PDM LED Current Modulation Eliminates Audible Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing LED light bulb dimming technologies face complexity in circuitry due to the need for current-driven LED devices, leading to potential audible noise and flicker issues, and require higher dimming resolution for smooth illumination reduction.
Innovation Solution
The use of pulse density modulation (PDM) on the primary side of the LED power circuitry, combined with a bridge rectifier and DC-DC controller, to distribute the on-time of LED devices over the entire cycle, reducing energy transfer and eliminating strong fundamental repetition frequencies, thereby achieving smooth dimming without noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse width modulation (PWM) is used to control LED dimming, then illumination can be reduced, but audible noise and flicker occur due to strong fundamental repetition frequency
Solution Approach 1:
The patent applies periodic action by using pulse density modulation (PDM) to distribute LED on-time across the entire cycle in a periodic manner. Instead of concentrating switching activity at fixed intervals like PWM, PDM spreads the periodic switching events throughout the modulation cycle, thereby reducing the strong fundamental repetition frequency that causes audible noise and flicker while maintaining effective dimming control.
2Illumination intensity
If complex circuitry is used to enable LED dimming control, then illumination can be adjusted, but device complexity increases
Solution Approach 1:
The patent introduces an intermediary approach by implementing PDM control on the primary side of the LED power circuitry. This intermediary control mechanism allows dimming to be achieved through modulation of the primary side current rather than requiring complex secondary side circuitry, thereby reducing overall device complexity while maintaining effective illumination control.
3Illumination intensity
If conventional dimming control is used, then illumination can be reduced, but dimming resolution is insufficient for smooth illumination adjustment
Solution Approach 1:
The patent applies parameter changes by transitioning from PWM's fixed-frequency switching to PDM's variable-density pulse distribution. This fundamental parameter change in the modulation approach enables continuous adjustment of LED on-time across the entire cycle, providing fine-grained control over illumination levels and achieving high dimming resolution for smooth illumination adjustment without the stepped transitions inherent in conventional methods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise control of LED dimming, reducing audible noise and flicker, and increasing dimming resolution, ensuring smooth and flicker-free illumination adjustment.
Implementation Method 1
A bridge rectifier circuit is used to transform an AC voltage into a full wave rectified DC voltage
Implementation Method 2
a transformer comprising a transistor controlled by a DC-DC controller... transfer primary side energy through the transformer to the string of LED diodes
Data Source
AI summary
A modulated current of an LED device provides a capability to dim of the light produced by a string of LED device. The current modulation takes the form of pulse width modulation (PWM) or pulse density modulation (PDM). The modulation is produced on the primary side of a transformer and coupled to the string of LED diodes that are coupled to the secondary side of the transformer. The modulation is varied to change the current of the LED devices and therefore the light intensity of the LED devices.