A Delta-Sigma Modulated Multi-MHz GaN Half-Bridge featuring Zero-Voltage Switching and Blanking Time Compensation

Abstract

This paper proposes a method to control a soft-switching gallium-nitride (GaN) based half-bridge with a delta-sigma (ΔΣ) modulator at multi-megahertz switching frequencies. A GaN-based High Electron Mobility Transistor (HEMT) can be operated at very high switching frequencies. However operating at these switching frequencies can be challenging as pulse-width modulators have several drawbacks when requiring zero-voltage switching with a variable switching frequency. Therefore a ΔΣ-modulator is extended to support zero-voltage switching operation for the entire output range. Also a compensation scheme is implemented that reduces the output voltage distortion due to blanking time. As a result of the proposed ΔΣ modulation scheme, the switching frequency automatically varies to minimize the inductor current ripple. The proposed method is validated in simulation including system non-idealities. Additionally the converter switching frequency range and zero-voltage switching behavior of the half-bridge is analyzed. Results show an improvement up to 14dB in output voltage distortion compared to the same PWM modulated converter with a constant switching frequency. Besides, the PWM modulated converter is not continuously soft-switching and has unnecessarily large inductor current ripple especially at small modulation indices.