0
\$\begingroup\$

schematic

simulate this circuit – Schematic created using CircuitLab

Will this circuit work with the raspberry pi and will the rpi be safe? I want the motor to turn on when GPIO_2 is set high. It is a DC motor and the transistor is a BC635 (I couldn't change the parameters on the diagram).

\$\endgroup\$
1
  • 1
    \$\begingroup\$ What current does the motor need to take in your application? \$\endgroup\$
    – Andy aka
    Commented Dec 19, 2015 at 18:21

2 Answers 2

3
\$\begingroup\$

Your motor needs to be current limited to 1A or you are likely to damage the BC635. I also think there may be a chance that your GPIO current may not be sufficient to drive the transistor to get ~1A into the motor: -

enter image description here

What this part of the data sheet tells you is the to get 500 mA into the motor requires a base current that is only 25 times smaller at 20 mA - you need to verify that your GPIO can supply this current without risk to the RaPi.

Note also that if you need to activate your motor to close to 9V under mechanical heavy (ish) loads you might even have to push 50 mA into the base of the transistor.

And of course, you always need a base resistor because the GPIO pin may be able to supply more than 50 mA i.e. the base resistor is there to protect the transistor and the GPIO pin.


RaPi current appears to be about 16mA maximum according to this document below: -

enter image description here

See also this Q&A on SE.RaPi

\$\endgroup\$
2
\$\begingroup\$

Your circuit will work, although you must add a resistor to limit the base current of the transistor.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ @MattYoung - I replaced 'should' with 'must', perhaps it would be more clear that way ;) \$\endgroup\$
    – v.m.
    Commented Dec 19, 2015 at 16:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.