Many fans now come with additional features that provide greater control over fan speed and operation to improve system performance. Having a fan run constantly even when maximum cooling is not required does not result in an efficient system and can reduce the operating lifetime of a fan. That is why many systems now monitor the temperature within an enclosure and only operate a fan when it is required. However, this can present problems with thermal lag or a fault condition if the fan was unable to start due to an obstruction. To address this, most modern DC fans feature auto-restart protection that detects when a fan motor is prevented from rotating and automatically cuts the drive current. Additional features include tachometer signal, rotation detector, and PWM control signal. Tachometer signal detects the rotational speed of the fan motor and provides a pulsed output that can be used within control circuitry where if the motor stops, the output stops pulsing and stays at either a logic high or logic low. The rotation detection feature doubles as a lock sensor; if the fan motor stops, the output is driven to a logic high and remains at a logic low during normal operation. Pulse Width Modulation (PWM) gives the ability to control the speed of the fan. The duty cycle of this input determines the speed of the fan’s rotation, the relationship between the duty cycle, and whether the fan’s speed is linear. When used in conjunction with a simple algorithm running on a microcontroller it is possible to create a sophisticated thermal management solution that can adapt to system conditions and provide more efficient operation.