From: email@example.com (carltons)
Subject: Re: type of NPN transistor for minimul voltage drop C to E
References: <6jzD9.165153$MGm1.firstname.lastname@example.org> <email@example.com>
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Sat, 23 Nov 2002 15:20:35 GMT
Date: Sat, 23 Nov 2002 15:20:36 GMT
In article , Winfield Hill
> John S. Dyson firstname.lastname@example.org wrote...
> >> Brill Pappin wrote:
> >>> Any ideas an what type of transistor I should look at to get
> >>> the minimum voltage drop when on (NPN)?
A whole lot of other stuff in between with no one asking the question of:
"How low a voltage?". If the OP needs zero or close to it, then use a
relay. Is switching speed an issue? Is voltage polarity? What is the
budget for a device? What resources are available to the OP as far as
obtaining the parts, etc. ? What is the space available? .... on and on
and on. Solutions are provided and the problem has not even been defined.
BTW, at saturation, the base collector and base emitter are both forward
biased. Unless this forward bias voltage is the same for both junctions,
you won't have zero volts from collector to emitter on the bipolar
switch. Ithink that you would have to have the same doping levels in both
the emitter and the collector to get this even close and then you would
have to include the IR losses due to wirebonds, forward current, etc.
What this has to do with anything in this discussion I will leave to
others to mangle. I mean, manage. Flamers: yes you could change the
forward biases and increase or decrease IR and get the same voltage, but
don't get ridiculous.
The reverse-beta numbers are very nice to know, they're not in
> the data sheet; Thanks John, for these numbers!
> - Win
You're right. The reverse betas are not usually provided, but only a
manager would hook up a transistor in reverse. ;-)