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Applet Worksheet

Problem:

Select R_b for Vc = 5v, assume we are suing a Vcc = 10V, Rc = 1K and ß = 80.

Solution:

First we can find the voltage across the collector resistor Rc:

V_Rc = Vcc -Vc = 10- 5 = 5V.

Since we have got V_Rc, then we can easily compute Ic, the current flowing through Rc, as

Ic = V_Rc/Rc = 5V/1K = 5 mA

Then we have I_B:

I_B = Ic / ß = 5mA / 80 = 0.063mA

On the other hand, since

V_Rb = Vcc - V_Be = 10 - 0.6V = 9.4V

so, the R_B value should be:

R_B = V_Rb/I_B = 9.4V/0.063mA = 150K