If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
IamSmooth wrote ...
Why can't an NPN be used instead?
Well, if you wish to increase regulator's current capability while keeping it's exact voltage, you need to use a PNP transistor this way.
You could use an NPN like 2N3055 as a voltage follower, by connecting the base to the regulator output and passing the supply through it. This will allow for lots of current but will add the Vbe to the output voltage, and regulation will depend on characteristics of the transistor (very poor in case of 2N3055).
Other than that, you could build the whole regulator yourself, using an error amplifier and a reference source. Look at this page for some more advanced designs:
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
But why won't it work with an NPN? If the collector is connected to the supply and the emitter to the output of the regulator, why won't it boost the current when the base is on?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I had to post again to add the picture. The question is what is the flaw with using an NPN instead of the PNP, and not what other solutions are available. I would think that the base gets a voltage allowing current to flow through the NPN as needed. So, what is wrong with this and why is the pNP the right choice?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
If connected like in your picture, the voltage emmiter will attempt to follow whatever the voltage is on the base - and hence you'll get output voltage nearly as high as your Vin, with little or no load - hence no regulation at all with this circuit.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
You can swap emitter and collector on a bipolar transistor, but it will work poorly. Forget trying that.
A pnp transistor has the base negative .6v (silicon) with respect to the emitter for the transitor to conduct, the emitter >>.6v positive with respect to the collector. A npn transistor is the opposite, the base must be .6v positive with repect to the emitter for the transistor to turn on, the collector is >>.6v positive with respect to the emitter. One decides to use a pnp or npn based upon this.
One way to model these in your mind is the difference between the base and emitter voltages is .6v. For a pnp, the base is .6v lower than the emitter, for a npn the base is .6v higher than the emitter, assuming there is not a lot of current limitation on the collector.
An emitter follower circuit is basically based upon that difference, the emitter voltage follows the base voltage with a delta of .6v once again so long as the collector current is not too limited (you need some base current limiting with resistors otherwise you'll blow out the transistor).
The bipolar transistor is a current amplifier, the transistor beta or Hfe is the collector-to-emitter current divided by the base-to-emitter current.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
outboard pass transistor
