Why silicon type transistors are more often used than germanium type?īecause silicon transistor has smaller cut-off current ICBO, small variations in ICBO due to variations in temperature and high operating temperature as compared to those in case of germanium type.Ĩ. The collector current IC and emitter current IE are relatively close in magnitude.ħ. The base current IB is always the smallest. The emitter current IE is always the largest one. Which of the transistor currents is always the largest? Which is always the smallest? Which two currents are relatively close in magnitude? The larger the β* value the larger the injected carriers across collector junction and hence collector current increases.Ħ. The larger the value of emitter injection efficiency, the larger the injected carriers at emitter junction and this increases the collector current. The ratio of collector current to base current is known as transport factor The ratio of current of injected carriers at emitter junction to the total emitter current is called the emitter junction efficiency. Explain what are ‘emitter injection efficiently’ and ‘base transport factor’ and how do they influence the transistor operation? with the change in transistor parameters or temperature rise, the operating point may shift and the amplifier output will be unstable.ĥ.produce distortion in the output signal.In case the transistor is not biased properly, it would : The amount of bias required is significant for the establishment of the operating or the Q-point which is dictated by the mode of operation desired. Discuss the need for biasing the transistor.įor normal operation, base-emitter junction should be forward biased and the collector-base junction reverse biased. Generally no arrow head is marked for collector since its reverse leakage current is always opposite to the direction of emitter current.Ĥ. The direction indicated the conventional direction of current flow( from emitter-to-base in case of p-n-p transistor and from base-to-emitter in case of n-p-n transistor). Explain what is the significance of the arrow-head in the transistor symbol?Īrrow head is always marked on the emitter. So it is called the current controlled device.ģ. The output voltage, current or power is controlled by the input current in a transistor. Why transistor is called current controlled device? Explain why an ordinary junction transistor is called bipolar?īecause the transistor operation is carried out by two types of charge carriers (majority and minority carriers), an ordinary transistor is called bipolar.Ģ. In contrast, the saturation and cut-off regions allow bipolar transistors to be used as switches because there is little electrical resistance between emitter and collector in the saturation region and little current flows in the cut-off region.1. Therefore, an amplifier circuit can be configured using the active area. When a bipolar transistor is in the active region, the collector current is basically h FE times the base current. Therefore, if the emitter and collector terminals are reversed, a bipolar transistor has a much lower h FE and does not function as intended. (For example, in the case of an npn transistor, the collector and the emitter on both sides of the p region of the base are n regions, which look the same.) However, the dopant concentrations in the collector and emitter regions are quite different. The structure of a bipolar transistor looks symmetrical. Two types of bipolar transistor are available, known as npn and pnp, based on the type of junction. Since the bipolar transistor was the first transistor to be invented, when one simply says "transistors," it sometimes means bipolar transistors. Whereas a field-effect transistor is a unipolar device, a bipolar transistor is so named because its operation involves two kinds of charge carriers, holes and electrons. Bipolar transistors are a type of transistor composed of pn junctions, which are also called bipolar junction transistors (BJTs).
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