Don't connect the bottom end of the 317 to zero volts, connect it to a negative reference instead.
How do you get 0v from an LM317?
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11th May 2009 10:01 AM #1Fudgecake
How do you get 0v from an LM317?
I'm a fairly new student to Electronics and I have to build a variable voltage regulator for my college project. I've got a fairly good idea how to do it using an LM317 but I don't know how to get the LM317 to go below its reference voltage of 1.2v. There is some info on the National Semiconductors datasheet, but when I modelled it on Multisim I couldn't get it to work very effectively. Any thoughts out there?
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11th May 2009 10:03 AM #2Nigel Goodwin
Super Moderator0PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk
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11th May 2009 10:09 AM Thread Starter #3Fudgecake
Thanks Nigel. I did try connecting the adjust leg to -10v on multisim 7 but I still seemed to be getting 0.3v when the pot was fully off. Is it possible that mutisim 7 would be giving me duff info. I'm due to have a crack at building this on Thursday but I'm not confident about it at the moment.
0
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11th May 2009 09:56 PM #4Hero999
You need a negative voltage.
Here's how it can be done very accurately using an op-amp.
0 to 13.8V LM317 Power Supply0
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12th May 2009 06:58 AM #5colin55
To get 0v from a LM317, put 2 diodes in series on the output.
0
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12th May 2009 07:30 AM #6ericgibbs
Super ModeratorYou can do its this, providing you dont mind screwing up the output voltage regulation with output current changes in the load.
Originally Posted by colin55
0Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
"Nigels Asm tutorials:" www.winpicprog.co.uk/
"Ian Rogers 'C' conversion of Nigels Asm tutorials:" http://www.electro-tech-online.com/c...torials-c.html
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12th May 2009 07:07 PM Thread Starter #7Fudgecake
Thanks for helping out with this gentlemen, I'll let you know how I get on!
Cheers0
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12th May 2009 07:42 PM #8crutschow
Use an LT3080 which can be adjusted down to zero volts.
0Zapper
Curmudgeon Elektroniker
--Inside every little problem is a big problem trying to get out.--
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12th May 2009 08:18 PM #9colin55
DigiKey have LT 3080 for $3.75 plus $4.95 post = $8.70
0Last edited by colin55; 12th May 2009 at 08:38 PM.
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12th May 2009 08:28 PM #10crutschow
The LM3080 is an op amp. The LT3080 is a regulator, which also is available from DigiKey. Originally Posted by colin55
0
Last edited by crutschow; 12th May 2009 at 08:29 PM.
Zapper
Curmudgeon Elektroniker
--Inside every little problem is a big problem trying to get out.--
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