I'm creating a split rail supply similar to that described in SLVA369A. In the inductor selection section (1.5) a 150uH part is selected. I looked at the datasheet for the chosen part (MSD1260-154ML) and that appears to be the inductance value of the coils when connected in parallel. The schematic show the coils connected in series. Shouldn't we be using looking for a component with a series inductance close to 136uH? What am I missing here?
Thanks,
Mike
Mike,
The schematic looks like the inductors are in series but they're actually only connected through the mutual inductance of the coupled inductor (see schematic below). The GND connection is confusing but it's essentially just taking the secondary isolated output and connecting it back to the primary to achieve the split supply.
The inductor datasheet says, "Inductance shown for each winding... When leads are connected in parallel, inductance is the same value."
When PH goes high, the primary winding is the inductance used since the secondary diode is not conducting.
When PH goes low, the primary and secondary in parallel is used since current flows through the primary and, through the mutual inductance, through the secondary as well.
-Sam
