I woke up this morning with an idea for -9v

[ExpAnonColin]

It didn't work.  The output is just 1v less than the V+.

Can anyone help me as to why not?  Do I need to have a V- before inverting, or can I do the 2 simultaneously?

-Colin[/img]

[Jason Stout]

Post edited for garbage content.... :oops:

[ExpAnonColin]

The circuit will invert any ripple that you have on the dc voltage. The output is less than 9V because of the opamp you used, its output cannot reach the power rail voltage.

All right, that makes sense.  Thanks.

-Colin

[Jason Stout]

Colin, I looked at your circuit again, and now I'm not sure of what it is doing! Disregard my previous post!

[ExpAnonColin]

Colin, I looked at your circuit again, and now I'm not sure of what it is doing! Disregard my previous post!

Well, what you said about inverting the ripple made sense, but I had thought that inverting the +9v would lead to -9v...  Which didn't make sense.  The bit about the op amp not handing 9v makes sense, but the 741 I'm using has a max of 15v, so it doesnt

-Colin

[gez]

Try this (at least it will work!  :wink: ):

http://www.intersil.com/data/an/an051.pdf

[Brian Marshall]

an ideal opamp can supply voltage at the output only to its supplied voltage.  If v+ is 9 and v- is 0 then it cant put out more than 9 volts or less than zero.  in reality most opamp start clipping before they actually get to the supply voltage.

either way you have the output grounded, so it will always equal 0 volts, unless you have dual polarity supply voltage, in which case it would have the least ristance to gound.

you cant get negative voltage with an opamp by its self.  

from the drawing you should be reading 0 volts, or close to it at the output

[Brian Marshall]

oh yeah, this might help too..

opamps isolate the ouput from the signal, but the output is NOT isolated from the power supply

Brian

[Nasse]

Dont worry, you have had some REM sleep, if you have had a dream. Maybe next morning you have something better...

[travissk]

In our EE labs, they keep reminding us that an opamp with +/- 15V cc voltages will operate over approximately -13.5 to +13.5V, at least linearly (before it saturates). I think this was due to the non-ideal nature of the parts inside but I'd have to dig my introduction to electronics book out again to check

[Mike Burgundy]

Think of it this way: an opamp is an AC amplifier, and sees DC as "no signal".
It (or at least most, I can't think of one that doesn't right now though) will also attempt to clamp the output DC level at the +input DC level (hence the connections to Vref via a largish resistor and DC-blocking caps in opamp circuits. It's not able to go beyond that, it's only ably to not-quite-reach-it (it's not a perfect world)
HIH

[ExpAnonColin]

Try this (at least it will work!  :wink: ):

http://www.intersil.com/data/an/an051.pdf

Ew, I hate buying little things like that... I've considered the 7660, but it doesn't seem worth it.  I might give up and use one, though.

from the drawing you should be reading 0 volts, or close to it at the output

It reads a little less than 9v.

Think of it this way: an opamp is an AC amplifier, and sees DC as "no signal".

That's what I needed to hear-thank you, thank you, thank you.

[smoguzbenjamin]

Why don't you try the charge pumps at geo?