Flyback Converter Leakage Energy Transfer for Zero-Voltage Switching
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Solution Overview
Problem
Current flyback circuits suffer from inefficiencies due to leakage inductance, leading to high spike voltages, EMI, and significant switching losses, particularly in heavy output loads, and existing solutions with auxiliary MOS switches result in large conduction losses and reliability issues.
Innovation Solution
A flyback converter circuit using a GaN switching transistor to transfer primary leakage inductance energy to the secondary winding before the main switching transistor turns on, achieving zero-voltage switching by controlling the GaN transistor based on switching frequency and signal thresholds, thereby reducing drain voltage to zero volts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an auxiliary MOS switch is added to recover leakage inductance energy, then the spike voltage is reduced, but the conduction loss increases due to large effective current and fixed switching time
Solution Approach 1:
The patent changes the switching parameters by using a GaN transistor instead of MOS switch, enabling variable switching time that adapts to different operating conditions. This reduces the effective current through the auxiliary switch and minimizes conduction loss while maintaining spike voltage suppression.
Solution Approach 2:
The patent employs a GaN transistor with extremely short reverse recovery time (effectively disposable switching action) compared to conventional MOS switches. This allows the auxiliary switch to operate with minimal conduction time, reducing energy loss while effectively managing leakage inductance energy.
2Stress or pressure
If an auxiliary MOS switch is used to absorb leakage inductance energy, then voltage stress is reduced, but reliability decreases due to long reverse recovery time and large reverse recovery current
Solution Approach 1:
The patent substitutes the conventional MOS switch mechanism with a GaN transistor that operates on different physical principles. The GaN device exhibits fundamentally different switching characteristics with negligible reverse recovery effects, eliminating the reliability issues associated with MOS switch body diode reverse recovery.
Solution Approach 2:
The patent uses GaN (gallium nitride) material which combines the benefits of wide bandgap properties with excellent switching characteristics. This composite approach integrates the advantages of high breakdown voltage capability with ultra-fast switching and minimal reverse recovery, achieving both voltage stress management and high reliability.
3Power
If the main switching transistor turns on during QR flyback mode with high input voltage, then power conversion is achieved, but significant turn-on losses occur due to high valley voltage
Solution Approach 1:
The patent implements preliminary action by having the auxiliary GaN switch activate before the main switching transistor. This pre-action clamps the voltage at the drain of the main transistor to near-zero levels, ensuring that when the main transistor turns on, it does so at zero voltage regardless of the input voltage level or operating mode.
Solution Approach 2:
The auxiliary GaN switch acts as an intermediary device between the leakage inductance and the main switching transistor. It mediates the energy transfer by providing a controlled path for leakage inductance current and maintaining zero voltage at the main transistor drain, thereby eliminating turn-on losses while preserving power conversion functionality.
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 enhances circuit efficiency and reliability by minimizing switching losses and eliminating reverse recovery issues, ensuring zero-voltage switching and improved performance across various operating modes.
Implementation Method 1
the second GaN switching transistor is configured to transfer stored energy of the primary winding's leakage inductance to the secondary winding before the first switching transistor turns on
Data Source
AI summary
Provided are a flyback converter circuit and an electronic device. The first end of the second GaN switching transistor of the circuit is coupled to the first switching transistor and the end of the primary winding, and its second end is coupled to another end of the primary winding via the second resistor connected in parallel. The first voltage divider resistor and the second voltage divider resistor are connected in series to obtain the voltage output by the auxiliary winding and transmit the corresponding second signal. By controlling the turning on and off of the second GaN switching transistor, the stored energy of the primary winding's leakage inductance is transferred to the secondary winding before the first switching transistor turns on. The first switching transistor is controlled to turn on only when the second GaN switching transistor is turned off and the second signal indicates a fall through zero.