Electronic – NGSPICE messing up BJT characteristics

bjtngspicesimulationspice

I'm trying to obtain BJT characteristics in NGSPICE, but for some reason the plots retrace to origin.

* BJT characteristics

RB 1 2 1Meg
RC 4 3 1k
QBJT 3 2 0 BC107B
V1 1 0 dc 12
V2 4 0 dc 10

.model BC107B   NPN(Is=7.049f Xti=3 Eg=1.11 Vaf=59.59 Bf=381.7 Ise=59.74f
+               Ne=1.522 Ikf=3.289 Nk=.5 Xtb=1.5 Br=2.359 Isc=192.9p Nc=1.954
+               Ikr=7.807 Rc=1.427 Cjc=5.38p Mjc=.329 Vjc=.6218 Fc=.5 Cje=11.5p
+               Mje=.2718 Vje=.5 Tr=10n Tf=438p Itf=5.716 Xtf=14.51 Vtf=10)
*       PHILIPS     pid=bc107b  case=TO18
*       91-08-02 dsq

.dc V2 0 10 0.1 V1 1.5 3.5 0.5 

************
.control
run
plot v(4,3)/1k vs v(3) 
.endc
************

.end

How do I resolve this issue?

Best Answer

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.

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Nested loops in ngspice

Your loop is wrong - you are not resetting g_act to g_start in the inner loop. Try this: (I've commented out the alter and op statements, you can add them back in with your circuit)

 *Loop Test
 .CONTROL
 let start_d = 0
 let delta_d = 0.5
 let stop_d = 1.81
 let start_g = -3
 let delta_g = 0.5
 let stop_g = 0.01
 let d_act = start_d
 let g_act = start_g

 while d_act le stop_d
      *alter vd0 dc d_act
     let g_act = start_g
      while g_act < stop_g
         *alter vg0 dc g_act
         *op
         echo run sim with d_act:"$&d_act" and g_act:"$&g_act"
         let g_act = g_act + delta_g
         end
 let d_act = d_act + delta_d
 end
 .ENDC
 .END

Electrical – Convert voltage controlled switch into ngspice

This link here has some info. If your trying to translate models

First make sure they are an equivalent model.

Design a simple test spice file that will test the model with a voltage source.
Test the model that you want to use in a different spice package so you know what the correct result is
Test the SW model and 'play around' with it until you get the same result.

It will take some work, but somebody's got to do it.

Best Answer

Related Solutions

Nested loops in ngspice

Electrical – Convert voltage controlled switch into ngspice

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