LED Drive Circuit With Hybrid Dimming for Flicker-Free Control
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Solution Overview
Problem
Existing LED light sources face challenges in efficiently controlling light intensity and color temperature, particularly in dimming scenarios, due to issues with current and voltage regulation, leading to potential flickering and improper operation.
Innovation Solution
A controllable impedance circuit coupled with a feedback loop and digital control circuit is used to adjust load current and voltage, employing pulse-width modulation and constant current reduction techniques to precisely control LED light sources, preventing erroneous operation and ensuring smooth dimming transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse-width modulation technique is used to dim LED light source, then light intensity control is achieved, but flickering may occur at certain dimming levels
Solution Approach 1:
The patent dynamically switches between PWM dimming and CCR dimming modes based on the target dimming level. At higher dimming levels, PWM is used for efficient intensity control, while at lower dimming levels, CCR is used to maintain stable current and eliminate flickering, thus adapting the dimming technique to the specific operating conditions
Solution Approach 2:
The patent changes the control parameter from duty cycle (PWM) to current magnitude (CCR) when transitioning to low dimming levels. This parameter change allows the system to maintain proper LED operation by using constant current reduction instead of reduced duty cycle, preventing flickering while achieving the desired low light intensity
2Illumination intensity
If constant current reduction dimming is used, then smooth dimming transitions are achieved, but control precision may be reduced compared to PWM
Solution Approach 1:
The system dynamically selects the optimal dimming technique based on the target dimming level. PWM provides precise digital control at higher levels, while CCR provides smooth analog transitions at lower levels, creating a hybrid approach that leverages the strengths of both methods across the full dimming range
Solution Approach 2:
The patent uses periodic PWM switching at higher dimming levels to achieve precise control through duty cycle variation, then transitions to continuous CCR operation at lower levels for smooth analog dimming, creating a periodic switching pattern between control modes that optimizes both precision and smoothness
3Illumination intensity
If multiple parallel strings of LEDs are used, then light output is increased, but current imbalance between strings may occur
Solution Approach 1:
The patent incorporates feedback mechanisms that monitor the actual current through the LED strings and adjust the drive signal accordingly. This feedback ensures that all parallel strings receive equal current distribution, preventing current imbalance and ensuring uniform light output across all strings
Solution Approach 2:
The patent uses current balancing circuits that equalize the voltage and current conditions across all parallel LED strings. By maintaining equipotential conditions at the connection points of parallel strings, the system ensures uniform current distribution and prevents imbalances that would lead to uneven light output
4Reliability
If LED driver regulates voltage, then voltage stability is achieved, but current control precision may be insufficient
Solution Approach 1:
The patent dynamically switches between voltage load control and current load control modes based on the LED string configuration and operating conditions. This dynamic adaptation allows the system to use voltage regulation when it provides sufficient performance while transitioning to precise current control when LED string variations require tighter current management
Solution Approach 2:
The patent changes the primary control parameter from voltage to current when LED string variations are detected. This parameter change allows the system to maintain voltage stability while achieving the current control precision needed for consistent LED performance across different string configurations
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.