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# Category: microelectronics by sedra and smith

# **6.69 All the transistors in the circuits of Fig. P6.69 are specified to have a minimum β of 50. Find approximate values for the collector voltages and calculate forced β for each of the transistors. (Hint: Initially, assume all transistors are operating in saturation, and verify the assumption.)

# *6.68 For the circuit in Fig. P6.68, find V B v I = 0 V, +2 V, –2.5 V, and –5 V. The BJTs have β=50.

# *6.67 Using β=∞, design the circuit shown in Fig. P6.67 so that the emitter currents of Q 1 , Q 2 , and Q 3 are 0.5 mA, 0.5 mA, and 1 mA, respectively, and V 3 V 5 =−2 V, and V 7 =1 V. For each resistor, select the nearest standard value utilizing the table of standard values for 5% resistors in Appendix J. Now, for β=100, find the values of V 3 , V 4 , V 5 , V 6 , and V 7

# *6.66 For the circuit shown in Fig. P6.66, find the labeled node voltages for:

# ***6.65 Consider the circuit shown in Fig. P6.65. It resembles that in Fig. 6.30 but includes other features. First, note diodes D 1 and D 2 are included to make design (and analysis) easier and to provide temperature compensation for the emitter–base voltages of Q 1 and Q 2 . Second, note resistor R, whose purpose is to provide negative feedback (more on this later in the book!). Using V BE and V D = 0.7 V independent of current, and β=∞, find the voltages V B1 , V E1 , V C1 , V B2 , V E2 , and V C2 , initially with R open-circuited and then with R connected. Repeat for β=100, with R open-circuited initially, then connected.

# 6.64 The pnp transistor in the circuit of Fig. P6.64 has β=50. Find the value for R C to obtain V C = +2 V. What happens if the transistor is replaced with another having β=100? Give the value of V C in the latter case.

# **6.63 It is required to design the circuit in Fig. P6.63 so that a current of 1 mA is established in the emitter and a voltage of −1 V appears at the collector. The transistor type used has a nominal β of 100. However, the β value can be as low as 50 and as high as 150. Your design should ensure that the specified emitter current is obtained when β=100 and that at the extreme values of β the emitter current does not change by more than 10% of its nominal value. Also, design for as large a value for R B as possible. Give the values of R B , R E , and R C to the nearest kilohm. What is the expected range of collector current and collector voltage corresponding to the full range of β values?

# *6.62 Repeat the analysis of the circuits in Problem 6.61 using β=100. Find all the labeled node voltages and branch currents.

# 6.61 For the circuits in Fig. P6.61, find values for the labeled node voltages and branch currents. Assume β to be very high.

# 6.60 For the circuit in Fig. P6.60, find V B , V E , and V C for R B = 100 k , 10 k , and 1 k . Let β=100.

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