Small variable +/- PSU with LM317 / LM337

Motivation

It comes in handy to have a small PSU with variable output voltages around to test modules with different voltages or drive small projects. The emphasis is on driving small projects. Tests are better done with a lab PSU. I just made a small PCB for a +/- 12..17V with LM317 and LM337. There is nothing special about it. Straight forward design. Because it is small the heatsinks are not that big and close together. Don't drive it to hard.

Update: If you don't need the output voltage to be changeable on the fly, you can drive this small PSU much harder by lowering the voltage drop over the voltage regulators LM317/LM337. This is achieved by selecting the right AC input voltage. The AC input voltage should match the DC output voltage. In this case the voltage drop at the voltage regulators is about 4V and the power dissipation is down to 4W when loaded with 1A. I have tested the small PSU for several hours loaded with 1A at 15V without any problem getting to hot. The test was done on the bench in free air. If you use an enclosure check for the air flow.

Specs and features

• Input: 18V/AC: Output variable : +/- 12..18V/1A (max. 500mA recommended)
• Input: 12V/AC: Output fixed to 12V/1A
• Input: 15V/AC: Output fixed to 15V/1A
• Input: 18V/AC: Output fixed to 18V/1A
• Schematic
• Pictures

Disclaimer

All schematic, pictures, drafts, descriptions and other text at the site www.haraldswerk.de and in the associated blog are, if not otherwise mentioned, owned and copyrighted by Harald Antes. They are free for private use only.

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