Quasi-Resonant Flyback Control With Dynamic Valley Locking
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Solution Overview
Problem
Flyback converters with quasi-resonant control face issues with high switching frequencies leading to electromagnetic interference, audio noise, and decreased efficiency due to increased switching losses.
Innovation Solution
A controller for a switching converter with quasi-resonant control, comprising a hysteresis feedback circuit, comparison circuits, a valley detection circuit, and a turn-on control circuit, which dynamically adjusts the target locked valley number based on hysteresis feedback and output signals to optimize switching frequency and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the switching frequency is increased to meet higher power density demands, then the power conversion capability is improved, but the switching losses increase proportionally resulting in decreased efficiency
Solution Approach 1:
The patent implements dynamic adjustment of the switching frequency through a control circuit that modifies the valley lock strategy based on real-time operating conditions. The controller dynamically changes the target locked valley number according to input voltage, output voltage, and load conditions, enabling the converter to operate at optimal frequencies rather than fixed high frequencies, thus reducing switching losses while maintaining power conversion capability
Solution Approach 2:
The patent changes the operating parameters by adjusting the switching frequency and valley lock strategy based on different operating modes. The control circuit monitors input/output voltages and load conditions to determine appropriate switching frequencies, transforming the system from static high-frequency operation to dynamic parameter-adjusted operation, thereby reducing switching losses at light loads while maintaining high power density at full load
2Power
If the switching frequency is increased to provide higher power density, then the power output capability is improved, but electromagnetic interference is generated affecting power grid quality and electronic devices
Solution Approach 1:
The control circuit dynamically adjusts the switching frequency based on operating conditions, reducing the frequency at light loads and high input voltages to minimize electromagnetic interference, while maintaining higher frequencies at full load to ensure adequate power output capability
Solution Approach 2:
The patent implements preliminary control by setting minimum time limits and minimum off-time before the power switch can be turned on, preventing the switching frequency from exceeding predetermined thresholds that would cause electromagnetic interference, thus proactively mitigating the harmful effect before it occurs
3Object-affected harmful factors
If a minimum time limit is set to limit the switching frequency, then electromagnetic interference is reduced, but audio noise and discontinuous output power are generated due to valley jumping
Solution Approach 1:
The patent implements dynamic valley lock strategy where the target locked valley number is adjusted based on operating conditions. This dynamic adjustment prevents the fixed minimum time limit from causing valley jumping between adjacent valleys, thereby eliminating audio noise while still maintaining electromagnetic interference reduction through controlled switching frequency
Solution Approach 2:
The control circuit uses feedback from input voltage, output voltage, and load conditions to dynamically determine the appropriate target locked valley number. This feedback mechanism ensures smooth transitions between valleys and prevents the discontinuous output power and audio noise associated with fixed minimum time limit approaches
4Object-affected harmful factors
If the switching frequency is limited using traditional minimum time limit method, then electromagnetic interference is reduced, but the switching converter cannot meet higher power density demands requiring much higher switching frequency
Solution Approach 1:
The patent implements dynamic frequency adjustment that allows high switching frequencies when needed for power density while automatically reducing frequency when electromagnetic interference becomes problematic. The control circuit adapts the switching frequency to operating conditions, providing high power density capability without the continuous electromagnetic interference of fixed high-frequency operation
Solution Approach 2:
The system dynamically changes the switching frequency parameter based on operating mode, input voltage, output voltage, and load conditions. This parameter adjustment enables the converter to achieve high power density when required while maintaining electromagnetic interference limits, resolving the contradiction between power density demands and EMI constraints
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
The solution effectively limits switching frequency, reduces electromagnetic interference and audio noise, and improves efficiency by dynamically adjusting the valley lock strategy based on input/output signals.
Implementation Method 1
when a current flowing through an energy storage component decreases to zero, the energy storage component resonates with a parasitic capacitance of a power switch
Implementation Method 2
The hysteresis feedback circuit is configured to generate a hysteresis feedback signal based on an output feedback signal
Data Source
AI summary
A controller of a switching converter having a switch and an energy storage component. The controller has a hysteresis feedback circuit for generating a hysteresis feedback signal based on an output feedback signal of the switching converter, a first comparison circuit for generating a first comparison signal by comparing the hysteresis feedback signal with a ramp signal, a second comparison circuit for generating a second comparison signal by comparing the output feedback signal with the ramp signal, and a turn-on control circuit. The turn-on control circuit generates a target locked valley number based on a valley pulse signal in response to one or more valleys of a voltage drop across the switch, the first comparison signal, the second comparison signal and a current locked valley number, and further generates a turning on control signal corresponding to the target locked valley number for turning ON the switch.