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Peak to peak noise detection circuit

Discussion in 'Electronic Design' started by Teddy, Apr 27, 2004.

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  1. Teddy

    Teddy Guest

    We are testing SMPS for peak-to-peak voltage noise and would like a
    quicker and easier way to test for noise failures than reading the
    noise level on an oscilloscope. The output is 12VDC, switching
    frequency is 200kHz, with transistor turn-on and turn-off noise spikes
    ringing at 20 to 60 MHz. We are mainly interested in whether the
    peak-to-peak value of these spikes is less than or greater than
    100mV.

    Any suggestions as to how to do this?

    Thanks.

    TD
     
  2. Joerg

    Joerg Guest

    Hi Teddy,

    You'd have to give more details. Noise riding on a DC output? That's easy,
    just run an AC-coupled AM detector with the threshold set at 100mV.

    Regards, Joerg
     
  3. Ban

    Ban Guest

    The 4 transistors should be in an RF-array, opamp is not critical.

    100k 10n 100k
    +---+------------+---+---------o +5
    | | GND GND | | GND
    | .-. | | | .-. |
    | | | --- .-. | | | .-.
    | | | --- | | | | | | |
    GND | '-' | | |1k| '-' | |
    | | +---+ '-' | | '-'
    .-. | | | | +--+ ___ |
    | | | +--------)---)---)--|------|___|--+
    | |1k| | | | | | ___ | |\
    '-' | | | | | | +---|___|--+---|+\
    || | |/ |< | |/ |< | | ___ | >-+--o
    o-||--+-|---| +-|---| +--)---|___|--+---|-/ |
    || |> |\ |> |\ | | |/ |
    | | | | | ___ | ___ |
    +---)------------)---)-----)---|___|--+--|___|-+
    | | | | |
    | | +---)-----+
    +---+ | | | all 100k
    10n| .-. | .-. |
    --- | | | | | |
    --- | | | | | |
    | '-' | '-' |
    GND | | | |
    +---+------------+---+---------o -5

    100k 100k
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
     
  4. legg

    legg Guest

    To measure accurately and record the data, you need instrumentation
    that can do this - I've only seen it done in GPIB setups.

    For an indication, you can peak detect using a differential bipolar
    pair - by measuring the dc imbalance required to cut off the
    ac-coupled detector side of the pair.

    If a fraction of the DC input is used as a reference for another
    comparator or a simple AD, an indication of percentage can be
    obtained. Indicator-only type circuits can be powered from the
    terminals being measured (if correctly polarized), or additional
    battery power can be used to power the AD.

    Usually, a properly designed SMPS has sufficient margin on published
    limits, so that an indicator-only measurement is sufficient assurance
    of correct circuit assembly and function.

    If the published limit is 100mV ppk, anything over 50mV ppk is highly
    suspect, and typical performance at room temperature should reflect a
    much lower value at room temperature. This lower value reflects the
    typical performance needed of products demonstrating compliance over
    the entire environmental range, as established in initial design
    verification and validation records, and extending over the design
    life of the product.

    RL
     
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