Analysis of leakage-inductance effect on characteristics of flyback converter without right half plane zero

Flyback DC-DC converters are often used as power supply for many electronic systems because of circuit simplicity. However, the conventional flyback converter has a drawback of instability occurrence due to a right-half-plane zero. We have proposed a solution to delete this right-half-plane zero and to keep the flyback converter always stable by introducing a novel control strategy. This method is to control the holding time of transformer's magnetizing current with the fixed discharging time. As a result, its operation goes well and the frequency bandwidth of the control-to-output transfer function is widened in case of a tight-coupled transformer. In practice, the transformer has leakage inductances, and it results in the characteristics variations. The effect of these leakage inductances becomes larger with the increase in switching frequency. The discussion on this effect is necessary for the design of high-frequency flyback converters. However, this effect has not been discussed in detail before. This paper discusses the effect of the leakage inductances on the static and dynamic characteristics of the novel flyback converter proposed previously and its mechanism through the analysis and the experiment. As a result, it is confirmed that the leakage inductances act as an equivalent resistance and that static load regulation is deteriorated, but the dynamic response is smoothed due to the increased dumping factor.