A Synchronous Boot-strapping Technique with Increased On-time and Improved Efficiency for High-side Gate-drive Power Delivery

In this work we demonstrate a synchronous bootstrap power delivery scheme applied to a high level count GaN-based flying capacitor multi-level (FCML) converter. The proposed approach is well suited for high-frequency operation as it eliminates conventional boot-strap diodes and allows for precise on-time control for a maximized conduction duration. Importantly, we note the synchronous boot-strapping scheme's capability for bi-directional energy transfer: Gate driver power can be injected into the chain from either a ground referenced supply, a high-side line referenced supply, or both simultaneously for further reduced voltage droop. A discrete 6-level FCML hardware prototype switching at 500 kHz (2.5 MHz effective) is designed and constructed to validate this approach. A maximum deviation in supply voltage of 156 mV throughout all 10 series stacked gate drivers for converter duty ratios spanning 15–85% is measured. Subsequently the need for local regulation throughout the gate-drive chain is eliminated, which in turn improves efficiency, simplifies design, and reduces cost.