DEPARTMENT OF ELECTRONICS AND COMPUTER ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY ROORKEE

EC -102 Problem Sheet IV Spring 2007-08

(BJT Characteristics and operation) 1. The input and output characteristics of a transistor in CB configuration are shown in Fig.1. The

emitter current of the transistor is 12 mA and VCB = 15 V. Determine (i) dc and ac input resistances of the transistor, (iii) dc and ac alpha and beta of the transistor, (iii) dc and ac output resistances of the transistor, and (iv) voltage gain of the transistor if a load resistance of 5 k is connected in the collector-base circuit.

2. The input and output characteristics of a transistor in CE configuration are shown in Fig.2. The

base current of the transistor is 0.2 mA and VCE = 15 V. Determine (i) dc and ac input resistances of the transistor, (iii) dc and ac alpha and beta of the transistor, (iii) dc and ac output resistances of the transistor, and (iv) voltage gain of the transistor if a load resistance of 5 k is connected in the collector-emitter circuit.

3. The input and output characteristics of a transistor in CE configuration are shown in Fig.3.

Determine (i) IB for VBE = 650 mV, (ii) VBE for IB = 15 A (iii) dc and ac input resistances for VBE = 650 mV, (iv) dc and ac input resistances for IB = 15 A, (v) dc and ac output resistances if for IB = 15 A and VCE = 5 V, (vi) dc and ac alpha and beta for IB = 15 A and VCE = 5 V.

4. The transistor having the characteristics shown in Fig. 1 is connected in CB configuration as

shown in Fig. 4. Let VCC = 20 V, RL = 1 k, and IE = 20 mA. Find ac input resistance, IC, VCB, VEB, VL, and voltage gain.

5. A silicon transistor with = 0.98 and collector-to-base reverse saturation current of 10 nA is

connected as shown in Fig. 5. Find , ICEO, IC, IE, and VCE. 6. The npn transistor in Fig. 6 has the characteristics as shown in Fig. 2. (i) Find VBB, if VCC = 15 V,

VCE = 4 V, and RL = 1 k (ii) If VCC = 20 V, find RL and VBB so that IC = 15 mA and VCE = 5 V. 7. In the circuit shown in Fig. 7, the silicon transistor has a VCE = 6 V when RC = 4 k and = 50.

Find IC and RB. 8. The npn transistor shown in Fig. 8 has the characteristics shown in Fig. 2 and its voltage drop VCE

at the Q point is 10 V. (i) Find IC, IB, and VBE from the characteristics, (ii) If an ac input of 0.1 sint mA is applied, find the output waveform for ac collector current and ac collector voltage, (iii) if the output ac current waveform is 5 sint mA, draw the input waveform for the ac base current.

9. Consider the BJT circuit shown in Fig. 9. The diodes in the input circuit are identical and have a

VT = 0.7 V. For an input voltage of 3 V, find the base current, collector current and the output voltage V0. Assume = 50.

10. For the transistor in Fig. 10, find the range of VBB for the transistor to be in (i) cutoff region, (ii)

active region. Given = 100, VBE (cut-in) = 0.5 V, VBE(sat) = 0.8 V, VCE(sat) = 0.2 V. 11. Find the minimum value of for the transistor of Fig. 11 to be in saturation.

1

Fig. 1(a) Fig. 1(b)

Fig. 2(a) Fig. 2(b)

2

Fig. 3(a)

IC(mA)

Fig. 3(b)

3

4