Offline Synchronous Rectifier Causal Circuit Resonant Converter
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Solution Overview
Problem
Resonant switching power converters experience significant power losses due to forward voltage across rectifiers, which limits their efficiency and increases electric-magnetic interference.
Innovation Solution
A synchronous rectifier is introduced, utilizing a power transistor and diode connected to a transformer, with a controller generating drive signals to control the transistor based on biasing conditions, including an inner-lock circuit and maximum-on-time circuit to manage switching times and prevent simultaneous activation of rectifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If rectifiers are used in resonant switching power converter, then isolation and basic rectification function are achieved, but significant power losses occur due to forward voltage
Solution Approach 1:
The patent changes the operating parameters of the rectification circuit by replacing fixed forward-voltage rectifiers with controllable synchronous rectifiers that operate in different modes (linear region for soft switching, saturation region for hard switching), thereby reducing power losses while maintaining rectification function
Solution Approach 2:
The patent substitutes the passive mechanical rectifier system with an active electronic control system using microprocessor-based control to manage the synchronous rectifiers, enabling optimized switching patterns that reduce energy loss
2Productivity
If synchronous rectifier with power transistor is introduced, then power losses are reduced and efficiency is enhanced, but device complexity increases due to additional control circuits
Solution Approach 1:
The patent implements self-service control where the controller automatically detects circuit states (such as current direction and voltage levels) and autonomously generates appropriate drive signals for the synchronous rectifiers, eliminating the need for complex external control circuits and reducing overall system complexity
Solution Approach 2:
The patent incorporates feedback mechanisms where the controller monitors circuit operating conditions and adjusts the switching patterns of synchronous rectifiers in real-time, enabling optimized efficiency while using simple control logic that reduces device complexity
3Loss of energy
If resonant switching is used, then high efficiency is achieved, but electric-magnetic interference increases
Solution Approach 1:
The patent employs periodic resonant switching action at optimized frequencies that achieve high efficiency while the periodic nature allows for predictable EMI patterns that can be managed through timing control and synchronization, reducing harmful interference
Solution Approach 2:
The patent converts the potential harmful EMI from resonant switching into a beneficial effect by using the resonant frequency to achieve soft switching conditions, where the same resonant oscillation that could cause EMI is instead used to minimize switching losses and improve efficiency
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 solution reduces power losses and enhances efficiency by enabling soft-switching of the power transistor, minimizing electric-magnetic interference and improving overall performance of the resonant switching power converter.
Implementation Method 1
A synchronous rectifier for a resonant switching power converter includes a power transistor and a diode connected to a transformer and an output of the resonant switching power converter for rectification
Implementation Method 2
An inductor 5 and a capacitor 40 form the resonant tank. The inductor 5 can be an inductance device or the leakage inductance of a primary winding NP of the transformer 10. The inductance L of the inductor 5 and the capacitance C of the capacitor 40 determine a resonance frequency f0 of the resonant tank
Implementation Method 3
The transformer 10 transfers the energy from the primary winding NP to secondary windings NS1, NS2 of the transformer 10
Data Source
AI summary
A synchronous rectifier of a resonant switching power converter is provided to improve efficiency. The synchronous rectifier includes a power transistor and a diode connected to a transformer and an output of the resonant switching power converter for ratifications. A controller generates a drive signal to control the power transistor in response to an on signal and an off signal. A causal circuit is developed to generate the off signal in accordance with the on signal. The on signal is enabled once the diode is forward biased. The on signal is coupled to enable the drive signal for switching on the power transistor. The off signal is coupled to disable the drive signal for switching off the power transistor. The off signal is enabled before the on signal is disabled.