Design of a Very High Frequency dc-dc boost converter

Abstract

Passive component volume is a perennial concern in power conversion. With new circuit architectures operating at extreme high frequencies it becomes possible to miniaturize the passive components needed for a power converter, and to achieve dramatic improvements in converter transient performance. This thesis focuses on the development of a Very High Frequency (VHF, 30 - 300 MHz) dc-dc boost converter using a MOSFET fabricated from a typical power process. Modeling and design studies reveal the possibility of building VHF dc-dc converters operable over the full automotive input voltage range (8 - 18 V) with transistors in a 50 V power process, through use of newly-developed resonant circuit topologies designed to minimize transistor voltage stress. Based on this, a study of the design of automotive boost converters was undertaken (e.g., for LED headlamp drivers at output voltages in the range of 22 - 33 V.) Two VHF boost converter prototypes using a [Phi]2 resonant boost topology were developed. The first design used an off the shelf RF power MOSFET, while the second uses a MOSFET fabricated in a BCD process with no special modifications.

(cont.) Soft switching and soft gating of the devices are employed to achieve efficient operation at a switching frequencies of 75 MHz in the first case and 50 MHz in the latter. In the 75 MHz case, efficiency ranges to 82%. The 50 MHz converter, has efficiencies in the high 70% range. Of note is low energy storage requirement of this topology. In the case of the 50 MHz converter, in particular, the largest inductor is 56 nH. Finally, closed-loop control is implemented and an evaluation of the transient characteristics reveals excellent performance.