Variable Master Current Mirror for LED String Balancing
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Solution Overview
Problem
In LED-based illumination devices, current imbalance among parallel LED strings with different forward voltage characteristics leads to inefficient operation, where one string may be under-driven while another is over-driven, affecting efficiency and reliability.
Innovation Solution
A variable master current mirror circuit is implemented, which includes a switching circuit and a current mirror circuit to dynamically balance currents across LED strings by identifying the string with the largest forward voltage and adjusting the current flow accordingly, ensuring equal currents through all strings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple LED strings are connected in parallel to a common current source, then the illumination device can provide sufficient total current, but current imbalance occurs among LED strings due to differences in forward voltage
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary between the common current source and multiple LED strings. The current mirror circuit receives a reference current and replicates it to provide equal currents to each LED string, thereby eliminating current imbalance caused by forward voltage differences while maintaining sufficient total current output.
Solution Approach 2:
The patent employs a variable master current mirror that dynamically adjusts the reference current based on the forward voltage characteristics of LED strings. By changing the reference current parameter in response to detected forward voltage levels, the system maintains optimal current distribution across all LED strings under varying operating conditions.
2Productivity
If LED strings with different forward voltages are connected in parallel, then more current flows through strings with lower forward voltage, but this causes overdriving and reduces LED lifetime
Solution Approach 1:
The patent implements a feedback mechanism where the system detects the forward voltage of each LED string and uses this information to adjust the current distribution. The current mirror circuit responds to forward voltage variations by modifying reference currents, ensuring that no LED string receives excessive current that would reduce its lifetime.
Solution Approach 2:
The patent uses a variable master current mirror that dynamically adapts to changing forward voltage conditions of LED strings. Instead of using fixed current values, the system continuously adjusts reference currents based on real-time forward voltage detection, maintaining optimal operating conditions for LED longevity.
3Illumination intensity
If LED strings with different forward voltages are connected in parallel, then some LED strings operate below their full light generating potential, but increasing current to these strings causes overdriving of other strings
Solution Approach 1:
The current mirror circuit acts as an intermediary that decouples the relationship between LED strings with different forward voltages. By providing independently controlled reference currents to each string through the current mirror, the system enables all strings to operate at their full light generating potential without causing overdriving of other strings.
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 prevents over-driving of LEDs during short failures, maintains balanced current flow, and extends the lifespan of LEDs by ensuring optimal operation across all strings, thereby enhancing efficiency and reliability.
Implementation Method 1
The current mirror circuit maintains equal currents through the LED strings with reference to the current through the master LED string
Data Source
AI summary
A variable master current mirror circuit may be used to balance the currents through parallel Light Emitting Diode (LED) strings in an illumination module when the LED string with the largest forward voltage changes due to events, such as a short failure of an LED. The variable master current mirror circuit includes a switching circuit that is coupled to the parallel LED strings and a current mirror circuit that is coupled to the parallel LED strings and the switching circuit. The switching circuit switchably connects the LED string with the largest forward voltage to the current mirror circuit as a master LED string. The current mirror circuit maintains equal currents through the LED strings with reference to the current through the master LED string.