Current Split Circuit for LED String Uniformity
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Solution Overview
Problem
Existing LED lighting systems face challenges in achieving equal current distribution between parallel-connected LED strings due to manufacturing variations, leading to uneven illumination and potential overheating, which is not resolved by current binning methods and limits dimming capabilities.
Innovation Solution
A current splitting circuit using transistors, specifically a reference channel and copy channels with bipolar transistors arranged as a current mirror, ensures equal current distribution between LED strings, eliminating the need for binning and allowing dimming in both pulse width modulation and continuous modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If LEDs are connected in parallel to achieve desired supply voltage, then the lighting system can operate within voltage limits, but the current distribution becomes unequal due to manufacturing variations
Solution Approach 1:
The patent uses a current mirror circuit that copies the current from a reference LED string to multiple parallel LED strings. The mirror transistors replicate the reference current, ensuring equal current distribution without requiring manual binning or matching of LED forward voltage characteristics.
Solution Approach 2:
The current mirror circuit acts as an intermediary between the power supply and the parallel LED strings. It mediates the current distribution by using the reference string as a template, automatically adjusting current allocation to maintain equality across all parallel strings despite manufacturing variations.
2Manufacturing precision
If LED strings are binned to achieve equal illumination, then current distribution improves, but manufacturing complexity and cost increase
Solution Approach 1:
Instead of manually binning LEDs during manufacturing, the patent uses a current mirror circuit that automatically copies the reference current to all parallel strings. This eliminates the need for complex binning processes while achieving the same current distribution uniformity.
Solution Approach 2:
The current mirror circuit performs self-adjustment by automatically sensing the reference current and replicating it across all parallel strings. The system self-regulates current distribution without requiring external intervention or complex manufacturing processes.
3Illumination intensity
If one LED string carries more current (hot channel), then illumination increases, but temperature rises causing thermal instability and potential damage
Solution Approach 1:
The current mirror circuit provides automatic feedback control by continuously monitoring the reference current and adjusting the current to all parallel strings accordingly. This feedback mechanism prevents any single string from drawing excessive current, thereby preventing thermal runaway and junction temperature instability.
Solution Approach 2:
The current mirror circuit proactively prevents thermal instability by equalizing current distribution before temperature deviations can occur. By ensuring equal current flow from the start, the system prevents the formation of hot channels that could lead to thermal runaway.
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 uniform illumination with less than 2% variation in LED strings, reduces manufacturing costs by eliminating binning, and enables dimming capabilities in both PWM and continuous modes, while reducing the overall system voltage.
Implementation Method 1
a current split circuit including a reference channel in series with a first string of LEDs and one or more copy channels, each in series with another string of LEDs, each copy channel tapping a portion of a voltage at the reference channel to substantially reduce the voltage required to power the lighting circuit
Data Source
AI summary
A system and method for equally splitting the current supplied to parallel connected strings of LEDs. The system and method includes a current splitting circuit such as a mirror circuit that divides the current substantially equally between two or more parallel connected strings of LEDs. The current splitting circuit ensures that illumination levels of the strings of LEDs are uniform without requiring the strings of LEDs to be binned. The current splitting circuit also allows the strings of LEDs to be dimmed in both pulse width modulation (PWM) and continuous modes.