help negative voltage

[japl]

hi

what is the easiest way (small circuit) to produce a negative voltage for a op-amp -VEE. the input would be a positive voltage say +12V to -12V.

thnxs for the help

 

[Nigel Goodwin]

hi

what is the easiest way (small circuit) to produce a negative voltage for a op-amp -VEE. the input would be a positive voltage say +12V to -12V.

thnxs for the help

Unfortunately, the ICL7660 is only rated at 10V, so that's prevents that been used :cry:

At a quick glance, I couldn't find a higher voltage version, but there may be one?.

Maxim give a design for doing this at http://www.maxim-ic.com/cookbook/powersupply/pdfs/+12to-12_500ma.pdf, but it looks rather complicated.

 

[Styx]

just order in a DCDC converter. Newport do some very small (in size) dual output SIL modules.

Check out (these are british)
rswww.com
www.farnell.com

farnell deliver to the public, RS dont like to

 

[k7elp60]

negative voltage

You could use a Linear Technology LT1054CN8 they are good to an input voltage of 15V. Digikey stocks them.

 

[plot]

i assume you are starting with a positive supply? if so, something along the lines of the following could be used... this creates a "floating ground"

of course, this contains an extra LED and Resistor to tell if it's powered, and the overall circuit will need to be slightly modified to accomidate 12 volts.

 

[Exo]

That will only work if the load draws equal amount of current on both the negative and positive side

 

[plot]

Since it's for an op-amp, it should draw the same from each side.

 

[bmcculla]

Look for a charge pump IC. You should be able to find one that will give you a negative voltage equal to the positive voltage input.

plot - I don't think you can assume that OpAmps draw the same current from both rails. For example: an opamp driving 25mA into a load will be drawing those 25ma from the positive rail.

Brent

 

[japl]

charge pump IC? can u give some examples of such IC's
thanks