LED Lighting System with Dynamic Bleeder Current Control
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Solution Overview
Problem
Dimmable LED lighting systems using TRIAC devices face premature turn-off due to insufficient bleeder current, leading to light flicker or failure, and unnecessary power consumption when the dimming function is not activated.
Innovation Solution
An LED lighting system with a bleeder circuit comprising three current sources, a current-sensing element, and a control unit that dynamically manages bleeder current based on system current feedback, ensuring the TRIAC remains conductive above the minimum holding current and reducing power consumption when dimming is not required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bleeder circuit is used to provide bleeder current for voltage management and preventing the dimmer switch from turning off prematurely, then the reliability of the dimmer switch is improved, but the power consumption increases unnecessarily when the dimming function is not activated
Solution Approach 1:
The patent implements dynamic control of the bleeder current by using a control unit that monitors system current levels and automatically adjusts the bleeder current source accordingly. When the system detects that the main current is sufficient to maintain TRIAC conduction, it reduces or eliminates the bleeder current, thereby eliminating unnecessary power consumption while maintaining reliability when needed.
Solution Approach 2:
The patent employs a feedback mechanism where the control unit continuously monitors the system current and uses this information to regulate the bleeder current output. This closed-loop control ensures that the bleeder current is supplied only when necessary to prevent TRIAC turn-off, optimizing the balance between reliability and power consumption.
2Reliability
If the TRIAC is designed to latch-on and continue conducting until forward current drops below holding current, then the switching reliability is improved, but the system becomes sensitive to insufficient current at turn-on when LED load presents high impedance
Solution Approach 1:
The patent applies preliminary action by providing a bleeder current that is activated before the main switching operation. This pre-supplied current ensures that the TRIAC receives sufficient current to latch-on reliably during turn-on, overcoming the high impedance condition of the LED load at startup. The bleeder current is prepared in advance to guarantee successful latching.
Solution Approach 2:
The bleeder current source acts as an intermediary element that bridges the gap between the high-impedance LED load and the TRIAC switching requirement. It provides the necessary intermediate current path to ensure the TRIAC latches properly without requiring the LED load to immediately supply sufficient current.
Data Source
AI summary
An LED lighting system includes a luminescent unit driven by a rectified AC voltage, a dimmer switch configured to adjusting a duty cycle of a system current, and a bleeder circuit. The bleeder circuit includes a first current source, a second current source, a third current source, a current-sensing element for providing a first feedback voltage associated with the system current, a capacitor, and a control unit. The control unit is configured to activate the first current source and deactivate the second current source for charging the capacitor when the system current exceeds a predetermined threshold, deactivate the first current source and activate the second current source for discharging the capacitor when the system current does not exceed the predetermined threshold, and deactivate the third current source to stop supplying the bleeder current according to a second feedback voltage established across the capacitor.