Leading-Edge Dimmer Detection Circuit for Low-Wattage LED Dimming
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Solution Overview
Problem
Conventional leading-edge phase-cut dimmers prematurely shut down due to low current levels in low-wattage lamps, leading to inaccurate dimming and energy delivery issues, and fail to communicate their type to other circuits effectively.
Innovation Solution
A circuit comprising an edge detector, pulse stretcher, and filter that detects rapidly rising edges in an input signal, stretches pulses, and generates an indicator signal to identify the presence of a leading-edge phase-cut dimmer, allowing for appropriate load adjustment to ensure accurate dimming and energy delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If leading-edge phase-cut dimmers are used to control low-wattage lamps, then power delivery to the load is reduced, but the dimmers prematurely shut down due to low current levels
Solution Approach 1:
The circuit detects the dimmer type before full operation begins, allowing the system to prepare appropriate compensation measures in advance. The edge detector and pulse stretcher identify leading-edge dimmers early in the operation cycle, enabling the control circuit to preemptively adjust parameters to prevent premature shutdown.
Solution Approach 2:
The circuit continuously monitors the input signal characteristics and uses this feedback to identify dimmer type. The edge detector observes signal transitions, the pulse stretcher processes these detections, and the filter generates a control signal based on the accumulated information, creating a closed-loop system that adjusts operation based on real-time conditions.
2Ease of operation
If leading-edge phase-cut dimmers operate at low current levels, then dimming control is achieved, but inaccurate dimming and energy delivery issues occur
Solution Approach 1:
The circuit changes operational parameters based on detected dimmer type. When a leading-edge dimmer is identified through edge detection and pulse stretching, the system adjusts current compensation parameters and timing characteristics to maintain accurate dimming control across the full range of dimming levels, preventing the inaccuracies that occur at low current levels.
3Device complexity
If simple dimmer detection is implemented, then circuit complexity is reduced, but reliable distinction between leading-edge and trailing-edge dimmers becomes difficult
Solution Approach 1:
The detection function is divided into three distinct circuit segments: the edge detector that identifies signal transitions, the pulse stretcher that extends and shapes detected pulses, and the filter that analyzes the stretched pulse pattern to generate the final dimmer type identification. This segmentation allows each component to perform its specific function with high precision while keeping individual component complexity low.
Solution Approach 2:
The pulse stretcher acts as an intermediary between the edge detector and the filter. It takes the brief edge detection signals and transforms them into extended, well-shaped pulses that are easier for the filter to analyze reliably. This intermediary processing stage enhances detection accuracy without requiring complex direct analysis circuits.
Data Source
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AI summary
In described examples, a dimmer detector (300) includes an edge detector (340) that detects whether an input signal (Vin) has a rapidly rising edge and generates an output signal pulse if a rapidly rising edge is detected. If the edge detector (340) outputs a signal pulse, a pulse stretcher (330) generates a stretched pulse having a duration that is longer than the signal pulse received from the edge detector (340). If the pulse stretcher (330) output signal includes at least a predetermined number of stretched pulses within a predetermined amount of time, a dimmer detect signal (DIM DET) signals the presence of a leading-edge phase-cut dimmer.