Is this possible. If not, please help!!

If so I could use help determining C1, C2, D1, R1...

Bottom line is i'd like to be able to access one, two, or possibly three of the outputs at the same time.



Thanks in advance guys!

 

Your different output voltages are all connected to ground!
Use a separate LM317 for each output voltage.

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Uncle $crooge

 

I agree with audioguru
C1 can be 0.1uf, I usually use a film dielectric capacitor.
C2 can be 10uf electrolytic
R1 is generally 240 ohms
D1 is generally a 1N400X series 1N4001 should be fine.

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The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best.
Show me a different way. I have an open mind.

 

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.

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Uncle $crooge

 

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.

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Angry!? I'm absolutely electrolytic!

Will have to make do with myspace now I guess...

 

You have just discovered the difference between typical and guaranteed specs. Try building a thousand of them, and see if they all work.

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Ron

 

You are lucky that your LM317 has a lower "operating current" than most.
With 40V across it, its max operating current is 10mA and at 1.25V output it needs min 125 ohms load (from its output to its adj terminal). A curve in the datasheet shows that its typical operating current is 3.5mA which drops to 1.5mA with a low voltage across it. So if your LM317 has its max operating current then with a low voltage across it, its output voltage would rise if the resistor from its output to its adj terminal is 292 ohms or higher.

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Uncle $crooge

 

Ah right, well it's lucky it works I guess then. Its being used at fairly low voltages and with a small load, so it should be ok.

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Angry!? I'm absolutely electrolytic!

Will have to make do with myspace now I guess...

 

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.
I am starting to realize that there are differences between IC's of the same number between manufactures.

__________________
The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best.
Show me a different way. I have an open mind.

 

The LM317T Data sheet seems to show the Variable resistor connected to ground! How would I hook this up then...







Thanks

 

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.
I think you don't understand the concept of GND. GND is not (usually) connected to earth. It is simply the common node (connection) in the circuit to which everything else is referenced. In your schematic, all your "outputs" are shorted together (to "-"), the resistors R2-R6 are all in parallel (which means they act just like a single resistor), and there is no GND. In a working circuit, "-" will normally be GND, although "+" could be the GND node, in which case you would have a negative voltage on "-", relative to GND.
I know this is confusing. Maybe one of the other guys can explain it better. :?

EDIT:
If you use the "Add an Attachment" window instead of posting images, they won't waste space by being repeated in a quote, which I did originally.

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Ron

 

Ron H Quoted:
Thanks Ron, thats all I really wanted to know.

You are right all resistors would act as one, smaller than the smallest one.
I realized this later last night.

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.



Thanks for your help and finally a sort of "non-political" answer!!!

 

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.

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Ron

 

Thanks Ron:

This device will power a number of devices at bedside such as an LED light for reading, a TENS unit, and even a pair of Frequency/music controled LED Goggles so it needs to be able to have multiple preset voltages for common devices. I'll have to go with the 6 LM317T circuits,
no big deal.

Brian