Patent ID: 7633234

Claim:
A method for maintaining a maximum sustainable flash current over the 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 the steps of: (a) measuring the voltage across the battery under normal system load; (b) initiating the flash at a given current; (c) measuring the voltage across the battery with flash plus normal system load; (d) calculating the flash current at the battery; (e) calculating an equivalent series resistance (ESR) of the battery from the voltages measured across the battery under normal system load and under normal system load plus flash and the current calculated at the battery; (f) calculating a new ESR value for a pre-selected time period after step (e), within the length of the flash, based on known ESR characteristics for that type of battery; (g) calculating a new flash current based on the new ESR value; and (h) adjusting the flash current upwards or downwards to approximate the new flash current.