LED Dimming Device Phase-Angle Control Zero Crossing Detection
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Solution Overview
Problem
Existing dimmers for LED lamps struggle to accurately determine the current zero crossing for phase-angle control, leading to inefficient dimming and potential overvoltages due to residual charge in the input capacitance.
Innovation Solution
A dimming device using a bidirectional switch with two switching devices, such as MOSFETs, that switches on both devices simultaneously and switches off one before an expected zero current crossing, measuring the voltage at the switched-off device to determine the current zero crossing for precise phase-angle control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse width modulation is used to dim LED lights, then the lighting output can be controlled, but electromagnetic interference is generated that disturbs other electronic devices
Solution Approach 1:
The patent introduces an intermediary circuit between the PWM signal source and the LED driver that converts the high-frequency PWM signal into a lower frequency signal or direct current signal. This intermediary transformation eliminates the electromagnetic interference while preserving the dimming control capability through alternative control mechanisms.
Solution Approach 2:
The patent replaces the electromagnetic PWM modulation method with an alternative control approach such as analog voltage control or current regulation. This substitution maintains the ability to control lighting output intensity while avoiding the generation of electromagnetic interference characteristic of pulse width modulation.
2Object-generated harmful factors
If analog dimming is used, then electromagnetic interference is reduced, but the dimming range is limited and minimum brightness cannot be achieved
Solution Approach 1:
The patent divides the dimming control into multiple stages or zones, combining different control methods for different brightness ranges. For example, using analog control for high brightness ranges and switching to PWM or other methods for low brightness ranges, thereby achieving both low electromagnetic interference and wide dimming range.
Solution Approach 2:
The patent implements a dynamic control system that automatically switches between different dimming methods based on the desired brightness level. The system adapts its control strategy in real-time, using analog dimming when low interference is needed and transitioning to other methods when maximum dimming range is required.
3Object-generated harmful factors
If pulse width modulation frequency is increased to reduce interference, then electromagnetic interference to radio receivers is reduced, but the complexity of the control system increases
Solution Approach 1:
The patent extracts the frequency modulation function from the main control system and implements it through a separate, dedicated circuit or component. This extraction simplifies the main control logic while achieving the desired interference reduction through specialized frequency management in the extracted portion of the system.
Data Source
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AI summary
Lighting devices (1), in particular LED lamps, should be capable of effective dimming using phase-angle control. For this purpose, a dimming device for power control of an AC-operated lighting device (1) is provided with a control unit for operating the lighting device (1) by means of phase-angle control. The control unit has a bidirectional switch with two switching devices (6, 7) for applying an AC supply voltage to the lighting device (1). The control unit is configured to switch on both switching devices (6, 7) simultaneously in each half-cycle of the AC supply voltage and to switch off one of the two switching devices before an expected zero current crossing. A measuring device (10, 11, 12) is connected to the control unit to measure a voltage across the switched-off switching device (6, 7).The control unit is further designed to determine a current zero crossing for phase-angle control based on the measured voltage.