Re: Voltage Scaling

Chris wrote:

On Mar 22, 10:40 am, ggo...@xxxxxxxxx wrote:

Hi all,

Can anyone help with the following,

I need to scale a control voltage which ranges from 0VDC to 5VDC, to:

1. 0V..15V (e.g. when Vcoltrol=2.5V, Vout should be 7.5V).

and

2. -3V to 3V (e.g. when Vcontrol=0V, Vout is -3V, when Vcontrol=2.5V,
Vout is 0V.. essentially a linear scaling..)

I have a power supply of +9V and nothing else (got suggestions to
connect +/-18V to an opamp but obviously, i dont have these voltage
ranges from the wall-wart, only +9V..)

How would you go about doing this?

Thanks,
Gilad.


Hi, Gilad. You aren't going to be doing anything with output voltages
above or below your power supply rails unless you do something with
your supply. By using a 555 and a handful of caps and diodes, you can
generate a +17V and -8V supply like this (view in fixed font or M$
Notepad):

|
| VCC VCC
| + +
| | |
| .-. |
| | |2K2 | N.C.
| | | .---o----o---. VCC
| '-' | 8 4 | +
| | | | |
| | | | D -
| o----o7 | ^
| | | | C | 2*Vcc - 1.4V
| | | | ||+ | D (~+17V)
| .-.15K| 3o----o----||---o--->|---o-------o
| | | | | | || |
| | | | LM555 | | +|
| '-' .-o2 | | C ---
| | | | | | ---
| | | | | | |
| o--o-o6 | | ===
| | | | | GND
| | | | |
| | | 1 5 | |
| --- '---o----o---' | C -Vcc+1.4V
| --- | N.C. | +|| D (~-7.6V)
| |.01uF | '----||---o---|<---o-------o
| | | || | |
| === === | |
| GND GND D V C---
| - ---
| C = 100 to 220uF, 25V | +|
| D = 1N4001 or 1N4148 | |
| === ===
| GND GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
Something tells me the above circuit is flawed.
Something about a diode seems to be out of place in the + output.
Also the voltages don't look correct referenced from the GND.
I just can't see how that is going to generate 17 Volts ?
the (-) output side looks ok how ever.
I guess if you were to use the (-) output as your common to the LM324
, you could get a single output effect of ~ 17 volts maybe..
Maybe I missed something, just an observation.

http://webpages.charter.net/jamie_5";

.

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