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Topic: kind of transistor for small dc motor (Read 2954 times) previous topic - next topic


Hi everybody,

first of all, thank you for this great forum which help me to intro to Arduino.

I want to control a small dc motor with a pin from Arduino. I saw a schematic here http://www.hispavila.com/3ds/atmega/motorescc_files/motorcc_tr.gif and I am wondering how can I know the kind of the transistor for this power (5v)? Also, why do I have to put a resistor in front of the Arduino's pin? It is protection? I know they are electronic questions.

Thanks in advance!


If you think about it, the voltage has very little to do with the choice of transistor.
Imagine you'd said "12V motor" - it could be a model railway loco...or a diesel engine starter motor.
Both could be termed "small".

The diagram suggests an NPN, but you need to know the stall current of the motor.

The resistor is there as a current-limiter.


Sorry, I didnt write details for the motor. Is a 3v motor so I think I dont need a transistor, do you agree?


Link specs of the motor.

As AWOL said volts don't matter. It's the current draw of the motor.


Mine is the first one: http://www.bitsbox.co.uk/motors.html

As I can see, I need 450 mA to feed the motor and Arduino┬┤s pin only provide 40 mA. Right?


Apr 08, 2011, 12:41 pm Last Edit: Apr 08, 2011, 12:43 pm by AWOL Reason: 1
Something like a TIP120?
I think even a 2n2222 would work.
Quite a lot of current for a small motor - no stall current posted.


I am interested on how do you know is TIP120? where do you look for? what is the way to know a specific transistor? thanks for your answers


I think the TIP120 may be overkill, but is a good solid common transistor to use for stuff like this.
It is a Darlington (actully it is two transistors in one package), so has high gain, and is good for up to about 5 amps (IIRC).

The 2n2222 is good for up to about 1 amp, but the gain is only about 1/3rd that of the TIP120.


but the motor only need 450 mA and you speak about 5 A


Yes. That's right 450mA < 5A

I have a bag full of them, so I use them a lot.


Thank you for explain it me so patiently. I will try with one of them ;-)

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