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 #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Good choise. And bad choise Good, because its easy. Its preferable. Bad, because its unsafe. A shared heatsink demands isolation. Remeber that you switch the mains there. So bad things are going to happen if you have a big heatsink, that allways just looks so sexy that you want to touch it The Heatsinks will also contribute to some capacitance at the drain if they are not electrically isolated.. i cant forsee the implications of this. it just feels bad might be totally ok. Still i would prefer earth referenced heatsinks. Maybe for the ease of layouting use 2 heatsinks and still put an isolation pad on them? you will know what makes you feel better when the time comes
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Haha, Patrick.. the mosfets dont matter for now The footprint is the same. This sort of stuff happens even on industrial scale in the 1000s.. If you are going to build the thing and debug it, you will have to go for lower voltages anyway. There is no point in soldering it and think it will work right away... so for testing the concept its all right.
The haldbridge has capacitors in series to block DC-Current. Think about it: when the halfbridge is switching its voltage goes from 0 to lets say 10V. Depending on the Dutycycle (assume 50%) the average (=DC) voltage will be 5V. Now.. as for DC an inductor is a short circuit! So without the capacitors you would shortcircuit the average halfbdridge ouptut voltage to whatever potential. If this explaination is too complicated think about it the other way around: what would be the right votlage to connect the Transformer to? You cant connect it to Ground, because the upper switch would charge the inductor to some current, and the lower mosfet will just short circuit the coil... so the current does not decay. The same is with VCC, but with opposite inductor current. The only way it works, if there is periodically +5V and -5V on the inductor..
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Ahh, thanks, yes. Basically the capacitors form a voltage divider. you get half the input voltage. This is basically a virtual ground (as amp builders would call it) so that now real GND is V-- and V++ is still V++.
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Sry hen, the caps do not divide the input voltage. Capacitors are AC-Voltage dividers only.. but placed at the supply (DC) they are just capacitors. You could achieve exactly the same when you place both capacitors in parallel to Ground (or in parallel to VCC). However the series version has some benefits.
You do not get half the input voltage because both caps are equal in size.. you do get half the input voltage because the duty cycle is 50%. If the DutyCyclew wouls be 25% you get only quater the input voltage. Or in a different case, if the capacitors are unequal, you would still get VCC/2 if you had 50% dutycycle.
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.
Need help with current limiting.
The Heatsinks will also contribute to some capacitance at the drain if they are not electrically isolated.. i cant forsee the implications of this. it just feels bad 
For both TO-220 and TO-247. but this circuit only uses TO-220.
