"24V DC Cooling Fan" Note Q2 below diode, PN junction itself is a good temperature sensor when the temperature rises, the forward junction voltage will drop, but it just added to the previous level of a control electrode E on, so ... ... (then, later on more clearly). The past few dedicated temperature sensors, can sometimes be done using the PN junction temperature sensor, especially bad germanium tube with temperature stability, the effect is actually better. Thus, this relationship is difficult to control the use of simulation tools to get the general effect of temperature, the thermal stability of the circuit can be some analysis and simulation software it a try. LZ The NTP-10K resistor should be NTC resistor or NTP, now cooling fans are brushless and eyed Hall, a few transistors, resistors and capacitors can make a few fans turn up.