Re: gEDA-user: Hfe Gain

["Phil Taylor" <phil@xxxxxxxxxxxxxxxxxxxxxxxx>]

Marc,

There's nothing that sez that if you have two txstors that match at 1mA DC
that they'll match (even closely) at 2 amps.  hfe is nonlinear with respect to
just about all parameters: Vce, temperature, I, etc.

Can you build a test rig and measure parts at the actual currents, temps, and
voltages you'll be using in your final ckt?

Also, depending on how close a match you want to get, you may need a good
number of parts to choose from ($$$).  If you can get away with sacrificing
some current, you can ballast the txstors with emitter resistors, to make some
of the mismatching go away.

Phil


Marc Price <mark.price13@xxxxxxxxxxxx> wrote:

> Seen as the Tesla coil mailing list is down i thought i might ask this 
> question here
> 
> i tested 2 x 2n3055 transistors and i read that you need to match the 2 
> but what
> i dont know is, do i need to have them exact or just close.
> 
> transistor 1 gain Hfe = 123
> transistor 2 gain Hfe = 194
> 
> Any ideas
> 
> Marc :-P
>