Here’s a tutorial from Maxim describing thermistors and how to use them in temperature tracking power supplies. Thermistors are resistors whose resistance changes with temperature, increases with PTC type and decreases with NTC.
This article provides a simple, intuitive tutorial on negative temperature coefficient (NTC) thermistors and how to make basic use of them in general, and specifically in power supply regulators. A good example application is their use to cancel temperature effects on LCD display contrast. Two simple NTC thermistor linearizing techniques are shown, and regulator design procedures and examples demonstrate their application. Each example includes a schematic and compares the measured output voltage versus temperature to the target.