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Old 12th May 2008, 11:44 AM   #1
sasmit is offline sasmit  India
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Default Obtaining a split supply from car battery

Hi,

Can anyone suggest a way to obtain +/- 12 v from 12 V car battery....commercial DC-DC converters are too expensive ... I have some vague idea tat we can do it using a Class AB audio amp ...anyone ?
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Old 12th May 2008, 01:54 PM   #2
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Are you more interested in making this yourself or just trying to save some money?

For an ambitious DIY project you could try this one.....

http://sound.westhost.com/project69.htm

This schematic shows how to get a +/-15v supply from the power rails of an amplifier....

http://www.bcae1.com/temp/HMR800-2Schematic.jpg

If you would rather just have an off the shelf DC-DC converter, let me know what a reasonable price would be for you. I have a 12v to +/-15v 330ma module I could let go for a fraction of it's retail price.

http://www.datel.com/data/power/bwr7-10wa-series.pdf
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Old 12th May 2008, 02:39 PM   #3
sasmit is offline sasmit  India
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I am interested in saving some money as well as making it myself so that I fix it if it fails for any reason or customize it for my requirements..my requirement is to drive ~ 100 W rms amp from it...so I need quite a heavy duty one....simmilarly sized supplies are quite expensive..
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Old 12th May 2008, 09:31 PM   #4
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Default Re: Obtaining a split supply from car battery

Quote:
Originally posted by sasmit
Hi,

Can anyone suggest a way to obtain +/- 12 v from 12 V car battery.......anyone ?

Quote:
Originally posted by sasmit
.....my requirement is to drive ~ 100 W rms amp from it...so I need quite a heavy duty one....simmilarly sized supplies are quite expensive..
For 100W RMS into 4W (presumably), your SMPS will need to put out, at an absolute minimum, +/-28V at +/-5A. For 2 x 100W into 4W, a good SMPS would be able to put out +/-32V at +/- 10A. +/-12V will enable you for only about 36W absolute max, more like 25W.

This is 640W, and it will indeed be substantial. Since it is unlikely your amps will putting out 100W continuously, component size may be able to be reduced, especially of forced-air cooling is used.

Hope this helps,

Steve
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Old 13th May 2008, 02:00 AM   #5
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Quote:
Originally posted by sasmit
I am interested in saving some money as well as making it myself so that I fix it if it fails for any reason or customize it for my requirements..my requirement is to drive ~ 100 W rms amp from it...so I need quite a heavy duty one....simmilarly sized supplies are quite expensive..
Sorry, I assumed you needed the supply for a line level circuit since you didn't specify.

There are plenty of TL494/SG3525 designs floating around that can get the job done.

Here is a TL494 design that isn't too complicated......

http://www.electronics-lab.com/projects/automotive/012/
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Old 13th May 2008, 09:08 AM   #6
sasmit is offline sasmit  India
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thanks for all the suggestions...I have one doubt though..I have a inverting unit at home for backup ...and it's based on SG3525 ..but the output is quite noisy...it's a square wave I guess ..are these designs sine wave ones and how clean is power output ?
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