ELT-306 WA5

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School

Thomas Edison State College *

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Course

306

Subject

Electrical Engineering

Date

Jan 9, 2024

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docx

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Uploaded by kevinalandro

Kevin Austin ELT-306 WA 5 Questions: 1. Describe what is meant by the voltage gain of an amplifier. The voltage gain of an amplifier is a measure of how much the output voltage of the amplifier increases in relation to the input voltage. A higher voltage gain indicates that the amplifier can amplify the input signal more effectively. Voltage gain (Av) is the ratio of the change in output voltage (ΔVo) to the change in input voltage (ΔVi): Av = ΔVo ΔVi or 20 ×lo g 10 ( Av ) 2. What is the primary purpose of coupling capacitors in transistor amplifiers? The primary purpose of coupling capacitors is to block DC components while allowing AC signals to pass through. Problems: 1. If the input voltage to an amplifier is 50 mV and the resulting output voltage is 3 V, calculate the voltage gain. Av = Vo Vi = 3 V 50 mV = 60 2. A transistor is biased with IE = 5 mA. Calculate r’e . r ' e = 25 mV 5 mA = 5 Ω

3. For the circuit shown, calculate: A. The input resistance at the base of the transistor. Rb= R 1 ∨ ¿ R 2 = 10 k Ω ∨ ¿ 2.2 k Ω = 1.8 k Ω B. The input resistance of the amplifier. Vb = Vcc R 2 R 1 + R 2 = 10 V 2.2 k Ω 12.2 k = 1.8 V V E = V B − 0.7 V = 1.8 − 0.7 = 1.1 V I E = V E R E = 1.1 V 820 Ω = 1.34 mA r ' e = 25 mV 1.34 mA = 18.66 Ω Rin = β×r' e = 200 × 18.66 = 3.72 k Ω Rintotal = 1.8 k Ω ∨ ¿ 3.72 Ω = 1.2 k Ω C. The voltage gain. Av = rc r' e = 3.6 k Ω 180 Ω = 20 4. If a circuit requires a capacitor to give good coupling at 200 Hz and the resistance the capacitor is connected to is 3 kΩ, what value capacitor is needed? C = 1 2 π f X C = 1 2 π ( 200 Hz )( 3 k Ω ) = 2.65 μF

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