I have this schematic for a DC motor in my arduino, now I want to add 9v battery.

But I've seen that people use TIP120 transistor, I have BC548B, can I just put the 9v with that transistor?

enter image description here

  • What are the ratings of your motor, or do you have a datasheet for. otherwise, connect to 9V directly and measure the current draw and add give that info too.
    – RSM
    May 3, 2015 at 14:26
  • The datasheet says 30 volt is the maximum.
    – Gerben
    May 3, 2015 at 17:17
  • @Gerben the transistor is max 100mA this is surely not good for a motor?
    – RSM
    May 4, 2015 at 7:29
  • That's the maximum. Just like you can put a 5w light bulb in the same socket as a 100w light bulb. The motor will use the amount of current it needs, even thought there might be more current available.
    – Gerben
    May 4, 2015 at 18:20
  • @Gerben and if the motor draws too much, poof, white smoke and fun :) The OP never stated a motor type. The OPs circuit is what they want to do(from what I can tell, with Vin as source), although if the motor ran on 5V it is possibly a low current then, but you could max the draw if the thing stalls or is under load. With a 5W you might not see much though.
    – RSM
    May 4, 2015 at 23:07

2 Answers 2


There are many circuits using the TIP120 NPN transistor because it is a darlington transistor. This is used because its max voltage is 60V and the max current is 5A, this means you can control a variety of external high current devices with low voltage circuitry because of the darlington arrangement.

You can use the BC548B with your motor(low current) and a 9V battery as it does handle 30V, but it is limited to 100mA, which is fine for tiny low current motors. But these are actually Amplifier transistors, so there main design area is not for inductive loads.

I recommend the TIP120 as this will ensure that you don't trash a transistor with current spikes as you could easily go over the 100mA spec of the BC548.


Firstly, I see no external power supply in your schematic.
Secondly, you certainly CANNOT use a BC548 for controlling a motor.
MOSFETS are the best.

  • If you use PWM, be sure to use a Transistor(preferably a MOSFET) that has max voltage 3times the supply voltage and a flyback diode.Also, measure the current drawn by the motor when connected directly to 9V supply.The max current rating of the transistor used should be approx 2 times the current drawn by the motor(in the prev test). May 5, 2015 at 11:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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