Design of a high density low-profile transformer

An algorithm is developed to design a transformer that has the highest power density and meets a given set of specifications. The maximum achievable power density for a given power level and output voltage is computed based on only one fundamental constraint, i.e. the efficiency or temperature rise requirement. A family of curves that present the relationship between the power density and transformer height are developed. It is found that there is an optimum height at which the power density peaks. The maximum achievable power density is determined along with the optimum operating frequency and core geometry. As a result, a transformer with a height of 6 mm and a power density of 600 W/in/sup 3/ was built for a 100 W, 3.3 V output active-clamped forward converter using self-drive synchronous rectifiers.