Synchronous Rectifier Reverse Current Stopping Circuit

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Solution Overview

Problem

Conventional reverse current stopping circuits in synchronous rectification type DC-DC converters face accuracy issues due to input voltage offset variations in comparators, leading to inefficient reverse current detection and prevention, especially under varying load conditions.

Innovation Solution

A reverse current stopping circuit that includes a comparator, a reverse current detector circuit, and a memory unit, which detects the switching terminal voltage after the synchronous rectification device is turned off, determines the inductor current direction, and adjusts the comparator's offset voltage to ensure the inductor current is zero at turn-off, thereby preventing reverse current flow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional comparator is used to detect reverse current, then the reverse current detection function is provided, but the detection accuracy deteriorates due to input voltage offset variations

Engineering Contradiction:

Improvereverse current detection accuracyVSAvoiddetection reliability under offset variation

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting the threshold voltage of the comparator based on the detected inductor current direction. When reverse current is detected, the threshold voltage is shifted to accommodate offset variations, thereby maintaining detection accuracy despite comparator imperfections

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback by using the detected switching terminal voltage and inductor current direction information to adjust the threshold voltage of the comparator. This closed-loop approach compensates for offset variations and improves detection reliability

Inventive Principle:

Principle #23Feedback

2Object-generated harmful factors

If the synchronous rectification device is turned off immediately upon reverse current detection, then reverse current flow is prevented, but the inductor current may not be accurately zeroed due to offset voltage

Engineering Contradiction:

Improvereverse current flowVSAvoidinductor current zero detection accuracy

Core Design Contradiction:

Object-generated harmful factorsVSMeasurement precision

Solution Approach 1:

The patent changes the threshold parameter of the comparator dynamically based on the detected current direction. By adjusting the threshold voltage offset, the system ensures that the turn-off decision is made at the correct inductor current zero-crossing point, preventing both reverse current and premature turn-off

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent performs preliminary detection of the switching terminal voltage and inductor current direction before making the turn-off decision. This preliminary action allows the system to prepare the appropriate threshold voltage shift, ensuring accurate zero-current detection and proper timing of the turn-off event

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If a fixed threshold comparator is used, then the circuit complexity is low, but the adaptability to varying load conditions and offset variations is poor

Engineering Contradiction:

Improvecomparator circuit complexityVSAvoidadaptability to offset and load variations

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent introduces dynamics into the comparator threshold by making it adjustable rather than fixed. The threshold voltage is dynamically modified based on the detected inductor current direction, allowing the system to adapt to different load conditions and comparator offset variations without significantly increasing circuit complexity

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent introduces an intermediary mechanism (threshold voltage adjustment circuit) that mediates between the fixed comparator and the varying operating conditions. This intermediary allows the system to compensate for offsets and adapt to load changes while maintaining a relatively simple overall circuit structure

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS7872461B2Reverse current stopping circuit of synchronous rectification type DC-DC converter

Publication Date: 2011.01.18 FUJI ELECTRIC CO LTD

AI summary

A reverse current stopping circuit includes a synchronous rectification device, a comparator for detecting a reverse current of an inductor, the synchronous rectification device being turned off when the reverse current is detected by the comparator, a reverse current detector circuit for detecting a switching terminal voltage after the synchronous rectification device is turned off, thereby determining a value of the inductor current to decide whether the inductor current is flowing in a reverse direction or a forward direction, and a memory unit for receiving a predetermined output signal from the reverse current detector circuit in accordance with a result of the reverse current detector circuit, and outputting a control signal for an offset voltage in accordance with the predetermined output signal. The offset voltage is changed in accordance with the control signal so as to adjust the inductor current to zero when the synchronous rectification device is turned off.