Given the circuit above having; V CC = 180 V, R C = 11,000, and a silicon transi

Question

Given the circuit above having; VCC = 180 V, RC = 11,000, and a silicon transistor with a current gain = 45.

a.)   If RB = 2 k, what is the output voltage (Vout) when the switch is at
position A? __________V

Position B? __________ V

b.) What is the approximate maximum value of RB for which the Vout voltages remain the same as in part (a) when the switch is operated? _________

c.) What are the minimum ratings required for the capabilities of this transistor's
collector current? ________ mA

Collector-emitter voltage? __________V

Explanation / Answer

a)If RB is in position A,Then transistor is off and no current flows through Rc .V(out) = Vcc = 180V.

in position B : Taking Vbe(on) = .7V ,ib = 89.65mA ; Ic = 45(89.65) = 4.03A which would give Vce negative .therefore transistor is in saturation.V(out) = 0.2V assuming Vce saturation = .2V.

b)The voltage in position A will not change for any big value also.So we have to woory about tthe second case ,if Vce = .2 ,Then this is the position exactly where we get maximum RB value. Ic = (180-.2)/11.000 = 16.34 mA.And IB = 16.34/45 = .363mA . So this should be the base current for maximum RB value.

RB = (180-.7)/.363mA = 493.94K .

c) the average value for collector current will be Ic = (16.34 + 0)/2 = 8.17mA and Vce = (180+.2)/2 = 90.1 if the trransistor has to operate in forward active region.

Please ask if you have any doubt .I am not sure of the question of last part(c) .But i have given the average value of what range it should be.

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