You can use NPN transistors for all applications using PNP transistors, right?? What is then the advantage of using PNP transistors versus NPN? Or are there situations when only the PNP can work, what for instance?
log
PNP's are like inverted inputs, I have a NPN and PNP on a amplifier I built, each pair of transistors are feed from the same input line, so as one turns on , the other turns off..... If it was only NPN then I would need a additional transistor or gate to invert the signal, the would also mean one transistor would be a fraction behind in switching than the other, increases circuit cost and footprint also..
I would like to use all NPN, there are a lot more options than PNP, finding high power "common" PNP is somewhat hard work.... getting specs to match NPN & PNP can be hard also.
if you replaced a PNP with a NPN you would blow up whatever you put in it. Also note that the connections may need to be swapped around also... they use PNP for rather a lot of reasons ;-)
persoanlly I don't like them, but oh well :) Chris
>No, if you mean you can just replace an NPN with a PNP. It's possible to have an all NPN solution sometimes, but there are other times when only an NPN (or a P-channel FET) will do.
Well, if you don't much care about switching time differences (PNPs are typically slower for good physical reasons) and other specs, a circuit may be much simpler using a PNP.
As an example, in power sensitive equipment, some parts are only powered up when necessary. If it is necessary to power the high side, then using an NPN would require an extra power supply *above* the power you are switching, meaning extra circuitry and probably not making it worthwhile because of the extra inefficiencies of the new supply (plus all the associated extra components)
If you wanted a simple NPN solution, then you would have to switch the low side, meaning all pins of the device to be powered would be at V+ while 'off'. In this situation, any devices connected to it would have to maintain the connected pins at V+. This is often simply not possible, especially if going across power domains.
Another example if the classic push-pull amplifier. This inherently symmetrical circuit requires an NPN and a PNP. There are tricks to use NPNs here, but it would still require a PNP or two to make it work properly.
There are myriad other examples, of course
Cheers
PeteS
Wrong!
For example if you want a constant current sink you'd use an npn. If you want constant current source you'd use pnp. Push-pull amplifier stage would use npn and pnp pair.
You need to read some more!
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Malcolm
Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK ( snipped-for-privacy@fullcircuit.com, snipped-for-privacy@fullcircuit.co.uk or snipped-for-privacy@iee.org). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see:
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You must be right. The manufacturers are just conning people by offering PNP's and the 'engineers' that are stupidly conned by these manufacturers into using these useless devices obviously don't know as much as yourself about designing with electronics.
Spread the word before it is too late.
Please close the door after you
these
For that matter, why must we use electrons? You can just as well use positrons in all applications, and stop worrying about "the current flows THIS way, so the charge carriers are flowing THAT way". With positrons, current and charge travel in the same direction, making electronics -- or should I say POSitronics? -- much much easier to understand!
Mark
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