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SEPIC CONVERTER INDUCTORS
Application Features The SEPIC converter allows the output voltage to be greater than, less than, or equal to a required nominal voltage. The output voltage polarity is the same as the input voltage thus allowing a common ground. DC isolation is provided by a capacitor. The two inductors can be wound on the same core. Efficiency is significantly higher than most other DC-DC converters. Requirements The SEPIC converter works best in a continuous-conduction mode. This is when the current through L1 never falls to zero. This is similar to the familiar DC choke input filter where the inductive reactance minimum is 2/3 of the minimum load resistance. One simple check is to make the nominal value equal to the load resistance to allow for a ± tolerance of the inductors and roll-off with DC. Since the voltage across capacitor C1 can reverse every cycle, a non-polarized capacitors should be used for C1. They should also have a low Equivalent Series Resistance (ESR). The diode's switching time needs to be fast in order not to generate high voltage spikes across the inductors. The inductor windings can be on the same core. Therefore, standard DC chokes like MCE's DL series with 2, 4, or 6 windings can be split. The average current through L2 is the same as the average load current.
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