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# how to calculated the resistance required to limit the current of a fan

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#### kbtan

##### Member level 2
how to calculated the resistance required to limit the current of a fan connected 2 a 8051 microcontroller
Here is a part of the diagram

Note: Calculate R as to limit the current

For a 12V fan, R= 0. :-D

---------- Post added at 17:23 ---------- Previous post was at 17:18 ----------

If the fan rated voltage is different, we need to know the power consumption,
Ifan=P/Ufan
R= (12V – Ufan)/Ifan

Also need to insert a series resistor from the output of microcontroller to the base of transistor, so no need the resistor pull-up to the +5V.

kbtan

### kbtan

Points: 2
I might be wrong but if the 12volts source is stable and always 12volts using a voltage regulator AND the fan works at 12volts does it need a limiting resistor??
If you power a 3volts led with constant stable 3 volts supply do you need a resistor to limit it? Apparently NO!

kbtan

### kbtan

Points: 2
excuse me,mister_rf can u tell me that what is Ufan

Ufan= UDC fan :grin:

#### Attachments

• DC fan.GIF
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kbtan

Points: 2