Vce(sat) of Transistor

[agg_mayur]

I want to know the voltage drop across Vce(sat), as i know that there is 0.7v drop across Vbe if i am using Si transistor.
In Rb and Rc values i think we have to set Rb > Rc if i am correct then why is it so?

 

[Tahmid]

Hi,
The Vce(sat) value varies with each transistor. It is stated in the datasheet and should be checked from there.

Hope this helps.
Tahmid.

 

[agg_mayur]

hi,
thanks for the reply.
Actually Vce is stated either .2 or .3 in Si type tranistor but we studied Si type have .7 drop and Ge have .3 drop.

 

[Tahmid]

Hi,
Actually it varies. eg. BC547 at Ic=10mA, Ib=0.5mA has Vce 0.09V to 0.25V, but at Ic=100mA, Ib=5mA has Vce 0.2V to 0.6V. On the other hand TIP3055 has Vce varying from 1.1V to 3V depending on Ib and Ic.

Hope this helps.
Tahmid.

 

[betwixt]

Tahmid is correct, Vce(sat) is not a perfect voltage, imagine it has a small resistance in series with it so the voltage increases slightly as more current flows.
From the 0.7V and 0.3V you see, it sounds more like Vbe than Vce you are measuring. To measure Vce, inject enough base current that the collector emitter voltage reaches it's minimum. When the C-E voltage falls no further the transistor is in saturation.

Brian.

 

[syeda amna]

Vce sat is the characterstic of the particular transistor. it is mentioned in datasheets. Rc and Rb are used to limit the collector current and base current respectively. the choise of these resistance depends on the design requirements. we can not say that Rb>Rc it is upto the design.