[sdiy] 1k tempcos

[Ian Fritz]

At 02:57 AM 7/10/2008, Louis van Dompselaar wrote:
>What do these VCOs actually require?  Some if not most
>DIY-ones are actually designed to take +3300ppm or +3500ppm
>tempcos.  Actually, I don't think I have ever seen one that requires
>+3000ppm (but someone will prove me wrong).

The correct value is 1/T = 3360 ppm/K.  Most tempcos have a tolerance in 
the tempco of at least +/- 10%, so a 3300ppm unit might be in a range of 
2970ppm to 3630.  For critical work it's best to start with a high value 
and pad it down with a series metal film resistor.  Or use my dial-a-tempco 
scheme to bring it in exactly.  :-)

http://home.comcast.net/~ijfritz/sy_cir9.htm

   Ian