bjt-5 - This equation is valid for 0 VO 4.8V When VO = 4.8V...

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This equation is valid for 0 V O 4 . 8V. When V O = 4 . 8V, the transistor Qp goes into saturation. When V O = 4 . 8V, the input voltage is found from Which yields V I = 2 . 8 V. For V I 2 . 8V, the transistor Qp remains biased in the saturation mode. The voltage transfer curve is shown in Figure 2.31(b). Comment: As shown in this example, the voltage transfer characteristics are determined by finding the range of input voltage values that biases the transistor in cutoff, the forward-active mode, or the saturation mode. Exercise Problem The circuit elements in Figure 5.27(a) are changed to R B = 200 k , R C = 4 k , and V + =9V. The transistor parameters are β = 100, V BE (on) =0 . 7V, and V CE (sat) = 0 . 2V. Plot the voltage transfer characteristics for 0 V I 9V. (Ans. For 0 V I 0 . 7V, Qn is cut off, V O = 9V; For V I 5 . 1V, Qn is in saturation, V O = 0 . 2V). Commonly Used Bipolar Circuits: dc Analysis There are a number of other bipolar transistor circuit configurations, in addition to the common-emitter circuits shown in Figures 2.24 and 2.26, that are commonly used. Several examples of such circuits are presented in this section. BJT circuits tend to be very similar in terms of dc analysis procedures, so that the same basic analysis approach will work regardless of the appearance of the circuit. We continue our dc analysis and design of bipolar circuits to increase our proficiency and to become more comfortable with these types of circuits. EXAMPLE Calculate the characteristics of a circuit containing an emitter resistor. For the circuit shown in Figure 2.32(a), let V BE ( on ) = 0 . 7V and β = 75. Note that the circuit has both positive and negative power supply voltages.
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Solution (Q-point values): Writing Kirchhoff’s voltage law equation around the B E loop, we have -----(2.36) Assuming the transistor is biased in the forward-active mode, we can write I E = ( 1 + β) I B . We can then solve Equation (2.36) for the base current: Figure 2.32 Circuit for Example: (a) circuit and (b) circuit showing current and voltage Values From Figure 2.32(b), the collector emitter voltage is
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Solution (load line): We again use Kirchhoff’s voltage law around the C– E loop.
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  • Spring '16
  • Transistor, Volt, Voltage divider, Resistor, Bipolar junction transistor, Bipolar transistor biasing

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