Posted on Dec 10, 2012 5844
Circuit provides a minimum of 7 V until the 9-V battery voltage falls to less than 2 V. When the battery voltage is above 7 V, the MAX630`s IC pin is low, putting it into the shutdown mode which draws only 10 nA. When the battery voltage falls to 7 V, the MAX8212 voltage detector`s output increases. The MAX630 then maintains the output voltage at 7 V. The low battery detector (LBD) is used to decrease the oscillator frequency when the battery voltage falls to 3 V, thereby increasing the output current capability of the circuit.
Note that this circuit, with or without the MAX8212, can be used to provide 5 V from 4 alkaline cells. The initial voltage is approximately 6 V, and the output is maintained at 5 V even when the battery voltage falls to less than 2 V.