LED Current Balancing Circuit with Single-Input Fault Detection

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Solution Overview

Problem

Multi-string LED topologies in automotive lighting applications face issues with current imbalance and fault detection, leading to potential LED damage due to voltage variations and failures, which existing current balancing circuits and fault detection methods fail to address effectively.

Innovation Solution

A lighting device circuit incorporating a reference LED string, a mirror LED string, an operational amplifier-based current mirror circuit, and a window comparator circuit with a single fault sense node that balances current and detects faults by comparing voltage levels at the fault sense node to reference high and low voltages, excluding the need for differential amplifiers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If multi-string LED topology is used to reduce power consumption, then fuel consumption is reduced, but current imbalance occurs between LED strings causing brightness variation and potential LED damage

Engineering Contradiction:

Improvepower consumptionVSAvoidcurrent balance

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent implements a feedback mechanism using operational amplifiers that continuously monitor the current through each LED string and adjust the driving signals to maintain equal current distribution. The system measures actual current values and compares them against target values, then dynamically adjusts transistor gate voltages to correct any imbalances, ensuring reliable operation while maintaining the energy-efficient multi-string topology.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent dynamically changes electrical parameters (voltage and current) in real-time to maintain current balance. By adjusting the driving voltage and current parameters for each LED string based on measured conditions, the system compensates for variations in LED forward voltage and current characteristics, preventing both brightness variation and potential damage from excessive current.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If traditional fault detection methods are used, then multiple voltage comparisons are required, but circuit complexity increases with additional components

Engineering Contradiction:

Improvefault detection accuracyVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges multiple fault detection functions into a single integrated circuit node. By combining the voltage comparison functions and fault detection logic into one unified node that monitors both LED strings simultaneously, the system achieves comprehensive fault detection without requiring separate comparison circuits for each string, thereby reducing overall circuit complexity while maintaining high reliability.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent creates a universal fault detection node that serves multiple functions: it monitors voltage levels, detects faults in both LED strings, and provides balance verification. This single node performs what would traditionally require multiple specialized components, reducing circuit complexity while maintaining comprehensive monitoring capability across the entire LED assembly.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 achieves precise current balancing between LED strings with less than 1% matching error and accurate fault detection, preventing damage and ensuring reliable operation by generating a fault indication signal when voltage levels exceed or fall below predefined references.

Implementation Method 1

an operational amplifier based current mirror circuit coupled to the reference LED string and to the mirror LED string

Methodology Applied

Scientific EffectCurrent mirror:

Implementation Method 2

an operational amplifier based current mirror circuit

Methodology Applied

Scientific EffectOperational amplifier:

Implementation Method 3

a window comparator circuit that includes only a single input that is coupled to a fault sense node... comparing voltage levels at the fault sense node to reference high and low voltages

Methodology Applied

Scientific EffectVoltage comparison:

Data Source

PatentUS11849516B2Multi-string LED current balancing circuit with fault detection

Publication Date: 2023.12.19 TEXAS INSTRUMENTS INC

AI summary

A lighting device circuit comprising: a reference LED string, a mirror LED string coupled in parallel to the reference LED string, an operational amplifier based current mirror circuit coupled to the reference LED string and to the mirror LED string, and a window comparator circuit that includes only a single input that is coupled to a fault sense node. The fault sense node directly connects to a drain node of a transistor within the operational amplifier based current mirror and a LED within the mirror LED string.