Electronic – Is it normal for LM317 to give a higher voltage without a load


I just built a small 5.1V regulator with LM317, using 220 and 680 ohm resistors. However, I measure 8.6V at the output without a load connected. Is this normal, i.e. under a load (about 120 ohm) it would drop to 5.1V? The input is a 9V/300mA unregulated wall wart, which reads about 13V without a load.

Best Answer

You need a minimum load of 10mA for it to be stable. A tip is to add a LED and run it on 5mA. You'll know whether the supply is on, and it will add additional load to make it stable.

Note that the adjustment resistors of 220+680 ohm also give some load, of about 5.6mA. Together with a LED you get more than the required 10mA.