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Consider the circuit arrangement shown in figure (1) for studying input and output characteristics of n-p-n transistor in CE configuration. Select the values of R_(B) and R_(C ) for a transistor whose V_(BE)=0.7V, so that the transistor is operating at point Q as shown in the characteristics shown in figure (2). Given that the input impedance of the transistor is very small and V_(C C)=V_(BB)=16V, also find the voltage gain and power gain of circuit making appropriate assumptions. |
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Answer» Solution :Graph in FIGURE-2 is for `I_(B)=30muA`. For point Q on it, `I_(C )=4mA=4xx10^(-3)A and V_(CE)=8V` For output part of above figure, `V_(C C)=I_(C )R_(C )+V_(CE)` `therefore 16=(4xx10^(-3))R_(C )+8` `therefore R_(C )=(8)/(4xx10^(-3))=2xx10^(3)Omega=2kOmega` For INPUT part of above figure-1, `V_(B B)=I_(B)R_(B)+V_(BE)` `therefore 16=(30xx10^(-6))R_(B)+0.7` `therefore R_(B)=(15.3)/(30xx10^(-6))=5.1xx10^(5)Omega=510xx10^(3)Omega` `=510kOmega` Voltage gained, `A_(V)=beta(R_(C ))/(R_(B))=((I_(C ))/(I_(B)))((R_(C ))/(R_(B)))` `therefore A_(v)=((4xx10^(-3))/(30xx10^(-6)))((2xx10^(3))/(510xx10^(3)))` `therefore A_(V)=0.52` Power gained, `A_(P)=A_(V)A_(i)=A_(V)beta=A_(V)((I_(C ))/(I_(B)))` `therefore A_(P)=0.52xx(4xx10^(-3))/(30xx10^(-6))` `therefore A_(P)=69.33` |
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