Method and apparatus for maximizing the sustainable flash of a handheld portable electronic device
A method and apparatus for maintaining a maximum sustained flash current over the whole length of a flash using a programmable current drive in a handheld portable device powered by a battery. The method involves measuring the battery voltage before and after a flash is initiated and calculating the equivalent series resistance (ESR) of the battery. The calculated ESR is then used to adjust the flash current. The process may be repeated to correct for errors in the flash current.
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 (V b1 ) under normal system load;
(b) determining if a high current load (I highload1 ) occurred during the measurement taken in (a);
(c) initiating the flash at a given current;
(d) measuring a voltage across the battery with flash (V b2 ) after a first pre-selected period after the flash is initiated;
(e) determining if the high current load (I highload2 ) 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 (I Max ) 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 I Max .
2. The method of claim 1 further including repeating (d) through (i) during the length of the flash.
3. The method of claim 2 further including the step of repetitively repeating (d) through (i) during the length of the flash.
4. The method of claim 2 wherein (d) through (i) are first performed approximately 2 ms from a start of the flash and are repeated at approximately 4 ms from the start of the flash.
5. The method of claim 1 wherein the handheld portable device has a feature that when active applies a given operating load and the measurements in (a) and (d) take into account the given operating load whether the feature is active or not.
6. The method of claim 5 wherein the given operating load is a WIFI TX/RX load and the measurements in (a) and (d) take into account the WIFI TX/RX load whether active or not.
7. The method of claim 1 wherein the given current is approximately 500 mA.
8. The method of claim 1 wherein the flash current is adjusted in (i) within 3 ms of initiating the flash.
9. The method of claim 1 including sampling the battery voltage at pre-selected intervals throughout the flash duration to assure that a battery droop due to ESR follows a predicted path and does not reset the device.
10. The method of claim 9 wherein the pre-selected interval is approximately every 2-3 ms.
11. The method of claim 1 wherein the flash is an LED flash.
12. The method of claim 1 wherein the flash is an OLED flash.
13. The method of claim 1 including sampling the voltage across various points in a circuit in the handheld device to assure that operation of the handheld device is not compromised.
14. The method of claim 13 wherein sampling is performed at pre-selected time intervals.
15. The method of claim 14 wherein the pre-selected time intervals are approximately every 3 ms.
16. A handheld portable device powered by a battery of a given type comprising:
a flash device;
a programmable current drive;
a voltage measuring device for measuring a voltage across the battery under normal system load when a flash command is first initiated and before the flash is initiated (V b1 );
a device for determining if a high current load (I highload1 ) occurred during the measurement of V b1 ;
a voltage measuring device for measuring a voltage across the battery under normal system load plus flash at first pre-selected period after the flash is initiated (V b2 );
a device for determining if the high current load (I highload2 ) occurred during the measurement of V b2 ;
a calculating device for calculating a first 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 V b1 and under normal system load plus flash (V b2 ) using the following formula—
E
S
R
=
[
V
b
1
-
V
b
2
I
flash
+
∑
I
highload
1
-
∑
I
highload
2
]
;
a calculating device for calculating a new ESR value for a second pre-selected period after the ESR calculated at the end of the first pre-selected period is calculated, within the length of the flash, based on known ESR characteristics for that type of battery;
a calculating device for calculating a maximum current allowed from the battery (I Max ) 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
wherein ESR2nd is the ESR calculated for the end of the second pre-selected period; and
wherein the programmable current drive is programmed to adjust the flash current upwards or downwards to approximate I Max .
17. The handheld portable device of claim 16 wherein the flash device is an LED.
18. The handheld portable device of claim 16 wherein the flash device is an OLED.