I don't remember the details of what you are looking for, but for=20
argument's sake, let's assume you want +5V in to give 0V out, and 0V in=20
to give -5V out.

You could use an LM311 voltage comparator. Use your +8V and -8V (or +-=20
5V) to power it.  Tie the output pin (7) to ground and tie the "ground"=20
pin to a pulldown resistor to -5V.  Tie the + input (2) to a voltage=20
between 0V and 5V (say 2.5V).  Apply the signal to the - input (3).

Kerry


alan smith wrote:
> hello...this goes back to a question I asked a few weeks ago.  Basically =
it was asking about generating a -5V signal from a +5V input.
>
> So I settled on a ADM222, old style RS232 driver and sure enough I can ge=
t the -8V drive.  But what I need is -5V so thinking....on the charge pump =
-V pin, putting a zener to clamp the voltage to -5V....or....feeding that -=
V pin with a regulated -5V, wondering if that might work.
>
> However the other problem is, when the input is positive, the output goes=
 positive, and I need that to be at the reference 0V level.  I tried to use=
 a pull down to ground on the +V charge pump, but that just pulled it from =
+8V to +5V.  I'm not an analog oriented person so...wondering if there is s=
ome sort of opamp based design that can only allow the negative swing to go=
 thru, and if its ever positive, keep it at the ground reference.  What hap=
pens if you ground the positive rail on an opamp and just provide negative =
power? =20
>
>
>  =20

--=20
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