Direct AC LED Dimmer Controller with Periodic Bleeder Circuit
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Solution Overview
Problem
Direct AC LED lighting devices face inefficiencies due to bleeder current losses when used with phase-cut dimmer switches, leading to increased energy consumption and greenhouse gas emissions, as they require a bleeder circuit to maintain a holding current for the TRIAC, resulting in unnecessary power losses.
Innovation Solution
A controller is implemented that switches off the bleeder circuit in response to the initial rising edge of the post diode bridge voltage, then switches it back on after a delay to discharge the voltage, ensuring the TRIAC is only triggered when the post diode bridge voltage exceeds the LED threshold, minimizing bleeder circuit power loss by confining it to the discharge period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bleeder circuit is continuously activated to maintain holding current for the TRIAC, then the TRIAC remains conducting and stable, but power loss increases due to unnecessary bleeder current
Solution Approach 1:
The bleeder circuit is activated periodically rather than continuously. The controller activates the bleeder circuit only during specific time intervals when the TRIAC needs to be kept conducting, and deactivates it when the TRIAC is already conducting or when no holding current is needed. This periodic activation reduces energy loss while maintaining TRIAC stability when required.
Solution Approach 2:
The controller monitors the state of the TRIAC and the post diode bridge voltage to determine when to activate or deactivate the bleeder circuit. This feedback mechanism ensures the bleeder circuit is only active when necessary to maintain TRIAC conduction, avoiding unnecessary power loss while ensuring reliability when needed.
2Reliability
If the bleeder circuit is activated early to ensure TRIAC conduction, then the TRIAC remains conducting, but the bleeder circuit operates longer than necessary increasing power loss
Solution Approach 1:
The controller activates the bleeder circuit in advance of when the TRIAC actually needs to be kept conducting, based on prediction of the voltage rise rate. This preliminary activation ensures the TRIAC will remain conducting when needed, but the controller then deactivates the bleeder circuit as soon as the TRIAC is confirmed conducting, minimizing the activation duration.
Solution Approach 2:
The controller dynamically adjusts the bleeder circuit activation timing based on the actual voltage rise rate and TRIAC state. Rather than using a fixed activation duration, the system adapts the activation timing and duration to the actual operating conditions, optimizing both reliability and energy efficiency.
3Speed
If the post diode bridge voltage rises quickly above LED threshold, then LED conduction is achieved faster, but the TRIAC may reset before the bleeder circuit can maintain holding current
Solution Approach 1:
The controller activates the bleeder circuit in advance of when the voltage is expected to rise above the LED threshold, based on prediction of the voltage rise rate. This ensures the bleeder circuit is already providing holding current when the voltage rises quickly, preventing TRIAC reset while maintaining fast voltage rise.
Solution Approach 2:
The controller monitors the actual voltage rise rate and adjusts the bleeder circuit activation timing accordingly. When the voltage rises quickly, the controller has already activated the bleeder circuit in advance, providing feedback control that ensures TRIAC conduction continuity regardless of the actual voltage rise speed.
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 approach significantly reduces bleeder current losses, enhancing the efficiency of direct AC LED lighting devices by minimizing power consumption and extending their compatibility with leading edge dimming applications, thereby reducing energy waste and emissions.
Implementation Method 1
the AC mains voltage is rectified through a rectifier such as a bridge diode rectifier to produce a rectified AC input voltage
Implementation Method 2
the TRIAC in a leading edge dimmer switch requires a minimum amount of holding current when conducting to prevent the TRIAC from resetting
Implementation Method 3
Bleeder circuit 110 couples to power rail 105 to conduct a holding current into ground
Implementation Method 4
When the rectified AC input voltage (which may also be denoted as a post diode bridge 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 controller that switches off a bleeder circuit following an initial rising edge for a post diode bridge voltage. The controller measures a first delay between a zero crossing for the post diode bridge voltage and the initial rising edge to estimate a triggering voltage for a leading edge dimmer switch. The controller determines a second delay following the initial rising edge responsive to the estimate of the triggering voltage. The controller may thus switch on the bleeder circuit at an expiration of the second delay so that bleeder circuit is only on for a duration sufficient to develop a voltage difference across the leading edge dimmer switch to equal the triggering voltage just as the post diode bridge voltage satisfies an LED threshold voltage.