PWM LED Driver Phase Shift Map for Current Ripple Reduction
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Solution Overview
Problem
High current load steps in LED lighting systems with many parallel connected LEDs can lead to voltage ripple, electromagnetic interference, and increased costs due to the need for large and expensive DC-DC converters, as well as complex thermal management and EMC issues.
Innovation Solution
A fixed phase shift map is applied to the duty-cycle values of LED pixels in a matrix, spreading the turn-on times over time to reduce current demand peaks, thereby minimizing load steps and avoiding undesirable effects like flicker and voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If many LEDs are connected in parallel to achieve high resolution light projection and matrix beam functionality, then the lighting system can provide advanced lighting effects and individual pixel control, but large current load steps occur causing voltage ripple and electromagnetic interference
Solution Approach 1:
The patent applies pulse width modulation (PWM) to control LED pixels periodically, switching them on and off in a time-multiplexed manner. This periodic action allows individual pixel control while distributing current demand over time, preventing large simultaneous current load steps that cause voltage ripple and electromagnetic interference.
Solution Approach 2:
The patent dynamically adjusts the turn-on timing of LED pixels within each PWM period based on their position in the matrix. By dynamically controlling when each pixel activates rather than having them all switch simultaneously, the system maintains individual pixel control capability while smoothing out current demand fluctuations.
2Power
If DC-DC converters are sized to handle peak current demands of parallel LED arrays, then sufficient power is available to drive all pixels, but the converters become large and expensive
Solution Approach 1:
By using PWM to periodically activate LED pixels instead of having them all on simultaneously, the peak power demand is reduced. This allows DC-DC converters to be sized for average power requirements rather than peak requirements, significantly reducing converter size and cost while still providing sufficient power capability when needed.
Solution Approach 2:
The system dynamically manages power delivery by controlling which pixels are active at any given time through PWM. This dynamic power management allows the power supply to operate at optimal efficiency levels and be sized appropriately for average load rather than peak load, reducing overall system cost and complexity.
3Ease of operation
If all LED pixels are switched on simultaneously during PWM dimming, then simple control logic is used, but large load steps occur causing thermal management issues and EMC problems
Solution Approach 1:
The patent implements PWM dimming where LED pixels are switched on and off periodically. By controlling the duty cycle of each pixel's activation within the PWM period, the system maintains simple control logic while preventing simultaneous switching of all pixels, thereby avoiding large load steps that cause thermal peaks and EMC issues.
Solution Approach 2:
The system dynamically staggers the turn-on timing of different LED pixels within each PWM period. This dynamic timing distribution simple yet effective - it spreads out the inrush current across multiple time slots rather than all at once, reducing thermal stress and electromagnetic interference while maintaining straightforward PWM control.
Data Source
AI summary
The disclosure describes techniques for driving a plurality of light emitting diodes (LEDs) arranged in a parallel connection by using PWM (Pulse Width Modulation) dimming. The techniques of this disclosure describe the generation and application of a fixed phase shift map to a driver matrix based on pixel position. Each pixel corresponds to an LED light source. In the fixed phase shift map, each pixel will have a pre-defined phase shift calculated to induce a determined variation in turn-on time for geometrically neighbouring pixels to spread out current demand over time during PWM dimming.