When I try to prove that Vce for saturation is below .2V and I take npn transistor I simply consider emitter to be at 0V and thus base emitter junction being forward biased base gets a voltage of (.7 V + x) where x is positive constant then to forward bias base collector junction I will have to have forward Voltage of at least .8V so collector voltage becomes .7v+x-.8v+z where z is a positive constant and x is greater then z so collector voltage should become -.1V+(x+z) thus What I am getting is Vce should be greater then -.1V When follow same procedure for PNP I get Vce greater then .1V which is totally in coherent with <.2V What I am doing wrong please help
**if you want to estimate Vce with a part number, it is helpful to use Vce(sat) @ Ic=10*Ib then go from there.
The hFE declines to about 10% of the max linear value at the rated Vce(sat). The Vce(sat)/Ic = Rce is a computed term that is often useful to know for a switch characteristic when choosing a device or a collector load. Rce decreases with increasing base current and collector current when saturated.
The actual Vbe depends on these values and could be 0.6V if Ic is 1mA and Vce=0.06V.
You can also see Rce (typ) @ 25'C at full saturation with Ic/Ib=10 for this part;
Rce=60 Ohms @ Ic=1 mA Vce= 60mV.
Rce= 5 Ohms @ Ic=10 mA Vce= 50mV.
Rce= 1.3 Ohms @ 100mA Vce = 130mV.
Rce = 0.8 Ohms @ 500 mA Vce= 400mV.
This trend is common but the ohmic scale reduces for higher power switching transistors.
2N4401 example General Purpose Small signal TO92
When operating in the linear region the collector is a high impedance current sink.