Resonant Hybrid Flyback Converter Startup Without LED Flicker
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Solution Overview
Problem
Resonant hybrid flyback converters for LED loads face challenges in start-up due to lack of load information, leading to slow closed-loop regulation and visible flicker caused by peak currents during the ramp-down operation of the low-side switch conduction phase.
Innovation Solution
A control circuit that progressively ramps down the initial duration of the low-side switch conduction phase until a target output voltage is reached, saves this duration for future use, and alternately drives the high-side and low-side switches based on the saved duration and regulated target input peak current, avoiding repetitive ramp-downs and peak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the converter performs progressive ramp-down of the low-side switch conduction phase duration during start-up, then the output voltage reaches the target value, but peak currents occur causing visible flicker
Solution Approach 1:
The control circuit performs a progressive ramp-down of the low-side switch conduction phase duration during start-up to reach the target output voltage, then saves this optimized duration for future operations. This preliminary action eliminates peak currents and flicker in subsequent start-ups by avoiding repetitive ramp-down sequences.
Solution Approach 2:
The control circuit monitors the output voltage during start-up, detects when the target output voltage is reached, and automatically saves the corresponding low-side switch conduction phase duration. This feedback mechanism ensures the optimal duration is captured and reused, preventing harmful peak currents in future operations.
2Reliability
If the converter repeatedly performs ramp-down operation during each start-up, then the output voltage is regulated, but the operation time increases
Solution Approach 1:
The control circuit performs the time-consuming progressive ramp-down operation only once during the first start-up to determine the optimal low-side switch conduction phase duration. This saved duration is then reused in subsequent start-ups, reducing the operation time from milliseconds to microseconds while maintaining proper voltage regulation.
Solution Approach 2:
The control circuit changes the operating parameter (low-side switch conduction phase duration) from a dynamic ramp-down sequence during start-up to a static saved value during normal operations. This parameter change eliminates repetitive adjustments and significantly reduces start-up operation time.
3Adaptability or versatility
If the converter lacks load information during start-up, then it can support various LED loads, but it cannot optimize the conduction phase duration
Solution Approach 1:
The control circuit automatically determines the optimal low-side switch conduction phase duration by performing a progressive ramp-down during the first start-up and saving the result. This self-service approach eliminates the need for external load information or manual configuration, allowing the converter to adapt to various LED loads while optimizing performance autonomously.
Solution Approach 2:
The control circuit performs a preliminary progressive ramp-down operation during the first start-up to automatically determine and save the optimal conduction phase duration specific to the connected load. This preliminary characterization enables the converter to achieve both load adaptability and operational optimization without requiring load information.
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 solution ensures stable start-up operations without flicker, protects circuit components, and adapts to load changes by recalling saved durations, thus improving the efficiency and reliability of the converter.
Implementation Method 1
induce an oscillation-based power supply via a resonant tank circuit
Implementation Method 2
inductively coupled primary-side and secondary-side circuits
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Disclosed is a resonant hybrid flyback converter (1), comprising inductively coupled primary-side and secondary-side circuits (11, 12); the primary-side circuit (11) comprising a high-side switch (111) and a low-side switch (112) arranged in series; and a control circuit (113). The control circuit (113) is operable to progressively ramp down a predefined initial duration (221, 22, Ton,ls) of the conduction phase of the low-side switch (112) until the converter (1) supplies a predefined target output voltage (VLED); save the down-ramped duration (222, 22, Ton,ls) of the conduction phase of the low-side switch (112); alternatingly drive the high-side switch (111) and the low-side switch (112) in accordance with an adjustable duration (21, Ton,hs) of the conduction phase of the high-side switch (111) in accordance with a regulated target input peak current (ÎN) of the converter (1), and the saved duration (222, 22, Ton,ls) of the conduction phase of the low-side switch (112); recall the saved duration (222, 22, Ton,ls) of the conduction phase of the low-side switch (112) following an interruption of operation of the converter (1); and proceed to the alternating drive operation. This avoids peak currents and visible flicker during a start-up of the converter.