Level shifting 0-5V to +-5V

FlyingFishFinger

What's the best way of doing this? We have a piece of equipment that needs a +-5V signal, but our source supplies 0-5V. A source of +-5V would cost us a couple hundred dollars more, so we would like to use a conversion if possible. Preferably something I might be able to build using logic or something not too complex...
Thanks

Rafael

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You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~

Phil Pilgrim (PhiPi)

Are you talking about a digital signal that switches between +5V and -5V or an analog signal that ranges beteen those two values? That's not clear from your post. Also, you need to specify the switching/slew rate required and what kind of load it has to drive. Then, perhaps, we can give you some assistance.

-Phil

Carl Hayes

Precisely so. ESPECIALLY what load it must drive.

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· -- Carl, nn5i@arrl.net

Mike Green

You will generally need a source of -5V appropriate for the load. For small loads, there are voltage inverters like the ICL7660A
(www.intersil.com/data/fn/fn3072.pdf) that can take an input of 5-10V and produce an output of -5V. Typically,
for an analog output, you'll have an opamp powered by +5V and -5V whose output voltage can swing between those two voltages.
The opamp can be biased to use 0-5V as its control voltage for the full range. For a digital +5V / -5V output, you could use a
transistor for switching like in the RS232 to TTL adapters that Parallax uses with the Stamps for programming. You could also
use something like a MAX3232 which includes the voltage inverter and the line driver all in one package. The output
voltage tends to vary with load, up to maybe +6V/-6V, but this could be reduced by adding some capacitive/resistive loading.

FlyingFishFinger

Sorry guys. I wasn't quite awake when I wrote my first post. It's an analog signal and I'm not sure exactly what the load is. But I'll be able to do it with opamps, I've done a bit of similar stuff before, I just didn't remember it at the time.
Thanks

Rafael

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~

Phil Pilgrim (PhiPi)

Rafael,

The MAX865 contains just the charge pump/inverter circuitry from the MAX232, so it will deliver an approximate +/-10V supply for your op amp. I would recommend using this wider supply range, so your opamp has enough headroom to drive a load. (There are so-called "rail-to-rail" op amps available that would work with a +/5V supply, but their load-driving capabilities at the extremes of their output range are almost nil.) When picking an op amp, be sure to pick one that can handle a capacitive load if you're driving a cable with it. I've had good success with an OP113 in apps like this.

-Phil

FlyingFishFinger

Sweet, that just solved my problem of finding a nice negative voltage converter [noparse]:)[/noparse]
Thanks alot!!

Rafael

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~

Post Edited (FlyingFishFinger) : 2/6/2009 7:23:09 PM GMT