LED Driver Dimming Strategy for Flicker Reduction

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Solution Overview

Problem

Conventional LED lighting systems face inefficiencies and flicker issues due to high active current values, which lead to increased noise, heat, and color variations when dimming, especially at lower brightness levels, as they maintain full active current values even during dimming, causing inductors to operate in discontinuous conduction mode and resulting in reduced efficiency and increased flicker.

Innovation Solution

Implementing a dimming strategy with two modes of operation: an active value varying mode for higher dimming levels and a duty cycle modulation mode for lower dimming levels, allowing the LED current to be reduced to an intermediate active value and further modulated, ensuring continuous conduction mode operation and minimizing peak current, thereby reducing noise and flicker.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If full active current values are maintained during dimming, then LED brightness can be controlled across full range, but noise and flicker increase due to inductors operating in discontinuous conduction mode

Engineering Contradiction:

Improvedimming control rangeVSAvoidnoise and flicker

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent changes the operating parameters of the LED driver by maintaining a minimum active current threshold while using duty cycle modulation to achieve dimming. This keeps the inductor in continuous conduction mode, eliminating the harmful discontinuous mode operation that causes noise and flicker, while still providing full dimming range control.

Inventive Principle:

Principle #35Parameter changes

2Illumination intensity

If high active current values are used during dimming, then LED can be driven at various brightness levels, but heat generation and color variations increase

Engineering Contradiction:

ImproveLED brightness levelsVSAvoidheat generation

Core Design Contradiction:

Illumination intensityVSTemperature

Solution Approach 1:

The patent modifies the current control strategy by establishing a minimum active current threshold that prevents the inductor from entering discontinuous conduction mode. This parameter change allows brightness control through duty cycle modulation rather than active current reduction, thereby maintaining lower operating temperatures and reducing LED color variations while providing full dimming range.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If duty cycle modulation is used at low dimming levels, then peak current is minimized, but complex two-mode control strategy is required

Engineering Contradiction:

Improvepeak current reductionVSAvoidcontrol strategy complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent segments the dimming control into two distinct modes: active current control for higher brightness levels and duty cycle modulation for lower brightness levels. This segmentation allows each mode to operate optimally in its respective range, minimizing peak current at low dimming levels while providing a structured approach to managing control complexity through clear mode transitions.

Inventive Principle:

Principle #1Segmentation

4Ease of operation

If inductors operate in discontinuous conduction mode, then full dimming range is achieved, but efficiency is reduced

Engineering Contradiction:

Improvefull dimming rangeVSAvoidsystem efficiency

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The patent changes the fundamental operating parameter by maintaining a minimum active current that prevents the inductor from entering discontinuous conduction mode. This parameter modification enables the system to achieve full dimming range through duty cycle modulation while maintaining continuous conduction mode operation, thereby preserving system efficiency throughout the entire dimming range.

Inventive Principle:

Principle #35Parameter changes

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 proposed solution enhances efficiency by maintaining continuous conduction mode, reducing noise and flicker, and achieving a full range of dimming with lower LED current values, resulting in improved performance and reduced operational complexities.

Implementation Method 1

LEDs are semiconductor devices and are driven by direct current. The lumen output intensity (i.e. brightness) of the LED approximately varies in direct proportion to the current flowing through the LED.

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS7759881B1LED lighting system with a multiple mode current control dimming strategy

Publication Date: 2010.07.20 SIGNIFY HOLDING BV

AI summary

A light emitting diode (LED) lighting system includes a controller to control current in one or more LEDs in response to a dimming level input. The LED lighting system implements a dimming strategy having two modes of operation that allow the LED lighting system to dim the LEDs using an active value of an LED current less than a full value LED current while maintaining continuous conduction mode operation. In an active value varying mode of operation, the controller varies an active value of the LED current for a first set of dimming levels. In an active value, duty cycle modulation mode of operation, the controller duty cycle modulates an active value of the LED current for a second set of dimming levels. In at least one embodiment, the active value of the LED current varies from a full active value to an intermediate active value as dimming levels decrease.