It also implies that reducing forward bias voltage decreases the current flow. This allows more carriers to reach the Collector which in turn increases the current flow from Emitter to Collector. To summarize, increasing the forward bias voltage, the Emitter-Base junction barrier is reduced. The Base is more negative than the Emitter by approximately 0.7 volts for Silicon semiconductor and 0.3 volts for Germanium semiconductor. The Collector Current or the Base Current can be calculated using the formula, This causes the current (I E) to flow from Emitter to Collector. As the Emitter is highly doped, it attracts lot of electrons that diffuse into the Base region.Īt the same time, electrons flow from negative terminal pushing the electrons near the Emitter-Base junction into the Emitter. Holes are pushed in the Emitter (P-region) crossing the depletion region into the base from positive terminal of the voltage source (V BE). The Base Emitter region is forward biased so that the voltage at the Emitter is at higher potential than at the Base (V BE). Reverse biasing creates no diffusion and hence no current flows between the terminals. This means that the Base is at higher potential than the Collector. The Base Collector region is reverse biased which uses external voltage source. 3 – Construction and Circuit Symbol of PNP Transistor In reverse biasing, the P-type semiconductor is connected with the negative terminal and N-type semiconductor is connected to the positive terminal.įig. A junction is said to be forward biased when a P-type semiconductor is connected with the positive terminal and N-type semiconductor is connected to the negative terminal. PNP Transistor works when Base Emitter junction is forward biased and the Base Collector junction is reverse biased. Only a few donor or acceptor atoms are required to produce changes in the resistivity of a semiconductor. Electrons travel slowly in a semiconductor and holes move more slowly than electrons. These elements are called semi-conductors. The fourth column of the periodic table contains certain elements which behave like both conductors and insulators under controlled conditions. To understand the working of a Transistor, it is necessary to know the characteristics of semiconductors. 2 – PNP Transistor Symbol How PNP Transistor Works A PNP Transistor is considered ‘ON’ when the Source Voltage connected to the Base is low and turned ‘OFF’ when it is high.įig. The PNP Transistor symbol shows an arrow pointing inwards from Emitter to the Base which indicates the direction of the conventional current flow. The structure is opposite to NPN transistor but similar in operation. The small Base current has the ability to control large Emitter current, as it is current controlled device. The current flow is due to the movement of holes. In PNP Transistors the electrons are minority charge carriers and holes are majority charge carriers. Disadvantages of PNP Transistor What is PNP TransistorĪ PNP Transistor is a type of Bipolar Junction Transistor which is composed of three layers where ‘N’ doped layer is sandwiched between two ‘P’ doped layers.Output Characteristics for Common-Base Configuration.Input Characteristics for Common-Base Configuration.
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