Asymmetric Half-Bridge Flyback ZVS in Discontinuous Resonant Mode
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Solution Overview
Problem
Traditional asymmetric half-bridge flyback power converters face challenges in achieving zero-voltage switching, particularly in discontinuous resonant modes, leading to increased switching losses due to un-discharged parasitic capacitance in MOSFETs.
Innovation Solution
The implementation of a discharging switch and resonant circuit to reverse-charge the magnetizing inductance before turning on the main switches, utilizing a reverse current to discharge parasitic capacitance and achieve zero-voltage switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If MOSFETs are used as switching components for PWM, then switching speed is fast and loss is low, but parasitic capacitance cannot be fully discharged before switch turn-on, causing cross voltage and switching loss
Solution Approach 1:
The resonant circuit is activated before the main switching action to pre-discharge the parasitic capacitance of the MOSFET. By using the resonant oscillation between the magnetizing inductance and parasitic capacitance, the voltage across the MOSFET is reduced to zero before turn-on, eliminating switching loss while maintaining fast switching capability
Solution Approach 2:
The parasitic capacitance, which was previously a harmful element causing switching loss, is transformed into a useful component of the resonant circuit. By introducing a resonant inductor to work with the parasitic capacitance, the system creates a resonant oscillation that actively discharges the capacitance before switching, converting the harmful parasitic effect into a beneficial zero-voltage switching mechanism
2Device complexity
If traditional asymmetric half-bridge flyback converter is used, then circuit structure is simple, but zero-voltage switching cannot be achieved in discontinuous resonant modes, leading to increased switching losses
Solution Approach 1:
The converter operates in two distinct modes depending on the energy state: continuous resonant mode at high energy and discontinuous resonant mode at low energy. The system dynamically transitions between these modes, with the discontinuous mode specifically designed to achieve zero-voltage switching when the resonant energy is depleted, thereby reducing switching losses across all operating conditions while maintaining relatively simple circuit structure
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
Enables zero-voltage switching in both continuous and discontinuous resonant modes, reducing switching losses and improving efficiency by effectively managing parasitic capacitance.
Implementation Method 1
When a current value of the magnetizing current is greater than or equal to a current threshold, the controller turns off the first switch so that a second parasitic capacitance of the second switch discharges toward the node. When the first switch is turned on and the second switch is turned off, the magnetizing inductance stores energy of a magnetizing current.
Implementation Method 2
When the first switch is turned on and the second switch is turned off, the magnetizing inductance stores energy of a magnetizing current
Implementation Method 3
When a current value of the magnetizing current is greater than or equal to a current threshold, the controller turns off the first switch so that a second parasitic capacitance of the second switch discharges toward the node
Data Source
AI summary
An asymmetric half-bridge flyback power converter includes a transformer, a resonant circuit, a first switch, a second switch, a discharging switch, an energy storage capacitor, and a controller. The first switch and the second switch are connected in series at a node, and the resonant circuit is coupled between the node and the transformer. The discharging switch is coupled between the node and the energy storage capacitor. When the power converter operates in a discontinuous resonant mode, and before the first switch is turned on by the controller, the discharging switch is first turned on so that the energy storage capacitor stores energy to rise a current flowing to the node.