LED Dimming Circuit Reference Control for Current Uniformity

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Solution Overview

Problem

Multiple strings of light emitting diodes (LEDs) are difficult to balance in terms of power due to voltage variations, even with tight voltage binning, resulting in large voltage differences between strings.

Innovation Solution

A balance circuit is employed that generates a reference voltage to control current through a first component string and tracks this current through additional component strings using resistors and field effect transistors, ensuring uniform current distribution across all strings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If voltage binning is employed to equalize LED string voltages, then voltage uniformity is improved, but large voltage differences still occur due to cumulative LED voltage variations

Engineering Contradiction:

Improvevoltage uniformityVSAvoidvoltage difference

Core Design Contradiction:

Stability of the object's compositionVSManufacturing precision

Solution Approach 1:

The patent employs feedback by using operational amplifiers to continuously monitor the voltage across each LED string and adjust the current accordingly. The op-amp compares the actual voltage with a reference voltage and modifies the current through the string to eliminate voltage differences, achieving uniform brightness across all strings.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the operating parameters by using variable current sources controlled by operational amplifiers to adjust the current through each LED string. This dynamic parameter adjustment compensates for voltage variations and ensures uniform voltage distribution across all strings.

Inventive Principle:

Principle #35Parameter changes

2Illumination intensity

If multiple LED strings are connected in parallel to increase brightness, then illumination intensity is improved, but current distribution becomes uneven leading to power imbalance

Engineering Contradiction:

ImprovebrightnessVSAvoidpower balance

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The patent uses feedback control through operational amplifiers that monitor the voltage across each parallel LED string and adjust the current distribution. This feedback mechanism ensures that each string receives the appropriate current to maintain uniform brightness and power balance across all parallel connections.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent segments the control of each LED string by providing individual current control circuits for each string. This segmentation allows independent adjustment of current to each string, ensuring uniform power distribution and preventing current imbalance in parallel configurations.

Inventive Principle:

Principle #1Segmentation

3Stability of the object's composition

If tight voltage binning is applied to reduce voltage variations, then voltage uniformity is improved, but manufacturing complexity and cost increase

Engineering Contradiction:

Improvevoltage uniformityVSAvoidbinning process

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The patent replaces complex pre-binning processes with a simpler feedback control system using operational amplifiers. This feedback mechanism dynamically adjusts current to compensate for voltage variations, achieving the same uniformity result without the need for tight voltage binning during manufacturing.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces operational amplifiers as intermediary control elements between the power source and LED strings. These intermediaries actively regulate current distribution to compensate for voltage variations, eliminating the need for complex binning procedures while maintaining voltage uniformity.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution allows for reliable and uniform dimming or brightening of all LED strings, maintaining current ratios to within less than 1% variation, effectively addressing the power balance issue.

Implementation Method 1

an operational amplifier which receives the reference voltage at one or more of its inputs and has an output coupled to a gate of the field effect transistor

Methodology Applied

Scientific EffectOperational amplifier voltage feedback control: Feedback

Implementation Method 2

a field effect transistor having a drain coupled to the second component string, an operational amplifier which receives the reference voltage at one or more of its inputs and has an output coupled to a gate of the field effect transistor

Methodology Applied

Scientific EffectField effect transistor conductivity control:

Implementation Method 3

a reference stage having an output node on which a reference voltage is generated to control current through a first component string and a first resistor connected to the first component string

Methodology Applied

Scientific EffectOhm's law: Ohm's Law

Data Source

PatentUS10897799B1Dimming circuit with reference control

Publication Date: 2021.01.19 APOGEE LIGHTING HLDG LLC

AI summary

A balance circuit includes a node on which a reference voltage is generated to control current through a first component string and a first resistor connected to the first component string. A stage receives the reference voltage to generate a tracking current through a second component string and a second resistor connected to the second component string, wherein a current through the first component string is uniformly tracked by the tracking current through the second component string.