I want to do a project based on the ICL7107 (here: http://www.circuitstoday.com/digital-voltmeter-using-icl7107). I have a adjustable power supply but it doesn't go negative. The project requires a -5V/0V/+5V power supply. What is the best way to power this from an adjustable benchtop power supply and hopefully also from a 6xAA battery pack at a nominal 9V also? I remember there being converters/regulators that do this but I don't recall where to find them. Thanks for your advice.
Check Linear Technology. They make several solutions.
Go pick a power opamp (2822 or 2030 for example), and use it to follower a 1:1 divider between the 9v and gnd. The voltage between 9v and the opamp's output will be 4.5v, and the opamp's output and ground is 4.5v. So you can treat the opamp's ouput as device ground, and the 9v becomes +4.5, and the real ground becomes device negative.
Using some of the terminology from the replies so far I scared up this part review on Google:
This really looks like exactly what you would want in this situation so I think I am going to order a few of these and check them out. Thanks for your help.
See post #26 on this thread, http://arduino.cc/forum/index.php/topic,135567.15.html
check them out.
Alternatively, you can look into the current capability of that part and ask yourself if it meets what your circuit requires.
dhenry:
check them out.
Alternatively, you can look into the current capability of that part and ask yourself if it meets what your circuit requires.
I'm going to look into what the circuit requires:
End Power Supply Character V- Supply Current ICL7107 Only - 0.6 mA (typ) 1.8 mA (max)
And assume the chip can supply that! 
The simplest method is to use a TLE2426 ?Rail Splitter. It provides the virtual ground or 1/2 the power applied across it. I attached a data sheet. It's also the method I'd use. An ICL7660 requires too many parts as do all the other answers. The ICL 7106 isn't that critical for power supply accuracy but the ground must be 1/2 Vcc.
I used a lot of the LCD version for DPM for soil testing devices and I used a 741 to provide the virtual ground. The problem exists because the input ground is at 1/2 Vcc nnot the absolute 0 voltage point. That's what the TLE2426 does, just supply a half Vcc point or "ground'. I also attached the ICL7660 and 7105 - 6 data sheets.
Bob
TLE2426.pdf (670 KB)
ICL7660-MAX1044.pdf (117 KB)
ICL7105_6.pdf (548 KB)
Docedison:
The simplest method is to use a TLE2426 ?Rail Splitter. It provides the virtual ground or 1/2 the power applied across it. I attached a data sheet. It's also the method I'd use. An ICL7660 requires too many parts as do all the other answers. The ICL 7106 isn't that critical for power supply accuracy but the ground must be 1/2 Vcc.
I used a lot of the LCD version for DPM for soil testing devices and I used a 741 to provide the virtual ground. The problem exists because the input ground is at 1/2 Vcc nnot the absolute 0 voltage point. That's what the TLE2426 does, just supply a half Vcc point or "ground'. I also attached the ICL7660 and 7105 - 6 data sheets.Bob
I was relying on Intersil's datasheet for the 7660 and it says all it needs is two external 10uF caps. The Maxim part is a little different.
That TLE2426 is a very neat part.
There are several different types of "Charge Pump" type converters... as a matter of fact any of the RS232 converters has both positive and negative charge pumps with available + and - outputs @ 12Vdc. You might get 10 to 20 mA of available current... Enough to form a power supply for a 7106 IC. I used the 7105's for DPM's from 2005 to 20008 when I retired. As a matter of fact I still have some of the PCB's I designed for a thermal sensor W/Panel Meter using an LCD display driven by the 7105. I used a PN2907 for the PN junction used to sense temperature. I also used a very similar circuit for a DPM for a soil conductivity meter. I used a 741 to level shift the input ground voltage from 1/2 Vcc to ground. Not too difficult to do at all, 3 resistors one Op-Amp and 3 resistors and some necessary bypassing are all that is required. I later changed the circuit to an LMC662 because I used a lot of them in other designs.
I do hope this has been helpful. Ginning up a '662 and some biasing for the inverting input is little more than a pot or two for get the values for gain and offset. Measure the "Input ground" relative to the - terminal of the battery and set the Op-Amp output to that voltage with the inverting input biasing pot and then If you need gain... put it before the level shifter. The second section of the LMC662 can be used for this purpose. I would also direct your attention to the MAX138/9 they are Very similar to the Intersil parts with some of the drawbacks fixed in a 'small' redesign of the IC. Maxim was good at that in their beginning, that is a big part of what made them really good. I've taken the liberty of attaching a data sheet... Not a good copy of the full paper one unfortunately... that sheet (about 15 pages) had application notes that covered the issues you are dealing with. BTW the TLE2426 can be had from Arrow for $1.02 Ea and they have 316 of them in stock.
You've several different engineering choices, interesting ones... Let me know how your project develops.
Bob
Docedison:
There are several different types of "Charge Pump" type converters... as a matter of fact any of the RS232 converters has both positive and negative charge pumps with available + and - outputs @ 12Vdc. You might get 10 to 20 mA of available current... Enough to form a power supply for a 7106 IC. I used the 7105's for DPM's from 2005 to 20008 when I retired. As a matter of fact I still have some of the PCB's I designed for a thermal sensor W/Panel Meter using an LCD display driven by the 7105. I used a PN2907 for the PN junction used to sense temperature. I also used a very similar circuit for a DPM for a soil conductivity meter. I used a 741 to level shift the input ground voltage from 1/2 Vcc to ground. Not too difficult to do at all, 3 resistors one Op-Amp and 3 resistors and some necessary bypassing are all that is required. I later changed the circuit to an LMC662 because I used a lot of them in other designs.
I do hope this has been helpful. Ginning up a '662 and some biasing for the inverting input is little more than a pot or two for get the values for gain and offset. Measure the "Input ground" relative to the - terminal of the battery and set the Op-Amp output to that voltage with the inverting input biasing pot and then If you need gain... put it before the level shifter. The second section of the LMC662 can be used for this purpose. I would also direct your attention to the MAX138/9 they are Very similar to the Intersil parts with some of the drawbacks fixed in a 'small' redesign of the IC. Maxim was good at that in their beginning, that is a big part of what made them really good. I've taken the liberty of attaching a data sheet... Not a good copy of the full paper one unfortunately... that sheet (about 15 pages) had application notes that covered the issues you are dealing with. BTW the TLE2426 can be had from Arrow for $1.02 Ea and they have 316 of them in stock.
You've several different engineering choices, interesting ones... Let me know how your project develops.Bob
Thanks again. Earlier today I got the itchy credit card trigger finger and ordered a few of the Intersil ICL7660s from Digikey after I read the other link on this chip that I posted and prior to your post. I already have a couple of ICL7107 chips so I think I am going to have all the important parts to implement this (I have all the passives and an appropriate display). When I do it next week I will post the results here. But I expect, and I hope at least, it won't be terribly hard to get this to work. If the power converter works, the rest of the implementation looks like it will be very straightforward. Thank you and everyone else for suggestions on my question.
And assume the chip can supply that!
Well, you can report back how that is working out.
dhenry:
And assume the chip can supply that!
Well, you can report back how that is working out.
OK, here are the results.
The power supply at an example voltage (bottom is powering the project):
The professional DMM's opinion:
The project's opinion.
The project voltage meter is good within 0.1V within the range of 0.3V to 50V (tested).
