From MAKE - A Pocket Size Power Supply

imageJason Poel Smith likes to shop at thrift stores as do I.  It's nice to be able to test electronics before making the decision to buy, but that can be a challenge for battery-powered gear.  Jason developed a simple LM317 circuit to adjust the output in 1.5 volt steps from a 9 volt battery, so that he can simulate from one to five cells and it connects to the device being tested with alligator clips.  Very ingenious and handy!  Complete instructions can be found in the MAKE Magazine article:  Pocket-Sized Power Supply.

One slight critisium and a common mistake however – the sample circuits shown in LM317 data sheets are based on the LM117 part, which has a lower minimum current draw (5 mA compared to 10 mA).  R1, used to adjust the output voltage, should be 120Ω instead of 240Ω as shown to meet the minimum load requirement to ensure regulation.  The other resistor values will have to be adjusted accordingly.

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