15V wall wart power supply

isak · Last edited by isak on Tue Dec 25, 2012 8:24 am; edited 1 time in total

Hi guys.

I stripboard the wall wart power supply from Ray's site and it's working great for -/+ 12V.

When trying to do the same for the 15V the (+) is ok, gives me 14.8V.
The (-) is giving me -17V.
I replaced the 7915 cause I thought it was bad, after replacing that it was the same results, (-)17V.
I wanted to build it again but before doing that I want to understand why it's putting out (-)17V?
Any ideas why?

This is the stripboard layout..

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

I thank you in advance,
Isak E.

Uncle Krunkus · Posted: Tue Dec 25, 2012 2:55 am Post subject:

I've had a pretty good look, and I can't see anything wrong with the stripboard layout. Which leads to the question, is your build exactly the same?
Also, you don't mention the voltage rating for the caps, this may need to go up. They all need at least 35V min.

isak · Posted: Tue Dec 25, 2012 3:18 am Post subject:

Hi uncle.

The caps are 50V
Tantalums 35V

And yes I did exactly as the layout shows.
I checked for shorts, I replaced the tantalums, replace the diods...and nothing!
Im driving my self crazy here, what could be wrong with such a simple board?

EDIT:
Another streang thing...
When taking the power plug off and keep on measuring with the multimeter the -17 goes down to -14.9V and stuck there for about 10 sec and only then discharges to 0.

isak · Posted: Tue Dec 25, 2012 5:18 am Post subject:

Do you think that I should add a trimmer to it?
If yes what would be the correct value?
I yes, should I add a resistor in series with it?

isak · Posted: Tue Dec 25, 2012 12:01 pm Post subject:

New findings...

I pul out the regulators from my good working -/+ 12V and replaced them to 7815 and 7915.
Guess what was the results?
The same!
It gives me +14.8V and -17V.

that's it I run out of ideas Confused

isak · Posted: Tue Dec 25, 2012 1:57 pm Post subject:

its working Very Happy

looking at Rays site i saw he added some load resistors (2.4k)
so i did that by using 3k.
from (-) to ground and from (+) to ground, that did the job and now i got +14.8 and -14.9, how cool is that? Smile

15.JPG

Description:

working -/+15V wall wart power supply.

Filesize:

447.29 KB

Viewed:

253 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

Uncle Krunkus · Posted: Tue Dec 25, 2012 5:27 pm Post subject:

Uncle Krunkus · Posted: Tue Dec 25, 2012 5:33 pm Post subject:

BTW,
(without your added load resistors) does it read -17V with a module attached?

Keep in mind that this may just be a standard behaviour of this type of PSU when it's not under load, and probably just a trade off of using this type of design. Ray designs things very well, but he often does things to help the cost factor for experimenters. A more advanced PSU will no doubt overcome such drawbacks, but at an increased cost.

elmegil · Posted: Tue Dec 25, 2012 9:37 pm Post subject:

Yah, Ray was commenting that the 7900's generally won't read correctly with no load....not sure about the difference between the 7912 and the 7915

isak · Posted: Wed Dec 26, 2012 12:02 am Post subject:

Thank you for the inputs guys.

Uncle,
To your question...
Well I didn't test it without the load resistor cause I was afraid that I will burn the module (IC's etc).
I test the module with the load resistors and it gave me the same read, +14.8V and -14.9V.

For the experiment matter do you think I should test it with no loads resistors?
Is it safe with -17V?

Uncle Krunkus · Posted: Wed Dec 26, 2012 2:11 pm Post subject:

I doubt that anything which is expecting -15V (pretty much as to be an op-amp) will suddenly go belly up at -17V. And you've already shown that as soon as it has a load, it reads -15V anyway. I'd definitely give it a go.

As far as a better PSU goes, there are a few options. Of course you can buy ready built linear PSUs specifically for analogue synth systems, check the net for them.
If you're comfortable (and respectful Wink

) working with mains power. There are also heaps of DIY options.
I built a +/-15V precision PSU which I documented in another thread. I'll find a link for it and add it soon.

isak · Posted: Wed Dec 26, 2012 4:19 pm Post subject:

Thanks uncle Smile

Ill be waiting for the link.

Uncle Krunkus · Posted: Wed Dec 26, 2012 10:43 pm Post subject:

Here it is.
http://electro-music.com/forum/topic-29075.html&postorder=asc&highlight=precision

isak · Posted: Thu Dec 27, 2012 2:06 am Post subject:

Thank for the link.

It's looks beauty project, well done!
I think it's to advaced for me
I don't want to play with V to much.