Phase-Control Dimming Circuit With Dynamic Overcurrent Protection
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Solution Overview
Problem
Prior art dimmer switches struggle to effectively control high-efficiency lighting loads like LEDs due to high input impedances in load regulation circuits, which can fail to conduct enough current to exceed the rated latching and holding currents of thyristors when used with forward phase-control dimming techniques.
Innovation Solution
A load control device comprising a controllably conductive device, a control circuit, and an overcurrent protection circuit, where the controllably conductive device is coupled between an AC power source and an electrical load, using a forward phase-control dimming technique to control power delivery, and the overcurrent protection circuit is disabled when the device is non-conductive to prevent false triggering during power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a forward phase-control dimmer switch is used with high-efficiency lighting loads, then power delivery control is achieved, but the load regulation circuit cannot conduct enough current to exceed the rated latching and holding currents of the thyristor
Solution Approach 1:
The patent introduces an overcurrent protection circuit as an intermediary component between the thyristor and the load regulation circuit. This circuit includes a current sense resistor that monitors current flow and provides feedback to ensure the thyristor receives sufficient current to maintain conduction, thereby resolving the issue where high input impedance prevents adequate current flow through the thyristor while still allowing power control functionality
2Reliability
If the overcurrent protection circuit remains enabled when the controllably conductive device is non-conductive, then overcurrent protection is maintained, but false triggering occurs during power delivery
Solution Approach 1:
The patent implements dynamic enabling and disabling of the overcurrent protection circuit based on the conduction state of the controllably conductive device. The control circuit enables the overcurrent protection circuit only when the main switch is conductive, and disables it when the switch is non-conductive. This dynamic adjustment prevents false triggering during power delivery while maintaining overcurrent protection when needed
Solution Approach 2:
The patent uses feedback from the control circuit to dynamically control the enabling state of the overcurrent protection circuit. The control circuit monitors the conduction state of the main switch and provides feedback signals to enable or disable the overcurrent protection circuit accordingly, ensuring proper coordination between switching operations and protection functionality
Data Source
AI summary
A load control device for controlling power delivered from an alternating-current power source to an electrical load may comprise a controllably conductive device, a control circuit, and an overcurrent protection circuit that is configured to be disabled when the controllably conductive device is non-conductive. The control circuit may be configured to control the controllably conductive device to be non-conductive at the beginning of each half-cycle of the AC power source and to render the controllably conductive device conductive at a firing time during each half-cycle (e.g., using a forward phase-control dimming technique). The overcurrent protection circuit may be configured to render the controllably conductive device non-conductive in the event of an overcurrent condition in the controllably conductive device. The overcurrent protection circuit may be disabled when the controllably conductive device is non-conductive and enabled after the firing time when the controllably conductive device is rendered conductive during each half-cycle.