Category: Electronic Tutorial

Approximate h-model: In the analysis of the transistor amplifier, we have as far used the exact h-model for the transistor. In practice, we may conveniently use an approximately h-model for the transistor which introduces an error of < 10% in most cases. This much error may be conveniently tolerated since the h-parameters themselves are not steady but vary considerably for the same type of transistor. We first derive this approximate CE h-model. Figure 1 gives the equivalent circuit of the CE amplifier using the exact h-model for the CE transistor.…

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Comparison of CE, CB and CC Configurations: It is useful to study the variation of AI, AV and Ri with change in load resistance RL for each of the three configurations. Similarly, we may study variation of R0 with change of source resistance RS. Figure 1, 2 and 3 plots for each of the three configurations, current gain AI, voltage gain AV and input resistance Ri respectively as function of load resistance RL for the typically transistor whose h-parameters are given in Table 4.1. From these curves we get the…

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Common Collector Amplifier or the Emitter Follower: Figure 1(a) gives the basic circuit of a common collector amplifier, popularly called emitter follower. Its voltage gain is close to unity (one) and, therefore, any increment in the input voltage i.e. the base voltage appears as an equal increment in the output voltage across the load resistor in the emitter circuit. Thus, the emitter may be said to follow the input signal and hence the name emitter follower. The input resistance Ri of a CC amplifier or emitter follower is very high,…

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Analysis of Common Base Amplifier (CB) using h-parameter: Figure 1 gives the basic circuit of a transistor (NPN type) used as a common base (CB) amplifier. In this case, Vs is the signal voltage, Vi is the actual voltage at the input terminals and V0 is the output voltage. Figure 2(a) gives the a.c. equivalent circuit obtained on having removed the dc source. On replacing the CB transistor with its small-signal two generator h-parameter model we get the equivalent circuit of figure 1(b). Here also we assume sinusoidal input. Hence…

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Transistor static characteristics curves are nonlinear. But for small signal operation, the point of operation moves about the quiescent operating point over a small range. Then the transistor parameters may be considered to be constant over this small range of operation. Derivation of h-Parameter model for transistor To drive the h-parameter model for a transistor, we consider the basic CE amplifier circuit of figure 1. The variable iB, iC, vB (=vBE) and vC(vCE) represent the instantaneous total values of currents and voltages. The input current iB and output voltage vC…

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