Question

Following figure is an incomplete circuit of common emitter transistor in CE configuration with the input forward biased.

1. Identify the transistor an NPN or PNP.

2. Complete the above circuit diagram by giving proper bias in the output and connect load resistance of 4 KΩ.

3. When the base current changes by 20µ A for V_BE = .02 V. What is the voltage gain of the amplifier, if I_C = 2mA 

4. npn transistors are preferred in devices with very high frequency source. Why?

Answer 1

1. npn transistor

2.

3. Input resistance, r₁ = \(\frac{ΔV_{BE}}{ΔI_B} =\frac{0.02}{20\times10^{-6}}\)  = 10³Ω

Current gain, β = \(\frac{ΔI_C}{ΔI_B}=\frac{2\times10^{-3}}{20\times10^{-6}}\)= 100

Voltage gain A_v = β\(\frac{R_L}{r_1}\)

= 100\(\frac{4\times10^3}{10^3}\) = 400

4. The resistance of a semiconductor decreases with rise in temperature.