Half-Bridge Converter Using Synchronized Rectifiers for Zero-Voltage Switching
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Solution Overview
Problem
Existing DC-DC converters, especially those used in AC-DC applications, face efficiency limitations due to the flyback topology's inherent inefficiencies, particularly at light loads and when dealing with multiple independent outputs, where the combination of energy transfer and storage in the same transformer reduces overall efficiency.
Innovation Solution
The proposed solution involves an isolated converter that operates in a forward mode, eliminating the need for post-regulators and utilizing a half bridge or full bridge topology with synchronized rectifiers that turn off at zero or slight negative current, ensuring zero voltage switching and monotonic voltage rise without spikes or ringing, thereby increasing efficiency and reducing core losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If flyback topology is used for isolated converter, then device complexity is reduced, but efficiency deteriorates due to inherent inefficiencies especially at light loads and with multiple outputs
Solution Approach 1:
The patent segments the energy transfer and storage functions by using a forward converter topology where energy is transferred from primary to secondary during the switch on-time, and stored in output inductors during both on and off times. This separation eliminates the inherent inefficiencies of flyback topology where energy transfer and storage occur simultaneously in the same transformer, achieving up to 98% efficiency while maintaining manageable device complexity
Solution Approach 2:
The patent implements dynamic frequency adjustment where the switching frequency decreases as load decreases, and dynamically controls the on-time of primary switchers to reduce magnetic flux and core loss. This dynamic operation maintains soft switching conditions across all load conditions while optimizing efficiency, particularly at light loads where frequency can be reduced to minimize core losses
2Loss of energy
If switching frequency is decreased for light load operation, then core loss is reduced, but maintaining zero voltage switching conditions becomes more difficult
Solution Approach 1:
The patent employs feedback control mechanisms where the controller monitors voltage and current conditions to dynamically adjust switching parameters. This feedback ensures that zero voltage switching conditions are maintained across all load conditions including light loads, while allowing frequency and on-time to be optimized for minimum core loss. The synchronized rectifiers provide feedback on secondary side conditions to coordinate primary switch timing
Solution Approach 2:
The patent changes operating parameters dynamically - adjusting switching frequency, on-time duration, and dead time based on load conditions. At light loads, frequency is decreased and on-time is reduced to minimize magnetic flux and core loss, while controller timing adjustments maintain zero voltage switching. The input and output voltage ranges are also accommodated through parameter adjustment to preserve soft switching
3Loss of energy
If on-time for primary switchers is reduced to decrease magnetic flux, then core loss is reduced, but energy transfer to secondary is also reduced requiring lower repetition frequency
Solution Approach 1:
The patent uses periodic switching action with variable duty cycle and frequency. By reducing on-time to decrease magnetic flux and core loss, the repetition frequency is also reduced proportionally to maintain appropriate energy transfer to the secondary. This periodic operation with adjusted parameters achieves light load efficiency while ensuring sufficient power delivery when needed
Solution Approach 2:
The patent implements dynamic control where on-time and repetition frequency are adjusted together based on load requirements. At light loads, both on-time is reduced to decrease magnetic flux and repetition frequency is reduced to match the lower energy transfer requirement, maintaining efficiency. The system dynamically adapts these parameters to match actual power demands
4Loss of energy
If synchronized rectifiers turn off at zero or slight negative current, then soft switching is achieved, but voltage across rectifiers must rise monotonically without ringing which limits topology options
Solution Approach 1:
The patent applies synchronized rectifiers that serve dual functions: as rectification elements during the off-time and as part of the soft switching mechanism. By turning them off at zero or slight negative current and ensuring monotonic voltage rise, they achieve soft switching while maintaining versatility for multiple output configurations including USB Power Delivery applications
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 achieves high efficiency across a wide range of loads, including light loads, with the isolated converter maintaining soft switching operations and achieving efficiencies up to 98% compared to the 95% efficiency of optimized flyback topologies, while being suitable for multiple outputs and compliant with USB Power Delivery Specifications.
Implementation Method 1
The converter which converters the power from the primary side to the secondary side across the isolation boundary
Implementation Method 2
the secondary switchers, referred in this patent application as synchronized rectifiers, for soft switching operation the turn off shall be done at zero or slight negative current
Data Source
AI summary
A half bridge switching cell includes two primary switching elements and a transformer with primary and secondary windings. Synchronized rectifiers correspond to the primary switching elements such that each of the synchronized rectifiers conducts when the corresponding primary switching element is not conducting. Each secondary winding is connected to one of the synchronous rectifiers and to a common connection and controlled current source. The primary switching elements conduct during offset times separated by a dead time. A magnetizing current flows through the secondary windings and synchronous rectifiers during the dead time. The magnetizing current flows into the primary winding when each of the synchronous rectifiers is turned off after the dead time, discharging a parasitic capacitance across the one of the primary switching elements when the corresponding synchronous rectifier is turned off, thereby creating a zero voltage switching condition at turn on for the primary switching elements.