Adaptive Current Limiting for Power Sources with ESR
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Solution Overview
Problem
In battery-operated systems, high load currents can cause system voltage drops, leading to reduced operating time and erratic behavior, as existing methods require calculating equivalent series resistance (ESR) to determine maximum loadable current, which is complex and not always accurate, especially with changing loads during events like camera flashes or TDMA transmission bursts.
Innovation Solution
The MAXFLASH method adapts load current by monitoring system voltage and using a comparator to adjust output current in increments, eliminating the need for ESR measurement during events like camera flashes, ensuring minimum system voltage is maintained by reducing current when voltage drops and increasing when it rises, using a block diagram and timing mechanisms to manage current effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high load current is drawn from the battery to charge the flash capacitor quickly, then charging speed is improved, but system voltage drops below the threshold for stable operation due to internal ESR
Solution Approach 1:
The patent implements dynamic current limiting that adapts to changing battery conditions. The current limit is not fixed but varies based on real-time voltage measurements and calculated ESR values. This allows the system to maximize charging current when battery conditions permit while automatically reducing current when voltage stability becomes compromised, resolving the contradiction between charging speed and voltage stability.
Solution Approach 2:
The system continuously monitors system voltage during flash capacitor charging and uses this feedback to calculate ESR in real-time. Based on the calculated ESR and current voltage level, the system dynamically adjusts the current limit for subsequent charging cycles. This closed-loop feedback mechanism ensures that charging current is optimized while maintaining system voltage above the stable operation threshold.
2Reliability
If system cut-off voltage is set artificially high to provide margin above unreliable operation point, then voltage stability is improved, but operating time is reduced
Solution Approach 1:
Instead of using a fixed, conservative cut-off voltage that reduces operating time, the patent dynamically determines the safe operating voltage threshold based on real-time ESR calculations. The system calculates the maximum allowable current draw that maintains voltage stability and adjusts the effective cut-off point accordingly. This allows the system to operate closer to the battery's true capacity limits while maintaining reliability.
Solution Approach 2:
The patent changes the parameter used for determining safe operation from a fixed voltage threshold to a dynamic threshold based on calculated ESR and current load conditions. By using ESR-based current limiting rather than voltage-based cut-off, the system can maintain more accurate voltage control throughout the battery discharge cycle, extending usable operating time while ensuring stability.
3Measurement precision
If ESR measurement and calculation are performed to determine maximum loadable current, then current management accuracy is improved, but device complexity increases due to additional hardware and software
Solution Approach 1:
The patent implements self-service by using the battery system's own operational characteristics (voltage drop during loading) to calculate ESR. Rather than requiring external measurement equipment, the system uses its built-in ADC and existing load structures to perform self-diagnosis and self-regulation. The ESR is calculated from voltage measurements taken during normal operation, eliminating the need for separate measurement hardware.
Solution Approach 2:
The patent changes the approach to ESR measurement from requiring dedicated high-precision measurement hardware to using standard ADC measurements taken during normal operation. By calculating ESR from voltage drops during controlled loading sequences that occur during normal device operation, the system achieves accurate current management without adding specialized measurement equipment or complex software routines.
4Measurement precision
If additional high precision high speed ADC and software are added to measure voltage drop and calculate ESR, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses its existing ADC to perform self-measurement of voltage drops during normal operation. Rather than adding external high-precision measurement equipment, the battery management system uses its own computational resources and existing sensing capabilities to calculate ESR from operational data. This self-service approach achieves accurate measurement without increasing hardware complexity.
Solution Approach 2:
The patent makes the existing ADC serve multiple functions: it is used both for normal voltage monitoring during operation and for measuring voltage drops to calculate ESR. By making the ADC multi-functional rather than adding a dedicated high-precision measurement ADC, the system achieves accurate ESR measurement capability without increasing hardware complexity or cost.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach maximizes output current without calculating ESR, extending battery life by maintaining stable system voltage during high-demand events, such as camera flashes or TDMA bursts, by dynamically adjusting current based on real-time voltage feedback, thus preventing voltage drops and optimizing battery usage.
Implementation Method 1
a comparator to adjust output current in increments, eliminating the need for ESR measurement during events like camera flashes
Data Source
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AI summary
Adaptive current limiting for any power source to limit power drain of one load on the power source to maintain a minimum power source voltage for proper operation of other loads on the power source. For battery applications, such as for flash systems, the invention allows the maximum output current of a boost converter to be utilized without having to calculate the system equivalent series resistance first. The invention also adjusts the current load up or down during a high load event to compensate for changes in other loads. The changes in current load are made in increments, with a hysteresis region avoiding constant up and down incrementing.