Bjt Exercise

Determine VCB in the transistor circuit shown in Figure 1. The transistor is made of silicon and has =150. Assume VCE = 0. 7 V. Figure 1 Ans:2. 85 V (4 marks) Determine the voltage gain, Av of the circuit shown in Figure 2. Assume = 200. Figure 2 Ans:Av = 291 (6 marks) For the common emitter amplifier circuit shown in Figure 3, (i) Draw the h parameter equivalent circuit. (ii) Derive the expression for voltage gain and input impedance in h parameters. (iii) If the transistor of Figure 3 has the following set of h parameters: hie = 2k; hfe = 100; hre = 5 ? 0-4; hoe = 2. 5 ? 10-5 S Find the voltage gain and ac input impedance. Figure 3 Ans:Zin = 1. 53k,Av = 375 (10 marks) Consider the circuit in Figure 4 below. Find the voltage gain of the amplifier. Figure 4 Ans:360 (8 marks) If CE were to be removed from the circuit in Figure 4, what would be the voltage gain? What do you conclude from the result of this calculation? Ans:5. 38. CE increases the voltage gain from 5. 38 to 360. (2 marks) Explain the operation of a transistor as an amplifier. | (5 marks)|

For the common emitter amplifier shown in Figure 5, determine the following: (i) internal emitter resistance, re’ (ii) input impedance , Zi (iii) voltage gain, Av Figure 5 Ans:r’e = 30. 56 ,Zi = 1/768 k, Av = 127. 6 (10 marks) Draw the generalized h-parameter equivalent circuit for the bipolar junction transistor connected in the common-emitter configuration. Ans: (5 marks) Give the equations relating the terminal variables Vi, Vo, IB, and IC in terms of the h-parameters for the transistor connected in the common-emitter configuration shown in Figure 6.

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Figure 6 Ans: (4 marks) The transistor used in the common-emitter amplifier of Figure 7 has the following hybrid parameter values: hie 1. 5 k? ,hfe 100,hoe 100 ? S,hre 0. Draw the small signal h-parameter equivalent circuit model of the amplifier. Assume that all capacitors have negligible reactance at the signal frequency. Figure 7 Ans: (6 marks) Define . Show that . (6 marks) (i)| How will you determine the input and output characteristics of a CE connection. (3 marks)| (ii)| Draw the input and output characteristics of CE connections. 4 marks)| For the common base circuit shown in Figure 8, determine IC and VCB. Assume the transistor to be silicon. | Figure 8(6 marks)| Determine VB, VE, IE, IC, IB, VC and VCE in Figure 9. | | | Figure 9| | (8 marks)| Figure 10 shows the design of a common emitter amplifier arrangement with hie = 1500? ; hfe = 50; hre = 4 ? 10-4; hoe = 5 ? 10-5 mho Find * ac input impedance of the amplifier * voltage gain and * output impedance Figure 10 Ans:Zin = 1320 ? , Av = -196, Zout = 5. 88k?

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