From: "Tom Faloon"
Subject: Re: Op-amp configuration question
Date: Wed, 2 Oct 2002 02:32:13 +0100
NNTP-Posting-Date: Wed, 2 Oct 2002 01:27:03 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
For the moment, ignore the two low value resistors, and the circuit is a
standard non inverting configuration.
Gain = (1 +10/16.5) = 1.61
For 6.2Volts in, the output is = 9.96 Volts (~ 10V as expected.)
Jim is right about the circuit providing a current source for a reference
Assume the 'reference' is a 6V2 zener device, with cathode to the amp's +
input, and anode to ground.
Now add the 383 R resistor between output and + input.
The current in that resistor will flow into the reference diode. It will be
constant, and will have low noise, since it is powered from the 10V
reference. It's value will be (10 - 6.2)/383 = 9.9mA This all makes sense.
That leaves one resistor unexplained. The 332R to +15V.
For the moment, I don't see how it has any bearing on the reference circuit.
(The LT1014 is well capable of sourcing the 10mA to the diode.)
Maybe it is related to the load?
Anyone got an idea?
Jim Thompson wrote in message
> On 1 Oct 2002 16:29:42 -0700,
> firstname.lastname@example.org (Dwight),
> In Newsgroup: sci.electronics.design,
> Article: ,
> Entitled: "Op-amp configuration question",
> Wrote the following:
> |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.
> Doesn't make sense. Please post a drawing. Sounds like a
> boot-strapped current source for the reference, but the numbers don't
> ...Jim Thompson
> | James E.Thompson, P.E. | mens |
> | Analog Innovations, Inc. | et |
> | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
> | Phoenix, Arizona Voice:(480)460-2350 | |
> | Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
> | http://www.analog-innovations.com | 1962 |
> For proper E-mail replies SWAP "-" and "_"
> I love to cook with wine. Sometimes I even put it in the food.