--- Spehro Pefhany <speff@interlog.com> wrote:

> At 07:44 PM 10/12/2005 -0700, you wrote:
> 
> >Unfortunately in real life I measure the gains
> quite
> >differently. The gains is not 100 for bc338 but in
> a
> >magnitude of 20?
> 
> The data sheet gives min/max figures for hFE at
> certain Vce and collector
> current and temperature.
> 
> hFE is quite dependent on collector current-- low at
> very low collector
> current, rising to a peak at some particular
> current, and lower again
> for high current. The two transistors you reference
> have quite different
> maximum current ratings as well, chances are the
> higher rated one has its
> peak gain at a higher collector current.
> 
> If you're measuring only 20 for hFE at a reasonable
> collector current,
> you might be doing something wrong. Remember that
> the hFE is measured
> at a Vce of 1V. If you allow the transistor to
> saturate (Vce < Vbe)
> then you enter the realm of "forced beta", where the
> current is
> limited by the load, not by the transistor.

  from this datasheet

http://www.fairchildsemi.com/ds/2N/2N3904.pdf

  what is the saturation voltage for Vce and Vbe. It
looks like the saturation for Vce is 0.2V?? While Vbe
is 0.85V. I am confused on this part(saturation).

Regards,
John

> 
> A forced beta (Ic/Ib) of 10-20 is normal for
> saturated switching designs.
> 
> Best regards,
> 
> Spehro Pefhany --"it's the network..."           
> "The Journey is the reward"
> speff@interlog.com             Info for
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