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audioguru said:Your different output voltages are all connected to ground!
Use a separate LM317 for each output voltage.
k7elp60 said:R1 is generally 240 ohms
You have just discovered the difference between typical and guaranteed specs. Try building a thousand of them, and see if they all work.Dr.EM said:Interesting, I used a 470 ohm on my 317 regulator, it seems to work fine :? . It is at 10.22v, no load, I added a load and it stays dead on 10.22v.
You are lucky that your LM317 has a lower "operating current" than most.Dr.EM said:Interesting, I used a 470 ohm on my 317 regulator, it seems to work fine :? . It is at 10.22v, no load, I added a load and it stays dead on 10.22v.
I guess it depends on which data sheet you look at. My sheet just happens to be from a 1982 National Linear Data Book. It shows some typical LM317 circuits that have a 240 ohm resistor. But the spec chart says minimum load current, typical 3.5 Ma, 10Ma maximum, so to be on the safe side use 120 ohms. Another interesting thing is the LM317Z(A 100Ma regulator. It has the same 5 Ma minimum load current as the the LM117.audioguru said:k7elp60 said:R1 is generally 240 ohms
Sorry, but if you look closely at the datasheet, the more expensive LM117 uses 240 ohms (as shown on the 1st page of the datasheet) and the cheaper LM317 uses 120 ohms as shown in the fine print.
With 240 ohms on an LM317 the output voltage could rise without a load.
To answer your original question: If you want multiple outputs that are each capable of supplying varying current to a load while keeping the voltage of each output constant, you have to have a separate regulator for each output.
You've got it. I personally prefer a pot and a meter, but if you have an application where you need multiple, pre-programmed voltages, then the switch and resistors option is a good one.iONic said:In other words, either I build a single regulator circuit using a 5 position switch to 5 different resistors (resulting in only one voltage outpot at a time) or I build 6 regulator circuits, one for each voltage I want.