Split-Auxiliary ZVS Flyback Converter for Lower Secondary Stress
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional zero-voltage-switching (ZVS) flyback converters experience secondary-side current and voltage stress due to body-diode conduction in the synchronous rectifier (SR) switch transistor during ZVS switch transistor on-time, leading to energy wastage and potential simultaneous conduction of power and SR switch transistors, known as punch through.
Innovation Solution
The implementation of a ZVS flyback converter with bifurcated auxiliary windings and diodes configured to allow charging and discharging currents through auxiliary capacitors, reducing body-diode conduction in the SR switch transistor by controlling the turns ratio of auxiliary windings to minimize secondary winding voltage and current stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ZVS switch transistor is switched on during resonant oscillation to achieve zero-voltage switching, then the drain-to-source voltage of the power switch transistor can be reduced to near zero, but body-diode conduction in the SR switch transistor occurs causing secondary-side current and voltage stress
Solution Approach 1:
The auxiliary winding is divided into two separate windings: a first auxiliary winding coupled to the ZVS switch transistor and a second auxiliary winding coupled to the SR switch transistor. This segmentation isolates the ZVS switching operation from the SR switch transistor, preventing body-diode conduction and secondary-side stress while maintaining ZVS functionality.
2Use of energy by moving object
If the ZVS switch transistor conducts during on-time, then auxiliary winding current ramps negatively to resonantly oscillate the drain-to-source voltage, but this causes body-diode conduction in the SR switch transistor wasting energy
Solution Approach 1:
By segmenting the auxiliary winding into two separate windings with dedicated diodes, the patent ensures that the negative auxiliary winding current flows only through the first auxiliary winding and first diode during ZVS on-time, completely preventing body-diode conduction in the SR switch transistor and eliminating the associated energy losses.
3Reliability
If body-diode conduction occurs in the SR switch transistor during ZVS on-time, then the resulting drain-to-source voltage can fool the SR switch controller to switch on, causing simultaneous conduction of power and SR switch transistors
Solution Approach 1:
The patent segments the auxiliary winding circuitry so that the ZVS switch transistor is coupled only to the first auxiliary winding and the SR switch transistor is coupled only to the second auxiliary winding. This isolation prevents false voltage signals from ZVS operation from affecting the SR switch controller, eliminating the punch-through risk.
Solution Approach 2:
The second auxiliary winding acts as an intermediary that isolates the SR switch transistor from the resonant oscillations and voltage variations occurring during ZVS operation. This intermediary structure prevents the SR switch controller from being fooled by ZVS-related voltage signals.
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 configuration reduces secondary-side current and voltage stress, eliminating body-diode conduction during ZVS switch transistor on-time and minimizing the risk of undesirable SR switch transistor triggering, thereby enhancing efficiency and reliability.
Implementation Method 1
the drain-to-source voltage VDS of the power switch transistor M1 resonantly oscillates after the power switch transistor M1 is switched off
Implementation Method 2
a primary winding current Ipri flows through a primary winding W1 of a transformer T
Implementation Method 3
a first diode configured to allow a charging current to flow from a positive terminal of the first auxiliary winding into a positive terminal of the auxiliary capacitor
Data Source
AI summary
A flyback converter is provided in which either auxiliary winding or the primary winding is split into two windings. In this fashion, a different turn ratio is presented to the secondary winding during the transformer reset period as compared to when an active-clamp transistor or a ZVS switch transistor is switched on.