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Adjustable bench supply 1.25–20 V

Bench build · Power, transformers and three-phase · Intermediate · about 60 minutes

1.25–20 V with a panel meter. Transformer, bridge and a big reservoir capacitor make about 32 V of rough DC; an LM317 turns it into a smooth, adjustable output. The pot sets V_out = 1.25 × (1 + R_pot ÷ 240 Ω), and the panel meter shows it.

Adjustable bench supply 1.25–20 V: the finished build running on the simulator's bench

Build it in the labGuided build, test sheet and fault finding, free in your browser.

Parts list

Test procedure

Each test has an expected value and a pass range, like a factory test sheet:

  1. Pot at minimum
  2. Pot at 72 %, 0.1 A load
  3. Ripple at 20 V

How it works

What it does: 1.25–20 V with a panel meter.

Build it (guided or ready-made), then run its test procedure below. Every test has an expected value and a pass range, just like a factory test sheet.

Background

The first serious project for generations of hobbyists, and still the most useful one.

More builds: power, transformers and three-phase