Electrical Engineering ⇒ Topic : Re-Transistor Model
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Gopal
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re-TRANSISTOR MODEL The bipolar junction transistors are current controlled devices. In the re model, a diode and a current controlled source are used in the transistor equivalent circuit to explain the behaviour. The common base bipolar junction transistor amplifier is shown in Figure (a) and its re-model is shown in Figure (b). The input impedance is: Figure (a) Common base bipolar junction Figure (b) Equivalent re-rnodel of (of PNP) transistor. Figure (a) The value of Zi is in the range of 0 to 50 Ω. Similarly, the output impedance is given by ZO = ∞ ............ (1) Then
In the common emitter configuration, the collector current Figure (1) is given by IC = βIB (a) CE mode (b) Equivalent circuit using re transistor model Figure (1) Common emitter configuration (for N-P-N transistor). In the common emitter configuration, the values of input impedance, Zi = βre, is in the range between a few hundred ohms (minimum value) to a maximum of about 7 to 8 KΩ In the above model, the output impedance re has not been shown. If the value ro, is available from manufacturer's data sheets, the output circuit can be drawn as shown in Figure (c). Figure (C) Output circuit for common emitter configuration. The output impedance for the circuit is: The voltage gain is: The current gain is: | |
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