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Define current gain in common base and common emitter amplifier and find the relation between them. |
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Answer» Solution :Current gain `alpha` is defined as the RATIO of collector current to the emitter current at constant collector VOLTAGE. Current gain `BETA` is defined as the ratio of the collector current to the base current at constant collector voltage. i.e. `beta=((I_(c))/(I_(B)))_(E_(ie))` Relation between `alpha` and `beta`. For n-p-n and p-n-p transistor, we have `I_(e)=I_(b)+I_(c)` or `(I_(e))/(I_(c))=(I_(e))/(I_(c))+1`......`(i)` Since current gain of common emitter amlifier, `alpha=(I_(c))/(I_(e))` And current gain of common base amplifier, `beta=(I_(c))/(I_(b))` So Eq. `(i)` becomes `(1)/(alpha)=(1)/(beta)+1` or `(1)/(beta)=(1)/(alpha)-1` or `beta=(alpha)/(1-alpha)` |
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