I have a transistor switching circuit which is already designed but i'm unable to figure out why those resistor values were chosen.
Rc= 4.7k; Ic= 1mA (output to 8051 controller); i/p voltage Vin= 3.2V.
Now, the base resistor used Rb= 2.2k. I can't figure out why? If Ic=1mA, then Ib= 5uA (considering beta=200). But Vin/Ib is not equal to 5uA..
what is going on??? have used a PNP transistor.
PS: sorry couldn't upload the circuit diagram, there seems to be some problem... Please try and help me out..