LED Driver Circuit Frequency Shift for Flicker Reduction
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Solution Overview
Problem
Existing LED drivers struggle to effectively reduce visible flicker, particularly due to the dynamic resistance of LEDs decreasing with improved efficiency, making it challenging to manage flicker frequencies that are sensitive to the human eye.
Innovation Solution
A driver circuit that increases the frequency of the predominant AC component in the power supplied to LED light sources, using a rectifier, capacitor, and switching device configuration to ensure the light source is driven by both the rectifier and capacitor outputs equally, thereby minimizing perceived flicker by shifting the predominant frequency to 200 Hz or above.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large electrolytic capacitors are added to bridge voltage fluctuations, then flicker reduction is achieved, but device complexity and space requirements increase
Solution Approach 1:
The patent changes the frequency parameter of the power supply to the LED from 50/60 Hz to 200 Hz or higher by using a rectifier configured to output at four times the mains frequency. This parameter change shifts the flicker to a frequency where human eyes are less sensitive, eliminating the need for large capacitors and complex circuits while still achieving flicker reduction
Solution Approach 2:
The patent replaces the mechanical/electrical approach of using large capacitors to smooth voltage fluctuations with an electrical frequency transformation approach. By using a rectifier and switching circuit to generate high-frequency power, the system achieves flicker reduction without mechanical moving parts or large energy storage components
2Use of energy by moving object
If LED efficiency is improved, then energy conversion increases, but dynamic resistance decreases making flicker reduction more challenging
Solution Approach 1:
The patent addresses the reduced dynamic resistance of efficient LEDs by changing the operating frequency parameter to 200 Hz or higher. At these higher frequencies, the LED's low dynamic resistance becomes an advantage rather than a disadvantage, as the rapid switching allows the LED to respond quickly while the high frequency pushes the flicker beyond human visual sensitivity
3Device complexity
If predominant frequency is kept at twice mains frequency (100 Hz or 120 Hz), then driver simplicity is maintained, but human eye sensitivity to flicker increases
Solution Approach 1:
The patent changes the predominant frequency from 100/120 Hz to 200 Hz or higher by using a full-wave rectifier with switching at four times the mains frequency. This simple parameter change in the circuit design shifts the flicker to a less sensitive frequency range while maintaining driver circuit simplicity
Solution Approach 2:
The patent employs periodic switching action at four times the mains frequency to generate the high-frequency power output. This periodic operation at a higher frequency than traditional designs achieves flicker reduction by pushing the modulation frequency beyond the most sensitive range of human visual perception
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 significantly reduces or eliminates visible flicker by ensuring the AC component at four times the primary frequency is greater than at the primary frequency and second harmonic, resulting in a substantial reduction of perceived light modulation.
Implementation Method 1
a rectifier having an input and an output, wherein the rectifier is configured to receive an AC supply voltage at its input
Implementation Method 2
a capacitor connected across the rectifier output; wherein the at least one light source is driven by the rectifier output during a first portion of a period of the AC supply voltage, wherein the at least one light source is driven by the capacitor during a second portion of the period
Data Source
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AI summary
A driver (100) supplies power to drive at least one light source(130). The driver includes: a current regulator (140) connected in series with the at least one light source; and a conditioning circuit (120) configured to receive an AC supply voltage(110)having a primary frequency of between about 50 Hz to 60 Hz, and further configured to condition the received AC supply voltage to supply power to the at least one light source, wherein the conditioned voltage has a non-zero DC component and an AC component, and wherein a magnitude of the AC component at a frequency that is four times the primary frequency is greater than a magnitude of the AC component at the primary frequency, and is also greater than a magnitude of the AC component at a second harmonic of the primary frequency.