Diode replacement

Discussion in 'General Electronics Chat' started by goodbyegti, Feb 9, 2007.

  1. goodbyegti

    Thread Starter Well-Known Member

    Apr 28, 2004
    59
    1
    I have shorted diode in a switch mode power supply.

    It is a 6AMP fast recovery type and forms part of a rectifier immediately after the mains input.

    What is the difference between fast and standard recovery and am i ok using a standard recovery replacement?

    I have my guesses but would like to hear your opinions.

    Thanks,
    Doug
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    A standard recovery diode will blow up almost instantly. Fast-recovery types have very low junction capacitance, allowing them to come out of conduction very quickly. Get the right replacement.
     
  3. goodbyegti

    Thread Starter Well-Known Member

    Apr 28, 2004
    59
    1
    Ahhh... i see, thanks for the tip!
     
  4. goodbyegti

    Thread Starter Well-Known Member

    Apr 28, 2004
    59
    1
    Out of interest when would you use a standard recovery rectifying diode?

    When you are using low frequency AC? I presume you would work this out from the time constant?
     
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    Use standard recovery for frequencies within it's specification. :)

    Normally AC is fine if the voltage and wattage are in range.
     
  6. goodbyegti

    Thread Starter Well-Known Member

    Apr 28, 2004
    59
    1
    I checked and the 'standard recovery diode' has specifications very similar to the old 'fast recovery diode' There is a very small difference in junction capacitance (50pf). I suppose fast recovery is more important on the output side of a SMPS when there's very high frequency. I couldn't find a suitable fast recovery diode so went for the standard one. Hopefully it won't blow up!
     
  7. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    If it is part of the Mains rectification, then I can't see why it would have to be Fast recovery....
     
  8. goodbyegti

    Thread Starter Well-Known Member

    Apr 28, 2004
    59
    1
    ..well, it hasn't blown up yet!

    I think it should be ok, but nice to know about fast recovery types all the same..
     
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