In many devices for cooling of parts, which scatters considerable power ham radio operators use a 12-volt miniature fans intended for use in personal computers. These fans are relatively affordable, as you can buy them in almost any store that sells cards for computers, or get to showdown faulty power supplies of personal computers.
In any case, the possibility of the use of the fan is limited by the need the presence of "the object" of the voltage source of 12 V. In some cases, no such source, but the need to install fan available. Thus it is desirable to feed the fan from the mains.
The figure shows a simple scheme of transformerless supply the fan from the power supply 220 V. circuit is a bridge rectifier with the capacitor C1, the reactive resistance of which decreases excess voltage.
The Zener diode VD5 protects the fan circuit from excess voltage when breakage or disconnection of the fan (for example, if it has a built-in the thermostat switch).
Capacitor C2 smoothes the rectified voltage ripple.
The fans at 12V exist at different values of the nominal current. In the diagram shows the capacitance of the capacitor C1 corresponding to the nominal current of the motor fan of 0.05 A. Calculate with some approximation is required capacitance C1 under the rated current of the fan according to the simplified formula:
C = I / OF 0.0725,
where the capacity is expressed in microfarads and the current I in A.
Then, the obtained capacitance value of the capacitor will round up to the nearest nominal standard value.
Zener DD can be replaced by a Zener diode 12…15 V.
Author: V. Khudyakov