MAX6641 typical application circuit is shown. This is used to drive N-channel PWMOUT side MOSFET, then control the fan speed. Remote PN junction temperature sensor available microprocessor (µP) the internal temperature to replace the transistor’s emitter. May choose CMPT3906, T3906, KST3906-TF, SMBT3906 models of discrete components such as transistors. Required transistor emitter forward voltage drop is expected to be at the highest temperature and 10µA current is greater than 0.25V; at the lowest expected temperature and 100µA current is less than 0.95V. Not use high-power transistor.