[sdiy] Thermosensitive Chip Resistors

[Ian Fritz]

Hi Jay --

These tempcos have been in the Digi catalog for some time now.  There was a 
previous discussion about them here last spring, which you might want to 
look up.

I measured the temperature dependent resistance on one of the large size 
(0805) 1.8k units, using a special setup with a large Al block for thermal 
stability/uniformity and a calibrated Wheatstone bridge.  I found that I 
had a bit of difficulty with small drifts in the readings, probably due to 
self-heating effects.  The tempco came out OK at about 3350ppm/K.  However, 
the quadratic coefficient of the fit came out several times larger that for 
other (full-size) tempcos I have measured.

A 10% tolerance in the tempco is typical, although 5% is sometimes 
found.  That's why I developed the dial-a-tempco circuit.

I haven't tried these tempcos in an actual VCO yet, but they should be OK 
unless you are real fussy about drift.  At least they are affordable.

   Ian


At 08:35 PM 1/2/2004, Jay Schwichtenberg wrote:
>I was thumbing (OK, drooling) at the new Digikey catalog I got today. I
>found these thermosensitive chip resistors in it:
>
>http://www.panasonic.com/industrial/components/pdf/AOF0000CE1.pdf
>
>Page 865 in catalog T041.
>
>They look interesting since some have a PTC of 3300 ppm/C, come in 1K and
>can fit under a chip. Only issue looks to be the +/-10% tracking tolerance.
>Anyone have any ideas if these would be good enought for expo tempco?
>
>Thanks
>Jay