On 5/12/06, Rich Graziano <rgrazia1@rochester.rr.com> wrote:
> You need a high beta.

Arguable. Beta or h21 defines the behaviour of the transistor in the
linear mode and not in the switching mode. This is the reason why a
switching transistor has usually a low measured beta. I've seen 2N2222
with beta between 10 and 30 working perfect, or this is a standard
value for beta for high power transistors running in linear mode at IC
>= 3A.
The Vbe voltage value (or the Ib current) requested for a switching
device is defined only by the manufacturing technology and by the
junction temperature.

Vasile

>
> ----- Original Message -----
> From: "Spehro Pefhany" <speff@interlog.com>
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> Sent: Friday, May 12, 2006 10:13 AM
> Subject: Re: [EE]: NPN Transistor with low switch on voltage?
>
>
> > At 02:29 PM 5/12/2006 +0100, you wrote:
> >>Hi all
> >>
> >>I'm finding it hard to search transistors by Vbe ON voltage,
> >>basically I need a NPN with a fairly high sensitivity, ie saturates
> >>at a small voltage on the base.
> >>
> >>Any ideas, nothing to specialised though, just cheap and fairly
> >>available.
> >>
> >>Thanks
> >>Ed
> >
> > That's because it's pretty much the same for *any* silicon BJT
> > at reasonable base currents (around 0.7V at room temperature).
> >
> >>Best regards,
> >
> > Spehro Pefhany --"it's the network..."            "The Journey is the
> > reward"
> > speff@interlog.com             Info for manufacturers:
> > http://www.trexon.com
> > Embedded software/hardware/analog  Info for designers:
> > http://www.speff.com
> > ->>Test equipment, parts OLED displys
> > http://search.ebay.com/_W0QQsassZspeff
> >
> >
> > --
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