Single Inductor LED Driver Current Regulation
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Solution Overview
Problem
Existing LED string drivers face inefficiencies in current regulation across multiple LED strings due to voltage mismatches, leading to power loss and increased heat generation, and require multiple inductors, which increase costs.
Innovation Solution
A single inductor multiple LED string driver with a switch control circuit and current-sensing control circuit generates digital control signals to regulate the on-time of LED switches, using a time-shared Single-Inductor-Multiple-Output (SIMO) architecture to pump current equally into each LED string, eliminating power loss from voltage differences and reducing the need for multiple inductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple separate switching converters with separate inductors are used for each LED string, then current regulation precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges multiple separate inductors into a single shared inductor that serves all LED strings. The controller alternately switches between different LED strings, allowing one inductor to perform the current regulation function for multiple strings sequentially, thereby reducing component count and complexity while maintaining regulation precision
Solution Approach 2:
The controller implements periodic switching between different LED strings connected to the same inductor. By alternately enabling different strings in a cyclic manner and regulating current to each during its active period, the system achieves precise current control for multiple strings using a single inductor
2Measurement precision
If separate current syncs are used for each LED string, then current matching is improved, but power loss increases due to voltage differences
Solution Approach 1:
The patent merges multiple separate current sync circuits into a single shared current sync circuit. This unified current sync regulates current for multiple LED strings sequentially, eliminating the redundant voltage drops that would occur across multiple separate current sync circuits, thereby reducing power loss while maintaining current matching
3Device complexity
If resistor ballasting is used for multiple LED strings, then device complexity is reduced, but current matching deteriorates due to voltage mismatches
Solution Approach 1:
The patent implements a feedback mechanism where the controller monitors the current through the shared inductor and adjusts the switching duration for each LED string accordingly. This closed-loop feedback ensures that despite using a single inductor and avoiding resistor ballasting, precise current matching is achieved by dynamically adjusting each string's active time based on real-time current measurements
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 ensures equal average current across all LED strings, reduces power loss, and lowers costs by using a single inductor, improving efficiency and matching currents without additional DC-to-DC conversion.
Implementation Method 1
A single inductor multiple LED string driver comprises a switch control circuit and a current-sensing control circuit. The switch control circuit generates a plurality of digital control signals that are used to control a plurality of LED switches coupled to a plurality of strings of LEDs... through a common inductor... to ground
Data Source
AI summary
A single inductor multiple LED string driver comprises a switch control circuit and a current-sensing control circuit. The switch control circuit generates a plurality of digital control signals that are used to control a plurality of switches coupled to a plurality of strings of LEDs. Each switch is selectively turned on and off by each corresponding digital control signal. The current-sensing control circuit determines an integrated charge amount provided by each current that flows from an input voltage through each LED string, through each switch, through a common inductor, and through a main switch to ground. In response to the determined integrated charge amount, the current-sensing control circuit generates an on-time control signal that controls the on-time of each switch such that the average current flowing across each LED string is equal to each other. Furthermore, the total current flowing across each LED string is regulated to a predefined value.