Flash LED Current Derating Using Local Junction Temperature Sensing
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Solution Overview
Problem
Current power management integrated circuits (PMICs) for mobile devices face challenges in thermal management due to elevated chip temperatures caused by concurrent operation of power-dissipating modules, leading to potential thermal shutdown and errors in current derating operations, particularly in modules like the Flash LED, where temperature alarms output voltage that needs conversion to current and may be distant from the module, causing latency and derating errors.
Innovation Solution
The method involves monitoring the local junction temperature of a module, converting it into a local junction current, comparing it with a reference current, and derating the current if it exceeds the reference to prevent thermal overloading, using a temperature sensor, current reference generator, current comparator, derating control generator, and LED current driver for automatic and smooth temperature derating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If voltage conversion is used to convert temperature alarm output to current for derating operation, then current derating can be implemented, but the process becomes complex and requires large look-up tables
Solution Approach 1:
The patent extracts the temperature sensing function directly into the LED driver circuit, eliminating the need for separate voltage-to-current conversion circuits and large look-up tables. The temperature sensor is integrated within the LED driver module, allowing direct current derating control without complex external processing.
Solution Approach 2:
The patent combines the temperature sensing function with the LED driver circuit into a single integrated module. This merging eliminates the need for separate voltage conversion circuits and simplifies the derating operation by providing direct current control based on local temperature feedback.
2Ease of manufacture
If temperature sensor is placed far from LED module, then integrated circuit design is simplified, but temperature measurement accuracy decreases
Solution Approach 1:
The patent implements local temperature sensing by placing the temperature sensor directly within the LED driver module, close to the LED components. This local quality approach ensures accurate temperature measurement of the specific module that requires derating, rather than using a remote general temperature sensor.
Solution Approach 2:
The patent segments the temperature sensing function to be distributed across multiple LED driver modules, with each module having its own local temperature sensor. This allows independent temperature monitoring and derating control for each module, improving overall system thermal management accuracy.
3Reliability
If current derating is implemented to prevent thermal overload, then thermal management is improved, but the control process becomes more complex
Solution Approach 1:
The patent implements self-service thermal management by integrating temperature sensing and derating control within the LED driver module itself. The module autonomously monitors its own temperature and adjusts its current accordingly, eliminating the need for complex external control systems.
Solution Approach 2:
The patent establishes a local feedback loop where the temperature sensor continuously monitors the LED driver module temperature and feeds this information back to the derating controller. This closed-loop feedback enables automatic current adjustment based on real-time temperature conditions, improving thermal management reliability.
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 provides efficient thermal management with reduced latency and errors, enabling flexible and automatic current derating, a compact design, and low cost, ensuring smooth operation of modules like the Flash LED by directly using temperature sensing for derating control, allowing precise control of derate thresholds and slopes.
Implementation Method 1
monitoring a local junction temperature of a module
Implementation Method 2
The local junction temperature is converted into a local junction current
Data Source
AI summary
A method and apparatus for derating current and for derating current for a camera flash. The method comprises monitoring a local junction temperature of a module. The local junction temperature is converted into a local junction current. The local junction current is then compared with a reference current, which is independent of temperature. After the current comparison and subtraction is made, a derate control current is obtained to generate the LED reference current. After the temperature crosses the temperature threshold, the derate control current is derated. Both the temperature threshold and current derate slope are programmable and precisely controlled. The LED output current is regulated and proportional to the LED reference current. If the local junction temperature is greater than the temperature threshold, the LED output current is derated at the moment of the camera flash to avoid thermal overload.