Inductorless Isolated Power Converter with Zero Voltage Switching
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Solution Overview
Problem
Isolated switching power converters face inefficiencies due to switching losses and reverse recovery voltage spikes caused by body diode conduction in synchronous rectifiers, which require high-voltage rated switches and result in increased part count and reduced power density.
Innovation Solution
An inductorless isolated switching power converter design that includes a transformer with a primary and secondary winding, where a controller switches the primary switch and synchronous rectifier to restrict body diode conduction, allowing for near zero voltage and current switching, thereby reducing switching losses and eliminating reverse recovery spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If synchronous rectifiers with body diodes are used in conventional isolated switching power converters, then rectification function is achieved, but reverse recovery voltage spikes occur and high-voltage rated switches are required
Solution Approach 1:
The controller turns on the synchronous rectifier a fixed time before the primary switch turns off, allowing the rectifier to conduct the transformer current before the body diode would otherwise conduct. This preliminary action prevents reverse recovery voltage spikes by ensuring the MOSFET is already on when current needs to flow, eliminating the harmful body diode conduction and reverse recovery effects
2Reliability
If output inductor is included in conventional power converters, then energy storage and filtering is achieved, but part count increases and power density decreases
Solution Approach 1:
The patent removes the output inductor from the power converter circuit while maintaining energy storage and filtering functions through the synchronous rectifier and transformer combination. The synchronous rectifier operates in a mode that naturally provides current continuity and filtering without requiring a separate output inductor component, thereby reducing part count and increasing power density
3Ease of operation
If primary switches switch on and off with voltage across them, then switching operation is simple, but switching losses occur
Solution Approach 1:
The controller coordinates the switching of primary switches and synchronous rectifiers such that the synchronous rectifier turns on before the primary switch turns off. This preliminary action on the secondary side reflects back to the primary side, enabling zero-voltage switching of the primary switches and eliminating switching losses while maintaining simple switching operation
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 design decreases the part count of the power converter, increases power density, and permits the use of lower voltage rated switches, achieving efficient operation by eliminating reverse recovery voltage spikes and reducing switching losses.
Implementation Method 1
switching on the primary switch to provide a first current through the primary winding to induce a second current in the secondary winding
Data Source
AI summary
A method of controlling an isolated switching power converter that includes a transformer with a primary side and a secondary side, at least one primary switch coupled to the primary side of the transformer and at least one synchronous rectifier coupled to the secondary side of the transformer is disclosed. The method includes turning on the synchronous rectifier a first fixed time after turning on the primary switch and turning off the synchronous rectifier a second fixed time after turning off the primary switch. Power converters for operation according to this method are also disclosed, including power converters without an output inductor.