A \"black box\" with three terminals labelled E, B, and C is connected in the ci

Question

A "black box" with three terminals labelled E, B, and C is connected in the circuit shown at the right. (a) Calculate VC and VE. (b) If terminal "B" is 0.6V higher in voltage than terminal E, calculate R1 and R2(in terms of IA), assuming that is very large compared to the 20 mu A flowing into the B terminal and can be neglect in settings up a voltage divider. (This "black box" is a silicon NPN transistor and C, B, and E will refer to the collector, base and emitter terminals when we study those devices).

Explanation / Answer

a) VC = 12 - 2(kohm) * 2(mA) = 8V VE = 1(kohm) * (2(ma) + 20(uA)) = 1 * 2.02 = 2.02V b) VB = VE + 0.6 = 2.62V If Id >> 20uA then the current in R1 and R2 can be considered the same, with a value of Id accross both resistors Then Id * R2 = VB ===> Id * R2 = 2.62 ===> R2 = 2.62 / Id Id * R1 = 12 - VB ===> Id * R1 = 9.38 ===> R1 = 9.38 / Id

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