thermistor temperature sensor circuit
if you want, i could post my circuit of a thermister. it is useful for simulating in PSPICE only.
if you use a thermistor you must make an effort to linearize your thermistor. you should also read "Transducer Interfacing Handbook" a guid to analog signal conditioning by Analog Devices. it is available in the forumn somewhere. see page 79
without more details about your application it is difficult to say how the best way is to implement your shut off scheme. genearlly, low power applications, say 50v 500mA or less the best is solid state switch. for higher power a relay is good. there are pros and cons to both. i like to use solid state relays wherever possible because they are smaller & available via free samples
Mr.Cool
Added after 2 minutes:
oh, and also where you put your thermister is important. probably you will paste it to the outside of the transformer. don't worry about thermal paste, it is not necessary to read steady-state temperatures.
your case temperature is a lot cooler than the temperature of your inner most coils. your core will usually pass its curie temperature after 120 to 135 C. depending on the size of your transformer, you might consider not allowing the outer case to be more than 80C.
Mr.Cool
Added after 2 minutes:
and as i keep thinking of it...
a 10Kohm thermister will not be good for you. because at temperatures of 80C, yoru thermister will be about 1kohm. and the difference in resistance between say 60C and 80C will only be about 5kohm, maybe less.
you should consider using a 100K thermister rated at a temperature near what your application calls for. if it is rated only at room temperature, then this is why you get a 100kohm, so that in the 60 to 80C range you still have some good resistance range to work with