Hello,

I don't understand this context.why in saturation characteristic transistor Base-Collector junction is forward biased.we have v_cc in collector

 

Hello and welcome alimech.

Try to explain your question in more detail.

Are you reading the AllAboutCircuits Ebook?

If you are please give a link to the page.

 

when transistor (NPN)is in saturation means "Base-Emitter junction is forward biased" and "Base-Collector junction is forward biased" .Base-Emitter is forwarded bias becuse the v_bb is positive but Base-Collector is connected to v_cc that is either positive.why Base-Collector junction is forward biased.im confused?
please explain for me.

 

The collector is not tied directly to Vcc unless you are thinking of a common collector arrangement. In other cases the collector is connected to the supply through a load resistance or impedance. In those circumstances with sufficient collector current, it is possible for the collector voltage to fall below the base voltage, in which circumstance the transistor is presumed to be in saturation. In that state the base-collector junction must be forward biased.

It's not always consistently stated in the literature, when saturation has been reached in a BJT - but the "condition" at which further increase in base current has no effect on the collector current magnitude is a reasonable choice of operating state for the device to be considered as being in saturation.

 

The collector is not tied directly to Vcc unless you are thinking of a common collector arrangement. In other cases the collector is connected to the supply through a load resistance or impedance. In those circumstances with sufficient collector current, it is possible for the collector voltage to fall below the base voltage, in which circumstance the transistor is presumed to be in saturation. In that state the base-collector junction must be forward biased.

It's not always consistently stated in the literature, when saturation has been reached in a BJT - but the "condition" at which further increase in base current has no effect on the collector current magnitude is a reasonable choice of operating state for the device to be considered as being in saturation.

That was a pretty good summary of the situation.