Power supply of the 12-volt fan from the mains. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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In many devices, hams use 12-volt miniature fans designed for use in personal computers to cool parts that dissipate significant power. Such fans are relatively affordable, as they can be bought at almost any store selling computer boards, or obtained from dismantling faulty power supplies for personal computers.
In any case, the possibility of using a fan is limited by the need to have a 12 V voltage source “on site”. In some cases, there is no such source, but there is a need to install a fan. In this case, it is desirable to power the fan from the mains.
The figure shows a simple circuit of a transformerless source for powering a fan from a 220 V mains. The circuit is a bridge rectifier with capacitor C1, on the reactance of which excess voltage drops.
The VD5 zener diode protects the fan circuit from overvoltage in the event of a fan break or shutdown (for example, if it has a built-in thermostat - switch).
Capacitor C2 smooths out the ripple of the rectified voltage.
12V fans exist for various current ratings. The diagram shows the capacitance of the capacitor C1, corresponding to the rated current of the fan motor 0,05 A. Calculate with some approximation the required capacitance C1 for the rated current of the fan using a simplified formula:
C \u0,0725d I / XNUMX,
where the capacitance C is expressed in microfarads, and the current I in A.
Then, round the obtained value of the capacitance of the capacitor to the nearest nominal standard value.
Zener diode D814D can be replaced with any 12 ... 15 V zener diode.
Author: Khudyakov V.
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