Ferocactus Posted February 7, 2006 Report Share Posted February 7, 2006 I'm building a variable power supply with the LM317 IC, but I can't find a 240 ohm resistor that datasheet recommends for R1. Can I replace it with a 220 ohm resistor? Quote Link to comment Share on other sites More sharing options...
Staigen Posted February 7, 2006 Report Share Posted February 7, 2006 Hi there Ferocactus, velcome to the forum :)Can I replace it with a 220 ohm resistor?Of course you can, but, as far as i know, the resistor should be 120 ohms for the LM317! The 240 ohms resistor is for the LM117! Look in the datasheet!//Staigen Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 8, 2006 Report Share Posted February 8, 2006 If the LM317 has a fairly high supply voltage and you turn down the output voltage to power something that draws a low current like a Cmos circuit, then if the programming resistor's value is more than 120 ohms then the output voltage will rise and destroy the Cmos circuit. Not all LM317's are the same. Some are identical to the LM117. Quote Link to comment Share on other sites More sharing options...
Staigen Posted February 8, 2006 Report Share Posted February 8, 2006 Ok Audioguru! Wich one of the LM317:s are identical to the LM117?//Staigen Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 8, 2006 Report Share Posted February 8, 2006 Ok Audioguru! Wich one of the LM317:s are identical to the LM117?//StaigenHee, hee. ;D ;DThe ones that are made at exactly 2:17PM GMT on a Wednesday. ;D ;DNot many people purchase LM117's. Sometimes the factory's yield in production is really good and many people are buying LM317's. So the good ones that should be labelled "LM117" are instead labelled "LM317".Alun in England was buying LM217's, that I have never seen. They were very good like an LM117 but cost about the same as an LM317. Quote Link to comment Share on other sites More sharing options...
Staigen Posted February 8, 2006 Report Share Posted February 8, 2006 Hehe, nice!//Staigen Quote Link to comment Share on other sites More sharing options...
Ferocactus Posted February 8, 2006 Author Report Share Posted February 8, 2006 Thanks for the help, guys! Quote Link to comment Share on other sites More sharing options...
Ferocactus Posted February 12, 2006 Author Report Share Posted February 12, 2006 Now I have another question. ;DI'm building a variable power supply whose output voltage is controlled by a push button and a 4017 IC. The complet project can be seen here: http://members.shaw.ca/roma/supply-4.htmlThere is a 0.4uF capacitor Quote Link to comment Share on other sites More sharing options...
Staigen Posted February 12, 2006 Report Share Posted February 12, 2006 HiYou can use any type of nonpolar cap here, and the value, i belive, can be somewere between 0.1 to 0.4 uF, but there seems to br some error in the schematic, there is no base return resistor to the 2N2222 transistor, a 100 Kohm resistor connected between base and emitter will be fine here, there is also no resistors in serie on the outputs!//Staigen Quote Link to comment Share on other sites More sharing options...
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