High-Frequency Planar Power Transformer for Switching Power Supplies

摘要

In this project, we proposed novel transformers for power supplies. Transformersconsists of cascade of sections of transmission lines, each a quarter-wave length long at the design frequency. Power conversion is through the propagation of electromagnetic waves instead of magnetic flux. Parallel strip lines sandwiching a printed circuit board were used as the transmission lines. Printed meandered striplines on a multi-layer structure were used to optimize the component size. Three printed stripline transformers are built on Teflon-fiberglass for a hundred MHz applications. S parameter tests for a 30 ohm load show the measured transformer ratio agrees excellently with the prediction. The overall efficiency is greater than 98% due to very low material losses. A transformer is also built on a lead zirconate titanate material with dielectric constant 1100 at 8 MHz. 40 cm quarter-wave strip lines are built on a 3.1 inch by 3.1 inch plate. Open circuit and short circuit tests on network analyzer show the actual quarter-wave length is at 8.3 MHz instead and the line impedance (4 Ohms) also agrees well with the design value (4.4 Ohms). The S parameter measurement of the transformer ratio does not show good results, however, due to high material losses.