Buck-Boost PWM Converter Current-Based Turn-Off for Reverse Conduction

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Solution Overview

Problem

Conventional buck/boost converters using MOSFETs face inefficiencies due to reverse current conduction causing additional losses and increased ripple current, especially when operating at light loads, as the complementary MOSFETs are not turned off promptly, leading to excessive heating and reduced converter efficiency.

Innovation Solution

Implementing a window comparator to generate gating signals that disable PWM signals for MOSFETs just before current zero-crossing, utilizing the intrinsic body diodes to prevent extended reverse conduction, thereby optimizing the turn-off timing of MOSFETs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the complementary MOSFET is kept on to conduct current through its body diode, then the converter can operate in discontinuous conduction mode, but conduction losses increase and efficiency decreases

Engineering Contradiction:

Improvediscontinuous conduction mode operationVSAvoidconduction losses

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The control circuit turns off the complementary MOSFET before the current reaches zero (predictive turn-off), preventing reverse current flow through the body diode. This preliminary action eliminates conduction losses while maintaining discontinuous conduction mode operation capability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control circuit uses current sensing and feedback mechanisms to detect when current is approaching zero, then adjusts the MOSFET turn-off timing accordingly. This feedback control optimizes the turn-off moment to prevent reverse conduction while maintaining efficient operation.

Inventive Principle:

Principle #23Feedback

2Loss of energy

If the complementary MOSFET is turned off when current reaches zero, then conduction losses are reduced, but the MOSFET may turn off too late causing reverse current and increased ripple current

Engineering Contradiction:

Improveconduction lossesVSAvoidripple current

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The control circuit implements predictive turn-off by turning off the complementary MOSFET before current reaches zero. This preliminary action prevents reverse current flow and reduces ripple current while maintaining low conduction losses.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control circuit applies preliminary anti-action by preemptively turning off the MOSFET to counteract the potential harmful reverse current flow before it can occur, thereby preventing both conduction losses and ripple current issues.

Inventive Principle:

Principle #9Preliminary anti-action

3Device complexity

If a single PWM command is issued per period, then the control processor operation is simplified, but the complementary device cannot be turned off in time to prevent reverse conduction

Engineering Contradiction:

Improvecontrol processor operationVSAvoidconduction losses

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The control function is segmented into two parts: the control processor issues a single PWM command for simplicity, while a separate control circuit handles the precise turn-off timing based on current feedback. This segmentation maintains simple processor operation while achieving optimal turn-off control.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An intermediary control circuit is introduced between the control processor and the MOSFET driver. This intermediary receives the simple PWM command and adds the sophisticated current-based turn-off control, acting as a mediator that bridges simple command issuance with complex timing control.

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 approach reduces conduction losses and minimizes ripple current, enhancing the efficiency and lifespan of the converter by ensuring timely MOSFET turn-off, even at light loads.

Implementation Method 1

The comparator circuit may include a window comparator circuit configured to generate first and second gating signals responsive to comparisons of the current sense signal to a first threshold and a second threshold, respectively

Methodology Applied

Scientific EffectComparator circuit voltage threshold comparison:

Implementation Method 2

utilizing the intrinsic body diodes to prevent extended reverse conduction

Methodology Applied

Scientific EffectBody diode current conduction: Diode

Implementation Method 3

a pulse width modulated (PWM) signal generator circuit configured to receive a duty command signal, to generate at least one PWM signal for the at least one transistor responsive to the duty command signal

Methodology Applied

Scientific EffectPulse width modulation: Phase Modulation

Data Source

PatentUS12556087B2Synchronous buck/boost PWM converters with current-based switching

Publication Date: 2026.02.17 EATON INTELLIGENT POWER LTD

AI summary

An apparatus includes a converter circuit (e.g., a buck/boost converter) comprising at least one transistor and a pulse width modulated (PWM) signal generator circuit configured to receive a duty command signal, to generate at least one PWM signal for the at least one transistor responsive to the duty command signal, and to selectively disable the at least one PWM signal responsive to at least one gating signal. The apparatus further includes a gating circuit configured to generate the at least one gating signal responsive to a current sense signal representing a current through the converter circuit.