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I want to generate -5 Volts from connecting AAA batteries in series, in order to temporarily replace a charge pump suspected of contributing noise to my embedded system. (See this answer (and its comments) in my previous question.)

Is this possible? I want to be sure the voltage is negative.

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closed as unclear what you're asking by Trevor_G, Brian Carlton, Eugene Sh., Nick Alexeev Nov 17 '17 at 3:04

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    \$\begingroup\$ Turn them upside down?? Seriously -5V with respect to what? \$\endgroup\$ – Trevor_G Nov 16 '17 at 20:06
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    \$\begingroup\$ @EugeneSh. I have an embedded system with lots of noise so i was advised to check if the charge pump contributes to that noise. That charge pump outputs -5V so i was asked to place -5V there and look if the noise exists. \$\endgroup\$ – user1584421 Nov 16 '17 at 20:29
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    \$\begingroup\$ @user1584421 grab a bench power supply. \$\endgroup\$ – Trevor_G Nov 16 '17 at 20:37
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    \$\begingroup\$ Batteries are indeed a good alternative when trying to compare supply noise, but they have their own issues. What's the tolerable range of voltages? You probably can find a collection of AAA cells which will at a given point of discharge total 5v for low current, but in general you'll be somewhat higher or lower depending if you use 3 or 4 cells and of what chemistry and state of charge. \$\endgroup\$ – Chris Stratton Nov 16 '17 at 21:04
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    \$\begingroup\$ Now that we know what you're trying to do, a key point for you to realize is that with batteries it doesn't really matter if you want a positive or negative supply, since you are free to connect their positive (rather than negative) side to ground - that would only be an issue with supplies already having a ground connection. So your question really reduces to how to get a ~5v supply from batteries, which would be greatly helped by knowing what the actual range of voltages you can tolerate is. \$\endgroup\$ – Chris Stratton Nov 16 '17 at 21:19
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Since I'm the one who asked you to try this in order to know if the noise in your circuit was due to the negative voltage charge pump or not...

3 brand new AAs in series will give you close to 5V, if they are a bit used it will be more like 4-4.5V but this doesn't really matter.

When you wire several batteries in series, the resulting assembly has a "+" terminal and a "-" terminal.

If you wire the "battery -" to "ground" then the "battery +" will be at +5V relative to ground.

If you wire the "battery +" to "ground" then the batteries will be the other way around and thus the "battery -" will be at -5V relative to ground.

In both cases there is 5V between the "battery +" and the "battery -" terminals. Which means there is -5V between the "battery -" and "battery +" terminals if you turn it around.

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  • \$\begingroup\$ omg peufeu! You are so helpful, i have to donate you some money! So if you take a look at this picture imgur.com/IFdkFMZ , the negative pin from the batteries will go where the Vout pin of the IC, and the positive pin from the batteries will go where the GND pic of the IC is, is this correct? \$\endgroup\$ – user1584421 Nov 16 '17 at 23:32
  • \$\begingroup\$ Yes, it is correct ;) Thanks LOL but no need for money \$\endgroup\$ – peufeu Nov 17 '17 at 10:12

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