Synchronous Rectification Conduction Detection Circuit

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Solution Overview

Problem

Accurately detecting the turn-off time of synchronous rectification MOSFETs is challenging due to low on-resistance and noise susceptibility, making it difficult to control switching operations effectively and reduce power loss in rectification processes.

Innovation Solution

A conduction detecting circuit that includes a low-pass filter, comparators, and logic operators to determine the end of synchronous rectification conduction intervals based on detection voltage and filtered voltage, enabling precise timing for turning on and off synchronous rectification transistors, thereby reducing noise influence and improving switching control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If synchronous rectification MOSFET is used to reduce power loss, then power efficiency is improved, but accurate detection of turn-off time becomes difficult due to low on-resistance and noise susceptibility

Engineering Contradiction:

Improvepower lossVSAvoiddetection precision

Core Design Contradiction:

Loss of energyVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary signal processing chain including a low-pass filter and comparators to detect the drain voltage of the synchronous rectification MOSFET. The low-pass filter removes high-frequency noise from the detection voltage, and the comparators convert the filtered voltage into clean digital signals that accurately indicate conduction intervals, thereby enabling precise detection despite the low on-resistance of the MOSFET

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct current measurement (which is susceptible to noise due to low on-resistance) with voltage-based detection using a low-pass filter and comparator circuit. This substitution transforms the detection mechanism from directly measuring weak current signals to measuring voltage signals that have been filtered and conditioned, thereby improving measurement precision without sacrificing power efficiency

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Loss of energy

If synchronous rectification MOSFET is turned off when current becomes zero, then power loss is reduced, but accurate current detection is difficult due to low on-resistance and noise

Engineering Contradiction:

Improvepower lossVSAvoidcurrent detection difficulty

Core Design Contradiction:

Loss of energyVSDifficulty of detecting and measuring

Solution Approach 1:

The patent uses an intermediary detection approach by monitoring the drain voltage of the synchronous rectification MOSFET instead of directly measuring the current. The low-pass filter acts as an intermediary to remove noise from the voltage signal, and the comparators serve as intermediaries to convert the voltage signal into reliable digital conduction interval signals, making detection feasible despite the challenging low on-resistance condition

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent creates a copied and processed version of the detection signal through the low-pass filter and comparator circuitry. Instead of directly using the noisy voltage signal that reflects the weak current, the system generates a cleaned, filtered, and thresholded copy of the signal that accurately represents the conduction intervals without the noise and distortion present in the original signal

Inventive Principle:

Principle #26Copying

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 allows for accurate detection of conduction intervals, enabling efficient switching operations that minimize power loss and improve the control of synchronous rectification processes, enhancing the overall performance of power supplies.

Implementation Method 1

a low-pass filter configured to generate a filtered voltage by receiving a detection voltage based on a drain voltage of the first synchronous rectification transistor

Methodology Applied

Scientific EffectLow-pass filtering: Filter (electronic)

Implementation Method 2

a first comparator configured to detect a time point at which the detection voltage decreases to be lower than the filtered voltage by at least a first reference voltage, and a second comparator configured to detect a time point at which the detection voltage increases to be higher than the filtered voltage by at least a second reference voltage

Methodology Applied

Scientific EffectVoltage comparison:

Data Source

PatentUS9350258B2Conduction detecting circuit, rectifying switch controlling circuit including the conduction detecting circuit and power supply for the rectifying switch controlling circuit to be applied

Publication Date: 2016.05.24 SEMICON COMPONENTS IND LLC

AI summary

A circuit configured to detect the conduction of a first body diode and a second body diode of the first and second synchronous rectification transistors is provided. The circuit includes a low-pass filter configured to generate a filtered voltage by receiving a detection voltage based on a drain voltage of the first synchronous rectification transistor and low-pass filtering the received drain voltage, a first comparator configured to compare whether the filtered voltage is higher than the detection voltage, and a second comparator configured to compare whether the detection voltage is higher than the filtered voltage. A time point of ending a first synchronous rectification conduction interval of the first body diode and a time point of a second synchronous rectification conduction interval of the second body diode are determined, according to outputs from the first and second comparators.