Low power switching regulator

This circuit is a simple battery-powered switching regulator provides 5V out from a 9V source with 80% efficiency and 50-mA output capability. When Q1 is oon , its collector voltage rises , forcing current trhough the iinductor. The output voltage rises , causing A1's output to rise . Q1 cutts off and the output drops low enough for A1 to turn Q1. The 1 uF capacitor ensures low battery impedance at high frequencies , preventing sag during switching. See schematic diagram below :