[sdiy] Was PTC/NTC intelectuall level of SDIY!
modcan at sympatico.ca
Fri Mar 21 02:16:16 CET 2008
At 06:37 PM 3/20/2008, you wrote:
>Hi Bruce --
>Many thanks for the detailed reply. The dual SMT transistors have
>been mentioned here several times, but you may be the first person
>using them seriously. I wonder if their series emitter resistance is
>different from the usual thru-hole parts. Those require a fair
>amount of compensation.
On the data sheet the figures for hie look similar to a thru-hole
2N3904 at 1-10K. I used to use CA3086 and have noticed that they
require less comp. than the 3086 in the same application.
I went with them because the Vbe matching is stated to be typically
better than 1mV.
>I have spent some time with the SMT tempco's. I measured them in a
>special bridge/heater setup I made a while back. The temp coeff was
>very close to optimal. But I had trouble getting steady
>readings. I found the same thing recently using one in an
>oscillating filter. Whenever the CV is changed, the pitch takes
>several seconds to stabilize. I think I have been seeing a bit of
>self heating. Maybe your potting method and the good coupling
>betwen the devices alleviates this.
I haven't noticed this phenomena but I do use a fair size glob of 5
min. epoxy which may be sinking any minor self heating.
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