Where does this emitter resistance equation come from?

[zhi_yi]

anybody, please tell me where does this equation come from??

re' = 25 mV / IE

thank you very much

 

[Alles Gute]

Re: emitter resistance

KT/q is 25mv
regards

 

[freewilly30]

Re: emitter resistance

it is the equation of the t-modek of bjt transistors when used in common base mode

 

[MRFGUY]

Re: emitter resistance

You can get the answer from the following link:

**broken link removed**

 

[zhi_yi]

Re: emitter resistance

thanks all for the helps, but i still confused with what is k, what is T, an what is q, please explain it and derivate the equation

thanks....

 

[VVV]

Re: emitter resistance

I cannot deduce the formula, but:
k=Boltzmann's constant; k=1.380658E-23 [J/K]
T=absolute temperature T=273.15+t[°C] [K]
q=electron's charge q=1.6E-19 [C]

So at room temp (300K), this quantity kT/q (thermal voltage) works out to about 25.89mV. So if the temperature is less than 300K (27°C), it will be closer to 25mV.
Usually, I consider it 26mV.

The formula you are referring to represents the input impedance of a transistor in CB. It it calculated as the ratio of voltage (thermal voltage) over current.

If you read carefully the paper posted by MRFGUY, you will see where it comes from.