On Thursday 09 August 2007, Bob Paddock wrote: > What do any of the circuit simulators give for this > configuration: > > With the emitter of a 2N3904 or 2N2222 hooked to +12V through > a 1k resistors, and the base grounded, what is the voltage > measured from the base to the collector? The collector is > open. > > Any (NG)Spice/GNUCap etc. users out there that can try it?
It doesn't simulate correctly. gnucap> build >q1 1 0 2 n >re 2 3 1k >vb 3 0 dc 12 >.model n npn > gnucap> print op v(nodes) vbe(q1) vce(q1) gnucap> op # v(1) v(2) v(3) vbe(q1) vce(q1) 27. 3.0568 12. 12. -12. -8.9432 gnucap> The BE junction is reverse biased, so it will act like a zener in the real circuit, about 5 volts. The simulation model does not include this effect, so Vbe simulates as -12. The collector voltage gets messed up by "gmin", which adds strays to avoid a singular matrix. I am not sure what it would be on a real circuit. It would be between 0 and Ve. What gnucap says depends on settings like gmin. If you build it, and measure it, the meter will influence the reading. Let's add the meter resistance..... gnucap> build >rmeter 1 0 10meg > gnucap> op # v(1) v(2) v(3) vbe(q1) vce(q1) 27. 119.99u 12. 12. -12. -12. gnucap> Gnucap and Spice use the same model, so the result should be the same. It doesn't model BE breakdown. Models make assumptions about how they will be used. If you go outside the valid region, you get bad results. _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user