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 #267
Joined: Mon Feb 27 2006, 09:44PM
Location:
Posts: 46
EDY19 wrote ...
There- Here is the new plan for a Half Bridge with a voltage doubler using 600V 30A diodes (which will be on a heatsink) and 2460uf per "leg." The Mosfets will be on a terminal strip, with leads bent 90 degrees so the mosfets are oriented vertically. 15V zener diodes will be across the mosfets too, I'm just going to put them where i can fit them after I build it
What is the purpose of the 6uF capacitor and the 10 Ohm resistors?
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
magnetomotive:
If you want to instantaneously open a switch and expect current to flow, you need to provide a source for it to come from. Foil or MKT capacitors tend to have a lower inductance and lower internal resistance than electrolytics. Therefore, the capacitors provide the current needed right on the switching transition -- the power supply or other smoothing caps can then take over after that, if that makes any sense.
The 10-ohm resistors are connected to the gates of the MOSFETs. Inductance of the gate-driver circuit, combined with the input capacitance of the MOSFET, can form a resonant circuit. On each switching cycle, the voltage on the MOSFET can overshoot and oscillate (imagine a decaying sinewave).
Because this oscillation might even be strong enough to let the MOSFET fall out of saturation, gate resistors are used to slow the switching time, and to lower the Q of the system. This means voltage spikes / oscillations have less magnitude, and less effect on the switch (and more importantly, the current flowing through it).
Registered Member #180
Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187
The electrolytic capacitors aren't "fast" enough, because they have a higher inductance and resistance current cannot flow as fast out of them. The smaller capacitance( 6uf) capacitor, is the opposite. It has low inductance and can supply alot of current very quickly, it drains really fast because of it's small size but by that time the big electrolytic caps can kick in.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I'm not sure how much use a 6 uF capacitor, no matter how high quality, will be I've no idea what frequency you intend to operate at, for example 250 kHz at 250 kHz the impedance of a 6 uF capacitor is just over 0.1 Ohm I have electrolytic (inverter grade) capacitors that have an effective impedance (capacitance, resistance, inductance) of less than 0.05 Ohms from 10 kHz to 1 MHz and only 0.006 Ohms at 100 kHz. So to save space and money you could just use electrolytics.
Check the specifications for your electrolytics fist though.
In any case the addition of the 6 uF capacitor will do no harm.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
I've no idea what frequency you intend to operate at, for example 250 kHz at 250 kHz the impedance of a 6 uF capacitor is just over 0.1 Ohm
Consider the speed of the switching may have content in the few MHz range. In this case, the 6uF is rather low impedance, and the lytics look worse because what ESL they do have looks pretty big now. But, i might agree that simply using high quality lytics for inverter use is probably enough. Most lytics scrounged from old electronics are probably NOT inverter grade and should be bypassed with a film cap. Its the same deal as logic design where .1uF caps are placed near each IC.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I think it's better without the film cap because; the actual desired output current (SSTC or DRSSTC) is composed of repetitive half-sinewaves at the output frequency switching transient currents and 3rd 5th 7th harmonics of the output frequency are undesirable anyway.
I have no data to support this, just a vague opinion.
I don't have your experience so just take it as a thought experiment - not an argument
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
I think you are mostly right, Sulaiman, but keep in mind that the current is not always soft switched. In that case, there is high di/dt across the device, so you do have high frequency harmonics produced. There is no way around this, and without the snubber cap there will be a voltage transient produced by the inductance of the half-bridge loop wiring and the di/dt. On the other hand, i did notice on my large IGBT h-bridge running many hundred amps, that the film caps didnt help at all. I used high quality (and very large) inverter grade electrolytic capacitors on the bridge and had a laminated bus structure for minimal inductance.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
When I was making my DRSSTC, I found that certain values of film capacitor would resonate with the stray inductances of the bus structure at harmonics of the operating frequency. The 1uF film caps that I tried first turned out to be exactly the wrong value, tuning the resonance to the second harmonic. With soft switching, the majority of the ripple current is, indeed, at the second harmonic. So the result was a huge mess, several times worse than without any film caps at all.
But with no film caps, there were nasty spikes, due to too much ESL and, I suppose, imperfect soft switching. (or stray capacitances, tail currents or whatever.) I experimented with different brands and values of film capacitor, and eventually got it looking good.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
I just found that the SCR that I have would work wonderfully (I think) for the two diodes in the doubler circuit-this way I can turn on the doubler with a small voltage instead of using a large switch and having the contacts burn out periodically from the near short circuit of the capacitors across them. My SCR is rated at 90A RMS and 1950A Itsm, so this should be fine, right? Or I suppose I could make the soft start circuit shown here: And in that case, +V would be taken after a rectifier on the hot 120V line, and the drain of that mosfet would be where the neutral terminal would connect to the doubler. Advantages/disadvantages to either? I'll be starting a project thread soon
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.