Neutral-Less Dimmer Circuit for Accurate Zero-Cross Detection
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Solution Overview
Problem
Conventional two-wire neutral-less dimmers experience inaccuracies in zero-crossing detection due to voltage drops across loads, particularly for low power loads like LED bulbs, which affect the conduction angle and dimming range.
Innovation Solution
The implementation of a zero crossing detection improvement circuit that includes first and second switches to block current from flowing through the power supply and snubber circuits during the off phase of the TRIAC, thereby reducing voltage drops and improving zero-crossing detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current flows through the power supply circuit and snubber circuit during the off phase, then the circuits can perform their respective functions (power supply to electronics and voltage transient limiting), but voltage drops occur across the loads which shift the zero-crossing detection reference point and reduce detection accuracy
Solution Approach 1:
The patent extracts the harmful effect by removing the current flow through the power supply circuit and snubber circuit during the critical zero-crossing detection period. Switches are introduced to isolate these circuits from the load during the off phase, eliminating the voltage drops that cause measurement errors in zero-crossing detection.
Solution Approach 2:
The patent applies preliminary action by proactively blocking current flow through the power supply and snubber circuits before zero-crossing detection occurs. The switches are controlled to open during the off phase, preventing the voltage drops that would otherwise shift the detection reference point and compromise accuracy.
2Adaptability or versatility
If the conduction angle is limited due to inaccurate zero-crossing detection, then the dimming range is reduced, but the voltage drop across low power loads cannot be eliminated without additional circuitry
Solution Approach 1:
The patent segments the operational phases by introducing controlled switches that isolate the power supply and snubber circuits during the off phase. This segmentation allows the zero-crossing detection to occur without interference from voltage drops, enabling full conduction angle range and complete dimming functionality.
Solution Approach 2:
The patent introduces switches as intermediary elements between the power supply/snubber circuits and the load. These switches mediate the current flow, blocking it during the off phase to prevent voltage drops that would otherwise limit the conduction angle and reduce dimming range.
3Measurement precision
If voltage drops across low impedance loads are significant, then the reference point for zero-crossing detection shifts and detection accuracy decreases, but increasing power supply current to compensate increases circuit complexity
Solution Approach 1:
The patent extracts the source of measurement error by removing the current flow through the power supply circuit during the off phase. By opening the switch, the circuit eliminates the voltage drop that shifts the zero-crossing reference point, achieving accurate detection without increasing overall circuit complexity.
Solution Approach 2:
The patent applies periodic action by controlling the switches to open during the off phase when zero-crossing detection is critical, and close during the on phase when power supply current is needed. This periodic switching achieves accurate detection without permanently increasing circuit complexity.
Data Source
AI summary
A dimmer includes a TRIAC, a zero crossing detection circuit coupled to the TRIAC and structured to detect zero crossing of line voltage; a gate control circuit coupled to a gate of the TRIAC and the zero crossing detection circuit, the gate control circuit structured to drive the gate of the TRIAC to switch between an on phase and an off phase; a power supply circuit coupled to the gate control circuit and the zero crossing detection circuit, the power supply circuit structured to supply power to at least the gate control circuit and the zero crossing detection circuit; a snubber circuit coupled to the TRIAC and structured to limit fast transient voltages; and a zero crossing detection improvement circuit comprising a first switch and a second switch and structured to block current from flowing through the power supply circuit and the snubber circuit during the off phase.