LED Dimming Inductor Charge Transfer Control

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Solution Overview

Problem

Existing LED dimming techniques lose current control and can cause flicker or result in LEDs appearing off at very low dimming settings, leading to inefficiencies and inaccurate dimming levels.

Innovation Solution

The implementation of 'extended charge transfer' and 'supplemental charge transfer' techniques, which allow the inductor to maintain connection to the voltage source until target current is reached and enable additional switching cycles during off-times, respectively, to maintain current control and precise dimming without flicker.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If conventional LED dimming techniques are used at very low dimming settings, then energy consumption is reduced, but current control is lost and flicker occurs

Engineering Contradiction:

Improveenergy consumptionVSAvoidcurrent control

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent applies preliminary action by pre-charging the output capacitor during the PWM off-time through the inductor before the PWM on-time begins. This preparatory charge transfer ensures that sufficient charge is available at the start of each PWM cycle, enabling stable current control even at very low dimming levels where traditional methods fail.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements continuity of useful action by extending charge transfer operations into the PWM off-time period. The inductor continues to transfer charge to the output capacitor during what would traditionally be a non-productive interval, ensuring continuous energy delivery to maintain LED current control without interruption or flicker.

Inventive Principle:

Principle #20Continuity of useful action

2Illumination intensity

If PWM duty cycle is reduced for deep dimming, then illumination intensity is reduced, but current control accuracy deteriorates

Engineering Contradiction:

Improvedimming levelVSAvoidcurrent control accuracy

Core Design Contradiction:

Illumination intensityVSMeasurement precision

Solution Approach 1:

By pre-charging the output capacitor during PWM off-time, the system ensures that each PWM on-time cycle starts with sufficient energy储备, enabling accurate current control even when the on-time duration is very short due to deep dimming requirements.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the timing parameters of charge transfer operations, extending them beyond the traditional PWM on-time window to include the off-time period. This parameter extension allows the system to accumulate sufficient charge even when PWM duty cycles are reduced for deep dimming, maintaining current control accuracy across the full dimming range.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If inductor connection time is extended to maintain current control, then energy delivery efficiency improves, but switching frequency increases

Engineering Contradiction:

Improvecurrent controlVSAvoidswitching frequency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent implements periodic action by organizing charge transfer operations into regular cycles that alternate between PWM on-time and off-time periods. The inductor performs charge transfer during designated intervals within each cycle, maintaining current control through rhythmic, predictable switching patterns rather than continuous operation.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

By utilizing both on-time and off-time periods for charge transfer, the system maintains continuous useful action throughout the entire switching cycle. The inductor alternates between charging and discharging phases, ensuring energy delivery continues without interruption while operating at efficient switching frequencies.

Inventive Principle:

Principle #20Continuity of useful action

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

Enables deep dimming of LEDs without losing current control, ensuring consistent and accurate dimming levels even at very low settings, preventing flicker and maintaining efficient energy delivery.

Implementation Method 1

A PWM switch can be used to connect and disconnect the one or more LEDs with a node that can be coupled to the output of the switching regulator circuit... In an inductive switching regulator circuit, an inductor can be used as an energy storage element

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS10123384B1LED dimming

Publication Date: 2018.11.06 ANALOG DEVICES INT UNLTD CO

AI summary

Techniques are provided for low, or deep, dimming of a light-emitting diode (LED) load. In an example, a method for deep dimming a light-emitting diode (LED) load can include, when a current of an inductor does not reach a target current by the end of an on-time of a pulse-width modulation (PWM) switch cycle, and, during an initial on-time of the PWM switch cycle, allowing the current of the inductor to reach the target current during a next “off” time interval of the PWM switch cycle, wherein the inductor is coupled to the LED via a PWM switch, and in response to the current of the inductor reaching the target current before the end of the on-time of a subsequent PWM switch cycle, interrupting energizing of the inductor at the end of the on-time of the PWM switch cycle.