LED Load Control Circuit for Smooth Low-End Dimming
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Solution Overview
Problem
Existing dimming methods for LED light sources result in perceptible changes in light intensity, particularly at low intensities, necessitating fine-tuning techniques to achieve smoother intensity adjustments.
Innovation Solution
A load control device with a load regulation circuit and control circuit that operates in normal and burst modes, adjusting load current through active and inactive states to achieve precise intensity control, using a switching device to regulate current magnitude and duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional dimming methods are used for LED light sources, then the light intensity can be reduced, but perceptible changes in light intensity occur making fine tuning difficult
Solution Approach 1:
The patent employs pulse-width modulation (PWM) to dim the LED light source by applying periodic pulses of rated current. By varying the duty cycle of these periodic pulses, the average current through the LEDs is controlled, enabling precise intensity adjustment. The periodic nature of the control signal allows for fine-grained intensity control that avoids perceptible steps, directly resolving the contradiction between achieving low intensity and maintaining control precision.
2Ease of operation
If the duty cycle of pulsed signal is varied to dim LED, then the average current varies to adjust light intensity, but perceptible changes occur near low end of intensity range
Solution Approach 1:
The patent changes the parameter being controlled from duty cycle alone to a combination of frequency and duty cycle. By operating in burst mode where the PWM signal is applied in bursts at a lower frequency, the system can achieve smoother intensity transitions. This parameter change allows for better control resolution near the low end of the intensity range, eliminating perceptible steps while maintaining ease of dimming operation.
Data Source
AI summary
A load control device for controlling the amount of power delivered to an electrical load is able to operate in a normal mode and a burst mode. The load control device may comprise a control circuit that activates an inverter circuit during active state periods and deactivates the inverter circuit during inactive state periods. The control circuit may operate in the normal mode to regulate an average magnitude of a load current conducted through the electrical load to be above a minimum rated current. The control circuit may operate in the burst mode to adjust the average magnitude of the load current to be below the minimum rated current. The control circuit may adjust the average magnitude of the load current by adjusting the length of the inactive state periods while holding the length of the active state periods constant.