A DC-DC converter converts voltage from a battery source providing a voltage Vin to a lower level. A four-level transistor stack selectively connects an input voltage and flying capacitor voltages to an output inductor. Stress reduction transistors limit the charging of the flying capacitors to Vin/3. The stress reduction transistors can also limit switching transistor voltages to Vin/3. Freewheel switches can be used to limit ringing in the output inductor.