6588Views13Replies

Author Options:

D.C input resistance of a BJT transistor in C.E configuration? Answered

what will be resistance across base and emitter of BJT in C.E configuration

13 Replies

user
iceng (author)2012-02-24

The base emitter junction is a Non-Linear semiconductor diode.
The DC resistance will change with the current used.

Select as Best AnswerUndo Best Answer

user
deepakmurali (author)iceng2012-02-25

can u say the range between which the value of input D.C resistance will vary?

Select as Best AnswerUndo Best Answer

user
iceng (author)deepakmurali2012-02-27

What transistor are you using, Then you or I can look-up the data sheet and
pick out the bias that will give you the small signal AC resistance range that
you seek.

Every transistor type has different specifications. Why do you think there are
so many different kinds available ??!?!!

Some serious designers will actually use a curve tracer to get the actual
transistor values for the best circuit function.

Select as Best AnswerUndo Best Answer

user

along with the resistance of the junction will the resistance of remaining parts of base and emitter affect the D.C input resistance?If so by what factor?
Can you explain by assuming your own BJT and base current?

Select as Best AnswerUndo Best Answer

user
iceng (author)2012-02-24

PN the well known junction

Select as Best AnswerUndo Best Answer

user
deepakmurali (author)iceng2012-02-25

What is that graph(without ohmic resistance)?

Select as Best AnswerUndo Best Answer

user
iceng (author)deepakmurali2012-02-27

Every Electronic Engineer immediately recognizes that base emitter
diode curve tracer VI plot above.

An Ohmic scale is not Linear it is a function of where the bias current
puts the junction into for a current gain condition.
After all BJTs are primarily current amplifiers.
Resistance = Voltage ( X axis ) divided by current ( Y axis ), Really !

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)2012-02-24
user

depends on the load in the sense?
Load will be connected across collector and ground(C.E configuration) and what this load has to do with input D.C resistance between Base and Emitter? Can you please explain

Select as Best AnswerUndo Best Answer

user

Take a look at the current and voltage in the transistor from the load lines: Resistance in the collector is Vcc-Vce/Ic Resistance referred to the base would be Ic/Hfe Vbe ~0.6V if the base is saturated, so Rb=Vbe x Hfe/Ic

Steve

Select as Best AnswerUndo Best Answer

user
rickharris (author)2012-02-24

Depends on which way you measure it.

One way almost open circuit the other way - depends.

Select as Best AnswerUndo Best Answer

user
deepakmurali (author)rickharris2012-02-25

I cant understand. Can you please explain?

Select as Best AnswerUndo Best Answer

user
rickharris (author)deepakmurali2012-02-25

The base emitter junction is a diode. If you measure the resistance one way it will be open circuit and the other way will depend on the transistor, it's state at the time you measure.

You need to read the transistor theory pages suggested in your other question so you can understand what the transistor does and why.

Select as Best AnswerUndo Best Answer