Solid State Lighting Dimming Range Extension via Phase Angle Detection
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Solution Overview
Problem
Conventional dimmers struggle to effectively reduce light output of solid state lighting loads, such as LEDs, at low dimming settings, leading to high minimum light output levels that are undesirable, especially due to human eye sensitivity at low light levels.
Innovation Solution
A system comprising a phase angle detector and a power converter that operates in open or closed loop modes based on the detected dimmer phase angle, generating a power control signal to adjust the light output of the solid state lighting load, allowing for selective dimming control even at low dimming levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional phase chopping dimmers are used with solid state lighting loads, then the dimming function is provided, but the minimum light output remains high (15-30% of maximum) which is undesirable
Solution Approach 1:
The patent introduces an intermediary control system between the dimmer and the solid state lighting load. This intermediary detects the dimmer's phase angle and generates appropriate PWM control signals to drive the lighting load, enabling the dimmer to effectively control light output down to very low levels rather than being limited to 15-30% minimum output.
Solution Approach 2:
The patent changes the control parameter from direct phase chopping to PWM duty cycle control based on detected phase angle. By mapping the dimmer's phase angle to a PWM duty cycle, the system can achieve finer control resolution and push the minimum light output much lower than conventional direct phase chopping methods.
2Illumination intensity
If phase chopping dimmers operate at low dimming settings, then dimming is achieved, but the human eye sensitivity makes the light output seem even higher than it actually is
Solution Approach 1:
The patent implements feedback by detecting the phase angle of the dimmer and using this information to adjust the PWM control signal accordingly. This closed-loop approach allows the system to compensate for human eye sensitivity at low light levels and provide more accurate perceived dimming control.
3Adaptability or versatility
If solid state lighting loads are connected to phase chopping dimmers, then dimming capability is provided, but problems occur such as low end drop out, triac misfiring, minimum load issues, high end flicker, and large steps in light output
Solution Approach 1:
The patent introduces an intermediary control circuit that detects the phase angle and generates PWM signals to drive the solid state lighting load. This intermediary buffer resolves the incompatibility between phase chopping dimmers and solid state lighting loads, eliminating issues like triac misfiring, drop out, and flicker while maintaining full dimming range.
Data Source
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AI summary
A system for controlling a level of light output by a solid state lighting load controlled by a dimmer includes a phase angle detector and a power converter. The phase angle detector is configured to detect a phase angle of the dimmer based on a rectified voltage from the dimmer and to determine a power control signal based on comparison of the detected phase angle with a predetermined first threshold. The power converter is configured to provide an output voltage to the solid state lighting load, the power converter operating in an open loop mode based on the rectified voltage from the dimmer when the detected phase angle is greater than the first threshold, and operating in a closed loop mode based on the rectified voltage from the dimmer and the determined power control signal from the detection circuit when the detected phase angle is less than the first threshold.