i want to use the tip122 darlington transistor with my atmega8 to control a 3A 12V geared DC motor. i found that the current gain is 1000 for tip122 from its datasheet. so the base current for 3A output is 3mA(am i wrong?). So i used a 1.6k resistor to limit the current from atmega8. I breadboarded the circuit and found that i get only 4v emitter voltage even though i the supply voltage is 12.4V. why is this so? i removed the resistor and again i get the same voltage( base current from atmega8 without resistor is 40mA). i simulated the circuit in Proteus and still the same result. So something is wrong? Please help me with this.

i want to use the TIP122 darlington transistor with my atmega8 to control a 3A 12V geared DC motor. i found that the current gain is 1000 for tip122 from its datasheet. so the base current for 3A output is 3mA(am i wrong?). So i used a 1.6k resistor to limit the current from atmega8. I breadboarded the circuit and found that i get only 4v emitter voltage even though i the supply voltage is 12.4V. why is this so? i removed the resistor and again i get the same voltage( base current from atmega8 without resistor is 40mA). i simulated the circuit in Proteus and still the same result. So something is wrong? Please help me with this.