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RF noise from a chip dc-dc step up module, fix?

Discussion in 'Radio and Wireless' started by supak111, Oct 3, 2015.

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  1. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    Hey guys I recently purchase a very cheap dc-dc step up model to bump up the voltage for a RF remote control box that I'm using for a gadget but it seems that these cheap models create too much RF noise which is messing with my 315mhz RF remote control receiver.

    Is there any way I can fix/shield this or I must buy a better dc-dc step up?

    [​IMG]


    FOUND THIS ONE, bit more expensive and has more components. Would it do a better job?

    [​IMG]
     
  2. Alec_t

    Alec_t

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    SMPS units are notoriously noisy. I may be wrong, but I doubt you'd see much difference in the RF emissions. The output caps on the two units are clearly different, and the inductors are different (so perhaps the switching frequencies), but who knows which combination would be worse for RF interference?
     
    davenn likes this.
  3. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    Is there anything else that can be used that will work without RF noise? Fairly cheaply as this isn't an expensive gadget
     
  4. GPG

    GPG

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    Sep 18, 2015
    What voltages? How much current?
     
  5. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    stepping up 12v from car battery to about 22v 300ma max
     
  6. duke37

    duke37

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    Jan 9, 2011
    You could put the gubbins in a metal box and filter the input and output leads. The components will not be very big to filter 315MHz.

    You could make an oscillator and use it to drive a voltage doubler. Keeping the switch speeds down may be sufficient for the purpose but would need fair sized capacitors to get 300mA. There may be chips to do this.
     
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Is this ambient RF noise or on the output of the device?
    Adam
     
  8. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    The voltage booster powers a simple eBay RF remote control box which in turn just drives a simple small geared motor. I'm not exactly sure if its the ambient RF or noise on the output. I'm guessing RF noise because my remote control only works if I'm very close to the antenna maybe 2-3 feet, but without the voltage booster the remote control can work from unto about 50 ft.

    Are you saying just put the V-booster in a small faraday cage? I'll try wrapping the thing in aluminum foil and see if the noise it reduced but there is a chance that the noise is on the output wires because when the v-booster is connected the RF box and relays on it just keep click ON OFF ON OFF. Relays on the RF box should just be constant ON when I hold any of the buttons on the the remote control.

    What I do know is the the noise is NOT from the gear motor. I know some cheap electric motors can cause RF interference but this one does not.
     
    Last edited: Oct 6, 2015
  9. duke37

    duke37

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    Jan 9, 2011
    I doubt if wrapping the device with foil will do much. You will not be able to seal it properly. A gap of a few mm will be a gaping hole at 315MHz.
    An aluminium box with bolt-in feed through capacitors or a copper box made from PCB board with solder-in feedthrough capacitors may do the job.

    Ferrite cores on the leads will help but it is all a matter of trial and error.:rolleyes:
     
  10. Alec_t

    Alec_t

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    Jul 7, 2015
    Do the motor and relay coils/contacts all have snubbers/RF-suppression-components attached?
     
  11. dorke

    dorke

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    Jun 20, 2015
    The 6009 smps reg. works at a switching freq of about 400khz.
    It will create lots of spurious frequencies along the full spectrum.
    The lack of appropriate RF filtering is clear.

    The simplest remedy :
    Try soldering two 1nF/50V COG/NPO(good RF type caps from AVX or other "legit" cap manufacture) on top of the two caps shown in the photo(SMD chip capacitors).
    It may do the job.
    A "Faraday cage shield" is another way ,
    but the filter is better since it will "kill" the noise at it source.

    smps_noise.jpg
     
  12. dorke

    dorke

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    Jun 20, 2015
    One more thing you can do is use Ferrite-core filters.
    Use them(if the caps alone didn't solve your problem) on both input and output wires(2 separate filters ).
    Loop each wire-pair 2 times through a filter,
    and secure as close as possible to the board.

    like these ones:
    EMI RFI ferrite core filters

     
  13. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

    327
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    Apr 29, 2012
    Ok. I'll try the 2 caps first just to see how much it helps, and then I'll try both caps and ferrite filters.

    I have some 10uf 50v cops, is that ok or it has to be a smaller cap uf cap?
     
  14. dorke

    dorke

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    Jun 20, 2015
    Well,
    It is very important that you use the NPO/COG ceramic SMD RF quality caps.
    from a very good manufacture like AVX or MURATA.

    the value should be around 1nF (a bit larger up to 4.7nF is o.k)

    If you don't it will not change a thing...
     
  15. duke37

    duke37

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    Jan 9, 2011
    The frequency you want to suppress is 315MHz which is quite high. To get the resonant frequency of a bypass capacitor sufficiently high, you need a small capacitor and very short leads. An electrolytic capacitor is of no use.
    Try 100pF disc ceramic across the two big input and output capacitors
     
  16. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    Ok sounds good guys. I don't have any ceramic caps on hand but I have old electronics sitting around so I'm sure Ill find some. Been kinda busy so haven't had time to try this yet
     
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