LED Control Circuit Sigma Delta Modulation EMI Reduction
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Solution Overview
Problem
Conventional LED control circuits using pulse width modulation result in high current peaks and electromagnetic interference (EMI), leading to uneven brightness distribution and optical interference in backlight systems, particularly when synchronized with video signals.
Innovation Solution
A control circuit employing sigma delta modulation with a combiner generating a control signal from a data signal and a noise signal, diversifying the switching times of LED strings to reduce EMI and achieve more even brightness distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse width modulation is used to control LED brightness, then LED brightness can be controlled, but high current peaks and electromagnetic interference occur
Solution Approach 1:
The patent applies periodic action by using pulse width modulation to control LED strings, switching them on and off periodically to achieve desired brightness levels. The switching is synchronized with video signal timing, creating regular periodic patterns that can be coordinated across multiple LED strings to reduce electromagnetic interference while maintaining brightness control.
Solution Approach 2:
The patent divides the backlight system into multiple independent LED strings that can be controlled separately. Each LED string is switched independently based on synchronization signals, which segments the overall current draw and electromagnetic interference into smaller, more manageable components that can be distributed over time.
2Reliability
If LED strings are switched synchronously with video signals, then synchronization is achieved, but optical interference and uneven brightness distribution occur
Solution Approach 1:
The patent applies local quality by introducing slight variations in the switching timing of different LED strings while maintaining overall synchronization with video signals. This creates local deviations from perfect synchronization that distribute the optical energy more evenly across the display, preventing the dark bands that would result from perfectly synchronized switching.
Solution Approach 2:
The patent introduces dynamic elements by varying the switching timing of LED strings in a controlled manner. Rather than fixed synchronous switching, the system dynamically adjusts switching times to distribute brightness more evenly while maintaining coordination with the video signal timeline.
Data Source
AI summary
A control circuit for controlling light emitting diodes comprises a switch for turning on or off a string of light emitting diodes. A combiner generates a control signal from a data signal and a noise signal. A sigma delta modulator receives the control signal and a clock signal with a clock period and generates a switching signal for controlling the switch.