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Old 4th May 2016, 02:14 AM   #1
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Default Opamp on battery

I am building a dac that is battery based until now. Now i am at the iv stage and would like to use the lme49990 opams, because i like their neutral sound.
Now my question : the lme49990 needs a positive and negative voltage, but i only have positive voltages on battery. Is there a way to generate a nehative voltage out of a battery or will i need to skip the lme49990 and choose a single voltage opamp ? Is there any single voltage opamp comparable to the lme49990 ?

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Old 4th May 2016, 02:40 AM   #2
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Use two batteries? Also keep in mind the high idle current of the LME49990 - it's around 10mA each at high voltages. This is probably one of the reasons why it performs so well, but still, for a battery supply, keep this high idle current in mind. And, don't starve it for voltage. It works very well at 17V supplies. (Note - this is the same thing as a 34V single supply as long as you get the inputs to be within the permissible input common mode voltage range.)

Or, one could simply design an effective power supply...?
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Old 4th May 2016, 02:48 AM   #3
jstott is offline jstott  United States
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As already mentioned, a pair of 9V batteries would be one option. Another possibility is an iC called a "rail splitter" (the TLE2426 is a good example). Their capacity to sink/source current is limited, but if it's just an opamp or two you should be fine.
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Old 4th May 2016, 07:44 PM   #4
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Rhanks for the help. The rail splitter is an option. Does it introduce much noise to the negative rail ?
The 10mA at idle are no problem. I use two 8ah lifepo4 batteries for 6,4v. Does the lme49990 behave much better at higher voltages ? I can give it +/-6V and not more at the moment. I read somewhere that it runs fine from 5V upwards. Is that right ?
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Old 4th May 2016, 07:50 PM   #5
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Ok, tle2426 generates a virtual ground and v/2 + and - voltage. This would mean 4 batteries for me. What about a chargepump like the max660 ? Would this function ?
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Old 5th May 2016, 08:29 AM   #6
AndrewT is offline AndrewT  Scotland
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AC couple the opamp and operate it from a single supply.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 5th May 2016, 12:10 PM   #7
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Originally Posted by AndrewT View Post
AC couple the opamp and operate it from a single supply.
Its a mobile design, i dont have any AC voltage, only batteries at 6.4V.

Nobody has an Idea ?
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Old 5th May 2016, 12:24 PM   #8
marce is offline marce  United Kingdom
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Location: Blackburn, Lancs


Last edited by marce; 5th May 2016 at 12:27 PM.
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Old 5th May 2016, 12:34 PM   #9
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Thanks. Now i understand. Thats an option of course.
I am also reading about passive IVs at the moment. What does sound better ? Opamp or passive IV ? Passive IV could make my problems go away.
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Old 6th May 2016, 01:34 AM   #10
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The data sheet specifies the LME49990 at 5V, and the distortion plots look very close to those for 15V, except for the output voltage swing of course. The output swing will be somewhat reduced, since it's not a rail-to-rail amplifier, but there is no rail-to-rail amp that can give you the same level of performance. So, a pair of 6.4V batteries should work well, and you avoid the hassles of a rail splitter or other AC coupling / biasing schemes.
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