Ttl Circuit Diagram - THE POWER SUPPLY Sometimes you will see a circuit as shown in the first diagram with 12v or +12v on the top rail and 0v or a negative sign or the word "negative" on the bottom rail. In this case the word negative means earth or "chassis of a car" and we commonly refer to this as "negative earth" or "negative chassis." In the second diagram, the output from a power supply has a positive 12. owden's Hobby Circuits. A small collection of electronic circuits for the hobbyist or student. Site includes 100+ circuit diagrams with text descriptions, several electronic calculators, links to related sites, commercial kits and projects, newsgroups, and educational areas..