Unbalanced LED Driver with Common Return Resistor
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing driver circuits for white light emitting diodes (WLEDs) in portable devices face challenges in maintaining uniform current flow and brightness, often requiring high-voltage power supplies or complex current mirror circuits that increase cost and may not ensure uniformity among WLEDs.
Innovation Solution
A driver system with multiple current sources, each coupled to a common return resistor and controlled by feedback voltage, allowing current to flow during non-overlapping time periods to maintain consistent current through parallel branches of series-coupled LEDs, using control logic to regulate the current flow and adjust the supply voltage dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If WLEDs are connected in series to ensure uniform current flow, then uniformity of current through WLEDs is improved, but voltage requirement increases and may exceed available power supply voltage
Solution Approach 1:
The patent divides the series-connected WLED string into multiple parallel branches, with each branch containing a subset of WLEDs. Current sources are assigned to each branch to independently control current flow, enabling uniform brightness distribution while operating at lower voltage levels that match available power supplies.
Solution Approach 2:
The patent introduces current sources as intermediary components between the power supply and WLED branches. These current sources act as mediators that regulate and distribute current uniformly across all WLEDs, eliminating the need for high-voltage series connection while maintaining current uniformity.
2Manufacturing precision
If current mirror circuits are used to match current through parallel WLED branches, then current uniformity is improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent implements self-service through feedback control mechanisms where each current source monitors its own output current through sense resistors and automatically adjusts to maintain uniform current distribution. This eliminates the need for complex external current mirror circuits while achieving the same current matching function.
Solution Approach 2:
The patent employs feedback control by connecting sense resistors in series with each WLED or branch and feeding back the voltage signals to control logic. The control logic adjusts current source outputs based on these feedback signals, ensuring uniform current distribution without requiring complex current mirror circuitry.
3Manufacturing precision
If current mirror circuits are used to ensure uniform current flow, then brightness uniformity among WLEDs is improved, but device cost increases significantly
Solution Approach 1:
The patent replaces expensive current mirror circuits with simpler, cheaper components including basic current sources, sense resistors, and feedback control logic. This substitution significantly reduces device cost while maintaining the ability to achieve uniform brightness across all WLEDs through feedback-based current regulation.
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 achieves uniform brightness across multiple WLEDs with reduced power supply voltage requirements, lower component size, and increased efficiency, while extending the operational life of the LEDs by maintaining consistent current levels and reducing cumulative photon production and junction temperature.
Implementation Method 1
The magnitude of the current flowing through each current source is substantially the same and is regulated based upon a feedback voltage across the common return resistor
Data Source
AI summary
The present disclosure describes systems and methods for driving light emitting diodes (LEDs). At least some embodiments include an LED driver system that includes a power supply, a plurality of current sources (each current source coupled between a common return resistor and one of a plurality of branches of series coupled LEDs, and each branch coupled between a corresponding current source and the power supply), and control logic coupled to the current sources (the control logic capable of controlling the current flow through each current source). Each of the current sources allows current to flow during one of a plurality of substantially non-overlapping time periods within a repeating time interval, each current source allowing current to flow during a different time period. The magnitude of the current flowing through each current source is substantially the same and is regulated based upon a feedback voltage across the common return resistor.