Can Higher Frequencies Reduce Magnetics Size? An Exploration of the Impact of Frequency on Optimized Flyback Transformers

摘要

A well-discussed strategy to miniaturize magnetic components is to increase frequency. The impact of frequency on the size of the transformer in a flyback converter is considered. Several flyback transformer optimization routines that employ accurate and computationally efficient loss models to evaluate practical designs have been built. Separate models were used for winding loss and core loss. For one of the routines, where size was fixed, an 18/11 pot core was picked and the transformer was optimized over a range of frequencies. For another, the optimization routine was allowed to choose the smallest transformer for a given temperature rise. The best performing designs, whether it was in terms of power loss or power density, fell in the 500 kHz--2 MHz range. This suggests that the biggest opportunities for miniaturization lie in this frequency range.;Impedance analyzer measurements were used to verify the winding loss model used in the optimization routine. Impedance analyzer measurements can be helpful in assessing inductor and transformer winding resistance and predicting winding loss, but the measured (Equivalent Series Resistance (ESR) does not directly correspond to winding resistance. Neglecting the effects of core loss and winding capacitance can yield significant errors in the prediction. A step-by-step method to account for such effects and extract winding resistance from an impedance measurement is also described. The proposed methodology is applicable to both inductors and multi-winding transformers. Several measurements are needed in this method; one is to determine the effects of core loss and the others yield the impedance from which winding resistance is extracted to form a resistance matrix. The winding resistance of a transformer was determined experimentally and the interactions between the winding resistance, effects of core loss, winding capacitance and inductance and their contributions to the measured impedance are demonstrated.