Is MOSFET signal as it should be?

Discussion in 'General Electronics Chat' started by stevenmahoney, Jan 25, 2013.

  1. stevenmahoney

    Thread Starter New Member

    Jan 25, 2013
    10
    0
    I have a power supply that I am repairing and I wanted to know if signals are as they suppose to be. here is the schematics:

    [​IMG]

    And here is what I got:

    [​IMG]

    Do signals look OK to you?

    Steven
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    Does the psu work, the signals look ok to me, the main signals to look for are B ,E they look like they are working, C will be near enough at Zero as its a current monitor signal, D will be at the supply of the IC as its a DC take over winding from the pulse transformer, A,B should be nearly the same square wave pulses, and the signal on pin 1 will be the shut down signal from the opto coupler.
     
  3. stevenmahoney

    Thread Starter New Member

    Jan 25, 2013
    10
    0
    Yes, the power supply works, I was just thrown off by that ringing... I expected a square signal at E. Can you tell me how that ringing comes to be? Especially little one on the top of the signal graph and larger one after that?

    Steven
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,854
    767
    How about the Values of R9,R10,R13.R11,R14?
    The number of IC1?
    The number of T1(MOSFET)?
     
  5. stevenmahoney

    Thread Starter New Member

    Jan 25, 2013
    10
    0
    R9 - 100 ohm
    R10 - 18 ohm
    R13 - 10 k
    R11 - 1 k
    R14 - 1 ohm
    IC1 - UC3843
    T1 - BUK456-800B
     
  6. stevenmahoney

    Thread Starter New Member

    Jan 25, 2013
    10
    0
    Thanks, Dodgydave
     
  7. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    This high frequency ringing (little one on the top of the signal graph ) are caused by primary winding leaking inductance and MOSFET parasitic capacitance.
    The low frequency ringing are caused by primary winding inductance and MOSFET parasitic capacitance. But this is quite normal, so no worries.
     
  8. stevenmahoney

    Thread Starter New Member

    Jan 25, 2013
    10
    0
    Thanks, Jony130! That is what I wanted to find out...
     
Loading...