BeginnerPower
LM317 Adjustable Low-Current Supply
Build a small adjustable regulator and use the LM317 reference equation to predict and measure output voltage.
Parts from the database
- LM317T × 1Adjustable linear regulator
Other supplies
- 9 V regulated DC adapterCommon build supply
- 240 Ω resistorCommon build supply
- 2 kΩ potentiometerCommon build supply
- 100 nF input capacitorCommon build supply
- 1 µF output capacitorCommon build supply
- multimeterCommon build supply
- low-current loadCommon build supply
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Connections
- Verify LM317T pinout for the exact maker/package; TI TO-220 marked-face pins are ADJ, OUT, IN and tab is OUT.
- Connect 9 V to IN, ground to return, 240 Ω from OUT to ADJ, and 2 kΩ pot from ADJ to ground (tie wiper to one end).
- Place 100 nF from IN to ground and 1 µF from OUT to ground. Measure output from OUT to ground.
Build steps
- Start with no load and the pot at minimum.
- Turn slowly while measuring; Vout≈1.25×(1+R2/R1), with R1=240 Ω and R2 from ADJ to ground.
- A 9 V input cannot produce a regulated 9 V output; headroom, load, and resistor range limit the top end.
- Add only a modest load after checking temperature.
Software and firmware setup
This is a hardware-only circuit; no firmware is required.
Test your build
Output varies smoothly from about 1.25 V upward, with the top value limited by input headroom and thermal conditions.
Troubleshooting
- Stuck near 1.25 V: check ADJ/OUT and pot wiring.
- Unexpected voltage: measure resistor values and check ground.
- Hot regulator: reduce load or input-to-output difference.
Safety and limitations
Low-current demonstrator only; it has no precision current limit and must not charge batteries unattended.
Manufacturer and platform documentation
Community Notes for This Project
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