I'm not asking the definition, but wondering how do the manufacturers measure this parameter's quantity in a lab for instance? For example for Ic Vce characteristics they keep Ib constant and they obtain plots. What is the procedure for obtaining reverse saturation current of a BJT?
Electronic – How is reverse saturation current of a BJT measured empirically
bjtcurrent measurementsaturation
Related Solutions
I don't know if you absolutely need to use NGSPICE, but with LTspice you would have no problems (see below).
Note: LTspice is completely free and has no limitations (no max number of parts, for example, like the free crippled version of other commercial simulators). It is one of the best simulators around (it is used by Linear Technology for in-house simulations - it is no toy). The program is lightweight (~40MB, IIRC), works under Windows and was developed to be run in Linux under WINE. The license is very liberal: you can also use it for commercial purposes, as long as you are not a competitor of Linear Technology (you do not work for a chip manufacturer, do you? :-).
The following snapshot illustrates the point. I just created an empty schematic and copied the essential part of your netlist into a spice directive in LTspice and plotted Ic after running the simulation. Here is the result:
Of course you could redraw the schematic from scratch, if you needed that, but if you only need the curves that is as easy as it gets.
But again at the same time "Vce under 0.2V" means there is saturation which means Ic must be maximum
The "theory" is just a "rule of thumb" when turning a BJT on to act like a switch. The current that flows is still dependent on base current and collector voltage: -
Once the collector voltage has lowered beyond a point the BJT leaves the "active" region and enters saturation where it is "like" a base-current-controlled variable resistor. See the different rising slopes extending from the origin - if you approximated these to straight lines each has a V/I ratio just like in a MOSFET: -
Of course it can be really confusing the way that MOSFET's saturation region IS NOT the BJT's saturation region but the reason is clear if you consider that for a BJT it is saturation of the base whereas in a MOSFET (or JFET) it is saturation of the DS channel - two totally alien effects but called the same thing.
EDITED SECTION
I've added this because some internet pictures of a BJT's operating characteristic are incorrect. See below at an incorrect diagram of the BJT in saturation: -
There is NOT one line representing all base currents - each base current graph is individual and not "merged" as per the incorrect picture above.
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Best Answer
Ies in this case is Is: Reverse Saturation Current. When they measure it, they just take several different current readings for several different Base Emitter voltages. They also do this at a "constant" temperature, or they use a cold junction reference to actively measure the temperature. Solve for the unknown. (Note: "Ies" = emitter saturation current, and this is a first order approximation) You could put the base-emitter into reverse bias, but you'd need to be very careful to not destroy the device as Vebo is generally around 5V or less! Where as the first technique has much more tolerance for not destroying your BJT that you might want to use.
Edit: A more precise answer due to some ambiguity of the question.
Where
Solve for as many of these as you feel like to find Is.