Connect with us

PWM output mirror??

Discussion in 'General Electronics Discussion' started by famosas, Jun 7, 2014.

Scroll to continue with content
  1. famosas

    famosas

    3
    0
    Jan 1, 2014
    Hi all, i was building a led driver simple buck converter circuit (second picture)using only discrete component. i want to ask if anyone know why my PWM wave output become mirrored? like in the picture. the yellow one is before i connected to the buck circuit. and when i connected to buck circuit it show 2 wave. the new wave is like a shadow to the 1st wave. and in the oscilloscope the frequency and the duty cycle go haywire. please help me. before this it works fine. what broken component in the buck circuit that can possibly caused this? please help me.
    thankss
     

    Attached Files:

  2. famosas

    famosas

    3
    0
    Jan 1, 2014
    **the red one is the shadow wave
     
  3. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    Use the Triggering Function of your Oscilloscope to have steady displayed waveform.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    Hi there and welcome to Electronics Point :)

    Connected WHAT to the buck circuit?
    Please start by posting the schematic of your buck regulator.
     
  5. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    I would guess a finger, since the schematic has a pushbutton switch.

    Bob
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    I don't think so. That schematic is a buck regulator, and the switch is a MOSFET. But without an actual schematic of the circuit, and some answers, who knows!
     
  7. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    I am being facetious. It thought it was showing a generic switch. Of course we need the full schematic.

    Of course, if he is using a P MOSFET, it explains why the signal is inverted.

    Bob
     
    Last edited: Jun 9, 2014
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    Yeah, I wondered. Sarcasm doesn't work well in a text medium. That's why we have emoticons :)
    I got the impression that the drive signal changes when he changes the load. Which of course it should.

    I don't like it when people post a vague question then disappear. It leaves us guessing, and wastes our time.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    I suspect you're using a P channel mosfet and that it turns on when you pull the gate low.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-