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dc-ac inverter

Discussion in 'General Electronics Discussion' started by Modus, Jan 7, 2014.

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  1. Modus


    Jan 7, 2014
    I want to build a dc-ac inverter and found the following schematic on the web.
    Just wonder about the transistors 2N3773 and want to replace them with MOSFET because less space and easier soldering on the PCB .
    Can you help me which MOSFET would be suitable and if I have to change something in the scheme to get it works properly.


    Attached Files:

    Last edited: Jan 7, 2014
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    You cannot simply replace Q5 and Q6 by MOSFETS. Together with Q3 and Q4, respectively, these transistors operate as Darlingon pairs. A MOSFET cannot be used this way because if turned on, VDS would fall below Vgs_threshold and turn off the MOSFET.

    Since a MOSFET doesn't require gate current (apart from charging and discharging the gate-source capacitance), the driver stage Q1/Q2 would also be unnecessary.

    Witht knowing what design parameters the circuit parameters that led to the original choice of the 2N3773) are important, it is hard to recommend a replacement for the BJTs.

    Here is an application document by Onsemi which describes SMPS topologies and specifically the choice of semiconductors for the SMPS (page 16 ff.). Another selection guide is here.
    This can help you redesin the power stage of the converter.

    Using the keywords "mosfet inverter circuit" Google will spit out lots of complete circuit designs using MOSFETS, not BJTs.
  3. Modus


    Jan 7, 2014
    Thank you for the great explanation. I see here is very difficult to change from transistor to mosfet... I tried also to find on the net some PC+MOSFET design but didn't find anything well explained. In this case I'll continue to make it in BJT version.
  4. Modus


    Jan 7, 2014
    Searching more, I found something what people tried.
    Is it possible that this works?

    Attached Files:

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