On Monday 01 September 2008, Jesus Genicio wrote: > I make the change in "is" and ok, the diode led run in 2.46 > volts with 5 volts in Vin but de vce with vin=0 is only the > 2.8 volst.....
> gnucap> tran 0 5 0.2 > #Time v(Vin) v(D1) v(Rc) vce(Q1) > 0. 3.2074f 2.1327 163.09n 2.8673 > .............. > 2.6 5. 2.5594 2.3628 0.077836 > ................. > > Vin=0 => Led off but v(d1)=2.13 Volts and led light. Sorry, > the "is" ok but there are some parameter more that configure > to make that diode run correctly?. > > One reply is that " you need more study of theory of > circuits" :)), please be pacient. Thanks. > > the only way that i found for this, is: > > vin=0, V(d1)=2.13 but ic=163nA and this is off.? Check the current ... You can probe it, but my calculator says I(Rc) = 652 uA. The LED won't light up on that. If you think of it like a resistor, you could substitute a 3.2 giga-ohm resistor for a similar result. Below the knee, a diode is essentially open, so there can be some voltage there with nearly no current. With a little bit of leakage in the transistor, some extra due to the simulator's "GMIN", .. There could easily be some volts across the LED. If you try it on a real circuit, you would get a similar situation, until you hook up the meter. Then all of the voltages change. A typical meter is equivalent to a 10 meg resistor. If all you care about is the LED, it is probably ok as is, but not a good design. You should add a "pull-up" resistor, from the collector of the transistor to the power supply, or in parallel with the LED. I think 100k is a good value. _______________________________________________ Help-gnucap mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-gnucap
