Forward Phase-Control Circuit With Switched 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 and current limitations, particularly when using forward phase-control dimming techniques, which can lead to insufficient current conduction and potential overcurrent conditions.
Innovation Solution
A load control device featuring a controllably conductive device, such as two FETs in anti-series connection, coupled with a control circuit using forward phase-control dimming and an overcurrent protection circuit that is disabled when the device is non-conductive, allowing for controlled power delivery and preventing overcurrent conditions by enabling the protection circuit only after the device is conductive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a prior-art forward phase-control dimmer switch is used with high-efficiency lighting loads, then energy saving 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 employs two FETs in anti-series connection that can dynamically switch between different conduction states. The FETs are controlled to provide sufficient latching current during turn-on and maintain proper holding current throughout operation, adapting to the high input impedance characteristics of LED loads while ensuring reliable thyristor operation throughout the conduction cycle
Solution Approach 2:
The invention changes the electrical parameters of the circuit by using FETs with specific gate control to modify the current waveform characteristics. The FETs are controlled to provide enhanced current pulses that exceed the thyristor's latching and holding current requirements, fundamentally altering the current delivery profile to match LED load requirements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution ensures reliable power control to high-efficiency lighting loads by preventing overcurrent conditions and ensuring sufficient current conduction, thereby maintaining the longevity and efficiency of LED lighting sources.
Implementation Method 1
a controllably conductive device, such as two FETs in anti-series connection, coupled with a control circuit using forward phase-control dimming
Implementation Method 2
an overcurrent protection circuit that is configured to be disabled when the device is non-conductive, allowing for controlled power delivery and preventing overcurrent conditions
Data Source
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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.