Since the early 80s, the computer industry has undergone great expansion. Processors are becoming faster and more powerful. Power management issues in computing systems are becoming more complex and challenging. An evolution began when the high-performance Pentium processor was driven by a non-standard, less-than-5V power supply, instead of drawing its power from the 5V plane on the system board. A so-called Voltage Regulator Module (VRM), is put close to the processor in order to provide the power as quickly as possible. Nowadays, for desktop and workstation applications, VRM input voltage has moved to the 12V output of the silver box. In the meantime, microprocessors will run at very low voltage (below 1V), will consume up to 100A of current, and will have dynamics of about 400A/us.

This work presents an investigation of three 12V VRM topologies: the synchronous buck converter, the tapped-inductor buck converter and the active-clamp couple-buck converter. The limitations of today¡¯s synchronous buck approach are identified. The extreme duty cycle of the current topology makes it difficult to design an efficient VRM with decent transient response.

The tapped-inductor buck and the active-clamp couple-buck converters are discussed as solutions. The transient response and efficiency of each type of converter are compared. Ripple cancellation is also addressed. The analytical and experimental results are presented: The tapped-inductor buck can improve the efficiency, but suffers a voltage spike, which nullifies its candidacy; the active-clamp couple-buck converter can improve the efficiency while maintaining good transient response, and it is therefore a good candidate for 12V VRMs.