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RFI in power supply

Discussion in 'Home Brew' started by Crusher, Oct 26, 2008.

  1. Crusher

    Crusher Well-Known Member

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    I built me a power supply using a LM350, but when I have amplifer hooked up to it, I have RF in supply. What can i do do reduce or alleviate this? I did a circuit as given on datasheet. But could not figure out anything for RF bypassing. Any help would be great.


     

  2. formulamojo

    formulamojo Active Member

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    Have you tried some ferrite chokes on the power lines coming out of the supply?
     
  3. Crusher

    Crusher Well-Known Member

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    Yes I have 3 8 awg wires from post. Each wire has 3 #43 .5by .5 inch ferrites.
     
  4. formulamojo

    formulamojo Active Member

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    hmmm
     
  5. W5LZ

    W5LZ Crotchety Old Bastard

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    The only power supply circuit I've found using the LM-350 shows no filtering on the output. Did you add a typical filtering circuit to your power supply? Not just the torroids, but a 'real live' 'LC' filter?
    - 'Doc
     
  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Have you tried adding RF bypassing to pin #1 the adj pin? Something between 0.01 and 1 uF to ground should do.
     
  7. Crusher

    Crusher Well-Known Member

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    Yes, it is recommended to use a .1/104 for input anyways. I think I have a 25uf as well. Guess I may have to experiment a bit more. I do not have an LC network on the output. This power supply is capable of 100+ Amps continous. So making an inductor that will handle that kinda dc current would be difficult at best. Yes?
     
  8. W5LZ

    W5LZ Crotchety Old Bastard

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    Yes? Definitely YES! That'd be one big choke. You might try just the caps though, some times works well enough. Haven't seen a choke that big in years, no idea if anyone is still selling them. Good luck.
    - 'Doc


    Or, see what others have used for output filtering. If it work, it works. Who cares where the idea came from?
     
  9. Beetle

    Beetle Sr. Member

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    Do you mean you don't have ANY filtering on the output of the PS? Not even some good-sized electrolytic capacitors?

    I hope you didn't try using it without at least that much filtering; you wouldn't be able to tell RF in the power supply from the raw, unfiltered 120 Hz DC.
     
  10. Crusher

    Crusher Well-Known Member

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    It has filtering, about 100,000uf. The regulator circuit is used in a circuit that combines 2 12V batteries. There shouldn't be much in the way of frequency strictly combining 2 batteries anyways. I have tested it and everything works fine other than I noticed that the light on the switch gets brighter as amp hooked to power supply is modulated. Everything else works fine. I added a bit more ferrite and a few more bypassing capacitors. Will have to test it later today and see what happens.
     
  11. Crusher

    Crusher Well-Known Member

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    Removed 2 capacitors that were installed in the regulator circuit and added 1 cap. of a different value and seems to work fine now.
     
  12. W5LZ

    W5LZ Crotchety Old Bastard

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    Good! Enjoy...
    - 'Doc
     
  13. Crusher

    Crusher Well-Known Member

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    Oh I definitely was last night shooting DX in the mobile. What the regulator circuit was for was for a motor maul of the 200A version.

    Thank you everyone
    73's
    Crusher
     

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