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Equivalent Power mosfet in HF tube welding machine

Discussion in 'General Electronics Discussion' started by mrcevall, Oct 15, 2017.

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  1. mrcevall


    Oct 15, 2017
    Hi everyone,

    I'm new in this forum, my english is a bit bad but I'll try to explain my problem.

    I dont have much experience in power electronics and
    I have this mosfet: ,

    The thing is, this mosfet is obsolete right know and I have problems getting replacements, so I need a easy to find equivalent mosfet,

    Mosfet came originally in a HF tube welding machine: some specs

    First stage, 3 phase six pulse rectifier 380Vac
    Final stage, 1 phase inverter, Output 500Vrms, switching frecuency 400kHz max.
    The inverter stage have 6 blocks with mosfets-diodes connected back to back (see attached photo) they work in two stages wih two diferent firing pulses (see attached photo). Each block have 16 mosfets-diodes in parallel

    Parallel diode is

    This are the best matches I could find:

    I'm fighting with switching times and Id / Vds characteristics, I cant find equivalent mosfet with good ones as original.

    I'm studying this problem but I want to hear opinions from more experienced people .

    Thanks for your help


    firing pulses

    firing pulses.jpg

    output voltage
    output voltage.jpg
  2. mrcevall


    Oct 15, 2017
    Yes I check most of them, the IXFN44N100Q3 is the most similar mosfet.

    What do you think about these parameters:

    Vgs(th) original is 3 - 5.5V and most of the similars are 3.5 - 6.0 or 6.5 V. I read Vgs values are critical when mosfets are connected in parallel because one can turn on and turn off faster/slower.
    Others parameters that differ in about 50-80% are Qg, switching times tdon, tdoff, tr and tf, and capacitances Ci, Co, Cr.
    I think Parasit diode is not important because is blocked with a Fast Recovery diode (DSEI 2x 61)
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