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 #579
Joined: Mon Mar 12 2007, 09:45AM
Location: Burntwood, Staffs, England
Posts: 46
I have a problem with MOSFETS I am building a singing arc with afly back - I have had one going or two working but mainly the MOSFETSget hot and fail after a few minutes BUT here is what I can not understand : I have Mosfets in a TO220 package , looking at them with the tab away from me I make it Gate Drain Source left to right = signal , V+ V- Ihave new Mosfets and used different types Irf 250 , Irf 530 etc all N chanel I have discharged the Gate and with my finger before soldering the SAME types in parallel But when I attach my 12 v battery to the drain and source leads - with a wound primary coil in series The leads are sshowing a current flow immediately EVEn if I disconnect / have not connected te gate What am I doing wrong - surely if ther is no signal / voltageon teh gate no current should flow via D- S - Plase help I have mad up five or six circuits now over several das and it is driving me bonkers
To clarify : I see the Mosfet lega being just the same position as a N P N transistor - Left = base . middle = colector, right emmittor and the Mosfet is the same left gate = signal middle leg Drain = Posative right source = to ground -chanel Tr.. Have I gotb this right ? Why are my MOsfets conducting with no signal to the ate ???
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
Stick a pulldown resistor between the gate and source to hold the gate off if no proper driver is connected, something like 1k. That will stop you going mad!
The gate is such high impedance it will 'float' on quite easily, or get 'jolted' on (by parasitic capacitances within the mosfet) just by connecting the circuit up.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
JamesH wrote ... ... Why are my MOsfets conducting with no signal to the ate ???
They are hungry.
Avalanche beat me to give the answer. This is a lesson every digital experimenter learns early (I figured it out age of about 12). "Not connected" does not necessarily mean Logic 0, or OFF. In most bipolar logic devices, open inputs are logic High, but not robustly so. For FET inputs, "not connected" means Voltage Defined by Leakage and Recent History. (the picture changes if you connect a voltmeter or oscilloscope to the gate).
See if you can touch the gate input with your finger, and get intermediate amount of drain current as your MOSFET switches at mains frequency. Done carelessly, that experiment can abuse the device under test, by electrostatic discharge.
[edit] Maybe you do have the pin assignments wrong -- there's no universal standard. If any pin is electrically connected to the thermal tab, it's probably the drain terminal. Can you measure the drain-source clamp diode between any two pins? If you have a DMM with a diode-test range, it will require six measurements, in each case with the unused terminal tied to the negative probe (assuming you know it's N-channel device).
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.
Help on MOSFET before I go MAD!!!!!!!!!!!
