LM317 Adjustable 1.25–25 V Bench Supply

Two resistors set any output voltage you want from a single regulator IC — the most-built linear power supply in electronics history.

Difficulty: Through-hole. Estimated build time: about 45 minutes. Estimated parts cost: about US$4.80. 7-part bill of materials with live supplier pricing. A linear adjustable bench supply built around the LM317 — a 3-pin regulator that holds 1.25 V across its output-to-adjust pins regardless of what is happening at the input.