A switching DC-DC converter with wide conversion range without extreme duty ratios

In DC-DC conversion applications, if a large range of input/output voltages ratio is required, the conventional transformerless DC/DC switching mode power converter (SMPC) topologies most operate at extreme duty ratios. This limits the operation in lower switching frequencies because of the minimum on-time of the switches. To overcome this problem, a new class of synthesis converter is proposed which has a voltage conversion ratio according to the quadratic of the duty ratios. This not only overcomes the problem of switching operation at extreme duty ratios, but also brings an extra advantage of a wider conversion range than a conventional converter with a step-down transformer could have. Furthermore, a zero-current-switch (ZCS) quasi-resonant converter (QRC) technique is also applied to the synthesis converter. It improves the high loss problem of the conventional pulse width modulation (PWM) converter, decreases the switching loss, and increases switching frequencies. Also, a new single cycle resonant converter (SCRC) technique based on ZCS/ZVS mixed switching is proposed to improve the limited load range of ZCS-QRC. Finally, some real circuits are implemented to test this new synthesis converter