Floating ground

Discussion in 'The Projects Forum' started by Marie, Feb 12, 2008.

  1. Marie

    Thread Starter Member

    Nov 20, 2007
    24
    0
    Hi,

    I need to mount an inverter using MOSFET IRF740. I decided to use IR2111 as gate drive and 6N137 as optocoupler.

    For the purpose of testing, i decided to use the circuit attached. The circuit works. My question is why must i connect the gate drive Comm to the ground of the power circuit; shouldn't these two grounds be different for the sake of isolation?

    Thanks
     
  2. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    You have isolation from the optocoupler.
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    What nanovate said

    I just wanted to add one thing, you may want to play with your gate resistor. From experience, I found that they are typically a bit lower than 22 ohms. I have used typically under 10 Ohms with the best results.

    Last year I had to design a boost converter from discrete components, so I had a lot of lab time playing with different values for the best results. Ended up with about 93% efficiency :D

    Steve
     
  4. Marie

    Thread Starter Member

    Nov 20, 2007
    24
    0
    Hi,

    I took note of what you all said, but what happen if instead of using an optocoupler, i use an isolated dc supply for Vcc of gate drive. Will isolation still be provided if the gate drive and high side driver are on the same ground?

    By the way, i'll try to use a resistor < 10ohms and see what happen. Thanks a lot.
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Yeah, the resistor is a fine balance. The goal of my school project was to make it as efficient as possible :)

    Steve
     
  6. Marie

    Thread Starter Member

    Nov 20, 2007
    24
    0
    Thanks for the links. In fact, i had already read them. The first link about gate driver mentions an isolated power supply. What i would like to know is if with an isolated supply + bootstrapping can i say that i'm providing isolation?

    About pulse transformers, they are not available on the local market:(
     
  7. Marie

    Thread Starter Member

    Nov 20, 2007
    24
    0
    Thanks. I understand what you mean; i've been mixing things.
     
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