At 08:57 AM 1/9/2006 -0500, you wrote:
>Spehro Pefhany wrote:
> > One obvious (?) purpose would be to have very low Vce (perhaps in the
> > single or low-double-digit mV range), and to avoid the need for a low
> > Rds(on) small-signal p-channel MOSFET.
>
>But that's pretty much true as long as the transistor is saturated.  You
>don't get much more by oversaturating the transistor.

Errr... I don't think so!

Quick test with a jellybean TO-92 PNP transistor shows a 3:1 improvement
going from forced beta of 5 to forced beta of 0.5 (11mV to 3.2mV) @ 0.5mA IC.
That's a very respectable 6 ohms equivalent Rds(on)- similar to a much
more expensive BSS84, and using a 8550 wot is so common you can find them
stuck into the bottom of your shoe from a short walk around Taipei or
Shenzhen. Also it will not be as temperature-sensitive. At 50 forced beta
there's a whopping 57mV of drop, (still well saturated of course).

>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
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


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