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[DPRG] Please Clarify when to use npn or pnp transistors (fwd)

Subject: [DPRG] Please Clarify when to use npn or pnp transistors (fwd)
From: Robert L. Jordan rljordan at airmail.net
Date: Wed Jul 11 14:33:16 CDT 2001

Rich,

I have an opinion but not much knowledge.
I use NPN to switch Positive ("source DC")
The collector is connected to +DC

I use PNP to switch Negative (Ground)("Sink power")
The collector is connected to -DC (gorund, common)

In an HBridge you can use "P Channel Mosefts" to switch Positive 
and "N Channel Mosfets" to switch ground. The P channel requires a 
voltage of about 7 volts above the source voltage to turn it on. (I 
think) You can use N channel Mosfets on the positive side too, but 
I'm not sure the pros and cons.

I hope to hear better answers to your question from others! 

Bob Jordan

Eric Yundt <eric at facetcorp.com> said:

> DPRG,
> 
> Anyone up for helping Rich?  Jim is no longer on the DPRG list
> and doesn't receive email sent to the "dprg.org" address.
> 
> Rich DeMartile wrote:
> > From: "Rich DeMartile" <rich_demartile at prodigy.net>
> > To: <jbrown at dprg.org>
> > Subject: Please Clarify when to use npn or pnp transistors
> > Date: Wed, 11 Jul 2001 01:16:30 -0700
> > 
> > Hello Jim,
> >     I'm new to this stuff.  I've studied solid state electronics 
for the
> > last couple months, built a solar tracking device that works for 
my
> > first project, and have a basic understanding of transistor 
usage.  What
> > I'd like to get cleared up is...when do you use pnp versus npn
> > transistors, mosfets etc.  I find lots of information regarding 
hole
> > flow versus electron flow, and I notice that sometimes one is 
used over
> > the other, but never why.  Looking at your page on H-bridge 
theory I
> > finally got my first clue to why pnp is used for ...(sourcing 
power?).
> > Could you please spend the time to explain to a layman what's the 
time
> > to use one type over another, and maybe some real life examples.  
I'm
> > starting to think that where the load is in relationship to the
> > transistor in a circuit dictates what type you would use.
> >     My lack of understanding in this area is preventing me from 
moving
> > forward into more exotic control schemes.  I've been limited to 
using
> > relays so far and they work just fine but...
> >     Anyway, I can tell you know about these things by how well 
you write
> > and explain things.  You can check out my solar tracker at the 
web site
> > I just started if you like.
> > 
> > http://pages.prodigy.net/rich_demartile/
> > 
> > Thanks in advance,
> > Rich DeMartile
> > rich_demartile at prodigy.net
> > 
> 
> --
> Eric
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> 



-- 
Robert L. Jordan (Bob)
www.robotfun.com



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