Synchronous Rectifier Switching via Secondary Voltage Transition Detection
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Solution Overview
Problem
Current synchronous rectification circuits in switching power supplies suffer from operational delays in voltage comparators, leading to overlapping conduction of primary and secondary windings and reduced energy conversion efficiency, with existing solutions either increasing circuit complexity or system costs.
Innovation Solution
A synchronous rectification circuit that detects positive or negative state transitions in the induction voltage of the secondary winding using a state transition detector and controller to control the switch, avoiding simultaneous conduction and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If voltage comparators are used to control the turning-on and turning-off of rectifying transistors, then the rectification function is achieved, but operational delay occurs leading to overlapping conduction and reduced energy conversion efficiency
Solution Approach 1:
The patent extracts the delay problem from the voltage comparator control path by using a separate sensing mechanism. The sense transistor detects the drain voltage directly without waiting for comparator processing, enabling the rectifying transistor to turn off before the primary switch turns on, thus eliminating the harmful delay while maintaining the rectification function.
Solution Approach 2:
The sense transistor performs preliminary detection of the drain voltage state before the main switching action occurs. By detecting the voltage at the drain terminal in advance, the control signal is prepared early enough to ensure the rectifying transistor turns off before the primary switch turns on, preventing overlapping conduction and improving energy efficiency.
2Loss of energy
If high-speed voltage comparators are used to reduce operational delay, then the energy conversion efficiency is improved, but the circuit design difficulty and area are increased
Solution Approach 1:
The patent replaces the expensive, complex high-speed voltage comparator with a simple, low-cost sense transistor that performs the critical timing function. The sense transistor is a basic semiconductor device that is inexpensive and occupies minimal circuit area, yet effectively solves the delay problem through direct voltage sensing and early signal generation.
Solution Approach 2:
The patent substitutes the electronic comparator-based control mechanism with a direct transistor sensing mechanism. Instead of using a voltage comparator to detect and process voltage signals, the sense transistor directly senses the drain voltage and generates the control signal, eliminating the need for complex comparator circuitry while achieving the same timing function.
3Loss of energy
If the primary winding switch signal is led directly to the synchronous rectification circuit, then the control response is improved, but high-voltage coupling devices are required increasing system costs
Solution Approach 1:
The patent enables the synchronous rectification circuit to self-regulate by using its own drain voltage as the sensing signal. The sense transistor monitors the local voltage conditions at the rectifying transistor's drain terminal, allowing the circuit to automatically generate the appropriate control signal without requiring external coupling from the primary winding, thereby avoiding high-voltage coupling devices and reducing system cost.
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
Enhances energy conversion efficiency and reduces power consumption by precisely controlling the switch based on state transitions, without the need for high-speed voltage comparators or high-voltage coupling devices.
Implementation Method 1
The state transition detector measures the transient variation signal of an induction voltage of the secondary winding
Data Source
AI summary
The present application provides a synchronous rectification circuit and a control method thereof. A switching element of the synchronous rectification circuit is controlled to turn on or turn off by detecting the occurrence of a positive or negative transition of the inductive voltage of the secondary winding. The synchronous rectification circuit comprises a transition detector for coupling to the secondary winding, a transition controller for coupling to the transition detector, and a switching element comprising a control terminal for coupling to the transition controller.