Direct AC LED Jitter Reduction via TRIAC On-Time Control
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Solution Overview
Problem
Direct AC LED lighting devices experience significant jitter when used with phase-cut dimmer switches, leading to unpredictable light intensity changes that discourage consumers from switching from incandescent bulbs.
Innovation Solution
An LED on-time controller is introduced to filter out variations in TRIAC on-times, maintaining constant LED on-time across AC half cycles by controlling the LED current source and using a comparator to determine when the post diode bridge voltage exceeds the LED threshold voltage, thereby reducing jitter-induced variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a direct AC LED lighting device is used with a phase-cut dimmer switch, then cost is reduced by eliminating the switching power converter, but jitter occurs causing random light intensity changes
Solution Approach 1:
The patent applies preliminary action by measuring the TRIAC on-time duration in advance before it causes jitter effects. The controller measures the actual on-time of the TRIAC during each AC half-cycle and uses this measurement to predict and compensate for potential jitter-induced variations in LED current, thereby preventing light intensity fluctuations before they occur.
Solution Approach 2:
The patent implements feedback by continuously monitoring the TRIAC on-time and using this information to adjust the LED current control. The controller measures the actual TRIAC conduction time and feeds this information back to modify the LED driving current accordingly, creating a closed-loop system that compensates for jitter effects and maintains stable light output.
2Ease of operation
If the TRIAC firing time varies due to dimmer switch jitter, then the LED current varies causing detectable light intensity changes, but the human eye can detect these changes which discourages users
Solution Approach 1:
The controller measures the TRIAC on-time duration in advance during each AC half-cycle, before the LED current is applied. By having this measurement ready beforehand, the system can immediately compensate for any firing time variations without delay, preventing detectable light intensity changes that would otherwise occur due to jitter.
Solution Approach 2:
The system establishes a feedback loop where the measured TRIAC on-time is continuously fed back to the LED current controller. This feedback mechanism allows the system to dynamically adjust the LED current based on actual TRIAC conduction time, thereby maintaining consistent light intensity despite variations in TRIAC firing time caused by dimmer switch jitter.
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
The solution effectively reduces jitter in direct AC LED lighting devices, ensuring consistent light intensity and user satisfaction, thereby promoting the adoption of direct AC LED devices over incandescent bulbs.
Implementation Method 1
The diode bridge rectifies a phase-cut AC input from the TRIAC to produce the post diode bridge voltage
Implementation Method 2
When the rectified AC input voltage rises above the LED threshold voltage for the LED, the controller controls the LED current
Data Source
AI summary
A direct AC LED lighting device is provided with a low-pass filter for filtering a threshold time in which a post diode bridge voltage exceeds an LED threshold voltage during a current AC half cycle for the post diode bridge voltage.