Transistor question

[Electronman]

Hello

A question about transistor's biasing:
The base-collector bias is in reverse bias when a transistor is at active regin.
so how does the current follow through B-C connection?

By the way, I am familier with the elctrons-holes story.

 

[audioguru]

The current in a transistor usually does not flow from base to collector. When there is base to emitter current then more current flows from emitter to collector.

When the transistor is saturated then the base voltage is much higher than the collector voltage so then some current flows from base to collector.

 

[Electronman]

Oh sorry I meant 'How does collector-emitter current follow through the transistor'.
Consider a NPN transistor at active zone, because the emitter-base connction is at forward bias so the electrons follow through emitter junction. but the base-collector bias is at reverse bias so how does electrons come into collector via emitter?

By the way consider the pic 'a' at the bellow link, while bothe base and collector conections are connected to positive surce so why the base-collector connection is biased? the pic bellow seems differnt than when we connect 2 sources to E-C and B-C to describe the bihavior of a transistor.

**broken link removed**

 

[audioguru]

The base to emitter voltage of a transistor is only about 0.7V. The collector voltage is usually set at half the supply voltage which is much higher than the base voltage.

 

[Electronman]

Thanks for your input and your comment on the pic.

So we just bias the base connection because of base-emitter connection, right?
I mean we just supply the base to turn the emitter's diode on, and then the current will follow into collector? Am I right?

but what about my main question? How do the electrons go into collector?
Before I took a look at reverse biasing of b-c connection I thought we have too bias the base connection because of base-collector, but it seems we bias it because of B-E diode?

 

[flat5]

I don't completely understand this but it does answer your question

Bipolar transistors are so named because they conduct by using both majority and
minority carriers. The three terminals of the BJT are named emitter, base and
collector. Two p-n junctions exist inside a BJT: the base/emitter junction and
base/collector junction. "The [BJT] is useful in amplifiers because the currents
at the emitter and collector are controllable by the relatively small base
current."

In an NPN transistor operating in the active region, the emitter-base junction
is forward biased, and electrons are injected into the base region. Because the
base is narrow, most of these electrons will diffuse into the reverse-biased
base-collector junction and be swept into the collector; perhaps one-hundredth
of the electrons will recombine in the base, which is the dominant mechanism in
the base current. By controlling the number of electrons that can leave the
base, the number of electrons entering the collector can be controlled.

 

[audioguru]

Negative feedback must be used to control the conduction of a transistor (its biasing) because its current gain is a range and is affected by temperature.
Negative feedback is also used to reduce the distortion that is caused by the exponential relationship of the transconductance, current gain and non-linearity of the current gain with changes of current.

 

[Electronman]

In an NPN transistor operating in the active region, the emitter-base junction
is forward biased, and electrons are injected into the base region. Because the
base is narrow, most of these electrons will diffuse into the reverse-biased
base-collector junction and be swept into the collector; perhaps one-hundredth
of the electrons will recombine in the base, which is the dominant mechanism in
the base current. By controlling the number of electrons that can leave the
base, the number of electrons entering the collector can be controlled.

Yea I have read that. but the question is why when the B-C biase is at its reverse bias the electrons follow through emitter into collector?
is that because the emitter and collector are both 'N' on a NPN transistor or 'p' on a PNP one?

 

[flat5]

I spent ten minutes trying to say what this site says and shows clearly.

Transistor Operating Details