LED Drive Circuit Offset Correction for Small Current Accuracy
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Solution Overview
Problem
Existing LED drivers face challenges in maintaining accuracy at small currents due to comparator offset, leading to unwanted light emission and electromagnetic noise, especially when packaged as an IC, where cost-effective offset countermeasures are limited.
Innovation Solution
Incorporating a detecting means, comparing means, and a driving voltage source with an offset correction mechanism, utilizing a constant current source and additional resistors to detect and correct the current flowing through the LED, ensuring accurate current control even with offset comparators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a comparator is used to control current through the LED, then current control function is achieved, but comparator offset causes unwanted current flow at small currents
Solution Approach 1:
A second resistor is introduced as an intermediary component in series with the LED and first resistor. This additional resistor enables voltage detection at a point that allows the comparator to accurately sense the voltage across the first resistor even when the LED current is small, thereby preventing unwanted current flow caused by comparator offset while maintaining current control functionality.
2Adaptability or versatility
If pulse-width modulation is used to generate multiple tones, then brightness control is achieved, but electromagnetic noise increases
Solution Approach 1:
The patent employs pulse-width modulation with periodic switching to control LED brightness. By modulating the duty cycle of periodic current pulses rather than using continuous current adjustment, the system achieves multiple brightness levels while the periodic nature of the signal helps contain electromagnetic noise within predictable frequency bands, reducing overall noise impact.
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 allows precise control of current through the LED at small currents, reducing electromagnetic noise and cost, while maintaining performance in low-current regions without the need for complex IC adjustments.
Implementation Method 1
a light-emitting element such as a light-emitting diode (LED)
Implementation Method 2
the LED 1 emits light
Data Source
AI summary
A drive device for a light-emitting element that improves accuracy while driving the light-emitting element at small currents for which a comparatively simple configuration is provided. The drive device includes detecting means, comparing means, a driving voltage source, and offset means. The detecting means detects a voltage corresponding to a current flowing through a first resistor for current detection. The first resistor is coupled to a light-emitting element in series. The comparing means compares a magnitude of the detection voltage of the detecting unit with a comparison voltage. The driving voltage source applies a voltage corresponding to a comparison result by the comparing means to a series circuit of the light-emitting element and the first resistor. The offset means corrects the voltage corresponding to a current flowing through the first resistor by a correction voltage.