# What is saturation region and saturation point?

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#### neofrkh

##### Junior Member level 1
Somebody plz explain me what is saturation region and saturation point
I read that saturation region is when collector and base is forward biased,
and collector is forward biased only when voltage across CE is less than 0.7V.
So why saturation point is not at 0.7V.

Re: saturation

saturation refers to the "ON" state of a BJT. BJTs are current-controlled devices. The coventional current flows from the collector to the emitter. Ideally, the Vce is zero volt. 0.7V is the Vbe not the Vce. When saturated, Vce is typically 0.2V. It largely depends on Ic and the resistance of the semiconductor material that forms the collector.

### neofrkh

Points: 2
Re: saturation

thanx for helping me out
plz tell me any LINK or any book which explains saturation in detail

saturation

Try this:
- Analysis and Design of Analog Integrated Circuits (4th Edition) by Paul R. Gray, Paul J. Hurst, Stephen H. Lewis, and Robert G. Meyer

Re: saturation

neofrkh said:
thanx for helping me out
plz tell me any LINK or any book which explains saturation in detail

better read "solid state pulse circuits" by david bell

try this one **broken link removed**

Re: saturation

no. transistor is in saturatin when be an cb junctions are forward bias and it's independent of ce junction . in saturation voltage across ce junction is less than 0.2 volt.

Re: saturation

al_valaee said:
no. transistor is in saturatin when be an cb junctions are forward bias and it's independent of ce junction . in saturation voltage across ce junction is less than 0.2 volt.

0.2V at Vce is the result of forward bias of be and cb.

Re: saturation

neofrkh,
Saturation, by definition, is the condition where the base-emitter and Collector-base junctions are both forward biased. There is no set voltage at which this happens. The be voltage is a function of the base current. If, for example, for a particular base current, the Vbe is 0.5 V, then the device is saturated for a Vcb of less than 0.5V.
Regards,
Kral

Re: saturation

Hi all,

Saturation Region ( and it's counter-part i.e., Cut-Off region) of Transistor are used in Digital Electronic Switching applications....So any fundamental book dealing with the said topic can help you out....

regards,
Sai

Re: saturation

I consulted many books and reached to the following conclusion:

In npn transistor,

‘Saturation region’ is when both the base-emitter (BE) and the base-collector (BC) junction is forward biased.

It occurs only when
V(BE)=0.7 and V(BC) >0 and V(CE) < 0.7

According to the following equations:
V(BC) = V(BE)- V(CE)
As V(BE) =0.7V;
V(BC) = 0.7- V(CE)
So, by the above equation,V(BC) is positive (forward-biased) only when V(CE) is less than 0.7V.

And ‘Saturation point”, V(CE)sat, is that minimum point where DC load line cuts the collector characteristic curve, and at that point maximum Ic(sat) flows, ideally this point should be at V(CE)=0V, but due to thermally generated electrons it is between 0.1V and 0.3V.

So, V(CE) can not go below V(CE)sat, and in some book they also give saturation region ‘a region below V(CE)sat’, i.e between 0<V(CE)<0.3, accordingly this okay as V(CE) b/w 0 to 0.3 : V(BC)>0, and V(CE)<0.7.

Re: saturation

neofrkh,
You are correct in your qualitative definition of saturation. However, as I mentioned in my earlier post, there is no fixed value of Vce where saturation occurs. The base-emitter diode voltage is an exponential function of base current, and therefore is not a fixed voltage. For typical values of bias, it is somewhere around 0.65V, but it varies with the base current. Whatever the Vbe is, satuaration exists when the Vcb is less than this Vbe value.
Regards,
Kral

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