Extending Battery Life with Switching Regulator

A normal 9V battery would be considered as dead battery when the voltage falls below 7 Volts. With this switching regulator, a  lifetime of a 9V battery will be extended by boosting the voltage if the battery voltage falls under 7.5V. This circuit will maintain the voltage at 7V until the battery voltage falls down to 2.2 volt, a point where this circuit would fail to maintain a 7V level at the output. At full battery capacity, this switching circuit will be inactive and draw only small current, about 215 uA. When the battery voltage falls below 7.5 volts then this circuit will start to switch and regulate the output at 7.0V, until the battery falls below 2.2V.  At 10 mA load and 5V battery voltage, this circuit give 80% efficiency. Here is the schematic diagram of the circuit:

[Circuit’s schematic diagram source: seekic.com]