This video explains the purpose of feedback resistors in a buck converter circuit and shows you how to calculate them. Then I show you how to build a high current adjustable power supply using an LM2678 and a potentiometer.

Parts list:
LM2678T-ADJ:
http://octopart.com/lm2678t-adjnopb-texas+instruments-15290279
Input electrolytic cap:
http://octopart.com/eeu-fm1h221-ecg-208642
Output electrolytic cap:
http://octopart.com/eeu-fr1c102b-panasonic-18987619
Input and output ceramic caps:
http://octopart.com/partsearch#!?q=UMK325BJ106MM-T
Bootstrap cap:
http://octopart.com/c420c104k5r5ta7200-kemet-193582
Schottky diode:
http://octopart.com/stps5l60-stmicroelectronics-334357
22uH inductor:
http://octopart.com/aiap-03-220-k-abracon-22130082
Potentiometer:
http://octopart.com/p090s-14t20br10k-bi+technologies-5426431
Schematic: