SiC/GaN MOSFET Short-Circuit Detection via Isolated Field Sensing

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Solution Overview

Problem

Existing power switching devices using SiC or GaN MOSFET transistors face challenges in detecting short circuits effectively due to high-frequency electromagnetic interference, which causes false alarms and requires a compromise between reactivity and immunity to electromagnetic interference, particularly in high-frequency applications like the railway sector.

Innovation Solution

A power switching device that measures current indirectly from the electromagnetic field radiated by the transistor, using a galvanically isolated antenna to decouple the protection circuit from the common mode current, allowing for precise detection of short circuits without direct connection to the source, thus reducing electromagnetic interference sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the protection circuit is directly connected to measure voltage between drain and source, then short-circuit detection capability is improved, but electromagnetic interference sensitivity increases causing false alarms

Engineering Contradiction:

Improveshort-circuit detection capabilityVSAvoidelectromagnetic interference sensitivity

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary measurement approach by detecting the electromagnetic field radiated by the transistor instead of directly measuring voltage at the drain-source terminals. This intermediary field measurement decouples the protection circuit from the high-frequency switching nodes, eliminating common-mode current interference while preserving short-circuit detection capability through field-based current sensing.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If reinforced filtering is inserted to filter common-mode current, then electromagnetic interference immunity is improved, but protection circuit response time increases

Engineering Contradiction:

Improveelectromagnetic interference immunityVSAvoidprotection circuit response time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces the traditional voltage-based measurement system with an electromagnetic field-based measurement system. This substitution eliminates the need for reinforced filtering components (such as common-mode chokes and complex RC filters) because the field-based measurement inherently rejects common-mode currents, achieving both EMI immunity and fast response time without the time penalty of filtering.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Speed

If SiC or GaN MOSFET transistors operate at high switching frequencies, then switching speed and efficiency are improved, but common-mode current increases causing false short-circuit alarms

Engineering Contradiction:

Improveswitching speedVSAvoidcommon-mode current

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful common-mode current into a useful measurement signal by detecting the electromagnetic field radiated by the transistor during switching. The high-frequency switching that generates common-mode current also produces a detectable electromagnetic field signature, which the protection circuit uses to monitor current flow and detect short-circuits without being affected by the common-mode interference.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 enables efficient and robust short-circuit detection with reduced false alarms and faster reaction times, maintaining the device's immunity to electromagnetic interference, ensuring reliable operation in high-frequency environments.

Implementation Method 1

the measurement module (14) is configured to indirectly measure the intensity of the main current (I) passing through the transistor (12) from the electromagnetic field radiated by the transistor (12)

Methodology Applied

Scientific EffectElectromagnetic radiation: Electromagnetic Induction

Implementation Method 2

the measurement module includes an antenna (18), galvanically isolated from the transistor (12), and capable of measuring the electromagnetic field radiated by the transistor (12)

Methodology Applied

Scientific EffectElectromagnetic field measurement: Electromagnetic Induction

Data Source

PatentEP3425801B1Short-circuit protection circuit for switching devices for sic or GAN mosfet transistor and associated method

Publication Date: 2024.05.08 ALSTOM HOLDINGS SA

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AI summary

The invention relates to a power switching device (10) comprising at least one SiC or GaN MOSFET transistor (12; 12a, 12b, 12c) suitable for carrying a main current (I; Ia, Ib, Ic); the switching device (10) comprising at least one measurement module (14; 14a, 14b, 14c) configured to indirectly measure the main current (I) of the transistor (12; 12a, 12b, 12c) from the electromagnetic field produced by the transistor (12; 12a, 12b, 12c) and at least one protection circuit (16; 16a, 16b, 16c) configured to detect a short circuit as a function of the sign of the time derivative of the main current (I; Ia, Ib, Ic).