Chip operating temperatures

[tom cloud]

>There are some resistors that increase resistance with temperature. I used
>some for a student lab where they were controling the heat with a computer
>and needed a lot of heat in a hurry but it needed to be fail safe. These
>resistors will put out a fast heat pulse and never get to hot to hold. 
>
>Gordon 
>
>Gordon Couger Senior Software Specialist
>Biosystems & Agricultural Engineering Dept.  Oklahoma State Univ.
>114 Ag Hall Stillwater, OK 74075
>gcouger at master.ceat.okstate.edu

Nichrome, tungsten, and most other resistance wires have pos. tempcos
but I don't think they have a steep enough curve to be self-limiting
in such an application as this.

Light bulbs are tungsten and have several neat uses: constant current
sources, current limiters, heaters, -- and ... light sources.

If I were going to make a heater for an electronic hootis for my car,
I'd want to be sure that it didn't drain my car's battery.  If it
didn't have to be on all the time, I'd make it come with the ignition
switch -- but then it'd have to have a real fast rise, and that
would mean it could also be destructive if it were not controlled.

There are flat, flexible heaters encapsulated in silicone made
especially to bond to PCB's and that's what I'd try to use, as
that would heat only the control circuitry -- which would require
less heat as less would be lost through the case to the outside.

There are metal cased resistors (check Dale Electronics in an
electronics catalog -- e.g. Newark) that bolt to metal.  Could
use one of those on an aluminum plate.

Put either one in the collector of a common emitter transistor amp,
put a thermistor mounted to the same plate in the base circuit and
voila' a self-regulating heater.  Could also just buy a small
thermostat and use it.