Jul 24th (Thu) @ 3:00pm: "Miniaturized and Efficient DC-DC Power Conversion," Sandeep Reddy Kukunuru, ECE PhD Defense

Location: Engineering Science Bldg (ESB), Room 2001
Zoom Meeting: https://ucsb.zoom.us/j/89142940467

Abstract

DC-DC power converters are widely employed in portable electronics, data centers, solar energy harvesting, and electric motor drives. The trade-off between converter volume and power conversion efficiency plays a vital role in determining overall solution size and run-time per charge cycle. Often, bulky inductors are required to achieve acceptable efficiency, and their size becomes a bottleneck in minimizing system footprint and cost.

This dissertation presents several innovations to address these challenges. First, a switched photovoltaic (PV) DC-DC converter is developed that eliminates the need for external passive energy storage elements by dynamically reconfiguring the PV cells themselves in a series-parallel configuration, leveraging their internal capacitance for voltage balancing. A maximum power point controller generates a switching clock whose frequency is proportional to the current mismatch among series-connected PV cells. The proof-of-concept prototype demonstrated up to 30% higher power harvesting efficiency under partial shading compared to prior work.

Second, a single-inductor N:1 resonant switched-capacitor ladder converter is introduced for converting a 9V bus to a 1.2V SoC supply. Switches are operated as rectifying diodes to enable automatic optimal phase-shift tracking, improving efficiency by up to 20%.

Third, an inductively assisted switched-capacitor (L-SC) converters, derived from series-parallel and ladder switched-capacitor topologies, are developed to reduce the average inductor current. This reduction mitigates dominant conduction losses or enables the use of compact inductors, improving both power conversion efficiency and power density. Two notable developments in this category include: (1) a 3:1 ladder L-SC converter tailored for USB 5V input to 0.6–1.2V SoC output. By reducing the normalized squared inductor RMS current by up to 50%, it enables the use of a compact 0402 inductor while achieving 87% peak efficiency and 1.63× higher peak power density compared to prior work; and (2) a reconfigurable 5-mode (L-SC)  converter designed for a 3.3V battery input and capable of generating a 0.5–2.5V output to support dynamic voltage scaling in SoCs.

Additionally, both the ladder L-SC  and resonant switched-capacitor topologies are extended to 48V input applications for data center point-of-load voltage regulation, delivering 5V and 9V outputs, respectively.

Bio

Sandeep Reddy Kukunuru received the B.Tech. degree in electrical engineering from Jawaharlal Nehru Technological University, Hyderabad, India, in 2006, and the M.Tech. degree in electrical engineering from the Indian Institute of Technology Delhi, New Delhi, India, in 2008. He is currently pursuing the Ph.D. degree in electrical engineering at the University of California at Santa Barbara, Santa Barbara, CA, USA.
From 2008 to 2020, he worked as an Analog Circuit Design Engineer at Cosmic Circuits (Cadence), Broadcom, Xilinx, and Samsung Electronics. His current research interests include inductively-assisted switched-capacitor, resonant power converters, and energy harvesting circuits for data center and portable applications.

Hosted By: ECE Professor Loai Salem

Submitted By: Sandeep Reddy Kukunuru <sandeepreddy@ucsb.edu>