NPN Transistor does not work

Hey everybody

I am in a place where I can´t get further without your help.
I have a motor I would like to run.
For that i am using transistors (BC546).
My problem is I can´t get any current through the transistor.
I have tried give it 5 volt on the base, but there is still some resistens (enough for the motor not to run).
it might be it is just me who can figure out to read the datasheet probably.
Hope you guys can help.


How is the circuit wired? Post a schematic.

The problem you have is the way you expect help when you haven't shown your circuit.

Just like this.
The problem is there is not getting any current through the transister, when the base is activated.

What kind of motor? Powering from Arduino is probably a bad idea.
You need a resistor between Arduino and transistor base.
Maybe you've already killed the transistor.

And may not matter too much at this stage, but you're better off putting the transistor on the low side (between motor and Arduino GND)

And you need to make sure you have the transistor facing the right way.

I Know I have already killed one transistor.
It is just a 6 volt motor, which works fine when I just give it 5 volt around the transistor.
What kind of resistens do i need?

I am sorry if i do not follow the requirement of getting help.
As you all can see I am new to this.

Your transistor is wired wrong. A NPN transistor needs to be a low side switch.

Powering a motor from the Arduino power supply will likely not work. You need a power supply capable of supplying the stall current of the motor (consult data sheet or calculate from supply voltage divided by motor winding resistance).

The diode is also required to protect the transistor from the motor inductive kick.
Change the 12V supply in the schematic to your 6V.
dc motor driver.jpg
NOTE: edited schematic to replace transistor base resistor according to MarkT (reply #11).

All you want to put into the base is 10mA or so.

What you are saying is that the voltage is not high enough on the emitter site of the transistor?

I Tried with a 255 ohms resistor. Didn´t work.

Put everything away, do some reading about basic electronics, watch some videos, learn how it should work instead of killing components repeatedly.

You did three things that will have each easily have destroyed the transistor.

  1. You had no current limiting resistor on the base so you forced too much current into the
    base and overloaded the Arduino pin connected to it.

  2. You used a transistor rated for 0.1A maximum to drive a motor. Motors take a lot of
    current (0.5A, 1A, 2A maybe, depending on your motor), you need a switching device
    up to the job, not a random small signal transistor.

  3. You did not have a free-wheel diode across the motor terminals - motors are inductive loads
    and inductive loads generate high voltage spikes if not prevented from doing so.

Note carefully the left hand circuit in GroundFungus's posting #7 - there is a resistor on the base
(which should be more like 150 ohms as it happens), there is a diode across the load and the transistor
ZTX1049A is rated for 4A continuous.

thank you Mark
I will try another transistor then.
Thanks for the help

Welcome to the forum.

Can you tell us your electronics, programming, arduino, hardware experience?
Do you have a DMM?
Can you post a picture of your project please, so we can see your layout?

Thanks... Tom.. :slight_smile: