Active Clamp Flyback Converter Resonance Control
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Solution Overview
Problem
Conventional active clamp flyback converters face issues with high conduction loss, poor SR control performance, and low efficiency due to multiple turn-on of the synchronous rectification switch and high RMS value of primary current, which are exacerbated by the dominance of clamping capacitor resonance.
Innovation Solution
The converter circuit design shifts the resonance dominance from the clamping capacitor to the output capacitor, employing a secondary-resonant scheme where the output capacitor Co dominates the resonant process, minimizing the effect of the clamping capacitor Cr, thereby eliminating double-turn-on issues and reducing RMS current values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If clamping capacitor Cr dominates the resonant process, then leakage inductance energy is recovered, but multiple turn-on of synchronous rectification switch occurs causing high conduction loss
Solution Approach 1:
The patent changes the resonant parameters by making the output capacitor Co dominate the resonant process instead of the clamping capacitor Cr. This is achieved by designing the circuit such that the resonant frequency is determined primarily by Co and the leakage inductance, rather than by Cr. This parameter change eliminates the multiple turn-on issue of the synchronous rectification switch while still recovering leakage inductance energy, thereby reducing conduction loss and improving SR control performance.
2Loss of energy
If clamping capacitor Cr dominates resonance, then leakage inductance is recovered, but RMS value of primary current increases
Solution Approach 1:
The patent modifies the resonant circuit parameters to make the output capacitor Co the dominant resonant element. By setting the resonant frequency ωo = 1/√(LoCo) where Lo is the leakage inductance and Co is the output capacitor, the circuit achieves a resonant mode where the primary current waveform is optimized. This parameter configuration reduces the RMS value of the primary current while maintaining leakage inductance recovery, thereby reducing conduction losses.
3Reliability
If output capacitor Co dominates resonance, then SR control stability improves, but circuit resonance characteristics change
Solution Approach 1:
The patent deliberately changes the resonance characteristics by making Co dominate over Cr in determining the resonant frequency. The design ensures that the resonant frequency is approximately ωo = 1/√(LoCo) rather than being determined by Cr. This parameter change stabilizes the synchronous rectification control by eliminating the multiple turn-on phenomenon, while the new resonance characteristics are intentionally designed and controlled to achieve the desired performance.
4Loss of energy
If clamping capacitor Cr is used for resonance, then leakage energy recovery is achieved, but efficiency decreases
Solution Approach 1:
The patent changes the resonant energy storage parameter from the clamping capacitor Cr to the output capacitor Co. By making Co the dominant resonant element, the circuit achieves a more efficient energy transfer mode where the resonant oscillation naturally controls the synchronous rectification switch timing. This eliminates the multiple turn-on loss and reduces overall energy loss, thereby improving converter efficiency while still recovering leakage inductance energy.
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 achieves reliable zero-current-switching performance, reduces conduction losses, and improves the efficiency of the active clamp flyback converter by minimizing the impact of clamping capacitor resonance, resulting in lower RMS current and improved control stability.
Implementation Method 1
the converter circuit has a secondary synchronous rectification operation, where during the second interval a current through the rectifying switch becomes substantially equal to zero less than two times regardless of: a) voltage at the input, b) average voltage across the output capacitor, and c) average current through the rectifying switch
Implementation Method 2
a transformer having a primary side and a secondary side; a primary circuit connected to the primary side of the transformer... a secondary circuit connected to the secondary side of the transformer
Data Source
AI summary
A converter circuit is disclosed. The converter circuit includes a transformer and a primary circuit connected to the primary side of the transformer, where the primary circuit includes a first switch connected to a ground. The converter circuit also includes a second switch connected to the first switch, and a clamping capacitor connected to the second switch and to the input. The converter circuit also includes a secondary circuit connected to the secondary side of the transformer, where the secondary circuit includes a rectifying element, and an output capacitor connected to the rectifying element. In addition, the output capacitor has a substantial effect on resonance of the converter circuit.