Synchronous Rectifier Control Circuit Slew Rate Detection

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Solution Overview

Problem

Synchronous rectifiers in isolated switching converters can experience mis-triggering due to voltage ringing, leading to inefficiencies and power waste, particularly in low power applications where diodes have higher power dissipation.

Innovation Solution

A control circuit is introduced that detects the slew rate of the voltage across the synchronous rectifier and maintains it in an off state when the slew rate is below a threshold, preventing mis-triggering by using a secondary control circuit with input terminals for a slew rate threshold adjusting signal and voltage across the synchronous rectifier to generate a control signal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a synchronous rectifier is used instead of a diode, then power dissipation is reduced and efficiency is improved, but voltage ringing causes mis-triggering of the synchronous rectifier

Engineering Contradiction:

Improvepower dissipationVSAvoidmis-triggering

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent introduces a control circuit as an intermediary between the voltage across the synchronous rectifier and the gate control signal. This control circuit processes the voltage signal to generate an accurate drive signal, preventing mis-triggering caused by voltage ringing while maintaining the low power dissipation benefits of synchronous rectification.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The control circuit uses feedback from the voltage across the synchronous rectifier to dynamically adjust the gate control signal. By continuously monitoring the voltage and using it to control the timing and duration of the drive signal, the system prevents mis-triggering while optimizing power efficiency.

Inventive Principle:

Principle #23Feedback

2Device complexity

If voltage across the synchronous rectifier is used to determine on and off states, then control is simplified, but voltage ringing causes inaccurate detection and mis-triggering

Engineering Contradiction:

Improvecontrol circuit complexityVSAvoidvoltage detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The control circuit acts as an intermediary that processes the raw voltage signal across the synchronous rectifier. It filters and conditions the signal to remove ringing effects, providing accurate detection information to the control logic while maintaining relatively simple overall circuit architecture.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct voltage threshold comparison with a control circuit-based approach that uses the voltage signal to generate timed control pulses. This substitution of the control mechanism eliminates mis-triggering from voltage ringing while keeping the system relatively simple through automated pulse generation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS10432104B2Control circuit for synchronous rectifier and the method thereof

Publication Date: 2019.10.01 CHENGDU MONOLITHIC POWER SYST

AI summary

A synchronous switching converter with an energy storage component and a synchronous rectifier coupled to the energy storage component, having: a secondary control circuit configured to receive a slew rate threshold adjusting signal and a voltage across the synchronous rectifier, and to provide a secondary control signal; wherein the secondary control circuit detects a slew rate of the voltage across the synchronous rectifier, and maintains the synchronous rectifier being off when the slew rate of the voltage across the synchronous rectifier is lower than a slew rate threshold.