Optimum Ferrite core characteristics for a 500 kHz switching mode converter transformer

Power supplies can be made more compact and light-weight by increasing their operating frequencies. Since it is possible to increase the switching frequency of the power supply to as high as 500 kHz without interfering with the BC band, research into the optimum operating magnetic flux density of the ferrite core was carried out for a 500 kHz switching transformer, with the following results: (1) Single-ended forward converter: ΔB = Bm - Br > 1,500 Gauss (2) Push-pull converter: ΔB = 2-Bm > 1,500 Gauss The core loss of the ferrite core should be less than 120 mW/cm³under the condition wherein ΔB = 500 Gauss, Ta = 90°C to 105°C. In accordance with these optimum ferrite core characteristics, a core material was developed for 500 kHz switching power supplies.