http://en.wikipedia.org/wiki/Voltage_regulator

http://www.ece.cmu.edu/~ee100/docs/Chapter5.pdf

http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm

http://www.reuk.co.uk/LM317-Voltage-Calculator.htm

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

http://en.wikipedia.org/wiki/Linear_regulator