I need a 12VDC voltage regulator that can produce at least 3A. My DC Source is 18.5volts 3.5A. I'm powering gsm shield, arduino, solenoids and etc. I only have here two LM317 regulator and their max current is only 1.5a based on the datasheet. The electronic shop near me doesn't have regulator that can produce more than or equal to 3A. My circuit has a master switch and backup battery that will turn on when the main supply is off. This is the schematic if i will use two regulators with master switch and back up, it is very complicated, and i want to reduce it as shown in the left of the picture by using only one regulator.