Theory of simple voltage dividing logic

[ykishore]

transistors doubt

can any one explain me the meaning of the following words??

If we were to decrease the bias current then the emitter-collector resistance would
increase. If the effective emitter-collector resistance rose above 10K then more
voltage would have to be measured on the voltmeter. If the emitter-collector
resistance increases then the emitter-collector voltage (as measured by the meter) will
rise and the voltage across Rc will decrease by the same amount. (the sum remaining
9V).

 

[eda4you]

Re: transistors doubt

can any one explain me the meaning of the following words??

If we were to decrease the bias current then the emitter-collector resistance would
increase. If the effective emitter-collector resistance rose above 10K then more
voltage would have to be measured on the voltmeter. If the emitter-collector
resistance increases then the emitter-collector voltage (as measured by the meter) will
rise and the voltage across Rc will decrease by the same amount. (the sum remaining
9V).

this sounds like a common emitter stage:

take a simple transistor model. Ic = gm * vbe and let gm be constant.
if the bias current or vbe respectively decrease, Ic will be smaller. Therefore the voltage drop in the collector resitor (not the transisitor) will be smaller since Ic*Rc=Vrc. For npn the Rc is connected between Vcc and collector. If Ib or Vbe increase --> Ic > --> Ic*Rc > ---> Vrc >. therefore the output (at the collector) will decrease. The 10kohms seems for me very loW!! don't make the fault and confuse small and large signal!!

 

[Borber]

Re: transistors doubt

What kind of resistance you are talking about: total or differential?

 

[Kevin Weddle]

Re: transistors doubt

This is simple voltage dividing logic. You decrease the base current so you decrease the collector current and the emitter current. The current is what allows the remaining resistors to drop the voltage. Hence you have a greater VCE.

 

[axhold]

Re: transistors doubt

there is a theory:Hfe=current of collector divid current of basic
this is a template that current controls current source

 

[axhold]

Re: transistors doubt

there is a theory:Hfe=current of collector divid current of basic
this is a template that current controls current source

 

[samcheetah]

Re: transistors doubt

there is a theory:Hfe=current of collector divid current of basic
this is a template that current controls current source

it is true that the base current is proportional to the collector current by a factor of Hfe. but this is only a by-product of the whole transistor action. u have to know which phenomenon happens first and which preceeds it. for a detailed insight into the real "transistor action" go to http://amasci.com/amateur/transis.html

 

[eda4you]

Re: transistors doubt

If you are searching for a more easier explanation look to

https://www.allaboutcircuits.com/vol_3/chpt_4/5.html

 

[mobile-it]

Re: transistors doubt

hxxp://www.radioelectronicschool.com/downloads/ceampsup.pdf

 

[yjkwon57]

Re: transistors doubt

You may understand the meaning if you understand the Ebers-Moll Model.