Active Clamp Flyback Control for Lower MOSFET Switching Loss
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing Active Clamp Flyback (ACF) solutions suffer from power losses due to increased body diode conduction and reverse recovery losses, which reduce efficiency and flux density in power transformers.
Innovation Solution
Implementing a controlling method that selectively turns on and off the active clamp switch at specific power converter switching cycles, maintaining a higher clamping voltage and recovering snubber energy without relying on resonating voltages for Zero Voltage Switching (ZVS).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the active clamp switch is turned on at every switching cycle to recover leakage inductance energy, then energy recovery is improved, but power losses in the active clamp switch and body diode increase
Solution Approach 1:
The active clamp switch is activated periodically rather than at every switching cycle. The controller selectively turns on the active clamp switch based on detected conditions (such as voltage across the primary switch), allowing energy recovery only when beneficial, thereby reducing unnecessary conduction and reverse recovery losses while maintaining effective leakage inductance energy recovery
2Reliability
If the active clamp switch is frequently turned on to maintain clamping voltage, then voltage clamping is improved, but switching losses increase
Solution Approach 1:
The controller detects the voltage across the primary switch and uses this feedback information to determine when to turn on the active clamp switch. This feedback mechanism ensures the active clamp switch is activated only when the clamping voltage needs to be maintained, avoiding unnecessary switching operations and reducing switching losses while preserving reliable voltage clamping
3Reliability
If the active clamp switch operates continuously to protect the primary switch, then switch protection is improved, but body diode conduction losses increase
Solution Approach 1:
The system uses the detected voltage conditions across the primary switch to self-determine when active clamp protection is needed. The controller monitors the voltage and activates the active clamp switch only when protection is actually required, rather than operating continuously. This selective operation maintains primary switch protection while minimizing body diode conduction losses by avoiding unnecessary active clamp switch activation
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
Reduces power losses by minimizing ACF MOSFET and body diode losses, maintaining efficient clamping and transformer flux density.
Implementation Method 1
the surge voltage is caused by the transformer leakage inductance and sudden turn off of the primary switch
Implementation Method 2
The transistor serves the diode function with its built in diode, and also is actively switched on to recycle of the snubber capacitor energy back to the transformer and input power source
Implementation Method 3
Another important aspect of active clamp is its resonate property, which can be used to soft switching the associated power switch
Data Source
AI summary
A controlling method of a power converter includes performing a first switch controlling step and a second switch controlling step. The first switch controlling step is performed to control a primary switch of the power converter by a first controlling signal. The second switch controlling step is performed to control an active clamp switch of the power converter by a second controlling signal. The primary switch is turned on by the first controlling signal at each of a plurality of power converter switching cycles. The active clamp switch is not turned on by the second controlling signal at a part of the power converter switching cycles, and the active clamp switch is turned on by the second controlling signal at another part of the power converter switching cycles.