Leading-edge phase-cut bleeder control for LED dimming
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Solution Overview
Problem
Conventional triac-based dimming units are incompatible with high-impedance lighting sources like LEDs due to insufficient synchronization, latching, and holding currents, leading to operational issues and inductive oscillations when bleeder circuits are used.
Innovation Solution
A bleeder arrangement with a controllable current sink and a controller that disables the sink in two stages after the leading-edge phase-cut device has latched, allowing for a gradual reduction in current to minimize inductive oscillations and ensure proper triac operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bleeder circuit is used to sink current for high-impedance loads, then the triac can operate properly, but inductive oscillations occur upon switch-off
Solution Approach 1:
The bleeder circuit transitions from a static on/off configuration to a dynamic multi-stage control system. The controller disables the current sink in at least two stages: first reducing current to an intermediate level, then gradually reducing it to zero. This dynamic approach allows the triac to settle and latch properly while minimizing inductive oscillations upon switch-off.
Solution Approach 2:
The single switch-off action is segmented into multiple discrete stages. Instead of disabling the current sink in one abrupt action, the invention divides the disablement process into at least two distinct stages: an intermediate reduction stage and a final reduction to zero stage. This segmentation allows controlled energy dissipation and reduces harmful oscillations.
2Loss of energy
If the current sink is disabled abruptly, then the bleeder circuit is efficient, but the triac does not latch properly
Solution Approach 1:
The controller implements dynamic multi-stage control of the current sink disablement process. By transitioning through intermediate current levels rather than abrupt switch-off, the system ensures the triac has sufficient time to settle and latch into its on-state. The gradual reduction maintains triac reliability while still achieving efficient energy management.
Solution Approach 2:
The controller performs preliminary action by reducing the current to an intermediate level before complete disablement. This intermediate stage provides a transition period that allows the triac to establish its latched state before the current is fully reduced to zero, ensuring proper latching while maintaining overall efficiency.
3Reliability
If a conventional bleeder circuit is used, then current is sunk to ensure triac operation, but the bleeder represents a source of loss
Solution Approach 1:
The bleeder circuit operates periodically rather than continuously. The controller disables the current sink during portions of the mains phase when it is not required, specifically after the triac has latched. This periodic operation maintains triac reliability when needed while minimizing energy losses during periods when the bleeder is disabled.
Solution Approach 2:
The system dynamically adjusts the bleeder circuit operation based on real-time conditions. By controlling the current sink to operate only during necessary periods and then disabling it in staged manner, the system optimizes the balance between ensuring triac operation and minimizing energy losses associated with continuous bleeder operation.
Data Source
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AI summary
A bleeder arrangement for a phase-cut circuit for a high-Impedance load and having a leading-edge phase-cut device is disclosed, the bleeder arrangement comprising: a controllable current sink adapted to sink a latching current through the leading-edge phase-cut device, and a controller for controlling the controllable current sink, wherein the controller is configured to disable the current sink after the leading-edge phase phase-cut device has latched in at least two stages. A controller for use in such an arrangement is also disclosed, as is a method of controller such a bleeder arrangement.