LED Drive Circuit with Negative Resistance Temperature Sensing
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Solution Overview
Problem
Existing LED drive circuits for small-size portable devices face challenges in maintaining sufficient luminance at room temperature without causing thermal damage to LED elements, as they must reduce current to prevent overheating, leading to the need for multiple LEDs to achieve adequate brightness.
Innovation Solution
An LED drive circuit that includes a constant-current output unit and a temperature sensing element with a negative resistance-temperature characteristic, connected in parallel to the LED element, allowing current division and adjustment based on temperature changes, ensuring the LED operates close to its allowable forward current without exceeding it at higher temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant current value is set to prevent thermal damage at high temperatures, then the LED element is protected from thermal damage, but the luminance at room temperature becomes insufficient
Solution Approach 1:
The patent applies the dynamics principle by introducing a temperature sensing element with negative resistance-temperature characteristic that automatically adjusts the current distribution between itself and the LED element based on temperature changes. At room temperature, most current flows to the LED element for high luminance; at high temperature, current automatically shifts to the temperature sensing element to protect the LED, eliminating the need for fixed conservative current settings.
Solution Approach 2:
The patent utilizes parameter changes by exploiting the temperature-dependent resistance characteristic of the temperature sensing element. The resistance of this element changes with temperature, which dynamically alters the current division ratio in the parallel circuit. This allows the system to adapt current distribution according to temperature conditions, achieving both high luminance at room temperature and thermal protection at elevated temperatures.
2Illumination intensity
If multiple LED elements are used to achieve sufficient luminance, then the luminance requirement is met, but the device size and component count increase
Solution Approach 1:
The patent introduces a temperature sensing element as an intermediary component that mediates current distribution to protect the LED element. This intermediary allows a single LED element to operate at higher currents safely by diverting excess current through the temperature sensing element when needed, thereby achieving sufficient luminance without requiring multiple LED elements.
3Reliability
If a constant current circuit is designed for high temperature operation, then thermal damage is avoided, but the current value must be much smaller than the allowable forward current at room temperatures
Solution Approach 1:
The patent applies partial action by using the temperature sensing element to absorb excess current that would otherwise be harmful to the LED element. The constant current output unit outputs a current that is larger than what the LED element alone can safely handle, and the temperature sensing element partially diverts this current based on temperature conditions, allowing the system to utilize higher current output while still protecting the LED.
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 configuration enables a higher current through the LED at room temperature while reducing current as temperature increases, achieving sufficient luminance without thermal damage and minimizing the number of LEDs required, thus optimizing performance and reducing component count in portable devices.
Implementation Method 1
a temperature sensing element with a negative resistance-temperature characteristic
Data Source
AI summary
An LED drive circuit that sufficiently exhibits the performance of an LED element to obtain a favorable luminance at room temperature, includes a constant-current circuit including an LED element, a constant-current output unit, and a temperature sensing element having a negative resistance-temperature coefficient. The LED element is connected to the constant-current output unit in series. The constant-current output unit is connected to the LED element in parallel. Due to changes in the resistance value of the constant-current output unit caused by changes in temperature, the value of a current passing through the LED element is increased at room temperature and the value of a current passing through the temperature sensing element is reduced at high temperature.