drawing transistor saturation Vbe/Ic curve

Thread Starter

gumof

Joined Jul 22, 2014
3
i got unknown transistor(couple of),
and i need to create spice model of it
-for simulation purposes
how to draw characteristic like that:


how circuit would look like to measure it ?
"..the ratio Ic/Ib = 10" -what that means in practice ??
 

crutschow

Joined Mar 14, 2008
34,452
Creating transistor Spice models from characteristic curves is not easy. The easiest is to find a comparable transistor that has a model.

Ic/Ib = 10 just means the the curve is measured with a base current always equal to 1/10th of the collector current (i.e. the transistor is saturated).

Below is such a plot in LTspice. It doesn't exactly match your posted plot so there obviously is some difference between the LTspice model and the transistor characteristics in the data sheet.

Sat Plot.gif
 
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Thread Starter

gumof

Joined Jul 22, 2014
3
and that means...
...simplifying if i place Rc = 1K, Rb=10K || Rc= 10K, Rb=100K
will be good enough ??
circuit like that:

to plot characteristic like in post#1
or it has to be done with current sources like your attach. ??:
 

crutschow

Joined Mar 14, 2008
34,452
It's better to use current sources to keep the base current exactly 1/10th of the collector current. Note that you have to step both sources simultaneously, not just one.

Why do you want to use voltage sources? Doesn't your simulator have a current source?
 

Thread Starter

gumof

Joined Jul 22, 2014
3
all right, thanks guys.
_obvious that i have to keep ratio :)

have you got any suggestion which current sources to build (or IC ?)
for that purpose (simple, good enough) ??

How about any company/paid service/anybody can grab/capture
transistor characteristic curves by curve tracer device (like B1505A)
or any other solution that provides reliable/accurate measurement ??
 

crutschow

Joined Mar 14, 2008
34,452
Certainly if you have access to a curve-tracer, that should do the measurements.

Otherwise you could simulate a current source with a couple power supplies and two series resistors, one to the transistor base and one to the collector. Add a ammeter in series with each resistor to monitor the currents.
 
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