Synchronous Rectifier Control for DC-DC Converter Efficiency

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Solution Overview

Problem

Existing power conversion circuits face inefficiencies due to the use of diodes, which result in losses and reduced performance, especially in bidirectional power transfer applications where precise control over load currents and input voltages is necessary.

Innovation Solution

The implementation of a DC-DC power conversion circuit with a synchronous rectifier configuration, where a second switch operates based on a calculated drive signal derived from the sensed transformer winding current, allowing for bi-directional power transfer and reduced switching losses by synchronizing the on-time of the synchronous rectifier with the current greater than zero.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If diodes are used in power conversion circuits, then the circuit structure is simple, but switching losses increase and efficiency decreases

Engineering Contradiction:

Improveswitching lossesVSAvoidcircuit structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent replaces passive diode rectification with active synchronous rectification using controlled switches (MOSFETs or IGBTs). The control circuitry generates drive signals to actively switch these devices, replacing the mechanical/passive diode operation with electronically controlled switching that reduces conduction losses while maintaining rectification function.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operating parameters of the power conversion circuit by transitioning from fixed diode voltage drops to variable resistance control through active switches. The synchronous rectifier switches can be controlled to have very low on-resistance compared to diode forward voltage drops, significantly reducing power losses during conduction.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If synchronous rectifier control is implemented, then efficiency improves, but control complexity increases

Engineering Contradiction:

Improvepower transfer efficiencyVSAvoidcontrol circuitry

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent employs feedback mechanisms where the control circuitry monitors circuit operation and adjusts synchronous rectifier switch timing accordingly. The control system detects voltage and current conditions to optimize the switching moments, ensuring efficient power transfer while adapting to changing load and input conditions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The control circuitry calculates and prepares drive signals for the synchronous rectifier switches in advance of the actual switching events. By predicting optimal switching timing based on circuit state, the control system reduces losses without requiring complex real-time decision-making during the switching instant.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If precise control over load currents is required, then performance improves, but measurement and control difficulty increases

Engineering Contradiction:

Improveload current controlVSAvoidcurrent sensing

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent uses intermediary sensing elements such as current transformers or shunt resistors to indirectly measure load currents. These intermediaries convert difficult-to-measure high currents into manageable signal levels that can be accurately processed by the control circuitry, maintaining measurement precision while reducing direct measurement complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

This configuration enhances efficiency by reducing switching losses and improving circuit performance, allowing for bidirectional power transfer while maintaining control over power transfer direction without interfering with the primary switch's duty cycle.

Implementation Method 1

Power transfer from a primary side to secondary side of the DC-DC power conversion circuitry is controlled by operating the first switch

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

a second switch operates as a synchronous rectifier. A drive signal for the second switch is calculated based on a sensed transformer winding current, and operation of the second switch is controlled based on the drive signal

Methodology Applied

Scientific EffectSynchronous rectification:

Data Source

PatentUS9912245B2Synchronous rectifier control method for a non-isolated DC/DC converter having a transformer with cross connected capacitors

Publication Date: 2018.03.06 TOYOTA JIDOSHA KK

AI summary

A power system includes DC-DC power conversion circuitry that has a first switch and a second switch on either side of a transformer, and the second switch is operates as a synchronous rectifier. Power transfer from a primary side to secondary side of the DC-DC power conversion circuitry is controlled by operating the first switch. A drive signal for the second switch is calculated based on a sensed transformer winding current, and operation of the second switch is controlled based on the drive signal.