LED Drive Circuit With Switched Feedback for Flicker-Free Dimming
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Solution Overview
Problem
Existing LED light source control technologies face challenges in efficiently regulating current and voltage to achieve precise intensity and color control, particularly in dimming applications, which can lead to erroneous operations and inefficient power management.
Innovation Solution
A controllable impedance circuit coupled with a feedback loop and digital control circuit that adjusts the peak and average load current through pulse-width modulation, using a combination of switching devices and filter circuits to generate drive signals for precise control of LED light sources, ensuring accurate intensity and color adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse-width modulation is used to dim LED light sources, then light intensity control is achieved, but visible flicker may occur
Solution Approach 1:
The patent employs pulse-width modulation (PWM) technique where a periodic pulsed signal with varying duty cycle is supplied to the LED light source. The periodic nature of the PWM signal enables precise control of average light intensity while maintaining stable operation by operating at frequencies above human visual perception thresholds, thereby preventing visible flicker.
Solution Approach 2:
The patent changes the duty cycle parameter of the PWM signal to control light intensity. By varying the duty cycle (the ratio of on-time to total period), the average current supplied to the LED is adjusted, thereby controlling the perceived light intensity without changing the peak current or frequency, thus avoiding visible flicker.
2Measurement precision
If current load control technique is used to regulate LED current, then light intensity precision is improved, but power management efficiency deteriorates
Solution Approach 1:
The patent uses PWM dimming where the peak current is kept constant during the on-time, maintaining precise current control for color stability. By switching the current on and off periodically rather than continuously reducing it, the system achieves both precision and efficiency.
Solution Approach 2:
The patent replaces continuous analog current control with digital PWM switching control. This substitution allows for more efficient power management by using switching devices that operate in saturation/cutoff regions rather than linear regions, reducing power dissipation while maintaining control precision through digital duty cycle adjustment.
3Stability of the object's composition
If voltage load control technique is used to regulate LED voltage, then operation stability is improved, but current balance between parallel strings deteriorates
Solution Approach 1:
The patent incorporates feedback circuits that monitor the current through each parallel LED string and adjust the driving signals accordingly. This feedback mechanism ensures that even under voltage control, the current is balanced across parallel strings by detecting and compensating for impedance variations.
Solution Approach 2:
The patent dynamically adjusts the duty cycle of PWM signals supplied to each parallel string based on real-time current measurements. By changing the duty cycle parameter individually for each string, the system maintains current balance while operating under voltage control conditions.
4Illumination intensity
If constant current reduction dimming is used to control LED intensity, then color stability is improved, but power management efficiency deteriorates
Solution Approach 1:
The patent employs PWM switching instead of continuous current reduction. The periodic switching at high frequency maintains constant peak current (ensuring color stability) while controlling average power consumption through duty cycle adjustment, achieving both color stability and power efficiency.
Solution Approach 2:
The patent replaces linear constant current reduction with switching-based PWM control. This substitution allows the system to operate switching devices in efficient saturation/cutoff modes rather than linear amplification modes, significantly reducing power dissipation while maintaining constant peak current for color stability.
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 solution enables precise control of LED light sources, preventing erroneous operations and optimizing power management by adjusting load currents and voltages, allowing for efficient dimming and color temperature adjustments without visible flicker.
Implementation Method 1
Light-emitting diode (LED) light sources (e.g., LED light engines) are replacing conventional incandescent, fluorescent, and halogen lamps
Implementation Method 2
a feedback circuit is configured to generate a feedback signal indicative of a magnitude of the load current conducted through the LED light source
Data Source
AI summary
A controllable lighting device may utilize a controllable impedance circuit to conduct a load current through an LED light source. The controllable impedance circuit may be coupled in series with a first switching device, which may be rendered conductive and non-conductive via a pulse-width modulated signal to adjust an average magnitude of the load current. The controllable lighting device may further comprise a control loop circuit that includes a second switching device. The second switching device may be rendered conductive and non-conductive in coordination with the first switching device to control when a feedback signal is provided to the control loop circuit and used to control the LED light source. The control loop circuit may be characterized by a time constant that is significantly greater than an operating period of the load current.