Re: gEDA-user: BC547 vs. 2N3904

[Karel Kulhavy <clock@xxxxxxxxxxxxx>]

On Mon, Oct 30, 2006 at 12:52:15PM +0100, Wojciech Kazubski wrote:
> > Do you like more BC547C for higher frequency applications or 2N3904?
> > I once did a simulation for some Ronja differential limiting amplifier
> > which showed that BC547C is a bit better than 2N3904 because, despite
> > it being lazy, it has higher amplification.
> 
> Yo can also use BF240 (SMD variant BF840) if you want to amplify up to some 
> 50MHz or even BFR91 (SMD=> BFR93) if faster transistors are needed. Those 
> transistors cannot be used for saturated switching. For such case try old 

Does driving the transistor into cutoff but not saturation also count
as saturation switching?

CL<
> 2N2369 or its derivatives (plastic or SMD). But faster the transistor, more 
> likely it oscillates.
> >
> > Is it possible to get rid of oscillating transistors by replacing the
> > hand-soldered airwire with a SMD on a 2-sided PCB with a ground-plane?
> 
> Very recommended.  Use shortest possible connections to ground and try not to 
> cut the ground plane with traces, especially long.
> >
> > What is the major cause of oscillations in high-frequency amplifiers?
> > Inductance of wires?
> 
> If your circuit oscillates well above the operating frequency it is mainly due 
> to inductance of wires plus parasitic capacitances inside the transistor. The 
> input-output capacitance is major cause of instability of resonant apmlifiers 
> (RF or IF) In this case oscillations are at or near operating frequency. 
> Sometimes amplifiers oscillate on LF due to bad supply decoupling.
> >
> Wojciech Kazubski
> 
> 
> _______________________________________________
> geda-user mailing list
> geda-user@xxxxxxxxxxxxxx
> http://www.seul.org/cgi-bin/mailman/listinfo/geda-user


_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user