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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
[Solved] Wall Wart PSU Multiple Output Voltages
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Xorophone



Joined: Mar 01, 2018
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Location: Sweden

PostPosted: Fri Mar 02, 2018 12:20 am    Post subject: [Solved] Wall Wart PSU Multiple Output Voltages Reply with quote  Mark this post and the followings unread

Hello!

I'm building an analog synthesizer (not modular) and I need a bipolar 15v supply for most of my modules (VCO, VCF etc), but I also need a 12v output for some of Ray Wilson's designs. What would be the best way to achieve this? Should I connect two parallel wall wart circuits to my 15v AC power supply or just somehow use a pair of 7812/7912 to convert it from 15vDC to 12vDC? If so, how do I do this? Are any extra components needed?

Thank you in advance and sorry for the beginner question.

Last edited by Xorophone on Sat Mar 03, 2018 8:12 am; edited 1 time in total
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Xorophone



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PostPosted: Fri Mar 02, 2018 12:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok so I researched it a little bit more (which I definitely should have done earlier. Sorry.) I made a schematic that I think would work.

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

Would this work? I'm getting my +15v source from Ray Wilson's wall wart supply PCB. Since it's bipolar and I only need unipolar 12v and 5v power I'm leaving the -15v side free.

What value should the middle capacitor be? 2uF, like if i'd used 2x 1uF capacitors in parallel?

Edit: The voltage regulator to the right is supposed to be a 7805. Thanks to Grumble for pointing that out.

Last edited by Xorophone on Fri Mar 02, 2018 3:05 pm; edited 1 time in total
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Grumble



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PostPosted: Fri Mar 02, 2018 2:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

the right voltage regulator should be a LM7805
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Xorophone



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PostPosted: Fri Mar 02, 2018 2:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
the right voltage regulator should be a LM7805


Oh yeah, you're right. I forgot to change it.

Apart from that, do you think the circuit will work? Any ideas what the value of the middle capacitor should be? Thank you for the reply by the way!
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Grumble



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PostPosted: Fri Mar 02, 2018 2:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

I’d use a 1uF parallel with a 100nF
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Xorophone



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PostPosted: Fri Mar 02, 2018 3:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
I’d use a 1uF parallel with a 100nF


Hmm.. Interesting! Any specific reason for that?
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Grumble



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PostPosted: Fri Mar 02, 2018 3:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

the 1uF filters the lower frequencies, and usualy have a somewhat higher inductance while the 100nF takes care of filtering the higher frequencies
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Xorophone



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PostPosted: Fri Mar 02, 2018 3:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
the 1uF filters the lower frequencies, and usualy have a somewhat higher inductance while the 100nF takes care of filtering the higher frequencies


Oh, I actually didn't know it made a difference compared to just using one capacitor. Thank you for the explanation!
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PHOBoS



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PostPosted: Fri Mar 02, 2018 9:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think for what you need this might be the best solution but it depends a bit on the maximum current. The main problem
will be heat dissipation. If you use another wallwart circuit for 12V there is a pretty big voltage drop (using 15V AC) which
can generate a lot of heat. If you put them after the 15V regulator they don't get as hot but the 15V regulators will have to
dissipate more. You do have to pay attention that you don't go over the maximum current the 15V regulators can handle
though. If you do need a reasonable amount of current for 12V your best bet would be another wallwart with a lower voltage.

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Xorophone



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PostPosted: Sat Mar 03, 2018 3:22 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
I think for what you need this might be the best solution but it depends a bit on the maximum current. The main problem
will be heat dissipation. If you use another wallwart circuit for 12V there is a pretty big voltage drop (using 15V AC) which
can generate a lot of heat. If you put them after the 15V regulator they don't get as hot but the 15V regulators will have to
dissipate more. You do have to pay attention that you don't go over the maximum current the 15V regulators can handle
though. If you do need a reasonable amount of current for 12V your best bet would be another wallwart with a lower voltage.


Thank you for the clarification! I'm pretty sure I won't be drawing too much current, but I'll do some calculations just to be on the safe side. I'll also use 78xx (and not 78Lxx) with small heat sinks, just for safe measure. Space isn't a problem.

Oh and since I'm not building a modular synth, the power consumption should stay the same pretty much all the time.
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PHOBoS



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PostPosted: Sat Mar 03, 2018 5:30 am    Post subject: Reply with quote  Mark this post and the followings unread

ow, where are my manners
welcome party!

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khakifridge



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PostPosted: Mon Mar 12, 2018 6:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Check what Ray says about powering from +-15V. For many of his projects, no changes at all are necessary. For others, you may find only a handful of component changes are needed.
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