sir, i've completed my AMIE degree through INSTITUTION OF ENGINEERS. Now i'm preparing for competitive exams.i request your help and guidance on my way.

i request to clear my doubt with reasonable explanation.


a common emitter transistor amplifier has a collector current of 1.0 mA when its base current is 25 micro ampere at the room temperature. it's input resistance is approximately equal to------------?



the answer given inthe book is 1000 ohms

 

The problem as you have stated it is missing a key parameter. That parameter is beta.

hgmjr

 

What you are being asked to compute is the intrinsic emitter-resistance reflected to the base.

hgmjr

 

give that Ic = 1ma and Ib = 25ua
beta is roughly ic/ib so that makes beta 40

input resistance is = 're * beta

're is 25mv/IE = 25

soooo input resistance = 1000

checks out to me...

 

give that Ic = 1ma and Ib = 25ua
beta is roughly ic/ib so that makes beta 40

input resistance is = 're * beta

're is 25mv/IE = 25

soooo input resistance = 1000

checks out to me...

sir, thank you. the book has also given me same solution.but in the book after calculating beta value=40, it is given that

for CE, Rm = (Vt(millivolts)(b+1))/1.025 milli amps

here at this point i was unable to undersatnd.

thank you for your solution sir.

i,m preparing for INDIAN ENGINEERING SERVICES. I've so many such unanswered problems.

sir i'm very new to this society. i don't know how to attach a file along with this quiery . i request you to suggest the way how i can add my files.

my e mail address is psmuni@gmail.com

 

Your book solution was just being more exact (pedantic) than S Lannan.

The equations are the same.
The 1.025 arises because Ie =Ic+Ib , Vt = 25 millivolts is an assumed standard value. the factor Beta+1 is more exact but most normally use just beta since beta >>1.

For most purposes 'rule of thumb methods' are good enough.

 

Hey Muni,
Gr8, i am also very new to this site. Me also wants to prepare for IES. but though I am in job, i dont get much time for study..

 

Doesn't the INSTITUTION OF INDIAN ENGINEERS teach basic electronics??
No text book??

 

Doesn't the INSTITUTION OF INDIAN ENGINEERS teach basic electronics??
No text book??

sir
definitely IE teaches basics. but still some doubt arises due to lack of proper application.
thank you for going through problem.