LED Bypass Switches Reduce Flickering via Shift Timing
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Solution Overview
Problem
Conventional light emitting systems with serially connected LEDs experience flickering and stroboscopic effects due to switching, which degrade light quality and lead to EMC issues.
Innovation Solution
A light emitting apparatus with parallel bypass switches connected to each LED, controlled by a driving unit that adjusts shift timing to reduce voltage drop variations, using PWM signals to manage the on/off states of LEDs, ensuring smooth transitions and minimizing flickering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If light emitting elements are switched on/off to control illumination, then illumination control is achieved, but flickering and stroboscopic effects occur
Solution Approach 1:
The bypass switch is activated before the light emitting element is turned off, and remains active until after the element is turned on again. This preliminary action ensures continuous current flow through the bypass path during the transition period, preventing flickering and stroboscopic effects while maintaining illumination control.
Solution Approach 2:
The bypass switch acts as an intermediary component that provides an alternative current path when the light emitting element is switched. This mediator ensures continuous current flow during transitions, eliminating flickering while still allowing the element to be controlled for illumination purposes.
2Object-affected harmful factors
If bypass switches are connected in parallel to each LED, then flickering is reduced, but device complexity increases
Solution Approach 1:
The bypass function is segmented and distributed to individual light emitting elements rather than using a single centralized bypass mechanism. Each element has its own bypass switch, allowing independent control and reducing interference between elements, though this does increase the total number of components.
Solution Approach 2:
The bypass switch is combined with the driving control unit, integrating the flicker-reduction function into the existing control architecture. This merging approach consolidates control functions and reduces the need for separate dedicated bypass control circuits.
3Stability of the object's composition
If shift timing of bypass switches is adjusted, then voltage drop variation is reduced, but control complexity increases
Solution Approach 1:
The bypass switches are activated periodically during each PWM cycle, with the activation timing shifted relative to the light emitting element switching. This periodic activation with controlled shift timing smooths out voltage drop variations while the control logic remains integrated within the existing PWM control framework.
Solution Approach 2:
The shift timing parameter of the bypass switch activation is adjusted to optimize voltage drop stability. By changing the temporal parameter of bypass switch activation relative to the element switching, voltage variations are reduced without requiring fundamental changes to the control architecture.
Data Source
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AI summary
A light emitting apparatus (1) comprising a light emitting array (2) having at least one light emitting string (4) of serial connected light emitting elements (5), wherein a bypass switch (6) is connected in parallel to each light emitting element (5) of said light emitting string (4) and a driving control unit (3) controlling the shift timing of the bypass switches (6) to reduce a variation of a voltage drop across the light emitting string (4).