![]() In fact, small signal amplifiers are the most common linear devices. Amplification means linear amplification. Therefore, a transistor acts as an amplifier when operating in the active state. When the transistor is in the active state, I C = I B. That is the transistor behaves as though a switch has been closed between the collector and emitter. In saturation, the collector and emitter are, in effect, shorted together. Bias stability can also mean stability with temperature, with aging, etc. That is collector emitter pathway is open If the transistor is cut-off, there is no base current, so there is no collector or emitter current. In the active state, collector current is β times the base current ( i.e. SATURATED : Emitter diode and collector diode are ON. wha do you mean by transistor biasing mean WebFor a transistor to function, the two PN junctions must be properly biased. In NPN transistor, the direction of movement of an electron is from the emitter to collector region. The NPN transistor amplifies the weak signal enter into the base and produces strong amplify signals at the collector end. The relations between the diode states and the transistor states are :ĬUT-OFF : Emitter diode and collector diode are OFF.ĪCTIVE : Emitter diode is ON and collector diode is OFF. Definition: The transistor in which one p-type material is placed between two n-type materials is known as NPN transistor. The state of a transistor is entirely determined by the states of the emitter diode and collector diode. We have seen above that transistor can act in one of the three states : cut-off, saturated and active. The junction between base and collector may be called collector diode. A DC bias voltage at the base of the transistor can be developed by a resistive voltage divider that consists of R 1 and R 2. The junction between base and emitter may be called emitter diode. A transistor has two pn junctions i.e., it is like two diodes. The reader may find the detailed discussion on transistor biasing in the next chapter. We provide biasing to the transistor to ensure that it operates in the active region. Consequently, the transistor will function normally in this region. In the active region, collector-base junction remains reverse biased while base-emitter junction remains forward biased. The region between cut off and saturation is known as active r egion. If base current is greater than I B( sat), then collector current cannot increase because collector-base junction is no longer reverse-biased. At saturation, collector-base junction no longer remains reverse biased and normal transistor action is lost. At this point, the base current is maximum and so is the collector current. ![]() The point where the load line intersects the I B = I B( sat) curve is called sa turation. The collector-emitter voltage is nearly equal to V C C i.e. At cut off, the base-emitter junction no longer remains forward biased and normal transistor action is lost. At this point, I B = 0 and only small collector current ( i.e. The point where the load line intersects the I B = 0 curve is known as cut off. ( i) shows CE transistor circuit while Fig.( ii) shows the output characteristcs along with the d.c. ![]()
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