Title page for ETD etd-04172008-110626


Type of Document Master's Thesis
Author Person, Clark Edwin
URN etd-04172008-110626
Title Selection of Primary Side Devices for LLC Resonant Converters
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Lee, Fred C. Committee Co-Chair
Wang, Fei Fred Committee Member
Xu, Ming Committee Member
Keywords
  • DC/DC
  • LLC Resonant Converter
  • Superjuction MOSFET
Date of Defense 2008-04-16
Availability unrestricted
Abstract
The demand for high power density, high efficiency bus converters has increased interest in resonant topologies, particularly the LLC resonant converter. LLC resonant converters offer several advantages in efficiency, power density, and hold up time extension capability. Among high voltage (>500V) MOSFETs, Super Junction MOSFETs, such as Infineon’s CoolMOS parts, offer lower Rds on than conventional parts and are a natural choice for this application to improve efficiency. However, there is a history of converter failure due to reverse recovery problems with the primary switch’s body diode. Before selecting CoolMOS devices for use in a LLC resonant converter, it is necessary to investigate its performance in this application. Field failures of PWM soft switching phase shift full bridge converters have been attributed to large reverse recovery charge in the primary side MOSFET body diode. Under low load conditions the device cannot fully recover, and the large reverse recovery current can cause the device to enter secondary break down, leading to failure. The unique structure of Super Junction MOSFETs, such as CoolMOS, avoid this failure mode by providing a different path for the reverse current; however, the reverse recovery charge of CoolMOS devices is large and can cause a loss of efficiency. For this reason, it is important to avoid conditions under which the reverse recovery characteristics of the body diode can be seen.
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