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Thread: Eliminate switch-mode power supply noise

  1. #1
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    Default Eliminate switch-mode power supply noise



    Hi all,
    I've got a Philips DVD player has a very noisy SMPS that radiates quite a lot of noise on to the mains input. As a result AM broadcast band radio reception is absolutely impossible within the house, due to the noise it radiates.

    I've fitted an external mains noise filter, (not a surge filter) but the reduction wasn't enough. Seriously thinking of junking the DVD player and getting a better one, but before doing that are there any cheap simple fixes, such as the standard three X class capacitors on the mains input (active to earth, neutral to earth and active to neutral) and replacing the electrolytics in the initial AC to DC conversion section of the circuit?



  2. #2
    Super Moderator Fernbay's Avatar
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    Cheaper to replace it with a $40 chinese DVD player rather than waste time trying to re-engineer the wheel ( or disc as the case may be )
    Reality is an invention of my imagination.
    ಠ_ಠ

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    Senior Member best4less's Avatar
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    There is your problem mate its a Philips LOL

    Like Fernbay said just get your self a cheepie and stick that one in the bedroom or something
    When you do things right, people won't be sure that you have done anything at all

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    Senior Member Studio1's Avatar
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    The problem with your Phillips DVD player is it is a chinese machine with a Phillips badge.

    China = cheap horrible ideas now abound

    SMPS are noisy because of how they operate. Good quality ones reduce the amount of noise radiated onto the mains (and into free air) by careful selection of quality componentry and careful design implementation.
    AM noise is never eliminated completely however. Anything with a cable hanging out the back is going to emit some AM carrier.

    Even FM broadcast transmitters emit a small AM content.

    To really get rid of AM noise, your solution would be to build a linear power supply. It's not worth it for this type of equipment.

    People keep telling me that Chinese standards will improve in time, like Japan did when they started to become world leaders - and I can believe this may happen.
    Sadly in the mean time we have to put up with a heap of junk that no one wants.

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    Junior Member thrasher12ga's Avatar
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    Yep, caps would help on the mains side. Low-value poly's etc.. RC circuit would be better, you could scab a few from old PC power supplies and stick them in.
    Also might help to run an earth with a cap back to the chassis, and perhaps pick a good cap value to filter the outputs - dunno offhand what to use without affecting the signal though.
    Or get another player

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    Senior Member trash's Avatar
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    I just had to have a look at the mother-out-law's cheapy hung ching DVD player which had shit itself. The power supply was a basket case and the more components I replaced, the more it tried to kill itself and take me with it.

    However, the voltage outputs are relatively simple. +5V, +12V and I suspect -5V. If I actually knew what the voltage should be, it would be very simple to strip out this board and and just supply the DC voltages from an external (linear) supply.
    As mentioned it might be a bit of a futile exercise for cost etc.

    The power supply in the hung ching isn't shielded at all. If you were a little handy with some sheets of brass from the hobby shop, carefully folding and soldering a box for the PSU (being careful not to short anything) and earthing it.

    Come to think of it.... the hung ching DVD isn't double insulated and it doesn't have an earth lead. Ah fvck it, who cares if it doesn't meet Australian standards, the Chinese could undercut us even if we didn't apply the standards ourselves.

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    Senior Member Arbiter's Avatar
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    Tell the outlaw to make sure she has one foot in a puddle of salty water and one hand on a kitchen tap before she attempts to turn it on.
    Cures both problems.
    Ok....your missus will be upset for a while but remember: Laugh and the world laughs with you, cry and you cry alone.

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    Senior Member mobihci's Avatar
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    Quote Originally Posted by Studio1 View Post
    The problem with your Phillips DVD player is it is a chinese machine with a Phillips badge.

    China = cheap horrible ideas now abound

    SMPS are noisy because of how they operate. Good quality ones reduce the amount of noise radiated onto the mains (and into free air) by careful selection of quality componentry and careful design implementation.
    AM noise is never eliminated completely however. Anything with a cable hanging out the back is going to emit some AM carrier.

    Even FM broadcast transmitters emit a small AM content.

    To really get rid of AM noise, your solution would be to build a linear power supply. It's not worth it for this type of equipment.

    People keep telling me that Chinese standards will improve in time, like Japan did when they started to become world leaders - and I can believe this may happen.
    Sadly in the mean time we have to put up with a heap of junk that no one wants.
    i dont think japan improved their quality at all, the world just come to accept it as higher quality due to the lower quality again of korean, chinese etc equipment. the sale of high quality equipment to the general public was doomed due to the fact that most people could not afford it which is why japan took most of the market from america and europe back in the 50s doing what china is doing now. cheaper alternatives offered a way for people with less money to afford a tv, washing machine etc and this has continued on through time with all devices. the problem is that high quality equipment now only lives in the industrial sector and really cannot be purchased at a reasonable price for commercial or home application.

    the only way to deal with the problem properly is to set tough standards for imported and manufactured goods and enforce them, but then nobody wants to upset our cashcow china.

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    Senior Member Studio1's Avatar
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    Quote Originally Posted by mobihci View Post
    nobody wants to upset our cashcow china.
    The removal of import tarriffs here cost our country dearly. It opened the floodgates for billions of tons of cheap chinese sh*t to come into the country and wipe out thousands of local jobs supplied by companies that just couldn't compete with the stupidly low prices of this crap.

    The simple solution? Re-instate the tarriffs and tell the chinese to keep their junk or sell it to someone else.

    The problem with that? They turn around and say "Ok, we no want your butter, cheese, milk powder and beef in our country" - and NZ loses a HUGE domestic export market, which really is the lifeblood of this country due to a free trade agreement with them.

    What would help is if people here refused to but this stuff. Kiwis unfortunately are, by and large, capitalists and dollar focused - so purchase are based on price, not quality. Some people have seen the light and refuse to buy chinese goods, but being a small island nation in the middle of nowhere, our choices are small - the range of products even smaller.

    Often it is impossible to buy something that isn't made in china.

    It's a no-win situation.
    Last edited by Studio1; 13-08-09 at 11:23 AM.

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