LED Matrix Current Demand Reduction via Staggered PWM Activation
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Solution Overview
Problem
The current pulse width modulation method for LED matrices results in high maximum current demand with steep edges, leading to increased harmonics and a heavy load on the current source, which can be disadvantageous for EMC and power supply systems, especially in large LED matrix applications.
Innovation Solution
The method involves adjusting the activation and deactivation points of LEDs within an elementary period to stagger their activation times, allowing some LEDs to be activated one after the other and dividing activation periods if necessary, to reduce simultaneous activation at the beginning of the period, thereby reducing the maximum current demand and step changes in the current profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If all LEDs are activated simultaneously at the beginning of the elementary period, then the LED matrix achieves full brightness quickly, but the current source experiences high maximum current demand with steep edges
Solution Approach 1:
The activation of LEDs is segmented into different time slots within the elementary period. Instead of activating all LEDs simultaneously, the patent divides them into groups that are activated sequentially. This segmentation of the activation process reduces the peak current demand while maintaining the overall brightness output of the LED matrix.
Solution Approach 2:
The patent employs periodic activation patterns where LEDs are activated in cycles throughout the elementary period. By distributing the activation events periodically across the period rather than concentrating them at the beginning, the current demand is smoothed out, reducing maximum current peaks while still achieving the desired brightness levels.
2Device complexity
If all LEDs are activated simultaneously, then the control system is simple to implement, but harmonics increase due to steep current edges
Solution Approach 1:
The control system is segmented to manage different LED groups with different activation timings. This segmentation allows for reduced harmonics by avoiding simultaneous activation of all LEDs, which creates steep current edges. The increased control complexity is minimal and justified by the significant reduction in electromagnetic interference.
3Power
If activation periods are staggered to reduce maximum current demand, then the load on the current source is reduced, but the activation control becomes more complex
Solution Approach 1:
The patent implements periodic activation patterns where LEDs are activated at regular intervals throughout the elementary period. This periodic approach simplifies the control logic compared to arbitrary staggering, as it follows a predictable pattern that can be easily implemented with standard PWM controllers, while still effectively reducing the maximum current demand on the power source.
Data Source
AI summary
A method for reducing the maximum demand of the current received by an LED matrix from a current source. Each LED of the LED matrix receiving a pulse width-modulated current from the current source, an activation period being assigned to each LED in an elementary period of the pulse width-modulated current, and/or a deactivation period is assigned, in which no current flows through the LED, the activation period and the deactivation period being able to be equal in length or shorter than the elementary period, and in the case that the activation period assigned to one of the LEDs and the deactivation period assigned to this LED are shorter than an elementary period, the activation period begins at an activation point in time and ends at a deactivation point in time, and the deactivation period begins at the deactivation point in time and ends at the activation point in time.