Zero-Crossing Timing Correction for Flicker-Free AC Dimmers
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Solution Overview
Problem
Conventional electrical load controllers, such as dimmers, inaccurately detect zero-crossings of AC waveforms due to asymmetry in zero-crossing detection and phase differences between the input AC waveform and the input signal waveform, leading to perceptible flickering and brightness variations in lighting loads.
Innovation Solution
An electrical load controller that applies error correction factors, in the form of time offsets, to adjust the detected zero-crossing times based on the asymmetry and phase differences, ensuring accurate determination of zero-crossings and frequency of the AC waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional zero-crossing detection is used in electrical load controllers, then the device complexity is reduced, but the measurement precision of zero-crossing times deteriorates due to asymmetry and phase differences
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing time offset values in a lookup table before operation. The microcontroller retrieves these pre-computed offsets during zero-crossing detection to correct timing errors, rather than performing complex real-time calculations. This approach improves measurement precision while keeping the runtime device complexity low.
Solution Approach 2:
The patent introduces an intermediary mechanism by using a lookup table that stores pre-computed time offset values. This intermediary structure mediates between the raw zero-crossing detection signal and the final corrected timing, allowing the system to achieve high precision without complex real-time computation logic in the control circuit.
2Illumination intensity
If precise zero-crossing control is implemented to minimize flickering, then the lighting quality improves, but the device complexity increases due to additional correction mechanisms
Solution Approach 1:
The patent uses preliminary action by pre-calculating time offset values during system initialization or manufacturing and storing them in a lookup table. During operation, the microcontroller simply retrieves these pre-computed values to correct zero-crossing timing, achieving stable lighting control without adding complex real-time computation hardware to the control circuit.
Solution Approach 2:
The system applies self-service by automatically compensating for its own timing errors using pre-stored correction values. The microcontroller performs self-correction of zero-crossing detection times by retrieving appropriate offsets from the lookup table based on detected waveform characteristics, eliminating the need for external calibration or manual adjustment mechanisms.
3Measurement precision
If time offset correction is applied to eliminate brightness variations, then the measurement precision of zero-crossing times improves, but the computational requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-computing all necessary time offset values before runtime and storing them in a lookup table. During operation, the microcontroller only needs to retrieve pre-calculated values based on simple waveform parameter matching, dramatically reducing computational load while maintaining high measurement precision for zero-crossing times.
Solution Approach 2:
The patent uses a lookup table structure that acts as a pre-computed resource, replacing expensive real-time computational operations with simple memory retrieval. The lookup table contains pre-calculated correction values that can be quickly accessed without intensive processing, effectively trading upfront computation for runtime efficiency.
Data Source
AI summary
Timing adjustment for accurate zero-crossing determination includes obtaining time offset(s) representing amounts of time between (i) zero-crossings of an input signal waveform, representative of an input AC waveform, input to a zero-crossing detector circuit and (ii) corresponding transitions of an output signal from an output of the circuit to a microcontroller, and determining times of the zero-crossings of the input AC waveform, which includes determining times of the corresponding transitions as detected by the microcontroller and adjusting the determined times using the time offset(s) to produce the times of the zero-crossings of the input AC waveform. In another aspect, input AC frequency is determined by determining pulse width(s) of pulse(s) of the output signal, and adjusting a half-cycle time corresponding to the pulse width(s) using the time offset(s) to provide a duration of half-cycles of the input AC waveform and inform a frequency of the input AC waveform.