Synchronous Rectification Controller for Flyback Power Supply
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Solution Overview
Problem
Conventional flyback power supplies face inefficiencies and safety concerns due to the power consumption of rectifier diodes and the critical timing requirements for turning ON and OFF rectifier switches in synchronous rectification processes.
Innovation Solution
The implementation of a synchronous rectification method using a secondary-side controller and rectifier switch, controlled by a SR controller that determines the timing of turning ON and OFF based on terminal signals from a detection winding, minimizing power consumption and optimizing conversion efficiency by adjusting deadtime durations based on output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a rectifier diode is used to rectify AC voltage, then the rectification function is achieved, but significant power is consumed due to forward voltage drop
Solution Approach 1:
The patent changes the operating parameters of the rectification system by using a MOSFET instead of a diode, allowing the rectification process to occur with minimal voltage drop across the switching element, thereby reducing power loss while maintaining reliable rectification function
Solution Approach 2:
The patent replaces the passive diode-based rectification mechanism with an active MOSFET-based synchronous rectification system controlled by a microcontroller, substituting a simple passive component with an actively controlled device to achieve better energy efficiency
2Loss of energy
If a rectifier switch is used to replace the rectifier diode, then power consumption is reduced, but the timing of turning ON and OFF becomes critical for both efficiency and safety
Solution Approach 1:
The patent implements a feedback control system where the microcontroller monitors the state of the rectifier switch and adjusts its timing based on system conditions, using feedback signals to optimize the switching timing and ensure safe operation while minimizing power loss
Solution Approach 2:
The system uses the existing transformer leakage inductance and parasitic capacitances to naturally shape the current and voltage waveforms during switching transitions, reducing the need for additional active components and simplifying the overall control requirements
3Reliability
If deadtime is extended to ensure safe operation of the rectifier switch, then safety is improved, but conversion efficiency decreases
Solution Approach 1:
The patent implements dynamic deadtime adjustment where the deadtime duration is not fixed but is adaptively modified based on operating conditions such as load current and voltage levels, allowing the system to maintain safety margins while minimizing the efficiency penalty associated with extended deadtime
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 reduces power consumption and enhances conversion efficiency while ensuring safety by precisely controlling the rectifier switch, improving the overall performance of the power supply.
Implementation Method 1
Switching of a power switch at the primary side causes voltage change across a primary winding of the transformer, and accordingly induces alternating-current (AC) voltage across a secondary winding of the transformer
Implementation Method 2
A rectifier switch should be turned OFF to provide an open circuit between two terminals when the two terminals are negatively biased, and be turned ON to provide a short circuit between the two terminals when they are positively biased
Data Source
AI summary
A power supply has a transformer, a rectifier switch, a secondary-side controller and two diodes. The transformer includes a primary winding, a secondary winding, and a detection winding, inductively coupling to one another. The rectifier switch is connected in series with the secondary winding between two output power lines. The secondary-side controller is electrically coupled to two ends of the detection winding, for controlling the rectifier switch in response to two terminal signals at the two ends respectively. The two diodes are back-to-back electrically connected in series between the two ends, and a joint connecting the two diodes is electrically connected to one of the two output power lines.