+ and - 5V from a battery?

[dirtydawggy]

Hey everyone,

First post on here so please be gentle.

I am working on a piece of test equipment that needs to be fairly mobile and wondered if anyone knew how to get +/- 5V from a mobile power source.

I have never really delved into this area before so I'm a bit wet behind the ears on the subject.

I thought of battery powered supply but not sure if that's possible these days.

Cheers

 

[Nigel Goodwin]

You need to give far more detail!, but an obvious answer from the little you've given is to use two batteries and 5V regulators.

 

[dirtydawggy]

Sorry about that Nigel.

It is for a circuit that measures light level on a detector and outputs a signal from a system of comparators. There are six comparators in each circuit all require +5V and only three require -5V.

Three circuits in total.

Still think the regulators would be best bet.
Would I run them from 9V batteries?

This any good for the -5V? : https://www.electro-tech-online.com/custompdfs/2007/02/Module2031736.pdf

They have a similar one for +5V.

Thanks for the reply.

 

[Shax]

Try looking on the RS website ( http://www.rswww.com ) .. They do some dc-dc dual output converters that should do what you need..

From previous experience, Maplins won't have what you need in stock anyway!!!

 

[audioguru]

A 78L05 positive regulator and a 79L05 negative regulator need a minimum 7V input voltage. A 9V battery's voltage quickly drops to less. You need low-dropout regulators that work fine when their input is 5.4V. Most IC manufacturers make low-dropout regulators.

You didn't attach your schematic for us to see if it can work from a single supply voltage. You didn't list the parts so we can't see if it can operate from only 5V instead of 10V.
You didn't say how much current is needed.

 

[Blueteeth]

Hi,

Assuming (big assumption here) that the current needed for the negative supply is minimal and yoyu wish to run it off just one battery, you could try a simple (and inefficient) 555 timer negative voltage generator:

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http://www.armory.com/~rstevew/Public/PSUs/-vgen.html

These convert a positive voltage to a negative voltage...meaning +5v supply -> +5v and -5v.

The negative voltage regulator you mentioned (maplin) requires a negative voltage input. So, if you use two 9v batteries, one for + and one for -, both rails would require regulation down to 5v. The 7905 regulates the negative rail, and the 7805 regulates the positive part

Similar to this setup:
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You 'could' use 8 AA batteries (12v), in series, which are tapped halfway, to give a GND. Then you'll have +6v and -6V, which you could then reduce down to about 5.4V using a diode. Or 4.8V using two diodes in series.

Many opamp designs that require a dual power supply (positive and negative with respect to gnd) use a simple voltage divider to give 4.5v from a 9v battery. That 4.5v becomes a virtual ground, the - form the battery becomes the -4.5v and the + becomes +4.5V. Although, that really does limit the current, and its particularly inefficient, for comparators, it should do just fine, that is if you can get away with not quite 5V, and do not wish to 'power' anything current hungry with it.

Aside from all the above, you can get negative voltage 'modules' which are fully enclosed switch mode power supplies in themselves. Their efficiency is around 75-85%, they're big and expensive.
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As for a 'chip' that will do what you want, I've used this with great success...but read the datasheet for current capabilities:
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Please note that most of the above will produce a negative voltage, similar to that of the input voltage. That is, if you put 9v in, you'll get about -9v out. You require +/-5v...so you could regulate the 9v down to 5v first, with a 7805.

There are so many ways to do this, just depends on what power supply you have available,one 9v battery? don't mind using 2? AA's, plug in PSU...

Well therse some idea's anyway.

Blueteeth

 

[cadstarsucks]

Hey everyone,

First post on here so please be gentle.

I am working on a piece of test equipment that needs to be fairly mobile and wondered if anyone knew how to get +/- 5V from a mobile power source.

I have never really delved into this area before so I'm a bit wet behind the ears on the subject.

I thought of battery powered supply but not sure if that's possible these days.

Cheers

Not the fanciest, but it will do the job for you:

https://focus.ti.com/docs/prod/folders/print/lt1054.html

D.