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 #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
The 7414 and/or 4069 hex inverter chips can both be used with a single capacitor and resistor to get a 50% duty cycle up to a few hundreds of KiloHertz. The oscillator tolerance will be as tight as your component tolerances.
the TL494 likewise can be used fairly easily to get a nice clean, stable square wave, but its somewhat limited in its operational frequency.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Dave Marshall wrote ...
The 7414 and/or 4069 hex inverter chips can both be used with a single capacitor and resistor to get a 50% duty cycle up to a few hundreds of KiloHertz. The oscillator tolerance will be as tight as your component tolerances.
yeah, I tried that, a 74HC14 oscillator, but it does not produce exactly 50% duty, in my case it was off by up to 10-20%
Registered Member #84
Joined: Thu Feb 09 2006, 01:06PM
Location: Dallas, TX
Posts: 47
Pass any of your square wave sources through a low pass (or better yet a bandpass) filter and turn it into a sine wave. It will then have a 50/50 duty cycle. Then, you can use a fast comparator to square it back up again. Or, you can possibly use it just as it is. I use sine waves for high speed ADC clocks all the time and it works great.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
I think that Wave Rider's idea of having your oscillator running at twice the desired frequency then dividing it by two - is the most reliable way of producing a 50:50 output..
I note Sulaiman's endorsement of Waverider's idea, and concur that is the only practical way of doing it. I hesitate to use the phrase "no-brainer", but it really is. For the cost of a 74HC74 (10 per $ or £) you get exactly* 50% duty cycle, out of the box, without trimming or tuning, regardless of frequency, temperature or supply drifts etc etc. Or a 4047, which is an oscillator and /2 in the same box.
* assuming adequate isolation between the output of the divide by 2 and the oscillator, it must not get FM'd by the output state * within the matching of the propagation, output L to H and output H to L slew times, and drive strengths * with Q and Q bar matching if you want complementary outputs
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I bought the 4047 today, I did not connect it so far but according to the data sheet it should output exactly 50% duty cycle and requies 2 external components (resistor and a cap).
Registered Member #514
Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295
I love the 4047... I use them as a replacement for 555s. So easy to get a stable 50% duty and a wide frequency range (0.1Hz - MHz). The output is a really nice square wave through the frequency range.
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.
50/50 duty cycle oscillator
