zamir89:
im trying to drive this 5v 2a stepper motor using tip 122 transistor ....after the connection the motor drive but the torque is not high enough as i can easily stop it using my hand....the resistor im using is 0.4ohm should i use 1Kohm as in this diagram so the motor will operate at high torque?
The diodes are in the wrong place, they go anode to collector, cathode to +ve motor
supply. You have possibly blown something.
You'll need ~6.5V supply to get to about 5V to the motor, since darlingtons drop lots
of voltage at high current. And enough amps in the power supply.