Page 1 of 3 123 LastLast
Results 1 to 10 of 23

Thread: How measure ripple/noise of psu

  1. #1
    Join Date
    May 2009
    Posts
    17
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default How measure ripple/noise of psu

    hi friends ;
    I want know how measure power supply ripple/noise .
    at first I want khonw : do we need a special filter beetwen psu and scope ? if yes .what is this filter?
    and next quastion is : how measure ripple in scope screen. what are difference between ripple an noise .
    thanks a lot.

  2. #2
    Join Date
    Oct 2006
    Location
    Moderator
    Posts
    6,504
    Thanks Thanks Given 
    149
    Thanks Thanks Received 
    3
    Thanked in
    2 Posts

    Default

    You need an oscilloscope to measure ripple and noise, and if you want to test to ATX spec, there must be two capacitors in parallel with the load: a 10uF electrolytic and a 0.1uF ceramic disk.

    Ripple is lower frequency waves in the waveform, while noise is higher frequency spikes.

  3. #3
    Join Date
    Nov 2007
    Location
    Richmond VA
    Posts
    1,581
    Thanks Thanks Given 
    18
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    what causes the two different frequencies?

    Is the noise at the switching frequency and the ripple at a lower frequency?
    "There is no way you can be Harvard Monday through Friday, and try to be Alabama on Saturday" -Art Guepe former University of Virginia head football coach

  4. #4
    Join Date
    May 2009
    Posts
    17
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    thanks. I test my power supply with this method . ripple was sensible but the noise spikes p-p were too high. you think what is this problem?

  5. #5
    Join Date
    Oct 2006
    Location
    Moderator
    Posts
    6,504
    Thanks Thanks Given 
    149
    Thanks Thanks Received 
    3
    Thanked in
    2 Posts

    Default

    Quote Originally Posted by HOOfan_1 View Post
    what causes the two different frequencies?

    Is the noise at the switching frequency and the ripple at a lower frequency?
    It can be caused by a few things. Depends on the unit, and whether or not it's faulty.

    Quote Originally Posted by seemps View Post
    thanks. I test my power supply with this method . ripple was sensible but the noise spikes p-p were too high. you think what is this problem?
    How were you loading the PSU? You can't really test them in the computer, because then you get interference from the rest of the components.

  6. #6
    Join Date
    Oct 2007
    Posts
    446
    Thanks Thanks Given 
    21
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    Quote Originally Posted by HOOfan_1 View Post
    what causes the two different frequencies?

    Is the noise at the switching frequency and the ripple at a lower frequency?
    Ripple is at the switching frequency (that's pretty much the definition) and noise is higher frequencies. They're hard to separate exactly, so the spec just gives a total.

    For a detailed discussion, see Linear App Note 101, "Minimizing Switching Regulator Residue in Linear Regulator Outputs".

    Ripple is inherent in switching regulator operation; they operate in discrete cycles. Noise is basically the "click" as the various switches slam open and shut.

  7. #7
    Join Date
    Nov 2007
    Location
    Richmond VA
    Posts
    1,581
    Thanks Thanks Given 
    18
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    switching frequencies are usually in the 900Hz-KHz range right?
    "There is no way you can be Harvard Monday through Friday, and try to be Alabama on Saturday" -Art Guepe former University of Virginia head football coach

  8. #8
    Join Date
    Oct 2007
    Posts
    446
    Thanks Thanks Given 
    21
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    Quote Originally Posted by HOOfan_1 View Post
    switching frequencies are usually in the 900Hz-KHz range right?
    No, switching frequencies are always well above the audible range. Higher powered supplies tend to be at lower frequencies; 50 kHz is popular with ATX power supplies. Smaller supplies are at higher frequencies in the 100–250 kHz range, and where space is at a premium, like cell phones, supplies can switch at MHz frequencies.

    I just measured a super-generic Aspire PSU at 49.7 kHz.

  9. #9
    Join Date
    Jul 2007
    Posts
    101
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    Power supplies can contain ripple at two frequencies.

    The switching frequency, and the switching frequency modulated at 2x line frequency. (100 or 120Hz).

  10. #10
    Join Date
    Jan 2010
    Location
    Greece
    Posts
    1,529
    Thanks Thanks Given 
    186
    Thanks Thanks Received 
    7
    Thanked in
    4 Posts

    Default

    Sorry to dig up such an old thread but I was wondering if a resistor (e.g. 1K) is needed before the capacitors to lower the Amps or the oscilloscope can cope with high Amps (with psu in full load)?
    Last edited by crmaris; 02-03-2010 at 08:25 PM.

Similar Threads

  1. PSU with good ripple noise for HTPC and internal DAC
    By Azzuro in forum PC Power Supply Discussion
    Replies: 18
    Last Post: 07-16-2018, 12:04 PM
  2. Lowest noise/ripple/regulation PS charts???
    By ths61 in forum PC Power Supply Discussion
    Replies: 11
    Last Post: 09-20-2014, 06:57 AM
  3. bad source power + noise or ripple? Corsair PSU advice
    By bob1234 in forum PC Power Supply Discussion
    Replies: 10
    Last Post: 04-01-2011, 12:28 AM
  4. Best +5V ripple/noise controlled power supply
    By ricyuyc in forum PC Power Supply Discussion
    Replies: 1
    Last Post: 06-02-2008, 03:28 PM
  5. Ripple/Noise discussion
    By Travis in forum PC Power Supply Discussion
    Replies: 8
    Last Post: 06-01-2008, 10:20 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •