Transistorgrab

Fan control with a 555 timer ic for a PC enclosure fan.

In the enclosure of my PC is installed an additional fan. From that I removed immediately after purchase the supply voltage because of the noise it generated.

However. To achieve a lower temperature inside of  the computer case but to keep the noise level low I trew together some components from my electronic stuff box and build a fan control.

The core component is a NE555. The whole circuit is build on as grid-style PC board. But I did the desing in EAGLE just because it gives me the possibility to place the components on a defined grid and makes the routing easy.

The application circuit from the datasheet of the menufacturer was changed so that the discrete resistors were replaced by a potentiometer. The on-time of the generated PWM can thus be changed but the frequency of the PWM will not change.

The choise of the components was defined by availability in my stuff box. With the potentiometer of 50 kOhm and the capacitor of 0.33 µF the frequency of the PWM calculates with 1/f=0.63*R*C of about 100 Hz.
The output power of the NE555 is rather low, that’s why there is the transistor BC140 as an amplifier of the PWM. Because the signal is a PWM there is no need to consider the operating point of the amplifier. The resistor to the base of the transistor only limits the current to the base.

The connection of the fan is made by cutting the connection wire and placing the circuit between fan and its power supply. The electrical connection will be made by screw terminal that are placed on the board.

Downloads for this article:
Eagle Board file, Eagle Schematic