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Topic: PNP and NPN beginner question (Read 1 time) previous topic - next topic

polymorph


However it turns out NPN transistors are about 3 times faster than PNP (same for n-channel over
p-channel FETs) in silicon due to the ~3 times greater mobility of electrons over holes.  So NPN and
n-channel are preferred when there's a choice.  Often you need both (CMOS circuitry for example
uses n-FETs and p-FETs equally).


Phew. I was starting to worry.
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

bmwnomad

Just to add a bit about identifying an NPN or PNP transistor in a schematic quickly without tracing the circuit, look at the arrow in the symbol.  If its "Not Pointing iN", then its an NPN.  If its "Point iN Please", then its a PNP.


MarkT

Also you can remember the arrow represents conventional current flow direction, just as with a diode. and
is on the emitter (which is normally forward biased).
[ I won't respond to messages, use the forum please ]

polymorph


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what is the diff between positive voltages and negative voltages??

Negatives are only used for audio amplifiers ;)


Where did you get that idea? There are loads of things out there that require more than just a positive above common that are not audio. Radio? AC powerlines? Transformers for a variety of purposes, not just audio, power, and RF, either.

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For us digitals, GND is the most negative we deal with.


Someone already flogged this with the example of ECL, but I'll also say that digital electronics must interface with the outside world. And the world is one big "return to zero" full of positives and negatives.

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If you tied all Positive supplies together and call them GND, you have everything else more or less negative.
And had problems using NPN transistors the usual way ;)


NPN bipolar and N channel JFETs and MOSFETs work just fine with a negative power supply with reference to ground. There is really nothing special about attaching the negative end of a battery or power supply to ground/common and the positive to a rail we call Power, it is just convention. Probably based on the aforementioned Benjamin Franklin guess about what charge the particles actually had, and people having an easier time thinking about current being supplied by the Positive end of a battery.
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

nish1013

Quote
Just to add a bit about identifying an NPN or PNP transistor in a schematic quickly without tracing the circuit, look at the arrow in the symbol.  If its "Not Pointing iN", then its an NPN.  If its "Point iN Please", then its a PNP.


awesome !!!  :D

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