A Novel Non-Isolated Full Bridge Topology for VRM Applications

Abstract

In this paper, a new non-isolated full bridge (NFB) topology is introduced to solve the narrow duty cycle and hard switching problems of the buck converter in low output voltage, high output current applications. In comparison to the Buck converter, it operates at a significantly wider duty cycle and can achieve zero voltage switching for the high side MOSFETs. The NFB significantly reduces the input peak current and transfers a portion of the primary side energy directly to the load thereby reducing the stress on the synchronous rectifiers and filter inductors. Using self-driven synchronous rectifiers, the body diode conduction loss is reduced since no dead time is required between the primary side MOSFETs and the synchronous rectifiers. Given these significant advantages, the NFB can achieve higher efficiency than a two and three phase interleaved buck at the same power level. The efficiency gain enables the NFB to operate at a high switching frequency thereby enabling smaller output inductors to be used to achieve improved dynamic performance. Experimental results and analysis demonstrate that the new NFB can significantly improve the performance of a voltage regulator. The prototype built operated at 500 kHz, 12 V input, 1 V output, up to 30 A load and achieved an efficiency of 84.4% at 30 A load. A 1 MHz prototype achieved a full load efficiency of 82.1%. In comparison, the efficiency of a two and three phase Buck prototype was 79.7% and 82.6% at 30 A load and at 500kHz switching frequency.