Step-down/up switching regulators, also called buck-boost converters, output a regulated voltage level that can be either higher or lower than the input voltage. By combining buck and boost technology into a single DC-DC converter, the step-down/up converter can handle a wide range of input voltages that are either higher or lower than required by the circuit.
Buck-boost converters are ideal for use in portable devices, where the power source is frequently a single battery. The battery voltage can swing from a value above that needed by the circuit (at full charge) to a value below what is needed (as the battery discharges). The buck-boost converter will step-down the voltage in the former situation and step-up the voltage in the latter.
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