>=20
> On Nov 10, 2010, at 6:31 PM, James Newton wrote:
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> Is there a diode like the 1N4148 that is made in such a way that the forw=
ard
> voltage from one diode to the next will be within a few percent of one
> another? E.g. they are made to close tolerance on the Vf spec?
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> Also of interest, how would one search for such a thing? I've tried "Diod=
e
> Vf tolerance" "Matching diode forward voltage" and several other
> combinations of keywords and it don't seem to be getting me anywhere.
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> What is it for? Multiple low cost, low resolution temperature sensors all
> fed into one A2D pin on a PIC. I only want the /highest/ reading from all
> the sensors. The point is multi unit over temperature protection, so exac=
t
> accuracy is NOT required... if it trips when the temp on any one unit
> reaches anything from 200 to 250'F I'll be happy. The sensor of choice is
> the LM235. The device being monitored is a TIP122.=20
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> Thanks in advance for any insight.
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> --
> James Newton
> 1-970-462-7764=20

Consider using a thermistor ( 10K ohm range and 1% accuracy ) can be had fo=
r 69 cents ( qty one ).
Use the thermistor in a voltage divider and feed the voltage to a precision=
 diode made from an op amp.
Baseline resistors and op amps and diodes can be isolated from the varying =
temperature.
This could be low cost. =20

Or you can feed the LM235 into a precision diode.

Gus in Denver
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