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My goal is to design a split power supply that I can use for different audio project. I need a +-2.8 V supply. My power input will be a 3.7 V nominal Li ion battery (or two of them). My questions are:

  1. Is it better or correct approach 1 or 2?
  2. If one battery is used, is it ok to regulate its output before creating the minus supply?
  3. If two batteries are used the only way is to regulate both (with two LDOs)?
  4. Would it be a problem in terms of heating if are about 0.5 A needed? (to be honest I don't understand exactly how much current my circuit will draw. I use one TL082 (datasheet 5.6 mA supply current) and two LM4880 (datasheet 250 mW at 8 ohm with 5 V per channel max).

thanks

schematic

simulate this circuit – Schematic created using CircuitLab

winny
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Status Re
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2 Answers2

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The primary problem with creating a split supply from a single ended source is the problem of "floating" grounds. With (2) everything will be fine as long as you draw the same current from V+ and V- . However, if you draw much more current from one leg, lets say V+, it will cause the V- voltage to increase dramatically, possibly exceeding your desired limits. This effect is directly proportional to the value of R1 and R2. Larger values resistance values will lead to worse "regulation". However, decreasing R1 and R2 will waste energy as heat in these resistors.

This makes approach (1) better for higher current applications. (2) might be adequate for very lower power applications where you are not concerned with the energy losses in R1 and R2.

Regulating the battery output in (2) will have no effect on the floating ground problem since the problem is caused by using R1 and R2 to determine the ground.

It's difficult to say more without knowing the exact application...

A buck converter with positive and negative outputs connected to a single battery might be the best solution. However, this might generate too much noise in a small signal processing application.

jdwaverly
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  • since it will be a pwr supply for an headphone amp, and in general something to use with other audio related projects, I would like to be as clean as possible. Therefore a regulated power supply is the best approach. (that or a transformer, wich in terms of space...) – Status Re Aug 16 '21 at 17:25
  • This might be useful https://electronics.stackexchange.com/questions/440854/headphone-amplifier-negative-charge-pump-vs-phantom-ground – jdwaverly Aug 17 '21 at 21:34
  • And this link from the same page explaining floating (or virtual) grounds. http://nwavguy.blogspot.com/2011/05/virtual-grounds-3-channel-amps.html – jdwaverly Aug 17 '21 at 21:37
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Texas Instruments makes a "rail splitter" IC. You feed it your positive and negative supply rails, and it synthesizes a precision ground halfway in between the two.

John R. Strohm
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