Flyback Converter Auxiliary Circuit for Wide-Range ZVS
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Solution Overview
Problem
Conventional zero voltage switching (ZVS) implementations in flyback converters are limited by the dependency on sufficient energy collection during the ZVS pulse turn-on phase, which can lead to high switching losses, especially at high input voltages.
Innovation Solution
A converter design that includes an auxiliary circuit with an auxiliary switch and capacitor to leverage leakage inductance energy, allowing the auxiliary capacitor to resonate with the leakage inductance before the main switch turn-on, creating a negative current to discharge the main switch's parasitic capacitance and achieve ZVS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional ZVS control strategy is used, then the system can achieve zero voltage switching at low input voltages, but at high input voltages the ZVS condition cannot be established leading to high switching losses
Solution Approach 1:
The auxiliary capacitor is pre-charged during the main switch on-state through the body diode of the auxiliary MOSFET. This preliminary energy storage ensures that when the main switch needs to turn on, the auxiliary capacitor already has sufficient energy to discharge through the resonance circuit and create the negative current needed to discharge the parasitic capacitance, enabling ZVS even at high input voltages where conventional methods fail
Solution Approach 2:
The auxiliary capacitor acts as an intermediary energy storage element between the input voltage source and the main switch. It captures energy during the on-state and releases it during the off-state to create the resonant discharge current. This intermediary mechanism decouples the ZVS achievement from direct dependency on input voltage level, allowing ZVS across a wide voltage range
2Reliability
If the auxiliary capacitor is charged during main switch on-state, then sufficient energy is stored to discharge parasitic capacitance, but this requires precise timing control of the auxiliary switch
Solution Approach 1:
The auxiliary MOSFET's body diode automatically conducts during the main switch on-state, charging the auxiliary capacitor without requiring active control. The capacitor charges naturally through the diode's forward conduction when current flows in that direction. This self-charging mechanism simplifies control complexity while ensuring reliable energy storage for subsequent ZVS operation
Solution Approach 2:
The auxiliary switch is controlled with periodic gating signals that synchronize with the main switch operation. The auxiliary MOSFET is turned on briefly at specific intervals to allow capacitor discharge through the resonance circuit, then turned off to allow recharging. This periodic control rhythm ensures consistent energy transfer and ZVS achievement across switching cycles
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 ensures ZVS conditions across a wide input voltage range, reducing switching losses and improving efficiency by recycling leakage inductance energy for zero voltage switching.
Implementation Method 1
the auxiliary capacitor to resonate with the leakage inductance before the main switch turn-on, creating a negative current to discharge the main switch's parasitic capacitance
Implementation Method 2
store inductively leaked energy from a primary side of the converter in the auxiliary capacitor
Data Source
Figure 1
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AI summary
Embodiments comprise a converter, comprising a first primary terminal and a second primary terminal for coupling the converter to a voltage source, a multi-winding inductor, comprising a primary winding and a secondary winding. Furthermore, the converter comprises a main switch wherein the primary winding and the main switch are connected in series between the first and second primary terminal. The converter further comprises a first secondary terminal and a second secondary terminal for coupling the converter with a load, an auxiliary circuit comprising an auxiliary switch, an auxiliary capacitor, wherein the auxiliary switch is connected in series with the auxiliary capacitor and a charge storage circuit comprising an output capacitor, wherein the output capacitor is arranged between the first and second secondary terminal. The charge storage circuit and the auxiliary circuit are connected in parallel to the secondary winding of the multi-winding inductor.