LED Driver Circuit Uniform Brightness via Segmented Current Sink
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Solution Overview
Problem
Existing drive circuits for LED arrays fail to maintain constant brightness across different numbers of activated LEDs, resulting in noticeable brightness differences between grids due to varying voltage drops across low side drivers.
Innovation Solution
The implementation of a low side driver with a logic circuit that controls a plurality of selectively actuated current sink paths with equal sinking resistances, ensuring a constant voltage drop regardless of the number of actuated LED segments, combined with a high side driver responsive to segment control signals for current supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common cathode driver configuration is used with a single low side driver per grid, then the circuit complexity is reduced, but the voltage drop across the low side driver varies with the number of activated LEDs causing brightness non-uniformity
Solution Approach 1:
The low side driver is segmented into multiple parallel current sink paths (first current sink path, second current sink path, etc.), each with matched sinking resistances. This segmentation allows the driver to independently control current sinking for different segments of LEDs, compensating for variations in the number of activated LEDs and maintaining uniform brightness across the display.
2Illumination intensity
If multiple current sink paths with equal sinking resistances are used in the low side driver, then brightness uniformity is maintained across different numbers of activated LEDs, but the device complexity increases
Solution Approach 1:
The circuit utilizes parameter matching by designing multiple current sink paths with equal sinking resistances (R1=R2=...=Rn). This parameter uniformity ensures that each path handles current equally, maintaining constant voltage drops and consistent LED brightness regardless of how many LEDs are activated, while the overall structure remains relatively simple.
3Ease of operation
If the low side driver sinks current for all activated LEDs in a grid, then the common cathode configuration is maintained, but the voltage drop varies causing noticeable brightness differences between grids
Solution Approach 1:
Multiple current sink paths with matched resistances act as intermediaries between the common cathode node and ground. These intermediary paths distribute the current sinking function across multiple parallel channels, each handling a portion of the total current. This mediation maintains the simplicity of the common cathode configuration while ensuring uniform voltage drops and consistent brightness across all grids.
Data Source
AI summary
An LED array includes a plurality of LED segments connected in a common cathode configuration at a common cathode node. A high side driver is operable responsive to segment control signals to selectively supply current to certain LED segments. A low side driver is provided to sink current from the common cathode node. A plurality of selectively actuated current sink paths are provided in each low side driver. A control logic circuit actuates a current sink path within the low side driver for each LED segment that is selectively supplied current by the high side driver. A substantially constant low side voltage drop through these sink paths is provided regardless of the number of LED segments that are supplied current by the high side driver so as to achieve a substantially constant LED segment brightness. A common anode configuration operating in an analogous way is also disclosed.