The TC642, TC646, TC647, TC648, TC649, TC650, TC651, TC652 and TC653 are pulse width modulation (PWM) fan speed controllers for DC brushless fans. These devices adjust the speed of the fan according to the temperature level, therefore reducing acoustic noise, minimizing power consumption, and extending fan life. A thermistor or other voltage output device can be used to set the required duty-cycle level for the TC64X family. On the other hand, the TC65X family contains an integrated temperature sensor for retreiving thermal data and adjusting the PWM cycle.