Adaptive Active Clamp Flyback Converter for Leakage Inductance Protection
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Solution Overview
Problem
In flyback converters, the rapid increase of drain-to-source voltage across the power switch transistor due to parasitic leakage inductance can lead to damage or catastrophic failure, and conventional snubber circuits reduce efficiency by dissipating energy.
Innovation Solution
An active-clamp flyback converter with an active-clamp switch, capacitor, and controller that measures the peak charge time of the active-clamp capacitor, switching on the active-clamp switch at a time equal to the difference between the power switch turn-on time and the peak charge time, thereby preventing resonant oscillation of the drain-to-source voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a snubber circuit is used to protect the power switch transistor from voltage spikes, then the reliability of the power switch transistor is improved, but the energy efficiency deteriorates due to energy dissipation in the snubber resistor
Solution Approach 1:
The patent converts the harmful resonant energy from the parasitic leakage inductance into a beneficial charged state of the active-clamp capacitor. Instead of dissipating energy through resistance, the circuit captures the resonant energy and stores it electrically in the active-clamp capacitor, which can then be reused to assist in the next switching cycle, thereby improving both protection and efficiency
Solution Approach 2:
The active-clamp capacitor serves as an intermediary energy storage element between the parasitic leakage inductance and the power switch transistor. It mediates the harmful voltage spikes by absorbing resonant energy during the off-time and releasing it during the on-time, replacing the traditional resistive snubber with a reactive energy storage mechanism that avoids energy dissipation
2Reliability
If the active-clamp switch is switched on immediately after the power switch turns off, then the protection against voltage spikes is improved, but the energy efficiency deteriorates due to prolonged conduction losses
Solution Approach 1:
The patent implements periodic switching of the active-clamp switch synchronized with the power switch cycle. The active-clamp switch is turned on only during specific intervals (when the power switch is off and resonant energy needs to be captured), and turned off during other intervals (when the power switch is on and conduction losses would be excessive), creating an optimized periodic operation pattern that balances protection and efficiency
Solution Approach 2:
The patent dynamically adjusts the timing and duration of the active-clamp switch conduction based on the real-time state of the circuit. By measuring the peak charge time and using adaptive timing control, the system optimizes the active-clamp switch on-time to capture resonant energy while minimizing conduction losses, making the protection mechanism adaptive rather than static
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 solution effectively reduces stress on the power switch transistor, maintains efficiency by avoiding energy dissipation, and allows zero-voltage switching, applicable in both continuous and discontinuous conduction modes.
Implementation Method 1
The serial combination of the active-clamp capacitor and the leakage inductance forms a resonant circuit that stores the leakage inductance energy that would otherwise cause the drain-to-source voltage of the power switch transistor to pulse to a potentially-damaging level.
Data Source
AI summary
An active-clamp flyback converter is provided with improved active-clamp switch control that switches on an active-clamp switch at an active-clamp switch on-time that equals a power switch on-time minus a peak charge time for an active-clamp capacitor. The peak charge time is the duration between the switching off of the power switch transistor and when the charging current through the active-clamp capacitor falls to zero. The controller measures this peak charge time following the switching off of the power switch transistor and then applies it to the subsequent switching on of the active-clamp switch so that the active-clamp switch is switched on at the power switch on-time minus the peak charge time.