Positive input, negative output request

[Karamel]

Hi,

I have to get -7V from +12v or +24v input. I have searched someting on internet. There are some solutions but I didn't choose anything which is the best solution for me.

I will use it for at070tn92 lcd screen and I have just single positive power supply.

What should I do to solve this problem?

[danadak]

Some approaches -

https://www.dropbox.com/s/k1yn4m7heaixvmg/ADinput%20negative%20inputs.zip?dl=0

Regards, Dana.

[Karamel]

Thanks for replying and information.

I will use it just an experiment for one time so, I think that, Can I use small another external power supply? Like phone charger unit? I can use minus side adjustable regulator which it could be Lm337 and maybe I can get -7V from it? Is it logical solution? 

[danadak]

Hacking apart the walwart could be problematic, maybe potted.

Depends how the regulator is designed inside the walwart, could be switching
and changing Vout a little more involved depending on IC regulator used.

You can get simple charge pumps, they are dirt cheap.

Regards, Dana.

[Rudane]

How much current do you need from the -7 V rail?

[jdraughn]

You could possibly use a +12v and +5v supply and make the +12v your ground and the +5v your -7v. The supplies need to be isolated from each other, but those are both very common voltages so it should be easy to find a couple of power bricks.

[tggzzz]

You could possibly use a +12v and +5v supply and make the +12v your ground and the +5v your -7v. The supplies need to be isolated from each other, but those are both very common voltages so it should be easy to find a couple of power bricks.

Power bricks often, but not always, have their 0V output connected to mains earth. Been there done that

[ion]

You could possibly use a +12v and +5v supply and make the +12v your ground and the +5v your -7v. The supplies need to be isolated from each other, but those are both very common voltages so it should be easy to find a couple of power bricks.

Power bricks often, but not always, have their 0V output connected to mains earth. Been there done that

Would be easier with an adjustable power adapter - set it to 7V and hook the positive to your circuit ground.  I haven't come across any that have an earth connection so it should work fine.