In modern power architectures, the conversion from the 48 V bus to the point of load (POL) voltage is performed in two steps. A switched tank converter (STC) converts the bus voltage down to the 12 V level. Then, a POL converter provides the supply voltage for CMOS circuitry. In the event of DC bus voltage fluctuations, the STC fixed conversion ratio forces the POL converter to operate in non-nominal conditions. This paper introduces a sigma-converter that employs an additional inductor-based converter, coupled with the STC, to achieve output voltage regulation. Compared to prior art, the additional converter is connected to a different internal node of the STC, providing the peak efficiency at the nominal input voltage, while guaranteeing high efficiency over the whole 38 V to 60 V input voltage range. Moreover, a hybrid control strategy, able to seamlessly change operating regime, is suggested to guarantee voltage regulation when the input voltage hovers near its nominal value. A prototype converter has been implemented on a PCB, achieving a peak efficiency of 97.6 % at 30 A load current and 48 V input voltage, and a power density of 900 W/inch3 at 60 A load current.
