Abstract: A fan rotation speed controlling device includes a first transistor, a second transistor, a third transistor, a fourth transistor, and at least one heat dissipation fan. The first transistor receives a pulse-width modulation (PWM) signal. The second transistor and the third transistor amplify the PWM signal. The fourth transistor receives the amplified PWM signal and changes its own working state according to the amplified PWM thereby controlling the magnitude of an output voltage. Consequently, the heat dissipation fan changes its rotation speed according to variation of the output voltage. The fan rotation speed controlling device is applicable to and can control the rotation speeds of a plurality of electrically connected fans which are of different specifications.

Abstract: A fan rotation speed controlling device includes a first transistor, a second transistor, a third transistor, a fourth transistor, and at least one heat dissipation fan. The first transistor receives a pulse-width modulation (PWM) signal. The second transistor and the third transistor amplify the PWM signal. The fourth transistor receives the amplified PWM signal and changes its own working state according to the amplified PWM thereby controlling the magnitude of an output voltage. Consequently, the heat dissipation fan changes its rotation speed according to variation of the output voltage. The fan rotation speed controlling device is applicable to and can control the rotation speeds of a plurality of electrically connected fans which are of different specifications.