Build a Variable Power Supply

Build a bench power supply with adjustable voltage output.

Overview

Every electronics workbench needs a variable power supply. Build one that provides 1.25V to 15V at up to 1A - perfect for most projects.

Components Needed

  • 1x LM317 adjustable regulator
  • 1x Transformer (12-15VAC)
  • 1x Bridge rectifier (1A)
  • 2x Filter capacitors (1000µF, 25V)
  • 2x 0.1µF ceramic capacitor
  • 1x 5kΩ potentiometer
  • 1x 220Ω resistor
  • 1x Voltage panel meter
  • 2x Binding posts
  • 1x Heatsink
  • 1x Enclosure

Instructions

  1. Rectifier Section

    Connect transformer secondary to bridge rectifier input. Add large filter capacitor across DC output. This converts AC to raw DC.

  2. Regulator Circuit

    LM317 output voltage = 1.25 × (1 + R2/R1). With R1 = 220Ω and R2 = 5kΩ pot, you get 1.25V to about 30V range (limited by input).

  3. Add Protection

    Add input and output capacitors as specified in LM317 datasheet. Consider adding a fuse and reverse polarity protection diode.

  4. Build the Enclosure

    Mount components safely in enclosure. Keep high voltage away from output terminals. Add voltage meter and adjustment knob to front panel.

Challenges

  • Add current limiting with an LM317 current source configuration
  • Add a second voltage display showing current
  • Build a dual-polarity supply (±15V) for op-amp projects