Pololu 9V Step-Up/Step-Down Voltage Regulator S18V20F9

This powerful step-up/step-down regulator efficiently produces a fixed 9 V output from input voltages between 3 V and 30 V while allowing a typical output current of up to 2 A when the input voltage is close to the output voltage and offering typical efficiencies of 80% to 90%. Its ability to convert both higher and lower input voltages makes it useful for applications where the power supply voltage can vary greatly, as with batteries that start above but discharge below the regulated voltage.