LM317/350 adjustable regulator question - Electronic Circuits Projects Diagrams Free

indecided · 29th January 2006, 12:21 AM

Hey guys,

I'm building a LM350-based adjustable power supply with a PC PSU being used as the current source. Since I noticed that the PSU also has -5v and -12v rails respectively, I was wondering if i could feed the LM350 with +12v and -12v, effectively giving it "24v", which would give me a voltage of about 0v -> 22.5v in theory to play with, versus a 0v -> 10.5v with just 12v input.

Can anyone tell me if i will run into problems? The main issue I see now is that (if it works) the -12v rail supplies meagre amperage (less then 1) while the +12v is capable of 8A easily. Will this hurt me in the short/long run?

Thanks!

john1 · 29th January 2006, 12:59 AM

http://www.national.com/pf/LM/LM350.html

john1 · 29th January 2006, 12:59 AM

http://www.national.com/pf/LM/LM350.html

Russlk · 29th January 2006, 02:25 AM

If you use the + and - 12 volt supplies, the current will be limited to the less than 1 amp supply and there is no point in using a 3 amp regulator.

eblc1388 · 29th January 2006, 09:58 AM

Use some selector or toggle switch to make connection of both the positive and negative connections of LM350 to different output leads of the power pack.

In this case you have the best combinations, 3A for up to 10.5V and 1A for up to 22V. Remember you usually need some loadings on the +5V output to keep the supply alive.

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29th January 2006, 12:21 AM	(permalink)
indecided	LM317/350 adjustable regulator question Hey guys, I'm building a LM350-based adjustable power supply with a PC PSU being used as the current source. Since I noticed that the PSU also has -5v and -12v rails respectively, I was wondering if i could feed the LM350 with +12v and -12v, effectively giving it "24v", which would give me a voltage of about 0v -> 22.5v in theory to play with, versus a 0v -> 10.5v with just 12v input. Can anyone tell me if i will run into problems? The main issue I see now is that (if it works) the -12v rail supplies meagre amperage (less then 1) while the +12v is capable of 8A easily. Will this hurt me in the short/long run? Thanks!

29th January 2006, 12:59 AM	(permalink)
john1	http://www.national.com/pf/LM/LM350.html

29th January 2006, 02:25 AM	(permalink)
Russlk	If you use the + and - 12 volt supplies, the current will be limited to the less than 1 amp supply and there is no point in using a 3 amp regulator. __________________ see my website: www.geocities.com/russlk

29th January 2006, 09:58 AM	(permalink)
eblc1388	Use some selector or toggle switch to make connection of both the positive and negative connections of LM350 to different output leads of the power pack. In this case you have the best combinations, 3A for up to 10.5V and 1A for up to 22V. Remember you usually need some loadings on the +5V output to keep the supply alive. __________________ L.Chung