GaN Bootstrap Supply in Half-Bridge Circuits Without QRR Losses
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Solution Overview
Problem
Conventional half-bridge topologies using GaN FETs face inefficiencies due to reverse recovery charges from Schottky or PN junction diodes, leading to significant losses at high switching frequencies, particularly in high voltage applications.
Innovation Solution
The implementation of a GaN FET as a bootstrap transistor in a half-bridge topology, synchronized with the low side transistor, eliminates the need for a high bootstrap supply voltage and reduces losses by utilizing zero reverse recovery charge, thereby enhancing switching performance and reducing capacitance requirements.
Engineering Contradictions & Design Principles
Engineering 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
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 high switching frequency operation without significant energy losses.
Solution Approach 2:
The patent substitutes the passive diode component with an active GaN FET device that can be synchronously controlled. This substitution replaces the inherent reverse recovery behavior of diodes with the controllable switching behavior of GaN FETs, eliminating the harmful reverse recovery charge effects.
2Reliability
If a high voltage Schottky diode is used to provide bootstrap power, then the high side transistor can be powered, but the diode has reverse recovery charge that increases losses at high frequencies
Solution Approach 1:
The patent changes the device type from a high voltage Schottky diode to a GaN FET. This parameter change maintains the ability to power the high side transistor while eliminating the reverse recovery charge problem, as GaN FETs have zero reverse recovery charge regardless of voltage level.
Solution Approach 2:
The GaN FET bootstrap device can be synchronously switched with the low side transistor, allowing the system to self-regulate the bootstrap power delivery without requiring a separate high voltage diode. The synchronous switching ensures power is delivered only when needed, reducing losses.
3Productivity
If conventional bootstrap methods are used with GaN FETs, then the half-bridge topology can operate, but reverse recovery charges become a significant portion of converter losses at high frequencies
Solution Approach 1:
The patent changes the bootstrap device parameter from a conventional diode to a GaN FET, which has zero reverse recovery charge. This enables the system to operate at high frequencies without the reverse recovery losses that would otherwise become significant at elevated operating frequencies.
Solution Approach 2:
The patent substitutes the conventional diode-based bootstrap method with a GaN FET-based synchronous switching approach. This substitution eliminates the frequency-dependent reverse recovery losses, allowing the converter to efficiently operate at high frequencies.
Data Source
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.