Waveform Shaping Circuit for GaN-HEMT Gate Voltage Limiting

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Solution Overview

Problem

Existing control ICs designed for Si-MOSFETs struggle to effectively drive GaN-HEMTs due to the latter's low gate driving voltage and narrow voltage range, leading to difficulties in reliably turning off GaN-HEMTs and potential overvoltage issues.

Innovation Solution

A waveform shaping circuit is introduced, comprising parallel circuits with capacitors and resistance elements coupled with Zener diodes, which shapes the input voltage to limit the negative gate voltage and suppress overvoltages, suitable for GaN-HEMTs and other FETs with low threshold voltages.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a control IC designed for Si-MOSFET is used to drive GaN-HEMT, then the control IC can be reused without modification, but the gate voltage cannot be properly limited leading to overvoltage issues and unreliable switching

Engineering Contradiction:

Improvecompatibility of control ICVSAvoidswitching reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

A waveform shaping circuit is introduced as an intermediary between the control IC and the GaN-HEMT. This circuit includes a first parallel circuit with a first capacitance element and first resistance element, and a second parallel circuit with a second capacitance element and second resistance element. The waveform shaping circuit converts the control voltage output from the Si-MOSFET-compatible control IC into a gate voltage that properly limits negative voltage and suppresses overvoltages, making the existing control IC compatible with GaN-HEMT while ensuring reliable switching operation

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The waveform shaping circuit changes the voltage parameters by converting a control voltage with a wide voltage range (7-20V for Si-MOSFET) into a gate voltage with a narrow voltage range (±4-5V for GaN-HEMT). The circuit uses RC time constants and Zener diodes to transform the voltage waveform characteristics, limiting the negative gate voltage to prevent overvoltage damage while maintaining the switching functionality

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the gate voltage range is widened to accommodate Si-MOSFET control IC output, then the control IC can be used, but the GaN-HEMT experiences overvoltage damage due to its narrow voltage tolerance

Engineering Contradiction:

Improvevoltage range compatibilityVSAvoidovervoltage damage

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The waveform shaping circuit converts the potentially harmful wide voltage range output from the control IC into a beneficial narrow voltage range signal suitable for GaN-HEMT. By using RC filtering and Zener diode voltage clamping, the circuit transforms the excessive voltage swing into a controlled gate voltage that stays within the ±4-5V safe operating range, effectively converting what would be a harmful overvoltage condition into a useful driving signal

Inventive Principle:

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

Solution Approach 2:

The waveform shaping circuit provides beforehand cushioning by pre-limiting the gate voltage before it reaches the GaN-HEMT. The first and second parallel RC circuits, combined with Zener diodes, are configured to clamp the voltage waveform in advance, preventing overvoltage from reaching the sensitive GaN-HEMT gate terminal. This protective action occurs continuously during operation, not just during fault conditions

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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

The waveform shaping circuit effectively limits the negative gate voltage and suppresses overvoltages, ensuring a stable voltage range suitable for GaN-HEMTs, avoiding the need for dedicated drivers and reducing costs while maintaining efficiency.

Implementation Method 1

a first Zener diode having a first anode coupled to the third terminal and the fourth terminal

Methodology Applied

Scientific EffectZener breakdown: Avalanche Breakdown

Data Source

PatentUS10432081B2Waveform shaping circuit, semiconductor device, and switching power supply device

Publication Date: 2019.10.01 FUJITSU LTD

AI summary

A waveform shaping circuit includes a first parallel circuit including a first capacitance element and a first resistance element coupled in parallel with each other, a positive pulse voltage being applied to a first terminal of the first capacitance element and a second terminal of the first resistance element, a gate terminal of a field-effect transistor being electrically coupled to a third terminal of the first capacitance element and a fourth terminal of the first resistance element, a first Zener diode having a first anode coupled to the third terminal and the fourth terminal, and a second parallel circuit including a second capacitance element and a second resistance element coupled in parallel with each other, a first cathode of the first Zener diode being coupled to a fifth terminal of the second capacitance element and a sixth terminal of the second resistance element.