Monday, 7 October 2019

current - A confusion about the formula for transistor Vbe Ic characterisitcs


Below is NPN BJT transistor Vbe Ic characteristics and the formula:


enter image description here


Many texts approximate this equation as:



Ic = Is*e^(Vbe/Ut)



and following this they say when Vbe=0, Ic becomes equal to Is.


But in real the equation is:




Ic = Is*(e^(Vbe/Ut) - 1)



And in this case when Vbe is set to zero Ic becomes zero.


So what is Is? Is it the Ic current when Vbe is set to zero volts? If so, why the real formula cannot predict it correctly? What really happens when Vbe is set to zero in a laboratory?




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