Designing a high-power power supply

Discussion in 'The Projects Forum' started by roddefig, Jul 12, 2008.

  1. roddefig

    Thread Starter Active Member

    Apr 29, 2008
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    I need to build a power supply for an audio power amplifier that I'm designing. It needs to provide 35 V at at least 10 amps.

    The particular amplifier I am building needs a regulated supply. I'm looking at using the LM5116 Buck Converter because of the 10 A current supply and the wide input range, which would make it easier to scrounge an appropriate transformer. Here's a link to the National page for the LM5116: http://www.national.com/pf/LM/LM5116.html

    Is this the best way to approach this design? Does anyone have any comments or suggestions?
     
  2. S_lannan

    Active Member

    Jun 20, 2007
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    first thing i would be asking is if this supply needs to be electrically isolated.
    is it going to be straight off the mains or off something else?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    For a 35v supply at 10A using a conventional transformer, the transformer will have two dimensions: LARGE and HEAVY! :eek: You would need a transformer capable of perhaps 11-12A @ 40VAC output. At 50-60Hz, it would be perhaps 5" to 8" in H/W/D, and weigh in around 10lb to 15lb (this is a sort of wild guess, extrapolating from a 120/240 60Hz 36VCT @2.8A transformer I have sitting in front of me).
    [eta]
    Tripped across a possibly suitable transformer online:
    5.3"x2.4" (135mmx61mm) 8.1lbs(3.7kg) 38vac@12.36A
    http://www.toroid.com/standard_transformers/rectifier_transformers/solid_amps_pn2.htm#749.382
    There's another:
    4.9"x2.4" (114mmx61mm) 6.7lbs(3.0kg) 38vac@10.14A
    http://www.toroid.com/standard_transformers/rectifier_transformers/solid_amps_pn2.htm#738.382

    It might be difficult to scrounge such a transformer.

    One of the techniques they're using nowadays is using high frequency drivers to switch current through a relatively small toroidal-wound bifilar (two windings) transformers. If you're switching current at 50kHz, the transformer can be quite a bit smaller and much lighter in weight.

    However, I'm afraid I don't have a ready-made design for you. Something like this will take a good bit of research.
     
    Last edited: Jul 12, 2008
  4. roddefig

    Thread Starter Active Member

    Apr 29, 2008
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    I'll be using a transformer to step the mains voltage down. Or at least, that's the plan.

    Heh, I figured as much. There are some transformers that fit that description lying around the lab at my university and I'm on good terms with the technicians so hopefully I can find something for the price of free. Thanks for the links to those two transformers, both of them look suitable.

    Do you have any links with more information (application notes, etc.)?

    I started designing from the speakers back, but about halfway through it struck me that designing the power supply for this monster was going to be as, or even more involved than designing the amplifier. Initially, I was planning on 200 W/channel but now I'd rather go with 150 W/channel just because of the transformer.
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
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    The June 2008 Elektor had has a go at designing a switched mode PSU especially for high power audio amps.

    Interesting article.
     
  6. roddefig

    Thread Starter Active Member

    Apr 29, 2008
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    Unfortunately, it costs money to download. Do you think it would be worth purchasing?
     
  7. theamber

    Active Member

    Jun 13, 2008
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    The easiest one to build will be a regulated PS, but will require a large transformer that you can find cheap at a scrap yard. If you want to be more efficient then you can build a Switch Mode PS which is very hard to build. For the regulated you can use an LM723 with external transistors for the voltage regulator in order to give you the 10A.
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
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    There are actually two article in this mag.
    One is a general article on smps the other a dedicated 400w smps for audio amps.

    Back issues are available cheaply from Elektor and possibly Jaycar in Oz,There is also a kit.
     
  9. studiot

    AAC Fanatic!

    Nov 9, 2007
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