# drawing transistor saturation Vbe/Ic curve

Discussion in 'General Electronics Chat' started by gumof, Jul 22, 2014.

1. ### gumof Thread Starter New Member

Jul 22, 2014
3
0
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 ??

2. ### crutschow Expert

Mar 14, 2008
12,991
3,227
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.

Last edited: Jul 22, 2014
3. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,383
495
Ic/Ib=10
Ic=10*Ib
When:
Ib=1 mA, Ic=10 mA
Ib=2 mA, Ic=20 mA
Ib=3 mA, Ic=30 mA
etc.

4. ### crutschow Expert

Mar 14, 2008
12,991
3,227
See the sim I added in my previous post.

5. ### gumof Thread Starter New Member

Jul 22, 2014
3
0
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. ??:

6. ### crutschow Expert

Mar 14, 2008
12,991
3,227
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?

7. ### gumof Thread Starter New Member

Jul 22, 2014
3
0
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 ??

8. ### crutschow Expert

Mar 14, 2008
12,991
3,227
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.