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Topic: kind of transistor for small dc motor (Read 1 time) previous topic - next topic

emarin

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!

AWOL

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.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

emarin

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

mark675

Link specs of the motor.

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

emarin

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?

AWOL

#5
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.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

emarin

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

AWOL

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.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

emarin

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

AWOL

Yes. That's right 450mA < 5A

I have a bag full of them, so I use them a lot.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

emarin

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

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