Author: GraemeCDate: 07:14 22-03-07
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Im trying to create a +/- 2.5V supply from a +/-5V. I have a couple
of 2.5V voltage references. Am I right in assuming that I need to get
hold of a -2.5V reference? I did read an article that showed how I
could use an inverter but I don't have any of those either.
There seems to be a gap in my knowledge because I don't really
understand the difference between a voltage reference and a voltage
regulator.
Thanks
G
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Author: John PopelishDate: 09:54 22-03-07
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GraemeC wrote:
> Im trying to create a +/- 2.5V supply from a +/-5V. I have a couple
> of 2.5V voltage references. Am I right in assuming that I need to get
> hold of a -2.5V reference? I did read an article that showed how I
> could use an inverter but I don't have any of those either.
>
> There seems to be a gap in my knowledge because I don't really
> understand the difference between a voltage reference and a voltage
> regulator.
If your 2.5 volt references are shunt type (two terminals
that hold 2.5 volts when an externally limited current is
passed through), you can use two of them to regulate a small
(milliamperes) supply. If you want a more significant
current from these supplies, you should use actual supply
regulators. The adjustable LM317 and LM337 pair can be set
to 2.5 volts output with a pair of resistors.
http://www.fairchildsemi.com/ds/LM/LM317.pdf
http://www.fairchildsemi.com/ds/LM%2FLM337.pdf
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Author: Jonathan KirwanDate: 10:09 22-03-07
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On 22 Mar 2007 04:14:07 -0700, "GraemeC"
<graeme.cunningham@googlemail.com> wrote:
>Im trying to create a +/- 2.5V supply from a +/-5V. I have a couple
>of 2.5V voltage references. Am I right in assuming that I need to get
>hold of a -2.5V reference? I did read an article that showed how I
>could use an inverter but I don't have any of those either.
You need a low-impedance driver set at 2.5V relative to your current
ground and this new low impedance driver needs to source or sink
(two-quadrant, if my hobbyist knowledge of terms is close to right.)
You don't say what your _current_ requirements will be. There's a
simple answer if you are talking about a few tens of mA. This is the
TLE2426 "rail splitter." Also, an opamp set up with the 2.5V
reference to its (+) input and its (-) tied to its output, which
drives the new center point "ground" might be okay, assuming your
opamp can deliver the current requirements you are looking for. (Or
just use a resistor divider instead of the 2.5V reference, to the (-)
input.) A discrete splitter could be formed out of transistors, too.
>There seems to be a gap in my knowledge because I don't really
>understand the difference between a voltage reference and a voltage
>regulator.
A reference usually has a very small _current_ drive capability -- not
uncommonly in microamps -- to name one important difference.
Jon
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Author: Jonathan KirwanDate: 10:11 22-03-07
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On Thu, 22 Mar 2007 14:09:22 GMT, Jonathan Kirwan
<jkirwan@easystreet.com> wrote:
>(Or
>just use a resistor divider instead of the 2.5V reference, to the (-)
>input.) A discrete splitter could be formed out of transistors, too.
Sorry, I meant (+), not (-).
Jon
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Author: JamieDate: 20:45 22-03-07
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GraemeC wrote:
> Im trying to create a +/- 2.5V supply from a +/-5V. I have a couple
> of 2.5V voltage references. Am I right in assuming that I need to get
> hold of a -2.5V reference? I did read an article that showed how I
> could use an inverter but I don't have any of those either.
>
> There seems to be a gap in my knowledge because I don't really
> understand the difference between a voltage reference and a voltage
> regulator.
>
> Thanks
>
> G
>
use a 2425 and turn it around.
the COM will be the - line and (IN) your common .
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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