PWM Ripple Reducer for LED Drivers
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Solution Overview
Problem
Single-stage LED drivers face challenges in reducing AC mains line ripple in LED current, which causes uncomfortable and harmful light fluctuations for the human eye, and existing solutions either increase BOM cost or reduce system efficiency.
Innovation Solution
A Pulse Width Modulation (PWM) controller is used to modulate the LED current at a high frequency, reducing the effect of lower-frequency ripple currents by performing PWM at a frequency higher than the ripple frequency, thereby minimizing the impact on human-perceived light variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a second-stage SMPS circuit is added to reduce LED ripple current, then the LED current ripple is reduced, but the BOM cost increases
Solution Approach 1:
The patent extracts only the essential function of ripple reduction from a complete second-stage SMPS circuit. By using a simple series switch controlled by PWM synchronized to the AC line frequency, it isolates and addresses only the ripple current issue without the complexity and cost of a full SMPS circuit, thereby reducing LED current ripple while avoiding increased BOM cost
Solution Approach 2:
The patent introduces an intermediary PWM-controlled switch between the single-stage SMPS output and the LEDs. This intermediary component acts as a buffer that filters out ripple current at the critical 100-120 Hz range without requiring a complete second conversion stage, thus reducing ripple while maintaining cost-effectiveness
2Object-affected harmful factors
If a constant-current LDO regulator is used to reduce LED ripple current, then the LED current ripple is reduced, but the system efficiency decreases due to headroom loss
Solution Approach 1:
The patent employs periodic PWM switching synchronized to the AC line frequency to counteract the ripple current. This periodic action creates a compensating effect that reduces ripple current at the problematic 100-120 Hz range without the continuous voltage drop and headroom loss associated with LDO regulators, thereby reducing ripple while maintaining system efficiency
Solution Approach 2:
The patent changes the operating parameters by using frequency-synchronized PWM switching rather than continuous linear regulation. By modulating the switch duty cycle dynamically based on the AC line cycle, it achieves ripple reduction through parameter modulation instead of fixed voltage dropping, avoiding the efficiency penalty of LDO headroom loss
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 solution effectively reduces LED ripple currents in the 100-120 Hz range with high efficiency and low BOM cost, ensuring comfortable and safe illumination for the human eye without the need for additional SMPS circuits or LDO regulators.
Implementation Method 1
A Pulse Width Modulation (PWM) controller is used to modulate the LED current at a high frequency, reducing the effect of lower-frequency ripple currents by performing PWM at a frequency higher than the ripple frequency
Data Source
AI summary
A circuit includes a power supply circuit and a ripple reduction circuit. The power supply circuit supplies a Direct Current (DC) lighting current to a light emitting circuit. The lighting current has a ripple current at a ripple frequency. The ripple reduction circuit receives the lighting current, and performs, based on the received lighting current, Pulse Width Modulation (PWM) of the lighting current at a PWM frequency. The PWM frequency is higher than the ripple frequency. By performing the PWM, the ripple reduction current reduces variations in a magnitude of the lighting current at the ripple frequency. The PWM frequency may be higher than a frequency at which variations in the magnitude of the light produced by the lighting circuit have a harmful effect on the human eye.