I am using TIP122 NPN transistor to control geared DC motor using this scheme:
I ordered transistors and they arrived today so I tested them in this circuit:
But the motor was rotating at just half speed as when connected straight to battery (without the transistor).
What could be the problem? Please help me...
The Emitter voltage is roughly 2*0.6V =>1.2V lower than the Base voltage (TIP122 is Darlington, that is, has two transistors inside) ..
In a bridge like yours you should consider PNP transistors as the "upper" switches ..