±45v lm317?
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 20th April 2012, 07:58 AM #1 linxiaoxin   diyAudio Member   Join Date: Apr 2012 ±45v lm317? hello,i need ±45v power,i get i picture on the internet ,but i do not know it is right or not ,who can help me ?
jan.didden
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Join Date: May 2002
Location: The great city of Turnhout, BE
Quote:
 Originally Posted by linxiaoxin hello,i need ±45v power,i get i picture on the internet ,but i do not know it is right or not ,who can help me ?
Easy. The voltage across R1 is ALWAYS 1.25V. So if you want to know the output voltage, you select the total of Vr1 + R2 to add voltage to the 1.25V.
An example: for output of 11.25V, you know that there will be 10V across R2+Rv1. (11.25 - 1.25). 10V is 8 times 1.25V on R1 so R2 + Vr1 = 8 times R1 = 8 times 220 = 1720 ohms.

For your 45V you know on R2 + Vr1 is 45-1.25 = 43.75V, so R2 + Vr1 = 43.75/1.25 * 220 = 7.7k....

For the -45 you can use an LM337 but the calculation is the same.

BTW This is also in the datasheet, very simple, you could easily find that yourself without worrying what is true or not. Datasheets are your friend! ;-)

jan didden
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Last edited by jan.didden; 20th April 2012 at 08:20 AM.

 20th April 2012, 08:22 AM #3 woodturner-fran   diyAudio Member   Join Date: Jan 2006 Location: Ireland Plus there are loads of online calculators to make it even easier. There are also LM317ht that can do 57v
linxiaoxin
diyAudio Member

Join Date: Apr 2012
Quote:
 Originally Posted by janneman Easy. The voltage across R1 is ALWAYS 1.25V. So if you want to know the output voltage, you select the total of Vr1 + R2 to add voltage to the 1.25V. An example: for output of 11.25V, you know that there will be 10V across R2+Rv1. (11.25 - 1.25). 10V is 8 times 1.25V on R1 so R2 + Vr1 = 8 times R1 = 8 times 220 = 1720 ohms. For your 45V you know on R2 + Vr1 is 45-1.25 = 43.75V, so R2 + Vr1 = 43.75/1.25 * 220 = 7.7k.... For the -45 you can use an LM337 but the calculation is the same. BTW This is also in the datasheet, very simple, you could easily find that yourself without worrying what is true or not. Datasheets are your friend! ;-) jan didden

thany you very much ,i see.

abraxalito
diyAudio Member

Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Beware the input-output voltage limit

For any input voltage above 40V, there's no short circuit protection with this device - I've seen at least one explode, so be very wary of shorting the output. On power-up transients too its possible to exceed the abs max.
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 22nd April 2012, 08:47 AM #6 Nisbeth   diyAudio Member     Join Date: Jan 2001 Location: Denmark LM783? /U.
 22nd April 2012, 09:08 AM #7 KatieandDad   diyAudio Member     Join Date: Nov 2011 Location: UK You'd be better off building a regulator using discrete components at that voltage. Have a look at http://www.kk-pcb.com for some ideas.
 22nd April 2012, 09:29 AM #8 KatieandDad   diyAudio Member     Join Date: Nov 2011 Location: UK Studio Reference Amplifier Post #6 shows another example of a higher voltage regulator.
 22nd April 2012, 02:00 PM #9 Gavin Jaing diyAudio Member   Join Date: Apr 2012 agree with KatieandDad You'd be better off building a regulator using discrete components at that voltage.
 22nd April 2012, 05:29 PM #10 MarianB   diyAudio Member     Join Date: Jul 2011 Location: Romania LM317 can only handle about 1,5A so be carefull on that part, if you need higher current than you will need to add a power tranzistor on it, but as the other have sayd it would be better with zenner diodes and a few transistors to supply the needed current, it would be much safer as you can add the protection you want/need.

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