US Patent 7661305 Airflow detection apparatus

An airflow detection apparatus configured to detect airflow of a fan includes a first transistor, an amplifier, an A/D converter, a microprocessor, an indicating circuit, and a stabilizing circuit configured for supplying a stable current to the first transistor. The base and the collector of the first transistor are connected to a power supply. The emitter of the first transistor is connected to the amplifier and the stabilizing circuit. The amplifier receives a voltage signal from between the base and the emitter of the first transistor. The voltage signal is converted into a digital signal by the A/D converter. The microprocessor processes the digital signal and output an indicating signal to the indicating circuit to indicate airflow status of the fan.