LED Driver Decoupling Dimmer Conduction Angle
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Solution Overview
Problem
Conventional phase-cut dimmers provide inconsistent performance when used with LED loads due to the difference in load characteristics compared to incandescent loads, leading to issues like inconsistent brightness control, dependence on conduction angle, and sensitivity to AC mains voltage variations, which limits the range of dimming and precision of LED output.
Innovation Solution
An illumination device with a microcontroller-based control circuit that decouples the power supply from the dimmer's conduction angle, using a dual-stage power supply with slow and fast control loops to regulate LED drive current independently of the dimmer's conduction angle, allowing for precise brightness control and adaptation to various dimmer configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If phase-cut dimmers are used to control LED loads, then power delivery can be adjusted by varying conduction angle, but inconsistent brightness control and sensitivity to AC mains voltage variations occur
Solution Approach 1:
The patent introduces an intermediary measurement and control system that measures the actual AC mains voltage and conduction angle, then calculates and applies the appropriate PWM duty cycle to compensate for variations. This intermediary layer decouples the direct relationship between dimmer position and LED brightness, ensuring consistent performance despite AC voltage fluctuations
Solution Approach 2:
The system implements feedback by continuously measuring the AC mains voltage and conduction angle during each half-cycle, then using this information to adjust the PWM duty cycle for the next cycle. This closed-loop control ensures that brightness remains consistent despite variations in AC voltage or dimmer characteristics
2Device complexity
If LED drive current is directly controlled by dimmer conduction angle, then simple control is achieved, but dependence on conduction angle limits dimming range and precision
Solution Approach 1:
The patent replaces the direct mechanical/electrical control relationship (dimmer conduction angle directly controlling LED current) with an electronic substitution using PWM control. The microcontroller measures the conduction angle and uses this information to generate precise PWM signals that independently control LED brightness, enabling fine dimming resolution and extended dimming range while eliminating conduction angle dependence
3Reliability
If conventional power supply is used with phase-cut dimmers, then basic LED operation is achieved, but AC transients and DC drift affect control accuracy
Solution Approach 1:
The patent applies preliminary action by measuring and compensating for AC transients and DC drift before they affect the LED drive current. The system proactively adjusts the PWM duty cycle based on measured voltage variations and drift conditions, preventing these issues from degrading control accuracy rather than reacting to them after they occur
Data Source
AI summary
An illumination device and method are provided for controlling light emitting diodes (LEDs). The LEDs (specifically, the LED loads) are controlled, e.g., brightness and color of the LED loads, independent of a phase-cut dimmer applied to the AC mains feeding a DC power supply. The power supply is active dependent upon the duration of a conduction angle supplied from the dimmer. The power supply, however, produces drive currents that are independent from the conduction angle by using a two-stage power supply and a relatively slow and fast control loops that are controlled through a microprocessor based control circuit. Parameters stored in the control circuit are drawn by the microprocessor to control the two-stage power supply to produce the drive currents independent and decoupled from the conduction angle yet dependent on the controller parameters.