In class AB each of the push-pull transistors is conducting for slightly more than the half cycle of conduction in class B, but much less than the full cycle of conduction of class A.Īs each cycle of the waveform crosses zero volts, both transistors are conducting momentarily and the bend in the characteristic of each one cancels out.Īnother advantage of class AB is that, using a complementary matched pair of transistors in emitter follower mode, also gives cheaper construction. 5.5.1, but the crossover distortion created by the non-linear section of the transistor’s input characteristic curve, near to cut off in class B is overcome. When both the junctions are forward biased, it is in saturation region.The class AB push-pull output circuit is slightly less efficient than class B because it uses a small quiescent current flowing, to bias the transistors just above cut off as shown in Fig. Cut off region is the region where the input current is below zero. ![]() The curve looks almost flat in the active region. In active region when the output voltage is increased there is very slight change in the output voltage. Here the values of output current I C and the output voltage V CE is noted keeping input current I B constant. Output characteristics is the relationship between the output current and the output voltage keeping input current constant. Output characteristics of Common Emitter Configuration Output Characteristics of Common Emitter Configuration: When the output voltage V CE is further increased the curve shifts right side. Then again the output voltage V CE is increased like 10V, 20V and kept constant and by increasing the input voltage V BE, the input current I B is noted.įrom the results it is observed that when the input voltage V BE is increased initially there is no current produced, further when it is increased the input current I B increases steeply. įirst the output voltage V CE is kept at zero and the input voltage V BE is gradually increased and the input current IB is noted. Here the input current is the base current I B, input voltage is base emitter voltage V BE and the output voltage is collector emitter voltage V CE. Input characteristics are the relationship between the input current and the input voltage keeping output voltage constant. Input characteristics of common emitter configuration Input Characteristics of Common Emitter Configuration: So this configuration is widely used for amplification. The input and output impedance are moderate in common emitter configuration and thus the current and voltage gain is moderate and the power gain is high. ![]() The input current I B is measured in ♚ because the base region is very lightly doped.Ĭommon emitter configuration of PNP transistor Emitter collector region acts like reverse biased diode and the depletion region is large. The input side is forward biased and the output side is reverse biased.Įmitter base region acts like forward biased diode and so the depletion region is very small. The output current I C is taken across the emitter and collector terminals. Input voltage V BE is applied between base and emitter terminals and output voltage V CE is applied across emitter and collector. This is the most commonly used configuration.Ĭircuit diagram of Common Emitter NPN and PNP Transistor:Ĭommon emitter configuration of NPN transistor So input is given between base and the emitter terminals and output is taken between collector and emitter terminals. In Common Emitter configuration, emitter terminal is taken as common for both input and output. Transistors have three terminals, so one terminal have to be taken as common terminal for both input and output. Two terminals are needed for input and two terminals for output.
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