Temperature Dependent LED Current Controller
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Solution Overview
Problem
Existing LED backlight systems in electronic displays face reliability issues due to varying ambient temperatures, which limit the maximum current that can be applied to LEDs, leading to potential catastrophic failure and increased costs, as traditional solutions like temperature regulation devices are costly, bulky, and not widely adopted.
Innovation Solution
A controller using temperature sensing diodes to detect ambient temperature changes and adjust the current through LEDs, allowing operation at or near maximum safe current levels without the need for negative temperature coefficient resistors, integrated as a single or multiple integrated circuit chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If LED current is increased to improve luminous intensity, then light output increases, but reliability deteriorates due to high probability of catastrophic failure at or near IMAX
Solution Approach 1:
The patent applies dynamics by making the LED current adaptive rather than static. The controller continuously monitors ambient temperature and dynamically adjusts the LED current accordingly. Below TSLP, the controller maintains current at or near IMAX for maximum luminous intensity. Above TSLP, it reduces current to stay below the decreasing IMAX threshold, preventing catastrophic failure while maximizing light output within safe operating limits.
Solution Approach 2:
The patent applies parameter changes by varying the LED operating current based on ambient temperature conditions. The system changes the current parameter from a fixed high value (near IMAX) when temperature is low, to a reduced value when temperature exceeds TSLP. This parameter adaptation allows the system to achieve high luminous intensity when safe and maintain reliability when temperature conditions require current reduction.
2Reliability
If LED current is reduced to operate within safe operating area at high temperatures, then reliability improves, but luminous intensity decreases requiring more LEDs
Solution Approach 1:
The system dynamically adjusts current based on temperature: operating at high current (near IMAX) when temperature is below TSLP to maximize luminous intensity, and automatically reducing current when temperature exceeds TSLP to maintain reliability. This eliminates the need for permanently reduced current operation and avoids requiring additional LEDs.
3Reliability
If temperature regulation devices are added to control LED ambient temperature, then LED current can be maintained at maximum safe levels, but device complexity and cost increase
Solution Approach 1:
The patent extracts the temperature sensing function from separate temperature regulation devices and integrates it directly into the LED driver circuitry. By using temperature sensing diodes built into the driver IC, the system obtains temperature information without adding external temperature regulation components, thereby maintaining LED safety while avoiding increased device complexity.
Solution Approach 2:
The LED driver circuit serves itself by incorporating temperature sensing capability directly into its structure. The temperature sensing diodes are part of the driver IC, allowing the circuit to autonomously monitor its own operating conditions and adjust current accordingly, eliminating the need for separate temperature regulation devices.
4Illumination intensity
If more LEDs are used to compensate for reduced current at high temperatures, then luminous intensity is maintained, but manufacturing cost increases
Solution Approach 1:
The system uses dynamic current adjustment to maintain adequate luminous intensity without requiring additional LEDs. By operating at high current when temperature is low and reducing current only when necessary above TSLP, the system maximizes the utilization of existing LEDs, avoiding the need to manufacture displays with higher LED counts.
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
Enables efficient regulation of LED current at or near maximum allowable levels across a wide temperature range, reducing the risk of failure and eliminating the need for expensive temperature regulation devices, while being cost-effective and integratable on a single chip.
Implementation Method 1
The present invention provides a controller for regulating current in light emitting diodes (LEDs) in electronic displays. The controller uses temperature sensing diodes to detect changes in the LED ambient temperature.
Implementation Method 2
As the LED ambient temperature changes, the forward voltage of the temperature sensing diode decreases.
Data Source
AI summary
The present invention provides a controller for regulating current in LEDs in electronic displays. The controller uses temperature sensing diodes to detect changes in the LED ambient temperature. As the LED ambient temperature changes, the forward voltage of the temperature sensing diode decreases. A signal processor adjusts the current passing through the LEDs based on the temperature induced changes in the forward voltage of the temperature sensing diodes. The present invention can reduce costs over the present methods of regulating current in LEDs and may more easily be integrated into a single integrated circuit chip. The temperature sensing may also be implemented outside the integrated circuit chip.