triggering many mosfets in one leg??

Discussion in 'The Projects Forum' started by onlyvinod56, Jun 14, 2012.

  1. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    Hello.

    My project is multi level inverter (diode clamped).
    The schematic and the required operation is in the attachment itself.
    The switching logic is fine. I got the output in the matlab too. (attachment 2&3).

    My question is:

    I know how to work with a 4 switch H-bridge. The high side mosfets need a different, dedicated ground. I have desgined some H-bridges using opto couplers or IR2110.

    Iam not satisfied with Using dedicated power supplies for each opto coupler. Of course its working good.

    But now, there are totally 7 mosfets require dedicated grounds. Is there any simple solution for this.
     
  2. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    one expecting solution:

    i can use any no.of ICs (ex: IR2101 or Ir2110).
    I have to use only single power supply.
     
    Last edited: Jun 14, 2012
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    If your trying for a "modified sine-wave" its usually done by feeding a sine wave and a saw tooth/triangle wave into a comparator to drive the mosfet drivers. If thats not what your doing maybe someone else will answer.
     
  4. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    Yes. I know that it is SPWM inverter.
    My problem is..... I'm generating the required pulses from a micro controller. Usually a mosfet/igbt will be triggered by giving a pulse to its gate with respect to its source/emitter. If all the outputs from the micro controller are connected to all the moset gates, then all the source pins of mosfets should be connected to the reference, which is the ground of micro controller. If a connection is made like this then all the source pins are shorted due to this same reference (ground) node.

    That's why a different dedicated power supply is required for each MOSFET. If it is a four switch h bridge, I have to use extra two power supplies other than the main power supply. But now in my project, total there are 16 mosfets have tobe used. So i need 14 power. Supplies. How can I avoid these many power supplies???
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    What your missing is that the out put is not as you are showing it. It is not "stair steps" like in you attachment. The output from the mosfets is a row of "teeth" going from very narrow to wide and back to narrow. And is done by one mosfet not many. Each of the "teeth" or spikes of the mosfet output is at the same real voltage level, it is the width of the spike that makes it 'seem' to be a sine wave.

    I don't know about micro's so I will try to explain what is done 'analog'. In the last post I mentioned a sine wave and triangle wave into a comparator. The sine wave would be the frequency you want the output to be (50 or 60 Hz I assume). This is the sine wave you put into the comparator. Then you decide how many "steps" you want. This is usually around 10 steps but can be more or less. You then multiply the "steps" times the frequency, and this is the "carrier frequency" the frequency of the triangle wave you put into the comparator.

    As the sine and triangle waves cross each other in the comparator, they signal the comparator output to turn on or off the mosfet. Doing this will then give you the output "sine wave" from the mosfet. The mosfet is only a switch, on or off, not a variable voltage device.

    Maybe this link will help to explain it - http://www.imakenews.com/eletra/mod...09&show=F,T,T,T,F,Article,F,F,F,F,T,T,F,F,T,T
     
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