Synchronous Rectifier Phase-Lock Feedback Resonant Converter
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Solution Overview
Problem
Existing synchronous rectifiers in power converters suffer from significant power losses due to forward voltage drops, which hinder achieving higher efficiency and low EMI performance.
Innovation Solution
A synchronous rectifier circuit comprising a power transistor, a diode, and a control circuit with a phase-lock circuit that generates a drive signal to switch on the power transistor only when the diode is forward biased, and switches it off using a pulse width shorter than the diode's turned-on period, with additional circuits for feedback regulation and pulse width reduction based on output load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional rectifiers are used in power converters, then the circuit structure is simple, but significant power losses occur due to forward voltage drops
Solution Approach 1:
The patent replaces conventional diode rectifiers with synchronous rectifiers using active power transistors (MOSFETs or IGBTs) that can be actively controlled. By changing the switching parameters and timing of these transistors through phase-lock circuits and feedback mechanisms, the forward voltage drop is eliminated, reducing power losses while maintaining manageable circuit complexity through integrated control
Solution Approach 2:
The patent implements feedback loops that monitor the output voltage and load conditions, then adjust the switching signals to the power transistors accordingly. This feedback mechanism enables the synchronous rectifier to adapt to varying load conditions, optimizing efficiency and reducing power losses dynamically while maintaining stable operation
2Productivity
If the pulse width of drive signal is extended to fully utilize diode conduction period, then rectification efficiency improves, but power transistor losses increase
Solution Approach 1:
The patent employs dynamic pulse width modulation where the drive signal width is continuously adjusted based on real-time feedback from the output voltage and load conditions. The phase-lock circuit dynamically synchronizes the power transistor switching with the resonant tank oscillations, optimizing the conduction period to maximize rectification efficiency while minimizing transistor losses through adaptive timing control
Solution Approach 2:
The patent uses partial action by applying drive signals that are shorter than the full diode conduction period. The phase-lock circuit generates pulsed drive signals that activate power transistors only during critical conduction intervals, achieving sufficient rectification efficiency without the excessive energy losses that would result from extended transistor conduction
3Loss of energy
If synchronous rectification is implemented to reduce power losses, then efficiency improves, but EMI performance may deteriorate
Solution Approach 1:
The patent leverages the natural periodic oscillations of the resonant tank circuit to synchronize power transistor switching. By locking the switching frequency to the resonant frequency and using periodic drive signals synchronized with the tank oscillations, the system achieves soft switching conditions that reduce electromagnetic interference while maintaining high efficiency synchronous rectification
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
The solution reduces power losses and enhances efficiency by optimizing the switching behavior of the power transistor, aligning with the goal of achieving higher efficiency and lower EMI in power converters.
Implementation Method 1
The control circuit generates a drive signal to switch on the power transistor once the diode is forward biased
Implementation Method 2
The leakage inductance L and the equivalent capacitance C of capacitors 41 and 42 determine the resonance frequency f0 of the resonant tank
Implementation Method 3
The transformer 10 transfers the energy from the primary winding NP to the secondary windings NS1 and NS2 of the transformer 10
Data Source
AI summary
A synchronous rectifier for a switching power converter is provided and includes a power transistor, a diode, and a control circuit. The power transistor and the diode are coupled to a transformer and an output of the power converter for the rectification. The control circuit generates a drive signal to switch on the power transistor once the diode is forward biased. The control circuit includes a phase-lock circuit. The phase-lock circuit generates an off signal to switch off the power transistor in response to a pulse width of the drive signal. The pulse width of the drive signal is shorter than a turned-on period of the diode. The phase-lock circuit further reduces the pulse width of the drive signal in response to a feedback signal. The feedback signal is correlated to an output load of the power converter.