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Homework7

# Homework7 - ECE 3040 Homework#7 1 We looked at BJTs used as...

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ECE 3040 Homework #7 1.) We looked at BJT’s used as amplifiers biased into forward active mode at great length. BJT’s can also be used as a switch, which requires biasing into other modes. Consider the following circuit. (a) What range of resistor Rc will allow the circuit to operate as an amplifier? (b) What mode is the transistor biased into when Rc=10K? (c) If the resistor Rc=1k ohm, what is the small signal voltage gain VoutAC/VinAC assuming C1 and C2 to be very large? (d) Repeat part c with a large capacitor in parallel with Re. (Hint for parts a and b: Use a 0.65 V turn on voltage for any forward biased junction. Also, when the transistor is not in forward active mode the transistor base current can not be used to determine the collector current due to loading (small input resistance in the base) of the bias circuit (R1 and R2) by the input resistance of the transistor. Under this condition, find Ib from Ic.) Use β =416 for all answers where β is valid. 2.) BJT transistors are often used as a switch bridging low voltage circuitry such as a digital logic circuit

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