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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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vladosh
Joined: Aug 02, 2010 Posts: 659 Location: macedonia
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Posted: Thu Oct 27, 2011 2:09 pm Post subject:
Secondary. |
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Thanks for the Doc. its a nice circuit & from T.Henry. I have his 8038 linear vco breadboarded and designed a stripboard version..... very nice...
So can I use this transformer to get +/- 12 V using the pink purple and white wire outputs using the right regulators??????
I've set up the rectifier part of the Thomas Henry PSU circuit using 4002's and the output gives a steady 13.6 V AC. Is this enough for +/-12V?? |
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
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Posted: Fri Oct 28, 2011 12:46 am Post subject:
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No,
Unless you can find a pair of wires which have 24VAC across them, and one which is in the middle, you won't be able to get +/-12DC out of this transformer. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Posted: Fri Oct 28, 2011 2:06 am Post subject:
transformers |
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Thanks again, krunkus.
so i could use it for the 5v i guess.
I ll have a look at buying one that puts out the right amount.
VERY GOOD Sah! |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
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Posted: Fri Oct 28, 2011 4:59 am Post subject:
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It'll give you +/-12, but only at 120mA per rail.
And regulating the 18-0-18 down to 12-0-12 DC is a bit of overkill really.
I'd go for a 15-0-15 if you can find it, with no other outputs. It will no doubt be able to deliver 1A per rail for the same size as this one. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
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Posted: Thu Nov 03, 2011 2:00 pm Post subject:
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If the BOM quotes 3A for the transformer, that just means that this set of components, in this configuration, can deal with 3A. (with the appropriate heatsinks on all the regulators)
If you use a 1A transformer, you can only draw 1A before the transformer would give up. So in that case the transformer would fail before anything else.
My advice is to make sure you have an appropriate fuse on the 240V input connections, AND if you want to avoid damaging the transformer, put a 1A fuse on EACH 15V line as it hits the regulator board. It may seem like a pain now, but when you short something and smoke starts coming out of your new transformer, you'll wish those fuses had been there.
Again, make sure you have reasonably sized heatsinks on your regulators. (Don't put them all on one heatsink, as this could cause a short, or use the correct insulation kits for them all)
If you haven't worked with 240V before, please get it checked by someone who has, even if it seems to work fine.
Apart from all that, I'd say it looks like a perfect PSU circuit to get started with. It's good to see someone putting the effort into a decent supply. It can make a big difference later to know that the PSU is a reliable one. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Posted: Sat Nov 05, 2011 11:01 am Post subject:
cap vals Subject description: 0.3 uf to 0.22uf?? |
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Ok! I've taken your advice and ordered the heatsinks and will incorporate fuses between the secondary outputs and regulators....Thing i'd like to ask now is that the circuit asks for 0.3uf caps on C3-C6 after C1 and C2 which are 100uF filtering caps. 0.3uF caps are hard to come by so I was wondering if I could use 0.22uF box caps instead. Would this have a seriously detrimental effect on the output to the regulator ics???
Thanks again.
Oh and Happy Guy Fawkes night!! |
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Uncle Krunkus
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Posted: Sat Nov 05, 2011 2:12 pm Post subject:
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That's fine.
Those smaller value caps near the regulators just help to stabilize the regulators when you have long wire runs on the output (AFAIK) In most situations you could do without them and not notice any significant difference.
As a general rule though, in PSUs, go for the next higher value in caps if you can't find the spec'd part. So I'd be going for .33uF (u33) or .39uF (u39)
If you've already got the .22uFs, they will work fine. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Uncle Krunkus
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Posted: Sun Nov 06, 2011 9:10 pm Post subject:
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Yeah, that bridge rectifier is fine. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Uncle Krunkus
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Posted: Tue Nov 08, 2011 5:51 pm Post subject:
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It looks pretty good, except,....
Check the pinouts of your regulators.
The 78XX series have GND on the middle pin (which you have right) input on the left (looking at the part no. legs down) output on the right. Yours look the other way around.
The 79XX series has a completely different pinout, including the GND NOT being the middle leg.
I also think you might need more room for the caps. Remember they need to be roughly twice the voltage rating of what they are handling. That means at least 25V for the first two. They will be a bit bigger than your current spacing. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
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Posted: Wed Nov 09, 2011 6:39 pm Post subject:
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Yeah, that looks pretty good now. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Posted: Thu Nov 10, 2011 1:40 pm Post subject:
The heat is on?? |
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Ok! I've started the stripboarding and have placed all the components ( caps/diodes/resistors) on the board. One more Q before wiring and testing: ).
I am putting the regulators on seperate anodised heatsinks ( small- about 1" tall).
Can I bolt the heatsinks to the back of the box which is metal ? or will this cause shorting problems???
Thanks .
Stevn. _________________ There's a crack in everything...Thats how glue manufacturers make a living. |
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
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Posted: Thu Nov 10, 2011 3:24 pm Post subject:
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Metal to metal means a short.
For the 78XX regs it would be okay, as all their baseplates are commoned to the middle leg which is ground, but the 79XX at least needs an insulator kit between it and the heatsink, or some other form of insulation between it's heatsink and the case. (You can get plastic/ceramic nuts and bolts, and spacers etc.)
This is, of course, assuming that you have the incoming mains earth connected to the case metal, which also connects to the system's 0V line. And yes, that's the way it should be done because it's safest that way. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Uncle Krunkus
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Posted: Thu Nov 10, 2011 7:31 pm Post subject:
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Yeah, that's fine. Just make sure it doesn't touch anything. _________________ What makes a space ours, is what we put there, and what we do there. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Posted: Fri Nov 11, 2011 6:08 am Post subject:
Good to go+ thanks. |
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Unkle Krunkus. Thanks for all your help. When I get some funds I'll send along a small donation to the site. ( probably enough for a round of cokes... )
It is great to be able to get help from and contribute to this site.
I'll keep posted on the build(s)..
All the best.
Steve. _________________ There's a crack in everything...Thats how glue manufacturers make a living. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Posted: Sun Nov 13, 2011 4:40 am Post subject:
here come the odd voltages..... |
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The board is built and has been tested. The negative supply shows -13.84V whilst the positive 12v shows 11.88V???
The 5V from the 7805 was showing just 3.8 so I removed the 2.2k resistor and got a full 5.00V.
I don't know whats wrong, I've upgraded the 1000uF 25V caps to 1000uF 50V but the readings are the same.. Is there a possibility of a faulty 7912 or could it be ground discepancies I don't know...
If I place a 220Ω resistor on the output of the 7912 and measure I get -11.48V which is nearer to the 11.88 of the 7812... I was thinking I could use the resistor on the 7912 and make due with 11.88 and -11.48V but hmm... ( BOLLOCKS!! )... _________________ There's a crack in everything...Thats how glue manufacturers make a living. |
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mubase
Joined: Mar 24, 2011 Posts: 117 Location: London UK
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
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Posted: Sun Nov 13, 2011 3:07 pm Post subject:
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That's actually pretty good for those types of regulators.
I think they are only spec'd for +/-5% anyway, and that's well within that.
The main thing is that the output (V) is no longer dependant on the load (A). _________________ What makes a space ours, is what we put there, and what we do there. |
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