Electronics and Communication Engineering - Electronic Devices and Circuits - Discussion
Discussion Forum : Electronic Devices and Circuits - Section 1 (Q.No. 22)
22.
An amplifier without feedback has a voltage gain of 50, input resistance of 1 kΩ and output resistance of 2.5 kΩ. The input resistance of the current shunt -ve feedback amplifier using the above amplifier with a feedback factor of 0.2 is
Answer: Option
Explanation:
Input Resistance with feedback for current shunt, 
.
Discussion:
11 comments Page 1 of 2.
Kartikey said:
3 years ago
1/11 is wrong answer, because in question voltage gain is given but there is a mixing of current so first we have.
To calculate current gain then we will use formula A/1+BA.
Thankyou!
To calculate current gain then we will use formula A/1+BA.
Thankyou!
(1)
Aravind said:
5 years ago
I agree. Thanks. @Sri Abhijit.
Sri Abhijit said:
5 years ago
1/11 is correct.
Because the formula is Ri/1+(alpha*beta),
So it will be 1/1+(50*0.2)= 1/11.
Because the formula is Ri/1+(alpha*beta),
So it will be 1/1+(50*0.2)= 1/11.
(1)
Sanjay said:
5 years ago
What about shunt series?
Gourab said:
6 years ago
What is 2.5kohm here? please elaborate.
Janhavi said:
7 years ago
@Ram Prasad.
Please, can you elaborate it.
Please, can you elaborate it.
Katekyo said:
8 years ago
Just remember that current shunt is shunt-shunt and when it's shunt, the R values reduce, so just divide R-value with the " sacrifice factor" (1+AB).
In this case, original Ri=1k, since its shunt in the input, just divide 1k by (1+50*0.2) = 1/11 kohms.
In this case, original Ri=1k, since its shunt in the input, just divide 1k by (1+50*0.2) = 1/11 kohms.
Prem Kumar said:
9 years ago
I agree @Ram Prasad.
The answer should be 1/5.
The answer should be 1/5.
(1)
Ajit said:
9 years ago
Ri' = Ri (1 + Aβ),
Ri' = 1 K (1 + 59 * 0.2),
Ri' = 11 K.
Ri' = 1 K (1 + 59 * 0.2),
Ri' = 11 K.
Vishaldeep said:
1 decade ago
RI(with feedback) = RI/(1+βA) = 1/(1+[50*0.2]) = 1/11.
Voltage gain is considered.
Voltage gain is considered.
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