Looked for hours on the net, with no success.
Even the 7905 data sheet is useless to me.

I nead to make a +-5volt supply. (5volts positive and 5 volts negative).

I know how to use a positive volts regulator.
You feed it's input with a voltage of about 3 volts higher.

But what about the -5 volt regulator.?
Does the input of the -5 volt regulator have to be -8volts, or -2volts or 5volts or 8volts, or can it be all?

Ideally, I would like to power these two regulators from a single 9volt source/battery.

Thanks

 

The easyest way wod be to center tap the 9V batery to get +4,5V and -4,5V.

The other option wod be an switch mode power suply runing on that batery.

__________________
Il give you shocking experience.

 

You can't center tap a single battery, but you could use that technique on two batteries.

Brian

 

Back to the old question- what do you want to do? Can't answer without a context. We don't know how much current you need or other critical details. Many times people asking that sort of questions may not even need negative voltage.

__________________
I thought what I'd do was I'd pretend I was one of those deaf-mutes.

 

For 7905, it can be -8V or more, meaning from -8V to -35V, anything else like -4V or less, or positive voltage like +2V, +9V etc...won't work.

No problem using the 7805. However, you do not have any negative voltage for the 7905 to regulate. The usual method is to use a 555 or other ICs oscillators to generate a square wave and rectify it into a negative voltage. Now you have the negative voltage higher than -5V so you can use the 7905 to give you regulated -5V output.

__________________
L.Chung

 

You fogot to mentchon the coil in the 555 timer oscilator.Since it feeds it the negative kickback of the coil that is made becose of the sqare wave.

But this method produces a lot of electrical noise.

__________________
Il give you shocking experience.

 

There are 2 main methods for getting negative regulated voltage. You either supply a negatve unregulated voltage (with additional negative voltage clearance for dropout), as others have mentioned, or you use dc-to-dc convertors, which are based on oscillators. The second method is mainly for low current appliucations. One common chip used for this is the 7660.

 

Not forgot, but coil/inductor not required in 555 design for negative voltage generator. Try Google for "555 negative voltage" and see designs that use only capacitors and diodes.

__________________
L.Chung

 

I want to supply an op-amp with +5volts and -5volts.
The op-amp is an TL072 JFET OP-AMP. recommended by Nigel.

The project is Automotive, so, primary supply is 12Volts DC.

 

Thats why i use norton op amps that dont need an dual suply.But then agen there output cant go negative whithout an dual suply.

do you need an negative output?

__________________
Il give you shocking experience.

 

just nead a negative 5v to op-amps negative supply. Thats all, nothing else.


I book I have talks about a 7660 voltage converter. It converts any positive voltage from 0 to 12 volts to a negative0-12volts.
I catalog I have ,also talks about dc-dc charge pumps, with that chip.

Maybe I'm onto somthing purpose made for op-amps?

thanks.

 

Most prpole use 2 baterys to do it.

__________________
Il give you shocking experience.

 

In the other thread I advised you to check my analogue PIC tutorial!, haven't you done that? - seeing as it answers this question for you - and gives both a circuit diagram and veroboard layout!.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

http://sound.westhost.com/project69.htm

This and your regulators should work ok, or;

http://sound.westhost.com/project95.htm

__________________
Angry!? I'm absolutely electrolytic!

Will have to make do with myspace now I guess...

 

Nigel Said I did go but,
WinPicProg PIC Tutorial
ERROR
The requested URL's could not be retrieved
so, I gave up trying.

Just now I went to your other link (forgot you had two websites).
"http://www.lpilsley.uklinux.net/picprog" <this site works, and yes I found the 7660 chip. Thanks for getting on my back about it.