MOSFET Current Balancing Circuit for LED Strings
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Solution Overview
Problem
Traditional current balancing circuits for parallel LED strings are complex and susceptible to temperature changes, failing to ensure equal current distribution across strings with different voltage drops, which can lead to LED failure due to excessive current variation.
Innovation Solution
A current balancing circuit utilizing metal oxide semiconductor field effect transistors (MOSFETs) with a reference line and resistors to dynamically regulate current through each LED string, maintaining equal current flow despite varying voltage drops by adjusting the MOSFET Drain to Source Resistance (RDS) and using a constant power source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional current balancing circuits are used for parallel LED strings, then current distribution can be controlled, but the circuit complexity increases and precision current control requirements are needed
Solution Approach 1:
The patent introduces a reference line as an intermediary element that couples to a specific node in the LED string. This reference line serves as a mediator that allows the transistor gates to sense voltage conditions without requiring complex direct measurement circuits, thereby simplifying the overall circuit architecture while maintaining reliable current distribution control.
Solution Approach 2:
The patent replaces complex precision current control circuits with a simpler voltage-based control mechanism using MOSFET transistors. By utilizing the voltage drop across LEDs and the reference line to control transistor gate voltages, the system achieves current balancing through voltage regulation rather than complex current sensing and control circuits.
2Reliability
If traditional current balancing methods are used, then current control can be achieved, but the circuits are susceptible to temperature changes
Solution Approach 1:
The patent implements a feedback mechanism where the voltage drop across the LED string is continuously monitored through the reference line coupled to a node between LEDs. This voltage information feeds back to the transistor gates, allowing the circuit to automatically adjust and compensate for temperature-induced variations in LED characteristics, thereby maintaining stable current control under varying temperature conditions.
Solution Approach 2:
The patent exploits the natural relationship between voltage drop and current in LED strings. By controlling the gate voltages of the transistors based on the voltage drops across parallel LED strings, the system dynamically adjusts operating parameters to compensate for temperature effects, maintaining consistent current distribution despite temperature changes.
3Device complexity
If parallel LED strings with different voltage drops are connected directly, then circuit simplicity is maintained, but current distribution becomes unbalanced causing LED failure
Solution Approach 1:
The patent introduces dynamic control elements (MOSFET transistors) that can actively adjust their resistance based on real-time voltage conditions. The transistor gate voltages are dynamically controlled by the reference line voltage, allowing the circuit to adapt and balance current distribution across parallel LED strings with different voltage drops, preventing any single string from receiving excessive current.
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 provides even illumination across LED strings with differing voltage drops, minimizing heat power losses and ensuring consistent current distribution, thus preventing LED failure and maintaining performance across temperature variations.
Implementation Method 1
adjusting the MOSFET Drain to Source Resistance (RDS)
Implementation Method 2
multiple strings of light emitting diodes (LEDs)
Data Source
AI summary
A circuit includes a primary light emitting diode (LED) string, a secondary LED string, a reference line, and primary and secondary transistors. The primary string includes a voltage drop, and a node disposed between two adjacent LEDs of the primary string. The secondary string is configured in parallel with the primary string. The secondary string has a voltage drop that is less than the primary voltage drop. The reference line is coupled to the node. The primary transistor includes a drain, a gate, and a source. The drain is coupled to a primary string output terminal. The gate is coupled to the reference line, and the source is coupled to a ground. The secondary transistor includes a drain, a gate, and a source. The drain is coupled to a secondary string output terminal. The gate is coupled to the reference line, and the source is coupled to the ground.