2--- TRANSISTOR

As switches BC547 (NPN Silicon) are the most used in small (5v-12V range) robotic circuits.





To drive high power circuits like motors, relays etc in robotics we use power transistors. NPN (TIP 120, 121, 122) and PNP (TIP 125, 126, 127) etc.





Let us now compare a normal transistor and a power transistor.

In BC548 we have Ic=0.1A whereas in TIP-122 we have Ic (continuous) =5 A and Ic (peak) =8 A.

Normal DC motors have current rating of 250 mA. So if we connect the motor to the collector of BC548 then it will not able to drive the motor because max. Ic of BC548 is 100mA. But a TIP or KS D880 can drive this motor. This is the main reason we use power transistor.

Second reason is the probability of damage because of the heat sink of the power transistor is very less. If some short circuit occurs the heat sink will get heated saving the transistor from getting damaged.