SR Controller Noise Immunity via Voltage Slope Prediction
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Solution Overview
Problem
In power conversion apparatuses using pulse width modulation (PWM) control, the synchronous rectification controller struggles to accurately determine the time to turn off the synchronous rectification transistor due to noise in the cross voltage between the drain and source, leading to decreased conversion efficiency and potential damage to internal components.
Innovation Solution
A synchronous rectification (SR) controller is designed to calculate the time length for turning off the SR transistor by using a geometric method based on the voltage values of detection and trigger signals, reducing the influence of noise in determining the optimal turn-off time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the synchronous rectification controller determines the turn-off time based on the cross voltage VDS reaching 0 volt, then the conversion efficiency can be improved, but the noise susceptibility increases causing inaccurate time determination
Solution Approach 1:
The controller predicts the turn-off time point before the actual event occurs by detecting the slope of the cross voltage and calculating when it will reach zero, rather than waiting for the voltage to actually reach zero. This preliminary calculation avoids the noisy region near zero voltage while still achieving accurate timing control for optimal conversion efficiency.
Solution Approach 2:
The patent introduces an intermediate calculation method that uses the voltage slope and threshold voltage as mediators to indirectly determine the turn-off time. Instead of directly monitoring the noisy zero-voltage point, the system uses the relationship between voltage change rate and threshold crossing to predict the future zero-voltage moment, thereby eliminating direct dependence on the noisy measurement point.
2Loss of energy
If the synchronous rectification transistor is controlled with precise timing, then the conversion efficiency improves, but the risk of simultaneous conduction with primary side power switch increases causing component damage
Solution Approach 1:
The controller performs preliminary timing calculation based on voltage slope prediction, determining the optimal turn-off moment before the actual switching occurs. This advance planning ensures precise control of the synchronous rectification transistor's conduction period, maximizing efficiency while maintaining safe operating margins to prevent simultaneous conduction with primary side switches.
3Productivity
If the cross voltage measurement is used for control, then the synchronous rectification can be achieved, but the noise interference increases causing control errors
Solution Approach 1:
The system uses voltage slope and threshold voltage as intermediary parameters to indirectly determine the turn-off time. By calculating based on the rate of voltage change rather than directly monitoring the noisy voltage level near zero, the system maintains accurate control while eliminating the harmful effect of noise interference on rectification performance.
Data Source
AI summary
A power conversion apparatus including a transformer, a synchronous rectification (SR) transistor and a SR controller is provided. The SR transistor is coupled between a secondary side of the transformer and an output terminal. The SR controller receives a cross voltage between a drain terminal and a source terminal of the SR transistor as a first detection signal. The SR controller obtains a first time length according to a voltage value of the first detection signal, a voltage value of a first trigger signal and a voltage value of a second trigger signal. The SR controller determines a time point to turn off the SR transistor according to the first time length.