Adaptive On-Time Control for High Efficiency Switched-Tank Converter

Switched-tank converter (STC) concept can leverage the advantages of wide bandgap devices. And it is especially suitable for GaN/SiC devices. This paper presents an improved STC with separate resonant branches and on-time control method to achieve efficiency improvement. Since the STC relies on resonant operation to reach high efficiency, the problems caused by unmatched resonant tanks in different resonant loops need to be studied and solved. The study shows that in most severe case, problems caused by the unmatched resonant tanks not only compromise the efficiency of STC, but also cause undesired damage to the STC. As a result, old simple control method that uses only two complementary control signals (50% duty cycle) is not good enough anymore. Hence, an improved STC as well as adaptive on-time control method have been proposed to ensure soft-switching and high efficiency operation of the STC. A 1.2kW prototype with 6:1 conversion ratio has been built to verify the effectiveness of the proposed control method. The experimental results show that with the proposed control, efficiency of the improved 6x STC is increased by 0.5% at 900W, which means power loss is reduced by 16.77%. A peak efficiency of 98.71% has been achieved.