fanspeed.avi
Author: admin
This is a video of my working prototype for an efficient PC case fan speed controller. Heating the Negative Temperature Coefficient resistor (aka NTC) causes the fan to speed up, so you could use epoxy to glue it to a strategic heatsink or leave it to detect general case air-temperature. Some time soon, I’ll publish the schematic and PCB design. The advantage of this design over simpler systems is that it does not need to produce heat to slow down the fan. It’s effectively a switch mode power supply. There are four stages. 1) Oscillator 2) Comparator (with NTC) 3) driver 4) output stage with buck circuit. The circuit uses PNP transistors to allow the fan to be connected between ground and the output stage, thus switching on the high-side. If you use a fan that has a tacho in it, and want to use the tacho output, this design makes it simple to interface as it’s referenced to ground. Many other designs use an NPN output stage which forces the fan – as the load – to be between the transistor and the 12v supply. To any internal electronics in the fan, this makes the fan’s reference float and therefore some difficulty to interface with it. The fan used in the video is a typical 12v brushless dc unit. It happens to have thermal control anyway but I was not using it. Any two wire fan would do just as well. You can use a three wire fan if you like. The third wire will give speed feedback pulses. (This is the tacho). The circuit has a variable setting so you can set the minimum …
admin