SiC MOSFET Desaturation Circuit for Fast Overcurrent Detection

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Solution Overview

Problem

Existing protection circuits for SiC MOSFETs in power converters lack sufficient speed and noise immunity to effectively handle high surge currents and fast switching transients, leading to potential device damage and system instability.

Innovation Solution

A protection circuit design that includes a high current source, a current mirror configuration, and a precharged circuit, tailored to the specific parameters of SiC MOSFETs, to provide fast and reliable overcurrent fault detection independent of current gradient.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If conventional protection circuits are used for SiC MOSFETs, then device destruction is prevented, but the response speed is too slow to handle fast switching transients and high surge currents

Engineering Contradiction:

Improveresponse speedVSAvoidprotection reliability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The protection circuit performs preliminary action by detecting overcurrent conditions before they cause device destruction. The circuit monitors current in real-time and triggers protective action at the earliest possible moment, preventing the need for post-failure recovery actions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces conventional slow mechanical/protection circuits with a faster electronic detection system that uses operational amplifiers and comparison circuits to detect overcurrent conditions electronically, achieving nanosecond-scale response times necessary for SiC MOSFET protection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-affected harmful factors

If conventional protection circuits are used for SiC MOSFETs, then system stability is maintained, but noise immunity is insufficient during fast switching transients

Engineering Contradiction:

Improvenoise immunityVSAvoidsystem stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The protection circuit introduces intermediary filtering elements (resistors and capacitors) between the current sensing node and the detection circuitry. These intermediaries filter out high-frequency switching noise while preserving the essential overcurrent signal, enabling reliable detection despite the noisy SiC MOSFET switching environment.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The circuit implements feedback mechanisms where the detected overcurrent condition feeds back to control the switching transistor, which in turn affects the current flow. This closed-loop feedback enables the system to maintain stability by automatically responding to disturbances while filtering out noise through the feedback path's inherent filtering characteristics.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS20250125607A1Desaturation configurations for power devices

Publication Date: 2025.04.17 ALPITRONIC SRL

AI summary

A protection circuit with fast responses and high noise immunity includes values of components in the protection circuit determined based on a circuit model of the protection circuit for specific power devices. Further, the circuit model includes overcurrent fault detection criterion based on a maximum current and voltage across power device, together with the transient response of the power device. The protection circuit includes an additional current source when used with a gate driver circuit having a built-in current source. The protection circuit further includes a precharged circuit configured to set the monitored voltage at a base voltage close to the threshold voltage to improve the fault detection responses with a smaller tolerance gap in voltage.