Re: How to linearly scale up and down a voltage?

From: Michael Noone (mnoone.uiuc.edu_at_127.0.0.1)
Date: 02/25/05 

Date: Fri, 25 Feb 2005 17:32:28 GMT

Mac <foo@bar.net> wrote in news:pan.2005.02.25.02.50.53.555873@bar.net:

> I've read some of the other replies and your replies to those replies.
>
> I think you have your first problem well in hand. Use a voltage
> divider with 1% tolerance resistors, and you should be good to go.
> Note that 200 Volts is pretty high, and can do a lot of damage if
> something goes wrong. Someone could even end up getting hurt. I am not
> dealing at all with the safety issues surrounding this thing.
>

Mr. Hill suggested I use an op-amp to buffer that voltage divider output -
and this makes excellent sense to me, as I would then not even have to
worry about the impedance of the circuit connected to the output of the
voltage divider circuit. This makes great sense to me - but I don't
understand why he suggested an apex op-amp - to me it seems that any normal
op-amp would be perfectly suitable. What do you think?

> For the second problem, there are other ways to potentially do this
> that are a LOT cheaper than using the high-voltage op-amps you priced.
>
> If the signal is AC, maybe you can use a transformer inside the
> feedback loop to an ordinary op-amp. What is the bandwidth of the
> signal? Is there a DC component?

I've been told the signal will be changing at about 1KHz. I think it may
actually be an entirely positive signal (never dipping below 0V), but I'm
not positive about that just yet. So it will be entirely DC.
 
> Or you could build some kind of switching regulator with high Voltage
> output transistors and opto-couple the transistor drivers to the
> control circuitry. With your relatively low current requirement, this
> shouldn't be too hard. In order to sink and source current, you might
> need something like an H-bridge.

Can you explain this circuit a bit more? I'm having trouble picturing it.
 
> But a lot depends on how Vin varies over time, and what the load is
> like. If it is a slow varying signal, then this approach could work.
> If it is a high bandwidth signal, you might have to look at something
> else.
>
> Good Luck!
> --Mac
The load is a bit wierd. It's some sort of polarized fluid. I'm not too
sure on the details of it as they haven't been given to me.

Thanks for all your help,

-Michael

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