Filtering Switching Power Supply Noise.

Discussion in 'General Electronics Chat' started by booboo, Jun 28, 2015.

  1. booboo

    Thread Starter Member

    Apr 25, 2015
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    Why a zener cannot regulate compeletly the current?
    I have one of this switching supply and use this to reduce the voltage for my circuit. now I have adjusted it to 5v but I think there is noise in my circuit. how much this circuit can help me?:

    [​IMG]

    Any idea?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Welcome to AAC!

    A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own.

    In addition, you have practiced the arcane art of necromancy, the revival of a long dead thread. Likely the OP (Original Poster) has solved his problem in the years that has passed, or thrown it away, or something.

    This was split from Will be low pass filter be good enough to remove switching supply noise
     
  3. ScottWang

    Moderator

    Aug 23, 2012
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  4. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    Hi
    Ok and thanks.

    Thanks for reply. in fact, I'm trying to use a TLC272CP and it doesn't work. this is my problem. my MCU is working very well. I have used several types of ferrite bead but couldn't help me. another problem I have is that I don't have oscope.:(
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    A straight forward voltage regulator chip should do the trick, but all of them need filter caps. Don't forget them.
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    I'd go a bit further than a ferrite bead - maybe up to a dozen turns of stout wire round some kind of core, you can get suitable cores from the mains in filter from some old set top box or PC PSU etc.

    A good starting point is the well known Pi filter, an input capacitor, an output capacitor and the inductor bridging the two. Low ESR electrolytics are recommended - and or add 0.1uF or so in parallel with both electrolytics.
     
  7. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    I tried an AMS1117 (an 5v LDO) to regulate it but didn't work. this is the schematic:

    [​IMG]
     
  8. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    The circuit in my first post and below didn't work.

    [​IMG]

    You are talking about something like this inductor in this PSU:

    [​IMG]

    I have removed it from the PSU. look at this photo:

    [​IMG]

    From right to left: 1- the coil(inductor) that I have removed from PSU. it has 10 leg (5 at right and 5 at left).
    2- The green core that I have used never so far.
    3- Four type ferrite bead that I have used but couldn't solve this problem.

    Now I have two choice. the green core or the yellow (10 leg). Which one is better for Pi filter? yellow? How to use it?
    and about shunt capacitors, How to choose their amounts?

    [​IMG]
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    The type of cores I meant would normally be to the right of the black & white wires along the top right edge above the heatsinks.

    You could try one of the windings on that salvaged PC PSU choke - it would most likely work, but is probably a fair bit bulkier than you need.

    The wire obviously need to handle the current you put through it, and the core needs to be big enough for a decent number of turns.
     
  10. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    You are speaking about those three yellow choke? which one is better? Is one of those smaller enough?
     
  11. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    Look at this picture:

    [​IMG]

    This is one of those small chokes. three below legs are connected together. for above legs also you can see how they are connected together.
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    The toroid choke has several windings on it - one of those windings might be suitable.

    The 3 others with plastic bobbins are all transformers. The small ones are the driver transformer from the chip to the power transistors, and the auxiliary 5V standby supply, they probably won't be very useful as chokes. A 12V secondary on the big one might do as a choke - but you run a risk of inducing high voltages on what was the primary.

    The core materials are slightly different between chokes and transformers, its best to use a choke as a choke unless you have detailed info on the specifications.
     
    booboo likes this.
  13. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    Thanks ian field
    Now it's better than earlier (the Op-Amp is working now. I mean I can see some changes at the output of it. the gain of Op-Amp is 350 and working in non-inverting amplifier mode.). I have used these legs:

    [​IMG]

    And connected it between the output leg of AMS1117 (leg number 3) and the capacitors (I mean 100uf). this is the schematic:

    [​IMG]
    Please note that I have changed the 100uf to 470uf. for 100uf it work approximately the same as 470uf.

    Any idea?
     
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