Problem: SMPS adapter effect on RF Reciever?

Discussion in 'General Electronics Chat' started by hazim, Oct 28, 2010.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
    Hi all,

    I'm building a small project that uses a 220VAC to 6VDC adapter. I'm using a small smps adapter's circuit board which can fit the required power. I think the smps circuit is working on about 100kHz. An RF receiver is to be placed with the smps converter in the same 'compact' box (I placed them inside an "empty" 220V-9V 1000mA wall adapter).

    The receiver takes power from the smps converter, and it's output is connected to a relay... actually details are not required for clarification, the problem happens when I put the parts inside the box (empty adapter) where the whole circuit doesn't function, while it works fine when the are outside it, i.e there's more distance between them.

    The receiver works on frequency 433MHz. Tomorrow I'll try in it.
    I'm ready for more information.
    Any idea about what would be actually happening? Any help is greatly appreciated.

  2. bertus


    Apr 5, 2008

    I think the 100 kHz from the SMPS has so many harmonics that the reciever sees a lot of noise from the SMPS and refuses to see the wanted signal.

    Is the power input of the reciever decoupled with a capacitor of about 0.1 uF?
    Is it possible to have a "shield" between the SMPS and the reciever?

  3. SgtWookie


    Jul 17, 2007
    SMPS are intrinsically very electrically noisy.

    You will probably find that if you enclose the SMPS entirely in a sealed metal housing (copper preferred, aluminum is passable) with both the supply inputs and the outputs filtered using ferrites as baluns going through grommeted holes, the noise emissions will be considerably reduced. If air cooling is required for the SMPS, drill a pattern of holes in the enclosure.

    It's best to connect the metal housing to earth ground.
  4. hazim

    Thread Starter Active Member

    Jan 3, 2008
    I tried enclosing the SMPS with aluminum, it's not possible to enclose all of it, I also used a ferrite at the SMPS output for filtering, and put a 0.1u ceramic capacitor at the supply input of the receiver, all of that didn't solve the problem. Using a 6V battery as a power supply solves the problem, so it's clear that the problem is from the SMPS.

    I'm thinking to use small 220V-6V 100mA transformer and a rectifier, the transformer has space inside the "empty adapter". There is a 220V-12V 100mA center-tapped transformers I can use, to obtain 6VDC at the output of the rectifier I have to use 6V output transformer or more?