GaN Bootstrap Supply for High-Voltage Half-Bridge Switching

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Solution Overview

Problem

Conventional half-bridge topologies using GaN FETs face inefficiencies due to reverse recovery charges of Schottky or PN junction diodes, leading to significant losses at high switching frequencies, particularly in high voltage applications.

Innovation Solution

A bootstrap supply using a GaN FET as a synchronous switch, eliminating the need for a high boot-strap supply voltage and reducing losses by employing a GaN field-effect transistor as the bootstrap device, which has zero reverse recovery charge, synchronized with the low side transistor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If Schottky or PN junction diodes are used in conventional half-bridge topology, then the bootstrap supply can be implemented, but reverse recovery charges cause significant losses at high switching frequencies

Engineering Contradiction:

Improveswitching frequencyVSAvoidreverse recovery charge losses

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent changes the key parameter of the bootstrap device from a diode (Schottky or PN junction) to a GaN FET. This parameter change eliminates reverse recovery charge losses because GaN FETs have zero reverse recovery charge, enabling efficient operation at high switching frequencies while maintaining bootstrap supply functionality

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes the passive diode component with an active GaN FET device. This substitution replaces the conventional diode-based bootstrap mechanism with a transistor-based synchronous switching mechanism that can be actively controlled to eliminate reverse recovery losses

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Power

If conventional bootstrap diodes are used, then the bootstrap capacitor can be charged, but the diodes have reverse recovery charge that increases losses proportionally to frequency

Engineering Contradiction:

Improvebootstrap supply voltageVSAvoidreverse recovery losses

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

The patent extracts and eliminates the harmful reverse recovery charge characteristic from the bootstrap circuit by removing the diode component entirely and replacing it with a GaN FET that does not exhibit reverse recovery effects, thereby taking out the source of energy losses

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the potential harm of using conventional diodes (reverse recovery losses) into a benefit by using GaN FETs whose zero reverse recovery charge characteristic directly eliminates the loss mechanism, turning what would be a problematic frequency-dependent loss into an advantage for high-frequency operation

Inventive Principle:

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

Data Source

PatentUS9667245B2High voltage zero Q<sub>RR </sub>bootstrap supply

Publication Date: 2017.05.30 EFFICIENT POWER CONVERSION CORP

AI summary

An electrical circuit arranged in a half bridge topology. The electrical circuit includes a high side transistor; a low side transistor; a gate driver and level shifter electrically coupled to a gate of the high side transistor; a gate driver electrically coupled to a gate of the low side transistor; a capacitor electrically coupled in parallel with the gate driver and level shifter; a voltage source electrically coupled to an input of the gate driver and level shifter and an input of the gate driver; and, a bootstrap transistor electrically coupled between the voltage source and the capacitor. A GaN field-effect transistor is synchronously switched with a low side device of the half bridge circuit.