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From: "Spehro Pefhany"
Subject: Re: Op-amp configuration question
User-Agent: tin/pre-1.4-19990216 ("Styrofoam") (UNIX) (Linux/2.2.14 (i586))
Date: Wed, 02 Oct 2002 00:51:28 GMT
NNTP-Posting-Date: Tue, 01 Oct 2002 20:51:28 EDT
The renowned Dwight wrote:
> I've got a schematic with an op-amp configuration I have never seen
> before. It's purpose is to take a 6.2V reference and amplify it to a
> 10V reference used elsewhere. It's set up like a non-inverting
> amplifier with the 6.2V to the + input, and a 10k R1 and a 16.5k R2
> for the divider at the - input. This much I understand. Where it
> confuses me is that there is a 332 ohm resistor pulling the output up
> to 15V, and a 383 ohm resistor from the output to the + input. What
> are these added components used for? The amp is a LT1014 and the 10V
> is used for pressure transducer excitation. Thanks for your help.
I think the 383 ohm resistor is a bootstrapped current source giving you
10mA nominally through the 6.2V Zener, as Jim said (10V-6.2V)/383R. The
other resistor is probably to get it to start reliably, and it forces the
output to sink about 5mA (4.6 or so) rather than sourcing current with no
load on the reference. The op-amp probably isn't all that good at sourcing
10mA with only 5V to the + rail, over temperature and all.
"it's the network..." "The Journey is the reward"
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