Pulsed-Output LED Driver Randomized Pulse Density Modulation
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Solution Overview
Problem
Conventional methods for dimming LEDs powered by constant voltage drivers cause variations in correlated color temperature and inconsistent dimming ranges, leading to visually detectable lumen variations and potential LED failure due to uneven forward voltage distribution.
Innovation Solution
A pulsed-output constant voltage LED driver utilizing randomized Pulse Density Modulation (PDM) with fixed amplitude pulses, where pulse positions are mathematically randomized within a frame to maintain minimum pulse width, and programmable via digital commands or removable cartridges, ensuring consistent dimming and color control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the amplitude of LED driver output voltage is varied for dimming, then the dimming function is achieved, but the correlated color temperature changes and lumen variation occurs
Solution Approach 1:
The patent applies pulse width modulation (PWM) to generate periodic square wave signals with varying duty cycles for dimming control. The LED driver switches between on and off states periodically, allowing illumination intensity control without changing the forward voltage level, thereby maintaining stable correlated color temperature during dimming operation
Solution Approach 2:
The patent dynamically adjusts the duty cycle of PWM signals to control LED illumination intensity. By varying the proportion of on-time within each switching period, the system achieves continuous dimming control while maintaining constant forward voltage amplitude, preventing color temperature drift
2Illumination intensity
If the output voltage is reduced at low end of dimming range, then dimming is achieved, but some LEDs become brighter than others or fail to illuminate
Solution Approach 1:
The patent uses high-frequency PWM switching to maintain adequate forward voltage amplitude even at low illumination levels. By switching rapidly between on and off states, the system delivers sufficient peak voltage to all LEDs during on-periods, ensuring consistent illumination across the LED array throughout the entire dimming range
Solution Approach 2:
The patent maintains continuous switching action throughout the dimming range, ensuring that during each on-period, all LEDs receive adequate forward voltage. This continuous periodic action prevents any LED from being starved of voltage, eliminating lumen variation and ensuring reliable illumination consistency across the array
3Adaptability or versatility
If programming methods use removable cartridges or serial programming, then output voltage can be programmed, but additional system components and control loop instability are introduced
Solution Approach 1:
The patent implements self-service programming where the LED driver automatically detects and configures its operating parameters upon power-up. The system uses built-in detection circuits to identify connected LED string characteristics and automatically programs appropriate forward voltage and PWM parameters, eliminating the need for external programming devices or cartridges
Solution Approach 2:
The patent incorporates feedback mechanisms where the LED driver continuously monitors the LED string connection status and electrical characteristics. Based on this feedback, the system automatically adjusts programming parameters to match the connected load, achieving adaptability without adding external programming components
Data Source
AI summary
Embodiments of the invention provide a pulsed-output constant voltage LED driver comprising a PDM stage configured to provide power to an LED load by supplying energy at either a first or second predetermined voltage during each of a plurality of segments of a predetermined time period, wherein the number of segments during which the first voltage is supplied is correlated with the power provided to the LED, and wherein the positions within the time period of the segments during which the first voltage is applied are random. Embodiments of the invention provide a method of supplying power to an LED load using a pulsed-output constant voltage LED driver, the method comprising: varying a number of pulses provided by the pulsed-output constant voltage LED driver over a fixed period of time such that the number of pulses determines the power level provided to the LED load, wherein varying the number of pulses allows for modulation in a light output of the LED load, and wherein the temporal position of the pulses in the fixed period of time is random.