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 #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Hi, I'm trying to protect a IC, I would like to limit the volts to 10, but the volts after a voltage divider might reach 100-200volts as quick pulses, with low current.
How would you size the zener, what parameters do you use?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
How much current can the voltage divider source? You need to be able to handle that. How much energy can the pulse deliver after the voltage divider? You need to be able to handle that. What's the requierd operate voltage and damage voltage to the IC. You need the zener specified so that it lies between those in the worst case.
But I don't think I've really told you anything here that isn't obvious.
Another option is a diode to the IC rail, as long as the capacitiance on the IC rail is sufficient to handle the charge delivered by the pulse from the voltage divider.
It's also good practice to put a series resistor after the clamping diode before the IC input pin.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Is the zener measured in watts, or the amount of resistance the zener has, sorry ambiquious question, can I just put a couple in parallel and as long as the current from the source be handled or diverted, it will stop the voltage raising? The IC can handle 15volt(maybe 18 max) What do you mean by diode on the IC rail, in parallel or in series? Is the resistor after the zener to limit the current in-case the zener changes with something?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
I think you ought to start by looking at a zener diode data sheet.
Its disspiation will be measured in watts. Its accuracy together with its slope resitance will tell you whether you can parallel them, I suspect the answer is probably not.
I said diode 'to' the IC rail, not 'on'. The concept is that instead of an X volt zener to ground to clamp a signal to x volts above ground, you use a silicon diode to the IC VCC rail to clamp the signal to VCC + 0.6v *as long* as the rail can sink the current that would flow to it. If it's a short pulse, then a big cap should be sufificnet.
A resistor between your clamping device and your damageable pin reduces the current that can flow into the node in the event of a transient spike on the clamp, or in the case of a diode and expected slight over-voltage. Another way to look at that is that the series resitor and the IC's internal input substrate diode do the 'protecting', as long as the voltage on the resistor and so the current is limited to something very reasonable, which allows you more freedom in specifying the clamp 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.
How do you size a ziner diode
