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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.

- The voltage across capacitor C
_{1} can reverse every cycle, so a non-polarized capacitors should be used for C_{1}. 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.

Reference

www.planetanalog.com