LED Driver Apparatus Forward Voltage Degradation Detection
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Solution Overview
Problem
Conventional protective circuits for LED arrays in LCDs often incorrectly determine degradation due to slow settling times or abnormal forward voltages, leading to erroneous open or short circuit detections.
Innovation Solution
An LED driving apparatus that extends the ON time of the dimming signal, delays the inputted dimming signal by 100 ns to 1000 ns, and measures the forward voltage at the declining edge to accurately detect LED array degradation by using a detection unit with comparators and flip-flops to determine if the LED array is open or short.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the conventional protective circuit measures forward voltage during normal operation, then the circuit can detect LED array degradation, but the measurement is affected by slow settling time of the constant current source and peak current effects, leading to erroneous detection
Solution Approach 1:
The patent applies preliminary action by turning off the constant current source before measuring forward voltage. This ensures that the measurement is taken after the settling time has elapsed and peak current effects have subsided, eliminating the sources of measurement error while maintaining reliable degradation detection
Solution Approach 2:
The patent introduces a control signal as an intermediary to coordinate the timing between the constant current source operation and the forward voltage measurement. This control signal ensures that measurement occurs only after the current source is turned off, separating the measurement process from the conditions that cause measurement errors
2Measurement precision
If the forward voltage is measured during the section where voltage drops due to slow settling time, then the measured voltage is higher than normal, but the protective circuit erroneously determines LED array short circuit
Solution Approach 1:
The patent turns off the constant current source before measurement to ensure that the forward voltage is measured after settling time has elapsed and peak current effects have disappeared, preventing erroneous high voltage readings that would indicate false short circuit conditions
Solution Approach 2:
The patent uses feedback by monitoring the forward voltage measurement results and comparing them against expected ranges. When the measurement is taken at the correct timing (after current source off), the feedback mechanism can accurately distinguish between normal voltage levels and actual degradation conditions, preventing false information loss
3Measurement precision
If the forward voltage is measured when voltage drops close to 0V due to peak current, then the measured voltage is lower than normal, but the protective circuit erroneously determines LED array open circuit
Solution Approach 1:
The patent turns off the constant current source before measuring forward voltage to eliminate peak current effects. This ensures that the measurement is taken when voltage has stabilized and is not artificially suppressed, preventing erroneous low voltage readings that would indicate false open circuit conditions
Solution Approach 2:
The patent employs feedback by comparing the measured forward voltage against predetermined thresholds. When measurement is performed at the correct timing (after current source off), the feedback mechanism can reliably distinguish between normal low voltage states and actual open circuit degradation, preventing false information loss
Data Source
AI summary
A Light Emitting Diode (LED) driving apparatus and a method of driving a LED backlight unit are provided. An LED driving apparatus includes: an input unit configured to receive a dimming signal, an extension unit configured to extend ON time of the inputted dimming signal, an LED driving unit configured to drive an LED array using the extended dimming signal, and a detection unit configured to detect a degradation of the LED array by measuring a forward voltage between the LED array and the LED driving unit.