Σ/sigma DC/DC conversion for computing and telecom applications

A novel DC/DC conversion architecture, Sigma/sigma DC/DC, is proposed. A tiny regulated converter with only about 2% of total output power is seamlessly mated with the unregulated resonant DC/DC transformer (DCX) which is responsible for about 98% of the total power during both the steady state and transient. The resonant DCX is always operated at the best point during steady state for the highest efficiency with the compelling features of negligible switching loss, simple driving of synchronous rectifier and fast dynamic response. By taking advantage of the ultra-low output impedance of the DCX, the tiny regulated converter is deemed to steer the big unregulated DCX toward the output voltage regulation, soft starting and output current limiting, and current sharing for N+l redundancy. Thus, the overall efficiency is determined by the DCX while the output regulations are executed by the tiny regulated converter. Theoretical analysis on the steady state and transient operation, as well as the design guideline is provided. Finally, 96% overall efficiency has been demonstrated in a 400 KHz 200 V/12 V DC/DC design.