Synchronous Rectifier Control Circuit for Reverse Current Prevention

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Solution Overview

Problem

Traditional power converters experience power loss and efficiency reduction due to reverse current issues at light load and no load conditions, which existing current sensing circuits fail to effectively mitigate without causing additional power loss and system complexity.

Innovation Solution

A prediction circuit generates a timing signal based on the control signal and switching signal to turn off the synchronous rectifier before reverse current occurs, using an input circuit and timer circuit to determine the charge and discharge signals and predict the discharge time of the inductor, thereby preventing reverse current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a current sensing circuit is used to detect and turn off the synchronous rectifier when reverse current occurs, then reverse current can be limited, but power loss increases and system complexity increases

Engineering Contradiction:

Improvereverse currentVSAvoidpower loss

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The patent applies preliminary action by predicting the discharge time of the inductor using a timer circuit before reverse current actually occurs. The synchronous rectifier is turned off in advance based on the predicted discharge time, preventing reverse current generation rather than detecting and responding to it after occurrence. This eliminates the need for current sensing circuits and their associated power losses.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces a timer circuit as an intermediary that generates timing signals based on the discharge time of the inductor. This timing signal serves as a mediator between the switching signal and the synchronous rectifier control, enabling the rectifier to be turned off at the precise moment before reverse current occurs without requiring direct current sensing.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If a current sensing circuit is used to detect reverse current, then reverse current can be limited, but device complexity increases

Engineering Contradiction:

Improvereverse currentVSAvoidsystem complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the current sensing circuit from the system entirely. Instead of using complex current sensing components to detect reverse current, the solution uses a simple timer circuit that generates timing signals based on inductor discharge characteristics. This removes the harmful element (current sensing circuit) while achieving the same protective function.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent creates a temporal copy or model of the inductor discharge process using the timer circuit. The timer circuit replicates the discharge time characteristics without needing to physically sense the current, allowing the system to predict and respond to discharge completion based on time rather than direct current measurement.

Inventive Principle:

Principle #26Copying

Data Source

PatentUS7570038B2Control circuit to reduce reverse current of synchronous rectifier

Publication Date: 2009.08.04 SEMICON COMPONENTS IND LLC

AI summary

A control circuit for a power converter receives a switching signal that is applied to charge an inductor of the power converter. The control circuit includes a predication circuit that generates a timing signal in response to the switching signal. The timing signal is used to turn off a synchronous rectifier for preventing a reverse current during light load and no load conditions.