LED Drive Circuit Calibration for Brightness Stability
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Solution Overview
Problem
Existing semiconductor integrated circuits for driving white LED arrays face challenges in generating optimum drive voltage amidst temperature fluctuations and variations in LED characteristics, leading to reduced power efficiency and instability.
Innovation Solution
A semiconductor integrated circuit with a DC-DC converter, current driver, and logic unit that includes a D/A converter to generate a reference voltage based on detection signals from abnormality detectors, allowing for calibration of output DC voltages to maintain constant LED drive currents and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the output DC voltage is not adjusted for temperature fluctuations and LED characteristic variations, then the circuit structure remains simple, but the light emitting brightness becomes unstable and power consumption increases
Solution Approach 1:
The patent implements a feedback mechanism where abnormality detectors monitor the actual drive voltage to each LED, and this detection signal is fed back to the logic unit. The logic unit processes this feedback and adjusts the D/A converter output accordingly, creating a closed-loop control system that automatically compensates for temperature fluctuations and LED characteristic variations, thereby stabilizing light emitting brightness without requiring complex external circuitry
Solution Approach 2:
The system performs self-calibration through the calibration operation executed by the logic unit. The abnormality detectors continuously monitor LED performance, and when deviations are detected, the system automatically adjusts the drive voltage through the D/A converter without requiring external intervention. This self-service mechanism enables the circuit to maintain optimal performance autonomously, balancing brightness stability with circuit simplicity
2Illumination intensity
If the output DC voltage is increased to compensate for LED variations, then the light emitting brightness is maintained, but the power consumption increases
Solution Approach 1:
The patent employs dynamic voltage adjustment where the output DC voltage is not fixed but continuously adapted based on real-time feedback from abnormality detectors. The logic unit dynamically modifies the D/A converter output to provide only the necessary voltage increase to maintain brightness, rather than applying a constant high voltage. This dynamic approach ensures power is consumed only when and to the extent needed for brightness compensation, optimizing energy efficiency
Solution Approach 2:
The system changes the drive voltage parameter dynamically based on detected LED characteristics and temperature conditions. By adjusting the voltage parameter in response to actual device performance rather than using a fixed conservative value, the system achieves brightness stability while minimizing unnecessary power consumption increases
3Reliability
If a fixed reference voltage is used for driving LEDs, then the circuit operation is simple, but the drive voltage becomes suboptimal under varying temperature and LED characteristics
Solution Approach 1:
The patent implements a calibration operation that performs preliminary characterization of each LED's forward voltage characteristic. During this initial phase, the logic unit applies test voltages and measures actual LED responses, storing this information for subsequent operation. This preliminary action enables the system to establish optimized drive parameters before normal operation begins, improving voltage optimality without adding complexity to the ongoing drive mechanism
Solution Approach 2:
The reference voltage transitions from a static fixed value to a dynamic adjusted value through the D/A converter controlled by the logic unit. The system dynamically modifies the reference voltage based on calibration data and real-time feedback from abnormality detectors, enabling optimal drive voltage generation that adapts to temperature and LED variations while maintaining relatively simple circuit architecture
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
The solution enables the generation of optimal drive voltage for LEDs, stabilizing light emitting brightness and reducing power consumption across varying temperatures and LED characteristics, ensuring consistent performance and efficiency.
Implementation Method 1
The principle of light emission or luminescence thereof utilizes an electro-luminescence (EL) effect
Implementation Method 2
a fluorescent-material type white light emitting diode has a structure in which a chip for a light emitting diode is coated with a luminescent material
Data Source
AI summary
A DC-DC converter supplies an output voltage to a plurality of channels of a light emitting device array in common. A current driver has a plurality of driver units which drive the channels. Each of the driver units includes a drive transistor and a detector which detects an abnormality of a drive current. A logic unit generates digital data in response to a plurality of detection signals and supplies the same to a D/A converter. An analog reference voltage of the D/A converter is supplied to the DC-DC converter. The logic unit executes a calibration operation which determines digital data for setting the minimum output DC voltage at the normal operation of all the channels by sequential updating of the digital data.