The switching regulator which used LM2575-5.0 in this page. You can make the stable voltage by using the 3 terminal regulator like LM317. However, because the output electric current and the inputted electric current are the same approximately, the difference between the input electric power (The input voltage x The input electric current) and the output power (The output voltage x The output current) is consumed as the heat with the regulator. Because it is, the efficiency isn�t good.
Data sheet for LM2575
SIMPLE SWITCHER 1A Step-Down Voltage Regulator
http://www.national.com/pf/LM/LM2575.htm
