LED Drive Circuit With Coordinated Feedback for PWM Dimming
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Solution Overview
Problem
Existing LED light source control systems face challenges in efficiently regulating load current and voltage to achieve precise intensity and color temperature adjustments, particularly in dimming applications, which can lead to erroneous operations and inefficient power management.
Innovation Solution
A controllable impedance circuit with a feedback loop and digital control circuit is employed, using pulse-width modulation and constant current reduction techniques to adjust the load current and voltage, ensuring accurate intensity and color control while preventing erroneous operations by coordinating the responsiveness of control loop circuits to current feedback signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse-width modulation technique is used to dim LED light source, then light output intensity can be adjusted, but erroneous operations may occur due to improper coordination of control loop responsiveness
Solution Approach 1:
The patent implements a feedback mechanism where the control loop circuit monitors the state of the dimming control signal and adjusts its responsiveness to current feedback signals accordingly. The control loop circuit is configured to be responsive to current feedback signals during specific time periods when the dimming control signal is not causing erroneous operations, and unresponsive during time periods when erroneous operations occur. This feedback-based timing coordination resolves the contradiction by maintaining dimming functionality while preventing operational errors.
Solution Approach 2:
The control loop circuit dynamically adjusts its responsiveness characteristics based on the state of the dimming control signal. By changing the operational mode of the control loop circuit between responsive and unresponsive states according to the PWM signal phase, the system adapts to different operating conditions, allowing intensity adjustment without causing erroneous operations.
2Illumination intensity
If constant current reduction technique is used to dim LED light source, then light output intensity can be adjusted, but power management efficiency may be reduced
Solution Approach 1:
The patent employs pulse-width modulation which uses periodic pulsed signals with varying duty cycles to control LED intensity. This periodic action allows the LED to operate at full current during on-periods and zero current during off-periods, rather than continuously operating at reduced current levels. The result is more efficient power management compared to constant current reduction, as the LED receives full power when needed and zero power when not in use, minimizing energy waste.
3Ease of operation
If multiple parallel strings of LEDs are used in voltage load control technique, then current balance regulation element is needed to ensure equal impedance, but device complexity increases
Solution Approach 1:
The patent introduces a control loop circuit as an intermediary element that mediates between the voltage source and the parallel LED strings. This control loop circuit actively monitors and adjusts the voltage or current to maintain balance across parallel strings, replacing the need for complex passive impedance matching networks. The active control approach simplifies the overall circuit design while maintaining voltage load control capability.
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.