Analysis of SEPIC Converter at Different Switching Frequencies

Single Ended Primary Inductance Converter (SEPIC) which is commonly devoted as a switched power supply in many applications is presented in this work to conclude the effect of switching frequency on the output voltage time response, elements values, spectral analysis of output voltage and efficiency. For this goal, three circuits of SEPIC converters were designed at switching frequencies of 100KHZ, 400KHZ and 600KHZ. The operating conditions of the three circuits which include input voltage range, output voltage value, output voltage ripple and inductor ripple current are kept the same while the inductors and capacitors of the converters are calculated according to each switching frequency. The LTC1871 controller is utilized to produce a required duty cycle (D) to drive the converter. The implementation of the circuits was carried out using LTspice XVII. The results show that the higher switching leads to better time response of the output voltage with small values of passive components of the converter. However, the efficiency of the converter is decreased and the noise due to harmonics is increased. Therefore, the selection of switching frequency must be set accurately according to converter functions.