Im looking to make a converter that will have an input voltage of 12 v (have not tested for input amperage yet) and an output of 5v @ either 3 amps or 4.2 amps (current has still undetermined currently).

I would like to make it from scratch but will settle for modifying a prefabricated curicut. With the prefabricated circut the only thing I can think of is using an old usb car charger but im unclear on how to increase the output amprage.

If Its possible I will then build the curcits (~ 10 total units) and attach them into specific locations throughout my car.

 

LM2679-5.0 - Simple Switcher 5A Step-Down Voltage Regulator with Adjustable Current Limit.