GaN FET Drain Current Sensing via Gate Voltage

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Wide bandgap power converter circuits, particularly those using GaN devices, face challenges in overcurrent detection due to high fault current slew rates and temperature-dependent saturation currents, which complicates the selection of fault thresholds and can lead to increased switching losses and reduced protection effectiveness.

Innovation Solution

A power converter circuit that includes a wide bandgap field effect transistor with a current sensing circuit estimating drain terminal current based on gate-source voltage, a gate driving circuit generating maintenance signals, and overcurrent detection using a latching comparator to generate fault signals, allowing for flexible threshold selection independent of gate driver design or temperature.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If desaturation detection is used for overcurrent protection, then fault protection is provided, but the sensing diode adds capacitive loading which increases switching loss

Engineering Contradiction:

Improveovercurrent protectionVSAvoidswitching loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent extracts the sensing function from the traditional desaturation detection circuit by removing the sensing diode and its associated capacitive loading. Instead, it uses a separate current sensing circuit that estimates drain current based on gate-source voltage, thereby providing overcurrent protection without adding capacitive loading to the switching node that would increase switching losses.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces an intermediary approach by using gate-source voltage as a proxy to estimate drain current. Rather than directly sensing the drain current or using a sensing diode that loads the circuit, the invention uses the relationship between gate-source voltage and drain current as an indirect measurement method, avoiding the harmful capacitive loading while still enabling fault detection.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If desaturation protection is used, then fault detection is enabled, but significant settling time is required after drain terminal voltage falls which reduces protection speed

Engineering Contradiction:

Improvefault detectionVSAvoidsettling time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies preliminary action by continuously monitoring the gate-source voltage during normal operation to estimate drain current. This continuous monitoring allows the system to be ready to detect overcurrent conditions immediately without requiring settling time after voltage transients, as the sensing circuit is already active and tracking the current state.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces the mechanical/delayed response of traditional desaturation detection (which requires waiting for voltage to settle) with an electronic estimation method based on gate-source voltage. This substitution eliminates the settling time requirement by using a different physical relationship that provides immediate current information without being affected by voltage transients.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If fault threshold is matched to saturation current, then protection effectiveness is maximized, but threshold selection becomes complex due to temperature dependence

Engineering Contradiction:

Improveprotection effectivenessVSAvoidthreshold selection

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies universality by using a single sensing parameter (gate-source voltage) that can serve multiple functions: it enables both normal operation control and overcurrent protection. The gate-source voltage naturally adapts to temperature changes and device characteristics, providing a universal sensing method that works across different operating conditions without requiring complex temperature-compensated threshold circuits.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent utilizes parameter changes by leveraging the natural relationship between gate-source voltage and drain current, which changes with operating conditions. Rather than trying to maintain a fixed threshold that compensates for temperature effects, the invention allows the sensing parameter (gate-source voltage) to naturally vary with temperature and device state, simplifying threshold selection while maintaining protection effectiveness.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11705720B2Drain current sensing and fault protection circuit based on gate voltage for gate current driven field effect transistors

Publication Date: 2023.07.18 UNIVERSITY OF TENNESSEE RESEARCH FOUNDATION

AI summary

A power converter circuit includes a switch including a field effect transistor, the field effect transistor being a wide bandgap field effect transistor and being configured to maintain an on operational state responsive to a maintenance signal received through a gate terminal, a current sensing circuit that is configured to estimate a drain terminal current of the field effect transistor responsive to a voltage between the gate terminal of the field effect transistor and a source terminal of the field effect transistor, and a gate driving circuit that is configured to generate the maintenance signal responsive to the estimate of the drain terminal current.