LED Drive Circuit Feedback Control for Intensity and Color Temperature
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Solution Overview
Problem
Existing LED lighting systems face challenges in efficiently controlling the intensity and color temperature of LED light sources, particularly in achieving smooth dimming and maintaining optimal operating conditions across varying load currents and voltages, which can lead to inconsistent light output and reduced efficiency.
Innovation Solution
A controllable lighting device comprising an LED light source, an LED drive circuit, a feedback circuit, and a control circuit that adjusts the average load current by controlling the conductive device's on-time and off-time, with a power converter circuit generating a bus voltage and a control circuit that adjusts the bus voltage to maintain optimal operating periods, allowing for precise intensity and color temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If PWM dimming technique is used to control LED intensity, then the average current can be adjusted to vary light output intensity, but the peak current must be maintained constant which requires precise control and increases device complexity
Solution Approach 1:
The patent implements a feedback mechanism where the control circuit monitors the actual peak current through the LED string and adjusts the PWM duty cycle accordingly. This ensures that even when load conditions change, the peak current remains regulated while the average current varies to control intensity, resolving the contradiction between intensity control and control complexity
Solution Approach 2:
The control circuit dynamically adjusts the PWM duty cycle based on real-time feedback from the LED string's operating conditions. This dynamic adaptation allows the system to maintain peak current regulation while achieving smooth intensity dimming, reducing the need for overly complex fixed control mechanisms
2Illumination intensity
If CCR dimming technique is used to control LED intensity, then the DC current magnitude can be varied continuously, but this requires continuous current regulation which reduces efficiency and increases power loss
Solution Approach 1:
The patent employs PWM (pulse-width modulation) which uses periodic switching action rather than continuous current regulation. The control circuit switches the power supply on and off at high frequency, creating a pulsed current that averages to the desired intensity level. This periodic action eliminates continuous regulation requirements and significantly reduces power loss compared to CCR dimming
Solution Approach 2:
During the PWM on-time, the full peak current flows continuously through the LED string, ensuring optimal LED operation and efficiency. The useful action of current conduction is maintained continuously during the active period, while the overall average current is controlled by the duty cycle, avoiding the energy losses associated with continuous regulation
3Productivity
If multiple parallel strings of LEDs are used to increase light output, then the current capacity increases, but current imbalance between strings occurs requiring additional regulation elements
Solution Approach 1:
The control circuit is designed to universally control multiple parallel LED strings through a single integrated control mechanism. By monitoring the combined current or using a shared feedback path, the control circuit regulates all strings simultaneously, eliminating the need for separate regulation elements for each string and reducing overall device complexity
Solution Approach 2:
The patent merges the control functions for multiple parallel LED strings into a single control circuit that manages current distribution across all strings. This consolidation eliminates the need for separate current balance regulation elements for each string, reducing device complexity while maintaining current balance through unified control
4Illumination intensity
If the operating period is extended to reduce peak current, then the average current can be reduced for dimming, but the frequency of operation decreases which may affect LED performance
Solution Approach 1:
The control circuit dynamically adjusts the PWM duty cycle to achieve the desired average current level while maintaining a fixed, optimal operating period. This dynamic adjustment of duty cycle rather than period allows intensity control without affecting the frequency-related LED performance characteristics
Solution Approach 2:
The patent changes the control parameter from operating period to duty cycle. By adjusting the duty cycle (the proportion of the period when the switch is on) rather than changing the period itself, the system can control average current for dimming while maintaining a constant, optimal operating frequency that preserves LED performance
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 enables precise control over the intensity and color temperature of LED light sources, ensuring consistent and efficient light output across a wide range of intensities and color temperatures, improving the overall performance and reliability of LED lighting systems.
Implementation Method 1
a light-emitting diode (LED) light source
Data Source
AI summary
A controllable lighting device may comprise a drive circuit characterized by one or more cycles and a control circuit configured to control the drive circuit to conduct a load current through a light source of the lighting device. The control circuit may be configured to determine one or more operating parameters of the lighting device during a present cycle of the drive circuit based on a feedback signal indicative of a peak magnitude of the load current conducted through the light source. The control circuit may be able to adjust an average magnitude of the load current conducted through the light source so as to adjust an intensity of the light source towards a target intensity based on the operating parameters.