Because of using way LC filter and IC LM1084-12 (5A Low Dropout Positive Regulators) as a result can help regulate voltage well. If there is exceed noise 12V more although a little just will change this circuit has a little. And this circuit still can give the trend tall arrives at 5A can apply to the equipment cover very. The detail is other see from circuit picture and original website
http://linuxcar.sone.jp/reg.en.html