Valley-Controlled PFC Timing for Flicker-Free LED DCM
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Solution Overview
Problem
Converters for LED-based light sources operating in discontinuous conduction mode face regulation errors due to actual switch-on timing deviating from nominal timing, leading to low-frequency instability and visible light flicker.
Innovation Solution
A converter with actively switched power factor correction circuitry controls the switch-on timing to align with voltage valleys, using feedback control to adjust the timing in consecutive switching cycles, ensuring the actual timing oscillates between voltage valleys to match the nominal timing, thereby eliminating visible flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If valley switching is used to optimize switching performance, then switching efficiency is improved, but regulation accuracy deteriorates due to timing deviation from nominal value
Solution Approach 1:
The patent implements feedback control by detecting the actual valley timing of the switch voltage and comparing it with the nominal valley timing. The control circuitry adjusts the switching timing based on the detected error, ensuring that the actual switch-on timing aligns with the optimal valley point while maintaining accurate regulation of the DC parameter.
Solution Approach 2:
The control circuitry preliminarily determines the nominal valley timing using a control algorithm before actual switching occurs. This preliminary action allows the system to prepare the optimal switch-on timing in advance, then adjust based on actual valley detection to resolve the timing deviation.
2Loss of energy
If regulation of DC parameter is made slow to reduce switching frequency, then switching losses are reduced, but regulation stability deteriorates due to error accumulation causing light flicker
Solution Approach 1:
The feedback mechanism continuously monitors the actual switch-on timing and adjusts it to match the nominal timing. This prevents error accumulation over multiple switching cycles, maintaining regulation stability and eliminating light flicker while allowing for lower switching frequencies that reduce switching losses.
Data Source
AI summary
A converter (1) for operating an LED load is provided. The converter (1) comprises an actively switched power factor correction, PFC, circuitry (104-112), having a control circuitry (2-4) for controlling a switch (105) of the PFC circuitry (104-112). The control circuitry (2-4) is configured to control a switch-on timing of the switch (105) such that an output voltage (113, Vbus) of the PFC circuitry (104-112) is feedback-controlled in accordance with a nominal value (201). In a discontinuous conduction mode, DCM, the control circuitry (2-4) is configured to control an actual value (204, Toff_act) of the switch-on timing of the switch (105) in one or more switching cycles to be a time of a valley of a voltage across the switch (105) succeeding a nominal value (302, Toff_nom) of the switch-on timing of a control algorithm implemented by the control circuitry (2-4). The control circuitry (2-4) is further configured to control the actual value (204, Toff_act) of the switch-on timing of the switch (105) in one or more subsequent switching cycles being subsequent to the one or more switching cycles to be a time of a valley of the voltage across the switch (105) preceding the nominal value (302, Toff_nom) of the switch-on timing. This reconciles valley switching and avoidance of visible light flicker.