PURPOSE: To reduce the wind noise of a fan by feeding a high voltage to a tan motor at the time of starting and then lowering the voltage thereby decreas ing the r.p.m. of a cooling fan.

CONSTITUTION: Terminal A of a monostable multivibrator IC is pulled down to L level and a capacitor C and a resistor R5 are connected between terminal C and terminal R/C to pull up terminal B to a H level thus generating an L level pulse of predetermined duration (about 1sec). The pulse is applied to the base of a transistor Q2 to turn OFF the transistor Q2 thus opening the ground side of a variable resistor R2. The base of a transistor Q1 is biased through a resistor R1 to turn the transistor Q1 ON thus feeding a voltage of about 12V to a fan motor M. At the end of pulse period, the transistor Q2 is turned ON and the base of the transistor Q1 is biased with a voltage obtained by dividing 12V by means of the resistor R1 and the variable resistor R2. Supply voltage to the fan motor M is regulated properly through the variable resistor R2 thus controlling the r.p.m. thereof.