Calculate the resistor values and voltages Consider the circuit shown in Figure

Question

Calculate the resistor values and voltages

Consider the circuit shown in Figure 1.6.3.1: Redesign the circuit in Figure 1.6.3.1 such that Ic = 1 mA, I E = 1.2 mA, Vc = +2 v, and V CE = 0.2 V. Use supplies of V + = -V - = 15 V. Note that you must use the saturation model. Hand caaculations Sketch the circuit in your lab book, clearly labeling the transistor's three terminals. Based on the specificatins, calculate V E and V B. you now have enough information to calculate Rc and Rg. Are the calculated values available in your kit? Can you achieve this value by combining several resistors? Comment. What is ? What values of R1 and R2 do you need to use? Is the problem completely specified? Calculate the resistor values and voltages

Explanation / Answer

Solution :

Given values are :

Vce = 0.2V, Ic = 1mA, Ie = 1.2mA, Vc = 2V, V+ = -V- = 15V

As we know, Vce = Vc - Ve = 0.2V

so, Ve = Vc - Vce = 2 - 0.2 = 1.8V

But Ve =( Ie * Re) + V-

1.8V - V- = (1.2 mA)*Re

so Re = (1.8 + 15) / 1.2mA = 14 k ohm

Also Vc = (V+) - (Ic*Rc)

2V = 15V - (1mA * Rc)

Rc = (15 - 2) / 1mA

so Rc = 13 k ohm

we know that Vbe = 0.7 v (ideally)

but Vbe = Vb - Ve

0.7V = Vb - 1.8V

hence Vb = 0.7 + 1.8 = 2.5 V

Also we know that , Vb = (V+ - V-)*R2 / (R1+R2)

so 2.5V = (15+15)*R2 / (R1+R2)

2.5(R1+R2) = 30R2

2.5R1 = 27.5R2

so R1 / R2 = 27.5 / 2.5 = 11

hence R1 = 11*R2

Let R1 = 1 k ohm, R2 = 11 k ohm

And beta_forced = Ic / Ib

but Ie = Ic + Ib

so, Ib = Ie - Ic = 1.2mA - 1mA = 0.2 mA

so, beta_foced = Ic / Ib = 1mA / 0.2mA = 5

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