8/22/2023 0 Comments Pnp junctionIn NPN, the P-type semiconductor is sandwiched between the two N-type semiconductors. Bipolar junction Transistor is of two types, namely, NPN and PNP. Hence, the name current controlled device. Therefore, it’s like we can control the transistor action by differing the amount of applied current at the base terminal. It has three terminals in which the current applied to the base region controls the current flow in the emitter and collector. It is useful in switching circuits electronically. Popularly known as BJT, is a solid-state current controlled device. Thus, let us learn more about all this in the upcoming sections. To understand these carriers, terminals, and many more we need to go through the basics of transistors. In PNP transistors, the majority charge (current) carriers are holes and the electrons are the minority charge carriers. These diodes make junctions as are connected one after another and are called collector-base and base-emitter junction. The PNP transistor acts as two PN junction diodes connected one after another. The terminals are namely, emitter (E), base (B), and collector (C). This transistor is a three-terminal device. It is made by sandwiching an n-type semiconductor between the two p-type semiconductors. This link is the main feature of transistor action.A PNP transistor is nothing but a bipolar junction transistor (BJT). Therefore if a transistor has a Beta value of 50, then for every 50 electrons flowing between the emitter-collector terminals one electron will flow from the base terminal.īy combining the expressions for both Alpha, α and Beta, β the current gain of the transistor can be given as:Īs seen from the equations above, electron mobility between the Collector and Emitter circuits is the only link between these two circuits. Beta values normally range between 20 and 200 for most general purpose transistors. NPN transistors are good amplifying devices when the Beta value is large. The current gain of the transistor from the Collector terminal to the Base terminal is signified by Beta, ( β ). The current gain of the transistor from the Collector terminal to the Emitter terminal, Ic/Ie, is a function of the electrons diffusing across the junction. The ratio of the collector current to the emitter current is called Alpha (α). Since the physical construction of the transistor determines the electrical relationship between these three currents, (Ib), (Ic) and (Ie), any small change in the base current ( Ib ), will result in a much larger change in the collector current ( Ic ). Note: “Ic” is the current flowing into the collector terminal, “Ib” is the current flowing into the base terminal and “Ie” is the current flowing out of the emitter terminal. The current flowing out of the transistor must be equal to the currents flowing into the transistor as the emitter current is given as A nother way to display a NPN Transistor is shown in Figure 2 below. The Base terminal is always positive with respect to the Emitter. The voltage between the Base and Emitter ( V BE ), is positive at the Base and negative at the Emitter. \): NPN Transistor schematic.įor a bipolar NPN transistor to conduct the Collector is always more positive with respect to both the Base and the Emitter.
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