Flyback Converter Quasi-Resonant Trough Locking Control
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Solution Overview
Problem
Flyback converters operating in quasi-resonant mode often experience vibrations at turn-on points due to frequency control issues, leading to sound noise, especially when the ripple of the input voltage is large, making it difficult to accurately lock the turn-on trough and maintain high conversion efficiency.
Innovation Solution
A control circuit that determines the turn-on trough by checking if a time signal corresponding to a lock-on trough is within a threshold range, ensuring the power switch is turned on at the same ordinal number trough as the last cycle, using a discontinuous time reference signal to adjust the switching frequency and reduce vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If frequency control is used to operate the flyback converter in quasi-resonant mode, then conversion efficiency is improved, but vibrations and sound noise occur at turn-on points due to inaccurate locking of the turn-on trough
Solution Approach 1:
The patent implements a feedback mechanism where the control circuit monitors the actual turn-on trough position and compares it with the target trough position. Based on this comparison, the control circuit adjusts the switching frequency in real-time to ensure accurate locking of the turn-on trough, thereby eliminating vibrations and sound noise while maintaining high conversion efficiency.
Solution Approach 2:
The patent dynamically changes the switching frequency parameter based on the detected trough position. When the input voltage ripple causes the trough position to shift, the control circuit adjusts the switching frequency to track and lock onto the correct trough, ensuring optimal switching conditions and preventing harmful vibrations.
2Measurement precision
If the switching frequency is adjusted to track the turn-on trough, then accurate trough locking is achieved, but the control circuit complexity increases
Solution Approach 1:
The control circuit automatically detects the turn-on trough position and self-adjusts the switching frequency without requiring external intervention or complex external control systems. This self-service approach achieves accurate trough locking while minimizing additional circuit complexity by integrating the detection and adjustment functions within the existing control structure.
3Reliability
If the turn-on trough locking range is widened to accommodate large input voltage ripples, then trough locking reliability is improved, but switching losses increase
Solution Approach 1:
The patent implements a dynamic adjustment mechanism where the switching frequency is continuously adapted to track the turn-on trough position. This dynamic approach allows the system to maintain reliable trough locking across varying input voltage conditions while keeping switching losses minimal by always operating at the optimal frequency point.
Solution Approach 2:
The control circuit performs preliminary detection of the turn-on trough position before switching occurs and uses this information to pre-adjust the switching frequency. This preliminary action ensures that the converter is ready to switch at the optimal moment, maintaining both reliability and efficiency even under large input voltage ripple conditions.
Data Source
AI summary
A control circuit for controlling a power stage circuit of a switching converter, where the power stage circuit includes a magnetic component and a power switch, can include: the control circuit being configured to determine a turn-on trough of a current cycle by determining whether a time signal corresponding to a lock-on trough of the current cycle is within a threshold range, thereby controlling the power switch to be turned on at the determined turn-on trough; and whereby an ordinal number of the lock-on trough of the current cycle is the same as an ordinal number of the turn-on trough of the last cycle.