Flash Driver Current Control for Battery Droop Prevention
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Solution Overview
Problem
Handheld electronic devices with flash capabilities often experience battery droop due to high current draw from the LED camera flash, leading to device resets or shutdowns, as existing methods rely on worst-case assumptions and do not accurately estimate sustainable flash current.
Innovation Solution
A method and apparatus that determine the desired maximum flash current by calculating equivalent series resistance (ESR) and voltage values based on temperature and active loads, using a current sensor to adjust the flash current to prevent battery voltage drops, ensuring sustainable operation without resetting the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the LED camera flash operates at high current to provide sufficient light output, then the illumination intensity is improved, but the battery voltage drops causing device resets or shutdowns
Solution Approach 1:
The system performs preliminary measurements of battery voltage, temperature, and equivalent series resistance (ESR) before initiating the flash. Based on these measurements, the controller pre-calculates the maximum sustainable flash current that will not cause battery droop below the shutdown threshold, allowing the flash to operate at optimal intensity without risking device reset
Solution Approach 2:
The system dynamically adjusts flash operating parameters (current, duration) based on real-time battery conditions including voltage, temperature, and ESR. By changing these parameters adaptively rather than using fixed worst-case values, the system maximizes flash output while maintaining battery voltage above critical thresholds
2Reliability
If worst-case battery conditions are assumed to prevent battery droop, then device reliability is improved, but the flash current is limited below optimal levels reducing light output
Solution Approach 1:
The system implements feedback by continuously monitoring battery voltage, temperature, and ESR during flash operation. Based on this feedback, the controller adjusts the flash current in real-time to maintain battery voltage above the shutdown threshold while extracting maximum possible light output, eliminating the need for conservative worst-case assumptions
Solution Approach 2:
The system replaces conservative mechanical/design-based current limiting with an intelligent control system that uses sensor measurements and calculations to dynamically determine optimal flash current. This substitution of fixed mechanical limits with adaptive electronic control allows maximum light output while preventing battery droop
3Reliability
If the flash current is reduced to prevent battery droop, then device reliability is improved, but the illumination intensity decreases
Solution Approach 1:
The system transitions from static fixed current limiting to dynamic current adjustment. The flash current is continuously optimized based on real-time battery conditions, allowing maximum power consumption when battery capacity permits and reduced current only when necessary to prevent droop, thereby maximizing both reliability and light output
Data Source
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AI summary
A handheld electronic device (2,52,52') includes a processor (4); a battery (6); a flash device (10); a number of loads (14) powered by the battery; and a flash driver (16) outputting a flash current (12) to the flash device. The processor determines (83,30,32) a temperature (18) operatively associated with the battery and different voltage values (20) corresponding to different combinations of the loads as a function of the determined temperature, and starts (36) the flash device at a predetermined flash current value. The flash driver selects (38) a corresponding different voltage value as a function of: (a) a determined number of the loads which are active, or (b) a current flowing from the battery; determines (40) the battery voltage, and if the battery voltage is less than or equal to the corresponding different voltage value, reduces (42) the flash current below the predetermined flash current value until the battery voltage is greater than the corresponding different voltage value,