# Category: Bipolar Junction Transistors (BJTs) #### Consider following multi-stage cascade amplifier. The parameters for each transistor and components are b =100, Vbe 0.7V, and the coupled capacitor Is very large Determine the Q point (ic,Vce) both transistors Q1 and Q2 Draw the small signal equivalent circuit of the entire amplifier and find the values of all small signal circuit parameters. Determine the Input resistance Ris and the output resistance Ro. (lOpts)

... #### Section 6.3: BJT Circuits at DC 6.51 The transistor in the circuit of Fig. P6.51 has a very high β. Find V E and V C for V B (a) +2.0 V, (b) +1.7 V, and (c) 0 V.

... #### 6.40 Consider a transistor forwhich the base–emitter voltage drop is 0.7 V at 10 mA. What current flows for v BE = 0.5 V? Evaluate the ratio of the slopes of the i C –v BE curve at v BE = 700 mV and at v BE = 500 mV. The large ratio confirms the point that the BJT has an “apparent threshold” at v BE 0.5 V.

... #### **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?

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