ZVS Modulation Strategy for Constant High Frequency Four-Switch Buck-Boost Converters used in Envelope Tracking Power Supplies

Envelope Tracking (ET) is a technique used to improve the power efficiency of Linear Power Amplifiers (LPAs). It consists in modulating the LPA supply voltage according to the envelope of the communication signal to be reproduced. In order to accurately reproduce the envelope, Switching-Mode Power Converters (SMPCs) with a switching frequency in the megahertz range are mandatory, leading to high switching losses and degrading the overall performance of the ET system. In this work, a control strategy to achieve Zero Voltage Switching (ZVS) in a Four-Switch Buck-Boost (FSBB) converter with constant frequency is proposed to minimize the switching losses of high-bandwidth SMPCs in ET applications. The operation of a FSBB performing fast output voltage changes and the methodology used to achieve ZVS for any voltage are described. The idea is validated with a 10 MHz GaN-based prototype providing an output voltage that ranges between 0 V and 20 V and handling a peak output power of 45 W.