Zero Voltage Switching in CCM Flyback Converters
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Solution Overview
Problem
Conventional continuous conductance mode (CCM) flyback converters are unable to achieve zero-voltage switching due to the transformer remaining at least partially charged when transitioning the primary circuit from the off-state to the on-state, leading to parasitic power loss and reduced efficiency.
Innovation Solution
The solution involves creating a current imbalance across different portions of the secondary winding to reduce the voltage differential across the primary winding, allowing the primary switching transistor to be re-activated at or near a zero-voltage state by de-activating the secondary switch and re-activating the first switch, thereby reducing parasitic power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the primary switch is re-activated in conventional CCM flyback converters, then continuous power conversion is maintained, but parasitic power loss increases due to non-zero voltage across the switch
Solution Approach 1:
The patent applies preliminary action by de-activating the secondary switch before re-activating the primary switch. This sequence creates a current imbalance in the secondary winding that reduces the voltage differential across the primary winding to near-zero, allowing the primary switch to be re-activated with minimal parasitic power loss while maintaining continuous power conversion capability
Solution Approach 2:
The patent changes the operational parameters by creating a controlled current imbalance between the first and second winding portions of the secondary winding. This is achieved by de-activating the secondary switch at a specific timing, which alters the current distribution and consequently reduces the voltage stress on the primary switch during re-activation
2Loss of energy
If zero-voltage switching is achieved in CCM flyback converters, then efficiency increases, but switching control complexity increases
Solution Approach 1:
The patent employs feedback mechanisms through monitoring circuits that detect the voltage differential across the primary winding and the current status of the secondary switch. This feedback enables the control circuit to precisely time the de-activation of the secondary switch, creating the necessary current imbalance to achieve zero-voltage switching conditions while managing the increased control complexity
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 enables zero-voltage switching in CCM flyback converters, reducing power loss and allowing operation at or near discontinuous conduction mode efficiency while maintaining the benefits of CCM, such as smaller passive components and higher operating frequencies.
Implementation Method 1
A flyback converter is one type of SMPS that achieves voltage conversion with galvanic isolation between the input and any outputs
Implementation Method 2
A series inductor is coupled to the second winding portion of the secondary winding
Implementation Method 3
A SMPS usually includes at least one switch and an inductor or transformer
Data Source
AI summary
It is possible to achieve zero-voltage switching in continuous conductance mode (CCM) flyback converters by reducing the voltage differential across the primary winding immediately prior to transitioning the primary circuit from the off-state to the on-state. In one example, the voltage differential is reduced to the extent that polarity across the primary winding is reversed. In another example, the voltage differential across the primary winding is reduced significantly, but not to the extent that the polarity is reversed. Reducing the voltage differential across the primary winding may reduce a voltage potential across a current path of a switching transistor (e.g., a source-drain in a FET transistor) used to transition the primary circuit from the off-state to the on-state, which may decrease the parasitic power loss when the switching transistor is activated (closed).