How to control a 12V computer fan with TP121?

Other Hardware General Electronics
1

Hi,
I want to control a fan with a switch. When I press the button (switch on the diagram), the fan starts spinning, when I release, the fan stops.
However, no matter what I try, the fan starts and stops at random time. It seems that the potential at the transistor base is floating. What's very frustrating is that initially, the fan perfectly responds to pressing the button, but after a few minutes it starts spinning randomly.
Do you know what's going on?

tip121+Fan
tip121+Fan1553×455 71.5 KB

2

Why don't you just use the switch to turn the 12V to the fan on/off, No need for transistors.

Do you know what's going on?

Your circuit is wrong. First the transistor need to be a PNP type but it and the regulator are not necessary if you want to control the TIP121

2 Likes
3

can I do that without damaging the switch?

really?

4

Depends.
How many amps is the fan?
How many amps is the switch rated for?

really?

Yes

5

250 mA for 12 V. I use this type of switch:

arduino button
arduino button217×301 14.1 KB

how come it could wotk even 1 minute then?

6

The small transistor probably burned out after 1 minute.

You can do this:

image
image574×482 5.9 KB

1 Like
7

Thank you, I will try. No need for a 7805 either, I guess.

8

No you don't.
Make sure NOT to connect the Vcc pin on the button module to ANYTHING. It will have 12V on it, so it would be a good idea to put a piece of tape on it so it does not accidentally touch anything

9

Hi Jim-p, thank you, it works.

10

Great.
Have fun!

11

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