Flyback Converter Valley Sensing for Switching Loss Reduction
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Solution Overview
Problem
Conventional flyback power converter circuits face inefficiencies due to adaptive frequency adjustments, leading to higher switching losses and frequency hopping issues when the load condition changes, particularly because the primary side switch may not turn ON at valley points, resulting in increased power loss and reduced conversion efficiency.
Innovation Solution
A flyback power converter circuit with a conversion control circuit that calculates upper and lower limit frequencies based on output current, generates masking periods, and selects valley points for the primary side switch to turn ON, ensuring the switching frequency remains within optimal limits and reducing power loss by aligning switch ON times with valley points in the ringing signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If adaptive frequency adjustment is implemented to reduce switching loss at light loads, then switching loss is reduced, but the primary side switch may not turn ON at valley points, resulting in increased power loss and reduced conversion efficiency
Solution Approach 1:
The patent implements a feedback mechanism by detecting the ringing signal of the primary side switch and identifying valley points. The control circuit uses this feedback information to adjust the switching timing, ensuring the primary side switch turns ON at or near valley points. This closed-loop control resolves the contradiction by maintaining high conversion efficiency while still benefiting from adaptive frequency adjustment at light loads.
Solution Approach 2:
The patent dynamically adjusts the switching frequency and timing based on load conditions. At light loads, the frequency is reduced to minimize switching loss, while the valley detection mechanism dynamically adjusts the switching phase to maintain efficiency. This dynamic adaptation allows the system to optimize both switching loss and conversion efficiency across different operating conditions.
2Loss of energy
If switching frequency is reduced at light loads to minimize switching loss, then switching loss is reduced, but audio noise may increase due to operation below minimum frequency
Solution Approach 1:
The patent employs periodic valley detection and switching synchronization to maintain regular switching patterns even at reduced frequencies. By aligning switching events with the periodic ringing signal valleys, the system maintains a consistent rhythm that minimizes audio noise while still operating at lower frequencies to reduce switching loss.
3Power
If switching frequency is increased at heavy loads to meet power demand, then power output is increased, but switching loss increases due to operation above maximum frequency
Solution Approach 1:
The system dynamically adjusts switching frequency based on load demands, increasing it at heavy loads to meet power requirements. The valley detection mechanism simultaneously adjusts switching timing to occur at optimal points, ensuring that even at higher frequencies, switching loss is minimized by maintaining proper synchronization with the ringing signal.
4Device complexity
If fixed switching frequency is used to simplify control, then control complexity is reduced, but power loss increases due to inability to adapt to load changes
Solution Approach 1:
The patent implements a self-service control mechanism where the system automatically detects load conditions and adjusts switching frequency and timing without complex external control. The valley detection circuit autonomously identifies optimal switching points, and the control circuit self-adjusts parameters based on detected conditions, reducing power loss while maintaining relatively simple control architecture.
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 approach reduces power loss and enhances power conversion efficiency by ensuring the primary side switch operates at optimal frequencies, minimizing unwanted audio noise and switching losses across varying load conditions.
Implementation Method 1
a power transformer, which is coupled between the input voltage and the output voltage via electromagnetic induction
Implementation Method 2
a parasitic capacitor of the primary side switch and a primary side winding will constitute an inductor-capacitor oscillator circuit
Data Source
AI summary
A flyback power converter circuit includes: a power transformer, a primary side switch and a conversion control circuit. In a DCM, during a dead time, the conversion control circuit calculates an upper limit frequency corresponding to output current according to a frequency upper limit function, and obtains a frequency upper limit masking period according to a reciprocal of the upper limit frequency, wherein the frequency upper limit masking period is a period starting from when the primary side switch is turned ON. During an upper limit selection period, the conversion control circuit selects a valley among one or more valleys in a ringing signal related to a voltage across the primary side switch as an upper limit locked valley, so that the conversion control circuit once again turns ON the primary side switch at a beginning time point of the upper limit locked valley.