voltage across the battery (Vb1) under normal system load;

    (b) determining if a high current load (Ihighload1) occurred during the measurement taken in (a);

    (c) initiating the flash at a given current;

    (d) measuring a voltage across the battery with flash (Vb2) after a first pre-selected period after the flash is initiated;

    (e) determining if the high current load (Ihighload2) occurred during the measurement taken in (d);

    (f) calculating an equivalent series resistance (ESR) of the battery at the end of the first pre-selected period, from the voltages measured across the battery under normal system load and under normal system load plus flash using the formula—

    ;

    E



    S



    R
    = [ V b



    1
    - V b



    2
    I flash +



    I highload



    1
    -



    I highload



    2
    ]
    ;

    (g) calculating a new ESR value for a second pre-selected period after calculating the ESR in (f), within the length of the flash, based on known ESR characteristics for that type of battery;

    (h) calculating a maximum current allowed from the battery (IMax) and subtracting any high current loads that can occur during the flash using the formula—

    I Max = [ V b



    1
    - V Min
    E



    S



    R



    2



    nd
    ]
    -



    I highcurrent
    where ESR2nd is the ESR calculated for the end of the second pre-selected period; and

    (i) adjusting the flash current upwards or downwards to approximate the IMax.

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