Variable frequency pulse density modulation for efficient high frequency operation of series resonant converters operating as voltage regulators

Voltage regulators (VRs) powering microprocessors face stringent requirements on size; response; and efficiency. Presently, buck converters are used exclusively as VRs for their simple, well-understood behaviour despite their many shortfalls; while more suitable resonant converters are overlooked due to size and performance issues associated with their control methods. In this paper, variable frequency pulse density modulation (VF-PDM) control of the series resonant converter (SRC) is presented to enable resonant converter benefits to be realized in VR applications. It achieves efficient multi-megahertz switching frequency, ultra-fast transient response with minimal filter capacitance, and is inherently stable. It will be shown that the SRC under VF-PDM can outperform a two phase buck converter in every aspect including size, speed, and efficiency.