Gate Driver for Normally-On and Normally-Off Devices

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Solution Overview

Problem

High voltage MOSFETs face issues with turn-on resistance and gate oxide degradation, while conventional JFET structures require additional MOSFETs for driving and lack direct gate access, leading to voltage overstress and inefficiencies.

Innovation Solution

A gate driver system comprising a first driver for a normally-on device, a second driver for a normally-off device, and an under voltage detector to manage power supply conditions, allowing for direct control of the normally-off device to maintain an ON status and switch the normally-on device based on PWM signals, while monitoring and responding to under voltage conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a cascode structure with JFET and MOSFET is used, then voltage stress on devices is reduced, but the device complexity increases due to requiring one MOSFET for each JFET

Engineering Contradiction:

Improvevoltage stressVSAvoidstructure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent merges the control functions of separate JFET and MOSFET drivers into a single integrated driver circuit that directly controls the JFET gate. This consolidation eliminates the need for additional MOSFETs while maintaining voltage stress protection through integrated clamping circuits and controlled switching mechanisms.

Inventive Principle:

Principle #5Merging (Combining)

2Ease of operation

If direct access to JFET gate is implemented, then slew rate control is achieved, but the device complexity increases

Engineering Contradiction:

Improveslew rate controlVSAvoiddriver complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary driver stage that sits between the control signal and the JFET gate. This driver stage includes controlled current sources and clamping circuits that act as mediators to regulate the gate voltage transition rate, providing slew rate control without requiring complex external circuitry.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Speed

If hard switching turn-off is used, then switching speed is improved, but voltage overstress on MOSFET increases

Engineering Contradiction:

Improveswitching speedVSAvoidvoltage overstress

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent implements beforehand cushioning by incorporating clamping circuits and controlled turn-off mechanisms that limit voltage spikes before they can damage the devices. The driver circuit actively monitors and controls the switching transitions to prevent excessive voltage stress while maintaining fast switching performance.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS11705803B1Gate driver with improved switching performance and the driving method thereof

Publication Date: 2023.07.18 MONOLITHIC POWER SYSTEMS INC

AI summary

A gate driver is configured to drive a normally-on device and a normally-off device coupled in series. The gate driver controls the normally-on device in response to a PWM signal, and to control a normally-off device to maintain ON in normal operations. If an under voltage condition of a negative power supply of a first driver used to drive the normally-on device, or a positive power supply of a second driver used to drive the normally-off device, or an input supply voltage is detected, the normally-off device is controlled to be OFF.