# Question regarding the saturation region of a bjt?

Discussion in 'General Electronics Chat' started by nPab, Sep 16, 2014.

1. ### nPab Thread Starter New Member

Sep 16, 2014
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I always come across the statement that the collector current of a bjt is maximum when it is in saturation region and also people say that it is because the bjt is fully on when it is in the saturation region..

But when you observe the Ic vs Vce graph of a bjt for a particular Ib, we see that the linear region has a higher Ic compared to the saturation region (Obvious from the graph!). So how is the above statement correct?
Also why is it said that the bjt is fully on in the saturation region?

2. ### kubeek AAC Fanatic!

Sep 20, 2005
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Care to post the particular datasheet, so that we can talk about the same exact figure?

3. ### nPab Thread Starter New Member

Sep 16, 2014
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Isn't that general for all bjts...?
I needed a grasp on the concept...I don't understand why it is said that saturation region carries the highest collector current when the linear region is further up in the graph..
I'm talking about Ic vs Vce characteristics of a bjt...

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
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This statement is true only when we have a circuit with resistors and BJT.

5. ### nPab Thread Starter New Member

Sep 16, 2014
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Sorry jony130...I don't understand....how is the Ic vs Vce graph affected in presence of Rc?
Also shouldn't the linear region infact be called saturation region (I know I sound crazy..but bear with me) because isn't in the linear region where current changes negligibly with Vce?Also current in the linear region is higher than the saturation region right?(from the graph)...

6. ### Jony130 AAC Fanatic!

Feb 17, 2009
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Add a Rc resistor change a lot.
The load line is the answer. For example for Rc = 4.6K

As you can see now the maximum collector current is equal to
And for example for Ib = 400uA the collector current cannot be greater than 1.75mA

http://www.electronics-tutorials.ws/transistor/tran_2.html
http://pcbheaven.com/wikipages/Transistor_theory/?p=5

No, but don't worry, your logic is used in MOS. In MOS transistor linear/active region is cold a saturation region.

7. ### crutschow Expert

Mar 14, 2008
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As noted, you seem to be confusing the saturation region of a MOSFET with the saturation region of a BJT. Unfortunately, just to confuse us all, they are defined differently (and somewhat oppositely).

The linear region of a MOSFET is similar to the saturation region of a BJT. (load current changes proportional to the voltage).

The saturation region of a MOSFET is similar to the active region of a BJT (load current doesn't change much with a change in voltage).

The definition of BJT saturation is that the magnitude of the collector-emitter voltage (Vce) is equal to or less than the magnitude of the base-emitter voltage (Vbe). That's the region used when the transistor is performing as a switch.

Last edited: Sep 16, 2014

May 1, 2012
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