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 #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
EDIT: change thread title to reflect performance achieved.
I want to bodge an AT PC power supply to have a variable output voltage up to 30V (don't really care where the bottom end is). This is for powering my Titch SSTC.
Assuming that the AT has some similarities with this ATX supply and this AT supply in terms of the output and control stage then I should be able to find my way around it. Obvious differences are that there is no 5V standby and no 3V3 supply on the AT.
I intend to
Disconnect all rails except the 12V from the transformer
Uprate the capacitor and diode on the output
Disconnect overvoltage circuit (if any)
Locate and alter the feedback components to get maximum duty cycle on the transformer input (with suitable load on output) to figure out how many turns I need to add to the transformer to get my maximum output voltage
Add appropriate number of turns
Add variable resistor in feedback circuit to adjust output
Things to be concerned about
Stability could be affected
Saturation of transformer needs to be avoided
Fitting more turns ont already crowded transformer could be difficult - perhaps remove existing secondary if possible?
Any suggestions or tips most welcome, or if there is anything obvious that I have overlooked then please let me know.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hi James
The 12V rail on these things comes from a centre tapped winding rectified by a two-diode full wave rectifier. (Usually in a TO220 package on the output side heatsink: the TO247 is the 5V rectifier.) If you added another two diodes to make a bridge rectifier, got rid of all the 5V rectifier bits, and disconnected the centre tap then the same winding would want to output 24V.
**edit** sorry, that is the standard circuit for an ATX, I can't remember how the AT ones worked. There were all different circuits.
There's a thread on the old board that documents how I "overclocked" a 5V SMPS to 13.8V with some help from Richie Burnett. This might give you some pointers on how to get started.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Wee. Tradition continues...
Old threads are about ATX modding, though; AT's are almost extinct today.. I don't remember those electronics anymore
- woops, steve already got it.
I may be wrong, but I think that highest voltage that can be 'hacked' from single 12V rail was some 25V with ATX. I don't know if AT will get any better. -5V could probably be used but windings are almost surely too tiny..
About the transformers, I found it to be a very frustrating thing, unless you are very lucky.
Cores are stuck to their forms with some hardcore epoxy and is practically impossible to get apart in one piece. Mess isn't closely worth even buying a new transformer.
Best thing I can think off is using a real fullwave rectifier t double the output voltage at start.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
If I'm not mistaken, the 12V output from the xfmr also supplies power to the pwm chip (494), if you up this voltage to 30V, isn't it going to x-plod in your face?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
jmartis wrote ...
If I'm not mistaken, the 12V output from the xfmr also supplies power to the pwm chip (494), if you up this voltage to 30V, isn't it going to x-plod in your face?
494 works well up to 40V, LM393 and 339 up to 36 volts, and judging atx already acheiving to close voltages I don't think that would be a problem.
I'm although, confused with one thing; how TL hets it's startup power? It looks like transformer T2 does it, but in a rather wierd way (in series with main transformer?) Is thew supply ''kick-start'', or is that transformer actually same core as gate drive transformer? Steve?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hi Firkragg
In the ATX power supply schem posted by thedatastream, the 5V standby supply is a separate converter that runs all the time the PC is plugged in. It supplies just enough power to the TL494 to get it started. Once the main power supply is turned on, the +12V output powers the TL494 and driver transistors, through the diode marked D in the schem.
I have no idea how the AT schematic he posted works. I bet it has something to do with the mysterious point A. T2 in that circuit is a current transformer to operate the current limiter.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I have no idea how the AT schematic he posted works. I bet it has something to do with the mysterious point A. T2 in that circuit is a current transformer to operate the current limiter.
AT thingie was what I asked about.. never mind.
Datastream: ATX'-es are dirt cheap today, and if this thing starts sucking, it may be just easier to buy a new 350W supply for $10 and mod it
You can also series them for more power, but low voltage grounds of all except one supply must be floated.
Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
Hi folks, thanks for all the responses
I wonder if the AT engages in a bit of self oscillation to get enough energy through the winding to start up the TL494 (although a quick glance at the circuit doesn't reveal an obvious method).
Reasons for sticking with using an AT supply rather than buying an ATX are:
I've got two that were donated for free
They are a bit less complicated inside so I've got more chance of finding the correct components easily
Also, I'd prefer not to series the supplies, as I want a single ATX shaped box as the base of the coil - two boxes would be out of proportion and would mess up me feng shui like.
Putting the cores in a pan of boiling water, or perhas in the vacuum oven at work should allow me to separate them OK - should I need to that is. If the secondary is on the outside, I may be able to get away with just unwrapping the layers without dissasembling the core.
UVLO on the TL494 is 7V max, so if I make the bottom end of the adjust range = 8V and stick a heatsunk 7812 regulator between my adjustable output and the TL494 supply then that should be good enough. Too much voltage will affect the current being driven into the main bipolar transistor bases - I don't want to fry the gate drive circuit components.
I'll open up the power supply this lunchtime, have a look inside and let you know how I get on.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Putting the cores in a pan of boiling water, or perhas in the vacuum oven at work should allow me to separate them OK - should I need to that is. If the secondary is on the outside, I may be able to get away with just unwrapping the layers without dissasembling the core.
There is apsolutely no chance you are going to boil the cores off. The temperature needed for epoxy to melt was some 400C or so, with hot air gun. I completely charred the plastic form, and core ended broken in several places due to massive overheating.
To get 30V, as already suggested, you don't need to do anything with the transformer; using a full 4-diode bridge will give you 24V output wich I'm pretty sure for can be boosted to 30V:
You can then use one branch to provide power to supply's electronics without frying it.
This way you could get 50V out of most ATX supplies; you are probably the first one to do the same with AT.
From the moddng side, AT's arent any different than ATX, complexity isn't a factor there. ATX mods are already done and verified many times.
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.