This is a simple but efficient voltage regulator / buck-converter circuit.
High Side Mosfet driver for elegence and a 393 to power the charge pump and for the comparator circuit.
The IRF540 will power to 5A but the circuit will function at higher powers by changing the MOSFET.
The Zener Reference is 7.1v which the trim pot then allows you to select the output voltage (which must be lower). If...