LED Dimming via Analog Pulse Transmission Through Optocouplers
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Solution Overview
Problem
Flyback converters in solid-state lighting applications face challenges with triac-based dimming switches, leading to flicker issues due to the inefficiency of direct electrical signal transmission through isolating devices like optocouplers, which exhibit non-linearity and variable rise/fall times, affecting data rate and dimming control.
Innovation Solution
A technique using a pair of input pulses, including a data input pulse and a calibration input pulse, is employed to transmit an analog dimming value through an isolating device, where the primary side controller recovers the desired dimming level by comparing received pulses with delayed rise and fall times, allowing for quick adjustment of the power switch to achieve the desired dimming level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional triac-based dimming switches are used with flyback converters, then dimming control is achieved, but flicker occurs due to insufficient current through the triac switch at higher dimming settings
Solution Approach 1:
The patent replaces the mechanical triac-based dimming switch with an electronic dimming control system. The dimming switch communicates dimming commands electronically through an isolating device (optocoupler) to the primary-side controller, which then adjusts the power switch cycling to achieve the desired dimming level without the flicker issues associated with triac switches.
2Loss of information
If direct electrical signal transmission is used from secondary side to primary side for dimming control, then dimming level communication is achieved, but isolation between primary and secondary windings is destroyed
Solution Approach 1:
The patent introduces an isolating device (optocoupler) as an intermediary to transmit dimming commands from the secondary side to the primary side. The dimming switch drives a pulse through the optocoupler, which transfers the signal optically while maintaining electrical isolation between the primary and secondary windings, thus preserving safety and regulatory compliance.
3Reliability
If binary signaling is used through optocoupler for dimming control, then isolation is maintained, but data rate must be slowed due to non-linearity and variable rise/fall times of the optocoupler
Solution Approach 1:
The patent applies preliminary calibration action to characterize the optocoupler's transfer function and delay characteristics before normal operation. The system measures the actual rise and fall times of the optocoupler and uses this information to pre-compensate or adjust the timing of dimming commands, thereby maintaining accurate control despite the optocoupler's non-linear behavior and variable delays.
4Speed
If data rate is increased through optocoupler, then faster dimming response is achieved, but pulse width becomes too narrow to cross threshold voltage reliably
Solution Approach 1:
The patent implements dynamic adjustment of the dimming command parameters based on the optocoupler's actual performance characteristics. The system adaptively modifies pulse widths, frequencies, and timing to optimize the balance between response speed and reliable signal detection, rather than using fixed parameters. This dynamic approach allows the system to achieve faster response while maintaining reliability across varying operating conditions.
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 method effectively communicates dimming levels across isolating devices with variable rise and fall times, improving dimming control and reducing flicker issues by eliminating unknown delays, thus enhancing the reliability and efficiency of dimming control in flyback converters.
Implementation Method 1
the dimming command may be communicated through an isolating device such as an optocoupler or an isolating transformer
Implementation Method 2
The resulting current through the primary winding develops a magnetic field that stores energy. This stored energy is released when the power switch cycles off
Data Source
AI summary
An data transmission method is provided for transmitting analog data through an isolating device using a calibration input pulse and a data input pulse. The analog data may represent, for example, the desired dimming value for a flyback converter powering a solid state lighting system.