Load-Adaptive Auxiliary Capacitor Control in Flyback Converters
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Solution Overview
Problem
Conventional quasi-resonant flyback converters face challenges in suppressing radiated electromagnetic interference under heavy loads, which leads to high switching losses and low average efficiency, especially at light loads due to increased capacitance.
Innovation Solution
A switching power converter with an auxiliary circuit including an auxiliary switch and capacitor, where the control module adjusts the capacitance threshold based on load state, turning off the auxiliary switch at light loads to reduce capacitance and turning it on at heavy loads to maintain higher capacitance, thereby suppressing electromagnetic interference and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a capacitor is disposed in parallel to the transistor to suppress radiated electromagnetic interference, then electromagnetic interference is suppressed, but the overall capacitance increases resulting in high switching loss and low average efficiency
Solution Approach 1:
The patent applies the dynamics principle by making the capacitance value adjustable based on operating conditions. An auxiliary capacitor is introduced that can be dynamically connected or disconnected from the main capacitor through a control circuit. When the power supply operates at light load, the auxiliary capacitor is disconnected to maintain low total capacitance and reduce switching loss. When operating at heavy load, the auxiliary capacitor is connected to provide sufficient capacitance for EMI suppression. This dynamic adjustment resolves the contradiction between EMI suppression and switching loss reduction.
2Object-affected harmful factors
If the capacitance of the equivalent capacitor is increased to suppress electromagnetic interference, then electromagnetic interference suppression is improved, but the average efficiency at light load decreases
Solution Approach 1:
The patent applies the parameter changes principle by varying the total capacitance parameter according to the operating load conditions. The control circuit monitors the load state and adjusts the capacitance configuration accordingly. At light load conditions (e.g., below 30% of rated power), the auxiliary capacitor is disconnected, maintaining the equivalent capacitance at a low value (only the main capacitor remains). At heavy load conditions (e.g., above 30% of rated power), the auxiliary capacitor is connected, increasing the equivalent capacitance to a high value for effective EMI suppression. This parameter adaptation ensures high efficiency at light load while maintaining EMI compliance at heavy load.
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 reduces losses and enhances average efficiency by minimizing capacitance at light loads and utilizing the auxiliary capacitor at heavy loads to suppress electromagnetic interference.
Implementation Method 1
the auxiliary circuit includes an auxiliary switch and an auxiliary capacitor, and the auxiliary switch and the auxiliary capacitor are electrically connected in series
Data Source
AI summary
A switching power converter and a control method thereof are provided. First, a switching power converter is provided. The switching power converter includes a main switch and an auxiliary circuit electrically connected in parallel to the main switch, and the auxiliary circuit includes an auxiliary switch and an auxiliary capacitor electrically connected in series. Afterwards, a load state of the switching power converter is detected. When the load state of the switching power converter is light, the auxiliary switch is controlled to turn off for maintaining a capacitance of a first equivalent capacitor between a drain and a source of the main switch at a low threshold. When the load state of the switching power converter is heavy, the auxiliary switch is controlled to turn on for maintaining the capacitance of the first equivalent capacitor at a high threshold.