LED Driver PWM Noise Reduction via Phase Delay and Dynamic Compensation
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Solution Overview
Problem
LED drivers using pulse-width modulation (PWM) for dimming control often generate audio noise due to abrupt changes in load current, which conventional methods like phase delay techniques only partially alleviate.
Innovation Solution
A LED driver circuit incorporating a power converter, current regulator, operational amplifier, PWM logic circuit, and dynamic headroom controller that generates a compensation voltage and sense signal to adjust the duty ratio of the PWM signal, reducing load current ripples and stabilizing output voltage, thereby minimizing audio noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM signal is used for dimming control, then brightness regulation is achieved, but audio noise is generated due to abrupt load current changes
Solution Approach 1:
The patent divides the LED string into multiple groups with different phase delays, so that not all LEDs switch at the same time. This segmentation of the switching operation reduces the abrupt current change and consequently the audio noise while maintaining PWM dimming control functionality.
Solution Approach 2:
The patent introduces a phase delay mechanism that prepares different LED groups to switch at different times. By planning the switching sequence in advance with controlled delays, the system prevents simultaneous switching of all LEDs, thereby reducing the harmful audio noise effect.
2Object-generated harmful factors
If phase delay technique is applied to reduce audio noise, then noise amplitude is reduced, but transient response is slowed down
Solution Approach 1:
The patent applies different phase delay values to different LED string groups based on their specific characteristics and positions. This localized optimization allows each group to contribute to noise reduction while maintaining overall fast transient response, rather than applying a uniform delay that would slow down the entire system.
Solution Approach 2:
The patent dynamically adjusts the phase delay parameters based on operating conditions. The phase delay values are not fixed but can be modified to optimize the balance between noise reduction and transient response speed under different loading and dimming conditions.
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
The proposed solution effectively reduces the amplitude of output voltage ripples and stabilizes the output capacitor, preventing audio noise by dynamically adjusting the PWM signal duty ratio in response to load current variations, enhancing transient response and noise reduction.
Implementation Method 1
an operational amplifier that amplifies a difference between a reference voltage and a feedback signal related to the output voltage to generate a compensation voltage
Implementation Method 2
The output capacitor Cout will be charged or discharged by the ripples 18 and thus generates audio noise
Data Source
AI summary
A LED driver using a PWM signal for dimming control includes a power converter and a current regulator. The power converter provides an output voltage and a load current for a plurality of LEDs. The current regulator provides a load current dependent signal for the power converter to speed up load transient response caused by variation of the load current, to reduce the ripple of the output voltage, and thereby to avoid audio noise during PWM dimming.