LED Driver Circuit Current Balance and Voltage Regulation

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Solution Overview

Problem

LED backlight systems face issues with current differential among LEDs due to varying resistances, leading to variable luminance and potential damage, especially when a high power supply voltage is required, and existing over-voltage protection methods limit the number of LEDs in each string.

Innovation Solution

An LED driver circuit incorporating a switch-mode converter, controller, and feedback circuit with current and voltage sensing mechanisms, along with a gating circuit, to regulate and balance the current and voltage across multiple LED strings, ensuring consistent output and protecting against over-voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If over-voltage protection is implemented to prevent damage to LEDs during open circuit, then LED reliability is improved, but the number of LEDs in each string is limited

Engineering Contradiction:

ImproveLED reliabilityVSAvoidnumber of LEDs in each string

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent divides the LED backlight system into multiple parallel LED strings, each with its own current sensing and control mechanism. This segmentation allows the system to handle high total LED counts while maintaining safe voltage levels across individual strings through distributed control architecture.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements feedback control by sensing the voltage across each LED string and using this information to adjust the drive current accordingly. The feedback mechanism ensures that even with many LEDs in parallel, the voltage remains within safe limits, resolving the contradiction between reliability and quantity.

Inventive Principle:

Principle #23Feedback

2Illumination intensity

If a high power supply voltage is used to drive serially coupled LEDs, then the luminance output is improved, but the LED driver circuit has to tolerate high voltage stress

Engineering Contradiction:

Improveluminance outputVSAvoidvoltage stress on driver circuit

Core Design Contradiction:

Illumination intensityVSStress or pressure

Solution Approach 1:

The patent segments the high-voltage requirement across multiple parallel LED strings rather than concentrating it in a single long series string. Each string operates at a manageable voltage level, and the combined luminance output is achieved through parallel configuration, reducing voltage stress on individual driver circuit components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs dynamic current adjustment based on real-time voltage sensing in each LED string. The driver circuit dynamically modifies drive current to maintain optimal operating conditions, allowing high luminance output while preventing excessive voltage stress through adaptive control.

Inventive Principle:

Principle #15Dynamics

3Ease of manufacture

If the resistance of a particular LED is different from others, then manufacturing tolerance is improved, but current differential leads to variable luminance and potential damage

Engineering Contradiction:

Improvemanufacturing toleranceVSAvoidLED consistency

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent implements local quality control by providing individual current sensing and control for each LED string. This allows the system to accommodate manufacturing tolerances and resistance variations in individual LEDs while maintaining consistent overall performance through localized adjustment mechanisms.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The feedback control mechanism senses the actual current in each LED string and adjusts the drive signal to compensate for resistance variations. This ensures that even though manufacturing tolerances cause individual LED differences, the overall luminance remains consistent and reliability is maintained through active compensation.

Inventive Principle:

Principle #23Feedback

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 solution effectively balances current and voltage across LED strings, preventing damage and maintaining consistent luminance, even with varying resistances, while allowing for a larger number of LEDs to be used without over-voltage issues.

Implementation Method 1

The switch-mode converter comprises a power transfer device and a switch device

Methodology Applied

Scientific EffectSwitch-mode conversion:

Implementation Method 2

The feedback circuit comprises a current sensing circuit, a voltage sensing circuit

Methodology Applied

Scientific EffectVoltage sensing:

Implementation Method 3

The feedback circuit comprises a current sensing circuit, a voltage sensing circuit

Methodology Applied

Scientific EffectCurrent sensing:

Implementation Method 4

LEDs are a type of solid state semiconductor devices capable of converting electrical power into visible light

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS8907592B2Power systems for driving light emitting diodes and associated methods of control

Publication Date: 2014.12.09 MONOLITHIC POWER SYSTEMS INC

AI summary

Embodiments of LED driver circuits and the associated methods are disclosed herein. In one embodiment, the LED driver circuit comprises a switch-mode converter, a controller, a feedback circuit, and a gating circuit. The feedback circuit includes a current balance circuit. The gating circuit is responsive to both a current feedback signal and a voltage feedback signal and is configured to select one of them as the feedback signal.