DC-DC Regulator - clean output?

Discussion in 'The Projects Forum' started by danl, Sep 24, 2013.

  1. danl

    Thread Starter Member

    Sep 24, 2013
    32
    0
    I need to reduce 12VDC from a battery to a regulated 6VDC to power a 2.4gHertz RC receiver.
    I have a "synchronous buck converter" voltage regulator, 9-35VDC in, 6VDC out, rated at 5A. The spec claims "50mv ripple".
    Is the output likely "clean" enough not to cause problems with the RC receiver or the signal to the servos?
    Saw one reference that had a 1uF ceramic and a 15uF (450mOhmESR) tantalum capacitor across the output of this type of regulator. Saw another that had a small coil around the output leads.
    Here's a link to the regulator:
    http://www.ebay.com/itm/M3AO-DC-DC-Power-Converter-Regulator-Module-Step-Down-Adapter-12V-24V-6V-5A-/271266100789?_trksid=p3284.m263&_trkparms=algo%3DSIC%26its%3DI%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D21%26pmod%3D290967731174%26ps%3D54

    Any help much appreciated.
    Thanks,
    Dan
     
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
    609
    120
    What sort of battery is it danl?

    The 50mV quoted isn't bad but it doesn't cost too much to stick a few capacitors on the output if needed. I take it you haven't got a oscope?
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Depends on how sensitive the receiver is. Bear in mind, any switcher is a small radio station.

    How much is the load current?
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Most of the trouble is going to be from radiated EMI, not the ripple on the output.
     
  5. danl

    Thread Starter Member

    Sep 24, 2013
    32
    0
    Thanks for the quick replies.
    The battery is a large lead acid set.
    If ripple is not the main issue, but EMI is, what is the solution? Will EMI effect the 2.4GH or the servo signal (or both)?

    Did the caps I listed (1uF ceramic and 15 uF tantalum) sound like the right ones to use to smooth out the ripple?

    No, I don't have a scope. Wow - wish I did.

    The load current will be variable. The receiver will draw a constant low current, I'm guessing a about 200mA. The servos will draw a max of about 1A each. There are seven servos, but only one or two active at any time, and usually at lower than the 1A load.

    I plan to use the 5A rated regulator because it will all be in an enclosure w/ no ventilation.
     
  6. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    1) a lead acid battery IS a big capacitor, it just sucks at high frequencies.
    2) .1 ceramic and 15 tantalum are very good choices to get rid of high frequency noise.
    3) putting it all in a METAL box will suppress most of the radiated energy.
    4) Putting it all in a box will cause heat problems. Better be sure to mount hot parts to the metal box.
    5) I don't think you have a problem in the first place.

    Consider, if your 12 volt car battery had .1 volt of ripple on it, how much would that interfere with the starter motor solenoid? Less than 1%.

    If you talk to your FM radio, how much will that interfere with it receiving frequencies 10,000 times as high? That's the same frequency ratio as a 24 Khz switching supply compared to a 2.4 Ghz receiver.
     
  7. danl

    Thread Starter Member

    Sep 24, 2013
    32
    0
    #12

    Thanks for the thumbs up on the caps. Reassuring.

    The vreg is potted into a cast metal heat sink body. I suppose if I ground that, it would act like a radiation shield, yes?

    Thanks for the help.

    Oh... I like your motto...
    Similar to mine:
    "Often wrong, but never unsure."

    Great forum - thanks for all the FAST and helpful responses.
     
  8. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Yes. Bolt that sucker to something made of metal. It's already shielded except for the epoxy side.

    If it gets too hot, file off the raised rings around the bolt holes so you can get its belly against the cool metal.
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    That is seriously complicated question.:p
     
Loading...