How do I substitute a MOSFET in a SMPS?

Discussion in 'General Electronics Chat' started by Agent24, Oct 18, 2014.

  1. Agent24

    Thread Starter Member

    Jun 14, 2010
    When replacing a MOSFET used as the switching component in an SMPS, what needs to be taken into account?
    Which parameters are the most critical? Which can be changed (lower or higher)? Which (if any) must be the same?

    From logical consideration, I figure thus:

    1) Same type\polarity - duh!
    2) Same package type (preferably, unless you want to get creative)
    3) Same or higher voltage ratings
    4) Same or higher current ratings
    5) Same or higher power dissipation rating
    6) Same or lower RDSon
    7) Same gate threshold voltage
    8) Turn On\Off times same or faster

    Anything else I need to worry about?

    What about Input and Output Capacitance for example? Do these need to be the same? Is there some tolerance for change? Can they be lower but not higher or vice versa?

    The part in question I wish to replace is a 2SK2645. I see some cheap on eBay from China but fear they would be inferior or fake.