Dual power supply

Forum 2005-2010 (read only) Hardware Interfacing
1

Greetings,

I built a reef controller and (as always) I would like to add a pH probe. The op. amps. on the interface are working with a dual power supply (+/- 9 V). What is the simplest way to build a dual power for a few mAmps ? I was searching for a LM326, but seems like here in the US there is no way where you can get it. Any other option ?

Thanks and cheers,
Marian

2

What is the simplest way to build a dual power for a few mAmps

Two 9V batteries.

3

Thanks a lot, but you don't wanna do that (for long tern). The pH probe will be calibrated and chances are that the two bats will discharge at a different rate so your gain and slope are not gone stay steel.

Thanks again,
Marian

4

Thanks a lot, but you don't wanna do that (for long tern).

You didn't mention how long you needed it for. (or seabirds)
Lead-acids would be ideal, I imagine.

If you want +/- 9V, then the LM326 isn't really the one for you.

5

Have you looked at the Intersil ICL7660A? Not too sure whether the current would be sufficient though.

6

What is your unregulated source? Battery, solar, mains, fuel cell :)...?

How many are a "few" mA? Is the +/- 9V cast in stone? How much ripple can your application tolerate? You mention that a change in power supply voltage might affect calibration. Is it possible to use a ratiometric measurement so as to eliminate the supplies as an error source?

7

Gentlemen,

thanks a lot.
here is the link to the application: File:PH-sch.jpg - ProjectWiki

the dual power will drive nothing else but a TL062, so I assume up to 10 mA to be OK. +/- 9V is not cast in stone. It can go all the way up to +/- 15V.

Took a look at MAX738 and it looks like has been designed for +/- 5V.

I will look at the ICL7660.

cheers,
Marian

8

I've been looking at this rail splitter from TI. As I understand it, the input signal to the OP amp will never go below 0V, so I can use my op amp without a negative supply.

Maybe this can help you...

9

If you have a +5V logic supply in your system, Maxim has other parts that will give you +/- 12V but the ones with the precision and the low noise that it appears you need tend to need lots of parts to make them work.

If it was my project, I'd probably design/buy a simple linear supply:
transformer, bridge rectifier, filter caps, linear regulators, etc.

You haven't said enough about the rest of the system for me to have any more opinions.

10

(or seabirds)

;D

11

I like the idea of seabirds though. Especially the tall ones.

12

You could use one of these.

It supplies about 40mA each on the +12 and -12 supplies.

It's also available with a 12V (+-10%) input for the same price.

If you only need a small amount of current, it's cheaper than buying a pair of wall warts, and it should provide a closer match of the + and - voltages.

There are other makers of them, and you mioght be able to find some cheaper/better for your needs: I just happen to know about that one because we were ordering some other parts from Digi-Key when we needed a couple.

Be sure you read the datasheet: it needs added filter caps on the outputs.

Ran