The transistor operates in saturation region. Forward-Forward Biasing: In this Transistor Biasing, both collector and emitter are forward biased, as illustrated in Fig. Thus P-type collector receives the N (negative) terminal of the battery and the N-type collector receives the P (positive) terminal.Ģ. The collector receives a battery polarity opposite to its impurity type designation. Similarly, in N-P-N type, the emitter receives the N (negative) terminal, the base receives the P (positive) terminal. Thus, in the P-N-P type, the emitter receives the P (positive) terminal, and the base receives the N (negative) terminal. The battery polarities to the emitter and base are the same as the letter of the emitter and base impurity designations. Generally transistor is operated in this region for amplification.įor connecting batteries properly in the transistor circuits the following scheme may be remembered. In FR biasing the transistor is in active region and the collector current I C, depends upon the emitter current I E. If V BE is equal to 0.7 V it means the base is 0.7 V more positive. For example V BE represents the voltage of base with respect to the emitter. The voltages across the terminals of a transistor follow the usual double subscript voltage convention. Typical collector-to-base voltages might be anything between 3 V and 20 V for most types of transistors, although in many cases the collector-to-base voltage may exceed 20 volts even. Typical base-to-emitter voltages for both N-P-N and P-N-P transistors are 0.7 V for silicon and 0.3 V for germanium. 10.7(b) the emitter-base junction of P-N-P transistor is forward biased by connecting the positive terminal of battery V EB to the emitter and negative terminal to the base while collector-base junction is reverse biased by connecting the negative terminal of battery V CB to the collector and positive terminal to the base. 10.7(a), the emitter-base junction of N-P-N transistor is forward biased by connecting the negative terminal of battery V EB to the emitter and positive terminal to the base while collector-base junction is reverse biased by connecting the positive terminal of the battery V CB to the collector and negative terminal to the base. For this purpose a battery V EB is connected between emitter and base while a battery V CB is connected between the collector and base, as shown in Fig. This type of Transistor Biasing is known as FR biasing. Forward-Reverse Biasing: As already mentioned, for normal operation of a transistor emitter-base junction is always forward biased and collector-base junction is always reverse biased. Accordingly it may operate in different conditions as listed in Table 10.1.ġ. Different Operating Conditions For a Transistor:Ī transistor has two junctions (emitter-base and collector-base junctions), and each of these two junctions, may be forward biased or reverse biased, therefore, there are four possible ways of Transistor Biasing these two junctions. This is precisely what happens in a transistor. No emitter current means almost no collector current. Thus the magnitude of collector current l C depends upon the magnitude of emitter current I E. However, if the emitter-base junction is forward biased and the collector-base junction is reverse biased it is seen that almost whole (about 95%) of the current constituted by the emitter flows through collector circuit. Now if the Transistor Biasing of collector-base junction is ignored and only emitter-base junction, which is forward biased is considered then practically whole of the emitter current flows through the base i.e., I B = I E.
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