PWM Controller Circuit for LED String Color Consistency

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Solution Overview

Problem

Solid state lighting fixtures face challenges in achieving consistent color reproduction and brightness control due to variations in light emitting diodes, making it difficult to mimic the warm color behavior of incandescent lighting, especially at different brightness levels.

Innovation Solution

A solid state lighting apparatus with a string current Pulse Width Modulation (PWM) controller circuit that generates PWM signals with variable duty cycles to enable/disable string currents based on target color and brightness input signals, allowing for precise control of LED strings to achieve desired spectral power distribution and correlated color temperature.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If conventional solid state lighting fixtures use standard LED arrays, then energy efficiency is improved, but color consistency and brightness control are worsened

Engineering Contradiction:

Improveenergy efficiencyVSAvoidcolor consistency

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The LED array is divided into multiple independently controllable strings, each with its own current control circuit. This segmentation allows individual control of each string's brightness and color contribution, enabling precise color mixing and compensation for LED variations, thereby maintaining color consistency while preserving energy efficiency benefits

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system implements dynamic control of LED string currents through PWM modulation, allowing real-time adjustment of brightness and color temperature. This dynamic capability enables the fixture to maintain consistent color output across varying brightness levels by actively compensating for LED variations, resolving the contradiction between energy efficiency and color consistency

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If multiple LED strings are used to achieve color variation, then adaptability is improved, but device complexity is worsened

Engineering Contradiction:

Improvecolor temperature rangeVSAvoidcontrol circuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The control system is segmented into modular current control circuits, each dedicated to a specific LED string. This modular approach simplifies the overall control architecture by distributing functionality across independent units, making the system more adaptable while managing complexity through standardization

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each current control circuit is designed to be universal and multi-functional, capable of controlling any LED string regardless of its position or color characteristics. This universality reduces the need for specialized control circuits for each string, thereby expanding color temperature range without proportionally increasing device complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS9706611B2Solid state lighting apparatuses, circuits, methods, and computer program products providing targeted spectral power distribution output using pulse width modulation control

Publication Date: 2017.07.11 LED-IP MANAGEMENT LLC

AI summary

A solid state lighting apparatus can include a variable color input signal configured to indicate a target color of light output from the apparatus. A string current Pulse Width Modulation (PWM) controller circuit can be coupled to the variable color input signal, where the string current PWM controller circuit can be configured to generate a plurality of PWM signals having respective variable duty cycles to enable/disable respective particular string currents for respective variable times as the variable color input signal changes.